Community Ecology/Competition

community

group of species that occur together in space and time

physically, taxonomically, statistically, interactively

how communities can be defined

richness

number of species

evenness

equability of individuals among species

diversity indices

combination of richness and evenness

rank abundance curves

shows relative species abundance in an ecological community

Shannon-Wierner Index

measured richness + evenness

Simpsons Index

measures dominance

predation

one group is negatively affected while the other is positively affected

mutualism

both groups benefit

amensalism

one group is negatively affected while the other group is neutral

commensalism

one group is positive affected while the other group is neutral

apparent competition

indirect interaction where two prey species negatively affect each other because they share a common predator, rather than directly competing for resources

trophic cascade

the top predator controls the structure of an ecosystem by negatively affecting prey and positively affecting producers

Grinnell’s niche

habitat or environment an organism is capable of occupying

Elton’s niche

the role a species plays in the community

competitive exclusion principle

two species cannot coexist on one resource

Hutchinson’s niche

“n-dimensional hypervolume” based on biotic and abiotic components

fundamental niche

the full potential range of environmental conditions and resources a species can occupy, only based on climate tolerances

realized niche

restricted range a species actually occupies, limited by competition and predation

niche partitioning

competing species divide resources so they can coexist instead of outcompeting each other

limiting similarity

there is a limit to how similar two species can be in their niches and still coexist

competition

the simultaneous demand by two or more individuals or species for an essential shared resource that is in limited supply. mutually negative interaction

intraspecific competition

competition between members of the same species forces them into a wider range

scramble competition

lack of a resource harms all organisms

contest competition (interference)

the best competitors get enough resources

interspecific competition

reduction in population growth rate of one species due to the presence of another species

allelopathic activity

toxins that reduce growth or seed production of other plants

asymmetric competition

uneven division of resources; large competitors have greater effects

consumptive competition

use of a shared, renewable resource

pre-emptive competition

sessile organisms acquiring space

overgrowth competition

one individual overgrows and blocks resources to another

chemical competition

use of toxins that diffuses over environment (allelopathy)

territorial competition

active defense of space

encounter competition

transient interactions over a resource

Lotka-Volterra Model of Competition

measures interspecific and intraspecific competition. (a>1= greater interspecific, a<1= greater intraspecific)

Zero Net Growth Isocline

values of populations 1 and 2 that yield zero population growth for both species

founder control

outcome depends on starting densities, more abundant species will dominate

resource

any substance that leads to increased growth rates as its availability is increased

law of the minimum

the resource with lowest supply limits growth

R*Theory

minimum equilibrium resource requirement needed to maintain consumer population growth

R*Rule

species with lowest R* should competitively exclude all other species

substitutive/replacement

best for comparing relative strengths of intra and interspecific competition

additive

best for measuring magnitude of interspecific competition

response surface design

best for comparing magnitudes of intra and interspecific competition

removal experiments

often easier to remove rather than add competitors

target-neighbor study

single individual of one species vs. natural densities of competitors

Hutchinsonian Ratios

coexisting species differ in size by a factor of 1:3

Paradox of the Plankton

found that aquatic habitats provide many more niches than originally thought, homogeneity rarely exists, and plankton communities may never reach equilibrium.

niche partitioning

natural selection drives competing species into different patterns of resource use or different niches

niche shifts

changes in a species diet or habitat use due to the presence of competitor (indirect evidence for competition)

character displacement

morphological differences between species that allows for coexistence

Townsend niche

a summary of an organisms tolerances and requirements