Limits to adaptation along environmental gradients.

Area of Science:

• Evolutionary biology
• Population genetics
• Ecological niche theory

Background:

• Gene flow's dual role: increasing variation but potentially hindering local adaptation.
• Haldane's 1956 hypothesis of gene flow swamping adaptation at range margins.
• Contradiction with deterministic theory suggesting no such limits when variance evolves.

Purpose of the Study:

• Investigate the mechanisms causing sharp species range margins.
• Determine the role of genetic drift versus gene flow in limiting adaptation.
• Identify key parameters predicting adaptation failure at range edges.

Main Methods:

• Analytical modeling of gene flow and adaptation.
• Computer simulations of population dynamics and evolution.
• Identification of dimensionless parameters governing adaptation thresholds.

Main Results:

• Genetic drift, by reducing genetic variance, can create sharp species range margins.
• A simple threshold predicts adaptation failure based on environmental gradient and selection-drift efficacy.
• Sharp margins can occur even without abrupt environmental changes.

Conclusions:

• Genetic drift is a key factor in forming sharp species range margins.
• Gradual environmental changes can lead to sudden range fragmentation.
• Understanding these dynamics is crucial for predicting species' responses to environmental change.