Species Interactions and Community Ecology

Species Interactions and Community Ecology

• Types of Species Interactions:

  • Mutualism: Close interactions benefiting both parties (e.g., oxpeckers and giraffes).

  • Parasitism: One organism benefits (the parasite) at the expense of another (the host).

  • Commensalism: One species benefits while the other is not affected (rare in nature).

• Study of Oxpeckers:

  • Paul Weeks investigated the relationship between oxpeckers and cattle in Zimbabwe.

  • Results showed that cattle exposed to oxpeckers had higher tick infestations and slower wound recovery, suggesting the relationship may not be mutualistic.

• Importance of Co-evolution:

  • Species interactions can influence evolutionary modifications, leading to adaptations in response to pressures (e.g., faster antelopes due to predation by cheetahs).

  • Co-evolution evident between plants and their pollinators.

Symbiotic Relationships

• Types of Symbiosis:

  • Mutualism: Relationships benefiting both species (e.g., bull's horn acacia and ants).

  • Parasitism: Parasites harm hosts for nutrients (e.g., leeches, ticks).

  • Endoparasites vs. Ectoparasites: Endoparasites live within the host, while ectoparasites live on the exterior.

• Examples of Mutualism:

  • Cleaner fish removing parasites from other fish (e.g., wrasse and potato cod).

  • Honeyguides leading humans to beehives for mutual benefits.

Competition and its Effects

• Types of Competition:

  • Intraspecific: Same species compete for the same resources.

  • Interspecific: Different species compete, potentially reducing population sizes.

• Competitive Exclusion Principle: States that two species competing for the same limiting resources cannot coexist indefinitely.

• Resource Partitioning: Coexisting species use different resources or strategies to minimize competition.

Ecological Niches

• Concept of Niche:

  • Fundamental Niche: Potential resources a species can use.

  • Realized Niche: Actual resources used due to competition and other ecological factors.

• Character Displacement: Evolutionary changes that occur when similar species inhabit the same environment.

Community Dynamics: Effects of Disturbances

• Disturbances play a key role in shaping community structure.

  • Moderate disturbances can maintain high species richness (intermediate disturbance hypothesis).

• Primary vs. Secondary Succession:

  • Primary Succession: Colonization of barren habitats without soil (e.g., after volcanic eruptions).

  • Secondary Succession: Recovery of an ecosystem after disturbances (e.g., fire).

Island Biogeography

• Equilibrium Theory: Diversity of species on islands is determined by immigration rates and extinction rates, influenced by island size and distance from the mainland.

• Empirical Research: Studies by Simberloff and others confirm predictive power of the theory with experiments on small islands.

Ecological Communities & Gradients

• Clements vs. Gleason: Two views on community structure, where one sees communities as superorganisms and the other as collections of species adapted to similar conditions.

• Species Richness and Evenness: Species diversity impacts ecosystem function and resilience.

Study Break Questions

1. Explain the differences between mutualism, parasitism, and commensalism.

2. What are the consequences of interspecific competition on community structure?

3. Describe primary and secondary succession with examples.