Establishment success of sooty beech scale insects, Ultracoelostoma sp., on different host tree species in New Zealand

The sooty beech scale insect (Ultracoelostoma sp.) (Hemiptera: Margarodidae) exhibits a highly patchy distribution at local and regional scales. A major factor driving this common distributional phenomenon in other phloem-feeding insects is aggregation and local adaptation. The aim of this study was to determine if Ultracoelostoma was locally adapted to its natal host trees, by contrasting the establishment rates of first instar “crawlers” in reciprocal transfers to natal versus novel hosts. Although there are two closely-related species of sooty beech scale insect, the morphological characters of crawlers in this study were intermediate between those of U. assimile and U. brittini. However, all of the voucher specimens examined had consistent morphology, indicating that they belong to one species which we refer to as Ultracoelostoma sp. Reciprocal transfers of crawlers were carried out between individual red beech (Nothofagus fusca), as well as between mountain beech (N. solandri) and red beech trees, to ascertain if insects had become locally adapted to their individual host tree or to host species. In total, 480 crawlers were placed in enclosures on their natal and novel host trees, of which only 32 (6.7 %) became established. No evidence for local adaptation, either to individual host trees or to host tree species, was found. There was also no difference in crawler establishment between natal and novel hosts. However, crawlers originating from mountain beech trees had significantly higher establishment rates on both natal mountain beech and novel red beech hosts, than did crawlers originating from red beech trees. The superior ability of mountain beech crawlers to become established, even on novel red beech trees, suggests that scale insects on mountain beech trees have higher individual fitness (possibly due to maternal effects mediated by differences in host nutritional quality, defensive compounds or growth rate). This increased fitness may result in crawlers being better provisioned to search for appropriate establishment sites. The results of this study indicate that beech scale insects perform better on mountain beech at this site, although crawlers did not preferentially establish on mountain beech

Estimation of biomass from body length and width for tropical rainforest canopy invertebrates

Accurate estimates of invertebrate biomass are essential for quantifying community structure, food web dynamics and energy flow in terrestrial ecosystems. In this paper, length-mass and length × width-mass regressions were carried out for 18 invertebrate taxonomic groups collected from the canopy of an Australian tropical rainforest. In an additional analysis, invertebrates were divided among seven body shape categories based on the ratio of body length to body width (from short and squat to long and thin) in an attempt to develop accurate equations for estimating biomass that can be applied to any taxonomic group in any locality. For most groups, the inclusion of body width to the predictor variable improved the model, confirming that body shape is an important factor in the accuracy of biomass estimations. The most accurate method for estimating invertebrate biomass was the use of taxon-specific equations, followed by equations based on body shape. Single whole-fauna equations were very inaccurate for estimating biomass, especially for insects that are either very squat or very long and thin. In accordance with previous studies, it was concluded that the most accurate method for estimating invertebrate biomass from proxy body measurements is the use of taxon-specific regression equations, especially those that incorporate body width in the model. However, equations based on body shape categories may be useful for estimating the biomass of groups for which no length-mass relationship has been determined, while single, whole-fauna equations should be avoided

The importance of flowers for beetle biodiversity and abundance

The rainforest canopy supports a large, but as yet uncertain proportion of global biodiversity (Price 2002; Ozanne et al. 2003; Grimbacher and Stork 2007). The high species richness of plants and animals in the canopy and their interactions have been shown to be strongly influential in determining food web dynamics (Novotny et al. 2010) and form the basis for many estimates of global species richness (Erwin 1982; Stork 1993; Ødegaard 2000a; Novotny et al. 2002; Hamilton et al. 2010). However, while the high diversity of invertebrates in rainforest canopies is acknowledged (Southwood 1961; Erwin 1982; Moran and Southwood 1982; Stork 1988), the logistical difficulties in accessing the canopy have placed sampling limitations on previous biodiversity and ecological studies. Consequently, most studies to date have used sampling techniques that indiscriminately sample many arboreal microhabitats together, such as insecticide fogging (Erwin 1982; Moran and Southwood 1982; Stork 1988) or flight interception/Malaise traps (Stork and Grimbacher 2006), or focus only on sampling species from leaves as the dominant habitat (Novotny and Basset 2005)

Variation in beetle community structure across five microhabitats in Australian tropical rainforest trees

1. Beetles (Coleoptera) are the most species-rich and ecologically diverse group of organisms in tropical rainforest canopies. This study reports on the distribution of the beetle community on five discrete canopy microhabitats (mature leaves, new leaves, flowers, fruit, and suspended dead wood) on 23 tree species in an Australian tropical rainforest. We tested the hypothesis that the beetle fauna will vary in community structure between microhabitats based on differences in the quantity, quality as a food source and availability of different canopy microhabitats.\ud \ud 2. There was substantial variation in dominant beetle families in terms of abundance between microhabitats. All assemblages contained a high number of rare species, with flowers supporting most of the more abundant species. Consequently, the flower-visitor assemblage was more heterogeneous than expected by chance, whereas the mature leaf assemblage was more even in the proportional abundances of species than expected.\ud \ud 3. The distribution of singletons was also non-random and flowers, which are spatially and temporally restricted, supported fewer singletons than expected by chance, whereas mature leaves and dead wood supported more. These differences were insensitive to beetle feeding guild, and are most likely related to variation in microhabitat distribution and availability, which influenced relative sampling efforts and the probability of random microhabitat/beetle associations.\ud \ud 4. High dissimilarity in species overlap between microhabitats suggests that each microhabitat attracts a unique beetle assemblage, which has an additive effect on canopy-wide species richness patterns. Consequently, biodiversity studies that focus on single microhabitats may inadvertently omit a large proportion of canopy species

Canopy invertebrate community composition on rainforest trees: different microhabitats support very different invertebrate communities

Tropical rainforest canopies are renowned for their high invertebrate diversity and abundance. The canopy comprises a range of microhabitats representing very different food resources (including photosynthetic, reproductive, and structural tissues). As these resources vary considerably in temporal and spatial availability, nutritional quality, chemical protection and other attributes, we hypothesized that microhabitats support structurally different invertebrate communities. To test this we used the Australian Canopy Crane to sample invertebrates from mature leaves, flush leaves, flowers, fruit and suspended dead wood from 23 plant species. Invertebrate faunas on different microhabitats varied in taxonomic composition and feeding guild structure in support of the microhabitat differentiation hypothesis. Herbivores were found predominantly on new leaves (Hemiptera, Lepidoptera) and especially flowers (Coleoptera, Thysanoptera), but were relatively uncommon on mature leaves. Instead, the mature foliage community was dominated by predators, especially spiders and ants, and supported high abundances of saprophages. Ripe fruit and dead wood were scarce canopy resources that were utilized by a relatively small number of invertebrates, mostly saprophages and fungivores. Flowers supported a more heterogeneous fauna than the leaves in terms of proportional abundances of taxonomic groups and feeding guilds, both within tree species (evenness) and between tree species (non-uniformity). These results demonstrate microhabitat differentiation in a rainforest canopy and are the first to quantify differences in taxonomic composition, guild structure and abundance patterns between such diverse invertebrate assemblages within host trees. We conclude that studies based only on sampling one microhabitat, and leaves in particular, may provide a distorted picture of invertebrate community structure

The specialization and structure of antagonistic and mutualistic networks of beetles on rainforest canopy trees

Different kinds of species interactions can lead to different structures within ecological networks. Antagonistic interactions (such as between herbivores and host plants) often promote increasing host specificity within a compartmentalized network structure, whereas mutualistic networks (such as pollination networks) are associated with higher levels of generalization and form nested network structures. However, we recently showed that the host specificity of flower-visiting beetles from three different feeding guilds (herbivores, fungivores, and predators) in an Australian rainforest canopy was equal to that of herbivores on leaves, suggesting that antagonistic herbivores on leaves are no more specialized than flower-visitors. We therefore set out to test whether similarities in the host specificity of these different assemblages reflect similarities in underlying network structures. As shown before at the species level, mutualistic communities on flowers showed levels of specialization at the network scale similar to those of the antagonistic herbivore community on leaves. However, the network structure differed, with flower-visiting assemblages displaying a significantly more nested structure than folivores, and folivores displaying a significantly more compartmentalized structure than flower-visitors. These results, which need further testing in other forest systems, demonstrate that both antagonistic and mutualistic interactions can result in equally high levels of host specialization among beetle assemblages in tropical rainforests. If this is a widespread phenomenon, it may alter our current perceptions of food web dynamics, species diversity patterns, and co-evolution in tropical rainforests

Insects on flowers: the unexpectedly high biodiversity of flower-visiting beetles in a tropical rainforest canopy

Insect biodiversity peaks in tropical rainforest environments where a large but as yet unknown proportion of species are found in the canopy. While there has been a proliferation of insect biodiversity research undertaken in the rainforest canopy, most studies focus solely on insects that inhabit the foliage. In a recent paper, we examined the distribution of canopy insects across five microhabitats (mature leaves, new leaves, flowers, fruit and suspended dead wood) in an Australian tropical rainforest, showing that the density (per dry weight gram of microhabitat) of insects on flowers were ten to ten thousand times higher than on the leaves. Flowers also supported a much higher number of species than expected based on their contribution to total forest biomass. Elsewhere we show that most of these beetle species were specialized to flowers with little overlap in species composition between different canopy microhabitats. Here we expand our discussion of the implications of our results with respect to specialization and the generation of insect biodiversity in the rainforest canopy. Lastly, we identify future directions for research into the biodiversity and specialization of flower-visitors in complex tropical rainforests

Low host specificity of beetles associated with fruit falls in lowland tropical rainforest of north-east Australia

Most host-specificity studies of tropical rainforest insects have focused on those species feeding on leaves. Apart from the fruit flies, the level of specialisation among fruit-associated insects is poorly known. The relative contribution to local species richness made by insects feeding or associated with fallen fruits is also unknown. Beetles from fruit falls over a 5-year period in lowland tropical rainforest at Cape Tribulation, Australia were sampled. A total of 5157 individual beetles of 73 species were sampled from the fruits of 18 different plant species. Only a few species were of frugivorous families, and most species are likely utilising resources associated with the breakdown of the fruits. The size of the fruit fall-associated beetle assemblage (73 spp) was small compared with the number of species collected during a 4-year sampling program conducted at the same site prior to the current study using 10 combined Malaise-Flight Interception Traps (1473 spp, 77 families). The number of beetles and species collected from fruit that were very strongly correlated with the number of times fruit falls from a particular species of plant were sampled. The locally common palm, Normanbya normanbyi, produced fruit throughout the year and supported the largest number of fruit-associated species. It is suggested that this might be a keystone resource for local fruit fall-associated insect species. Although most beetle species showed a preference for the fruits of a particular plant species, overall host specificity for beetles was low. This is probably because fruit resources at this site are spatially and temporally patchy. Our results challenge the notion that most insects associated with fruit falls in tropical rainforests are highly host-specific