Interspecific Competition

interspecific competition

can limit the range of resources or habitat used by a species

involves two or more species

intraspecific competition

competition between same species

how does niche overlap determine the intensity of competition

Similarity of niches can influence whether species coexist and the extent of interspecific competition

inter and intraspecific competition may occur simultaneously

species fundamental niche

solid curves on a graph

represents resource use in the absence of other species (no competition)

species realized niche

dash curves on a graph

represents resource use in the presence of competing species

Competition coefficients (alpha and beta)

variables in the Lotka-Volterra competition model that quantify the negative effect of one species on another's population growth relative to the effect of that species on itself

competitive exclusion principle

states that complete competitors cannot coexist

how non-resource factors can change competitive outcomes

environmental factors that influence survival, growth, and reproduction of a species (but are not resources that are consumed) --> pH, Temp

spacial and temporal variation in resource availiablity

competition for multiple limiting resources

resource partitioning

how ecological conditions under which species with similar niches can coexist

niche partitioning

differentiation of resources or habitats to reduce direct competition

resource partitioning

The division of environmental resources by coexisting species such that the niche of each species differs by one or more significant factors from the niches of all coexisting species

exploitation

interspecific competition

indirectly through depletion of shared resources

manatees and green sea turtles both grazing on sea grass

interference

interspecific competition

direct confrontation (contest)

hermit crabs compete aggressively over shells

consumption

One species inhibits another by consuming a shared resource Competition between squirrels, deer, and birds for acorns

preemption

One species occupies space and inhibits the establishment of another species. Competition between sessile organisms, such as barnacles

overgrowth

one species grows over another, inhibiting access to essential resource. Taller trees shading smaller trees in forest

chemical interaction

chemicals released by one species inhibit growth or kill another species. Allelopathy in plants

territorial

behavior of one species that excludes another species from a specific location that is defended as a territory. Bird keeping other birds from nesting in its territory

encounter

nonterritorial encounters between individuals of different species affect one or more of the species involved. Scavengers fighting over a dead animal carcass

Lotka-Volterra Model

mathematical modeling of competition

unstable equilibrium

possible outcome of interspecific competition

Each species inhibits the growth of other species more than its own growth

Cuban treefrog (Osteopilus septentrionalis) vs. native treefrogs (Hyla cinerea). Compete for food, space, and breeding sites.

stable coexistence

Possible outcome of interspecific competition

intraspecific competition has a greater influence than interspecific competition

Niche differentiation. Darwin's Finches

species 1 wins, species 2 loses

Possible outcome of interspecific competition

Species 2's population eventually declines to zero.

Species 1 has a stronger effect on both its own and the other species' growth

High competition coefficient

species 2 wins, species 1 loses

Possible outcome of interspecific competition

In both cases the losing species can shift its niche or move elsewhere

coexistence

often involves partitioning available resources

1. There is spatial or temporal variability in use of shared resource(s)

2. Fluctuations in environmental conditions allow competitors to coexist, prevents one species from displacing others

3. Competition leads to natural selection for species' characteristics that minimize overlap in resource use = resource partitioning