Ecological Niche Concepts and Coexistence

Ecological niche definition and scope

An ecological niche describes how a species fits into its environment—how it responds to conditions such as resources, competitors, predators, parasites, and pathogens, and how it in turn affects those same factors. The scope of “niche” varies by definition: the Grinnellian niche focuses on habitat requirements and behavioral adaptations (often using abiotic variables like climate and terrain), the Eltonian niche emphasizes a species’ role in the biotic environment (its relations to food and enemies, including how it changes resources and interactions), and the Hutchinsonian niche represents an n-dimensional “hypervolume” of environmental conditions and resources needed for persistence, distinguishing between the fundamental niche (potential without competitors) and the realized niche (actual use under biotic pressures). Contemporary niche theory integrates these views using consumer–resource models by defining an “impact niche” (effects on resources and other consumers, aligning with the Eltonian idea) and a “requirement niche” (conditions where the species can survive and reproduce, aligning with the Hutchinsonian realized niche). Under this framework, coexistence of two species requires overlapping requirement niches and each species outcompeting the other for different limiting resources. The topic also covers niche differentiation as a process that helps competing species coexist, but notes exceptions where species may coexist without clear niche separation, and explains how niche concepts relate to geographic range: realized geographic range is typically a subset of the fundamental range constrained by biotic interactions and abiotic barriers. Niche parameters (the dimensions/axes of biotic and abiotic variables) and niche width distinguish specialists from generalists.

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Species responses to resources, competitors, predators

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