Community Ecology: Diversity, Sampling Curves & Island Biogeography

taxonomic affinity

grouping species by what kind of organism they are

guild

species that use the same resource

functional group

species that function in similar ways

ways to define a community

habitat or environment, taxonomic affinity, guild, functional group

species diversity

combines species richness and species evenness

species richness (S)

the number of species in a community

species evenness (J)

relative abundances of species compared with one another

biodiversity

the variety of life at all levels: genes, species, and ecosystems

when evenness is 1

all species are equally abundant

J near 0

one species dominates

minimum Shannon diversity

0

when H = 0

only one species is present

higher H

more diverse community

steeper rank abundance curve

less even

flatter rank abundance curve

more even

physically defined community

all the species associated with a specific habitat type

biologically defined community

species associated with an abundant species in the area

why island species-area slopes are steeper

small islands lose proportionally more species than mainland areas of the same size

theory of island biogeography

a method for asking how island area and isolation act together to produce species diversity patterns

equilibrium species richness (Seq)

where the immigration rate equals the extinction rate

extinction rate as S increases

rises

immigration rate as S increases

falls

I > E

S increases

E > I

S decreases

what island area shifts

the extinction curve

what island isolation shifts

the immigration curve

smaller island

higher extinction curve, lower Seq

larger island

lower extinction curve, higher Seq

more isolated island

lower immigration curve, lower Seq

less isolated island

higher immigration curve, higher Seq

island with the highest Seq

large and close

island with the lowest Seq

small and far

what immigration and extinction rates depend on

number of species already present and island characteristics such as size and isolation

neutral model

ignores species identity and focuses on probabilistic processes such as immigration, extinction, and speciation

change in species richness formula

delta S = speciation - extinction + immigration

key to island biogeography

immigration and extinction

species composition at equilibrium

keeps changing, because immigration and extinction still occur

alpha diversity

diversity within a community (species richness within a regional group)

beta diversity

change in species composition between communities (species richness between communities)

gamma diversity

total diversity across an entire region

beta diversity formula

beta = gamma / alpha

latitudinal diversity gradient

species richness increases with decreasing latitude

exception to the latitudinal diversity gradient

seabirds

three hypotheses for the latitudinal diversity gradient

diversification rate, diversification time, carrying capacity

diversification rate hypothesis

the tropics have the most land area and stable temperatures, which may increase diversification rates

diversification time hypothesis

the tropics have been climatically stable longer, giving species more time to evolve

competition

a non-trophic interaction in which individuals are harmed by their shared use of a resource that limits their ability to grow, reproduce, or survive

intraspecific competition

competition between individuals of the same species

interspecific competition

competition between individuals of different species

type of competition that matters most for community structure

interspecific competition

exploitation competition

reducing access to a resource by reducing the availability of that resource (indirect)

interference competition

reducing access to a resource by directly interfering with a competitor (direct)

asymmetrical competition

competition in which one species is harmed more than the other

competitive exclusion principle

two species that use a limiting resource in the same way cannot coexist indefinitely

fundamental niche

the full set of resources and biotic and abiotic requirements that allow a species to survive, grow, and reproduce

realized niche

the restricted set of resources or conditions a species is limited to, due to species interactions

what can alter the outcome of competition

the physical environment, disturbance, and predation

when competing species are more likely to coexist

when they use resources in different ways

resource partitioning

species use a limited resource in different ways

character displacement

the shift in phenotypes through time in response to competition

competition coefficient alpha

per capita negative competitive effect of species 2 on species 1

competition coefficient beta

per capita negative competitive effect of species 1 on species 2

isoclines do not cross

competitive exclusion

isoclines cross with alpha and beta > 1

unstable equilibrium; the winner depends on initial conditions

isoclines cross with alpha and beta < 1

stable coexistence

condition for stable coexistence

intraspecific competition > interspecific competition

two ways to competitively exclude another species

be a stronger competitor or have a higher carrying capacity

predation

a trophic interaction in which an individual of one species consumes some or all of an individual of another species

optimal foraging theory

animals maximize energy gained per unit of feeding time and minimize risks

physical defenses

large size, spines and thorns, body armor

mimicry

prey resembles another organism that is toxic or fierce

crypsis

prey is camouflaged or resembles its background

inaccessibility

prey lives where the predator cannot reach it

masting

plants produce huge numbers of seeds in some years and hardly any in others

prey switching

predators eat the most common prey

host range of parasites

parasites feed on one or a few host species, but hosts have multiple parasite species

host categories in disease models

susceptible, infected, recovered, dead

when a disease becomes established

dI/dt > 0

threshold density

the density of susceptible hosts above which a disease will spread

S relative to ST for disease control

S < ST

ST for disease control

high

ways to reduce S

vaccination or culling

habitat mutualism

one partner provides the other with living space or favorable habitat

trophic mutualism

a mutualist receives energy or nutrients from its partner

facilitation

commensalism and mutualism

interactions not included in a food web

competition, facilitation, amensalism

interaction web

a diagram of both trophic and non-trophic interactions in a community

competitive hierarchy

one species outcompetes all others, so its effect on one competitor does not benefit another

competitive network

interactions among multiple species in which no species wins every pairwise competitive interaction

what competitive networks allow

coexistence

trophic cascade

a carnivore eats an herbivore, and the decrease in herbivores has a positive effect on a primary producer

trophic facilitation

a consumer is indirectly facilitated by a positive interaction between its prey and another species

trophic cascade vs. trophic facilitation

trophic cascade links are all trophic; trophic facilitation links are not all trophic

density-mediated indirect interaction (DMII)

species A affects the density of species B, with consequences for species C

trait-mediated indirect interaction (TMII)

species A affects the behavior or another trait of species B, with consequences for species C

inhibition model of succession

early successional species delay succession by interfering with later colonists

tolerance model of succession

early successional species have neither a positive nor negative influence on later colonists

traits of early successional species

r-selected: good dispersers, fast growers, early maturity, high reproductive rates

traits of late successional species

K-selected: good competitors, slower growers, later maturity, long-lived

facilitation model of sucession

early successional species have a positive influence on later colonists