Kj Bonham

Diversity and abundance of some ground-dwelling invertebrates in plantation vs. native forests in Tasmania, Australia

Land snails, millipedes, carabid beetles and velvet worms (Onychophora) were methodically hand-sampled at 46 localities on paired plots in conifer or eucalypt plantations and in nearby native forest in northwest Tasmania. Native land snails and millipedes were less diverse in plantations than in native forests, and introduced land snails were several times more abundant in plantations. Many taxa, however, including a velvet worm previously considered to be threatened by plantation development, and including almost half the taxa represented by 10 or more specimens, were found at least as commonly in plantations as in native forests. Invertebrate conservation may be assisted by specific forestry operations, including windrowing, mound ploughing, and leaving waste prunings and thinnings to rot. Plantation development on cleared farmland can allow invertebrates to re-invade from adjacent bush remnants, reducing the risk of local extinctions.

Classic metapopulations are rare among common beetle species from a naturally fragmented landscape

1. The general importance of metacommunity and metapopulation theories is poorly understood because few studies have examined responses of the suite of species that occupy the same fragmented landscape. In this study, we examined the importance of spatial ecological theories using a large-scale, naturally fragmented landscape. 2. We measured the occurrence and abundance of 44 common beetle species in 31 natural rainforest fragments in Tasmania, Australia. We tested for an effect on beetle distribution of geographic variables (patch area, patch isolation and amount of surrounding habitat) and of environmental variables based on plant species, after first accounting for spatial autocorrelation using principal coordinates of neighbour matrices. The environmental variables described a productivity gradient and a post-fire succession from eucalypt-dominated forest to late-successional rainforest. 3. Few species had distributions consistent with a metapopulation. However, the amount of surrounding habitat and patch isolation influenced the occurrence or abundance of 30% of beetle species, implying that dispersal into or out of patches was an important process. 4. Three species showed a distribution that could arise by interactions with dominant competitors or predators with higher occurrence in small patches. 5. Environmental effects were more commonly observed than spatial effects. Twenty-three per cent of species showed evidence of habitat-driven, deterministic metapopulations. Furthermore, almost half of the species were influenced by the plant succession or productivity gradient, including effects at the within-patch, patch and regional scales. The beetle succession involved an increase in the frequency of many species, and the addition of new species, with little evidence of species turnover. Niche-related ecological theory such as the species-sorting metacommunity theory was therefore the most broadly applicable concept. 6. We conclude that classic and source-sink metapopulations are probably rare in this large-scale, naturally fragmented system, although dispersal processes like those occurring in metapopulations may have a substantial influence on community composition. However, deterministic processes (niche specialisation, species-sorting metacommunities and deterministic metapopulations) drive the occurrence or frequency of the majority of species. We urge further research into the prevalence of spatial ecological processes in large-scale natural ecosystems to expand our understanding of the processes that may be important in nature.

Single-species sampling in Tasmania: an inefficient approach to invertebrate conservation?

In recent years the distributions of a number of geographically restricted Tasmanian invertebrates have been carefully mapped by single-species sampling (SSS). We review 29 such projects targeted at 16 species. The average return of new locality records was only one per 1.3 person-days in the field. In almost all cases the SSS was aimed at improving the knowledge base for invertebrate conservation, and the principal end users of the results have been land managers, not biologists. It is suggested that more of the limited resources available for intensive fieldwork be directed to sampling functional groups of taxa, rather than single species, in areas prioritised by need for land management advice.