ch 18: community structure pt 2

diffuse interactions

involve many species; any one interaction may not be crucial; combined effect may have large impacts

- interactions involving many species

- removal of one may have little effects, but removal of many has a significant effect

- ex. the lynx, coyote, ans horned owl all prey on the snowshoe hare in cycles

what are diffuse interactions

diffuse mutualism

each partner may interact with more than one other partner

a single plant species may depend on a variety of animal species for successful reproduction

- ex. many pollinators for one plant

describe diffuse mutualism

- removal of one species has little effect

- removal of many species has a large effect

how would you determine experimentally if interactions are diffuse

food chain

series of steps in an ecosystem in which organisms transfer energy by eating and being eaten

food web

network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem

- intertidal zone in the pacific northwest

- variety of invertebrate herbivores are all preyed upon by the starfish Pisaster

- when the sea star is left, there is no change in the numbers of prey species from beginning to end (15)

- when the sea star is removed, there are only 8 prey species left at the end

- this means that the 8 species left were superior and outcompeted the other 7

- example of keystone predation

describe Paine's Pisaster removal experiments

keystone predation

the predator enhances the survival of one or more less competitive species by reducing the abundance of the more competitive species

the predator enhances one or more inferior competitors by reducing the abundance of the superior competitors

what is keystone predation

indirect commensalism

an interaction in which one species benefits another species indirectly, through an intermediary species, without itself being helped or harmed

indirect interaction is beneficial to one member but does not affect the other

what is indirect commensalism

- pond in colorado consists of larval salamander, midge larva, daphnia rosea, and daphnia pulux

- the daphnia rosea (small) and daphnia pulux (large - superior) compete with one another (-/-)

- the midge larvae preys on the daphnia rosea (+/-)

- the larval salamander preys on the daphnia pulux (+/-)

- the larval salamander is indirectly benefiting the midge larva and daphnia rosea by preying on the superior competitor

example of indirect commensalism

primary producers

the first producers of energy-rich compounds that are later used by other organisms

primary consumers

animals that feed on producers; ex. herbivores

secondary consumers

carnivores that eat herbivores

tertiary consumers

carnivores that eat other carnivores

bottom up control

when the abundances of trophic groups are determined by the amount of energy available from producers

top down control

when the abundance of trophic groups is determined by the existence of predators at the top of the food web

- any given trophic level is controlled (limited) by the productivity and abundance of populations in the trophic level below

- bottom levels control top levels

describe bottom up control

- predator populations control the abundance of prey species, and the prey of the prey, etc.

- top trophic levels control bottom levels

describe top down control

- environmental conditions and tolerances of species (species will live where they can)

- basic resource and nutrient availability

- habitat complexity/heterogeneity (more complex habitats have more niches)

what are other factors influencing community structure