Beetle Responses to Habitat Fragmentation Depend on Ecological Traits, Habitat Condition, and Remnant Size

Abstract

Under extreme (>80%) levels of habitat loss and fragmentation, exponentially increasing risks of extinction have been predicted; however, the proportion of species that will decline is uncertain. Factors influencing species declines include patch characteristics, such as size and condition, and species' ecological traits, such as dispersal ability. In central New South Wales, Australia, 90% of the mallee woodland has been cleared for agriculture. At each of three 100-km2 locations, we sampled beetles in 10 sites and asked: (1) How is the impact of habitat loss and fragmentation mediated by remnant condition and size? (2) What proportion of the beetle fauna is declining? (3) Are ecological traits based on body size, trophic group, flight, and position relative to the ground correlated with beetle responses to habitat loss and fragmentation? Seven of 34 beetle species (21%) occurred in fragmented and isolated populations in the agricultural landscape, implying that they may be at risk of local extinction. Most declining species depended on large remnants, but two species were confined to disturbed linear remnants, emphasizing the importance of diverse management regimes for invertebrate conservation. In contrast, approximately one-quarter of the beetle fauna survived in paddocks and so was not at risk of decline. Greatest species richness was observed in narrow linear remnants, not square reserves, because of the influx of species from the matrix and the presence of strip-specialist species. Flying ability and position explained most of the variation in species responses to fragmentation. Flightless species or species living underground were most vulnerable to decline in agricultural landscapes. Combinations of traits were also implicated in beetle responses, however, suggesting that causal mechanisms involve more than just the effects of flight or position. To identify species vulnerable to decline in fragmented landscapes, then, many traits need to be considered simultaneously.