Nature of Communities and Changes in Communities Flashcards
Groups of interacting species that occur together at the same place and time circumscribed by natural, arbitrary, or artificial boundaries
Communities
Nexus of geography, resources, and phylogeny
Community Ecology
Phylogenetically related group of species; a clade
Taxon
Group of species that use the same resources even though they are taxonomically distant
Guild
Subset of a community that includes species that function in similar ways but may or may not use similar resources
Functional Group
Group of species that share a common resource and occur in the same community.
Local guild
Group of phylogenetically related species in a community
Assemblage
A phylogenetically bound group of species that use a similar set of resources with a community
Ensemble
In Community assembly, Community membership depends on these three things:
- Arriving at a site
- Coping with the site’s physical environment
- Interacting with the other species living there
Similarities between community ecology and genetics
Both population genetics and community ecology are concerned with variation over space and time in the relative abundance and diversity of discrete biological variants (alleles for population genetics, species for community ecology)
A representation of the trophic or energetic connections among species within a community
Food Web
Groups of species that have similar ways of interacting and obtaining energy
Trophic Levels
Representation of the trophic (vertical) and non-trophic (horizontal) interactions among species in a traditional food web
Interaction web
Occurs when the rate of consumption at one trophic level results in a change in species abundance or composition at lower trophic levels (lower = to producer)
Trophic Cascade; sea otters eating urchin increases abundance of kelp (primary producer)
Occurs when a consumer is indirectly helped by a positive interaction between its prey and another species
Trophic Facilitation
Competitive interactions among multiple species in which every species has a negative effect on every other species
Competitive networks
Buffer strong direct competition so that no one species dominates the interaction
Indirect species interactions
Similar to competitive network but is more linear, i.e. species B dominates C, species A dominates B, therefore species A also dominates C.
Competitive Hierarchy
The effect of one species on the abundance of another species
Interaction Strength
Set of characteristics that shape a community
Community structure
Number of species in a community
Species richness
Commonness or rarity of species (relative abundances)
Species evenness
Combination of species richness and evenness
Species diversity
How to interpret a rank-abundance curve?
Plot the proportional abundance od each species in rank order
Richness - longer x-axis present
Evenness - steep curve = less even, gentle curve = more even
Calculated by plotting species richness as a function of sampling effort
Species Accumulation Curve
Why does the species accumulation curve plateu
The more you sample, the less new species will pop up in each sample until eventually you have already sampled everything
Single species that defines much of the structure of a community (Dominant in terms of biomass or size)
Dominant/Foundation Species
A species whose actions change the physical character of its environment
Ecosystem Engineers (red flag)
Species that have large effects not because of their abundance, but because of the vital roles they play in their communities
Keystone Species
Species that may have the same function in the community as other species within a larger functional group
Redundant species
States that the more species are present in an ecological unit, the rate of ecosystem function also increases but up to some point; beyond this point, species do not have any more effect on ecosystem function.
Redundancy Hypothesis
Directional change in the species composition of communities over time initiated by natural or anthropogenic disturbance
Succession
Discrete event that damages or kills residents on a site
Distrubance
Disturbance that kills all residents of all species on site
Catastrophic Disturbance
Disturbance that falls short of wiping out all organisms from a site. Leaves residual organisms or biological legacies
Non-catastrophic disturbance
Abiotic factor reducing growth, reproduction, or survival of individuals
Stress
Disturbance is a product of?
Intensity, Frequency, and Extent
Succession that occurs after the creation of a “blank slate” either through catastrophic disturbance or de novo creation of a new site
Primary Succession
Succession that occurs after non-catastrophic disturbance
Secondary succession
Stable end point that experiences little change until a particularly intense disturbance sends the community back to an earlier stage
Climax/Climax stage
How does succession progress (Trajectory of Succession)?
- When the effect of a disturbance is catastrophic, a pioneer stage is formed thru the process of primary succession
- Secondary succession occurs after a disturbance alters a community greatly but does not destroy all life
- Intense disturbance at any stage can reset the community to a previous stage
Studied Lake Michigan sand dunes - late 1800s
- Concluded that sites on the dunes were older further inland, i.e., formed a “chronosequence” from which temporal change could be inferred
Henry Chandler Cowles
Radical, “superorganism” view of communities; species interact to promote a directed pattern of community development through “seral” stages, ending in a “climax” community
Frederick Clements
Proposed the “individualistic view of succession” in which “every species is a law unto itself”
- Stated that communities are not a predictable and repeatable result of coordinated interactions among species
Henry Gleason
Three Models of Succession
- Facilitation
- Tolerance
- Inhibition
Succession model where early-colonizing species modify the environment and enhance the establishment of later-arriving species; most likely in primary succession
Facilitation
Succession model where early-colonizing species modify the environment but have no effect on later-arriving species
Tolerance
Succession model where early-colonizing species modify the environment in ways that actively inhibit later-arriving species
Inhibition
Species richness generally increases or decreases with successional age?
Increases
The inability of a community that has undergone change to shift back to the original community type, even when the original conditions are restored
Hysteresis
