Exam 4 Final Unit 4

Population Ecology 

Genetics: An interbreeding group of individuals comprising one gene pool

Ecology: A group of individuals living in a particular place

Primary Population Parameter:

• Increasing Population: Natality( Births) + Immigration (incoming organisms) 

• Decreasing Population: Mortality ( deaths) + Emigration

Basic Measures: Range, Abundance, Dispersion, density ( number/area) 

• Crude( Total #/ total area of suitable habitat) vs Ecological Density

• Absolute Vs Relative Estimate

  • Difficult to determine actual #

  • A common technique is a capture and release study

Density Regulating Factors

• Density Independent Factors: Environmental factors

  • Severe drought

  • Severe cold

  • Dependent on density: how many other organisms are you competing with

• Density Dependent Factors: Usually Biological

  • Interspecific vs Interspecific Interactions

• Positive Density Independence: As the population gets bigger, more organisms are growing and need more resources 

• Negative Density Dependence: Greater population→ increased risk for disease and rate of mortality increases

Population growth equations:

• Discrete Generations: 

• Instantaneous

• Differential Formula

Logistic Growth: Most populations will stop growing as density increases

• K= Carrying Capacity= point where b= d,  R

• (K-N)/K  

  • N= # of organisms already there

  • When N is low, this is ~1 ( population for carrying capacity)

  • When N is high, this is ~0( population is close to carrying capacity)

Pearl Verhulst Equation and Logistic curve

• dN/dt = rN(1-N/K)

• As you increase the population there are less offspring being produced but more organisms are reproduced

• Population Growth Rate is Greatest at the Inflection point of the curve (1/2K)

  • Maximum Sustainable Yield: Maximum amount of population (ex fish) that you can take while maintaining a 1/2K population ( stable population)

    • Doesn’t work in real life- Humans are selfish

Logistic Growth in Paramecium-

• Populations do respond to limited resources in environment

Mortality and Survivorship curve 

• Longevity

  • Physiological- Edepc

  • Ecological- How long they actually live in the world

  • 3 Generals Stages of life

    • Pre-reproduction

    • Reproduction

    • Post-reproduction

Survivorship Curve: Shows what age many individuals are still alive

• Type I: High survival rate until they reach later years (scenensis) 

  • Typical of mammals

• Type II: Constant mortality rate: 

  • Typical of birds

• Type III: High mortality of young, after they reach a certain size they typically live longer lives. 

  • Typical of fish 

Natality and Fertility Curves

Natality Usually only consider females, females are the only ones that reproduce 

• Birth rates: Crude ( ex 50 births/1000/year)

• Age specific, mx ( x= specific age)

• Different species show different Lifetime patterns

Life Tables: Can be established from  cohort, static or remains study 

• Fecundity Data you can calculate

  • Number of New offspring produced

  • Predicted Population at any age

  • Population Growth rate

  • Net Reproductive rate

  • Generation Time

• Elements:

  • nx: number alive at age

  • lx: proportion surviving

  • dx: number of deaths over that year

  • qx: mortality rate

  • ex: expectation of further life

Age Structures/Pyramids 

Interspecies Interactions: Competition

• Logistic Equation- How many of me there are and how many of them there are

• ɑ= Population limiting effect of Species 2 on Species 1

• β= Population limiting effect of Species 1 on Species 2

Competition Equations:

Gause’s Principle of Competitive Exclusion

• “Complete Competitors cannot coexist.”

• Competitive Exclusion has rarely been observed in field studies due to 

  • Competition not expected( ex., Disease or predators), Abundant resources, and temporary habitats 

  • We usually only observe the outcome: “The Ghost of Competitions past”

  • If we see competition happening, it matters; if we don’t see competition happening, it already happened. 

Patterns Suggesting Past Competition:

• Slight Niche differences in Sympatric Close relatives

  • Would expect divergent selection: Specializing and niche partitioning of birds

• In Oak Forest:

  • Blue Titmouse: Small insects from leaf surfaces in the canopy

  • Great titmouse: Feeds mostly on the ground

  • March Titmouse: large insects of the lower tree

• In Pine Forest

  • Coal Titmouse: feeds at the top of the tree

  • Willow titmouse: eats seeds and vegetable matter

  • Crested Titmouse: feeds on the ground

• Robert Macarthur’s Warbler Study

  • These species all eat the same caterpillars but hunt in different parts of trees. 

• Niche Differentiation Among Guild Species:

  • Guild: A group of species living in the same functional way in a community 

  • Ex: Competition between Rodents and Ants:

    • Rodents eat medium-sized, and some large seeds

    • Ants: eat smaller seeds and some medium-sized seeds 

• Character Displacement ( Wilson and MacArthur) 

  • Niche difference in species where they are sympatric

  • When seed-eating finches  lived on separate islands, they ate almost identical range of seeds for both islands

  • Where the seed-eating finches co-exist, they differentiate into eating other types of food.

• Character or Ecological Release

  • Species were originally together but became separate. Bird moved to an area without competition and can explore wayyy more niches

• Abrupt Species change Along an environmental Gradient

  • In the absence of competition, we’d expect a gradual transition from one species to another: an abrupt transition implies each is excluding the other from one side of the range. Ex: Warblers in New Guinea. 

Interspecies Interactions: Predation

Equilibrium Isoclines for Prey and Predator Populations

Predator and Prey Densities Interact Overtime: 

Lotka-Volterra Prediction: Predator-Prey Cycle

• Oscillation, where the predator cycle flags slightly behind prey

Steps:

1. An increase in the prey population allows for an increase in the predator population 

2. An increase in predator population causes a decline in the prey population

3. A decrease in the prey population causes a decrease in the predator population

4. A decrease in predator population allows an increase in the prey population. 

Field Studies of Lynx vs Snowshoe hares:

1. Elton’s Study of Lynx vs Snowshoe hares

2. Opuntia vs Cactoblastis 

   1. Cactus (Cactoblastis)was introduced and had no enemies in Australia. A moth Opuntia was introduced to eat the cactus so that meadows can be used for sheep grazing again

3. Lynx and Prey switching in Newfoundland

   1. 1. Wolves were eliminated from Newfoundland → increased Caribou and snowshoe hares

   2. 2. Lynx are perfectly adapted for hunting snowshoe hares = increased Lynx population

   3. 3. Lynx started preying on caribou calves at night when caribou go to sleep

   4. 4. Eventually, the lynx population decreased, and the snowshoe hare has recovered

   5. 5.  Lynx started hunting snowshoe hares again. 

   6. When lynx get desperate, they hunt arctic hares. 

Predator Functional Response:

Density of Prey Population:

• Type I: Predators are consuming as many as they are able to

• Type II: The more of they prey the predator is catching, the harder it is to catch the next one

• Type III: Predators don’t get many at the beginning. Will catch more prey until you reach a slight decline. 

Density of 

Why does Consumption increase slowly at low prey population density?

1. Prey hide and are hard to find

2. Practice and Search Images: Predators learn what to look for when tracking down prey

3. Prey Switching: Choose to put more effort into the prey they like better. When you can’t get your #1 prey, you put effort into the 2nd best.

Community Ecology 

“All of the population of species living together in a particular area”

Overlap in Tree Species Ranges:

• Each species is doing their own thing instead of coming as a package

• A general consensus favors the Individualistic Mode

• However, Too much emphasis on plants, maybe animals are more organismic

• Communities that are stable and rich in species ( K-selecting)

Keystone Species: Species that substantially affect the structure of communities despite the fact they individuals of the species may not be particularly numerous. 

1. Dominant Autotrophs:oaks, bluestem grasses

2. Ecosystem Engineers ( beavers, elephants, corals)

3. Top Predators( Paine’s study of sea stars)

   1. Sea stars: keep more dominant mollusks in control so that other species can also grow in the ecosystem.

Niche: Profession of a Species

• Fundamental Niche or  Pre-competition niche

• Realized niche or post- competition Niche

Limiting Similarity: A concept of theoretical ecology and community ecology that proposes the existence of a maximum level of niche overlap between two given species that will allow for continued coexistence. 

Competitive Exclusion Principle: Controlling for all else, two species competing for exactly the same resources cannot stably coexist. 

Guilds: Within a given trophic level, a group of species that feeds on similar items. 

• Ex; Different species of nectar-feeding insects constitute a guild

Species Richness- Number of Species in a community

Species Diversity Indices- Also take into account relative abundance ( equity or evenness) 

Master Gradient of Species Diversity; States by Alfres Russell Wallace

• As Latitude decreases, species diversity increases

• Ex

Factors Hypothesized to Increase Diversity:

• Evolutionary Age: In millions of years

• Ecological Age ( succession): How long since a major disturbance( event that reset environment) 

• Favorable Climate ( Water, sunlight) 

• Productivity: How much photosynthesis is going on, how much food is available at the bottom of the food chain

• Climate Stability/Predictability- r or K-selecting

• Spatial Heterogeneity- Corals Create 3D structures, suitable for algae and mollusks

• Habitat Diversity/ Area: Increase area + increase habitat→ increase diversity 

• Competition 

• Keystone predators

• 3- Dimensionality 

• Intermediate Level of Disturbance:

  • A frequently disturbed area ( hurricanes) it will have relatively few species present

  • Habitat not disturbed for a long time will have had time for predators to compete with other species. 

Habitat Diversity and Species Diversity

• Using species diversity index

• Different (increased) elevation of trees have different birds- taller trees have increased diversity. 

Habitat Heterogeneity

• Deserts have a greater diversity of habitats than marshes, but marshes have much greater productivity(photosynthesis and turning light into energy for the food chain)

Intermediate Disturbance Hypothesis

• More species are present in a community that occasionally experiences disturbances than a community that experiences frequent or rare disturbances. Due to:

  • Creation of habitat heterogeneity 

  • Prevention of Dominance by a Superior Competitor or predator

Species Area Curves: 

• Larger Aquatic or terrestrial Ares contain a greater number of species 

• MacArthru And Wilson formula; S=cAz or Log S = log c + z log A

• When the Slope = 2, that is the typical ballpark for most organisms 

 Effects of Habitat loss and fragmentation

• 90-50 rule: Loss of 90% of habitat results in loss of 50% of species

• Causes “Edge Effects 

Succession: The process by which the species composition of a community changes overtime 

• Primary Succession: Initial Development of ecosystem. In location devoid of plants 

• Secondary Succession: Recovery of an ecosystem after a major disturbance 

  • Ex: Abandoned farms in New England after farmers depleted nutrients in soil

• Traditional View in Succession: 

  • Directional, predicable orderly series of stages (seral stages) 

  • Similar sequence on Similar Sites

  • Process is Controlled biotically

    • Shade is established

    • Vegetation starts to stabilize

    • Final equilibrium( The Climax Community) is determined by physical Factors ( climate, underlying rocks etc.)

• Major Steps in Succession

  • 1. Initial Colonization by “Pioneer Species”

  • 2. Site Modification by Colonizers

  • 3. Species Replacements By Climax Species

• More detailed Description of Changes

1. Progressive Soil development

2. Structural Complexity of Plant community Increased

3. Nutrient Pool Increased, more nutrients are held my plants

4. “Standing Crop” Biomass increased\

5. New biomass accumulation shows, respiration increases until eventually they are equal, then no net increase in biomass

6. Microclimate changes

7. Species Replacements Occur

8. Selection Changes from r to K-selecting

9. Species Diversity Changes ( may decline at Climax)

10. Food Chain Lengthen and becomes more complex

• Species Richness Changes as Succession Proceed

Secondary Succession In Eastern North America

Stages

• Annual phase: Annual Weeds (1-2 yrs)

• Meadow Phase: Perennial Grasses & Herbs (2-15 yrs)

• Shrub phase: Shade-tolerant shrubs(15-50 yrs)

• Tree phase: Fast growing canopy forming species ( 50-200 yrs) 

• Climax Deciduous Forest: shade tolerate Dominants (200+ yrs) 

Balance Betwen Immigration and Extinction determines species Richness of a Community

• Effects of Island Size and Isolation

• Combination of the 2 Effects: BE ABLE TO DRAW THIS!!

Nature Reserve Design

SLOSS: Single Large or Several Small (Reserves) 

Productivity and Energy Flow in Ecosystems:

• Energy Flows: nutrient Cycles

• Primary Productivity : The rate at which solar ( or rarely chemical) energy is captured and converted into chemical bonds by photosynthesis( or chemosysnthesis) 

• Primary Production: The Amount of Assimilation

• Standing Crop: The biomass of producers present in a given area of an ecosystem at a particular time 

• Gross Primary Production Or productivity- Respiration= Net Primary Production or Productivity ( P

• On average 60% goes to respiration, 40% to producing more biomass

Secondary Productivity/Production

Trophic Levels and “Food Chains”

• Primary Producers- Autotrophs

• Primary Consumers- herbivores

• Secondary Consumers- Carnivores

• Teritary Consumers- Carnivores

• Quaternary Consumers - Carnivores

“Green” and “Brown” Food Webs

• In almost all Biomes, most primary Producrion goes to decomposers rather than higher level consumers

• Grasslands, Rain forest, deciduous forests: between 90%-95% goes directly to decomposers

• Oceans and upwelling zones: 60%-65% goes directly to decomposers

Ecologial Efficency

• Developed my Ray Lindeman

• ( Pg at level N+1)/(Pg at Level N) x 100

• Only a small percentage of the Pg at one level is converted to Pg at the next higher level 

• Typical efficiency is ~10%

Tropic Pyramids

Food Chains are usually 4-5 levels with 90% of energy lost at each step