David M. Forsyth

Propagule size and the relative success of exotic ungulate and bird introductions to New Zealand.

We investigated factors affecting the success of 14 species of ungulates introduced to New Zealand around 1851–1926. The 11 successful species had a shorter maximum life span and were introduced in greater numbers than the three unsuccessful species. Because introduction effort was confounded with other life‐history traits, we examined whether independent introductions of the same species were more likely to succeed when a greater number of individuals were introduced. For the six species with introductions that both succeeded and failed, successful introductions always involved an equal or greater number of individuals than unsuccessful introductions of the same species. For all independent introductions, there was a highly significant relationship between the number of individuals introduced and introduction success. When data for ungulate and bird introductions to New Zealand were combined, a variable categorizing species as ungulate or bird was a highly significant predictor of introduction success, after variation in introduction effort was controlled. For a given number of individuals introduced, ungulates were much more likely to succeed than birds.

Using presence-only and presence-absence data to estimate the current and potential distributions of established invasive species.

1.Predicting the current and potential distributions of established invasive species is critical for evaluating management options, but methods for differentiating these distributions have received little attention. In particular, there is uncertainty among invasive species managers about the value of information from incidental sightings compared to data from designed field surveys. This study compares the two approaches, and develops a unifying framework, using the case of invasive sambar deer Cervus unicolor in Victoria, Australia. 2.We first used 391 incidental sightings of sambar deer and 12 biophysical variables to construct a presence-only habitat suitability model using Maxent. We then used that model to stratify field sampling, with proportionately greater sampling of cells with high predicted habitat suitability. Field sampling, consisting of faecal pellet surveys, sign surveys and camera trapping, was conducted in 80 4-km2 grid cells. A Bayesian state-space occupancy model was used to predict probability of suitable habitat from the field data. 3.The Maxent and occupancy models predicted similar spatial distributions of habitat suitability for sambar deer in Victoria and there was a strong positive correlation between the rankings of cells by the two approaches. The congruence of the two models suggests that any spatial and detection biases in the presence-only data were relatively unimportant in our study. 4.We predicted the extent of suitable habitat from the occupancy model using a threshold that gave a false negative error rate of 0·05. The current distribution was the suitable habitat within a kernel that had a 99·5% chance of including the presence locations pooled from incidental sightings and field surveys: the potential distribution was suitable habitat outside that kernel. Several discrete areas of potential distribution were identified as priorities for surveillance monitoring with the aim of detecting and managing incursions of sambar deer. 5.Synthesis and applications.Our framework enables managers to robustly estimate the current and potential distributions of established invasive species using either presence-only and/or presence–absence data. Managers can then focus control and/or containment actions within the current distribution and establish surveillance monitoring to detect incursions within the potential distribution.

Modeling the Relationship Between Fecal Pellet Indices and Deer Density

Abstract Although fecal pellet counts have been widely used to index changes in deer abundance in forests, few studies have modeled the relationship between the indices and deer density. We examined the relationships between 3 fecal pellet indices (total pellets, pellet groups, and pellet frequency) and the density of deer (primarily red deer [Cervus elaphus scoticus]) in 20 enclosures in the North and South islands of New Zealand. In each enclosure we estimated the 3 indices on 30 randomly located 150-m transects, with each transect having 30 circular plots of 3.14 m2. We developed 4 candidate models (1 linear and 3 nonlinear) to describe the relationship between the indices and deer density. We used a Bayesian analysis to account for uncertainty in the estimates of deer abundance and to facilitate fitting models that included random transect effects. The 4 models explained the relationship between the 3 indices and deer density similarly well. The slopes of the linear relationships between the 3 indices and deer density were positive. Our results suggest that fecal pellet counts may be useful indices of deer abundance.

Diet and diet preferences of introduced ungulates (Order: Artiodactyla) in New Zealand

Abstract Understanding the diet and diet preferences of introduced ungulates is a crucial step towards modelling their trophic interactions and managing their impacts. We collated information on the diet of 8 introduced ungulates (Order: Artiodactyla) from 19 studies in New Zealand. A total of 185 indigenous plant genera (379 species) was recorded as eaten. Five studies assessed diet choice by 4 ungulate species (red deer, fallow deer, white‐tailed deer, and feral goats) in forests. Of the 60 plant species or genera present in two or more studies, 8 were always “preferred” (eaten more than expected from their availability) and 15 were always “avoided” (proportionately less eaten than was available); most others were “not selected” (eaten in proportion to their availability). From these data we constructed a table of preferences for commonly occurring forest plant species. Ungulates preferred woody species with low foliar lignin. Although there was no significant relationship between diet choice and foliar N, avoided species all had low foliar N. Ungulate preferences for fern species were closely related to foliar P concentrations, but not to foliar N concentrations. Since relatively few plant species were consistently preferred, we conclude that many native species have neutral resistance to ungulate herbivory, a conclusion that is contrary to the notion that the New Zealand flora is especially vulnerable to introduced herbivores.

Control of pest mammals for biodiversity protection in Australia. II. Reliability of knowledge

Foxes, wild dogs, feral cats, rabbits, feral pigs, and feral goats are believed to have deleterious impacts on native biodiversity in Australia. However, although considerable resources have been expended controlling these six pest species, there are few reliable estimates of the effects of pest control on native biodiversity. We first show why reliable knowledge of the effects of pest animal control operations can be gained only by adopting proper experimental designs (i.e. treatment and non-treatment areas, replication, and random assignment of treatment and non-treatment areas) and monitoring of both the pest and biodiversity. We then review the design of 1915 pest control actions conducted with the aim of protecting native biodiversity in Australia during 1990-2003. Most (67.5%) pest control actions consisted of a single treatment area without monitoring of either the pest or biodiversity. Only 2.4% of pest control actions had one or more treatment and non-treatment areas, and very few treatment and non-treatment areas (0.3%) were randomly assigned. Replication of treatment and non-treatment areas occurred in only 1.0% of pest control actions. The field of wildlife management has been strongly criticised for its slow adoption of the tenets of experimentation to examine the effects of management actions, and our results show that this criticism applies to mammalian pest control in Australia. Until the principles of experimental design are adopted, knowledge of the effects of mammalian pest control in Australia will remain unreliable.

Control of pest mammals for biodiversity protection in Australia. I. Patterns of control and monitoring.

Foxes, wild dogs, feral cats, rabbits, feral pigs and feral goats are believed to have deleterious impacts on native biodiversity in Australia. However, although considerable resources have been expended controlling these six species, little is known about national patterns and costs of control and monitoring. We therefore conducted a survey of pest-control operations undertaken by conservation-focused organisations in Australia. A total of 1306 control operations were reported, with most conducted during 1998-2003: there was little information prior to 1990. Foxes and rabbits were the most, and feral cats the least, frequently controlled pest species. The total area on which control was undertaken in 2003, the year for which most information was available, ranged from ~0.4 × 10 4 km 2 for feral cats to ~10.7 × 10 4 km 2 for foxes. A wide range of techniques and intensities were used to control each of the six species. The estimated cost of labour expended on control in 2003 ranged from

Interspecific and Geographic Variation in the Diets of Sympatric Carnivores: Dingoes/Wild Dogs and Red Foxes in South-Eastern Australia

0.4 × 10 6 for feral cats to

A SUBSTANTIAL ENERGETIC COST TO MALE REPRODUCTION IN A SEXUALLY DIMORPHIC UNGULATE

5.3 × 10 6 for foxes. Monitoring of the pest or biodiversity occurred in 50-56% of control actions in which foxes, wild dogs and feral cats were targeted, but only 22-26% of control actions in which rabbits, feral pigs and feral goats were targeted. Our results are discussed in relation to previous studies of pest animal control and monitoring in Australia.

Diets of native and introduced mammalian herbivores in shrub-encroached grassy woodland, south-eastern Australia.

Dingoes/wild dogs (Canis dingo/familiaris) and red foxes (Vulpes vulpes) are widespread carnivores in southern Australia and are controlled to reduce predation on domestic livestock and native fauna. We used the occurrence of food items in 5875 dingo/wild dog scats and 11,569 fox scats to evaluate interspecific and geographic differences in the diets of these species within nine regions of Victoria, south-eastern Australia. The nine regions encompass a wide variety of ecosystems. Diet overlap between dingoes/wild dogs and foxes varied among regions, from low to near complete overlap. The diet of foxes was broader than dingoes/wild dogs in all but three regions, with the former usually containing more insects, reptiles and plant material. By contrast, dingoes/wild dogs more regularly consumed larger mammals, supporting the hypothesis that niche partitioning occurs on the basis of mammalian prey size. The key mammalian food items for dingoes/wild dogs across all regions were black wallaby (Wallabia bicolor), brushtail possum species (Trichosurus spp.), common wombat (Vombatus ursinus), sambar deer (Rusa unicolor), cattle (Bos taurus) and European rabbit (Oryctolagus cuniculus). The key mammalian food items for foxes across all regions were European rabbit, sheep (Ovis aries) and house mouse (Mus musculus). Foxes consumed 6.1 times the number of individuals of threatened Critical Weight Range native mammal species than did dingoes/wild dogs. The occurrence of intraguild predation was asymmetrical; dingoes/wild dogs consumed greater biomass of the smaller fox. The substantial geographic variation in diet indicates that dingoes/wild dogs and foxes alter their diet in accordance with changing food availability. We provide checklists of taxa recorded in the diets of dingoes/wild dogs and foxes as a resource for managers and researchers wishing to understand the potential impacts of policy and management decisions on dingoes/wild dogs, foxes and the food resources they interact with.

Movements and habitat selection by wild dogs in eastern Victoria

Whereas the energetic costs of reproduction for female ungulates are well documented, those of males are not. We investigated age- and sex-specific changes in the kidney fat reserves of a large sample of Himalayan tahr (Hemitragus jemlahicus), a highly sexually dimorphic and polygynous mountain ungulate, during and following the mating period. Subadult male tahr (2–4 years old) obtain copulations opportunistically by “coursing,” whereas adult males (>4 years old) spend more time traveling and searching for females, and obtain copulations after engaging in more time-consuming “tending” and “blocking” displays. If there is a cost to these reproductive behaviors, we predicted that (1) the kidney fat index (KFI) of reproductive males (≥2 years old) should decline during the mating period relative to females and nonreproductive males, and (2) that the KFI of adult males should decline more than that of subadult males. We formulated our predictions into a series of candidate models, including three covariates also likely to affect fat reserves, and compared support for these models using Akaikes Information Criterion (AIC). The best-fitting model revealed that fat reserves in females and nonreproductive males changed similarly: Fat reserves increased during the mating period, in late autumn and early winter, reached a peak in mid-winter, and then declined throughout the remainder of winter and early spring. In contrast, the fat reserves of reproductive males declined during the mating period, as predicted, and remained low throughout winter. The extent of decline in fat reserves was greater in adult males than in subadult males, also as predicted. Our results strongly imply that male tahr incur a substantial energetic cost for engaging in reproduction and that they trade off reproductive success with reduced body condition during winter, which may lower survival.