Abundance Of Mammalian Predators Research Articles

Introduced mammalian predators influence demography and trait variation of a New Zealand stag beetle

Most species co-evolve with their predators and develop strategies to avoid predation. This is not possible when a novel predator invades an environment. Native residents must quickly adapt to their new predator or face local extinction. Intense competition for mating opportunities exerts significant selective pressure that can drive the evolution of exaggerated structures across taxa. However, these elaborate traits can elevate the risk of predation for some organisms. In the present study, we observe the effect that rats have had on a population of endemic New Zealand stag beetles, Geodorcus helmsi. Rats in Rakiura | Stewart Island often prey on stag beetles, taking them to a sheltered area to eat them and discard any uneaten parts of the beetle, namely the head and mandibles. We compared the head size, mandible size and numbers of predated and non-predated male and female beetles in three sites in Rakiura | Stewart Island that differ in their abundance of mammalian predators. We found that the population demography and the size of the beetles differed significantly between sites. Additionally, we determined whether predated beetles were larger than non-predated beetles, across multiple years, regardless of site. We found that overall the predated specimens were larger than the non-predated beetles. The trends found here suggest that exaggeration of the male mandibles increases the predation risk of these iconic beetles, acting as a limit to mandible size.Implications for insect conservationOur results show for the first time the effect that novel predators can have on a population of animals with exaggerated sexually selected traits. The presence of novel predators can cause a shift in both population demography and trait distribution.

Decline of the boreal willow grouse (Lagopus\xa0lagopus) has been accelerated by more frequent snow-free springs

Climate change has influenced a range of species across the globe. Yet, to state a noted decline in the abundance of a given species as a consequence of a specific environmental change, for instance, spatially explicit long-term data are a prerequisite. This study assessed the extent to which prolonged snow-free periods in autumn and spring have contributed to the decline of the willow grouse, the only forest grouse changing into a white winter plumage. Time-series data of willow grouse numbers from summer surveys across the study area were integrated with local data on weather (snow cover), mammalian predator abundance and hunting intensity. Modelling was conducted with a hierarchical Bayesian Poisson model, acknowledging year-, area- and location-specific variability. The results show that while willow grouse numbers had decreased continuously across the study landscapes, the decrease was accelerated at the sites where, and during the years when the preceding April was the most snow-free. This indicates a mismatch between the change into a white winter plumage and the presence of snow, turning the bird into an ill-camouflaged prey. The results thus also confirm past hypotheses where local declines of the species have been attributed to prolonged snow-free periods. Across our study area, autumns and springs have become more snow-free, and the trend has been predicted to continue. Thus, in addition to conservation actions, the future of a species such as the willow grouse is also dependent on its ability to adapt to the changed environmental conditions.

Do prey densities determine preferences of mammalian predators for habitat edges in an agricultural landscape?

Increased predation pressure along habitat edges is often associated with increased predator activity. However, factors affecting predator affinity for habitat edges remain largely untested. Here, we tested the hypothesis that the high prevalence of mammalian predators along habitat edges arises due to increased abundance of their principal prey – small mammals. Gradients in the abundance of carnivores and small mammals across a habitat edge gradient (secondary mixed forest interior vs. secondary mixed forest interior/grassland edge vs. grassland interior) were monitored during a 2-year survey performed in a fragmented central European landscape. Our data provide support for the hypothesis that a high abundance of carnivores in habitat edges was associated with increased numbers of small mammals. The abundance of mammalian predators and small mammals consistently increased in habitat edges. Moreover, prey densities tended to explain carnivore patch preferences even when statistically controlling for the effect of habitat type (edge vs. interior habitats), suggesting a direct causality between carnivore habitat preferences and actual prey density. Interestingly the small mustelids (least weasel, Mustela nivalis, and ermine stoat, Mustela erminea) exhibited lower flexibility in adjustment of their spatial activity according to prey densities, in contrast to remaining carnivores. We suppose that this pattern may be caused by differences in agility/home-range size or performance intraguild competition between small mustelids and remaining carnivore species.

Predation on wader nests in Europe

The population declines of waders in Europe are widely considered to have resulted from habitat loss and degradation due to agricultural changes. However, recent empirical evidence suggests that levels of predation on wader nests are unsustainably high in many cases, even in some situations where breeding habitat is otherwise favourable. We review the published and ‘grey’ literature on nest predation on waders in Europe and quantify the relative importance of the major predators. Nest cameras offer the least biased method of identifying and quantifying nest predators. A small number of camera studies, in combination with others utilizing nest temperature loggers, indicate that nocturnal/mammalian predators make the largest contribution to wader nest predation. More than half of site‐years or studies reviewed reported clutch failure rates of over 50% attributable to predation alone, a rate that is likely to be associated with declining populations, although parameters such as chick and adult survival will also affect population trends. Correlates of wader nest predation are documented, with time of season, field type and management, distance to habitat/field edge, wader nest density, and abundance of mammalian predators being most consistently identified. Future directions of research into wader productivity are discussed, and we suggest that studies quantify additional life‐history parameters such as chick survival, as well as examining the predator community, wherever possible.

The effect of scent-station precipitation covers on visitations by mammalian carnivores and eastern cottontails

Abstract The distribution and abundance of mammalian predators are difficult to monitor because of their elusive nature. One tool used to monitor predators is strategically placed tracking stations. Precipitation often renders tracking stations unreadable by obscuring tracks and other sign. In our study we sought to evaluate the feasibility of placing covers over stations to protect tracking surfaces from precipitation. Survival of the cover structures was negatively correlated with wind speed and positively correlated with woodlands. This suggested that covers might be best used in areas with low wind speeds and/or in forests or other sites that provide shelter from wind. Covers appeared to negatively affect visitations by coyotes (Canis latrans), bobcats (Lynx rufus), and eastern cottontails (Sylvilagus floridanus), but not raccoons (Procyon lotor) or Virginia opossums (Didelphis virginiana). Track quality was not substantially different for covered stations during light rain or snow.

Relative abundance of mammalian predators in the upper Waitaki Basin, South Island, New Zealand

An intensive predator trapping programme was implemented in the upper Waitaki Basin, New Zealand from October 1997 to January 1998. The aim of the programme was to prevent increased predation on vulnerable braided river fauna following decline in rabbits due to rabbit haemorrhagic disease (RHD). Fourteen sites were trapped using a standardised method, and trap catch results provided a relative index of predator abundance. In 101 650 trapnights, 1067 hedgehogs, 328 ferrets, 196 cats, 96 rats and 69 stoats were caught. Predator guilds varied among sites and guild composition tended to change through time; for example, stoat and rat catch rates increased. Cat and ferret catch rates increased in the last month of trapping, which suggested that juvenile dispersal and immigration by adult predators from surrounding areas were high. This study provides baseline information on predator abundance and predator guilds in the upper Waitaki Basin against which future trapping programmes can be compared, in order to assess changes in predator populations since the introduction of RHD.

Impact of Food and Predation on the Snowshoe Hare Cycle

Snowshoe hare populations in the boreal forests of North America go through 10-year cycles. Supplemental food and mammalian predator abundance were manipulated in a factorial design on 1-square-kilometer areas for 8 years in the Yukon. Two blocks of forest were fertilized to test for nutrient effects. Predator exclosure doubled and food addition tripled hare density during the cyclic peak and decline. Predator exclosure combined with food addition increased density 11-fold. Added nutrients increased plant growth but not hare density. Food and predation together had a more than additive effect, which suggests that a three-trophic-level interaction generates hare cycles.