MODULE 11: Local Adaptation, Niches, Generalists & Specialists

Local adaptation

When populations have highest fitness in their home environment compared to foreign populations.

Testing local adaptation: common garden

Individuals from different populations grown in a shared environment to reveal genetically based differences.

Testing local adaptation: reciprocal transplant

Populations swapped into each other's habitats; each should perform best in its home habitat if locally adapted.

Sulfidic vs. non-sulfidic fish example

Fish survive best in their native water type; immigrants have reduced survival—evidence of local adaptation.

Ecological niche

The full multidimensional range of environmental conditions where a species/population can survive and reproduce.

Niche components

Includes climate, habitat, diet, predators, competitors, parasites, and microhabitat conditions.

Generalist

Organism that performs well across a wide range of environmental conditions.

Generalist advantages

High tolerance, broad diet, ability to colonize new habitats, better persistence under change.

Generalist costs

Plasticity is costly, acclimation takes time, responses may be maladaptive if the environment shifts unpredictably.

Specialist

Organism that performs extremely well in a narrow range of environmental conditions.

Specialist advantages

High efficiency in specific environments, reduced competition, effective resource use.

Specialist costs

Vulnerable to environmental change, limited dispersal, higher extinction risk.

Range expansion and genetic diversity

Serial founder effects reduce genetic diversity toward the range edge; original range has highest diversity.

Generalists and gene flow

High performance across habitats increases dispersal; populations remain genetically similar.

Specialists and gene flow

Low performance outside preferred habitat reduces dispersal; promotes differentiation and possibly speciation.

Local adaptation and gene flow

Local adaptation restricts gene flow because immigrants have low fitness in non-native environments.

Individual specialization

Individuals within a population use different diets or microhabitats despite being the same species.

TNW (Total Niche Width)

The full range of resources used by the entire population.

BIC (Between-Individual Component)

Portion of TNW explained by differences among individuals' specializations.

WIC (Within-Individual Component)

The resource breadth used by a single individual.

Importance of specialization

Influences competition, frequency-dependent selection, population stability, and potential for divergence.