Interactions - Competition Flashcards
What are the types of competition?
(1) Interference
(2) Resource
What are the scales of competition?
(1) Intraspecific
(2) Interspecific
Why are there competing species?
(1) Adaptive radiation
(2) Speciation
Interference competitions
Direct antagonistic behavior towards other individuals
Resource competition
Indirect competition due to use of shared resource
Intraspecific competition
Competition for resources between individuals of the same species
Intraspecific competition regulates population growth in a density-______ way.
dependent
How is intraspecific competition related to carrying capacity (K) of logistic population growth?
As a population uses up resources, the growth rate of the population slows and reaches K, the carrying capacity
When genetic factors influences resource use efficiency, evolution tends to ______ the competitive ability within the population.
Increase
Interspecific competition
Competition for resources between individuals of different species
Most intense competition will occur between species that are ____.
Similar
Niche partitioning/differentiation/segregation
Ecological process where natural selection drives competing species into distinct resource use patterns for co-existence.
The logistic equation of population growth models the rate of population increase limited by what kind(s) of competition?
Intraspecific only.
How can we model population growth influenced by both intraspecific and interspecific competition?
Lotka-Volterra Model
How does the Lotka-Volterra model work?
A new factor (αN) is added to the logistic population growth equation to represent the contribution of interspecific competition (The equivalent number of species 1 competitors represented by interspecific competitors (i.e., individuals of species 2))
α = competition coefficient. For example, the competitive effect of 1 gull = 1/4 the competitive effect of pelican, the same species.
If α < 1 then ____.
Co-occur. Interspecific competition < intraspecific competition.
If α > 1 then ____.
Species with the larger competition coefficient outcompetes/replaces the other.
How can we predict when population growth in two competing species will stop?
Using the Lotka =-Volterra Model.
N1 = K1 - α(2 on 1)N2
N2 = K2 - α(1 on 2)N1
When can species coexist?
When intraspecific competition is greater than interspecific competition.
K1 < K2/α21
K2 < K1/α12
Competitive Exclusion Principle
Two species with identical niches cannot coexist indefinitely. One will out-compete the other for limited resources.
What is known as the concept that two species with identical niches cannot coexist indefinitely (one will out-compete the other for limited resources)?
Competitive Exclusion Principle
Adaptive radiation
Process where species rapidly diversify into new forms. Typically when resources become available, new “challenges” arise, or new niches are opened.
How are different species created?
(1) Allopatric speciation
(2) Sympatric speciation
(3) Centrifugal speciation
Allopatric speciation
Population is separated by a geographic barrier (barrier to gene flow) and diverges to become two distinct species
Sympatric speciation
Multiple species evolve from a single ancestral species over the same geographic range (no physical barrier). The barrier to gene flow in internal; sometimes when new resource is introduced (e.g. green vs red apple)
Centrifugal speciation
A changed environment expands/contracts the geographic range where a species can survive. this may leave pocket populations behind that can diverge from the parent population
Phase plane/State-space graphs
Species 1 abundance (x) vs Species 2 abundance (y). Each point represents a combination of abundances of the two species.
A phase plane is a plot of two system variables against each other (one on the x-axis, the other on the y-axis). Unlike a time-series plot, time is not shown explicitly. If values of the two variables don’t change over time, the phase plane plot will only show a single point. If the variables change over time, the phase plane plot shows how they change relative to each other.
Zero isocline
Indicates the conditions under which the population (N1) will not grow or shrink. Straight line on the graph for a species where the species’ population does not increase or decrease. This is found by setting dN/dt = 0 and solving for N (N1 = k1 - α12N2).
Same (isos) and slope (klisi), because it connects a series of points where the rate of change of some variable has the same slope. When we graph species relationships in ecology, the isoclines we use are usually zero-growth isoclines. These show the population sizes at which the growth rate of one of the two species is zero. Above the isocline, the population decreases, and below the isocline it increases.
What causes competition?
Resource limitation.
The green species, Iguana A, is faster-moving and can find cactus plants better than the other two iguanas. Otherwise, they are all identical. In this scenario, a new type of cactus has recently appeared on the island that grows fast and reproduces prolifically. Thus, all iguanas find and eat as much food as they want. What do you think will happen to the population sizes of the three different species?
They will stay about equal. Since resources are unlimited, they will all grow exponentially and there is no need for competition.
Allelopathy
A type of interference competition that involves releasing poisons, used by plants
Preemption
Preemption is interference competition that occurs when an individual prevents other individuals from occupying a location by occupying the space first.
Competition coefficient
The per capita effect of a second species on the growth of one species (α)
The population of species 1 is at a carrying capacity of 500. If you add 100 of species 2 (α12 = 0.5), how many individuals of species 1 is displaced? What if α12 = 2? What if α12 = 0?
α12 = 0.5 —-> (0.5)(100) = 50
α12 = 2 —-> (2)(100) = 200
If α12 = 0, there is no competition, and no individuals are displaced.
Does the intrinsic growth rate (r) determine whether or not a population can grow?
No. It does not contribute to when dN/dt =0. It determines the maximum rate a population can grow when resources are abundant.
Phase portrait
A phase portrait, plotted on a phase plane, is a type of two-dimensional graph that describes how a dynamic system will change over a short period of time, given different initial values for the graphed variables. It depicts (usually using arrows) trajectories of change for each combination of the two variables.
When an arrow on the phase portrait points straight up, what does this indicate about how population sizes will change over a short time period?
X population size doesn’t change, only Y
When an arrow on the phase portrait points straight right, what does this indicate about how population sizes will change over a short time period?
Y population size doesn’t change, only X
How can we determine whether two species will coexist using Lotka-Volterra phase planes?
If the isoclines intersect and K1 < K2/α21 and also K2 < K1/α12, then there is a stable state and coexistence is possible.
How can we determine which species will outcompete the other using Lotka-Volterra phase planes?
The species whose isocline is furthest from the origin will eliminate the other.
How can we make a competitor outcompete another?
Increasing α or K.
When both the probiotic bacteria and the pathogen bacteria compete more strongly with bacteria of the other strain than with bacteria of their own strain (i.e., interspecific competition is greater than intraspecific competition), which population wins?
Either can win. The winner is determined by the relative initial population sizes of the two strains.
What are the possible outcomes that can be predicted from isoclines?
(1) Outcompetition
(2) Stable equilibrium (higher intraspecific competition)
(2) Unstable equilibrium (higher interspecific competition, dependent on starting values)
What leads to stable equilibrium?
Intraspecific > Interspecific competition
What leads to UN-stable equilibrium?
Intraspecific < Interspecific competition
