Population cycles - competition

intraspecific competition

an interaction between individuals of the same species brought about by a shared requirement for a resource in limited supply

interspecific competition

an interaction between individuals of different species brought about by a shared requirement for a resource in limited supply

fundamental niche

full range of conditions and resources needed by a species to grow, survive and reproduce

• competition restricts a species to a portion of its fundamental niche

realized niche

portion of the fundamental niche a species actually uses as a result of competition

• may/may not occupy the part of fundamental niche allowing highest growth/reproduction (fitness)

niche overlap

when 2+ species use a portion of same resource (food, habitat) simultaneously

degree of potential competition

amount of overlap

3 possible outcomes when one species is introduced to an area where another species exists

1. coexistence without competition (resources not limited)

2. coexistence with competition (moderately limited) (asymmetrical competition, competitively dominant, resource partitioning)

3. one species is eliminated (very limited)(competitive exclusion principle)

asymmetrical competition

one species is more strongly affected by competition

competitively dominant

species least affected by competition

resource partitioning

each species uses a portion of the same resource (can reduce competition among co occurring species)

competitive exclusion principle

two species with the same resource requirements cannot co exist when those resources are scarce relative to demand

explain competition in plants

plants compete with neighbour plants of same or dif species. interactions complicated by:

• below ground competition - root competition for water and nutrients

• above ground competition - shoot competition for light

evidence of competition in animals, explain

• contraction of a fundamental niche in presence of another competing species

• expansion of a realized niche in absence of another competing species (competitive release)

• asymmetrical competition and competitively dominant

assume competitive interactions among populations result in

• a stabilization of population growth for both populations

• or elimination of one population from the system

lotka volterra model for interspecific competition

• extension of the logistic equation

• differential equations express the rate of non linear growth of populations of competing species

a_^ij

coefficient of competition, effect of an individual of species j on exponential growth of species i

a_ijN_j

converts population of j into units of species i

a_ijN_j/K_i

proportion of K_i that is used by equivalent units of species i

dNi/dt=riNi (1 - Ni/Ki - aijNj / Ki) explain the equation

1-Ni/Ki = intraspecific (i on i)

aijNj/Ki = interspecific (j on i)

dNj/dt= rjNj (1-Nj/Kj - aijNj/Kj) explain

1-Nj/Kj = intraspecific (j on j)

aijNi/Kj = interspecific (i on j)

when do competitive abilities shift

as abiotic factors change

• relative competitive abilities of species adapted to different environmental conditions may shift as conditions change

competition involves _____ resources and species..

multiple, niche overlap is very complex

competition acts as what for inds

as a selective pressure for inds to maximize resource access to increase fitness

resource partitioning is often thought to be due to

competition among species in the past (ghosts of competition past) but hard to prove

why is resource partitioning from the past hard to prove

• no information if species coexisted in past

• species respond to natural selection differently and are different (did/do not compete)

• species may have been competitively excluded leaving different species (did/do not compete)

the ______ niche is the portion of the ______ niche as species actually exploits as a result of competition

realized, fundamental

possible outcomes of interspecific interactions are

co-exist without competing, co-exist with competion, competitive exclusion

there is evidence of interspecific competition in plants and animals, where one species is competitively dominant over the other, called ______ competition

asymmetrical

when a competitively dominant species is removed this may result in _______ of the less dominant species

competitive release

______ models are an extension of the logistic equation, whereby interspecific competition effectively ____ K for competing species

lotka volterra, decrease