Fig. 53.9

Fig. 53.10

Soay Sheep – Hirta Island

I. Population Ecology

D. Population Dynamics3. Life History Strategies

• Finite amount of energy to allocate among growth, reproduction, metabolism

• Some species maximize reproduction; others maximize survival

a. r-selection• Opportunistic species in variable environments• Population usually much higher or much lower

than carrying capacity• Many weed/pest species

b. K-selection• Usually in stable environments• Population usually at/near carrying capacity• Many endangered species Why?

I. Population Ecology

D. Population Dynamics4. Factors Affecting Population Growth/Size

a. Density-Independent Factors• Catastrophic events• Ex: Floods, fires, drought, storms, extreme weather• Some aggregated organisms and social animals can

enhance resistance to density-independent factors• Ex: Emperor penguins, clustered plants/animals

b. Density-Dependent Factors• Effects increase as population size increases1. Competition – Limit = resources (food, water, etc.)Territoriality – Limit = space availability1. Health – Includes disease2. Predation – Selective by predator(s)3. Wastes – Toxic at higher concentrations4. Other Factors – Ex: Aggression at higher densities

Soay Sheep – Hirta IslandFig. 53.16

I. Population Ecology

D. Population Dynamics4. Factors Affecting Population Dynamics

a. Density-Independent Factors• Catastrophic events• Ex: Floods, fires, drought, storms, extreme weather• Some aggregated organisms and social animals can

enhance resistance to density-independent factors• Ex: Emperor penguins, clustered plants/animals

b. Density-Dependent Factors• Effects increase as population size increases1. Competition – Limit = resources (food, water, etc.)2. Territoriality – Limit = space availability3. Health – Includes disease4. Predation – Selective by predator(s)5. Wastes – Toxic at higher concentrations6. Other Factors – Ex: Aggression at higher densities

I. Population Ecology

D. Population Dynamics5. Population Stability

• Stability usually related to lifespan, reproductive rate

a. Environmental factors• Resource availability• Recruitment

Fig. 53.18

Isle Royale

I. Population Ecology

D. Population Dynamics5. Population Stability

• Stability usually related to lifespan, reproductive rate

a. Environmental factors• Resource availability• Recruitment

b. Immigration• Metapopulations may be more stable than

isolated populations

Fig. 53.21

Glanville Fritillary

I. Population Ecology

D. Population Dynamics5. Population Stability

• Stability usually related to lifespan, reproductive rate

a. Environmental factors• Resource availability• Recruitment

b. Immigration• Metapopulations may be more stable than

isolated populations

c. Combined factors• Resources, predation, etc.

Fig. 53.19

II. Community Ecology

• Focus on interspecific interactions• May be direct or indirect

A. Competition• Two or more species competing for scarce

resource• Ex: Two plant species competing for water

• May be detrimental to one or both species

1. Competitive exclusion• No two species can use same set of resources in

same area at same time• Competitively dominant species tend to force

extinction of competitively inferior species

II. Community Ecology

A. Competition2. Ecological niche

• Species’ ecological role in a community• Includes use of abiotic and biotic resources• Niche occupied by a species may be narrower than

range of conditions tolerated by species• Fundamental niche vs. realized niche

Fig. 54.3

II. Community Ecology

A. Competition3. Resource partitioning

• Competitive exclusion can be minimized if competing species modify niches to reduce overlap

• Usually involves dividing resource

Fig. 54.2

Anolis Dominican Republic

II. Community Ecology

A. Competition4. Character displacement

• Resource partitioning may lead to directional selection on one or both species

• Directional selection may lead to divergence in traits

Fig. 54.4

II. Community Ecology

B. Predation• Involves consumption of prey by predator• Predator usually has adaptations to facilitate capture of

prey• Natural selection acts on both predator and prey

• Coevolution1. Strategies

a. Pursuit predation• Predators chase prey to capture them• Predator usually faster, stronger, &/or more agile than

prey• Some species hunt in groups

b. Ambush predation• Predators lie in wait for prey• Predators usually camouflaged or concealed• May involve lures

c. Aggressive mimicry• Ex: Bolas spider mimics odor of female moths to

attract male moths

II. Community Ecology

B. Predation2. Predator avoidance

a. Escape• Running/Swimming/Flying away

b. Mechanical defenses• Ex: Porcupine quills, armadillo armor

c. Social behavior• Ex: Schooling, standing watch

d. Chemical defenses• Ex: Poison dart frog, skunk

e. Defensive coloration

Cryptic coloration

- Canyon tree frog

Aposematic coloration

- Poison dart frog

Batesian mimicry Fig. 54.5

Müllerian mimicry

II. Community Ecology

C. Herbivory• Consumption of plants by animals• Most herbivores are small

• Ex: Insects, snails/slugs

• Herbivores adapted to consume plants• Some plants have anti-herbivore defenses

• Physical – Ex: Thorns, spines• Chemical – Ex: Nicotine in tobacco, pyrethrins in

chrysanthemums

• Coevolution has affected herbivore evolution• Ex: Monarch butterfly caterpillars can eat milkweed

• Toxic to most herbivores• Nearly exclusive access to food source• Can sequester noxious compounds for defense

II. Community Ecology

D. Parasitism• Parasite benefits at expense of host

• Host harmed in process• Ex: Tapeworm absorbs nutrients from host digestive

system

• Endoparasites – Live within body of host• Ectoparasites – Live outside body of host• Parasitoids – Lay eggs on/in host; larvae feed

on host, eventually killing host• Many parasites have complex life cycles

Fig. 33.12

Fig. 33.11Schistosoma mansoni

II. Community Ecology

E. Disease• Widespread disease outbreaks may alter

community composition and dynamics• Ex: Dutch elm disease• Ex: Sudden oak death• Ex: Avian flu• Ex: West Nile virus