Darren F. Ward

Relative roles of climatic suitability and anthropogenic influence in determining the pattern of spread in a global invader

Because invasive species threaten the integrity of natural ecosystems, a major goal in ecology is to develop predictive models to determine which species may become widespread and where they may invade. Indeed, considerable progress has been made in understanding the factors that influence the local pattern of spread for specific invaders and the factors that are correlated with the number of introduced species that have become established in a given region. However, few studies have examined the relative importance of multiple drivers of invasion success for widespread species at global scales. Here, we use a dataset of >5,000 presence/absence records to examine the interplay between climatic suitability, biotic resistance by native taxa, human-aided dispersal, and human modification of habitats, in shaping the distribution of one of the worlds most notorious invasive species, the Argentine ant (Linepithema humile). Climatic suitability and the extent of human modification of habitats are primarily responsible for the distribution of this global invader. However, we also found some evidence for biotic resistance by native communities. Somewhat surprisingly, and despite the often cited importance of propagule pressure as a crucial driver of invasions, metrics of the magnitude of international traded commodities among countries were not related to global distribution patterns. Together, our analyses on the global-scale distribution of this invasive species provide strong evidence for the interplay of biotic and abiotic determinants of spread and also highlight the challenges of limiting the spread and subsequent impact of highly invasive species.

The conservation status of New Zealand Hymenoptera

Two species of New Zealand Hymenoptera, a colletid bee Leioproctus nunui and a gasteruptiid Gasteruption scintillans, are considered Threatened: both are ranked Nationally Critical. Twenty taxa are At Risk, comprising two taxa that are Declining with the remainder classified as Naturally Uncommon. A further 47 taxa are Data Deficient, and 669 known species are either Not Threatened or Introduced and Naturalised.

Twenty years of Argentine ants in New Zealand: past research and future priorities for applied management

The Argentine ant, Linepithema humile (Mayr), is a highly invasive global pest. It has been just over twenty years since Argentine ants were fi rst discovered in New Zealand. Through the result of human-mediated dispersal, they are now relatively widespread, but patchily distributed, in many North Island towns and cities, and also in several locations in the South Island. This review provides a short history of Argentine ant invasion within New Zealand and research conducted to date. It suggests that Argentine ants are still only at the beginning of their invasion in New Zealand, and that estimated treatment costs are set to greatly increase over the next twenty years; but that an opportunity exists to slow the spread of the ants given substantial regional co-ordination. Targeted regional efforts are also needed to protect specific valued sites (e.g. off-shore islands, vulnerable conservation areas). The review identifies knowledge gaps and priority areas which need a timely response as opportunities to restrict the distribution and impact of this species will continue to diminish through the growth of existing populations and increased establishment of new populations.

More than just records: analysing natural history collections for biodiversity planning.

Natural History Collections (NHCs) play a central role as sources of data for biodiversity and conservation. Yet, few NHCs have examined whether the data they contain is adequately representative of local biodiversity. I examined over 15,000 databased records of Hymenoptera from 1435 locations across New Zealand collected over the past 90 years. These records are assessed in terms of their geographical, temporal, and environmental coverage across New Zealand. Results showed that the spatial coverage of records was significantly biased, with the top four areas contributing over 51% of all records. Temporal biases were also evident, with a large proportion (40%) of records collected within a short time period. The lack of repeat visits to specific locations indicated that the current set of NHC records would be of limited use for long-term ecological research. Consequently, analyses and interpretation of historical data, for example, shifts in community composition, would be limited. However, in general, NHC records provided good coverage of the diversity of New Zealand habitats and climatic environments, although fewer NHC records were represented at cooler temperatures (<5°C) and the highest rainfalls (>5000 mm/yr). Analyses of NHCs can be greatly enhanced by using simple techniques that examine collection records in terms of environmental and geographical space. NHCs that initiate a systematic sampling strategy will provide higher quality data for biodiversity research than ad hoc or point samples, as is currently the norm. Although NHCs provide a rich source of information they could be far better utilised in a range of large-scale ecological and conservation studies.

The value of RTUs and parataxonomy versus taxonomic species

Parataxonomy and the sorting of specimens to recognisable taxonomic units (RTUs) are common approaches to invertebrate biodiversity studies worldwide. However, there is an urgent need to assess and validate the use of RTUs as opposed to taxonomic species. Beetle (Coleoptera) assemblages were sampled from native and willow dominated riparian zones in the Hunua Ranges, Auckland. Beetles were sorted to RTUs by a parataxonomist, and then identified by a specialist Coleopterist. A comparison of the unverified (RTU) dataset with the verified (taxonomic species) dataset showed an overall 5.6% error rate, with seven more taxonomic species being identified than assigned to RTUs. RTU accuracy was problematic for several families, including Staphylinidae, Cryptophagidae and Latridiidae. However, in terms of ecological interpretation, both datasets gave almost identical results. Ranking of sites by species/RTU richness and the composition of the beetle fauna identified the same trends. Despite these results, we suggest that the RTU approach is overrated because of the loss in biological information associated with the RTU approach. We suggest the use of RTUs offers considerably less than a taxonomic species approach for invertebrate conservation in New Zealand, particularly in the long-term.

Critical issues facing New Zealand entomology

Here, we identify current high-priority issues in New Zealand entomology. These ‘critical issues’ were defined by being of national entomological interest, and in urgent need of research or attention. The issues were derived in consultation with the Entomological Society of New Zealand members and as part of a workshop at the 62nd New Zealand Entomological Society Conference. We present a list of nine priority areas (presented here without any ranking priority). These areas are: 1. conserving indigenous invertebrate diversity; 2. limiting predator pressure exerted by exotic vertebrate predators; 3. limiting the effects of invasive invertebrates, especially Vespula wasps in honeydew beech forests; understanding the influence of pesticides and pathogens on honey bees; 4. maintaining and enhancing efficient biosecurity systems to keep out invasive pests and diseases; 5. enhancing support for taxonomy; 6. enhancing entomological teaching, training and support for entomology graduates; 7. utilising the hidden knowledge of retired entomologists; and 8. supporting amateurs in entomology. For each of these topics we briefly discuss the state of the current situation or knowledge gaps. We consider this a road map to enhance entomology in New Zealand.

Assessing the risk of invasive ants: a simple and flexible scorecard approach

Abstract.Numerous ant species are being transported around globe through international trade, many of which become invasive. To mitigate the potential impacts of invasive ant species, an assessment system is needed which is simple, can be tailored for specific-user and regional requirements, and has the potential to integrate a variety of additional information. Here we present such a system, which has been used in New Zealand to determine which ant species pose the greatest threat to natural ecosystems. However, the scorecard system could be applied widely around the globe for assessing the threat of invasive ant species.

Microbial community structure in the gut of the New Zealand insect Auckland tree weta (Hemideina thoracica)

The endemic New Zealand weta is an enigmatic insect. Although the insect is well known by its distinctive name, considerable size, and morphology, many basic aspects of weta biology remain unknown. Here, we employed cultivation-independent enumeration techniques and rRNA gene sequencing to investigate the gut microbiota of the Auckland tree weta (Hemideina thoracica). Fluorescence in situ hybridisation performed on different sections of the gut revealed a bacterial community of fluctuating density, while rRNA gene-targeted amplicon pyrosequencing revealed the presence of a microbial community containing high bacterial diversity, but an apparent absence of archaea. Bacteria were further studied using full-length 16S rRNA gene sequences, with statistical testing of bacterial community membership against publicly available termite- and cockroach-derived sequences, revealing that the weta gut microbiota is similar to that of cockroaches. These data represent the first analysis of the weta microbiota and provide initial insights into the potential function of these microorganisms.

Invasive interactions: can Argentine ants indirectly increase the reproductive output of a weed?

The direct and indirect interactions of invasive ants with plants, insect herbivores, and Hemiptera are complex. While ant and Hemiptera interactions with native plants have been well studied, the effects of invasive ant–scale insect mutualisms on the reproductive output of invasive weeds have not. The study system consisted of Argentine ants (Linepithema humile), boneseed (Chrysanthemoides monilifera monilifera), and sap-sucking scale insects (Hemiptera: Saissetia oleae and Parasaissetia nigra), all of which are invasive in New Zealand. We examined the direct and indirect effects of Argentine ants on scale insects and other invertebrates (especially herbivores) and on plant reproductive output. Argentine ants spent one-third of their time specifically associated with scale insects in tending behaviours. The invertebrate community was significantly different between uninfested and infested plants, with fewer predators and herbivores on ant-infested plants. Herbivore damage was significantly reduced on plants with Argentine ants, but sooty mould colonisation was greater where ants were present. Herbivore damage increased when ants were excluded from plants. Boneseed plants infested with Argentine ants produced significantly more fruits than plants without ants. The increase in reproductive output in the presence of ants may be due to increased pollination as the result of pollinators being forced to relocate frequently to avoid attack by ants, resulting in an increase in pollen transfer and higher fruit/seed set. The consequences of Argentine ant invasion can be varied; not only does their invasion have consequences for maintaining biodiversity, ant invasion may also affect weed and pest management strategies.

Impacts of Argentine ants on invertebrate communities with below-ground consequences.

The Argentine ant, Linepithema humile (Mayr), is an invasive species that has been associated with various negative impacts in native communities around the world. These impacts, as for other invasive ants, are principally towards native ant species, and impacts on below-ground processes such as decomposition remain largely unexplored. We investigated the relationship between Argentine ants and invertebrate fauna, litter decomposition and soil microbial activity between paired invaded and uninvaded sites at two locations in Auckland, New Zealand, where there has been no research to date on their impacts. We examined the diversity and composition of invertebrate and microorganisms communities, and differences in soil and litter components. The composition of invertebrates (Order-level, ant and beetle species) was different between invaded and uninvaded sites, with fewer ants, isopods, amphipods, and fungus-feeding beetles at the invaded sites, whereas Collembola were more abundant at the invaded sites. There were significant differences in soil chemistry, including higher carbon and nitrogen microbial biomass at uninvaded sites. Several litter components were significantly different for Macropiper excelsum. The fibre content of litter was higher, and key nutrients (e.g. nitrogen) were lower, at invaded sites, indicating less breakdown of litter at invaded sites. A greater knowledge of the history of invasion at a site would clarify variation in the impacts of Argentine ants, but their persistence in the ground litter layer may have long-term implications for soil and plant health in native ecosystems.