Lecture 14: The Nature of Communities Flashcards
What are communities?
Groups of interacting species that occur together at the same place and time
Physically defined community
Might encompass all the species in a sand dune, mountain stream, or a desert
Biologically defined community
- Might include all species associated with a kelp forest, freshwater bog, or a coral reef
- This approach emphasizes importance of an abundant species, such as trees
Subsets of species can be defined as __
- Taxonomic affinity
- Guild
- Functional group
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
Food Webs
- organize species based on trophic or energetic interactions
- tell little about the strength of interactions or their importance in the community
- don’t include non trophic interactions
Trophic levels
First level: Primary producers (autotrophs) – plants and algae
Second level: Primary consumers – herbivores
Third level: Secondary consumers – carnivores
Fourth level:Tertiary consumers – carnivores
Omnivores
- feeding on more than one trophic level
Interaction webs
more accurately describe both the trophic (vertical) and non-trophic (horizontal) interactions than a traditional food web
Community structure
The set of characteristics that shape communities
- Species richness
- Species Evenness
- Species diversity
Species richness
number of species in a community
Species evenness
relative abundances compared with one another
Species diversity
combines species richness and species evenness
Shannon Index
- equation in notes
- pi = proportion of individuals in the species
- s = number of species in the community
Biodiversity
- describes diversity at multiple spatial scales, from genes to species to communities. Implicit is the interconnectedness of all the components
Genetic Diversity
affects the viability of populations, which in turn affects species diversity in a community
Rank abundance curves
- plot the proportional abundance of each species (pi ) relative to the others in rank order
- Relative abundances can suggest what species interactions might be occurring
Species composition
- identity of species in a community
- Two communities could have identical species diversity values, but have completely different species.
Species accumulation curves
- species richness is plotted as a function of the total number of individuals that have been counted
- These curves can help determine when most or all of the species in a community have been observed.
Spatial scale
- really important
- If we sampled bacteria in tropical soils at the same scale as Costa Rican moths, the bacterial diversity would be immense in comparison.
- The study highlights how little we know about community structure of rarely studied assemblages, such as microbial communities.
Direct Interactions
occur between two species competition, predation, and facilitation
- A –> B
Indirect interactions
- Occur when the relationship b/w two species is mediated by a third (or more) species
- Ex. Pollination depends on bees; the bee population is influenced by mice that prey on bees’ nests; mice are eaten by cats. An increase in the cat population can impact the flowers