Abiotic conditions mediate intraguild interactions between mammalian carnivores

Intraguild (IG) interactions are common among mammalian carnivores, can include intraguild predation (IGP) and interspecific killing (IK), and are often asymmetrical, where a larger more dominant species (IG_predator ) kills a smaller one (IG_prey ). According to ecological theory, the potential for an IG_predator and IG_prey to coexist depends on whether the direct consumptive benefits for the IG_predator are substantial (IGP) or insignificant (IK), the extent to which the IG_prey is the superior exploitative competitor on shared prey resources, and overall ecosystem productivity. We used resource selection models and spatially explicit age and harvest data for two closely related mesopredators that engage in IG interactions, American martens (Martes americana; IG_prey ) and fishers (Pekania pennanti; IG_predator ), to identify drivers of distributions, delineate areas of sympatry and allopatry, and explore the role of an apex predator (coyote; Canis latrans) on these interactions. Model selection revealed that fisher use of this landscape was strongly influenced by late winter abiotic conditions, but other bottom-up (forest composition) and top-down (coyote abundance) factors also influenced their distribution. Overall, fisher probability of use was higher where late winter temperatures were warmer, snowpack was deeper, and measures of productivity were greater. Martens were constrained to areas of the landscape where the probability of fisher use, coyote abundance, and productivity were low and selected for forest conditions that presumably maximized prey availability. Marten age data indicated an increased proportion of juveniles outside of the predicted area of sympatry, suggesting that few animals survived >1.5 years in this area that supported higher densities of fishers and coyotes. Consistent with asymmetrical IG interaction theory, the IG_predator (fishers and, to a lesser degree, coyotes) competitively excluded the IG_prey (martens) from more productive, milder temperature habitats, whereas IG_predators and IG_prey coexisted in low productivity environments, where a combination of abiotic and biotic conditions enabled the IG_prey to be the superior exploitative competitor.

Sex-specific graphs: Relating group-specific topology to demographic and landscape data

Sex-specific genetic structure is a commonly observed pattern among vertebrate species. Facing differential selective pressures, individuals may adopt sex-specific life history traits that ultimately shape genetic variation among populations. Although differential dispersal dynamics are commonly detected in the literature, few studies have used genetic structure to investigate sex-specific functional connectivity. The recent use of graph theoretic approaches in landscape genetics has demonstrated network capacities to describe complex system behaviours where network topology represents genetic interaction among subunits. Here, we partition the overall genetic structure into sex-specific graphs, revealing different male and female dispersal dynamics of a fisher (Pekania [Martes] pennanti) metapopulation in southern Ontario. Our analyses based on network topologies supported the hypothesis of male-biased dispersal. Furthermore, we demonstrated that the effect of the landscape, identified at the population level, could be partitioned among sex-specific strata. We found that female connectivity was negatively correlated with snow depth, whereas connectivity among males was not. Our findings underscore the potential of conducting sex-specific analysis by identifying landscape elements or configuration that differentially promotes or impedes functional connectivity between sexes, revealing processes that may otherwise remain cryptic. We propose that the sex-specific graph approach would be applicable to other vagile species where differential sex-specific processes are expected to occur.

Ranging behaviour and movements of the red fox in remnant forest habitats

Context The Eurasian red fox (Vulpes vulpes) is a widespread pest in mixed agricultural and remnant forest habitats in southern Australia, and is controlled most commonly with baits containing poison (1080) to protect both agricultural and ecological assets. An understanding of fox movements in such habitats should assist in the strategic placement of baits and increase bait encounters by foxes across the landscape, thus improving the success of control efforts. Aims We seek to understand the ranges, movements and habitat use of foxes to aid the development of effective management plans. The fate of tracked animals was examined during a control program. Methods We radio-tracked 10 foxes using VHF transmitters and three foxes using GPS receivers during control operations in a remnant forest area near Dubbo, New South Wales. We used VHF location fixes to estimate fox range areas and GPS fixes to describe temporal and spatial aspects of fox movements and range use, focal points of activity and potential bait encounters. Selection of forest versus cleared areas was assessed, as was the impact of control operations on collared foxes. Key results Range areas (mean ± s.e.; 95% minimum convex polygon) for VHF- and GPS-tracked foxes were 420 ha ± 74 and 4462 ha ± 1799 respectively. Only small parts of range areas were visited on a daily basis, with little overlap. Animals were often within 200 m of roads and crossed or travelled on roads more than expected. At least 75% of collared foxes were probably poisoned in the control program. Conclusions Foxes occupy large ranges and move long distances in the study region, with little daily overlap, so successful defence of range areas is unlikely. Control efforts successfully poisoned foxes but also limited data collection because of reduced tracking periods. Implications The large and variable areas occupied by foxes suggested that control efforts need to be on-going, coordinated across the landscape, and use a minimum bait density of 0.5 baits per 100 ha in remnant forest habitat to ensure that gaps are minimised. Control operations should target roads and forest edges for bait placement, and increase the time that baits are available, to increase fox encounters and maximise the success of control efforts.

An evaluation of territory mapping to estimate fisher density

We evaluated winter-territory mapping as a method for estimating fisher (Martes pennanti) density in a 210-km2 survey area in north-central Massachusetts in 1994 and 1995 by comparing estimates with simultaneous camera mark–resight estimates. Assuming intrasexual territoriality and accounting for all occupied habitat, territories of resident radio-marked fishers were mapped (mean = 54% of all territories in the study area), and those of unmarked resident fishers were identified from tracks and photographs. The total number indicated a population of 40 (19/100 km2) and 49 (23/100 km2) residents for 1994 and 1995, respectively. Results from replicated automatic-camera capture–mark–resight surveys suggested slightly higher total numbers and densities of fishers in 1994 (44.5; 21/100 km2) and 1995 (52.9; 25/100 km2), but these estimates likely also included nonresident juveniles. Territory mapping and automatic-camera mark–resight methods resulted in very similar population estimates, but both require large numbers of radio-marked fishers to effectively detect small population changes (e.g., such as the 20% observed in this study). Individually marking animals would enhance mark–recapture estimates.

Spacing patterns and territoriality of the stone marten

Sixteen stone martens (Martes foina) were intensively radio-tracked in central Italy in order to assess their spacing patterns. Home-range sizes and distances travelled per night were analysed with respect to sex, age, season, and habitat. Intrasexual territoriality is confirmed for the species; home-range edges appeared to be determined by the dispersion of neighbours' territories. Home-range size was positively correlated with the presence of woodland (less abundant and more dispersed resources). Males travelled longer distances than females, although home-range sizes did not differ significantly by sex; males did not move more during the rutting season than in other seasons. Subadults were tolerated by adults for varying periods, then in some cases they started an exploring phase before settling into a vacant territory. Stone martens' spacing patterns were affected by sex, age, social interactions, and resources. In particular, social patterns appear to be a key influencing factor, as territoriality, parental behaviour, mating interactions, and dispersal of young can account for site fidelity, dispersion of home ranges, and distance travelled. In particular, our data indicate the importance of the extended relationship between the mating pair, which is probably related to male parental investment, in determining the spacing patterns of the species.