Chapter 14 - Lecture

Chapter 14: Exploitative Interactions

Overview of Exploitative Interactions

• Defined as an interaction that enhances the fitness of one individual while reducing the fitness of the second individual.

• Types of exploitative interactions include:

  • Predation: Predators kill and consume other organisms.

  • Herbivory: Herbivores consume plant material.

  • Parasitism: Parasites live on host organisms and reduce host fitness without typically killing them.

  • Pathogenesis: Pathogens induce disease in organisms.

  • Parasitoids: Insect larvae that consume the host, generally leading to host death.

Conceptual Framework

• Concept 14.1: Predators, parasites, and pathogens significantly influence the distribution and abundance of prey and host populations.

• Concept 14.2: Relationships among predators, prey, hosts, and pathogens are dynamic and subject to change.

• Concept 14.3: For populations to survive exploitation, hosts and prey often need refuges.

• Concept 14.5: Exploitative interactions create intricate webs of relationships among various populations, complicating broad generalizations.

Section 14.1: Impact of Exploitation on Abundance

• Predators and parasites have substantial effects on prey population distributions and structures.

• These interactions impact not only numbers but also ecological structures and community dynamics.

Section 14.2: Dynamics of Predator-Prey Relationships

Population Cycles of Snowshoe Hares and Lynx

• Snowshoe Hares (Lepus americanus) and Lynx (Lynx canadensis) populations exhibit well-documented abundance cycles.

• Abundance fluctuation theories:

  • Elton's Theory: Variations driven by solar radiation.

  • Keith's Theories: Ranging from disease, physiological stress due to high density, starvation from food scarcity, to predator-driven cycles.

Influence of Food Supply and Predators

• Hares inhabit conifer-dominated boreal forests where their prey density fluctuates based on food supply and predation rates.

• Densities of hares can significantly impact local vegetation and ecological dynamics.

• In winter, overgrazing can diminish food biomass, affecting hare health and sustainability.

• Experiments by Krebs et al. (1995) show that increased food availability, reduced predation, and a combination of both can raise hare populations.

Section 14.3: Refuges Needed for Survival

• Refuge: Necessary for hosts to persist in the face of exploitation.

Lab Experiments and Mathematical Models

• Gause's experiment with Paramecium and Didinium illustrates extinction due to predation; in presence of refuges, Paramecium survived while Didinium went extinct.

• Study on mite populations in different habitats maintained cyclical populations over extended periods due to the presence of refuge-like conditions.

Section 14.4: Complex Exploitative Interactions

Manipulative Behaviors

• Certain parasites can manipulate host behavior for their benefit:

  • Acanthocephalans increase the likelihood of amphipods being predated by changing their behavior.

• Puccinia monoica fungus alters mustards' growth to attract pollinators and ensure reproduction of the fungus by mimicking flowers.

Implications of Competition

• The presence of parasites can significantly influence competition among species, as seen in flour beetles studied by Park.

• The protozoan Adelina tribolii affects the competitive dynamics between Tribolium species based on its presence or absence.

Conclusion: Exploitative Interactions in Ecological Systems

• Understanding exploitative interactions and their complexities is essential in appreciating ecological relationships and population dynamics. These interactions can lead to unexpected ecological outcomes affecting biodiversity and ecosystem health.