Community Structure Flashcards
Community
Interactions between
populations of species within a
common area
Community zones reflect…
changes in species
composition over space
Community zones are based on…
dominant species or physical conditions (temp, alt, salinity)
Ecotones are
sharp boundaries between zones
Ecotones usually have
high diversity of species
independent communities
Species can be in a community because they share
similar habitat requirements:
interdependent communities
species can be in a community because they
depend on each other:
Methods to quantify a community
1) Species richness: number of species
2) Abundance: number of individuals of each species
3) Rank-abundance curves
4) Species diversity indexes
Abundance normally shows a
log-normal distribution
The majority of species
show
intermediate values
of abundance
Rank-abundance curves illustrate
both species
richness and species evenness
Species richness
number of species (points)
within each community
Species evenness
comparison of the
relative abundance of each species in
a community
Maximum evenness:
all species have
the same relative abundance
Simpson’s varies between
1 (if S = 1) and S
Shannon’s varies between
0 (if S = 1) and ln S
Factors affecting species richness
1) Resources
2) Habitat diversity and connectivity
3) Presence of keystone species
4) Frequency and magnitude of disturbances
Most common pattern for species richness
Hump shaped
(stl arch shape)
Higher habitat diversity and connectivity
increase species richness
More diverse habitats can offer more
potential niches
More connected habitats promote
dispersal
Keystone species affect the ____ despite not being very abundant
structure of a community
keystone species considered ecosystem engineers
beavers
Intermediate levels of disturbance maintain
more diverse communities
Food chain:
linear representation of species
that consume each other
(transfer of energy and
nutrients).
Food web:
all possible
feeding relationships among
the species of a community
(way more realistic).
Trophic levels
help understanding food webs with high
species richness
Terciary consumers
top predators: large carnivores that consume
herbivores and mesopredators; parasites
Secondary consumers
(mesopredators: small carnivores that consume
herbivores; parasites, parasitoids)
Primary consumers
(herbivores, parasites, parasitoids)
Producers
(mostly photosynthesis: plants, algae)
Guilds
group species feeding on similar items within
each trophic level
Trophic cascade
(indirect effects initiated by a predator)
Indirect effects can even happen
between
neighboring communities
Bottom-up control:
the abundance of trophic
groups is determined by the
energy available from
producers.
Top-down control:
the abundance of trophic
groups is determined by the
existence of top predators.
