Measuring the dispersal of saproxylic insects: a key characteristic for their conservation

In the discipline of nature conservation it is important to understand under which circumstances populations can survive by compensating local extinctions with colonizations. Many saproxylic (= wood-dwelling) insect species have declining populations and are regarded as threatened due to low habitat availability in managed forests. Several methods have been used to better understand the dispersal biology and colonization ability of saproxylic insects with declining populations. The present article summarizes and compares the results of such studies. When the same species have been studied using several methods, the results are consistent, but different aspects of dispersal biology are revealed with different methods. Capture-recapture and telemetry are direct methods that can be used to quantify dispersal rate and range in the field. Studies of genetic structure and occupancy patterns are complementary, as they reveal the consequences of dispersals that have taken place over a larger spatial and temporal scale than is possible to study with direct methods. Because colonization, rather than dispersal, is important for population persistence, colonization experiments provide useful information. To obtain information relevant for conservation work, dispersal studies should be conducted on model species that are representative of threatened species. Colonization ability probability differs between common and rare species, and therefore it is important to also study the dispersal of rare species, even if it is more difficult.