Dispersal of Saproxylic Insects

Abstract

Dispersal is a key trait of species that is required to maintain gene flow between habitat patches. Furthermore, it allows the colonization of new habitats and thus affects population dynamics, extinction risk of populations, and species distributions. Dispersal enables species to persist in a changing environment. Saproxylic insects, depending on deadwood at some stage during their life cycle, must compensate local extinctions resulting from the decay of deadwood with colonizations of new deadwood structures locally and on the landscape scale. Their dispersal strategies are shaped by a suite of driving forces such as spatial and temporal variability of deadwood structures in the environment, feeding strategy, resource competition, kin competition, and inbreeding avoidance. The importance of each factor in selecting for a dispersal strategy will vary among species depending on their life history and interactions with the environment, such as the longevity of the deadwood habitat used. Species using a more transient habitat, such as freshly killed wood, have better dispersal abilities than those in more persistent habitats such as tree hollows that may exist for several decades. Dispersal abilities of only a few saproxylic insect species are known, and these comprise mostly pest species or flagship species of interest to conservation. Dispersal distances vary greatly from a few meters in passalids dispersing by walking to over 100 km in some flying bark beetles. Knowledge of dispersal abilities is of paramount importance though, as it can help to improve conservation strategies and forest management especially in terms of spatial distribution of suitable habitats to enhance species persistence. In this chapter we first review the factors driving dispersal ability and our current knowledge on dispersal distances of saproxylic insects. We provide an overview of different methods used to measure dispersal ability of saproxylic species. We discuss whether saproxylic species are rather dispersal or habitat limited and identify open questions in the study of dispersal of saproxylic insects.