Understanding the dynamics of species distributions under climate change: linking empirical evidence, ecological theory, and statistical models

Climate change is threatening biota all over the world through dictating changes in species distributions. The ability to predict the effects of climate on species distributions requires an understanding of how climatic and disturbance factors relate to species distributions. I examined the relationship between climate, disturbance, and geographic distributions of vascular plants in the western United States. Within the mountain ranges of California, woody plants have largely shifted their distributions downhill during the 20th century. These shifts were strongly related to observed changes in climatic water balance, consistent with theoretical predictions. Downhill shifts were most prominent for species occurring at higher elevations where environmental conditions were marginal. Downhill shifts were observed at nested spatial scales where changes in climatic conditions were consistent, but at all scales were unrelated to species ecological traits. Niche models based entirely on climatic variables were highly accurate both within and across time periods. The inclusion of fire occurrence as an additional explanatory variable did not affect model likelihood or niche model transferability, due primarily to climatic influences on fire occurrence. Departure from historical return interval influenced total model likelihood when it was included as an additional explanatory variable for species adapted to high frequency return intervals, but did not improve model transferability for most species. Regeneration of tree species occurred within a narrower range of climatic conditions than adults. Species with greater niche breadth displayed greater differences between adult and regeneration niches. Both adults and juveniles displayed higher sensitivity to climatic variables representing mortality risk than to variables representing growth potential. Spatially explicit models of regeneration indicated overestimation of tree ranges based on niche models and the potential for future range contractions. These results were consistent across species

Ecology of a central Appalachian white-tailed deer herd at low density

White-tailed deer (Odocoileus virginianus) are the most abundant big game species in North America and serve as the dominant herbivore in the majority of the Appalachian region. Despite the abundance of research conducted on this species, relatively little is known of the ecology of white-tailed deer occurring at low densities. Our study population experienced a 75% decline in population density and a three-fold increase in habitat disturbance via timber harvests between 2002 and 2005. From May 2006 to April 2008 I examined the home-range, survival, and herbivory patterns of a central Appalachian white-tailed deer herd that has recently experienced both a substantial decline in population density and now occurs at extremely low densities (1--3/km 2). Home-range and core-area size did not differ among age classes in any season. Annual home-range size of yearlings (505 ha) was larger than for adults (313 ha), although core-area size did not differ. Within age classes there were no seasonal differences in home-range or core-area size. Home-range site-fidelity did not differ among age classes for any season or among seasons for any age class. Core-area site fidelity was higher in fall (74%) than in summer (45%) or winter (36%) when pooled across age classes but did not differ among age classes. Survival was lower during the fall (0.89) than during summer (0.99) or winter (0.94). Human-induced mortalities (n = 12) constituted 67% of all observed mortalities during the study; all mortalities were in the adult age class. Woody browse abundance differed among plot types, with clearcut interior (50.16 twigs/plot) plots having more browse than clearcut edge (31.95 twigs/plot) or mature forest (18.93 twigs/plot) plots. Browsing rates of woody plants was higher in clearcut edge plots (5.55%) than in clearcut interior (3.99%) or mature forest plots (3.32%). Observed home-range and core-area sizes were substantially larger than previously reported for the same population prior to declines in density. This supports previous work that suggests home-range size is inversely related to population density and positively correlated with habitat disturbance. Survival rates were similar to previously reported, suggesting that adult survival is robust to changes in population density. Previously reported browsing rates were approximately 5 times the levels reported herein, however such a decrease would be expected with reduced population density and an increase in browse abundance, both of which occurred on the study site

Winter Habitat Associations of Blackbirds and Starlings Wintering in the South-Central United States

Birds can cause extensive crop damage in the United States. In some regions, depredating species comprise a substantial portion of the total avian population, emphasizing their importance both economically and ecologically. We used the National Audubon Society Christmas Bird Count data from the south-central United States and mixed-effects models to identify habitat factors associated with population trend and abundance for 5 species: red-winged blackbird (Agelaius phoeniceus), common grackle (Quiscalus quiscula), rusty blackbird (Euphagus carolinus), Brewer’s blackbird (Euphagus cyanocephalus), and European starling (Sturnus vulgaris). Overall, we found positive associations between bird abundance and agricultural land-cover for all species. Relationships between abundance and other land-cover types were species-specific, often with contrasting relationships among species. Likewise, we found no consistent patterns among abundance and climate. Of the 5 species, only red-winged blackbirds had a significant population trend in our study area, increasing annually by 2.4%. There was marginal evidence to suggest population increases for rusty blackbirds, whereas all other species showed no trend in population size within our study area. Our study provides managers who are interested in limiting crop damage in the south-central United States with novel information on habitat associations in the region that could be used to improve management and control action

Can fire atlas data improve species distribution model projections?

Correlative species distribution models (SDMs) are widely used in studies of climate change impacts, yet are often criticized for failing to incorporate disturbance processes that can influence species distributions. Here we use two temporally independent data sets of vascular plant distributions, climate data, and fire atlas data to examine the influence of disturbance history on SDM projection accuracy through time in the mountain ranges of California, USA. We used hierarchical partitioning to examine the influence of fire occurrence on the distribution of 144 vascular plant species and built a suite of SDMs to examine how the inclusion of fire-related predictors (fire occurrence and departure from historical fire return intervals) affects SDM projection accuracy. Fire occurrence provided the least explanatory power among predictor variables for predicting species’ distributions, but provided improved explanatory power for species whose regeneration is tied closely to fire. A measure of the departure from historic fire return interval had greater explanatory power for calibrating modern SDMs than fire occurrence. This variable did not improve internal model accuracy for most species, although it did provide marginal improvement to models for species adapted to high-frequency fire regimes. Fire occurrence and fire return interval departure were strongly related to the climatic covariates used in SDM development, suggesting that improvements in model accuracy may not be expected due to limited additional explanatory power. Our results suggest that the inclusion of coarse-scale measures of disturbance in SDMs may not be necessary to predict species distributions under climate change, particularly for disturbance processes that are largely mediated by climate

Characteristics of Non-Fatal Attacks by Black Bears: Conterminous United States, 2000–2017

Attacks on humans by bears (Ursus spp.) have increased in recent decades, as both human and bear populations have increased. To help mitigate the risk of future attacks, it is important to understand the circumstances in past attacks. Information and analyses exist regarding fatal attacks by both American black bears (Ursus americanus) and brown bears (U. arctos) as well as non-fatal attacks by brown bears. No similarly thorough analyses on non-fatal attacks by black bears are available. Our study addressed this information gap by analyzing all (n = 210) agency-confirmed, non-fatal attacks by black bears in the 48 conterminous United States during 2000 to 2017. Most attacks were defensive (52%), while 15% were predatory and 33% were food-motivated. Of defensive attacks, 85% were by female bears, and 91% of those females had young. Of predatory attacks, 95% were by male bears, and of food-motivated attacks, 80% were by male bears. Forty percent of defensive attacks by female bears involved dogs (Canis lupus familiaris). Sixty-four percent had an attractant present during the attack and 74% indicated there were reports of property damage by bears or of bears getting a food-reward in the area prior to the attack. A classification and regression tree model show the highest proportion of severe attacks were among a female victim who was with a dog and who fought back during an attack. When compared with previous studies of fatal attacks by black bears, which are typically predatory attacks by male bears, our results illustrate clear differences between fatal and non-fatal attacks. Our study also lends evidence to the hypothesis that dogs can trigger defensive attacks by black bears. These results have implications for risk assessment, attack mitigation, and how we advise the public to respond to an attacking bear

Modeling plant ranges over 75 years of climate change in California, USA: temporal transferability and species traits

Species distribution model (SDM) projections under future climate scenarios are increasingly being used to inform resource management and conservation strategies. A critical assumption for projecting climate change responses is that SDMs are transferable through time, an assumption that is largely untested because investigators often lack temporally independent data for assessing transferability. Further, understanding how the ecology of species influences temporal transferability is critical yet almost wholly lacking. This raises two questions. (1) Are SDM projections transferable in time? (2) Does temporal transferability relate to species ecological traits? To address these questions we developed SDMs for 133 vascular plant species using data from the mountain ranges of California (USA) from two time periods: the 1930s and the present day. We forecast historical models over 75 years of measured climate change and assessed their projections against current distributions. Similarly, we hindcast contemporary models and compared their projections to historical data. We quantified transferability and related it to species ecological traits including physiognomy, endemism, dispersal capacity, fire adaptation, and commonness. We found that non-endemic species with greater dispersal capacity, intermediate levels of prevalence, and little fire adaptation had higher transferability than endemic species with limited dispersal capacity that rely on fire for reproduction. We demonstrate that variability in model performance was driven principally by differences among species as compared to model algorithms or time period of model calibration. Further, our results suggest that the traits correlated with prediction accuracy in a single time period may not be related to transferability between time periods. Our findings provide a priori guidance for the suitability of SDM as an approach for forecasting climate change responses for certain taxa

Estimating the Age of Male Gray Wolves (Canis lupus) Using Baculum Measurements

Morphological characteristics of the bacula of 62 Gray Wolves (Canis lupus) harvested in Wisconsin were related to age estimates generated from cementum annuli analyses. Baculum analysis suggested that 47 of 62 wolves (75.8%) were correctly classified as the appropriate age category (pup, yearling, adult) assessed by cementum analyses; however, this success was limited for yearlings (53.5%) and adults (38.5%). Results could not corroborate future use of this approach for rapid aging of dead wolves. there remains a need for a wolf-aging technique that can be broadly implemented in a timely and cost-effectivemanner, while also preserving the inherent trophy value of an intact skull

Implantation and Parturition Dates of North American River Otters, Lontra canadensis, in Southern Missouri

Despite numerous studies of reproductive dynamics of the North American River Otter (Lontra canadensis), relatively little information exists on the implantation or parturition dates of North American River Otters in the wild. We collected carcasses of North American River Otters that had been legally harvested in southern Missouri, USA, between 1997 and 1999 as part of a larger population dynamics study. Embryos (n = 28) were removed from a subset of North American River Otters (n = 9) during necropsy. Using harvest dates and crown–rump length measurements of embryos, we estimated implantation dates, which ranged from 7 December to 12 January, and parturition dates, which ranged from 8 February to 15 March (assuming an implantation time of 63 days). Our results are similar to other studies that have reported parturition dates ranging from mid-January to early May in more extreme latitudes. Our results suggest that variation in implantation and parturition dates among populations are likely related to factors affected by latitude such as photoperiod and winter weather severity

Spatially Explicit Modeling of Blackbird Abundance in the Prairie Pothole Region

Knowledge of factors influencing animal abundance is important to wildlife biologists developing management plans. This is especially true for economically important species such as blackbirds (Icteridae), which cause more than $100 million in crop damages annually in the United States. Using data from the North American Breeding Bird Survey, the National Land Cover Dataset, and the National Climatic Data Center, we modeled effects of regional environmental variables on relative abundance of 3 blackbird species (red-winged blackbird, Agelaius phoeniceus; yellow-headed blackbird, Xanthocephalus xanthocephalus; common grackle, Quiscalus quiscula) in the Prairie Pothole Region of the central United States. We evaluated landscape covariates at 3 logarithmically related spatial scales (1,000 ha, 10,000 ha, and 100,000 ha) and modeled weather variables at the 100,000-ha scale. We constructed models a priori using information from published habitat associations. We fit models with WinBUGS using Markov chain Monte Carlo techniques. Both landscape and weather variables contributed strongly to predicting blackbird relative abundance (95% credibility interval did not overlap 0). Variables with the strongest associations with blackbird relative abundance were the percentage of wetland area and precipitation amount from the year before bird surveys were conducted. The influence of spatial scale appeared small—models with the same variables expressed at different scales were often in the best model subset. This large-scale study elucidated regional effects of weather and landscape variables, suggesting that management strategies aimed at reducing damages caused by these species should consider the broader landscape, including weather effects, because such factors may outweigh the influence of localized conditions or site-specific management actions. The regional species distributional models we developed for blackbirds provide a tool for understanding these broader landscape effects and guiding wildlife management practices to areas that are optimally beneficial. Published 2015. This article is a U.S. Government work and is in the public domain in the USA

Effects of territorial status and life history on sandhill crane population dynamics in south central Wisconsin

Population growth rate in long-lived bird species is often most sensitive to changes in adult survival. Sandhill cranes (Antigone canadensis Linnaeus, 1758) have long lifespans, small broods, and delayed first reproduction. Only territorial, adult cranes participate in breeding, and territory acquisition reflects the interplay between the availability of suitable territories and variation in mortality of adult birds occupying those territories. We estimated vital rates of a population at equilibrium using long-term resightings data (2000-2014; n = 451 marked individuals) in a multi-state mark-resight model and used a stage-structured projection matrix to assess how strongly territorial adult survival affects population growth rate. Elasticity analysis indicated territorial birds surviving and retaining territories had a 2.58 times greater impact on population growth compared to the next most important transition rate (survival of non-territorial adults remaining non-territorial). Knowing how changes in vital rates of various stage classes will differentially impact population growth rate allows for targeted management actions including encouraging growth in recovering populations, assessing opportunity for recreational harvest, or maintaining populations at a desired level. This study also highlights the value of collecting demographic data for all population segments, from which one can derive reproductive output or growth rate.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author