Integrating plant stoichiometry and feeding experiments: state-dependent forage choice and its implications on body mass

Intraspecific feeding choices account for a large portion of herbivore foraging in many ecosystems. Plant resource quality is heterogeneously distributed, affected by nutrient availability and growing conditions. Herbivores navigate landscapes, making feeding decisions according to food qualities, but also energetic and nutritional demands. We test three non-exclusive foraging hypotheses using the snowshoe hare (Lepus americanus): 1) herbivores feeding choices and body conditions respond to intraspecific plant quality variation, 2) feeding responses are mitigated when energetic demands are high, and 3) feeding responses are inflated when nutritional demands are high. We measured black spruce (Picea mariana) nitrogen, phosphorus, and terpene compositions, as indicators of quality, within a snowshoe hare trapping grid and found plant growing conditions to explain spruce quality variation (R2 < 0.36). We then offered two qualities of spruce (H1) from the trapping grid to hares in cafeteria-style experiments and measured their feeding and body condition responses (n = 75). We proxied energetic demands (H2) with ambient temperature and coat insulation (% white coat) and nutritional demands (H3) with the spruce quality (nitrogen and phosphorus content) in home ranges. Hares that preferred higher-quality spruce lost less weight during experiments (p = 0.018). The results supported our energetic predictions: hares in colder temperatures and with less-insulative coats (lower % white) consumed more spruce and were less selective towards high-quality spruce. Collectively, we found variation in plant growing conditions within herbivore home ranges substantial enough to affect herbivore body conditions, but any plant-herbivore interactions are also mediated by animal energetic states.

Movement patterns of the grey field slug (Deroceras reticulatum) in an arable field

We report the results of an experiment on radio-tracking of individual grey field slugs in an arable field and associated data modelling designed to investigate the effect of slug population density in their movement. Slugs were collected in a commercial winter wheat field in which a 5x6 trapping grid had been established with 2m distance between traps. The slugs were taken to the laboratory, radio-tagged using a recently developed procedure, and following a recovery period released into the same field. Seventeen tagged slugs were released singly (sparse release) on the same grid node on which they had been caught. Eleven tagged slugs were released as a group (dense release). Each of the slugs was radio-tracked for approximately 10 h during which their position was recorded ten times. The tracking data were analysed using the Correlated Random Walk framework. The analysis revealed that all components of slug movement (mean speed, turning angles and movement/resting times) were significantly different between the two treatments. On average, the slugs released as a group disperse more slowly than slugs released individually and their turning angle has a clear anticlockwise bias. The results clearly suggest that population density is a factor regulating slug movement.

Contact rates with nesting birds before and after invasive snake removal: estimating the effects of trap-based control

Invasive predators are responsible for almost 60% of all vertebrate extinctions worldwide with the most vulnerable faunas occurring on islands. The brown treesnake (Boigairregularis) is a notorious invasive predator that caused the extirpation or extinction of most native forest birds on Guam. The success of avian reintroduction efforts on Guam will depend on whether snake-control techniques sufficiently reduce contact rates between brown treesnakes and reintroduced birds. Mouse-lure traps can successfully reduce brown treesnake populations at local scales. Over a 22-week period both with and without active snake removal, we evaluated snake-trap contact rates for mouse- and bird-lure traps. Bird-lure traps served as a proxy for reintroduced nesting birds. Overall, mouse-lure traps caught more snakes per trap night than did bird-lure traps. However, cameras revealed that bird-lure traps had a snake contact rate almost 15 times greater than the number of successfully captured snakes. Snakes that entered bird-lure traps tended to be larger and in better body condition and were mostly captured in bird-lure traps, despite numerous adjacent mouse-lure traps. Traps placed along grid edges caught more snakes than interior traps, suggesting continuous immigration into the trapping grid within which bird-lure traps were located. Contact between snakes and bird-lure traps was equivalent before and after snake removal, suggesting mouse-lure traps did not adequately reduce the density of snakes that posed a risk to birds, at least at the timescale of this project. This study provides evidence that some snakes exhibit prey selectivity for live birds over live mouse lures. Reliance on a single control tool and lure may be inadequate for support of avian reintroductions and could lead to unintended harvest-driven trait changes of this invasive predator.

Diet and breeding of the rufous spiny bandicoot Echymipera rufescens australis, Iron Range, Cape York Peninsula

A population of the rufous spiny bandicoot Echymipera rufescens australis was studied for 14 months by live-trapping, and diets were determined by faecal analysis. The population had a high density (approximately 48 individuals on a trapping grid of 2.25 ha). A wide variety of foods were eaten, but fruits and seeds contributed the largest proportion of material to faeces, followed by invertebrates, fungi and dicot plants. Echymipera rufescens may potentially be a significant seed disperser for some plants, such as Pandanus zea. There was a short breeding season, with births occurring between December and March. Females produced one or two litters per year. Mean litter size was just under three, and litter size increased with the mother?s mass. Females produced a mean of 4.9 young per year. We conclude that although E. rufescens is a ?typical? bandicoot in that it is omnivorous and has high fecundity, it is more frugivorous and has a somewhat lower reproductive rate than other Australian bandicoots.

How effective are grid trapping, oil cards and track boards in monitoring bush rat populations?

Monitoring populations is a key component of wildlife conservation and management. This study aimed to evaluate the effectiveness of abundance indices used for estimating populations of the bush rat Rattus fuscipes. The study was conducted on Fraser Island, Queensland, Australia. A trapping grid consisting of 5 x 5 trap stations, 20 m apart, was used because this configuration was typical of those used for small mammal trapping in Australia. Capture-recapture data were collected from trapping 18 grids over four consecutive nights, immediately followed by two consecutive nights of conducting oil card and track indices. On 11 grids, model Mb was selected by the CAPTURE model selection procedure, indicating increased capture probability after first capture (trap-happy). The estimated trappable population size (�) on these grids was not precise with the standard error on average being 28% of �. On the other seven grids, the number of animals caught was too small (<3) to estimate model parameters.. The main problem of the grid trapping was that some grids caught too few animals to estimate �. Our data suggest that the minimum grid area for estimating useful � is one that would catch more than 8 individuals. The minimum grid area varies depending on the density of rats and should be determined by a pilot trapping study. The number of trapping occasions can be increased until a specific precision of � is reached. The correlation between track index and � was near the 0.05 significance level indicating tracks are potentially a reliable index for monitoring bush rat populations. The oil card index was not significantly correlated with �.

Estimating the probability of eradication of painted apple moth from Auckland

A set of assumptions can be used to estimate the confidence that a continuing lack of detection reflects successful eradication of a pest population This approach is applied to the painted apple moth (Teia anartoides) in Auckland New Zealand based on its known population biology and sterile insect recapture results The analysis suggests that it is extremely unlikely that any wild population might have survived near the core trapping areas beyond mid January 2004 but that there was a significant chance that a small wild population could have remained undetected until then in less intensively trapped areas The moth trapped in Mt Eden in January 2004 plausibly indicates an undetected population there but a continued lack of trap catches over the subsequent year suggests that it is very unlikely that any wild populations now remain undetected within the trapping grid This analysis could be easily adapted for other species targeted for eradication

Effects of trap position, trap history, microhabitat and season on capture probabilities of small mammals in a wet eucalypt forest

In this study, we use data drawn from a series of trapping events on four 0.5-ha trapping grids surveyed in the wet eucalypt forests of central Victoria, south-eastern Australia, to identify relationships between capture probabilities and several factors of interest for three species of small mammals that are common throughout the forests of this region: the agile antechinus (Antechinus agilis), the dusky antechinus (Antechinus swainsonii) and the bush rat (Rattus fuscipes). The design of our study – four regular trapping grids – generated spatio-temporal data with binary responses and many covariates. We used powerful and relatively new statistical methodology to deal with the spatio-temporal dependence patterns in the data – analytical problems that are common in trapping data such as these modelled here. Although A. agilis, A. swainsonii and R. fuscipes are among the best studied mammals in Australia, our data analysis produced new perspectives on their probability of being captured. In particular, we quantified how capture probability is affected by trap position within a trapping grid, day of capture in a sequence of trapping days, history of trap occupancy over time by different species and sexes of those species, time of the year or season, and microhabitat attributes. Our insights are discussed in terms of their consequences for trapping protocols that might be applied in the field.

Home range and microhabitat use by the long-footed potoroo, Potorous longipes

Long-footed potoroos were studied at two widely-separated sites in Victoria, one in regenerating eucalypt forest in East Gippsland and the other in old-growth forest in Central Gippsland. Trap-revealed use of microhabitat at Bellbird (East Gippsland) showed a change from the 1980s to 1990s, with an increased amount of foraging in more open, drier areas. Over the same period, there was an increase in the size of home range of animals and a near-doubling of the minimum numbers of animals known to be alive on the trapping grid at Bellbird. These changes occurred over a period when few environmental changes occurred on the grid other than control of feral predators. Radio-tracking data from 12 animals at the two sites showed a similar trend in use of microhabitat by most animals, but there was individual variation. Differences between the sites were that home-range size was smaller at the Riley trapping grid (Central Gippsland), there was greater overlap in home range, and animals there foraged for significantly shorter bouts. This confirmed earlier speculation from reproductive and dietary studies that there is better quality habitat at Riley, but the sites were so dissimilar that differences in home range and foraging could not be ascribed to either the logging regime or to geographical differences between the sites.