Rodent populations on the northern Great Plains respond to weather variation at a landscape scale

Small rodent communities and their associated damage to wheat-groundnut agriculture systems

Abstract Rodents can cause significant damage to wheat-groundnut crops in developing countries, as well as to stored produce and infrastructure, affecting food security and income of small-holder farmers. Wheat (Triticum aestivum) and groundnuts (Arachis hypogea) are important cash crops for local farmers in Pakistan. Field experiments were performed to assess the extent of rodent damage to wheat-groundnut crops throughout their growth stages (i.e, germination, flowering/peg formation and maturity) in the agro-ecological zones of Pothwar Plateau, Pakistan. We used a quadrat method to record the number of damaged crop plants. On the basis of the trapping data four rodent species were captured from wheat-groundnut cropping systems which were responsible for causing damage, i.e., lesser bandicoot rat (Bandicota bengalensis) was the main species, followed by the short-tailed mole rat (Nesokia indica), the Indian gerbil (Tatera indica) and the bush rat (Golunda ellioti). In both crops, the maximum damage was recorded at crop maturity (10.7 and 14.4%, respectively). The lowest reported damage to wheat and groundnuts was at the germination stage (3.5% and 6.0%, respectively). The lower damage reported at germination could be due to availability of non-crop vegetation at field borders that may be a potential factor influencing damage. Our findings clearly show the considerable amount of damage caused by rodents to wheat-groundnut at maturity across all the agro-ecological zones of Pothwar and indicated that the small mammal composition was more related to maturity stage/season of crops, when the availability of food and climatic condition were favorable and having security under crop shelter. More detailed studies are needed to fully understand the population and breeding ecology of the relevant rodent pest species in relation to damage patterns to optimize management beyond individual structural measures.

Mapping the Relative Habitat Quality Values for the Burrowing Owls (Athene cunicularia) of the Canadian Prairies Using an Innovative Parameterization Approach in the InVEST HQ Module

The range and population of Burrowing Owls (BOs) are declining in the Canadian Prairies. Multiple anthropogenic sources of degradation (threat) are attributed to this trend. Yet, the cumulative degradation caused by these sources has not been quantified across this landscape. Using the InVEST Habitat Quality (HQ) module and a novel approach to parameterize the relative sensitivity scores in this framework, we quantified, mapped, and evaluated the relative HQ values for these species in the prairies. The results illustrate significant differences in the HQ values between the current range and areas within the historical range of these species that do not spatially intersect with their current spatial extent. However, the variations of HQ values are not statistically significant under the different spatial scenarios considered across the current breeding grounds. Nevertheless, the results within the specific land use/cover categories illustrate meaningful variations in the HQ values across the current range of these species. Our findings suggest that the existing declining trends could only be attributed to the synergistic impact of the considered threats and other factors undermining the essential ecological processes for these birds. The results also highlight the importance of expanding the spatial extent of the existing conservation measures to prevent further loss of these charismatic migratory birds from the prairie landscape. A good starting point is to consider the HQ change index, a measure defined to illustrate the relative habitat degradation under different sources of degradation. Further studies are still required to determine the spatiotemporal impacts of all sources of degradation on the habitat of these endangered species in Canada and across their global range.

Movement patterns and home ranges of male and female Snowy Owls (Bubo scandiacus) wintering on the Canadian prairies

Meeting energy requirements during the nonbreeding season is important for many animals and some defend winter territories to secure a food supply. In birds of prey, females, the larger and competitively dominant sex, may monopolize areas with higher prey abundance than males. We thus predicted that female Snowy Owls (Bubo scandiacus (Linnaeus, 1758)), which might acquire the high-quality habitats and individuals in better body condition, would be able to persist on smaller home ranges, travel shorter distances, and spend proportionally more time on a home range than males, during the winter. On the prairies in central Saskatchewan, we deployed satellite transmitters on 11 male and 12 female Snowy Owls over two winters. There were no significant differences between the sexes in home-range size or the amount of travelling during the winter months. Mean first home range (95% minimum convex polygon) size was 54.4 km2 for males, 31.9 km2 (estimated marginal means) for females, and 53.8 km2 for the sexes combined. However, within sexes, home-range size was negatively correlated with body condition as predicted. A lack of defense of home-range perimeters against conspecifics could increase variation in home-range size and movement patterns and reduce differences between the sexes.

A damped precipitation-driven, bottom-up model for deer mouse population abundance in the northwestern United States

Small-mammal population densities can be regulated by bottom-up (food availability) and top-down (predation) forces. In 1993, an El Niño Southern Oscillation event was followed by a cluster of human hantavirus with pulmonary syndrome in the southwestern United States. An upward trophic cascade hypothesis was proposed as an explanation for the outbreak: Increased plant productivity as a consequence of El Niño precipitations led to an unusual increase in distribution and abundance of deer mice (Peromyscus maniculatus; reservoir host of Sin Nombre virus). Could such drastic events occur in mesic habitats, where plant productivity in response to climate conditions is likely to be much less dramatic? In this work, we investigate to what extent deer mouse populations follow a precipitation-driven, bottom-up model in central and western Montana and discuss important conditions for such a model to be possible. We found positive correlations between deer mouse abundance and on-the-ground measured plant productivity with a several-month lag in three of six study sites. This effect was weaker when deer mouse populations were more abundant, indicating density-dependent effects. Dispersal resulting from territoriality may be important in attenuating local density increments in spite of high food availability. In addition, there is evidence that population abundance in the study area could respond to other abiotic factors. In particular, precipitation in the form of snow may reduce deer mice survival, thus compensating the benefits of improved plant productivity. Deer mouse populations in Montana study sites follow complex dynamics determined by multiple limiting factors, leading to a damped precipitation-driven bottom-up regulation. This prevents dramatic changes in rodent abundances after sudden increments of food availability, such as those observed in other regions.

Seasonal weather patterns drive population vital rates and persistence in a stream fish

Climate change affects seasonal weather patterns, but little is known about the relative importance of seasonal weather patterns on animal population vital rates. Even when such information exists, data are typically only available from intensive fieldwork (e.g., mark-recapture studies) at a limited spatial extent. Here, we investigated effects of seasonal air temperature and precipitation (fall, winter, and spring) on survival and recruitment of brook trout (Salvelinus fontinalis) at a broad spatial scale using a novel stage-structured population model. The data were a 15-year record of brook trout abundance from 72 sites distributed across a 170-km-long mountain range in Shenandoah National Park, Virginia, USA. Population vital rates responded differently to weather and site-specific conditions. Specifically, young-of-year survival was most strongly affected by spring temperature, adult survival by elevation and per-capita recruitment by winter precipitation. Low fall precipitation and high winter precipitation, the latter of which is predicted to increase under climate change for the study region, had the strongest negative effects on trout populations. Simulations show that trout abundance could be greatly reduced under constant high winter precipitation, consistent with the expected effects of gravel-scouring flows on eggs and newly hatched individuals. However, high-elevation sites would be less vulnerable to local extinction because they supported higher adult survival. Furthermore, the majority of brook trout populations are projected to persist if high winter precipitation occurs only intermittently (≤3 of 5 years) due to density-dependent recruitment. Variable drivers of vital rates should be commonly found in animal populations characterized by ontogenetic changes in habitat, and such stage-structured effects may increase population persistence to changing climate by not affecting all life stages simultaneously. Yet, our results also demonstrate that weather patterns during seemingly less consequential seasons (e.g., winter precipitation) can have major impacts on animal population dynamics.