Important Terms and Definitions

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Lecture 15
Communities are groups of interacting species that occur together at the same place and time
Trophic levels are groups pf species that have similar ways of obtaining energy (e.g
Primary producers, primary consumers)
Omnivores- feed on more than one trophic level, consume both animals and plants
We can classify interactions as: Vertical or Horizontal (horizontal = competition)
Community structure is the set of characteristics that shape communities
Species richness-the number of species in a community
Species evenness- relative abundances compares with one another
Species diversity combines species richness and species evenness (a measure)
There are several quantitative species diversity indices. The most commonly used it the
Shannon index:
We can quantify how evenly distributed individuals are among species using an evenness
measure (equitability) Where Hmax = lnS (S- #of species)
Biodiversity describes the diversity of important ecological entities that span multiple spatial
scales, from genes to species to communities. Implicit is the interconnectedness of all
components of diversity.
Rank abundance curves plot the proportional abundances of each species (pi) relative to the
others in rank order
Species accumulation curves-species richness is plotted as a function of the totally number of
individuals that have been counted with each sample
Species composition- the identity of species present in the community
Direct interactions occur between two species (e.g. competition predation, and facilitation)
Indirect interactions occur when the relationship between two species is mediated by a third
or more species
A trophic cascade is when a predator relieves pressure on trophic levels below the prey
Trophic facilitation occurs when a consumer is indirectly facilitated by a positive interaction
between its prey and another species
There are two ways that that species have large impacts on other species: 1)
Dominant species 2) Keystone species
Dominant species (foundation species) can have a large effect on other species and species
diversity by virtue of high abundance or biomass
Dominant species may also be ecosystem engineers
Keystone species have a strong effect because of their roles in the community
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