Landscape genetics

Landscape genetics is the integration of population genetics, landscape ecology, and spatial statistics to understand how landscape structure influences genetic variation and gene flow. The field was formalized in the early 2000s by researchers including Stephanie Manel, Rolf Holderegger, and Louis Bernatchez, who recognized that the spatial arrangement of habitat, barriers, and corridors leaves signatures in genetic data that can be read as maps of population connectivity.

The central premise is that gene flow is not simply a function of Euclidean distance but of the resistance that landscapes offer to movement. A river may be an insurmountable barrier to a terrestrial mammal but a corridor for an aquatic insect. A highway may fragment a forest for a ground-dwelling bird but have no effect on a wind-dispersed plant. Landscape genetics replaces the straight-line distance of isolation-by-distance models with resistance surfaces — maps of how difficult each landscape element is to cross — and uses circuit theory or least-cost path analysis to predict genetic connectivity.

The methods fall into two broad categories. Least-cost path approaches model dispersal as movement along paths that minimize cumulative resistance, treating the landscape as a cost surface. Circuit theory approaches model dispersal as random walks across the entire landscape, treating it as an electrical circuit where habitat is conductive and barriers are resistive. Circuit theory has the advantage of predicting multiple alternative routes and capturing the redundancy of landscape connectivity; least-cost paths capture the preference for optimal routes but miss the breadth of the movement front.

Landscape genetics has direct applications to conservation. It can identify corridors that maintain gene flow between protected areas, predict the genetic consequences of proposed development, and detect cryptic population structure that is invisible to standard ecological surveys. It connects to patch dynamics by showing how the spatial arrangement of patches — not merely their number and quality — determines the genetic health of the regional system.