Limited surrogacy between predatory arthropods along an altitudinal gradient in subtropical rainforest

Abstract

Biodiversity surveys are often forced to regard single taxa as surrogates for other groups within the same guild. Recently, concerns regarding impacts of climate change have driven a large body of research involving assemblage changes across elevational gradients. Such gradients have commonly been used to investigate changes within invertebrate assemblages, however, surrogacy of patterns displayed between taxa are rarely tested. Without sufficient testing of surrogacy among invertebrate groups, the impacts of described patterns in an ecosystem context, and their implications for biodiversity, remain either unknown or misinterpreted. To address this issue, we investigated changes in the communities of three different groups of predatory epigaeic arthropods, ants, predatory beetles and spiders, along an altitudinal gradient in subtropical rainforest in south-eastern Queensland, Australia. Predatory arthropods were sampled with pitfall traps at four replicate plots at each of five elevations; 300, 500, 700, 900 and 1100 m above sea level (a.s.l.). The three groups displayed differential responses to altitude. Ants responded most clearly with a decline in species richness and progressive change in composition with increasing altitude with depauperate fauna at the highest elevation. Beetles were abundant and species rich throughout the gradient although they were most speciose at 900 m a.s.l. Beetle assemblages progressively changed from low to high elevations, but assemblages at the highest elevation were distinct due to numerous species restricted to this altitude. The abundance and species richness of spiders were similar throughout the gradient, but spiders were distinctly separated into low (300-700 m a.s.l.) and high (900-1100 m a.s.l.) altitude assemblages. Our results indicate that predictions about the impacts of climate change on ecosystem processes such as predation will vary, especially at the highest elevations, according to taxonomic group sampled.