Interspecific Competition Flashcards
Define interspecific competition
competition between individuals by the shared use of one or more resources that are in limited supply, resulting in a mutual reduction in fitness
What are the two main types of competition
- exploitation competition
- interference competition
Define exploitation competition
(also known as resource or scramble competition)
when individuals interact indirectly as they compete for a common limiting resource
What are examples of common limiting resources in exploitation competition
food/nutrients, habitat, space, light
limiting resources mean that they do not have ample amount (ex. even though need oxygen, there is lots of it so doesn’t count)
Define interference competition
(also known as contest competition)
is direct competition when individuals interfere or impede the access of others to a resource even if the resource is not in limited supply
Examples of interference competition
tree canopies blocking light, territoriality, changes to the environment such as plants releasing chemicals to forbid other plants to grow there, or direct fighting/hoarding
Explain example of exploitation and interference competition in dung beetles
use feces to feed themselves and their larvae
exploitation = dung is a limited resource and quickly removed (rolled, buried. etc).
interference = beetles often fight over dung
exploitation and interference competition often occur ______
simultaneously
they found that beetles who “won” in interference competition were often ____
larger and have a higher body temperature
Explain how competition can be size-symmetric or size-asymmetric
size symmetric = the resource acquired is proportional to the size of the individuals, structure, etc. ex. root nutrients because if they are 2x larger they will get 2x more nutrients
size asymmetric = the resource acquired is not proportional to the size of individuals, structures, etc. ex. large canopy gets all the light, small canopy gets little to none
Explain example of exploitation and interference competition in plants
exploitation = roots competing for limiting resource of nitrogen. root competition is size symmetric, while shoots compete for access to light and is size-asymmetric.
interference = plants produce toxic chemicals to inhibit other plants from living there (allelopathy)
Define the Lokta-Volterra model
model that describes the outcome of competition between two species over ecological time
Explain the competition coefficients a and b for interspecific competition
a = makes species 2 individuals equivalent to species 1 individuals in terms of their effect on the population growth of species 1
b = opposite
they measure the competitive effects of one species on another in terms of effect on population growth
If each individual of species 2 has the same effect as 2.5 individuals of species 1 on the population growth of species 1, then what are the coefficients
a = 2.5
What is the goal of the lokta-volterra model
to determine the equilibrium when the 2 species have reached their combined saturation densities
When do equilibriums occur to give a zero-growth isoclines for both species
N1 = 0 (extinction)
N1 = K1-aN2
N2 = 0 (extinction)
N2 = K2-bN1
Explain Case 1 and 2 of competition
competitive dominance
case 1 = species 1 outcompetes species 2
case 2 = species 2 outcompetes species 1
the winner is the growth rate that is further out
stable equilibrium = K1 for N1 (x-axis) and K2 for N2 (y-axis)
Explain Case 3 of competition
bistability
the winner depends on initial conditions
unstable equilibrium is where they cross
stable are at either species K1 or K2
the winner is whichever is further out, changes for vertical or horizontal
outcome indeterminant in bottom corner because doesn’t favour either
Explain case 4 of competition
stable coexistence
species 1 and 2 coexist stably
the stable equilibrium is where they cross compared to unstable being either K1 or K2
In case 3, what type of competition is typically stronger
interspecific because the equilibrium is when only 1 or the other species exists
In case 4, what type of competition is typically stronger
intraspecific competition because the equilibrium is when both species can exist stably
Explain Case 5 of competition
neutral coexistence
Species 1 and 2 coexist neutrally the whole time along their coincident isoclines
What are the 2 comments about Case 5
- probably not likely that the isoclines are exactly coincident
- not stable coexistence, but neutral coexistence meaning random fluctuations so do not tend to return to the same equilibrium, exclusion can occur under extreme conditions
What are the 4 cons of LV model
- all individuals are equivalent (no age or stage structure or individual variability)
- assumes inhibitory functions of intra and interspecific competition are linear functions of density
- real ecosystems vary over space and time, but the model assumes K and competition coefficients are constant
- difficult to apply to multiple species
What are the 5 pros of the LV model
- simple
- makes testable predictions
- often successfully predicts patterns of exclusion and coexistence
- sometimes predicts equilibrium densities
- explains outcome of competition and related to intra and inter, carrying capacity and effect of others
linking competition and community structure is an application of _____ theory
niche
Define ecological niche
describes both the range of conditions necessary for persistence of a species, where it lives, and the resources it requires (what, where, how it acquires)
Explain the graph of the generic description of a niche
peak is the level/value that the species uses the resource most. intraspecific competition and generalization highest in the middle and specialization and interspecific competition higher on the outside
if interspecific competition is greater than intraspecific competition, it predicts
exclusion
or natural selection could act on the niches and allow for coexistence
why is important that niches have multiple dimensions that do not overlap
niches can overlap in certain dimensions, but not all because then would be exact same and couldn’t coexist
Explain how competition can be size-symmetric or size-asymmetric
size symmetric = the resource acquired is proportional to the size of the individuals, structure, etc. ex. root nutrients because if they are 2x larger they will get 2x more nutrients
size asymmetric = the resource acquired is not proportional to the size of individuals, structures, etc. ex. large canopy gets all the light, small canopy gets little to none
