Interactions of Multiple Species

Direct interactions

occur between two species and include trophic and non-trophic

Indirect interactions

relationship between two species is mediated by a third (or more) species

trophic cascade

when rate of consumption at one trophic level results in a change in species abundance or composition at lower trophic levels

trophic facilitation

when a consumer is indirectly helped by a positive interaction between its prey and another species

competitive networks

competitive interactions among multiple species in which every species has a negative effect on every other species (results in circular food web and weaker competitive interactions)

Interaction strength

effect of one species on abundance of another species

Foundation species

species with large effects on other specise and thus on species diversity of communities because of size and abundance

ecosystem engineers

species that act by bioengineering their environment because they create, modify, or maintain physical habitat for themselves and other species

keystone species

species that have large effects not because of abundance but because of the vital role they play in their communities (their effect is often large in proportion to their size and abundance)

redundant

species with the same function in their communities as other species within a larger functional group 

trophic level

feeding category

omninvores

feed at multiple trophic levels

controls on the number of trophic levels

amount of energy entering a system via primary productivity, frequency of disturbances/other agents of change (more impactful when primary producers are disturbed), area of an ecosystem

food webs

diagram showing connections among organisms

determinants of trophic interaction strength:

removal experiments, observing feeding preferences, comparing food webs, predator and prey body sizes

pisaster keystone species

greater influence on energy flow and community composition than abundance or biomass predicts

stability of food webs is dependent on…

complexity of ecosystems, distributions, buffering influence of weak interactions and of changes in prey choice

higher plant diversity leads to …

more stability in higher trophic levels (except for specialists)

portfolio effect

variation in population of 1 species cancels out variation in another so overall abundance remains the same