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KEYWORDS: abundance estimation, age-at-harvest data, model evaluation, model Selection, numerical optimization, population reconstruction, residual analyses
Statistical population reconstruction can be a valuable tool for monitoring the status and trends of game populations at large spatial scales using age-at-harvest data. Despite their utility and increasing use in demographic studies, it is necessary that these models be evaluated before their results are applied. We recommend practitioners evaluate their fitted population models using a variety of approaches, including residual analyses, point-deletion techniques and sensitivity analyses, and we illustrate these techniques using several case studies. Although we stress the value of these quantitative procedures, the final evaluation criterion should be the biological realism of the estimated demographic parameters and trends. Auxiliary field data should be used whenever possible in this final model check. After investigators are satisfied that the selected model(s) is/are adequate, this auxiliary data can be incorporated in a final stage of the analyses to further improve accuracy and precision of the population projections. The procedures we outline and recommendations we make will improve the credibility and utility of results of population reconstruction modeling.
Knowing kill rate is essential for knowing the basic nature of predation. We compared estimates of kill rate for previously observed wolf-prey systems with new observations from wolves Canis lupus which preyed on white-tailed deer Odocoileus virginianus in Michigan, USA. For the five packs that we studied during 2001-2004, the mean kill rate was 0.68 kill/pack/day (∼7.7 kg/wolf/day). However, kill rates varied considerably. In particular, the coefficient of variation associated with the means was 0.55 for kills/pack/day and 0.68 for kg/wolf/day. Our analysis of previously observed kill rates also revealed a negative correlation between the duration of observation and the estimated kill rate. This correlation is the basis for showing how most published estimates of kill rate for wolves during winter tend to overestimate, by 50%, the season-long average kill rate during winter. The negative association between duration of observation and estimated kill rate occurs, in part, because wolves are unable to maintain very high kill rates for a long time. We also document how estimates of kill rate based on ground tracking tended to be 3.3 times greater than aerial-based estimates (2.4 vs 7.9 kg/wolf/day). Ground tracking is better able to detect multiple carcasses at one site, and better able to detect carcasses when wolves bed far from their kills. These previously undocumented biases are surprising given that wolves are so extensively studied.
Exurban development is consuming wildlife habitat within the Greater Yellowstone Ecosystem with potential consequences to the long-term conservation of grizzly bears Ursus arctos. We assessed the impacts of alternative future land-use scenarios by linking an existing regression-based simulation model predicting rural development with a spatially explicit model that predicted bear survival. Using demographic criteria that predict population trajectory, we portioned habitats into either source or sink, and projected the loss of source habitat associated with four different build out (new home construction) scenarios through 2020. Under boom growth, we predicted that 12 km2 of source habitat were converted to sink habitat within the Grizzly Bear Recovery Zone (RZ), 189 km2 were converted within the current distribution of grizzly bears outside of the RZ, and 289 km2 were converted in the area outside the RZ identified as suitable grizzly bear habitat. Our findings showed that extremely low densities of residential development created sink habitats. We suggest that tools, such as those outlined in this article, in addition to zoning and subdivision regulation may prove more practical, and the most effective means of retaining large areas of undeveloped land and conserving grizzly bear source habitat will likely require a landscape-scale approach. We recommend a focus on land conservation efforts that retain open space (easements, purchases and trades) coupled with the implementation of ‘bear community programmes’ on an ecosystem wide basis in an effort to minimize human-bear conflicts, minimize management-related bear mortalities associated with preventable conflicts and to safeguard human communities. Our approach has application to other species and areas, and it has illustrated how spatially explicit demographic models can be combined with models predicting land-use change to help focus conservation priorities.
The practice of feeding brown bears Ursus arctos for recreational purposes is common in the easternmost areas of Finland, but this may, however, result in human-habituated bears. From 1995 to 2008, 3% of all bears killed by humans (N = 1,108 bears) in Finland represented incidents where bears were either killed for reasons of human safety under a license issued by the police or as a result of actual emergency situations where bears were shot in self defence. We constructed binary logistic regression models for comparing bears shot under police license and in self defence with bears killed in regular sport hunting by using the sex of the bear, human density, bear observation density and the distance from the nearest feeding site as independent variables. High human density was the most important factor differentiating bears shot under a license issued by police from bears killed in sport hunting. The difference in human density was largest for places located far from feeding sites. Increasing distance from feeding sites differentiated bears shot under police license and in self defence from sport hunted bears. The sex of the bears and the density of bear observation were more weakly associated with the category of shooting. Our study did not provide evidence that bear feeding for recreational purposes is associated with the nuisance-bear problem in Finland. Nevertheless, some risks for human safety might be associated with artificial bear feeding for tourism purposes. If the practice of feeding bears continues to be accepted by Finnish legislation, game management should include an action plan for occasions when bears visiting feeding sites will lose their wariness of humans.
During 2006, we conducted riparian surveys to detect river otter Lontra canadensis latrines at 15 bridge-suites along riverine habitats in southwestern Pennsylvania and western Maryland, USA. We defined a bridge-suite as consisting of survey locations at the bridge, a random site and a site chosen by application of a Pattern Recognition Model developed for predicting the location of latrines, with each survey location consisting of both shorelines along a 200-m section of the river. We used occupancy modeling to assess the influence of the continuous covariate SiteScore (a probability derived from Pattern Recognition modeling, with higher scores predicting habitat conditions where river otters are most likely to establish latrines). We also included two categorical covariates with the modeling, each with three factor levels: SiteType (consisting of the three survey locations within a bridge-suite: Bridge, Random and Select, chosen based on having the highest SiteScore among non-Bridge sites within a bridge-suite) and Season (spring, summer and fall) on the probability of detecting a positive site (i.e. a site with ≥ 1 latrine). The selected model suggested that probabilities of detection were positively related to SiteScore (i.e. habitat quality), higher in spring and fall than in summer, and higher at Selected and Random sites than at Bridge sites. In our study areas, efficacy of surveys to detect river otter signs (i.e. scats at latrines) would be considerably enhanced by considering habitat quality when selecting survey locations and by conducting surveys during spring or fall.
The aim of our study was to evaluate the ochratoxin A (OTA) concentration in the blood serum and kidneys of wild boars Sus scrofa in two consecutive years. We took samples from wild boars hunted in five regions of northwestern Poland during November and December 2006 (N = 39) and throughout 2007 (N = 62). The body weight of the animals ranged from 35 to 100 kg. As a control, we used 20 pigs Sus scrofa domestica of an average body weight of 100 kg. We extracted the OTA and then purified it on immunoaffinity columns. The amount of OTA was determined using HPLC-FLD. The OTA concentration varied among individual animals, some of which had extremely high levels in their blood serum (1,170 ng/ml) and kidneys (97 ng/g). The 2006 average OTA concentration in the serum was similar to the average found in 2007 (6.15 ng/ml and 5.91 ng/ml, respectively). In 2006, the concentration of OTA in the serum of wild boars was > 3 times higher than the concentration found in the serum of pigs. We detected a higher level of OTA in the kidneys of wild boars in both 2006 (1.77 ng/g) and 2007 (2.34 ng/g) than the levels present in the kidneys of pigs (0.59 ng/g). In conclusion, the content of OTA in the serum and kidneys of wild boars changed with year and region. The OTA levels in wild boars from certain regions were much higher than in other regions, and such high levels may cause nephropathy in wild boars and thus pose a possible threat to consumers.
An understanding of mortality patterns, and especially the variation in juvenile mortality, is an important component in vertebrate population dynamics. Our study investigates, for the first time, neonate mortality and two levels of spatial behaviour, in a free-ranging fallow deer Dama dama population in southwestern Sweden. In the summers of 2008 and 2009, 36 fawns were marked with radio-collars. Neonate mortality calculated by the Kaplan-Meier method was 23.6%. Mortality caused by predation was low, since only one of eight non-surviving fawns died from predation, probably by red fox Vulpes vulpes. The spatial behaviour of the neonates was examined by habitat selection at home-range level, which in fact is a selection made by the mother, and at bed-site level within that habitat. Compositional analysis revealed a significant preference for arable land, pasture and coniferous forest between 5-15 m high, compared to young forest. Selected bed sites showed significantly lower visibility and higher amount of canopy cover than random sites. Surprisingly, we did not find any relationship between canopy cover and visibility in selected bed sites while it showed a significant and negative relationship at random bed sites. We interpret this finding as while high canopy cover and low visibility covary at the habitat level, fawns seem to select these two bed-site variables independently, perhaps for thermoregulatory reasons. Since there are few predators in our study area and predation pressure is low, this behaviour is not connected to actual survival rates in this area, but would rather be in support of the hypothesis of ‘pleiotropy’ as thermoregulatory reasons for bed-site selection in neonate fawns might be the most important contemporary selection force in the absence of large predators.
Europe's remaining ancient woodland is highly fragmented and many specialist woodland plants persist as isolated relictual populations. Their apparent dispersal limitation and failure to colonise more recently established secondary woodlands may reflect a loss of vectors and mechanisms for dispersal. This is in contrast to long-distance dispersal events evidenced both by paleoecology and some contemporary observations. Although increasing populations of deer are recognised as important dispersers of plant seeds, particularly for species with no apparent dispersal mechanism, the potential for deer to disperse ancient woodland plants has not been studied previously in the UK, where remaining ancient woodland fragments are frequently surrounded by arable landscapes. Viable seed content of 616 faecal samples collected from a guild of mammalian herbivores; red deer Cervus elaphus, fallow deer Dama dama, roe deer Capreolus capreolus, reeves' muntjac Muntiacus reevesi and brown hare Lepus europaeus, over five months and from four coppiced ancient semi-natural woodlands in eastern England, was assessed. Following cold stratification and sowing in a controlled greenhouse, 502 seedlings of 41 species germinated. Three species, constituting just 1.8% of the total individual seedlings recorded, were characteristic of woodland habitats, including only one ancient woodland indicator species, wood speedwell Veronica montana. Germinated plant species were instead characteristic of non-woodland habitats including grassland, arable and ruderal communities. The four most abundant species were the widespread grass common bent Agrostis capillaris, the ruderal greater plantain Plantago major and the two crop species, wheat Triticum spp. and rape Brassica napus. Mammalian herbivory in these ancient woodland fragments provided few dispersal benefits for the woodland plant community. Instead, larger free-ranging herbivores transported large volumes of propagules of ruderal agrarian and open-habitat species from surrounding habitats into ancient woodland fragments.
Body mass is an important life history trait related to survival, mating success and fecundity in ungulates. Accordingly, we may expect that both body mass and reproductive measurements at the population level can be used as valid indices of population condition. However, several factors may modify the relationship between body mass and fecundity because of trade-offs between maturity and early body growth, and varying mortality patterns and sex/age structure among populations. To evaluate the use of such indices for population monitoring and examine the current variation in moose Alces alces population condition in Fennoscandia, we studied the spatio-temporal relationship between calving rate, twinning rate and average autumn calf body mass of moose in Norway and Finland. Calving rate and twinning rate were based on moose observations by hunters while body mass was the average carcass mass of harvested calves. We found a positive relationship between indices both within and among populations. Calves were on average heavier and the observed recruitment rates higher in Finland than in Norway, which is consistent with the higher moose density and presumably lower primary productivity (higher altitude) of moose ranges in Norway. We also found higher observed recruitment rates in populations and years with more even adult sex ratios (females per male) and low relative harvest rates of calves. This suggests that variation in recruitment rate is not only a matter of nutritional condition, but is also affected by varying hunting regulations and harvest structure. For monitoring purposes, we believe that twinning rate is best suited for ranking populations according to nutritional status as this index is closely related to fitness and is relatively insensitive to variation in perinatal and harvest mortality. However, variation in calf body mass may better reflect temporal variation in living conditions. This is because early body growth is sensitive to variation in food availability (and quality) and because body mass may respond more instantaneously than recruitment indices to adverse conditions. Accordingly, we found both calving rate and twinning rate to be best related to variation in mean calf body mass in the previous year.
Past analysis has shown that the population dynamics of Alpine ibex Capra ibex ibex are regulated by both population density and winter snow accumulation. However, recent time series of the ibex counts in the Gran Paradiso National Park, Italy, show interesting trends in comparison with historical snow data: while the winter snow depth has steadily decreased since the beginning of the 1980s, the ibex population experienced rapid growth during the 1980s and the early 1990s, followed by a strong decrease. To explain these dynamics, we built novel age-structured population models in which demographic parameters depended on density and snow depth. They included a non-monotonic effect of snow depth and density on the vital rates, the age and sex structure of the population, and spatial segregation between females and males. Using information criteria (AICc, BIC and SRM), we selected the best models and found that: 1) snow and density interacted in determining the demography of all population sex and age classes, thus confirming that unfavourable climatic conditions intensified the density dependence of the population, 2) the effect of snow was non-monotonic on weaning success and rate of demographic variation of kids, which were maximal for intermediate snow depths, and 3) accounting for spatial segregation between sexes improved the fitting of the models, which suggests that the different use of space made by males and females influenced intraspecific competition. When the selected models were recalibrated using past data and used to simulate recent trends, they underestimated both the rapid growth of the 1980s-1990s and the recent decline of the population. Using the novel sex- and age-structured models, we found that the underestimation of the peak was mainly due to deficiencies of adult demography models, while the overestimation of the recent population abundance was caused by shortcomings in the models of recruitment.
During the necropsy of a red fox Vulpes vulpes that had died from poisoning, we found a nodule of 2 × 3 cm in size in the gastric wall, which was caused by the nematode Spirocerca lupi. The histological features of the parasite include a smooth cuticle, large chords of the hypodermis, muscle cells of the polymyarian/coelomyarian type and large intestine cells with prominent microvillus border. The nodule was infiltrating different layers of the gastric wall and consisted of granulation tissue, with various inflammatory cells and active fibroblasts. This is the first report of S. lupi infection in the red fox in Greece.
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