Altitudinal variation of parasitic Hymenoptera assemblages in Australian subtropical rainforest

Abstract

Patterns of species assemblages along altitudinal gradients provide insights into ecological patterns and processes. Parasitoids play an important role in ecosystems, yet there are few studies on parasitoid assemblages, partly because of difficulty in identification of parasitoids to species or their surrogates, morphospecies. The aim of this study is to assess differences in assemblages of parasitic Hymenoptera along an altitudinal gradient at both the family and morphospecies level, and the potential of environmental variables for explaining these differences.We sampled from four replicate sites at each of five elevations (approximately 300, 500, 700, 900 and 1100 m above sea level (asl)) within continuous subtropical rainforest of the Border Ranges National Park in New South Wales, Australia. At each site, we operated a Malaise trap for 10 days in December 2011 and again in February 2012. Parasitic wasps were sorted to families, and two of the common families (Diapriidae and Ichneumonidae) were further sorted to morphospecies. At both family and morphospecies level, we found gradual altitudinal turnover with a clear separation between ‘upland’ (900 and 1100 m asl) and ‘lowland’ (300 and 500 m asl) assemblages. Unlike parallel studies of some other major taxa, we did not detect distinct assemblages at each altitude at the taxonomic resolution used. In addition, response patterns were different between the two sampling occasions. Changes in assemblage composition were best explained by either altitude or temperature. Although parasitic Hymenoptera do not respond as clearly to changes in altitude as some other taxa, the changes detected here, even at the family level, are important given the role parasitoids play in ecosystem functioning.