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47 Cards in this Set

  • Front
  • Back
Species Richness
the number of species in a community
Species Evenness
relative abundance compared with one another
Species Diversity
combines species richness and species evenness

-Shannon Index = (summation)p•ln(p)

p = proportion of individuals in the ith species
-index ranges from 0 - infinity
Rank-abundance curves
(comparison of diversity)
proportional abundance of each species vs abundance rank -- compare between communities
-each line = 1 community
-flatter slopes = higher species evenness
Species accumulation curves
species richness vs species abundnace
-not always accurate because some species are more difficult to sample than others
alpha diversity
measured locally, at a single site
beta diversity
measures the uniqueness -- the differences between two sties (measure of turnover)
gamma diversity
measured over a large scale
factors that control diversity in a community are -
(1) Regional species pool
(2) Dispersal of immigration
(3) Abiotic factors
(4) Species interactions (biotic factors
tendency of a community to remain the same in structure and function
-stability increases as diversity increases
-sensitivity of a community to perturbation, probability that greater-or-equal to 1 species will go extinct over some spatial scale
mechanisms for increased diversity
(1) Complementarity
(2) Sampling Effect
local deterministic processes that lead to increasing ecosystem function with each species added
-eg facilitation, niche differentiation
Sampling Effect
-local regional and stochastic processes lead to some species that alone have large effects on community function being included in the local pool, and driving ecosystem function
a discrete event that injures or kills some individuals and creates opportunities for others (abiotic or biotic)
abiotic factor that reduces the growth of reproduction of some individuals and creates opportunities for others
changes in species composition over time as a result of disturbance or stressor to the community
primary succession
colonization of habitats devoid of life (rare)
secondary succession
space opens up, but some residual organisms survive
early species
good dispersers, fast growing, allocation to growth and reproduction, tolerance of harsh conditions
late species
worse dispersers, slower growing, but better competitors or better defended
what are the four models of succession
(1) facilitation
(2) tolerance-neutral
(3) inhibition
(4) lottery
only early successional species (pioneer species) can establish -- they facilitate the establishment of other species
intitial stages of colonization are not limited to pioneer species. these species do not facilitate the colonization by species of later stages, those occuring later are simply those tolerant of environmental conditions occurring later in succession
any species that can survive in an area as an adult can colonize the area in early stages. Early occupants of an area modify the environment in a way that makes the area less suitable for both early and late successional species
random chance who gets there first, can be replaced by anyone
What was Clement's view on the nature of succession?
-holistic view - community as superorganism
-community is the essential unit
-nature of succession = the community can reproduce itself "repeating with essential fidelity the stages of its development".
What was Gleason's view on the nature of succession
-individualistic view - community as random association of individuals
-species, not communities are the essential unit
-nature of succession = succession results from the individual responses of different species to the prevailing environmental conditions
ability of a community to withstand perturbation
speed a community returns to its former state after its been perturbed
How are forest fires affected by global climate change?
timing of spring snowmelt, fire season length, temperature, time of first snowfall
What are some consequences of increases CO2 in the atmosphere?
Greenhouse effect :
-increased temperature and sea level
-plants move up in elevation
-phenological mismatch
-increase in ocean acidity (carbonic acid)
study of the relationship between climate and the timing of ecological events
CO2 fertilization effect
most plants respond to increasing CO2 by increasing photosynthesis
-eventually this increased photosynthesis levels off
Why do forests plateau in responses to CO2 enrichments?
(1) limited Nitrogen/nutrient availability
(2) limits n water availability
(3) changes in temperature
(4) environmental pollution
species area relationship
increase in area correlates with in an increase in species
Why does species richness increase with area?
-extinctions are less likely with larger population sizes
-more area in which colonists might land
-more heterogeneity
Immigration rates decline as the island gets more species because -
-fewer of the immigrants are different from those already on the island
-it is more difficult for immigrants to establish in a more diverse system
Extinction rate increases as the island gets more species because -
-more species make a larger pool of potential extinctions
-more species means a smaller population of each species, increasing extinction risk
-more diverse islands are more competitive, leading to extinctions
When an island is further from the mainland --
-the rate of immigration decreases
-the rate of extinction remains the same
When an island is larger --
-rate of extinction decreases (more space = larger populations)
-rate of immigration stays the same
Equilibrium theory of island biogeography
superimpose the immigration and extinction curves
-where the lines intersect (where immigration = extinction) is the equilibrium population
Species Turnover
even though species richness is predicted to equilibrate, the identity of the species should be in flux
What are the three predictions of Island Biogeography Theory?
(1) species richness results from the balance between immigration and extinction
(2) larger islands should have more species than further islands due to reduced extinction rates
(3) islands nearer the mainland should have more species than further islands due to enhanced immigration rates
Neutral Theory
species coexist because they are so similar in their birth and death rates
-species are so evenly matched that they take an exceedingly long time to exclude each other
-speciation takes place a faster rate than extinction (speciation occurs at at constant rate)
Will species go extinct faster in a large or small community?
small community

(larger communities are more stable)
Ecological drift
the influence of random demographic stochasticity (birth, death, immigration rates) on community composition.
-very large communities show slower drift
Coexistence occurs when -
the stabilizing effects of niche differences exceed the differences in competitive ability between species