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