Lecture 11 - competition for husky

Competition Overview

  • Competition is an interaction with negative effects between two individuals depending on the same limiting resource.

    • Intraspecific competition: competition within the same species, related to density-dependent population growth.

    • Interspecific competition: competition among individuals of different species.

Importance of Competition

  • Understanding competition is crucial as it organizes ecological processes that control the composition of natural communities.

  • Applications of competition concepts extend to the management of agriculture, forests, wildlife, and natural resources.

Measuring Competition

  • Types of Competition

  • The study of how competition affects niches and resource allocation among species.

    • Strategies to measure competition and understand its dynamics and outcomes.

Historical Context

  • Tansley's Experiment (1917): First test of competition in plants.

    • Hypothesis: Different species are adapted to specific soil types leading to competitive superiority.

      • Predictions:

        1. Each species performs best in its native soil.

        2. Outcomes depend on the soil type when grown together.

  • Notable Species:

    • Galium saxatile (Heath bedstraw): Acidic soil specialist.

    • Galium sylvestre (White bedstraw): Alkaline soil specialist.

    • Common Garden Experiments: Measure plant competition under different soil conditions.

Animal Competition Studies

  • Chihuahuan Desert, Arizona (Brown and Munger, 1985): Exclosure experiments focused on granivores.

    • Results: Excluding large granivores led to higher populations of small granivores without significant effects on non-competing insectivores.

Niche Relationships and Competition

  • Degree of niche overlap impacts competition levels.

  • Complete Competitors: Compete for the same niche and are limited by the same resource.

  • Competitive Exclusion Principle: Complete competitors cannot coexist indefinitely; one species will outcompete the other.

Resource Limitation

  • Not all resources limit consumer populations.

  • Liebig’s Law of the Minimum: Population growth continues until limited by the most constrained resource.

Competitive Exclusion in Lab Studies

  • Gause's Experiment (1934): Two species of Paramecium grown with a food source showed that only one species survived.

    • Illustrates competitive exclusion principle.

Field Studies on Competition

  • Joseph Connell's barnacle study demonstrated how competition influences species distribution across tidal zones.

    • In drier areas, Chthamalus adapts better, while Balanus thrives in wetter conditions.

Coexistence of Competing Species

  • Species can coexist if they are not complete competitors and are limited by different resources.

  • Greater ecological differences reduce competition likelihood, promoting coexistence.

Modeling Competition Outcomes

  • Lotka-Volterra Competition Model: Extends logistic population models to include interspecies competition effects.

    • Involves two equations to reflect the impacts of each species on one another through competition coefficients (α and β).

Competition Coefficients

  • α: Competitive effect of species 2 on species 1.

  • β: Competitive effect of species 1 on species 2.

  • Example: Food requirements can be translated into 'equivalents' to compare competitive pressures between species.

Equilibrium Conditions

  • Analyzing conditions when growth is zero for one or both species leads to predicting competition outcomes.

  • Includes plotting isoclines for species growth and how population sizes interact at equilibrium.

Prediction Outcomes in Competition

  • Outcome 1: One species goes extinct if its isocline is farther.

  • Outcome 2: The opposite species goes extinct under similar conditions.

  • Outcome 3: Unstable equilibriums where fluctuating conditions may lead to one species dominating.

  • Outcome 4: Stable coexistence when interspecific competition is weaker than intraspecific competition.

Competition Mechanisms

  • Exploitation Competition: One species outcompetes another by more efficient resource utilization.

  • Interference Competition: One species prevents another from accessing resources directly (e.g., via aggressive behavior or chemical means).

  • Allelopathy: Existence of chemical barriers that inhibit neighboring plant growth, thus limiting competition.

Apparent Competition

  • Indirect competition where species compete via shared predators or parasites affecting their population dynamics.

    • Example: Pheasants supporting nematodes that adversely affect partridge populations.

Practice Problem

  • Utilize Lotka-Volterra model to apply predictions based on given population densities, competition coefficients, and outcomes.