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.