Chapter 14 - Lecture

Chapter 14: 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.

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.

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.

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.

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.

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.

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.

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.

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.