Stephen Hartley

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.

Scaling Down: On the Challenge of Estimating Abundance from Occurrence Patterns

One of the key goals of ecology is to explain the distri-bution and abundance of species. It has become apparent,however, that even to describe these matters is fraughtwith difficulty. The abundance or rarity of a species canbe described in many ways, ranging from global geograph-ical range through regional ubiquity and population struc-ture down to local population size or cover. These differentaspects of abundance can be thought of as different scalesof analysis and indeed can be reflected by mapping a pop-ulation at varying scales of resolution. There is, however,a fundamental asymmetry in such maps; a fine-scale mapof a given area can be used to generate a coarse-scale map,but a coarse-scale map does not provide enough infor-mation to produce a fine-scale map. This is unfortunate,as a considerable amount of coarse-scale informationabout species distributions is available in many countries(e.g., Perring and Walters 1962; Jalas and Suominen 1987),but management decisions in conservation biology andother applied disciplines often require fine-scale (e.g., pop-ulation) data.Fortunately, the situation is not as bleak as it may seemat first glance. Even if fine-scale maps cannot be generatedfrom coarse ones, it may be possible to infer some of theimportant properties of the fine-scale map from coarse-scale information. One of us (W. E. Kunin) recently dem-onstrated that some properties of a species distributionbehave in similar ways at different scales, making it pos-sible (at least in principle) to extrapolate coarse-scale in-formation down to finer scales (Kunin 1998). “Scale-area

Temperature-dependent development of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae): a degree-day model with implications for range limits in New Zealand.

The Argentine ant, Linepithema humile, is an invasive species with the potential to cause significant economic and ecological damage in New Zealand. Using published information on rates of development, we induced parameters for a cumulative degree-day model for each life-stage of the Argentine ant.A summary model suggested that complete development, from egg to worker, requires approximately 445 degree-days above a threshold of 15.9°C. Meteorological records of air and soil temperatures indicated a number of sites in New Zealand that fulfil this minimum temperature requirement on an annual basis. Maps based on soil temperature data indicated suitable conditions as far south as Central Otago, while air temperature data predicted a more limited northerly distribution in Northland and Hawkes Bay. Additional factors, such as microclimatic variation, thermoregulatory behaviour, biotic interactions and dispersal opportunities will also be important in determining the precise range limits of the Argentine ant in New Zealand.

The widespread collapse of an invasive species: Argentine ants (Linepithema humile) in New Zealand.

Synergies between invasive species and climate change are widely considered to be a major biodiversity threat. However, invasive species are also hypothesized to be susceptible to population collapse, as we demonstrate for a globally important invasive species in New Zealand. We observed Argentine ant populations to have collapsed in 40 per cent of surveyed sites. Populations had a mean survival time of 14.1 years (95% CI = 12.9–15.3 years). Resident ant communities had recovered or partly recovered after their collapse. Our models suggest that climate change will delay colony collapse, as increasing temperature and decreasing rainfall significantly increased their longevity, but only by a few years. Economic and environmental costs of invasive species may be small if populations collapse on their own accord.

Argentine and other ants (Hymenoptera: Formicidae) in New Zealand horticultural ecosystems: distribution, hemipteran hosts, and review

Approximately 30 exotic ant species have been introduced into New Zealand, including the Argentine ant Linepithema humile (Mayr). Many of these ant species are known to affect horticulture worldwide by tending hemipteran insects. These ants may protect these hemiptera from their natural enemies, resulting in higher pest densities and potential economic loss. Our aim in this work was to survey the ant species associated with the various horticultural crops in the North Island. Our focus was on L. humile, but we also collected other ants and associated hemipteran species. Linepithema humile appeared to be an opportunistic species and was found on fifteen of eighteen common horticultural crops that we surveyed, as well as on a variety of other plants. It was observed tending 15 different species of hemipteran insects. Linepithema humile has been previously observed tending some of these hemipteran insects overseas, such as the black scale Saissetia oleae (Olivier). Other observed L. humile-hemipteran-plant associations reported here have not previously been recorded, such as with the spirea aphid Aphis spiraecola Patch on plum trees. Eleven other species of ants were found on horticultural crops. Paratrechina vaga (Forel) was common and also tended hemipteran insects on apple, citrus, and tamarillo. Other common ants were Tetramorium grassii Emery, Monomorium antarcticum (Smith), Pheidole rugosula Forel and Ph. vigilans (Smith). Another adventive ant, Ph. megacephala (Fab.), was only sampled in Auckland despite having been in New Zealand for over 50 years. Many of these invasive ants thus do not appear threatening to horticultural crops, though L. humile appears likely to be a significant economic pest for a variety of crops.

Trophic-level responses differ at plant, plot, and fragment levels in urban native forest fragments: a hierarchical analysis

1. Using a hierarchical generalised linear model we examined effects of landscape fragmentation (fragment area, isolation, and urbanisation of the surrounding matrix), within‐fragment habitat quality (host plant abundance and plant species richness), and properties of the individual trees, on plant herbivore and parasitoid abundance.

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.

Online trading tools as a method of estimating propagule pressure via the pet-release pathway

The increasing amount of internet trade in live animals has facilitated the sale and circulation of exotic species all over the world. This is an area of concern, as the deliberate or accidental release of pets is an important pathway by which exotic species are often introduced into new environments, often with negative effects on the local species and ecosystems. Internet trading sites were used to determine the distribution and magnitude of propagule pressure of red-eared slider turtles (RES; Trachemys scripta elegans) within the New Zealand pet trade. Sites were tracked daily from October 1, 2007 to September 30, 2009 and information on age, sex, season, and location was recorded. More than 1,500 sales and 80 reports of lost/found RES were recorded. Unsurprisingly, the highest number of sales and lost/found RES was in Auckland, the region with the highest human population. Females were more often reported as lost or found than males, despite a similar sex ratio of sales. The type and quality of information gathered in this manner is not perfect, as it only provides an estimate of minimum numbers of animals that are being traded/lost into the environment, but nonetheless, provides useful data when planning a management or eradication plan for feral turtles in New Zealand. Of concern, our results highlighted areas where turtles were most often being released in New Zealand, being those areas predicted to be the most climatically-suitable for this species, and in which incubation conditions were most likely to be met. Monitoring online sales of exotic species provides useful demographic information, as well as an indication of propagule pressure via the pet-release pathway. This technique is applicable to other species and may be a useful tool to help determine locations at risk of the establishment of other exotic species.

Scaling Biodiversity: Species distribution patterns, diversity scaling and testing for fractals in southern African birds

PART I Spatial scaling of species richness and distribution 13 2 Species–area curves and the geometry of nature Michael W. Palmer 15 3 The distribution of species: occupancy, scale, and rarity Fangliang He and Rick Condit 32 4 Species distribution patterns, diversity scaling and testing for fractals in southern African birds Jack J. Lennon, William E. Kunin, Stephen Hartley and Kevin J. Gaston 51 5 Geometry of species distributions: random clustering and scale invariance Arnošt L. Šizling and David Storch 77 6 Toward a mechanistic basis for a unified theory of spatial structure in ecological communities at multiple spatial scales John Harte 101

Nest-based information transfer and foraging activation in the common wasp ( Vespula vulgaris )

The apparent absence of intra-nest signals and communication about food resources (recruitment) among social wasps does not rule out the possibility of information transfer and coordinated foraging among nestmates. In the present study, we tested the hypothesis that the common wasp (Vespula vulgaris) shows nest-based information transfer and foraging activation: an increase in the probability of an individual leaving the nest as a result of information about resources received from successful foragers. We controlled for the possibility of local enhancement, chemical trails at the food source and climatic variation. We found evidence that food choice and discovery of resources in the field by naïve foragers were assisted by information previously or simultaneously provided by experienced nestmates. This information was related to chemical cues associated with the food and possibly to its location. Our observations suggest piloting between common wasp foragers. At the trained nest, there was a change in foraging effort at the colony level when known resources were available. Reactivated, experienced foragers were the main group responsible for the increase in foraging traffic rate observed at the colony level. To our knowledge, this is the first study clearly demonstrating nest-based information transfer about food resources in V. vulgaris and one of the few providing evidence of foraging activation in social wasps. Our data are consistent with the possibility of recruitment in this group of social insects.