When log‐dwellers meet loggers: impacts of forest fragmentation on two endemic log‐dwelling beetles in southeastern Australia

Abstract

Anthropogenic activities continue to cause massive fragmentation and reduction of forest area worldwide. With fragmentation and reduction of habitat recognized as the greatest threats to biodiversity, the implementation of improved, informed and conservation-based forestry practices is essential, and requires a greater understanding of the responses of different organisms to forest fragmentation. While genetic techniques can add invaluable insights to fragmentation studies they have rarely been employed, particularly for multiple species. In the present study, we combined genetic information, obtained from allozyme loci and anonymous single copy nuclear DNA markers, with ecological data to investigate the impacts of forest fragmentation on two log-dwelling beetles with different life histories, in an 'islands of bush in a sea of pine' model, at Tumut in New South Wales, Australia. Both the relatively mobile (i.e. has high dispersal ability and/or broad habitat range) Adelium calosomoides and the less mobile Apasis puncticeps showed reduced mobility and gene flow in fragmented compared to continuous forest: there was significantly greater isolation by distance and stronger local structure revealed by spatial autocorrelation in fragmented forest. Analysis of patch and species characteristics revealed that genetic and demographic structure may be influenced by log degradation class for both species, and number of potential dispersal barriers, distance from continuous forest and desiccation intolerance/moisture preference for Ap. puncticeps. Thus the pine plantation matrix poses a barrier or filter for gene flow and mobility in both beetle species.

Isolation by distance in saproxylic beetles may increase with niche specialization

“…For example, in Apasis puncticeps, an Australian tenebrionid beetle dependent on decaying Eucalyptus logs, inbreeding in a local population increased with decreasing connectivity of the habitat patch (number of potential dispersal barriers between a fragment and the continuous forest; Schmuki et al 2006). Both mechanisms, i.e., small effective number of founder individuals during habitat colonisation, and restricted gene flow between habitat patches, may potentially be responsible for substantial amounts of inbreeding in both O. barnabita and P. marmorata.…”

A decade of change in the saproxylic beetle fauna of eucalypt logs in the Warra long-term log-decay experiment, Tasmania. 1. Description of the fauna and seasonality patterns

“…Winged species would be considered to be potential dispersers over greater distances (and perhaps have other characteristics of r-strategists) than functionally flightless species, which might meet more of the criteria for K-strategists (Pianka 1970). On this basis, logs should initially harbour rapidly reproducing species with the means to disperse rapidly and over longer distances; but as decomposition progresses, rotting logs might increasingly favour slowly reproducing species for which short-distance dispersal mechanisms such as crawling are adequate (Baur et al 2005;Schmuki et al 2006). Theory would therefore suggest-and others have found (Langor et al 2008)-that the representation of flightlessness in beetle assemblages should increase with decomposition.…”

Restricted dispersal in a flying beetle assessed by telemetry

“…A low capacity to establish new populations far from present ones should especially be expected for species in habitats with low temporal and high spatial variability in carrying capacity, because they are assumed to have low dispersal rates (Southwood 1962;Johnson and Gaines 1990;Nilsson and Baranowski 1997;Travis and Dytham 1999). To study dispersal of woodliving insects is difficult, but recent genetic (Schmuki et al 2006) and capture-recapture (Ranius and Hedin 2001) studies suggest limited dispersal for some species.…”