Interspecific Competition Flashcards
Intraspecific Competition
competition among members of the same species, a density dependent population control mechanism
Interspecific Competition
Competition among members of different species
Interference Competition
Competition involving direct interaction between competitors such that the action of one species inhibits other species
ex. production of toxins by competing plants (allelopathy)
ex. occupation and control of a limited space and aggressive encounters
Resource (exploitation) Competition
competition involving more indirect inhibitory effects such as those arising from reduced availability of a resource, this in turn affects competing species’ growth, reproduction, or survivorship
What do alpha and beta represent in the Lotka-Volterra equations?
competition coefficients, conversion/scaling factors to convert species 2 individuals into an equivalent number of species 1 individuals
-alpha is the conversion factor for expressing the inhibitory effect of an individual of species 2 on species 1
beta is the conversion factor for expressing the inhibitory effect of an individual of species 1 on species 2
what does it mean if alpha is greater than 1 in the lotka-volterra equations?
the competitive effect of an individual of species 2 on the population growth rate of species 1 is greater than that of an individual of species 1
What do the L-V zero growth curves for species 1 and 2 represent and how are they determined?
- The conditions under which both species are at equilibrium and their growth rates are 0
o N1=K1-αN2 (for species 1)
o Need X and Y intercepts to plot this curve
o When dN1/dt=0 and dN2/dt=0 (N1=βN2 and N2=αN1)
What happens to the population of species 1 inside of the zero growth curve? Outside of the curve?
- Solve for X and Y intercepts of 0 growth curve of species 1 (when species 2 =0 and when species 1 =0)
o N1=K1- αN2 - Populations inside (to the left) of the diagonal line will increase in size and come to equilibrium at some point defined by a combination of N1 and N2 values
- Populations outside (to the right) of this line will decrease until they reach the line
What happens to the population of species 2 below the zero growth curve? Above the curve?
- Can solve for 0 growth curve for species 2: N2=K2- βN1, find X and Y intercepts
- Populations inside (below) the diagonal line will increase in size and come to equilibrium at some point defined by a combination of N1 and N2 values
- Populations outside (above) this line will decrease until they reach the line
How are the joint population trajectories of species 1 and 2 determined when both graphs are superimposed?
- The joint population trajectories can be determined by using vector addition
Given a Lotka-Volterra graph showing the zero growth curves for two species, be able to determine the outcome of competition between the species.
- Species 1 wins, species 2 wins, outcome determined by initial numbers of species ½, both species coexist in a stable equilibrium
Provide a biological interpretation of each of the four possible outcomes of the L-V graphs.
- Species 1 or 2 wins—strong interspecific competitors can exclude weak interspecific competitors under all conditions
- Vectors directed away from cross point, winner determined by initial densities of species—unstable equilibrium—when interspecific competition is more important than intraspecific competition, and the competitors are fairly equal in their competitive abilities, outcome will most likely depend on the initial densities of each species
- Vectors directed toward cross point, both populations coexist at densities below their carrying capacities—stable equilibrium—when interspecific competition is less important than intraspecific competition, two species may coexist at a stable equilibrium because each species reaches its carrying capacity before reaching a population level that can threaten the other species, but they are both below their carrying capacities so, in a competitive situation, neither population reaches densities as high as it does without competition, supporting that the sign of the interaction is always negative
What was the outcome of Gause’s competition with protozoans?
- When grown together, P. caudatum was eliminated, competitively excluded by P. aurelia
What type of competition was shown by the conell’s barnacles experiment?
- Interference competition—fund niche of Chthamalus extended into Balanus zone, Balanus restricted Chthamalus to realized niche higher on shoreline via competitive exclusion
- Interspecific competition—the few Chthamalus that could survive were much smaller, produced fewer offspring, reducing fecundity
Why was Chthamalus restricted to a realized niche higher up the shoreline in the conell’s barnacles experiment?
- They were restricted by Balanus by competitive exclusion, Balanus smothered or damaged any Chthamalus that attempted to grow in their zone
Which of the two species (Chthamalus or Balanus) has a broader fundamental niche in Conell’s barnacles experiment?
- Chthamalus
What characteristic enabled Chthamalus to survive in the higher intertidal zone in conell’s barnacels experiment?
- Tolerance to desiccation (dryness)
What type of competition was shown by tilman et al’s diatoms experiment?
- Exploitation (resource) competition—Synedra maintained concentration of silicate at a level too low for Asterionella to survive and reproduce
How did the fundamental niches differ between the species examined in Tilman et al’s diatom experiment?
- When grown together, Synedra had a realized niche while Asterionella did not, competitive exclusion
How did Synedra competitively exclude Asterionella from the culture medium in tilman et al’s diatom experiment?
- Synedra maintained concentration of silicate at a level too low for Asterionella to survive and reproduce
What is “diffuse competition” and its possible consequences for a species?
- When a species experiences minimal competitive interactions along several resource gradients with a number of species, resulted by competitive exclusion
- Can competitively exclude a species or greatly reduce its numbers
According to Pielou, what are four conditions that must be met for competitive exclusion to occur?
- The competitors must remain genetically unchanged for a sufficiently long period for one species to exclude the other
o Can’t find a way to coexist by avoiding competition (favored over time) - Immigrants from areas with different conditions can’t move into the population of the losing species, there can be no replacements for those “killed in battle”
- The environment must remain constant, rules can’t be changed during the game
- Competition must continue long enough for an equilibrium to be reached, game has to be played long enough for a winner to be determined
How does niche differentiation promote coexistence between two species?
- It can prevent or reduce interspecific competition by concentrating competitive effects more within species than between them (case 4 of the L-V model)
- Can be accomplished by resource partitioning where organisms living in the same habitat may utilize different resources
- Or by showing different microhabitat preferences that lead to differential resource utilization
o Feed at different parts of the same tree
Provide an example of coexistence due to resource partitioning in nature.
- Different bill sizes and shapes allow Galapagos finches to feed on different food resources
