integrated lec 19 Flashcards
species interactions
types:
-Competition(-/-): both species are harmed
-Predation (-/+): Predator benefits; prey is harmed.
Mutualism (+/+): Both species benefit.
Competition
Intra-specific competition:
Among individuals of the same species.
Example: Limited food within a population.
Inter-specific competition:
Among individuals of different species.
Example: Birds and squirrels competing for seeds.
Types of Competition:
-Scramble/Exploitative: Indirect competition via depletion of shared resources.
-Contest/Interference: Direct competition, such as territorial disputes.
lotka-volterra model of competition
extension of logistic growth model:
–> dN1/dt = r1N1 (1- (N1+a12N2)/K1)
competition coefficients(aij):
-aij: per-capita effect of species j on species i
-e.g.: squirrels consume more seeds than sparrows; a quantifies this difference
competition exclusion principle
Two species competing for the same niche cannot coexist indefinitely.
Stable coexistence requires:
Intra-specific competition > Inter-specific competition.
species coexistence
Four possible outcomes of Lotka-Volterra competition:
Stable coexistence.
Species 1 wins.
Species 2 wins.
Outcome depends on initial population sizes.
empirical testing of competition - connell’s barnacle study
observation: competition and desiccation limit barnacle distributions.
experiment: Removal of competitors altered species ranges.
paradox of the plankton
Problem: How do many species coexist in seemingly simple environments with limited resources?
Possible Explanations:
Fluctuating environmental conditions.
Niches not perfectly overlapping.
Character Displacement
Definition: Coexisting similar species evolve differences to reduce competition.
Example: Divergence in beak size among finches.
Scaling Competition
Community-level Effects:
-Competition reduces species diversity by excluding inferior competitors.
Challenges:
-Scaling from simple lab systems (e.g., two species) to complex ecosystems.
Scramble/Exploitative Competition:
No direct interaction.
Example: A squirrel consumes seeds, leaving less for birds.
Contest/Interference Competition:
Direct interaction.
Example: Two animals fighting over territory
lotka-volterra competition model
extends logistic growth by adding inter-specific competition terms
a12
effect of species 2 on 1
Competitive Exclusion Principle
Definition: Two species with identical niches cannot stably coexist.
Example: Invasive species outcompete native species.
Conditions for Coexistence:
Competition within a species must be stronger than competition between species.
paradox of the plankton
Problem: Why do so many species coexist in simple environments (e.g., lakes)?
Proposed Solutions:
-Environmental variability prevents any one species from dominating.
-Partitioning of niches, even in subtle ways.
What are the main differences between intra- and inter-specific competition?
Identity of Competitors:
Intraspecific Competition: Occurs between individuals of the same species.
Interspecific Competition: Occurs between individuals of different species.
Resource Overlap and Intensity:
Intraspecific Competition: Often more intense because members of the same species have nearly identical resource needs (e.g., same diet, habitat requirements). As a result, they heavily compete over the exact same sets of resources.
Interspecific Competition: Generally less intense for any single resource because different species rarely have perfectly overlapping niches. They may share some resources, but their resource use often differs, reducing direct competition.
Population-Level Effects:
Intraspecific Competition: Plays a key role in regulating population size and density. As population size increases, resource availability per individual declines, which can limit population growth and lead to density-dependent population regulation.
Interspecific Competition: Influences community structure and species diversity. It can prevent one species from completely dominating resources and can drive species to adopt more specialized niches or to partition resources to reduce overlap.
Evolutionary Consequences:
Intraspecific Competition: Strong intraspecific competition can lead to directional or stabilizing selection within the species. Traits that improve resource acquisition or reduce competition with conspecifics are favored, potentially leading to character displacement over time.
Interspecific Competition: Can lead to evolutionary changes that reduce niche overlap between species. Over generations, species may undergo character displacement, niche differentiation, or resource partitioning, allowing them to coexist with reduced direct competition.
Ecological Outcomes:
Intraspecific Competition: May limit individual growth, survival, and reproduction within a species, thus shaping population dynamics.
Interspecific Competition: Can influence which species persist in a given community, how they are distributed, and can drive competitive exclusion if one species consistently outcompetes another, leading to changes in community composition.
Summary:
Intraspecific competition is competition within a single species, often resulting in strong resource limitation and playing a critical role in population regulation and evolution of traits within that species. Interspecific competition is competition between different species, shaping community structure, driving species to differentiate their resource use, and influencing biodiversity and the coexistence of species in ecological communities.
How does the Lotka-Volterra model incorporate inter-specific competition?
The Lotka-Volterra model for interspecific competition is an extension of the logistic growth model that incorporates additional terms to reflect the influence of one species on another’s population growth.
In other words, it takes the standard logistic equation for each species and adds competition coefficients to quantify how individuals of another species affect its population growth rate
Ecological Significance:
By incorporating these terms, the Lotka-Volterra competition model can predict outcomes of competitive interactions—such as stable coexistence, competitive exclusion of one species by the other, or priority effects depending on initial conditions. It highlights how interspecific competition alters population dynamics by reducing the effective carrying capacity each species experiences due to the presence of the other.
In summary, the Lotka-Volterra model integrates interspecific competition by adding competition coefficients to each species’ logistic growth equation, thereby demonstrating how one species can limit the population size of another and influencing the equilibrium states of both populations in a community.
