EARLY DETECTION AND ERADICATION OF INVADING RATS

Invasive rats continue to colonize rat-free islands around the world. To prevent rats from establishing on rat-free islands, especially following their eradication, biosecurity actions are required to enable early detection and elimination. Rats arrive at islands by both human transportation and by swimming. There are very little data on the rates of rat transportation by humans, although it is known that they are not negligible. There are better data on the distances rats can swim, allowing estimates to be made of the risk of reinvasion of islands close to source populations. Biosecurity prioritization must take place across all rat-free islands, balancing the likelihood and impact of rat establishment. Dense grids of poison bait stations are not preferable for preventing rat invasion. Instead, surveillance systems that integrate multiple device types appear to be best for intercepting invading rats, but must be tested to ensure they are effective. This can be done by releasing a controlled number of monitored rats onto a rat-free island. Islands can now be maintained rat-free despite non-negligible reinvasion rates; however, in some cases islands must be managed within a larger meta-population context and eradication may never be achieved

Data from: Exploring the interaction of avian frugivory and plant spatial heterogeneity and its effect on seed dispersal kernels using a simulation model

Seed dispersal by avian frugivores is one of the key processes influencing plant spatial patterns, but may fail if there is disruption of plant-frugivore mutualisms, such as decline in abundance of dispersers, fragmentation of habitat, or isolation of individual trees. We used simulation model experiments to examine the interaction between frugivore density and behaviour and the spatial arrangement of fruiting plants and its effect on seed dispersal kernels. We focussed on two New Zealand canopy tree species that produce large fruits and are dispersed predominantly by one avian frugivore (Hemiphaga novaeseelandiae). Although the mean seed dispersal distance decreased when trees became more aggregated, there were more frugivore flights between tree clusters, consequently stretching the tails of the dispersal kernels. Conversely, when trees were less aggregated in the landscape, mean dispersal distances increased because seeds were deposited over larger areas, but the kernels had shorter tails. While there were no statistically meaningful changes in kernel parameters when frugivore density changed, decreases in density did cause a proportional reduction in the total number of dispersed seeds. However, birds were forced to move further when fruit availability and fruit ripening were low. Sensitivity analysis showed that dispersal kernels were primarily influenced by the model parameters relating to disperser behaviour, especially those determining attractiveness based on distance to candidate fruiting trees. Our results suggest that the spatial arrangement of plants plays an important role in seed dispersal processes – although tree aggregation curbed the mean seed dispersal distance, it was accompanied by occasional long distance events, and tree dispersion caused an increase in mean dispersal distance, both potentially increasing the probability of seeds finding suitable habitats for germination and growth. Even though low frugivore densities did not cause dispersal failure, there were negative effects on the quantity of seed dispersal because fewer seeds were dispersed

Quantifying the direct transfer costs of common brushtail possum dispersal using least-cost modelling: a combined cost-surface and accumulated-cost dispersal kernel approach.

Dispersal costs need to be quantified from empirical data and incorporated into dispersal models to improve our understanding of the dispersal process. We are interested in quantifying how landscape features affect the immediately incurred direct costs associated with the transfer of an organism from one location to another. We propose that least-cost modelling is one method that can be used to quantify direct transfer costs. By representing the landscape as a cost-surface, which describes the costs associated with traversing different landscape features, least-cost modelling is often applied to measure connectivity between locations in accumulated-cost units that are a combination of both the distance travelled and the costs traversed. However, we take an additional step by defining an accumulated-cost dispersal kernel, which describes the probability of dispersal in accumulated-cost units. This novel combination of cost-surface and accumulated-cost dispersal kernel enables the transfer stage of dispersal to incorporate the effects of landscape features by modifying the direction of dispersal based on the cost-surface and the distance of dispersal based on the accumulated-cost dispersal kernel. We apply this approach to the common brushtail possum (Trichosurus vulpecula) within the North Island of New Zealand, demonstrating how commonly collected empirical dispersal data can be used to calibrate a cost-surface and associated accumulated-cost dispersal kernel. Our results indicate that considerable improvements could be made to the modelling of the transfer stage of possum dispersal by using a cost-surface and associated accumulated-cost dispersal kernel instead of a more traditional straight-line distance based dispersal kernel. We envisage a variety of ways in which the information from this novel combination of a cost-surface and accumulated-cost dispersal kernel could be gainfully incorporated into existing dispersal models. This would enable more realistic modelling of the direct transfer costs associated with the dispersal process, without requiring existing dispersal models to be abandoned

Invasive Rodents on Tropical Islands: Eradication Recommendations from Mexico

Central to the growing field of island ecological restoration is the removal of invasive rodents. The lack of information on rodent tropical ecology is a limiting factor for the success of such eradication attempts on tropical islands worldwide. In Mexico, 14 successful rodent eradications have occurred, 6 of them on dry and wet tropical islands, and the others on temperate islands. All recent projects included research components in order to inform management strategies. Here we summarize the main research findings and management recommendations, using the case of Isabel Island to illustrate how efficacy and efficiency of conservation initiatives can be improved when informed by directed research

Stoat d-loop alignment

FASTA file containing the alignment of stoat (Mustela erminea) d-loop sequences from Europe and the haplotypes found in New Zealand (with genbank accession numbers)

Data from: An invasive non-native mammal population conserves genetic diversity lost from its native range

Invasive, non-native species are one of the major causes of global biodiversity loss. Although they are, by definition, successful in their non-native range, their populations generally show major reductions in their genetic diversity during the demographic bottleneck they experience during colonization. By investigating the mitochondrial genetic diversity of an invasive non-native species, the stoat Mustela erminea, in New Zealand and comparing it to diversity in the species’ native range in Great Britain, we reveal the opposite effect. We demonstrate that the New Zealand stoat population contains four mitochondrial haplotypes that have not been found in the native range. Stoats in Britain rely heavily on introduced rabbits Oryctolagus cuniculus as their primary prey and were introduced to New Zealand in a misguided attempt at biological control of rabbits, which had also been introduced there. While invasive stoats have since decimated the New Zealand avifauna, native stoat populations were themselves decimated by the introduction to Britain of Myxoma virus as a control measure for rabbits. We highlight the irony that while introduced species (rabbits) and subsequent biocontrol (myxomatosis) have caused population crashes of native stoats, invasive stoats in New Zealand, which were also introduced for biological control, now contain more genetic haplotypes than their most likely native source