(11-11) - Notes Competition and Niche Space

Competition (General Definition)

An interaction in which both individuals experience a cost (–/–). Even if one ultimately gets the resource, the process of competing is costly to both.

Resource (in ecology)

Any limited factor organisms compete for—such as food, water, mates, sunlight, or nesting sites.

Intraspecific Competition

Competition that occurs within a species. Often intense because individuals have identical needs and completely overlapping niche requirements.

Interspecific Competition

Competition between different species for shared resources. Can lead to niche shifts, exclusion, or resource partitioning.

Density-Dependent Growth

Population growth slows at high density because intraspecific competition reduces available resources, causing populations to fluctuate around carrying capacity (K).

General Adaptation Syndrome (GAS)

A physiological stress response (“fight or flight”) that provides short-term survival advantages but long-term costs, such as reduced immunity and reproduction.

Spongy Moth (Lymantria dispar) Example

A real-world case of intraspecific competition where extremely high caterpillar densities caused severe food shortage, massive die-offs, and density-dependent population decline.

Niche (General Definition)

All environmental factors that influence a species’ survival, growth, and reproduction—where, when, and how a species makes its living.

Hutchinson’s n-Dimensional Hypervolume

A niche concept describing species requirements across many environmental dimensions (n = number of important factors).

Fundamental Niche

The full range of environmental conditions a species could use if no other species interacted with it (purely abiotic space).

Realized Niche

The actual space a species occupies after interactions like competition, predation, or disease restrict it.

Niche Overlap

When two species share similar requirements; higher overlap means more competition pressure.

Competitive Exclusion Principle

Two species with identical niches cannot coexist indefinitely; the better competitor will exclude the weaker one from the area.

Evolutionary Arms Race (competition context)

When competing species evolve adaptations to outcompete each other, leading to continuous counter-adaptations.

Resource Partitioning

Differences in how, when, or where species use a resource that allow similar species to coexist by reducing direct competition.

Resource Segregation

The specific feature or niche dimension in which similar species differ most—reflecting past competition (e.g., habitat, body size, feeding type).

MacArthur’s Warblers (Example)

Species of warblers coexist by feeding in different parts of the same tree—classic example of resource partitioning.

Lack’s Passerines (Example)

Segregation among similar bird species primarily in habitat preferences, with other differences like body size and feeding habits following.

Scramble (Exploitative) Competition

Competition where individuals indirectly compete by using up the same resource; they target the resource, not each other.

Interference Competition

Competition where individuals directly interact, obstructing or fighting competitors rather than just exploiting the resource.

Examples of Competition Mechanisms

Dung beetles: Often scramble competition (competing for dung piles).
Barnacles: Interference (overgrowing or pushing each other off rock space).
Hyenas vs. scavengers: Interference (actively warding off competitors).
Salvia plants: Interference (chemical inhibition of neighbors).