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Community Ecology

Chapter 56

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Biological Communities

• Community: all the organisms that live together in a specific place

– Evolve together

– Forage together

– Compete

– Cooperate

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• Individualistic concept: a community is a group of species that happen to occur together at one place– species respond independently to

changing environmental conditions– The composition of a Community can

change

Biological Communities

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Ecological Niche

• Niche: An Organism’s way of life

– Habitat

– Food

– Temp. range

– Reproduction

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Ecological Niche

• Fundamental niche: the entire niche that a species is capable of using.

• Realized niche: actual niche in which the species can establish a stable population

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Ecological Niche

study of barnacles

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Ecological Niche

• causes of niche restriction

– Competition

– Predators

– Absence of pollinators

– Presence of herbivores

Billock

Billock

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Ecological Niche

Principle of competitive exclusion: no two species can occupy the same niche when resources are limited

•Species may divide up the resources, (resource partitioning)

•natural selection can then lead to adaptive radiation

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Resource partitioning

among sympatric

lizard species

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Ecological Niche

Character displacement in Darwin’s finches

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Predator-Prey

• Predation and coevolution

1. Predation provides strong selective pressure on the prey population

2. Features that decrease the probability of capture are strongly favored

3. Predator populations counteradapt to continue eating the prey

Coevolution race

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Examples of prey adaptations:•Chemical defenses•Camouflage•Warning coloration•mimicry

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Species Interactions

• Symbiosis: two or more kinds of organisms interact in more-or-less permanent relationships

• All symbiotic relationships carry the potential for coevolution

• Three major types of symbiosis– Commensalism– Mutualism– Parasitism

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Species Interactions

• Commensalism benefits one species and is neutral to the other

– Spanish moss: an epiphyte hangs from trees

Shark and Pilot Fish

Barnacles and Whales

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Species Interactions

• Mutualism benefits both species

• Coevolution: flowering plants and insectsAnts and acacias– Acacias provide

hollow thorns and food– Ants provide

protection from herbivores

Human Intestine and E.Coli

Zebra and Oxpecker Bird

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Species Interactions

• Parasitism benefits one species at the expense of another

• Can be external or internal parasites

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Species Interactions

External parasite: the yellow vines are the flowering plant dodder, it is a parasite that obtains its food from the host plant it grows on

Heartworm and Dogs

Mistletoe and Mesquite Tree

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Species Interactions

• Ecological processes can interact

– Predation reduces competition• Superior competitors become more

numerous and attract predators• This allows other species to survive

when they could have been out competed

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Species Interactions

Starfish eat barnacles, allowing other species to thrive instead of being crowded out by the explosive population of barnacles

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• Keystone species: species whose effects are greater than expected

• Examples:– Sea star predation on barnacles– Beaver ponds– Top predators

Species Interactions

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Species Interactions

Beavers construct dams and transform flowing streams into ponds, creating new habitats for many plants and animals