Chris J. Burwell

The use of ants and other soil and litter arthropods as bio-indicators of the impacts of rainforest clearing and subsequent land use

The present study investigated the impacts of rainforest clearance, and associated subsequent land␣use for pasture, on assemblages of soil and litter arthropods in eastern subtropical Australia. We assessed the utility of soil and litter arthropods as potential bio-indicators of cleared and forested habitats. Arthropods were sampled from 24 sites (12 sites each in rainforest and pasture) using two methods (extraction from litter, pitfall traps). Responses of taxa were analysed at various levels of taxonomic resolution, including ‘coarse’ arthropods (all arthropods sorted to Order/Class), ant genera and ant species. Multivariate analyses of arthropod composition indicated that an increase in the level of taxonomic resolution did not provide a commensurate increase in the sensitivity of assemblage response. Indicator values (IndVals), computed for each taxon, showed that a number of arthropod taxa may have potential as bio-indicators of habitat change. However the use of many of these, especially many ant species found in our study, may be unreliable because even after extensive numbers of sites were sampled, most species showed patchy distributions. To overcome this problem, we generated ‘composite indices’, by combining information from sets of indicator taxa. The utility of these composite indices is discussed.

Bat predation on eared moths: a test of the allotonic frequency hypothesis

Many species of moths (Lepidoptera) possess ears which enable them to hear the echolocation calls of bats and avoid predation. The range of best hearing of eared moths is to frequencies usually between 20 and 50 kHz; therefore, bats with calls above or below these frequencies are predicted to capture eared moths more frequently than other bats. This prediction is the basis of the allotonic frequency hypothesis. We conducted a field test of the hypothesis using three species of flutter-detecting bats which capture flying insects. The species were diadem leafnosed bat Hipposideros diadema (call frequency 55-58 kHz), eastern horseshoe bat Rhinolophus megaphyllus (67-71 kHz) and dusky leafnosed bat H. ater (160-164 kHz). Eared moths represented only 7.2% of individuals among prey remains of H. diadema. Moths dominated the diet of both R. megaphyllus and H. ater, being present in almost all faeces and representing the vast majority of prey remains. However, R. megaphyllus captured predominantly non-eared moths (Anthelidae, Lasiocampidae, Hepialidae) or Gelechioid moths, a superfamily which has not been tested for hearing. By contrast, H. ater fed mostly on eared moths, predominantly members of the family Noctuidae. Eared moths made up 91.7% and 82.5% of all moths captured by H. ater at two sites. The data show that the incorporation of eared moths in the diet was much higher in the bat species, H. ater, with a call frequency well above the range of best hearing of moths. This result supports the allotonic frequency hypothesis. Our study indicates that flutter-detecting bats could have imposed selective pressures on moths during the evolution of moth hearing.

Changes in host–parasitoid food web structure with elevation

Gradients in elevation are increasingly used to investigate how species respond to changes in local climatic conditions. Whilst many studies have shown elevational patterns in species richness and turnover, little is known about how food web structure is affected by elevation. Contrasting responses of predator and prey species to elevation may lead to changes in food web structure. We investigated how the quantitative structure of a herbivore-parasitoid food web changes with elevation in an Australian subtropical rain forest. On four occasions, spread over 1 year, we hand-collected leaf miners at twelve sites, along three elevational gradients (between 493 m and 1159 m a.s.l). A total of 5030 insects, including 603 parasitoids, were reared, and summary food webs were created for each site. We also carried out a replicated manipulative experiment by translocating an abundant leaf-mining weevil Platynotocis sp., which largely escaped parasitism at high elevations (≥ 900 m a.s.l.), to lower, warmer elevations, to test if it would experience higher parasitism pressure. We found strong evidence that the environmental change that occurs with increasing elevation affects food web structure. Quantitative measures of generality, vulnerability and interaction evenness decreased significantly with increasing elevation (and decreasing temperature), whilst elevation did not have a significant effect on connectance. Mined plant composition also had a significant effect on generality and vulnerability, but not on interaction evenness. Several relatively abundant species of leaf miner appeared to escape parasitism at higher elevations, but contrary to our prediction, Platynotocis sp. did not experience greater levels of parasitism when translocated to lower elevations. Our study indicates that leaf-mining herbivores and their parasitoids respond differently to environmental conditions imposed by elevation, thus producing structural changes in their food webs. Increasing temperatures and changes in vegetation communities that are likely to result from climate change may have a restructuring effect on host-parasitoid food webs. Our translocation experiment, however, indicated that leaf miners currently escaping parasitism at high elevations may not automatically experience higher parasitism under warmer conditions and future changes in food web structure may depend on the ability of parasitoids to adapt to novel hosts.

Dietary Benefits of Twilight Foraging by the Insectivorous Bat Hipposideros speoris1

Although bats are nocturnal, many species emerge from roosts to forage during twilight, despite a presumed high risk of predation at this time. Here, we describe twilight foraging by a maternity colony of Schneider’s leafnosed bat (Hipposideros speoris) in the dry zone of Sri Lanka and determine the dietary benefits of such behavior. Bats usually began foraging during dusk, sometimes before sunset, and also foraged during twilight in the morning. Mean use of available twilight by four radio-tagged bats was 75 percent. Twilight foraging made up, on average, 47 percent of the total foraging time of these bats (range = 25-96%), although twilight consisted of only 12 percent of the available time between sunset and sunrise the next morning. Eight species of potential predators (7 birds and 1 mammal) were observed within a 1 km radius of the colony, of which 5 species are predicted to regularly capture bats. Bats took a wide diversity of prey (1 1 insect orders, including at least 27 families, and spiders) that ranged in wing length from 2.0 to 54.0 mm. Major orders in the diet were Coleoptera, Lepidoptera, and Diptera. Prey of secondary importance included Hemiptera, Hymenoptera, Isoptera, and Neuroptera. Bats captured large numbers of insects that were only available or had marked peaks in abundance during twilight. These groups included small, swarming insects (especially flies) that have peaks in flight activity at dusk and dawn, large diurnal species (especially dragonflies) that have crepuscular activity, and winged termites that emerge in swarms at dusk. Access to these insects was a clear benefit of twilight foraging. Ki word: activity patterns; bats; diet; foraging; Hipposideros speoris; nautical twilight; predation; Sigirzja; Sri Lanka. BATS (CHIROPTERA) ARE A DIVERSE A N D WIDELY DISTRIBUTED ORDER of mammals that forage almost exclusively during night (ie., between sunset and sunrise; Speakman 1990, 1995; cf: Thomson et al. 1998). Although the risk of predation faced by bats is presumed to be greater during twilight ( i e . , dusk and dawn) than true night, many species leave their roosts before dark (Jones & Rydell 1994), potentially exposing themselves to diurnal predators (Fenton et al. 1994). Twilight activity must have ’ Received 16 May 2000; revision accepted 18 December 2000. Current address and address for correspondence: Parks and Wildlife Commission of the Northern Territory, Arid Zone Research Institute, PO. Box 1046, Alice Springs, Northern Territory, Australia 0871. considerable fitness benefits for the behavior to persist in the face of high predation risks (Duvergk et al. 2000). Jones and Rydell (1994) have proposed that twilight activity allowed bats to exploit Nematocera and other small flies that show marked peaks in flight activity during twilight (especially at dusk) and very little activity during most of true night (Pandian & Chandrashekaran 1980, Racey & Swift 1985, Rydell et al. 1996). Twilight foraging by bats, however, has other potential benefits, especially in tropical regions where insect diversity is very high. First, bats can gain access to groups of insects (particularly winged termites and ants) that emerge in large numbers at dusk. Further, bats can increase their prey range by capturing diurnal insects during twilight (Pavey & Burwell 1998).

Foraging ecology of three species of hipposiderid bats in tropical rainforest in north-east Australia

We studied the foraging ecology of three species of hipposiderid bats - Hipposideros diadema (mean forearm length: 82 mm), H. cervinus (47 mm) and H. ater (41 mm) - in tropical, lowland rainforest in north-east Queensland, Australia. H. diadema foraged by perching within gaps and flying out to intercept slow-flying insects. The two smaller species typically foraged during flight, in undisturbed forest and gaps, and captured insects by aerial hawking. Seven arthropod taxa were identified in faeces of H. cervinus, with Coleoptera and Lepidoptera being present in most faeces. Percentage volume of moth scales was generally low: 35 of 60 faeces had a volume of 90%. No other taxa were frequently present in faeces of H. ater. Differences in foraging ecology between H. diadema and the smaller species were related to its large size and low manoeuvrability. The dietary differences we found between H. ater and H. cervinus were unexpected, because both species have high-frequency echolocation calls (160-164 and 144-145 kHz, respectively), which suggested that both would capture predominantly moths. Our data show that pairs of hipposiderid species with only small differences in call frequencies may consume different prey taxa; however, we contend that dietary variation is more likely to result from differences in body size, wing morphology, and tooth, jaw, and cranial morphology.

Comparison of point counts and automated acoustic monitoring: detecting birds in a rainforest biodiversity survey

Abstract To monitor assemblages of animals, ecologists need effective methods for detecting and recording the distributions of species within target areas in restricted periods of time. In this study, we compared the effectiveness of a traditional avian biodiversity assessment technique (point counts) with a relatively new method (automated acoustic recordings) along an elevational gradient in rainforest in central Queensland, Australia. On average, point counts detected more species than acoustic recordings of an equivalent length of time (n = 40, P = <0.001). We suggest these results are driven by the visual detection of additional species during point counts. Despite the fact that point counts detected more species than acoustic recordings, datasets generated by both methods showed similar patterns in the community response to change in elevation. There was significant overlap in the species detected using both methods, but each detected several unique species. Consequently, we recommend the use of both techniques in tandem for future biodiversity assessments, as their respective strengths and weaknesses are complementary.

Ground dwelling ants as surrogates for establishing conservation priorities in the Australian wet tropics.

Abstract This study aims to identify a set of areas with high biodiversity value over a small spatial scale within the Australian Wet Tropics. We identified sites of high biodiversity value across an altitudinal gradient of ground dwelling ant communities using three measures of biodiversity. The three measures considered were estimated species richness, complementarity between sites and evolutionary history. The latter measure was derived using the systematic nomenclature of the ants to infer a surrogate phylogeny. The goal of conservation assessments could then be achieved by choosing the most diverse site combinations. This approach was found to be valuable for identifying the most diverse site combinations across an altitudinal gradient that could ensure the preservation of terrestrial ground dwelling invertebrates in the Australian Wet Tropics.

Foraging ecology of the horseshoe bat, Rhinolophus megaphyllus (Rhinolophidae), in eastern Australia

The foraging ecology of the eastern horseshoe bat, Rhinolophus megaphyllus, was examined at five sites spread along 2100 km of its Australian distribution in coastal Queensland. Foraging strategy and prey-capture behaviour of light-tagged bats were similar across sites. Bats were observed foraging during continuous flight at all sites, whereas perch hunting was observed (rarely) at only one site. Bats captured insects by aerial hawking, with a single record of gleaning. In rainforest bats spent most time close to vegetation whereas openings were favoured in open forest/woodland. Only flying insects were captured and, although a wide range of taxa was taken, Lepidoptera (all sites) and Coleoptera (all sites except one) were the primary prey. Occurrence in faeces of Lepidoptera, Coleoptera, and other taxa combined, varied across sites and across seasons, but there was no three-way interaction between taxon, site and season. Comparison of insect taxa in faeces with those captured in a light-trap set at foraging grounds indicated that insects were selectively captured by R. megaphyllus. The foraging ecology of R. megaphyllus is similar to that of other horseshoe bats in its relative stability across a large geographic range. Although the species is currently not of conservation concern in Australia, aspects of its foraging ecology suggest that it may become regionally threatened in areas with high levels of vegetation clearance.

Effects of isolation on the colonisation of restored habitat patches by forest‐dependent arthropods of soil and litter

Abstract.  1 A novel experimental approach was taken to investigate the effects of distance from rainforest remnants on the recolonisation patterns of ants and other soil and litter arthropods in ‘restored’ habitat patches within a pasture matrix. 2 Experimental habitat patches were created by adding a thick mulch of sterilised woodchips and leaves, and simulating shade using shadecloth, to create conditions similar to those that occur during rainforest restoration. These patches were deployed at five experimental sites in the Maleny plateau of subtropical eastern Australia. Artificial habitat patches were located at varying distances from a rainforest edge at each site, as well as within the rainforest. The experiment also included a test for efficacy of inoculation, which involved translocation of a small quantity of litter (containing live arthropods) from rainforest habitat to isolated habitat patches. 3 The results showed that, after 9 months, there was little colonisation by rainforest‐dependent taxa in any of the experimental plots beyond those closely adjacent to forest patches. Inoculation was unsuccessful in increasing the extent of arthropod establishment. 4 A number of explanations that potentially account for the observed results are suggested. An experimental approach provides an opportunity to test explicitly for factors considered important for the development of biota in restored habitat patches. There are, however, unavoidable limitations associated with the design of experiments that simulate small‐scale analogues of restoration treatments. Avoiding these limitations may require controlled and replicated efforts in experimental restoration over larger areas, based on collaborations between researchers and practitioners.

Morphological alteration in response to endogeic habitat and ant association in two new planthopper species from New Caledonia (Hemiptera: Auchenorrhyncha: Fulgoromorpha: Delphacidae)

Two new endogeic species of the delphacid genus Notuchus are described from New Caledonia, Notuchus kaori sp. nov. and Notuchus ninguae sp. nov. Both species are soil‐dwelling and display the highest degree of troglomorphy observed in any subterranean Fulgoromorpha species. Notuchus kaori appears to be associated with ants of the genus Paratrechina (Formicidae: Formicinae). Information on their ecology and distribution is provided, and morphological characters which may be indicative of adaptation to the subterranean environment and/or the degree of integration into the host society are discussed.