COMMUNITY ECOLOGYCH 54

• Community: a group of populations of species interacting

I. Community Interactions

• Classified by whether they help, harm, or have no effect on species involved– Interspecific interactions involve different

species– Intraspecific interactions involve one

species

1. Interspecies competition (+/-):

• two different species compete for the same resource.

• This often results in one species succeeding over the other

• Results in competitive exclusion

2. Resource partitioning (0/0): • when species coexist despite their

competition for the same resources because they live in slightly different niches

3. predation (+/-)

• when one species negatively uses another species for food.

• Evolutionary adaptations that allow predator to capture prey– acute sense of smell – speed – claws, fangs, stingers, poisons

• evolutionary adaptations of prey– defensive adaptations: chemicals to thwart

predator– behavioral adaptations: herding/schooling,

hiding, fleeing

– morphological adaptations:• Camouflage or cryptic coloration allows an animal to

blend into its surroundings

– Aposematic or warning colorations of an animal that warns predators that they should be avoided

– Mimicry: when two species resemble each other •mullarian: animals with the same

mechanism of defense share the same coloration• batesian: one animal with no defenses

resembles another animal with defenses

4. Symbiosis occurs when two species live in close contact • Mutualism (+/+): both species benefit • Commensalism (+/0): one species benefits • Parasitism (+/-): one species benefits and

the other is harmed

• species diversity: the variety of different species on a community. Has 2 components: – species richness: the number of different

species in the community – relative abundance: the amount of each

species in the community

II. Species Diversity and Community Structure

• communities with high diversity are:–more productive and stable–more likely to recover from

environmental stress–more resistant to invasive species

1. Dominant species

• most abundant species in the community • ex: sugar maple is abundant species in

northeast forests and provides shade and good quality soil

• what might happen if the dominant species declined in number?

• How did it become a dominant species?

2. Invasive/introduced species

• Organisms that are introduced to a new community, usually by humans

• Why are they so successful?

3. Keystone species

• Affects community structure not by being abundant but by its role in the community

• Ex: sea otters

III. Ecological Succession and Community Disturbances

• A. Community Disturbances • A change in a community due to the destruction

of resources and death of organisms oNatural disturbances

Fire, hurricane, volcanos oHuman disturbances

Clearing of land, sinking of ships • Community disturbance could be positive or

negative

B. Ecological Succession: Colonization of new species into the disturbed area

• Primary succession: –when a force like a volcano destroys

everything in community even soil –moss and lichen grow on hardened lava

and make soil – small plants like grasses start growing in

soil from blown in seeds – shrubs and trees start to grow

• Secondary succession –When a force like a tornado or an

abandoned farm destroys everything but leaves soil intact –Grasses start to grow then shrubs and

trees