ch. 18: community structure Flashcards
ecotone
- boundary b/w adjacent communities
- transitional zone b/w ecosystems where there is a mix of species in both adjacent ecosystems
- boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species
interdependent communities
communities in which species depend on each other to exist
independent communities
communities in which species DO NOT depend on each other to exist
species richness
the number of species in community
relative abundance
proportion of individuals in a community represented by each species
- n/N
- n = number of individuals of 1 species
- N - total number of individuals of all species
log-normal distribution
normal (bell-shaped curve) distribution that uses log-scale
- on x-axis
rank-abundance curve
curve plot of relative abundance of each species in a community in rank order form most abundant species–>least abundant species
species evenness
comparison of relative abundance of each species in community
Simpson’s index
measurement of species diversity
key-stone species
species that substantially affects the structure of communities despite the fact that individuals of species might not be particularly numerous
intermediate disturbances hypothesis
hypothesis that more species are present in community that occasionally experiences disturbances than in community that experience frequent of rare disturbances
food chain
linear representation of how diff species in a community feed on each other
food web
complex and realistic representation of how species feed on each other in a community
trophic levels
level in a food chain or food web
primary consumer
species that eats producers
secondary consumer
species that eats primary consumer
tertiary consumer
species that eats secondary consumer
omnivore
species that feeds at several trophic levels
guild
w/in trophic level; group of species that feeds on similar items
direct effect
interaction b/w 2 species that does involve other species
indirect effect
interaction b/w 2 species that involves 1+ intermediate species
density-mediated indirect effects
indirect effect caused by changes in density of intermediate species
trait-mediated indirect effects
indirect effect caused by changes in traits of intermediate species
trophic cascade
indirect effects in a community initiated by predator
bottom-up control
when abundance of trophic groups in nature are determined by amnt of energy available from the producers in a community
top-down control
when abundance of trophic groups is determined by existence of predators at top of food web
community stability
ability of community to maintain particular structure
community resistance
amnt that a community changes when acted upon by some disturbances, such as addition and removal of species
alternative stable states
when community is disturbed so much that species composition and relative abundance of populations in community change, and new community structures is resistant to further change
native
organisms naturally found in an ecosystem
nonnative (Exotic, alien, invasive)
any organism not found naturally in ecosystem
- usually transported by humans
indicator
organisms that serve as early warnings of damage to a community
keystone species
organism has a disproportionate effect on the rest of the ecosystem
- strong interactions w/ other species affect life of others
- not necessarily numerous
- process out materials out of proportion to numbers/biomass
removal of keystone species can cause…
a community to collapse
keystone species increase
prey diversity (and overall ecosystem diversity)
ecosystem engineers
keystone species that affect communities by influencing the structure of a habitat
communities are categorized by their…
dominant organisms
- (or by physical conditions that affect distribution of species)
define community
assemblage of species living together in area
succession
communities change over time
community interactions
predation, competition, mating
most salt tolerant mangroves?
landward
edge effects
important aspect of community structure is the boundary b/w 1 habitat and others
2 types of ecotones
sharp or flat
types of edge effects
inherent, induced, narrow, wide, convoluted, perforated
wide edge effect
substantial distances separates border point where physical conditions and vegetation do not differ from interior patch
convoluted edge effect
border is non-linear
perforated edge effect
border has gaps that host other habitats
typically there is greater __ ___ where the edge effect occurs
species richness
___ surveys can demonstrate the existence of an ecotone
line-transect
__ changes in distribution of species should occur across the ecotone
sharp
interdependent communities
communities in which species depend on each other to exist
- removing a species should cause other species to decline
independent communities
communities in which species DO NOT depend on each other to exist
- removing a species should cause neutral or positive changes in other species’ fitness
community structure
species interactions b/w 2 species at a time
- combine species interactions
keystone species are usually the…
- top predators
- ecosystem engineers
zonation
- zones w/ diff ranges of environmental conditions and species
- reflect range of tolerance for species in zones
sharp boundaries (ecotones)
closed communities
indistinct boundaries (ecotones)
open communities
inherent edge effect
natural features stabilize the border location
induced edge effect
transient, natural, or human-related activities
- subject borders to successional changes over time
narrow edge effect
one habitat abruptly ends and another begins
Clements
viewed species in a community as interdependent super organism with distinct ecotones
Gleason
viewed species as responding idiosyncratically to environmental gradient
community concepts: most research supports _____ model
Gleason’s individualistic
abrupt changes in species distributions may be the result of…
abrupt changes in abiotic conditions
to plot species evenness (rank-abundance curve)…
rank most abundant species (1), next most abundant (2), etc.
what is biodiversity? (3 parts)
species richness, species abundance, species diversity
scales of biodiversity: alpha diversity
species biodiversity of local community (natural habitat patch)
- w/in habitat diversity
scales of biodiversity: beta diversity
number of species 2 communities DO NOT share
- change (or turnover) in species composition b/w 2 distinct communities
- b/w habitat diversity
- highest when habitats vary over fine spatial scales
scales of biodiversity: gamma diversity
total species richness over a large geographic area such as biome, continent, or ocean basin
-measure of overall diversity for diff ecosystems w/in 1 region
Menhinick’s index (D)
number of species divided by sqrt (number of individuals in sample)
- the larger the sample, the more species you would expect
- D = s / sqrt(N)
- takes into account richness and evenness
species evenness
- quantitative measurement
- measure of the abundance of individuals in each species
- free from variations, equal in measure/quantity
simpsons index
common measure of species diversity; (ranges from 1 –> max number of species in community)
- S = 1/ (summation(p^2))
- s = species richness
- p = relative abundance of each species in community
Shannon’s index (H’)
H’ = (-) summation (p)(ln p)
Simpson’s index: high D value
good and means the habitat is diverse, species rich, and able to withstand some environmental impact
Simpson’s index: low D value
poor and means that habitat is low in species, so a small change to environment would have a serious impact
- ex: pollution
can 2 species occupy the exact same niche at the same time?
no! because of the competitive exclusion principle (one will be better)
