8.2.2 Community Ecology

Biotic factors

living or once living organism in an ecosystem

• plants, animals, predators, prey, detritus

Abiotic factors

nonliving factors in an ecosystem

• water, soil, sunlight, temperature

Intraspecific

within species

Interspecific

Between species

Levels of Ecological Organization

1. Organism

2. Population

3. Community

4. Ecosystem

5. Biome

6. Biosphere

Organism

an individual organism

population

a group of organisms of the same species

community

all organism living in a particular area

ecosystem

all organisms and the environment they live in (biotic + abiotic)

Biome

ecosystem with similar biotic and abiotic characteristics grouped together

Biosphere

everywhere on earth where life lives

Niche

the position of a species in an ecosystem, its ecological role

What determines a niche?

• tolerable abiotic factors — Temperature, pH, sunlight

• food sources

• shelter

Interspecific interactions

1. Competition

2. predation

3. herbivory

4. symbiosis

   1. mutualism

   2. commensalism

   3. parasitism

Intraspecific competition

competition within a species

Interspecific competition

competition b/w species

Competitive exclusion principle

2 species can’t have EXACTLY the same niche and stably coexist

Resource partitioning

division of limited resources among species

• there may be SOME niche overlap but not EXACT overlap

Predation +/-

member of one species (predator) eats all or part of the body of a member of another species (prey)

includes herbivory

Evolutionary arms race

a type of coevolution that results in back-and-forth adaptations between predator and prey

includes plants & herbivores

symbiosis

long-term intimate association between two species

can be positive or negative

1. Mutualism

2. commensalism

3. parasitism

Mutualism +/+

both partners benefit from their interactions

Commensalism +/0

one partner benefits while the other neither benefits nor is harmed

but this is almost never perfectly neutral

• slight harm or benefit

parasitism +/-

one partner benefits while other is harmed

• parasite benefits

• host is harmed

parasite evolution

• parasites can be very host specific

• parasites will coevolve and speciate with host

evolution of mutualism

parasitism → commensalism → mutualism

• parasites harm hosts but need hosts to survive

• doing less harm to host can be more adaptive

• doing no harm to host can be more adaptive

• helping the host can be more adaptive