Community Ecology Study Guide

Community

A group of populations of different species living close enough to interact

Interspecific interactions

interactions with different species

Intraspecific interactions

interactions among members of the same species

Different levels of interspecific interactions

positive (+), negative (-) and neutral (0)

Competition (-/-)

Two or more species compete for a resource that is in short supply

Predatation (+/ - )

One species ( the predator ) kills and eats the other ( the prey). Predication has led to diverse adaptations, including mimicry

Herbivory (+/ - )

An herbivore eats part of a plant or alga. Plants have various chemical and mechanical defenses against herbivory, and herbivores have specialized adaptations for feeding.

Symbiosis

Individuals of two or more species live in close contact with one another. Includes parasitism, mutualism, and commensalism.

Paratisim ( +/ -)

The parasite derives its nourishment from a second organism, its host, which is harmed.

Mutualism (+/ +)

Both species benefit from the interaction

Commensalism (+/0)

One species benefits from the interaction, while the other is unaffected by it.

Facilitation (+/+ or +/0)

Species have positive effects on the survival and reproduction of other species without the intimate contact of a symbiosis.

Competitive exclusion principle

two species cannot coexist in a community if their niches are identical

Why cant two species coexist in a community if their niches are identical ?

The one with the slight reproductive advantage will eliminate the other

Resourse partitioning

Differences in niches that enable similar species to coexist

Ecological niche

The sum total of an organisms use of abiotic and biotic reseourses in the environment

Abiotic factors

Sunlight, temp, pH, water - non-living chemical and physical parts of an environment that shape the environment

Biotic factors

Any living components of an ecosystem that shape or influence their environment and other organisms- (ex: plants, animals )

Funademtal niche

Where a species can live ( dream life with zero competition) - shaped by abiotic factors

Realized niche

Where a species does live - where you are forced to settle for after competition pushes you out of your favorite spots- shaped by biotic factors

What is smaller- Fundamental niche or realized niche

Realized niche is always smaller or equal to fundamental niche

Predation defensive adaptation ( Cryptic coloration )

camouflaged by coloring

Predation defensive adaptation ( Aposematic or warning coloration)

bright color or poisonous animals Predation defensive adaptation

Predation defensive adaptation (Bayesian mimicry)

harmless species mimic color of harmful species

Predation defensive adaptation (Mullerian mimicry)

2 bad tasting species resemble each other; both to be avoided

Predation defensive adaptation ( Herbivory )

plants avoid this by chemical toxins, spines, and thorns

Species diversity

species richness (# of diff species) + relative abundance of each species

Closer to 1

more diverse

Closer to 0

less diverse

Highly diverse communities are more resistant to what?

invasive species

What is the trophic structure in a community determined by?

The feeding relationships between organisms

Trophic levels

links in trophic structure

Food chain

The transfer of food energy from plants, herbivores, carnivores, decomposers

What limits the length of a food chain?

• inefficiency of energy transfer along chain

• long food chains less stable than short chains

Food webs

two or more food chains linked together

a given species may weave into the web at more than one trophic level

Dominant species

has the highest biomass or is the more abundant in the community

Keystone species

exert control on community structure by their important ecological niches - has a disproportionately large effect on its natural environment relative to its abundance

Disturbance

Changes a community by removing organisms or changing resources availability ( fire, drought, flood, storm, human activity)

Ecological succession

communities of plants and animals replace one another over time following a new land formation or a disturbance

Primary succession

Plants and animals invade where soil has not yet formed (ex: colonization of volcanic island or glacier)

Secondary succession

An existing ecosystem recovers after a disturbance that clears out most plant life but leaves the soil intact ( ex: abandoned farm, forest fire )

Biogeographic Factors

Important factors:

Lattitude: species more diverse in tropics than poles

Area: larger areas more diverse

Biogeographic islands

natural labs for studying species diversity- influenced by size and distance

• Larger islands lead to greater immigration and lower extinction

• Far from mainland- immigration falls, extinction rate increases