Lecture: Chapter 17-18 Community Structure and Factors of Influence Flashcards
Communities
Groups of interacting species that occur together at the same place and time
Synergistic
The interactions are synergistic; they make communities into something more than the sum of their parts
What are communities?
In practical terms, ecologists usually define communities based on physical or biological characteristics.
Physical: all the species in a sand dune, a mountain stream or a desert
Biological: all the species associated with a kelp forest, a freshwater bog, or a coral reef
Taxonomic affinity
All bird species in a community
Guild
Group of species that use the same resources
Functional group
species that function in similar ways, but do not necessarily use the same resources
Species diversity and species composition are important discriptors of community structure
Community structure is the set of characteristics that shape communities
Species richness
the number of species in a community
Species evenness
Relative abundances of species comapred with one another. how many individuals belong to each species - are they distributed fairly equally or rather unequally
Species diversity
Combines species richness and species evenness
Shannon index
H = -E(pi)(ln(pi))
Species diversity (and biodiversity) are often used more broadly to mean the number of species in a community
define biodiversity
Biodiversity describes diversity at multiple spatial scales, from genes to species to communities.
- species diversity
- genetic variation
- habitat variation (spatial heterogeneity)
Rank abundance curves
Plot the proportional abundance of each species (pi) relative to the others in rank order
Species accumulation curves
species richness is plotted as a function of the total number of individuals that have been counted
Species composition
identity of species in a community
Two communities could have identical species diversity values, but have completely different species.
The identity of species is critical to understanding community strucutre
Dominant species or foundation species
Have large effects on other species, and thus species diversity, by virtue of their considerable abundance or biomass
Keystone species
Strong effects because of their roles in the community. Disproportionate impact on the community relative to their abundance or biomass
Keystone predators
predators that often function as keystone species within communities
Food webs
Conceptual models of the trophic interactions within communities. Organize species and describe interactions based on trophic or energetic interactions
Trophic Levels
Primary producers: plants and algae
Primary consumers: herbivores
Secondary consumers: carnivores
Tertiary consumers: carnivores
control of energy flow - bottom-up
The bottom-up view: the abundance of organisms at a trophic level is determined by the trophic level below it
control of energy flow - top-down
The top-down view: Energy flow is governed by predator consumption rates at the highest trophic lvel, which influences multiple trophic levels below them. HSS (Hairston, smith, slobodkin) hypothesis. “The world is greeen’
Trophic cascade
Change at one trophic level results in alternating responses of trophic levels below.
Mediated by “trophic” relations - feeding
How are communities characterized?
By complex networks of direct and indirect interactions that vary in strength and direction
Direct interactions
occur between two species (e.g. competition, predation)
indirect interactions
Occur when the relationship between two species is mediated by a third (or more) species
trophic cascade
a carnivore eats an herbivore (a direct negative effect on the herbivore)
the decrease in herbivore abundance has a positive effect on a primary producer
The keystone predator effect
A predator witha species prefernece
selectively removes competitive dominant species
allows other species that would be excluded by the dominant competitor to persist
species richness
differs among communities due to variation in regional species pools, abiotic conditions and species interactions
resource partioning
among the species in a community reduces compeition and increases species richness.
Competing species coexist by using resources in different ways/
