Questions: Species Interactions: Competition, Predation, Mutualism, and Parasitism

Question 1

Two bird species feed on the same insects in the same forest. Over evolutionary time, one species specializes on canopy insects while the other specializes on forest-floor insects. This pattern is best explained by:

• A. Competitive exclusion driving one species to local extinction
• B. Resource partitioning reducing niche overlap and enabling coexistence
• C. Mutualistic coevolution between the two bird species
• D. Predator-prey dynamics separating their foraging zones

Answer: (B)

Resource partitioning is the division of a shared resource along some axis (space, time, prey size, etc.) that reduces competitive overlap and allows ecologically similar species to coexist. This is distinct from competitive exclusion (where one species is eliminated) and mutualism (where both species benefit from the interaction).

Question 2

Parasitism typically harms the host population and is therefore generally detrimental to ecosystem biodiversity.

• T. True
• F. False

Answer: False

Parasites can maintain biodiversity by preferentially infecting dominant competitor species, preventing competitive exclusion and freeing resources for subordinate species. Parasitism that regulates the most abundant host can act as a stabilizing force in communities, increasing species diversity rather than decreasing it.

Question 3

What is Gause's competitive exclusion principle, and why does it not strictly apply in most real ecosystems?

Model answer: Gause's principle states that two species competing for identical resources in a constant, homogeneous environment cannot coexist indefinitely — one will exclude the other. It does not strictly apply in real ecosystems because environmental heterogeneity, disturbance, and niche partitioning prevent any species from fully and permanently out-competing another.

The principle assumes constant, identical environments where competitive advantages are fixed. Real environments vary in space and time, creating shifting competitive landscapes where different species have advantages under different conditions. This allows many species with overlapping niches to coexist through mechanisms like the storage effect, frequency-dependent selection, and spatial refuges.