I. 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

I. 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

I. 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

I. 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

Batesian Mimicry

Sam Crothers

I. 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

I. 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

I. 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

I. Community Ecology

F. Mutualism• Symbiotic relationship in which both partners

benefit• Ex: Ants & acacia trees• Ex: Nitrogen fixing bacteria (Rhizobium) & legumes• Ex: Zooxanthellae & reef-building corals• Ex: Mycorrhizae & plants• Ex: Anemones & clownfish

I. Community Ecology

G. Commensalism• One organism benefits, other isn’t harmed or

helped• Ex: Cattle egrets and cowbirds & ungulates (expose

insects while grazing)

• Hard to document (both species usually affected to some degree)

• Ex: Some commensal birds may remove ticks & other ectoparasites from herbivores