Community Ecology

Niche ecology

Interactions ultimately define the realized niche out of the fundamental niche

fundamental niche

The niche species could potentially occupy.

realized niche

The niche species actually occupies.

Communities

sets of populations of different species that live in the same area and can potentially interact

characteristics of communities

- the species that are present

- the abundance of each species

- how the species interact

antagonistic interactions

Competition, predation, parasitism, and herbivory are interactions in which at least one species is harmed.

Interspecific competition

occurs when different species use the same limiting resource (space, food, light, silence, mates, water)

Intraspecific competition

when individuals of the same species use the same limiting resource

Competitive exclusion

two species with similar niches will clash competitively over limiting resources, therefore one will always be the loser and one the winner

Predation

Species A captures, kills, and feeds on individual of Species B

- Generalist: not usually a species-specific interaction

- some predators are highly evolved for efficiency at capturing one specific species of prey - Specialists

Herbivory

Species A captures and feeds on Species B

- Specialists or generalists

Parasitism

- usually species-specific

- can be a pretty complex relationship

Resource Partitioning

reducing competition between closely related groups or those who use the same resource in very similar ways

habitat refuges

- allow prey populations to persist

- cycles of increase and decline of both predators and prey...

top-down control

when a consumer limits a prey population

crypsis

camouflage

aposematic coloration

warn predators of toxicity or distastefulness (to deter predation)

mimicry

• Prey appearance/behavior resembles something hazardous

• Prey can also mimic each other to amplify the impact

Mutualisms

interactions in which both species benefit.

obligate relationships

absolutely required Rather than "facultative" or optional

symbiotic relationship

close interaction between species in which one species lives in or on the other

Three key ecologically important mutualisms for humans

1. Digestive symbioses: a population of cellulose-digesting microbes (bacteria, protozoa, yeast, and other fungi) living in the gut of an herbivore.

2. One-celled algae called zooxanthellae provide photosynthetically-produced nutrients for corals (This mutualism is the basis of the food web for the entire ocean system on Earth.)

3. Bees forage for nectar and pollen and cross-pollinate plants in the process...to the tune of about 265 billion dollars!

Commensalisms

e interactions in which one species benefits and the other has zero impact.

Why is species diversity important?

Diverse communities should capture more resources and produce more biomass

places in which biodiversity is reduced will support less life overall

Trophic structure

Feeding relationships between organisms in a community.

Food webs

represent feeding relationships as a flow of energy through the community.

Food chains

more simplistic representations of trophic relationships.

Trophic Pyramid

broad base to narrow apex

Keystone Species

When the integrity of the community depends on the presence of a stable population of a single species.

Ecosystem Engineers

type of keystone species

• Actively shaping the physical environment around themselves

• Secondarily creating habitat for others

Succession

a process of recovery from disturbance

Theory of Island Biogeography

The number of species that occupy a habitat depends on two factors:

1. Island size

2. Distance of island from source of colonists

Islands can be thought of as a natural habitat fragmentation 'experiment' in evolutionary time!

Species-Area relationship

endemic species

species that are native to and found only within a limited area

- result of diversification of immigrants into a variety of niches.