COMMUNITY ECOLOGY

OBJECTIVES:

• Describe types of relationships among organisms.• Compare primary and secondary succession.

Community Interactions

Community = a group of populations of different species living close enough to interact.

Types of Interactions:•Competition,•Predation,•Symbiosis.

Competition

• The competitive exclusion principle states that when two species compete for the same resource or niche, eventually the one with the slight reproductive advantage will eliminate the other.

Predation• A true predator kills and eats the

other animals (prey).

• A parasite spends most or all of its life living on another organism (host) and feeding on its tissues.

• A herbivore is an animal that eats plants.

SymbiosisSymbiosis = “living together”; several types:

Mutualism =

both species benefit.

Parasitism =

one organism benefits and the other is harmed.

Commensalism = one organism benefits; the other is neither harmed nor benefited.

Ecological Succession

http://www.youtube.com/watch?v=V49IovRSJDs

Succession – gradual change in the composition of species over time; frequently following a disturbance.

1. Primary succession - succession on a new site by pioneer species such as lichens; eventually larger plants replace the pioneer species.

Lichen = fungus living with algae or cyanobacteria (mutualism).

Example: colonization after volcanic eruption.

Primary succession

2. Secondary succession – changes occurring where soil and vegetation already exist.

Example: gradual changes after a fire.

• Climax community =stable, mature community that undergoes little succession.

Secondary succession

Hmm…1. Does primary or secondary succession take longer? Why?

2. Are pioneer species r-selected or K-selected species?

3. How do species cause changes in the habitat that will result in different species composition?

Species Diversity= measures the number of different species in a community and the relative abundance of each species.

Dominant species have the highest biomass (the sum weight of all members of a population).

Keystone species have a strong influence on the survival of other species; their removal results in dramatic changes in the makeup of species in a community.

Keystone species examples: sea otter, grizzly bear, wolf.

Invasive species:http://www.youtube.com/watch?v=HAY_UsGjyZk

An introduced (non-native) species that may compete with native species for resources such as food, space, and water.

Examples: tamarisk, zebra mussels, kudzu.

Note: Most non-native species are not invasive.

Hmm…• How do keystone species maintain balance in ecosystems?

• How does the introduction of a non-native species influence the balance of an ecosystem?

MATH CONNECTION

The daily caloric requirements for male versus female killer whales (orcas) is shown below:

• Male killer whale: 308,000 kcal/day• Female killer whale: 187,000 kcal/day

Calculate the average caloric value of a sea otter assuming a male orca consumes five sea otters each day to meet its caloric requirement. Give your answer to the nearest hundredth.