Community Ecology Flashcards
Community
an association of interacting species inhabiting a defined area at a particular scale over a particular span of time
Communities are often considered as
associations of a particular group
taxonomic, guilds(live same way), life form, functional
Foundational species
Species which provide a key role in shaping structure within a community
coral reefs
Keystone species
Species that have a disproportionate impact the community structure relative to the abundance of other species
If removed, the loss of keystones leads to a dramatic change in structure
Invasive species
Species that are not native to the habitat and disrupt the community
* Characterized by an ability to grow quickly and reduce local biodiversity
Community structure includes:
-the relative abundance of species within the
community
-the number of species & diversity
-species composition
Community diversity is a combination of the
1) Total number of species there are as well as
2) their relative abundance
Species Richness (s)
the number of species in a community
Species Evenness
the relative abundance of the various species within a community.
Species Diversity
a measure of diversity that increases with species evenness and species richness
Species abundance
measure of how common or rare a species is
how can species abundance be measured (3)
1)Number of individuals
2) Species cover- visual estimation(algae, plants)
3) Species biomass
measuring Species biomass
- Quantifiable as fresh or dry weight(plants), slow and destructive, precise
measuring number of individuals
Used when organisms form distinct
entities, like birds.
not useful for clonal organisms
measuring species cover
Visual estimation. Used when identifying individuals is
not trivial, like in algae, plants. Quick and non-destructive but less precise
Species dominance
communities include a dominant species usually
few species will be dominant or rare. Most species in the community will occur in moderate abundances
if only one or two species dominate a
community,
a majority of the interactions within that community
will involve those species
bundance is usually quantified in__________ – and graphed using a _______________ distribution
relative terms, lognormalw
in species abundance distributions, most species have
very few species have
intermediate abundances
high numbers or low numbers
why does overlooking rare species happen often in abundance curves?
the more you sample, the more species you will find and will come closer to a lognormal distribution curve
the more diverse a community is
the more stable it is
Gamma diversity
OVERALL diversity within a region / landscape
Alpha diversity
Diversity within a particular area within a region / landscape
* Consider it a subset of gamma
Beta diversity
a measure of the diversity among locations within a region.
* Usually measured as the amount of species change between
ecosystems, calculated as:
* gamma divided by alpha.
β diversity tells you how different patches are from each
other
Species evenness
-The relative population size of each species
-An ecosystem dominated by one species will have
low evenness
ie species being represented equally
Biodiversity=
species richness and evenness
Shannon-Wiener diversity Index
(H’)
s =
number of species in community
pi =
proportion of the ith species.
Rank Abundance Curves:\
where are high abundance species plotted
Plot of relative abundance of species against their rank in
abundance
-The flatter the curve (aka, decreased slope), the more even the community
-Dots ranked according to their abundances, with high-abundance species plotted on the left side of the curve.
What are the factors that increase / decrease biodiversity?
(1) Time-more time to evole and colonize, higher biodiversity
(2) Global change-pollution, invasive species decrease biodiversity
(3) Complexity-more complex envonments more biodiversity
(4) Exploitation and limitation, some predator, nutrient limitation, decrease competition and increase biodiversity
how does environment complexity influence biodiversity
heterogenous environment –> more niches, more biodiversity
homogenous environment –> less niches, less biodiversity
Species composition:
the species that occur in a given community at a given time
How does species diversity influence ecological function?
- complementarity
2.facilitation
3.species selection
complementarity
-A given ecological service will be at its greatest for
communities in which all resources and/or
microenvironments are being exploited / occupied.
-a single species with a single niche can only
make use of a fraction of the environmental variation
Facilitation
-Some species may enhance the growth of others
ie reduce salinity
-May be particularly important in stressful environments
Species selection / sampling effect
-Basic idea is that species differ in the inherent rates of delivery of ecological services
As the number of different species increase in a community over time, the odds of said community containing at least one species with enhanced function increases
-is not a benefit of diversity per se, but rather it increases the probability of enhanced ecosystem function.
Increases in genetic diversity can lead to an
increases in
species diversity within a community.
Genotypes likely differ in
- how species forage to resources,
- where plants put roots and leaves,
- susceptibility to disease,
- ability to outcompete rivals.
