Chapter 13: competition

• Interference: direct and or aggressive interaction between individuals
• Intraspecific: competition with members of own species
• Intraspecific competition among herbaceous plants: plant growth rates and weights increase in low density populations.
• Competition for intense at higher population densities
• Usually leads to morality among competing plants”self-thinning”
• Intraspecific competition among arthropods:
• The degree of competition is due to population aggregations,rapid growth,and the mobile nature of food supply.
• Result of limited resources.
• Interspecific: competition between individuals of more than 2 species
• Gause: principle of competitive exclusion
• Two species with identical niches cannot coexist indefinitely
• In a given set of conditions,one will be a better competitor and thus have higher fitness,eventually excluding the other.
• Grants found differences in beak size among ground finches translates directly into diet
• Size of seeds eaten can be estimated by measuring beak depths
• Individuals with deepest(southwest)beaks are fed on the hardest seeds.
• The niches are multi-dimensional
• Two species may have complete overlap on one or more dimensions
• Two species cannot have complete overlap on all dimensions
• If there were complete overlap in all dimensions then they would be the same species
• Competition occurs where niches overlap with regard to limited resources
• Gause demonstrated resources composition with paramecium caudatum and p.aurelia in presence of two different concentrations of preys ( Bacillus pyocyaneus)
• When grown alone, carrying capacity determined by intraspecific competition
• When grown together,p.caudatum quickly declined, reduced resource supplies increased competition.
• Flour beetles(tribolium spp.) infest stored grain products
• T-confusum and T. castaneum demonstrated interspecific competition under varied environmental conditions.
• Growing the two species together suggested interspecific competition restricts the realized niches of both species to fewer environmental conditions.
• Connell studied interspecific competition in barnacles.balanus plays a role in determining lower limit of chthamalus within intertidal zone.
• Niche restriction were well understood
• Upper intertidal zone: removal of balanus has little effect on chthamalus N; suggests little competition.
• Middle intertidal zone: removal of Balanus has a major effect on chthamalus N; competitive effect is significant.
• Balanus does play a role in determining the lower limit of chthamalus within the intertidal zone.
• Fundamental niche restrictions were well understood but did not account for all actual pattrents: actual realized niche.
• Competition restrict species to their realized(or actual ) niches spaces
• If competitive interactions are strong and pervasive enough they may produce an evolutionary adaptive response in the competitor population.
• A change in the fundamental niches
• Competition is always bad for the individual but may drive an adaptive change for the population.
• Competition and niches of small rodents:
• Hypothesis: if competition among rodents is mainly for food, then a small carnivorous rodent population would increase response to removal of larger granivorous rodents.
• Reference: insectivorous rodents would show little or no response
• Did the results support the hypothesis?

Chapter 14: Exploitative interactions

• Exploitative interactions weave populations into a web of relationships that defy easy generalization
• predators , parasites, and pathogens influence the distribution,abundance and structure of prey and host populations
• Predator-prey host parasite and host pathogen relationships are dynamic
• To persist in the face of exploitin, hosts and prey need refuges.
• Models incorporating the ratio of prey to predator numbers better predict predator functional response in many ecological circumstances.
• An increased exploitation of resources, or an interference with resource acquisition
• Exploitation competition: indirect inhibitory effects arising from reduced availability of resources; the competitor is a more effective exploiter/user
• Only happens when the resource in question is limiting “use it or lose it”
• Interference competition: direct inhibitory effects arising from reduced use of resources or reduced.
• Territoriality,allelopathy
• Reduced success for any individuals involved
• Interaction between populations that enhances fitness of one individual while reducing fitness of the exploited individual.
• Predation:killing and or consuming
• Carnivory
• Herbivory : granivores, frugivores
• Pathogens: induce disease; may kill host
• Parasitism: consume, but killing the host is not the aim.
• Complex interactions
• Parasites may alter host behavior
• Spiny-headed worm( acanthocephalans) alters behavior of amphipods-> make it more likely to be eaten by a vertebrate host.
• Infected amphipods swim towards light, which is usually indicative of shallow water and thus closer to predators.
• Their intent is to get into their next host; getting the previous host killed is a side effect
• Blister beetle larvae & burrowing bees
• Larvae mimic female pheromones
• Swarm into male bee during mating attempt
• Then swarm into female during later mating effort
• Return to burrow,consume pollen & nectar stores and eggs & larvae
• mojave:> 11 high on grass
• oregon:<4 high on grass
• Modified pheromones
• • Parasitoids: consume and kill the host
• The predator/ Prey paradox
• The predator directly influences the growth and survival of the prey Nh;prey density influences the growth and survival of the predator Np
• The joint evolution of the two or more taxa
• Usually involves reciprocating selection pressures
• A game of adaptation and counter adaptation; an arm race
• Exploitation competition: the presence or absence of a protozoan parasite (Adelina tribolli) influences competition in flour beetles (Tribolium)
• Adelina lives as an intracellular parasite
• Reduces density of T.castaneum but has little effect on T.confusum
• T.castaneum is usually the strongest competitor however in the presence of adelina t confusum outcompetes
• Exploitation affects distribution, abundance, and community structure
• – Larvae can represent up to 25% of the biomass of benthic animals.
• – But such high numbers reduce the abundance of their own food supply.
• Lindstrom et al. (1994) examined the spread and effects of mange mites (Sarcoptes scabiei) on foxes in Sweden and, indirectly, on the foxes’ prey.
• Mange →Hair loss, deterioration, and death in foxes.
• – Fox populations declined by 70%
• Mountain hares (Lepus timidus), increased 2-4 times after the predator population declined.
• SO: relationships between predators and prey are temporally dynamic
• Abundance cycles of snowshoe hares and their predators
• Hares: boreal forest habitat dominated by conifers. Dense growth of understory shrubs
• Winter browse: buds and stems of shrubs and saplings
• Shoots produced after heavy browsing can increase levels of plants' chemical defenses. Reducing unstable food supplies
• Elton proposed abundance cycle driven by variation in solar radiation
• Keith suggested “overpopulation theories”
• Decimation by disease and parasitism
• Physiological stress at high density
• Starvation due to reduced food
• Snowshoe Hares-Role of predator
• Predation can account for 60-98% of mortality during peak densities.
• Hare populations increase; their food supply decreases →starvation and weight loss lead to increased predation.
• All of the above decrease hare population
• Utida: reciprocal interactions in adzuki bean weevils callosobruchus chinensis over several generations.
• Adzuki bean
• Bean weevil
• Parasitoid wasp
• Most laboratory experiments have failed in the most have led to the extinction of one population within a relatively short period.

Refuges

• More than one type: spatial/physical, escape,size,numbers
• To persist in the face of exploitation, hosts and prey need refuges.
• Gasue attempted to produce population cycles with p.caudatum and didinium nasutum.
• Didinium quickly consumed all paramecium and went extinct (both populations extinct)
• Added sediment for paramecium refuge.
• Some paramecium survived after Didinium extinction
• Six-spotted mite ( eotetranychus sexmaculatus
• Predatory mite ( typhlodromus occidentalis
• Wooden post launching pads maintained population oscillations spanning 6 months
• Living in a large group can act as a “refuge.”
• Predator’s response to increased prey density
• Prey consumed (predator) X predators(area)= prey consumed (area)
• Prey can reduce individual probability of being eaten by living in dense populations

Chapter 15: Mutualisms

• Mutualisms-: interactions beneficial to both species
• Facultative: where species survive without the interaction
• Obligate: where both species require the interaction for survival
• Symbiosis: specialized form of mutualism where the species become physiologically integrated. These interactions may be facultative or obligate.
• Mycorrhizae - a fungus / plant root association. • Plant provides fungus with carbohydrates
• • Fungus provides plant with P and increases absorbing power of the roots Most are facultative All are symbiose
• • AMF: Arbuscular Mycorrhizal Fungi
• •Arbuscules – sites of material exchange
• •Hyphae – filamentous growth; the body of the fungus
• •Vesicles – storage organs
• • Ectomycorrhizae
• •Form “mantle” around roots
• •Both increase access to immobile nutrients
• Allen and Allen: water relations of Agropyron smithii.
• – Associated plants: higher leaf water potentials.
• • An effect of greater P access?
• Nutrient Availability and the “Mutualistic Balance Sheet”
• – Resource availability controls plant allocation
• – Fertilization→ less root allocation
• – Reduced root allocation → selection for better M.F. competitors
• Johnson:
• More mutualistic: fungal partner provides plants with greater quantities of nutrients in trade for less photosynthetic product.
• – Less mutualistic: fungal partner receives equal or greater quantity of photosynthetic product in trade for low quantity of nutrients.
• In nutrient-poor environments, many plants will invest disproportionately in roots.
• – Found higher root investment in low N soils.

Chapter 16: Species Abundance & Diversity

• • Abundance & rarity
• • Both richness and evenness determine diversity
• • Environmental complexity affects diversity
• • Intermediate levels of disturbance can positively impact diversity
• Communities: Association of interacting species inhabiting a defined area
• • Community Structure: Incorporates # of species, relative abundance, spp. diversity, etc.
• • Guild*: Group of organisms that all “make their living” in the same fashion
• • Life form*: Structure & growth dynamics
• • *Functional traits: shared function in the community or ecosystem
• An ecological community: is an assemblage of plant and animal populations that interact and influence one another.
• Communities can be structured in four ways:

1. Physiognomic - physical structure (mostly re: plants)
2. Species composition - diversity
3. Trophic - energy transfer, functional groups
4. Temporal - seasonal or diurnal activity

• Abundance and Rarity
• There are regularities in the relative abundance of species in communities that hold regardless of the ecosystem
• Frank Preston developed concept of distribution of commonness and rarity.
• Lognormal Distribution of Abundance
• – Lognormal Distributions : Bell-shaped curves. – In most lognormal distributions, only part of the curve is apparent.
• » Sample size has large effect.
• » Significant effort to capture rare species
• FACTORS AFFECTING DIVERSITY

1. • Climatic stability
2. • Resource division
3. • Predation
4. • Disturbance

• • Hutchinson:
• – Phytoplankton communities:
• – Appear paradoxical because they live in relatively simple environments and compete for same nutrients
• Environmental heterogeneity may account for significant portion of the diversity
• • Jordan:
• – Diversity in tropical forests organized in two ways:
• • Large number of species live within most tropical forest communities.
• • Large number of plant communities in a given area, each with a distinctive species composition
• Disturbance Characteristics:

1. • size - area of impact
2. • frequency - # events per unit time
3. • turnover - time between disturbances
4. • intensity - physical force of the event
5. • severity - impact on the biota

• Intermediate Disturbance Hypothesis
• ❖ Both high and low levels of disturbance reduce diversity.
• ▪ Intermediate levels promote higher diversity.
• ➢ Given sufficient time between disturbances, a wide variety of species may colonize, but competitive exclusion is prevented.
• • No / rare disturbance → only good competitors succeed
• • Efficient species / good interference competitors / K-selected species
• • Intermediate disturbance → a variety of species colonize, but competitive exclusion is prohibited • Severe / frequent disturbance → only tolerant species succeed;
• competitive exclusion likely prohibited / r-selected species favored

Chapter 17 – Species Interactions, Community Structure

• Food webs summarize the feeding relations in a community.
• • Indirect interactions between species are fundamental to communities.
• • The feeding activities of a few keystone species may control the structure of communities.
• • Mutualists can act as keystone species.
• • Application: Human Modification of Food Webs

Community webs

• • Feeding relations among tropical freshwater fish – Winemiller’s research in Venezuela & Costa Rica
• – Food web representations:
• • Only included common species.
• • Top-predator sink.
• • Excluded weakest trophic links.
• Strong Interactions and Food Web Structure • Research by Paine: • Suggested feeding activities of a few species may have a dominant influence on community structure. – Suggested criterion for strong interaction is degree of influence on community structure.
• • Tscharntke: studied food webs associated with wetland reeds (Phragmites australis). – Parasitic fly Giraudiella inclusa. • Attacked by 14 species of parasitoid wasps. – Predator specialization – Distinguished weak and strong interactions. • Determination of keystone species.

Indirect interactions

• Effects of one species on another through a third species – Examples: • Trophic cascades (Chapter 18) • Indirect commensalism (+/0) • Complex relationships! • Martinsen, Driebe, Whitham • Beavers fell cottonwood trees → stump resprouts – Benefit to leaf beetles
• Effects of one species on another through a third species – Examples: • Trophic cascades (Chapter 18) • Indirect commensalism • Apparent competition – (Orrock, Witter, Reichman) Indirect Interactions

Keystone Species

• • Few members of the community with inordinately large influence • Paine’s theory: – Predators keep prey below K – Reduction in competitive exclusion – Greater # of species can coexist
• • Lubchenco’s snail grazer research We’ve seen some examples of impacts of top predators on whole communities, but what about a very simple example of consumer effects?
• Lubchenco’s snail grazer research -Snails sometimes increase, sometimes decrease algal diversity -To explain herbivores’ differing effects on plant diversity, they looked at: – Herbivore food preference. – Competitive relationships between plant species in the local community. – Variance in feeding preferences and competitive relationships across environments. Consumers’ Effects on Local Diversity
• • Lubchenco’s snail grazer research Key species: Snail species: Littorina littorea Green algae; Enteromorpha sp.; preferred food, & more competitive algae Red algae; Chondrus sp.; less palatable & less competitive Other algae spp.; ephemerals; non-dominant High densities of preferred algae = Low snail density High densities of non-palatable algae = High snail density
• Lubchenco’s study: – Medium snail density - Competitive exclusion eliminated, and algal diversity increased
• Lubchenco’s study: – High snail density - Feeding requirements are high enough that snails eat preferred algae and less-preferred algae. • Algal diversity decreased
• High snail density - Feeding requirements are high enough that snails eat preferred algae and less-preferred algae. • Algal diversity decreased. Consumers’ Effects on Local Diversity Lubchenco’s study:
• – Low snail density - Enteromorpha dominates tide pool
• – Medium snail density - Competitive exclusion eliminated, and algal diversity increased
• – High snail density - Feeding requirements are high enough that snails eat preferred algae and less-preferred algae. • Algal diversity decreased
• • Christian’s study: • Native ants disperse ~30% of shrubland seeds in fynbos of South Africa. – Seed-dispersing ants bury seeds • Argentine ants displace native ant species – Substantial reductions in seedling recruitment by plants producing large seeds
• Power’s research: • Do California roach (Hsperoleucas symmetricus), and steelhead trout (Oncorhhyncus mykiss) significantly influence food web structure? – Predatory fish decrease algal densities. • Low predator density increased midge production. – Increased feeding pressure on algal populations. » Thus, fish act as Keystone Species.
• • Power’s research: • Do California roach (Hsperoleucas symmetricus), and steelhead trout (Oncorhhyncus mykiss) significantly influence food web structure? – Predatory fish decrease algal densities. • Low predator density increased midge production. – Increased feeding pressure on algal populations. » Thus, fish act as Keystone Species. Mutualists (not top predators) as Keystone Species • Cleaner fish in a coral reef system • Ant seed dispersers
• Introduction to Consumer Effects on Local Diversity
• Definition of consumer effects on local diversity
• Importance of understanding consumer effects in intertidal communities
• Key Species in Consumer Effects Research
• Snail species: Littorina littorea
• Green algae: Enteromorpha sp.
• Lubchenco's Study on Consumer Effects
• Impact of snail density on algal diversity
• Competitive exclusion and increase in algal diversity at medium snail density
• Feeding requirements and decrease in algal diversity at high snail density
• Support for Connell's Hypothesis
• Evidence of support for Connell's hypothesis in intertidal communities
• Application of Connell's hypothesis in communities with prairie dogs
• Disturbance and Productivity
• Relationship between disturbance, productivity, and species diversity
• Generalizations about species diversity in relation to environmental complexity and disturbance
• Determination of Keystone Species
• Importance of determining keystone species in intertidal communities
• Examples of keystone species and their impact on community structure
• Strong Interactions and Food Web Structure
• Study of food webs associated with wetland reeds
• Predator specialization and parasitic interactions in the food web
• Conclusion and Implications
• Summary of findings from consumer effects research
• Implications for conservation and management of intertidal communities

Chapter 8

• The effects of female mate choice on the evolution of ornamentation in males can be reduced by natural selection.
• Female in some species select mates based on the males ability to provide important resources
• Mating in wild plant population can be nonrandom
• Evolution of sociality in many species apes appears driven by the need for group defense of high quality territories and or defense of mates and you
• Kin selection and ecological constraints may have played key roles in the evolution of eusociality
• Behavioral ecology: study of social relations within and or between populations
• Sociobiology: branch of biology concerned with study of social relations; can significantly impact fitness of individuals and or populations.
• Fitness: number of offspring (genetic material) contributed by an individual to future generations.
• Male/Female: Depends on gamete size;Anisogamy
• Hermaphrodite: both functions: both gametes
• Sexual selection:difference in reproduction among individuals as a result of difference in mating success due to intrasexual selection( winner mate in competition within one sex) and or intersexual selection ( the opposite sex choosing a mate can be based on behavior, physical traits, observable fitness)

Mates choice and sexual selection in guppies

• Female select:prefer brightly colored males.
• Advantages traits: brightness,number of spots, total pigmented area
• Brightly colored males attract predators
• Endler’s natural selection study:Lab conditions,fields condition
• Panorpa scorpionflies: Adult males guard dead inverts; large prey more impressive, larger males more successful
• Nonrandom mating in plant populations: a comparative method experiment ; attempt to isolate a variable of interest by utilizing different species or populations.
• Cooperative breeding: benefits to helpers; inclusive fitness, inherited territory,kin selection
• Inclusive fitness: improves survival & reproduction of family groups
• Inherited territory: increase future reproductive success
• Kin selection: evolutionary force favoring helping behaviors
• Evolution of sociality: cooperative breeding, group defense, resource sharing
• Inclusive fitness: RgB-C>0~ RgB>c
• Rg:genetic relatedness
• B:reproductive benefit to the helper
• C: cost to the helper
• Green Woodhoopoes:• Philopatric species • Scarcity of cavities • Young remain and assist • Territory quality is important
• Florida Scrub Jay Aphelocoma coerulescens: •Cooperative breeders •Territorial groups: • Single breeding pair • 1-6 helpers • Pairs with help are ~ 1.5x more successful •Only cooperative in Florida range •Restricted habitat; no new territories

Cooperation among African Lions

• Kin Selection: Female cooperatively nurse, Prides protect young
• Males: Potential for siring depends on rank, disadvantageous to be in large coalition of unrelated males
• Eusociality: More complex level of sociality, defined by: multiple generations cohabitating, cooperative care of young

Population distribution & Abundance

• The environment limits the geographic distribution of every species.
• Clumped,random,and regular distribution.
• On small scales, individuals within populations are distributed in patterents that may be random, regular or clumped
• On large scales,individuals within all populations are clumped.
• Population density declines with increasing organism size
• Population: A group of individuals of a single species inhabiting a specific area
• Characterized by the number of individuals and their density
• Additional characteristics of a population include age distribution,growth rates,distribution,and abundance.
• Crude density: number of organism per unit area
• Ecological density: number of organism per unit of suitable habitat
• NO matter how uniform a habitat may appear it is not uniformly habitable because of micro-differences in light, moisture, temperature or other factors.
• Distribution: limited by physical environment; physiological/ behavioral compensation is finite

Niches

• Grinnell: focused on the effects of the physical environment
• Elton: included biotic and abiotic factors
• Niche: Summarizes environmental factors that influence growth, survival, and reproduction of a species.
• – Fundamental niche: is this “hypervolume,” or a theoretical range of conditions in which we may find a species.
• – Realized niche: includes interactions such as competition (or facilitation) that may restrict (or expand) environments where a species may live
• Kangaroo Distributions and Climate:
• – Macropus giganteus- Eastern Grey • Eastern 1/3 of continent.
• Macropus fuliginosus- Western Grey • Southern regions.
• Macropus rufus - Red • Arid / semiarid interior.

Tiger Beetle w/ Cold Climate Preference

• Cicindela longilabris
• – Tiger Beetle species
• – Metabolic rates higher; prefers temperatures lower than most other species
• • Traditional theory: desert shrubs are regularly spaced due to competition.
• – Phillips and MacMahon: distribution changes over time
• – Young shrubs clumped for ~3 reasons: • Seeds germinate at safe sites (establishment filter) • Seeds not dispersed from parent areas • Asexual (vegetative) reproduction – Middle-age shrubs randomly distributed – Older, larger shrubs regularly distributed due to
• In general, population density declines with increasing organism size. –
• Damuth found the population density of herbivorous mammals decreased with increased body size
• – Peters and Wassenberg found aquatic invertebrates tend to have higher population densities than terrestrial invertebrates of similar size.
• – Also, mammals tend to have higher population densities than birds of similar size.
• Plant population density decreases with increasing plant size.
• – Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities.
• Rabinowitz’ definition of commonness & rarity based on: • 1) range • 2) tolerance • 3) pop. size

Application: Rarity & Vulnerability to Extinction

• Range size and population size are not independent
• Abundant species usually widely distributed; rarer organisms usually have small, restricted distributions
• Rarity I: • Falco peregrinus • Panthera tigris • Extensive range • Broad habitat tolerance • Small local populations
• Rarity II: • Passenger pigeon • Harelip sucker fish • Extensive habitat range • Large populations • Narrow habitat tolerance
• Extreme Rarity: • Mountain Gorilla • Giant Panda • California Condor
• An estimated 7,725 animal species, many of which live in Africa and Asia, are currently threatened with extinction, largely due to land use change, and also hunting
• Globally: 32% of frogs and toads are T and E; 46.9% of salamanders are T And E

Dispersal and Population Dynamics

• Dispersal can increase or decrease local populations’ densities
• • Ongoing dispersal may join multiple subpopulations to form a metapopulation
• • Survivorship curves summarize patterns of survival in a population
• • Age distributions of populations reflect their history of survival and reproduction, and their potential for future growth
• • Life tables, combined with a species’ fecundity schedule can be used to estimate net reproductive rate (R0 ), geometric rate of increase (λ), generation time (T), and per capita rate of increase ®
• • Species’ distributions may (will!) change in response to climate shifts
• • Short generation times often linked to high rates of dispersal
• Expanding / invasive populations serve as an excellent source of observational information on dispersal
• Africanized Honeybees:Apis mellifera,Africanized (“killer”) honeybees disperse much faster than European honeybees., Within 30 years they occupied most of South America, Mexico, and all of Central America.
• Collared Doves:• Not influenced by humans. • Took place in small jumps; pulsed dispersal. – 45 km/yr
• Holling’s Functional Response Models:
• – Type 1: Feeding increases linearly with food density
• – Type 2: Feeding increases first linearly, then slows
• – Type 3: S-shaped; related to searching, then handling • At low food density, searching is limiter
• • Intermediate density: searching reduced, handling becomes important
• • High density: Levels off due to handling *Related to numerical response

# Lentic Ecosystems

## Lakes

- Most of the world's accessible freshwater is found in a few large lakes.

- The Great Lakes of North America contain approximately 20% of the world's freshwater.

- Other large lakes include Lake Baikal, Lake Tanganyika, and Lake Titicaca.

## Lentic Systems

- Lentic systems refer to standing water ecosystems, such as lakes.

- Examples of lentic systems include the Great Lakes, Lake Baikal, Lake Tanganyika, and Lake Titicaca.

• Great Lakes – ~20%

• Lake Baikal – ~20%

• Lake Tanganyika – <20%

• Lake Titicaca – Highest elevation navigable

## Physical Conditions of Lentic Systems

- Light: The color of a lake depends on the absorption of light and biological activity.

- Temperature: Lakes become thermally stratified as they warm.

- Water Movement: Wind-driven mixing of the water column is ecologically important.

## Seasonal Temperature Changes in Lakes

- In temperate lakes, temperature changes occur throughout the year:

1. January: Frozen surface, no mixing.

2. March: Temperatures become equal, wind causes mixing.

3. April: Thermocline forms, mixing slows.

4. June: Stratified, with distinct layers.

5. October: Temperatures equalizing.

6. November: Temperatures become equal, wind causes mixing.

## Chemical Conditions of Lentic Systems

- Oxygen:

- Oligotrophic lakes have low biological production and are generally well oxygenated.

- Eutrophic lakes have high biological production and are often depleted of oxygen, especially due to human activities.

- Chemical conditions in lakes depend on temperature, depth, and nutrient inputs.

## Human Influences on Lakes

- Human populations have had a profound, usually negative effect on lakes.

- Municipal and agricultural runoff contribute to pollution in lakes.

- The introduction of exotic species, such as Zebra Mussels, can disrupt the balance of lake ecosystems.

## Wetlands

- Wetlands are another type of lentic ecosystem.

- Examples of wetlands include marshes, swamps, bogs, and fens.

- Marshes are herbaceous-dominated and almost always inundated.

- Swamps are woody-dominated and not necessarily always inundated.

- Bogs are characterized by peat deposits, acidic water, and low nutrient content.

- Fens are similar to bogs but are fed by groundwater, have less acidic water, higher nutrient content, and more diversity.

## Temperature Relations in Lentic Ecosystem # Importance of Microclimate

tolerance ranges and extremes vary

1. Animals: 40-50 °C is upper limit for activity, some survive freezing when dormant

2. Plants: 0-70 °C when active, well below 0 when dormant a. Algae in hot springs b. Snow algae c. Thermophilic bacteria 40 → 90 oC, psychrophilic -2 → 9 oC

3. Upper limits – due to protein denaturization, especially enzymes

4. Lower limits – freeze damage, cell lysing and dehydration

Microclimate refers to small-scale weather variations that can occur within a larger climate. Both plants and animals have the ability to select microclimates in order to avoid temperature extremes. Here are some factors that contribute to the importance of microclimate:

1. Altitude: Higher altitude generally corresponds to lower temperatures. This is because as you go higher in elevation, the air becomes thinner and less able to retain heat. Therefore, organisms can find cooler temperatures by moving to higher altitudes.

2. Aspect: Aspect refers to the direction that a slope or surface faces. Different aspects can offer contrasting environments in terms of temperature. For example, a north-facing slope may receive less direct sunlight and be cooler than a south-facing slope.

3. Vegetation: Vegetation plays a crucial role in creating microclimates. Plants can provide shade, which can lower temperatures in their immediate vicinity. Additionally, different types of vegetation can have different effects on temperature and moisture levels.

4. Ground Color: The color of the ground can also influence microclimates. Darker-colored surfaces absorb more heat from the sun, leading to higher temperatures. Lighter-colored surfaces reflect more heat, resulting in cooler temperatures.

5. Bodies of Water: Bodies of water, such as lakes and oceans, can have a stabilizing effect on temperature. Water has a high specific heat, meaning it can absorb a large amount of heat energy without a significant change in temperature. This can help moderate the temperature of the surrounding area.

6. Thermal Stability of Aquatic Environments: Water has other properties that contribute to the thermal stability of aquatic environments. The latent heat of vaporization refers to the large amount of heat energy absorbed by water as it evaporates. This process can help cool the surrounding area. The latent heat of fusion, on the other hand, is the energy that water gives up to its environment as it freezes. This can help warm the surrounding area.

By selecting microclimates, organisms can find conditions that are more suitable for their survival and avoid temperature extremes that may be detrimental to their health. # Microclimates

Microclimates are small-scale weather variations that can be found within larger environments. Both plants and animals have the ability to select microclimates in order to avoid extreme temperatures. Here are some factors that contribute to the creation of microclimates:

- Altitude: Higher altitudes generally have lower temperatures. This means that organisms can find cooler microclimates by moving to higher elevations.

- Aspect: Different aspects, or orientations, of the land can offer contrasting environments. For example, a north-facing slope may be cooler and shadier than a south-facing slope.

- Vegetation: The presence of vegetation can create microclimates. Trees provide shade and can lower temperatures, while dense vegetation can trap heat and create warmer microclimates.

- Ground Color: The color of the ground can affect temperature. Dark-colored surfaces absorb more heat, while light-colored surfaces reflect more heat.

- Bodies of Water: Bodies of water can moderate temperatures by absorbing and releasing heat. Organisms can find cooler microclimates near bodies of water.

- Boulders and Burrows: Large rocks and burrows can provide shelter and insulation, creating microclimates with more stable temperatures.

# Acclimation

Acclimation is a reversible change in morphology and/or physiology within an individual in response to a change in the environment. It allows organisms to adjust to different environmental conditions. Here are some examples of acclimation:

- Different forms of acetylcholinesterase: Acetylcholinesterase is an enzyme involved in nerve signal transmission. Some organisms have different forms of this enzyme that are more effective at different temperatures. For example, one form may be more effective at 2°C, while another form may be more effective at 17°C.

- Cloned individuals of A. lentiformis: A study conducted on A. lentiformis (big saltbush) found that individuals grown in hot (43/30°C) and cold (23/18°C) conditions showed acclimation. The individuals grown in hot conditions had different morphological and physiological characteristics compared to those grown in cold conditions.

# Adaptation

Adaptation is an evolutionary response at the population level that involves changes in gene frequencies. It is a long-term process that allows populations to become better suited to their environments. Adaptations can be morphological, physiological, or behavioral. Acclimation can also be considered an adaptation, as it allows individuals to adjust to their immediate environment # Thermoregulation in Animals

## Introduction

Thermoregulation is the process by which animals maintain their body temperature within a certain range, regardless of the environmental temperature. This is important for the proper functioning of physiological processes in the body. In thermoregulation, animals balance the heat gained from the environment with the heat lost from their bodies.

## Heat Gain

Animals can gain heat through various mechanisms:

- Convection: Heat can be gained or lost through the movement of air or water around the body. For example, sitting near a warm fire or swimming in warm water can increase heat gain through convection.

- Electromagnetic radiation: Animals can absorb heat from the sun or other sources of radiation. This is particularly important for animals that bask in the sun to warm up.

- Metabolism: Birds and mammals have the ability to generate heat through metabolic processes. This heat is produced as a byproduct of energy production in the body.

## Heat Loss

Animals can lose heat through different processes:

- Evaporation: Heat is lost when water evaporates from the body surface. This is particularly important for animals that sweat or pant to cool down.

- Convection: Heat can also be lost through convection, where warm air or water moves away from the body, taking heat with it.

- Conduction: Heat can be transferred from the body to a cooler object through direct contact. For example, sitting on a cold surface can result in heat loss through conduction.

## Thermoregulation Strategies

Animals have different strategies to regulate their body temperature:

- Poikilotherms: These animals have body temperatures that fluctuate with the environmental temperatures. They rely on external heat sources to warm up and cool down. Examples include reptiles and amphibians.

- Homeotherms: These animals maintain a constant body temperature regardless of the environmental temperature. They have mechanisms to generate or dissipate heat as needed. Most homeotherms are endotherms.

- Ectotherms: These animals rely solely on external heat sources to regulate their body temperature. They do not have the ability to generate heat internally. Examples include reptiles and some fish.

- Endotherms: These animals can generate heat internally through metabolic processes. They have a higher metabolic rate compared to ectotherms, allowing them to maintain a constant body temperature even in cold environments. Birds and mammals are endotherms.

## Exceptions and Grey Areas

While the terms poik

# Temperature Regulation in Animals

## Homeotherms and Endotherms

- Most homeotherms are endotherms, meaning they generate their own body heat.

- However, not all homeotherms are endotherms.

- Homeotherms can also exhibit a degree of ectothermy, where they rely on external sources of heat to regulate their body temperature.

- There are always exceptions and grey areas in temperature regulation among animals.

## Ectotherms and Poikilotherms

- Ectotherms are animals that rely on external sources of heat to regulate their body temperature.

- Not all poikilotherms are ectotherms.

- Some poikilotherms can exhibit a great degree of endothermy, where they can generate their own body heat.

- Examples of poikilotherms with endothermy include certain lizard species.

## Temperature Regulation by Ectothermic Animals

- Ectothermic animals, such as the horned lizard, have different strategies for temperature regulation.

- Some grasshopper species can adjust for radiative heating by varying the intensity of pigmentation during development.

## Temperature Regulation by Endothermic Animals

- Endothermic animals have both behavioral and physiological mechanisms for temperature regulation.

- Behavioral mechanisms include migration, burrowing, body orientation, nocturnal activity, hibernation, torpor, and aestivation.

- Physiological mechanisms include thermal windows, insulation, shivering, evaporation, vaso-constriction/dilation, counter-current exchange, and diapause.

- Endotherms have the advantage of being able to quickly generate heat, leading to homeothermy and the ability to exploit a range of habitats.

- However, being endothermic also comes with a high energy cost and a lower limit to body size.

## Temperature Regulation in Plants

- Plants also have mechanisms for temperature regulation.

- They can enter a state of dormancy or sto # Plant Growth and Adaptation

Plants have various mechanisms to adapt to their environment and optimize their growth. Some of these adaptations include leaf size, growth form, dormancy, stomatal control, and pubescence. Let's explore these concepts further:

## Leaf Size

- Leaf size can vary among different plant species and can be influenced by environmental factors.

- Larger leaves are generally found in plants growing in shaded areas, as they have a larger surface area to capture sunlight for photosynthesis.

- Smaller leaves are often found in plants growing in arid environments, as they reduce water loss through transpiration.

## Growth Form

- Growth form refers to the overall shape and structure of a plant.

- Different plant species have different growth forms, such as trees, shrubs, or herbs.

- The growth form of a plant can be influenced by factors like light availability, competition for resources, and environmental conditions.

## Dormancy

- Dormancy is a period of reduced metabolic activity in plants.

- It is often triggered by unfavorable environmental conditions, such as extreme temperatures or drought.

- During dormancy, plants conserve energy and resources until conditions become more favorable for growth.

## Stomatal Control

- Stomata are small openings on the surface of leaves that regulate gas exchange and water loss in plants.

- Plants can control the opening and closing of stomata to regulate water loss and carbon dioxide uptake.

- Stomatal control is influenced by factors like light intensity, humidity, and carbon dioxide levels.

## Pubescence

- Pubescence refers to the presence of fine hairs or trichomes on the surface of leaves or stems.

- These hairs can help reduce water loss by creating a microclimate around the plant, reducing evaporation.

- Pubescence can also provide protection against herbivores and excessive sunlight.

## Thermoregulation

- Plants have mechanisms to regulate their temperature and adapt to different temperature conditions.

- Some plants exhibit diaheliotropic growth, where they orient their leaves perpendicular to the sun's rays to minimize heat absorption.

- Other plants exhibit paraheliotropic growth, where they orient their leaves parallel to the sun's rays to maximize heat absorption.

- Plants can also undergo dormancy or adjust their stomatal control, leaf size, and pubescence to regulate their temperature.

## Generalizations

1. Plants find it more challenging to adapt to high temperatures compared to low temperatures.

2. Temperature tolerance range in many temperate # Physiological Damage due to Anaerobic Conditions

Anaerobic conditions refer to environments where there is a lack of oxygen. In such conditions, organisms that rely on aerobic respiration for energy production may experience physiological damage. Here are some examples of physiological damage that can occur due to anaerobic conditions:

1. **Lack of Oxygen**: The absence of oxygen can lead to a decrease in the availability of oxygen for cellular respiration. This can result in a reduced production of ATP (adenosine triphosphate), which is the main energy currency of cells. Without sufficient ATP, cells may not be able to carry out their normal functions, leading to physiological damage.

2. **Accumulation of Toxic Substances**: In anaerobic conditions, certain metabolic processes may be altered, leading to the accumulation of toxic substances. For example:

- **Ammonia (NH4)**: In the absence of oxygen, nitrogen-containing compounds may be converted into ammonia. High levels of ammonia can be toxic to cells and can disrupt various physiological processes.

- **Hydrogen Sulfide (H2S)**: Anaerobic conditions can promote the production of hydrogen sulfide, which is a toxic gas. Exposure to high levels of hydrogen sulfide can cause damage to tissues and organs.

- **Methane (CH4)**: Methane is another byproduct of anaerobic metabolism. While it is not directly toxic to cells, high levels of methane can displace oxygen in the environment, further exacerbating the lack of oxygen for aerobic organisms.

# Effects on Animals

Anaerobic conditions can have various effects on animals, leading to both immediate and long-term consequences. Here are some examples:

1. **Drowning**: Animals that rely on oxygen from the air, such as mammals and birds, can drown in anaerobic conditions where there is no access to oxygen. This can result in suffocation and death.

2. **Loss of Insulation**: Aquatic animals, such as fish, rely on a layer of mucus or specialized structures to maintain insulation and protect themselves from temperature changes. In anaerobic conditions, the loss of insulation can make them more vulnerable to temperature fluctuations and other environmental stressors.

3. **Loss of Nesting Sites**: Anaerobic conditions can lead to changes in the availability of suitable nesting sites for animals. For example, in wetland areas where anaerobic conditions prevail, the loss of nesting sites can

# Water Content of Air

## Relative Humidity

- Relative humidity is the ratio of the water vapor density to the saturation water vapor density, multiplied by 100.

- Water vapor density is the amount of water vapor per unit volume of air.

- Saturation water vapor density is the maximum amount of water vapor that air can hold at a given temperature.

- Saturation water vapor density changes with temperature.

## Atmospheric Pressure

- Total atmospheric pressure is the pressure exerted by all gases in the air.

- Water vapor pressure is the partial pressure due to water vapor.

- Saturation water vapor pressure is the pressure exerted by water vapor in air that is saturated with water.

- Vapor pressure deficit is the difference between the water vapor pressure and the saturation water vapor pressure at a particular temperature.

# Water Movement Between Soils and Plants

## Water Potential

- Water potential (Ψ) is the capacity of water to exert force.

- Pure water has a water potential of 0.

- Water potential in nature is generally negative.

## Factors Affecting Water Potential

- Ψsolute measures the reduction in water potential due to dissolved substances.

- Ψmatric is the water's tendency to adhere to container walls, creating matric forces.

- Ψpressure is the reduction in water potential due to negative pressure created by water evaporating from leaves.

## Water Movement

- Water moves from the soil to the plant as long as the water potential of the plant is lower than the water potential of the soil.

- The Scholander-type pressure bomb chamber is used to measure water potential.

## Other Mechanisms

- Guttation is when root pressure forces excess water from leaves.

- Hydraulic redistribution is the movement of water within the soil by plant roots.

# Water Acquisition

## Frost Flowers

- "Frost flowers" are delicate ice structures that form on plants in cold conditions. # Water Acquisition by Plants

Plants have different strategies for acquiring water depending on the availability of water in their environment. The extent of root development in plants often reflects these differences.

- In dry environments, plants develop deeper roots to extract water from deep within the soil profile.

- Studies conducted on common Japanese grasses, Digitaria adscendens and Eleusine indica, found that D. adscendens, a dune grass, had a 7x increase in root mass compared to E. indica, which is not a dune inhabitant.

# Water Regulation on Land - Plants

Plants have mechanisms to regulate their water balance and minimize water loss through a process called transpiration. The water balance equation for plants is:

Wip = Wr + Wa - Wt - Ws

- Wip represents the plant's internal water.

- Wr represents water absorption by the roots.

- Wa represents water absorption from the air.

- Wt represents transpiration.

- Ws represents secretions.

To regulate their water balance, plants have various adaptations:

- Stomatal control: Plants can open and close their stomata to control the rate of transpiration.

- Short growth cycle: Some plants have shorter growth cycles to minimize water loss.

- Dormancy: Plants can enter a dormant state during periods of water scarcity.

- Succulence (CAM photosynthesis): Some plants have adapted to store water in their tissues and use a different type of photosynthesis called CAM photosynthesis.

- Phreatophyte: Plants with deep roots that can extract water from deep within the soil profile.

- Leaf adaptations: Plants have various leaf adaptations to minimize water loss, such as thick cuticles, small stomates, sunken stomates, pubescence (fine hairs on the leaf surface), and leaf rolling.

# Water Regulation on Land - Animals

Animals also have mechanisms to regulate their water balance and minimize water loss. The water balance equation for animals is:

Wia = Wd + Wf + Wa - We - Ws

- Wia represents the animal's internal water.

- Wd represents water obtained through drinking.

- Wf represents water obtained through food.

- Wa represents water absorbed from the air.

- We represents water loss through evaporation.

- Ws represents water loss through secretion/excretion.

# Dissimilar Organisms with Similar Approaches to Desert Life

Despite being different organisms, some species have similar approaches to survive in desert environments:

- # Desert Adaptations

## Scorpions

- Slow down their activities to conserve energy and reduce water loss.

- Stay in shaded areas to avoid direct sunlight and reduce heat absorption.

- Have long lifespans.

- Have low metabolic rates, meaning they require less energy to survive.

## Cicadas (Diceroprocta apache)

- Remain active even on the hottest days.

- Perch on branch tips to take advantage of cooler microclimates.

- Reduce their abdomen temperature by feeding on xylem fluid of pinyon pine trees. This fluid helps cool their bodies.

These are two examples of how different organisms have adapted to survive in the desert. Scorpions have a slower and more energy-conserving approach, while cicadas have developed strategies to regulate their body temperature and remain active in extreme heat.

# Chapter 8: Evolution of Social Relations

## Effects of Female Mate Choice on Male Ornamentation

- Female mate choice can influence the evolution of ornamentation in males.

- However, other sources of natural selection can reduce the effects of female mate choice.

- In some species, females select mates based on the male's ability to provide important resources.

## Nonrandom Mating in Wild Plant Populations

- Mating in wild plant populations can be nonrandom.

- This means that certain individuals are more likely to mate with each other than with others.

## Evolution of Sociality

- The evolution of sociality in many species is driven by the need for group defense of high-quality territories and/or defense of mates and young.

- Kin selection and ecological constraints may have played key roles in the evolution of eusociality.

## Terminology

- **Behavioral Ecology**: The study of social relations within and/or between populations.

- **Sociobiology**: The branch of biology concerned with the study of social relations.

- **Fitness**: The number of offspring (genetic material) contributed by an individual to future generations.

- **Male/Female**: The designation depends on gamete size (anisogamy).

- **Hermaphrodite**: An organism that has both male and female reproductive functions.

- **Sexual Selection**: Differences in reproductive rates resulting from differing mating success, including intrasexual and intersexual selection.

- **Intrasexual Selection**: Competition within one sex, where the winner mates.

- **Intersexual Selection**: Selection based on mate choice, where individuals of one sex choose mates based on certain traits.

Examples:

- Bluehead wrasse (Thalassoma bifasciatum) is an example of a species where males develop bright blue heads to attract females.

- Slipper limpet (Crepidula fornicata) is an example of a hermaphroditic species where individuals can function as both males and females.

Note: The study notes provided are concise summaries of the concepts discussed in Chapter 8. It is recommended to refer to the textbook or lecture materials for a more comprehensive understanding of the topic. # Sexual Selection and Mate Choice

Sexual selection refers to the differences in reproduction among individuals as a result of differences in mating success due to intrasexual selection (competition within one sex) and/or intersexual selection (the opposite sex choosing a mate). It plays a role in shaping the evolution of certain traits and behaviors related to mating.

## Intrasexual Selection

- Intrasexual selection involves competition within one sex, where individuals compete for access to mates.

- The winner of the competition typically mates with the opposite sex.

- This type of selection can lead to the evolution of traits that enhance an individual's ability to compete, such as physical strength or aggressive behavior.

## Intersexual Selection

- Intersexual selection involves the opposite sex choosing a mate based on certain traits or behaviors.

- Mate choice can be based on various factors, including behavior, physical traits, observable fitness, and other advantageous traits.

- The selection process by the opposite sex can influence the evolution of traits that are preferred by mates.

## Does Sexual Selection Ensure the Best Adapted Individuals Mate?

- Sexual selection does not necessarily ensure that the best adapted individuals (i.e., the best genotype) will mate.

- Mate choice is often based on certain traits or behaviors that may not directly correlate with overall fitness or adaptation.

- For example, in some cases, brightly colored males may be preferred by females, but this can also make them more visible to predators.

## Examples of Mate Choice in Guppies and Scorpionflies

### Guppies

- Female guppies tend to select or prefer brightly colored males.

- Advantageous traits that females look for include brightness, number of spots, and total pigmented area.

- However, brightly colored males may also attract predators, creating a potential negative tradeoff.

### Scorpionflies

- Male scorpionflies guard dead invertebrates as a resource for potential mates.

- Larger prey items are more impressive and can increase the male's chances of mating.

- Larger males are generally more successful in attracting mates.

## Nonrandom Mating in Plant Populations

- Nonrandom mating can also occur in plant populations.

- A comparative method experiment can be used to study nonrandom mating by utilizing different species or populations.

- The goal is to isolate a variable of interest and observe its effect on mating patterns.

Overall, sexual selection and mate choice play important roles in shaping the evolution of traits and behaviors related to mating. It is not always the case that the best adapted individuals will mate # Evolution of Sociality

Sociality refers to the behavior of individuals within a population that involves interactions and cooperation with others. It can be observed in various species, including plants and animals. The evolution of sociality is influenced by factors such as nonrandom mating, cooperative breeding, group defense, resource sharing, and inclusive fitness.

## Nonrandom Mating in Plant Populations

Nonrandom mating in plant populations refers to the phenomenon where mating between individuals is not random but influenced by certain factors. Evidence of nonrandom mating has been observed in both field and laboratory experiments. Some possible causes of nonrandom mating include maternal control and pollen competition.

## Cooperative Breeding

Cooperative breeding is a form of sociality observed in certain species where individuals within a family group work together to raise offspring. This behavior benefits the helpers in several ways:

- Inclusive fitness: By helping to improve the survival and reproduction of the family group, helpers increase their own inclusive fitness.

- Inherited territory: Helpers may gain future reproductive success by inheriting the territory of the breeding pair.

- Kin selection: Kin selection is an evolutionary force that favors helping behaviors among genetically related individuals.

## Evolution of Sociality in Green Woodhoopoes

Research conducted by Ligon and Ligon on Green Woodhoopoes, a philopatric species with a scarcity of cavities, has shed light on the evolution of sociality. Some key findings include:

- Young individuals remain and assist in the family group.

- Territory quality plays an important role in the evolution of sociality.

- The lifetime reproductive success of males and females in social groups is an area of further study.

## Evolution of Sociality in Florida Scrub Jay

The Florida Scrub Jay, a cooperative breeder, exhibits sociality in its territorial groups. Some notable observations include:

- Territorial groups consist of a single breeding pair and 1-6 helpers.

- Pairs with helpers are approximately 1.5 times more successful than those without helpers.

- Cooperative breeding is only observed in the Florida range of the species, where restricted habitat limits the availability of new territories.

## Cooperation Among African Lions

Cooperation among African lions is another example of sociality in the animal kingdom. African lions live in prides consisting of multiple females, their offspring, and a few adult males. Cooperation within the pride allows for efficient hunting, defense of territory, and care of young.

Overall, the evolution of sociality is influenced by various factors such # Evolution of Sociality

## Eusociality

- Eusociality is a more complex level of sociality characterized by:

- Multiple generations co-habitating

- Cooperative care of young

- Division of individuals into reproductive and non-reproductive castes

- Examples of eusocial species include ants and bees

## Comparative Method Experiment

- The comparative method is used to isolate a variable of interest by studying different species or populations

- In the context of eusociality, researchers may compare different ant species to understand the evolution of sociality

## Kin Selection

- Kin selection is an evolutionary force that favors helping behaviors among related individuals

- It explains altruistic behavior in nature, where individuals may sacrifice their own well-being to benefit their relatives

- Examples of kin selection in action include:

- Females cooperatively nursing offspring

- Prides of lions protecting young

## Males in Social Groups

- In social groups, the potential for siring offspring often depends on rank

- It may be disadvantageous for males to be in a large coalition of unrelated males

## Limited Breeding Opportunities

- Limited breeding opportunities can drive the evolution of sociality

- Cooperative breeding, where individuals help raise offspring that are not their own, can provide benefits such as inclusive fitness and inherited territory

- Inclusive fitness refers to the improvement of survival and reproduction of family members, increasing future reproductive success

## Other Explanations for Altruistic Behavior

- While inclusive fitness and kin selection are rational explanations for altruistic behavior in nature, there may be other factors at play

- Further research is needed to fully understand the complexities of social behavior and altruism in different species

# Population Ecology

## Introduction to Population Ecology

- Population ecology is the study of how populations of organisms interact with their environment

- It focuses on understanding the dynamics of population size, growth, and distribution

## Genetics and Population Ecology

- Genetic factors play a role in population ecology, influencing traits and adaptations that affect survival and reproduction

## Characteristics of Populations

- Populations have certain characteristics that can be studied, including:

- Dispersion: how individuals are distributed within a population

- Mortality/survivorship: patterns of death and survival within a population

- Age structure: the distribution of individuals across different age groups

- Birth rate: the rate at which new individuals are born into a population

- Growth

# Population Ecology

## Introduction / Genetics

- Population: A group of individuals of a single species inhabiting a specific area.

- Characteristics of a population include the number of individuals, their density, age distributions, growth rates, distribution, and abundance.

- The environment limits the geographic distribution of every species.

- On small scales, individuals within populations are distributed in patterns that may be random, regular, or clumped.

- On large scales, individuals within all populations are clumped.

- Population density declines with increasing organism size.

## Dispersion

- Dispersion refers to the pattern of spacing among individuals within a population.

- There are three main types of dispersion:

- Clumped: Individuals are grouped together in patches or clusters.

- Random: Individuals are spaced randomly throughout the population.

- Regular: Individuals are evenly spaced throughout the population.

## Mortality/Survivorship

- Mortality refers to the death rate within a population.

- Survivorship refers to the proportion of individuals that survive to a given age.

- Survivorship curves can be classified into three types:

- Type I: High survivorship in early and middle life, followed by a rapid decline in old age.

- Type II: Constant survivorship throughout the lifespan.

- Type III: Low survivorship in early life, followed by a period of high survivorship.

## Age Structure

- Age structure refers to the distribution of individuals in different age groups within a population.

- It provides insights into the reproductive potential and future growth of a population.

- Age structure diagrams can be classified into three types:

- Expanding: A large proportion of individuals are in younger age groups, indicating high reproductive potential and potential for population growth.

- Stable: The proportion of individuals in each age group remains relatively constant, indicating a stable population.

- Declining: A large proportion of individuals are in older age groups, indicating low reproductive potential and potential for population decline.

## Birth Rate

- Birth rate refers to the number of offspring produced per unit of time within a population.

- It is influenced by factors such as reproductive age, reproductive success, and environmental conditions.

- High birth rates can lead to population growth, while low birth rates can lead to population decline.

## Growth

- Population growth refers to the change in population size over time.

- It is influenced by birth rates, death rates, immigration (individuals moving into the population), and emigration (individuals moving out # Study Notes: Distribution Patterns and Organism Interactions

## Distribution Patterns

- Organisms within populations can be distributed in different ways:

- Uniform: evenly spaced individuals

- Clumped: individuals grouped together

- Random: individuals scattered randomly

### Distributions of Desert Shrubs

- Traditional theory suggests that desert shrubs are regularly spaced due to competition.

- However, studies by Phillips and MacMahon have shown that the distribution of desert shrubs can change over time.

- Young shrubs tend to be clumped for several reasons:

- Seeds germinate at safe sites (establishment filter)

- Seeds are not dispersed far from parent areas

- Asexual (vegetative) reproduction

- Middle-aged shrubs are randomly distributed.

- Older, larger shrubs are regularly distributed.

## Organism Interactions

### Competition

- As populations increase in density, competition for resources becomes more intense.

- Competition can lead to changes in distribution patterns, organism interactions, and organism size.

- Different types of competition:

- Intraspecific competition: competition between individuals of the same species

- Interspecific competition: competition between individuals of different species

### Organism Size and Population Density

- In general, population density tends to decline with increasing organism size.

- Damuth's study found that the population density of herbivorous mammals decreased with increased body size.

- This could be due to larger organisms requiring more resources and space, leading to lower population densities.

## Microclimates and Species Preferences

- Different species may have different preferences for temperature and climate.

- For example, the Tiger Beetle species Cicindela longilabris has a higher metabolic rate and prefers lower temperatures compared to other species.

- This preference for colder climates may result in the species occupying different microclimates within a larger habitat.

Remember to review these concepts and their implications for distribution patterns, organism interactions, and organism size as populations increase in density. # Organism Size and Population Density

- Damuth found that the population density of herbivorous mammals decreases as body size increases.

- Peters and Wassenberg found that aquatic invertebrates generally have higher population densities than terrestrial invertebrates of similar size.

- Mammals tend to have higher population densities than birds of similar size.

# Plant Size and Population Density

- Plant population density decreases as plant size increases.

- Tree seedlings can live at high densities, but as the trees grow, density progressively declines until mature trees are at low densities.

- This is known as the "self-thinning" principle.

# Application: Rarity & Vulnerability to Extinction

- Rabinowitz defined commonness and rarity based on range, tolerance, and population size.

- Range size and population size are not independent; abundant species are usually widely distributed, while rarer organisms have small, restricted distributions.

## Rarity I

- Examples: Falco peregrinus, Panthera tigris

- Extensive range

- Broad habitat tolerance

- Small local populations

## Rarity II

- Examples: Passenger pigeon, Harelip sucker fish

- Extensive habitat range

- Large populations

- Narrow habitat tolerance

## Extreme Rarity

- Examples: Mountain Gorilla, Giant Panda, California Condor

- Endangered species with very small populations

# Endangered Species

- Mammals: 510 species

- Birds: 532 species

- Reptiles: 174 species

- Amphibians: 1,180 species

- Fish: 491 species

- An estimated 7,725 animal species, many of which live in Africa and Asia, are currently threatened with extinction due to land use change and hunting.

# Consequences of Limiting Resources and Importance of Preventing Extinctions

- When resources become limiting over time, there can be several possible consequences:

- Competition among individuals for limited resources

- Decline in population size

- Changes in species composition and diversity

- It is important to prevent or limit extinctions because:

- Every species plays a role in maintaining ecosystem balance and functioning.

- Loss of species can disrupt food webs and ecological interactions.

- Biodiversity is important for human well-being, providing ecosystem services such as clean air and water, pollination, and climate regulation.

- Extinctions can have cascading effects on other species and ecosystems. # TINCTION

## Factors contributing to extinction

- Habitat alteration: 30%

- Commercial hunting: 21%

- Exotic introductions: 16%

- Sport hunting: 12%

- Hunting for food: 6%

- Collections: 5%

- Pollution: 3%

- Miscellaneous: 7%

## Minimum viable population

- The minimum viable population is the population size below which extinction cannot be avoided.

## Resource limitation and extinction

- As resources become limiting, the chances of extinction increase.

- Time is a crucial factor in determining the likelihood of extinction.

- When resources are limited, competition among individuals for those resources increases, leading to a higher risk of extinction.

- Fluctuating equilibrium: This refers to the balance between population growth and resource availability. When resources are abundant, populations can grow. However, when resources become limited, populations may decline or even go extinct.

## Extinction of Frogs, Toads, and Salamanders

- 32% of frogs and toads are threatened or endangered.

- 46.9% of salamanders are threatened or endangered.

- These numbers indicate the high vulnerability of these amphibian species to extinction globally.

# Chapter 10: Population Dynamics

## Dispersal and Population Dynamics

- Dispersal can either increase or decrease local population densities.

- Dispersal involves the movement of individuals into (immigration) or out of (emigration) a local population.

- Dispersal is often understudied because it often involves the movement of small individuals (seeds, larvae, etc.) over large areas.

- Short generation times are often associated with high rates of dispersal.

## Survivorship Curves

- Survivorship curves summarize patterns of survival in a population.

- They show the proportion of individuals surviving at different ages.

- There are three types of survivorship curves:

1. Type I: High survivorship in early and middle life, followed by a rapid decline in old age. Example: Humans.

2. Type II: Constant survivorship throughout life. Example: Birds.

3. Type III: Low survivorship in early life, followed by a period of high survivorship. Example: Insects.

## Age Distributions

- Age distributions of populations reflect their history of survival and reproduction, as well as their potential for future growth.

- Age distributions can be used to estimate the net reproductive rate (R0), geometric rate of increase (λ), generation time (T), and per capita rate of increase (r) of a species.

## Species Distributions and Climate Shifts

- Species' distributions may change in response to climate shifts.

- Climate change can cause shifts in temperature and precipitation patterns, which can affect the suitable habitat for a species.

- Species may need to disperse to find new suitable habitats as their current habitats become less favorable.

## Examples of Dispersal

1. Africanized Honeybees:

- Africanized honeybees disperse much faster than European honeybees.

- Within 30 years, they occupied most of South America, Mexico, and all of Central America.

2. Collared Doves:

- Collared doves spread from Turkey into Europe after 1900.

- The dispersal of collared doves began suddenly.

## Population Dynamics Equation

The population dynamics equation is used to calculate the population size at a given time (Nt) based on the population size at the previous time (Nt-1) and various factors:

Nt = Nt-1 + B + I - D - E

- B: Births or births from # Dispersal in Response to Changing Food Supply

Dispersal is the movement of individuals from one area to another. It can occur in response to changing food supply, among other factors. Here are some key points to understand about dispersal in response to changing food supply:

- Holling observed that there are numerical responses to increased prey availability. This means that when there is more food available, the population of predators that feed on that food also increases.

- Increased prey density leads to an increased density of predators. This is because more prey means more food available for predators, which allows them to reproduce and increase their population.

- Individuals may move into new areas in response to higher prey densities. When there is an abundance of food in a particular area, individuals may disperse to that area in order to take advantage of the available resources.

- Prey populations are generally more responsive to environmental conditions than predator populations. This means that changes in prey populations are often more noticeable and occur more rapidly in response to changes in food supply.

Holling's Functional Response Models describe how feeding behavior changes with food density. There are three types of functional responses:

1. Type 1: Feeding increases linearly with food density.

2. Type 2: Feeding increases first linearly, then slows down.

3. Type 3: Feeding follows an S-shaped curve, with an initial slow increase, followed by a rapid increase, and then leveling off.

The type of functional response observed depends on the density of the food supply. At low food density, searching for food is the limiting factor. At intermediate density, searching is reduced and handling (consuming the food) becomes more important. At high food density, feeding levels off due to the time it takes to handle each individual prey item.

In summary, dispersal in response to changing food supply is a common phenomenon observed in nature. When there is an increase in prey availability, predators may disperse to areas with higher prey densities. Prey populations are generally more responsive to changes in food supply than predator populations. The type of functional response observed depends on the density of the food supply, with different factors becoming limiting at different densities. # Dispersal in Response to Changing Food Supply

- Increased prey availability can lead to increased density of predators.

- Prey populations are more responsive to environmental conditions than predator populations.

- Individuals may move into new areas in response to higher prey densities.

# Dispersal in Rivers and Streams

- Drift: gradual passive downstream movement in rivers and streams.

- Spates: flash flood events that can cause movement of organisms downstream.

- Colonization Cycle: involves upstream/downstream dispersal, movement, and reproduction.

# Metapopulations

- A metapopulation is a group of subpopulations living on patches of habitat connected by an exchange of individuals.

- Alpine Butterfly study: Marked butterflies in 20 meadows and found that most were recaptured in the original meadow, but a small percentage dispersed to different meadows. Butterflies in smaller meadows were more likely to disperse.

- Lesser Kestrels study: Found that younger breeding females and males were more likely to disperse to other subpopulations. Distance between colonies and frequency of dispersal showed a negative correlation, with smaller subpopulations being more likely to emigrate.

# Patterns of Survival

- Organisms within populations can be distributed not only in space, but also in time.

- Survivorship curves and life tables are used to study patterns of survival.

- Three main methods of estimation for life tables: cohort life table, identify individuals born at the same time and keep track of their survival. # Life Tables and Age Distribution

## Life Tables

- Life tables are used to study the mortality and survival patterns of a population.

- They record the age at death of individuals in a population.

- The static life table is a commonly used type of life table that calculates the difference in the proportion of individuals in each age class.

- It assumes that the differences in mortality rates between age classes are representative of the overall mortality pattern in the population.

## Survivorship Curve

- A survivorship curve is a graphical representation of the mortality and survival patterns in a population.

- It is constructed using data from a life table.

- The survivorship curve for Dall Sheep, collected by Murie, showed a bi-modal mortality pattern, with high mortality rates in the first year and between 9-13 years of age.

## Types of Survivorship Curves

1. Type I: Most songbirds and Dall Sheep exhibit a Type I survivorship curve, where there is high survival among the young and most mortality occurs in old age.

2. Type II: Cliome, a perennial plant, exhibits a Type II survivorship curve, where the mortality rate is relatively constant throughout the lifespan.

3. Type III: Some organisms, such as certain insects and plants, exhibit a Type III survivorship curve, where there is high mortality among the young and high survival among a few individuals that reach adulthood.

## Age Distribution

- Age distribution refers to the proportion of individuals in a population at different age classes.

- It reflects the population's history of survival, reproduction, and growth potential.

- The age distribution can be affected by various aspects of life history, including reproductive strategies (once or multiple), sexual selection (success in finding a mate), and social behaviors (altruistic fitness and kin selection).

## Age Distribution

- Age distributions reflect a population's history of survival, reproduction, and growth potential.

- It is affected by aspects of Life History, such as reproductive strategies, sexual selection, and social behaviors.

- Age distribution can be biased towards certain age groups, depending on the population's characteristics.

- Examples:

- Dall sheep: Type I age distribution

- Most songbirds: Type II age distribution

- Cliome, a perennial plant: Type III age distribution

## Rates of Population Change

- Rates of population change can be estimated using life tables and other factors.

- Birth rate: Number of young born per reproductive individual over a given period of time.

- Fecundity schedule: Tabulation of birth rates for reproductive individuals of different ages.

- Key measures that can be estimated:

- Net reproductive rate (R0): Average number of offspring left behind by each individual.

- R0 = 1 for a perfectly stable population.

- R0 > 1 for an increasing population.

- R0 < 1 for a declining population.

- Geometric rate of increase (λ): Ratio of population size at two points in time.

- Generation time (T): Average age of reproduction.

- Per capita rate of increase (r)

## Examples

- Miller data: Age distribution of Quercus alba (White Oaks) biased towards young trees, indicating a stable or growing population.

- Galapagos finches (Geospiza spp.): Age distribution affected by environmental variation, such as droughts and reproductive output increase in response to favorable conditions. # Population Ecology Study Notes

## Rates of Population Change

- Rate of increase (r) is the population size (N) divided by the time span (t), which is determined by the birth rate minus the death rate.

- The net reproductive rate (R0) is the average number of offspring left by an individual for a population.

- The growth rate of a population can be estimated using the geometric rate of increase (λ) for populations with non-overlapping generations.

- The geometric rate of increase (λ) is equal to the net reproductive rate (R0) for populations with non-overlapping generations.

- The geometric rate of increase (λ) is not equal to the net reproductive rate (R0) for populations with overlapping generations.

## Survivorship & Seed Production in Phlox drummondii

- Survivorship refers to the number or proportion of individuals surviving at different ages.

- Phlox drummondii has age classes and the survivorship can be represented by a graph.

- The average number of offspring at any given age is called the fecundity schedule.

- The product of the number of individuals surviving at each age (lx) and the number of offspring at each age (mx) gives the average number of offspring left by an individual for the population (Σ lxmx).

- The net reproductive rate (R0) is the sum of the average number of offspring left by an individual for the population (Σ lxmx).

## Rates of Population Change in Different Species

- Pulsed breeding species, like Phlox drummondii, have non-overlapping generations and the geometric rate of increase (λ) can be used to estimate the growth rate.

- Continuous breeding species, like Kinosternon subrubrum, have overlapping generations and the geometric rate of increase (λ) does not equal the net reproductive rate (R0).

- The net reproductive rate (R0) is not applicable for continuous breeding species as not all individuals reproduce and there are multiple nesting events during a year.

## Growth and Per Capita Rate of Increase

- The per capita rate of increase (r) can be estimated by calculating the natural logarithm of the ratio of the population size at two time intervals (Nt/Nt-1) divided by the time interval (t).

- The per capita rate of increase (r) can also be estimated using the natural logarithm of the net reproductive rate (R0) divided by the generation time (T).

# Reproduction

Reproduction is the biological process by which new individuals of the same species are produced. It is essential for the survival and continuation of a species. There are two main types of reproduction: sexual reproduction and asexual reproduction.

## Sexual Reproduction

- In sexual reproduction, two parents contribute genetic material to produce offspring that inherit traits from both parents.

- The process involves the fusion of specialized cells called gametes, which are produced by the male and female reproductive organs.

- The offspring produced through sexual reproduction exhibit genetic variation, which can be advantageous for the survival of a species in changing environments.

- Examples of sexual reproduction include the mating of animals and the pollination of plants.

## Asexual Reproduction

- In asexual reproduction, a single parent produces offspring that are genetically identical to the parent.

- There is no fusion of gametes, and the offspring are clones of the parent.

- Asexual reproduction is advantageous in stable environments as it allows for rapid reproduction and colonization.

- Examples of asexual reproduction include binary fission in bacteria, budding in yeast, and vegetative propagation in plants.

# Population Growth

## Non-Pulsed Reproduction

- Growth in a non-limiting environment where generations may overlap.

## Logistic Population Growth

- As resources are depleted, population growth rate slows and eventually stops.

- Sigmoidal (S-shaped) population growth curve.

- Carrying capacity (K) is the number of individuals the environment can support.

- Finite amount of resources can only support a finite number of individuals.

## Limits to Population Growth

- Environment limits population growth by altering birth and death rates.

- Density-dependent factors: disease, resource competition, predation.

- Density-independent factors: natural disasters, weather.

## Galapagos Finch Population Growth

- Boag and Grant studied Geospiza fortis finch population.

- After a drought, the population fell drastically.

- Abundance of seeds and caterpillars caused the population to grow after heavy rainfall.

## Cactus Finches and Cactus Reproduction

- Grant and Grant studied how finches utilized cacti.

- Finches consume nectar, pollen, seed coating, seeds, and insects from cacti.

- Finches tend to destroy stigmas, reducing the availability of seeds.

- Opuntia helleri is the main source for cactus finches. # Human Population Growth

- Human population dynamics refers to the study of how the human population changes over time.

- The distribution of the human population is virtually ubiquitous, meaning that humans are found in almost every part of the world. However, the distribution is not uniform, meaning that some areas have higher population densities than others.

- Humans have an extremely high ability to acclimate, meaning that they can adapt to different environments and conditions.

## Population Dynamics in Specific Countries

### Sweden

- The population of Sweden is stable, with a growth rate (r) of 0.000. This means that the population is neither increasing nor decreasing significantly.

- The slight growth in the population is due to immigration, but overall, the population remains stable.

### Hungary

- The population of Hungary is decreasing, with a growth rate (r) of -0.0039. This means that the population is declining slowly.

- The decline in population is due to factors such as low birth rates and emigration.

### Rwanda

- The population of Rwanda is increasing rapidly, with a growth rate (r) of 0.027. This means that the population is growing at a significant rate.

- The high population growth in Rwanda is due to factors such as high birth rates and improved healthcare leading to lower mortality rates.

# Life History and Reproductive Strategies

- Life history refers to the adaptations or characteristics of organisms that influence reproduction.

- Resources are limiting, so organisms have to make trade-offs between the number and size of offspring.

- The probability of dying increases with age, and reproduction increases the probability of dying.

## Age-specific Reproduction

- Early reproduction: Reproducing at a young age.

- Pros: More energy stored for reproduction.

- Cons: Greater chance of dying before reproduction.

- Late reproduction: Reproducing later in life.

- Pros: Less energy stored for reproduction.

- Cons: Less time for offspring to grow and reproduce.

## Semelparity vs Iteroparity

- Semelparity: Reproducing once in a lifetime.

- "Bet" on survival of offspring.

- Examples: Salmon, annual plants, many insects.

- Usually produce lots of small offspring.

- Iteroparity: Reproducing more than once in a lifetime.

- "Bet" on survival of parents.

- Examples: Mammals, woody plants, most vertebrates.

- Usually produce few but large offspring. # Offspring Size and Number

## Offspring Size

- Large offspring examples: mammals, woody plants, most vertebrates

- Large offspring are more common in benign and predictable environments

- Large offspring are produced when resources are abundant

- Large offspring have higher survival rates and better chances of competing for resources

## Offspring Number

- Small offspring examples: fish, insects, some plants

- Small offspring are more common in harsh and unpredictable environments

- Small offspring are produced when resources are limited

- Small offspring have higher reproductive rates and can produce more offspring

## Semelparity vs Iteroparity

- Semelparity: organisms reproduce only once in their lifetime

- Iteroparity: organisms reproduce multiple times in their lifetime

- Semelparity is more common in harsh and unpredictable environments

- Iteroparity is more common in benign and predictable environments

## Trade-offs

- There is a trade-off between the number and size of offspring

- Limited resources require organisms to make choices between producing a few large offspring or many small offspring

- Large offspring have higher survival rates but lower reproductive rates

- Small offspring have lower survival rates but higher reproductive rates

## Effects of Offspring Size and Number

- Larger eggs result in smaller clutches (number of offspring produced at once)

- Smaller eggs result in larger clutches

- Lower dispersal of offspring leads to greater genetic isolation and rapid gene differentiation

## Fitness

- Fitness depends on multiple factors and cannot be determined solely based on offspring size or number

- Fish laying bigger eggs may have higher survival rates for their offspring, but smaller eggs may allow for higher reproductive rates

- Fitness is a complex concept influenced by various interacting factors

# Seed Size and Number in Plants

## Seed Size

- Plants exhibit a broad range of seed production

- Seed size is influenced by two major factors:

- Plant growth form

- Dispersal mode

## Plant Growth Form

- Different plant species have different growth forms (e.g., trees, shrubs, herbs)

- Plant growth form can influence seed size

- Larger plants tend to produce larger seeds, while smaller plants produce smaller seeds

## Dispersal Mode

- Different plant species have different dispersal modes (e.g., wind dispersal, animal dispersal)

- Dispersal mode can influence seed size

- Seeds that rely on wind dispersal tend to be smaller, while seeds that rely on animal dispersal tend to

# Seed Size and Number in Plants

In plants, there is a broad range of seed production. The size and number of seeds produced by plants are influenced by two major factors: plant growth form and dispersal mode.

## Plant Growth Form

- Graminoids: Grasses and similar plants.

- Forbs: Herbaceous plants that are not graminoids.

- Woody Plants: Plants with woody thickening of tissues (lignification).

- Climbers: Climbing plants, which can be either woody (lianas) or herbaceous (vines).

- Woody plant and climber seeds are generally around 10 times the mass of those of graminoids or forbs.

## Dispersal Mode

- Unassisted: Seeds that do not have specialized structures for dispersal.

- Adhesion: Seeds with hooks, spines, or barbs that allow them to stick to surfaces.

- Wind: Seeds with wings, hairs, or other resistance structures that enable them to be carried by the wind.

- Ant: Seeds with an oil surface coating (elaiosome) that attracts ants for dispersal.

- Vertebrate: Seeds enclosed in fruits or arils that are eaten by animals and dispersed through their droppings.

- Scatterhoarded: Seeds that are gathered and stored by animals for later consumption.

Small plants tend to produce a large number of small seeds, which is advantageous in areas with high disturbance. On the other hand, larger seeds are fewer in number but have a higher capability of surviving environmental stresses.

Seed size variation plays a significant role in seedling performance and recruitment success. Larger seeds are generally more successful in establishing and growing into seedlings compared to smaller seeds.

Reference:

Jakobsson, A., & Eriksson, O. (2000). A comparative study of seed number, seed size, seedling size and recruitment in grassland plants. Oikos, 88(3), 494-502. # Seed Size and Seedling Performance

- Seed size variation can explain differences in recruitment success.

- Larger seeds tend to produce larger seedlings.

- Larger seedlings have increased recruitment potential.

- Energy reserves in larger seeds contribute to seedling growth.

- Rapid growth helps seedlings penetrate thick litter layers.

- However, the effect of seed size on seedling performance depends on environmental conditions.

# Adult Survival and Reproductive Allocation

- Energy budgets differ before and after sexual maturity.

- Before sexual maturity, energy is allocated to maintenance and growth.

- After sexual maturity, energy is allocated to maintenance, growth, and reproduction.

- Delaying reproduction allows for faster growth and larger size.

- Larger size and stored energy enhance reproductive ability.

- However, delaying reproduction also increases the chance of not reproducing.

# Life History Variation Among Species

- Snakes and lizards with higher survival rates reach maturity later.

- Fish with higher adult mortality show earlier reproductive maturity.

- Fish with higher adult mortality also invest more reproductive energy.

- Factors influencing life history variation among species include:

- Mortality rate

- Maximum length

- Age at reproductive maturity

- Reproductive effort (measured by GonadoSomatic Index)

# Life History Variation Within Species

- Adult survival can influence life history variation within species.

- Bertschy and Fox studied the influence of adult survival on pumpkinseed sunfish life histories.

- Factors influencing life history variation within species include:

- Adult population distribution

- Age structure

- Juvenile survival # Life History Variation Within Species

## Influence of Adult Survival on Pumpkinseed Sunfish Life Histories

- Bertschy and Fox conducted a study on pumpkinseed sunfish to understand the influence of adult survival on their life histories.

- They looked at various factors such as adult population distribution, age structure, juvenile survival, and GSI (%).

- When adult survival is lower relative to juvenile survival, selection favors earlier allocation of greater resources to reproduction.

- On the other hand, when juvenile survival is lower relative to adult survival, selection favors later allocation of resources to reproduction.

# Life History Classification

## r-selection and K-selection

- MacArthur and Wilson proposed the concepts of r-selection and K-selection to classify life history strategies.

- r-selection refers to a high per capita rate of increase and is characterized by a high population growth rate.

- K-selection refers to efficient resource use and is characterized by a population that is close to its carrying capacity.

- It's important to note that r-selection and K-selection are endpoints of a spectrum, and most organisms fall somewhere in between.

- r-selection is favored in unpredictable environments, while K-selection is favored in predictable environments.

# r and K: Fundamental Contrasts

## Survivorship

- Type III survivorship curve is associated with r-selection, where there is high mortality early in life and few individuals survive to old age.

- Type I survivorship curve is associated with K-selection, where there is low mortality early in life and most individuals survive to old age.

# Plant Life Histories

## Variables Influencing Selective Pressures in Plants

- Grime proposed two important variables that exert selective pressures in plants: intensity of disturbance and intensity of stress.

- Intensity of disturbance refers to any process that limits plants by destroying biomass.

- Intensity of stress refers to external constraints that limit the rate of dry matter production.

## Environmental Extremes

- Four environmental extremes can be considered when studying plant life histories:

1. Low Disturbance : Low Stress

2. Low Disturbance : High Stress

3. High Disturbance : Low Stress

4. High Disturbance : High Stress

## Rude # Plant Life Histories

## Rals (highly disturbed habitats)

- Grow rapidly and produce seeds quickly.

- Comparable to r-selection.

## Stress-Tolerant (high stress - little to no disturbance)

- Grow slowly and conserve resources.

- Comparable to K-selection.

## Competitive (low disturbance / low stress)

- Grow well, but eventually compete with others for resources.

# Opportunistic, Equilibrium, and Periodic Life Histories

## Opportunistic Life History

- Characteristics:

- Rapid growth and reproduction.

- Short lifespan.

- High reproductive output.

- Examples: Weeds, annual plants.

## Equilibrium Life History

- Characteristics:

- Slow growth and reproduction.

- Long lifespan.

- Low reproductive output.

- Examples: Large trees, perennial plants.

## Periodic Life History

- Characteristics:

- Combination of rapid growth and reproduction with periods of slow growth and reproduction.

- Examples: Bamboo, agave plants.

# Lifetime Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

- Charnov et al. developed an approach to life history classification based on dimensionless (relative) numbers.

- Key life history features are converted to dimensionless numbers to remove the influences of time and size.

- This allows for easier identification of similarities and differences between groups.

# Generalizations

- There are as many variations in life history as there are species.

- The success of a life history depends on the environment being similar to that in which the strategy evolved.

- Differences in life history are a function of the environment, including interactions with other species.

- Differences in life history contribute to diversity within ecological communities.