INTRODUCTION

A characteristic of modern landscapes worldwide is that continuous habitats have become, largely due to human activities, mosaics of remnant habitat fragments embedded in an urban or agricultural matrix (see Chapter 9 by Leberg and colleagues). Landscape fragmentation can have distinct ecological (e.g., species extinction), demographic (e.g., lowered reproduction and elevated mortality), and genetic (e.g., less genetic diversity and increased inbreeding) consequences. In northern temperate regions, human impacts on natural landscapes date back several thousand years but, in most tropical landscapes, widespread human disturbance is more recent, with the heaviest impacts occurring during the last fifty years. Disturbance and fragmentation of once continuous habitats can have immediate, short-term, and long-term consequences for the management and conservation of genetic diversity within tropical plant species.

Immediate consequences

Landscape fragmentation has immediate consequences for the levels and distribution of genetic diversity that are not dependent on population genetic processes acting across subsequent generations. Three factors can have immediate effects on the genetic composition of fragmented populations: 1) the proportion of the original population that is removed, 2) the number of individuals that survive in each fragment, and 3) patterns of genetic variation present within natural populations prior to fragmentation (e.g., clusters of related individuals).