The isotopic niche of consumers represents biologically relevant information on resource and habitat use. Several tools have been developed to quantify niche size and overlap. Nonetheless, methods ...adapted by spatial ecologists to quantify animal home ranges can be modified for use in stable isotope ecology when data are not normally distributed in bivariate space.
We offer a tool that draws on existing spatial metrics, such as minimum convex polygon (MCP) and standard ellipse area (SEA), and add novel metrics using kernel utilization density (KUD) estimators to measure isotopic niche size and overlap. We present examples using empirical and simulated data to demonstrate the performance of the package kernel isotopic niches in r (rKIN) under various scenarios.
Results of niche size from MCP, SEA and KUD were highly correlated but divergent among datasets. Overall, the KUD method produced the largest niche sizes and was more sensitive to the distribution of the isotopic data. Pairwise estimates of overlap were highly variable, likely because MCP and SEA inherently include or exclude unused areas in the resulting niche estimate. Four bandwidth methods (reference, normal scale, plug‐in and biased cross‐validation) produced comparable estimates of niche size and overlap at various sample sizes (10–40). Niche size and overlap were consistent across sample sizes >15.
Use of rKIN will allow isotope ecologists to quantify niche shifts, expansions or contractions, as well as assess the performance of several estimation methods. The package also can be applied to other data types (e.g. principal component analysis, multi‐dimensional scaling) so long as axes and measurement units are identical and can be converted to Cartesian coordinates.
The authors offer a tool that draws on existing spatial metrics, such as minimum convex polygon and standard ellipse area, and add novel metrics using kernel utilization density estimators to measure isotopic niche size and overlap. rKIN will allow isotope ecologists to quantify niche shifts, expansions or contractions.
Earth has >8 billion people. Scholarly publications number nearly 7 million annually with >1 million in the life and biomedical sciences, and ≥52 professional journals specializing in conservation, ...ecology, or related disciplines. The challenges of applying ecological data to conservation and wildlife management can easily become overwhelming. Herein we offer reflective perspectives about the changing face of applied knowledge and engagement from our personal employment histories as ecologists working in agency, university, and non‐governmental organization (NGO) biologist positions. We suggest natural history will always be nature's glue, but knowledge steeped mostly in muddy boots and field biology are no longer the soup du jour of our profession. In many ways, new technologies have changed data collection and the scientific questions asked. Arguably, such change is not welcomed by all, but a change in overlap across decades is needed to sustain and improve upon how the planet's biological diversity can coexist with increasingly difficult human conditions. Given that 80% of the people in the United States live in urban areas, with similar numbers internationally, a future possibility may be an even greater divide between wild nature, ecological services, and enjoyment in the field. This is disturbing. Despite fundamental scientific insights that help understand critical components of the natural world, once society loses touch with nature, what will remain?
1. Body reserves of numerous taxa follow seasonal rhythms that are a function of temporal patterns in food availability and life-history events; however, tests of the theory underlying the allocation ...of somatic reserves for long-lived organisms are rare, especially for free-ranging mammals. We evaluated the hypothesis that allocation of somatic reserves to survival (i.e., metabolic processes) and reproduction should be sensitive to current nutritional state relative to seasonal thresholds in those reserves. 2. Our goal was to reveal the linkages between nutrition and life-history traits to understand how long-lived, iteroparous organisms balance the allocation of somatic reserves to reproduction, while retaining reserves as insurance for survival in unpredictable environments. Our evaluation was based on seasonal dynamics in fat (measured as ingesta-free body fat; IFBFat) and protein reserves (measured as ingesta-free, fat-free body mass; IFFFBMass) of 136 female mule deer (Odocoileus hemionus) over 8 years. 3. Although mean changes in fat and protein reserves were positive over summer and negative over winter, accretion and catabolism of those reserves was not consistent among individuals. Over winter, both lipid and protein stores available in autumn were catabolized in proportion to their availability above a post-winter threshold (5·8% IFBFat, 33 kg IFFFBMass); however, lean body tissue was spared at the expense of lipid reserves. 4. Female deer mostly synthesized lean body tissue over summer and committed post-winter fat reserves to reproduction relative to their availability above an autumn threshold (>8·6% IFBFat), which was lowered by 2·8 percentage points (pp) for each additional young recruited. Mothers reduced their autumn fat threshold to secure current reproductive investment and, thereby, endured a cost of reproduction at the expense of fat accumulation. 5. Allocation of somatic reserves occurred in a risk-sensitive framework; females allocated reserves relative to their availability above seasonal thresholds. In contrast to current notions of summer accretion and winter catabolism of body reserves, some individuals deposited reserves over winter and catabolized reserves over summer, mainly because regulation of individual condition was state-dependent. Consequently, behaviour and life-history strategies may be as much a function of nutritional contributions of the previous season as of the current one.
Temporal changes in net energy balance of animals strongly influence fitness; consequently, natural selection should favor behaviors that increase net energy balance by buffering individuals against ...negative effects of environmental variation. The relative importance of behavioral responses to climate-induced variation in costs vs. supplies of energy, however, is uncertain, as is the degree to which such responses are mediated by current stores of energy. We evaluated relationships among behavior, nutritional condition (i.e., energy state), and spatiotemporal variation in costs vs. supplies of energy available to a large-bodied endotherm, the North American elk (
Cervus elaphus
), occupying two ecosystems with contrasting climates and energy landscapes: a temperate, montane forest and an arid, high-elevation desert. We hypothesized that during spring through autumn, behavioral responses to the energy landscape would be both context dependent (i.e., would vary as a function of the contrasting environmental conditions experienced by elk in the forest vs. the desert), and state dependent (i.e., would vary as a function of the energy balance of an individual). We tested several predictions derived from that hypothesis by combining output from a biophysical model of the thermal environment with data on forage quality, animal locations, and nutritional condition of individuals. At the population level, elk in the desert selected areas that reduced costs of thermoregulation over those that provided the highest-quality forage. In the forest, however, costs imposed by the thermal environment were less pronounced, and elk selected areas that increased access to high-quality forage over those that reduced costs of thermoregulation. At the individual level, nutritional condition did not influence strength of selection for low-cost areas or high-quality forage among elk in the forest. In the desert, however, strength of selection for low-cost areas (but not forage quality) was state dependent; individuals in the poorest condition at the end of winter showed the strongest selection for areas that reduced costs of thermoregulation during spring and summer, and also expended the least amount of energy on locomotion. Our results highlight the importance of understanding the roles of behavior and nutritional condition in buffering endotherms against direct and indirect effects of climate on fitness.
Ungulates exhibit diverse mating systems that range from monogamous pair territories to highly polygynous leks. We review mating systems and behaviors across ungulates and offer a new approach ...synthesizing how interacting factors may shape those mating systems. Variability exists in mating systems among and within species of ungulates and likely is affected by predation risk, availability of resources (food and mates), habitat structure, and sociality. Ungulate mating systems may be labile as a consequence of the varying strength of those interacting factors. In addition, degree of polygyny and sexual dimorphism in size are associated with the evolution of mating systems. Neither male–male combat nor paternal care, however, can completely explain differences in sexual size dimorphism for ungulates, a necessary component in understanding the development of some mating systems. Whatever the evolutionary pathway, sexual segregation limits paternal care allowing more intense male–male competition. Selection of habitat structure, because it modifies risk of predation, is a major determinant of sociality for ungulates. Likewise, ruggedness and steepness of terrain limit the types of mating systems that can occur because of limitations in group size and cohesiveness, as well as the ability of males to herd even small groups of females effectively. The quality and defensibility of resources affect mating systems, as does the defensibility of females. Population density of females also may be a critical determinant of the types of mating systems that develop. Size of groups likewise constrains the types of mating tactics that males can employ. Our aim was to use those relationships to create a broad conceptual model that predicts how various environmental and social factors interact to structure mating systems in ungulates. This model provides a useful framework for future tests of the roles of both ecological and social conditions in influencing the social systems of ungulates.
We provide a new approach to understanding mating systems in ungulates. We integrate both social and environmental factors in doing so. We develop a predictive model to help understand the evolution of these unique behaviors, which should help to direct future studies.
Mammals are imperiled worldwide. Threats to terrestrial species are primarily from habitat loss or modification, and in some instances from commercial, illegal, or unregulated hunting. Terrestrial ...species are negatively affected throughout the tropics from deforestation. Threats to marine mammals are related to harvest, strikes in shipping lanes, pollution, and depleted levels of food resources. Hazards to marine species are pronounced in the North Atlantic Ocean, North Pacific Ocean, and oceans and seas flanking southeastern Asia. Protected areas designed to conserve mammals often are too small, too few, poorly delimited or isolated, and too unreliably supported. The new conservation science proposes that human livelihoods be considered alongside traditional preservationist perspectives. For conservation outside of protected areas to succeed, the protection of wild mammals and their habitats should result in benefit to local people, especially in rural or poor communities. Concerns about declining populations of large mammals in North America during the late 19th and early 20th centuries resulted in the institution of regulations that contributed to the recovery of many populations. Today, in North America and Europe, wild populations are thriving and legal hunting is allowed for a number of mammals, something that is less common in many developing countries, where illegal killing remains a threat to conservation. Nevertheless, populations of large mammals are resilient to regulated hunting because of density-dependent processes that result in increased reproduction, survival, and growth rates. Unfortunately, hunting is unregulated for cultural and economic reasons over much of the Earth. We are beginning to see effects of climate change and invasive species on risk of extinction for many species. The future of mammals, however, is entwined ultimately with the size, growth, and resource demands of the human population.
Migration is an adaptive strategy that enables animals to enhance resource availability and reduce risk of predation at a broad geographic scale. Ungulate migrations generally occur along traditional ...routes, many of which have been disrupted by anthropogenic disturbances. Spring migration in ungulates is of particular importance for conservation planning, because it is closely coupled with timing of parturition. The degree to which oil and gas development affects migratory patterns, and whether ungulate migration is sufficiently plastic to compensate for such changes, warrants additional study to better understand this critical conservation issue.
We studied timing and synchrony of departure from winter range and arrival to summer range of female mule deer (Odocoileus hemionus) in northwestern Colorado, USA, which has one of the largest natural-gas reserves currently under development in North America. We hypothesized that in addition to local weather, plant phenology, and individual life-history characteristics, patterns of spring migration would be modified by disturbances associated with natural-gas extraction. We captured 205 adult female mule deer, equipped them with GPS collars, and observed patterns of spring migration during 2008-2010.
Timing of spring migration was related to winter weather (particularly snow depth) and access to emerging vegetation, which varied among years, but was highly synchronous across study areas within years. Additionally, timing of migration was influenced by the collective effects of anthropogenic disturbance, rate of travel, distance traveled, and body condition of adult females. Rates of travel were more rapid over shorter migration distances in areas of high natural-gas development resulting in the delayed departure, but early arrival for females migrating in areas with high development compared with less-developed areas. Such shifts in behavior could have consequences for timing of arrival on birthing areas, especially where mule deer migrate over longer distances or for greater durations.
We analyzed harvest data to test hypotheses that nearly 4 decades of effort to reduce abundance of brown bears (Ursus arctos), black bears (U. americanus) and gray wolves (Canis lupus) in an 60,542 ...km2 area in south-central Alaska (Game Management Unit GMU 13) was positively correlated with moose (Alces alces) harvests in some time-lagged fashion. Predator-reduction efforts were progressively more aggressive over decades (both de facto and officially designated predator control) and did not have clear starting points which complicated our post hoc analyses. We documented no positive correlations (p > 0.05) between harvests of brown and black bears and subsequent moose harvests for any time lag. Moose harvest was negatively correlated with the previous years’ wolf harvest, but the relationship was weak (correlation = −0.33, p < 0.05). Consequently, we reject our hypotheses that harvest of predators was positively correlated with moose harvests. We also observed no differences in mean moose harvests during periods of officially designated wolf control (2005–2020) and a previous period (p > 0.50). We recommend that predator reductions designed to improve hunter harvests of moose be conducted within a research framework that will permit improved interpretations of results and the implementation of an adaptive-management approach to achieve management objectives.
Summary
The selection ratio (proportional resource use divided by proportional availability) is often used by ecologists to measure the degree to which individuals and populations are selective in ...their food sources and habitats. Yet, confidence interval approaches for this metric are scarce and poorly evaluated.
In this paper, we compare 13 methods that can be used to construct simultaneous confidence intervals for selection ratios. Seven of the methods are applicable when availabilities are unknown. These are bootstrapping and six methods adapted from relative risk (Katz‐log, adjusted‐log, Bailey, inverse hyperbolic sine, Koopman and Noether). The other six approaches are applicable when availabilities are known. These are bootstrapping, two existing methods for relative risk (Wald‐adjusted, Noether‐fixed) and three straightforward new methods (fixed‐log, Agresti–Coull‐adjusted and Bayes‐beta). None of the 13 approaches have been previously evaluated in the context of selection ratios.
In simulations with unknown availabilities, the Koopman method performed best, and the currently recommended Noether method performed worst. In simulations with fixed availabilities, the new Agresti–Coull‐adjusted, fixed‐log, Bayes‐beta methods all outperformed the currently recommended Wald‐adjusted method. In the context of real ecological data sets, the Noether and Wald‐adjusted methods produced anomalous results that putatively would alter management decisions. We note that our findings, including those for new methods, are directly conferrable to relative risk, allowing extension of our work to the many branches of biology that rely on this measure.
The poor performance of the Noether and Wald‐adjusted methods is troubling because these are currently the most widely used procedures for calculating confidence intervals for type I resource‐selection designs. Based on our findings, we recommend that the Noether method be replaced with the Koopman method, and the Wald‐adjusted method be replaced with the Agresti–Coull‐adjusted method.
We studied mountain lions (Puma concolor) and mule deer (Odocoileus hemionus) inhabiting a Great Basin ecosystem in Round Valley, California, to make inferences concerning predator–prey dynamics. Our ...purpose was to evaluate the relative role of top-down and bottom-up forcing on mule deer in this multiple-predator, multiple-prey system. We identified a period of decline (by 83%) of mule deer (1984–1990), and then a period of slow but steady increase (1991–1998). For mule deer, bitterbrush (Purshia tridentata) in diets, per capita availability of bitterbrush, kidney fat indexes, fetal rates (young per adult female), fetal weights, and survivorship of adults and young indicated that the period of decline was typical of a deer population near or above the carrying capacity (K) of its environment. Numbers of mountain lions also declined, but with a long time lag. The period of increase was typified by deer displaying life-history characteristics of a population below K, yet the finite rate of growth (λ = 1.10) remained below what would be expected for a population rebounding rapidly toward K (λ = 1.15–1.21) in the absence of limiting factors. Life-history characteristics were consistent with the mule deer population being regulated by bottom-up forcing through environmental effects on forage availability relative to population density; however, predation, mostly by mountain lions, was likely additive during the period of increase and thus, top-down forcing slowed but did not prevent population growth of mule deer. These outcomes indicate that resource availability (bottom-up processes) has an ever-present effect on dynamics of herbivore populations, but that the relationship can be altered by top-down effects. Indeed, top-down and bottom-up forces can act on populations simultaneously and, thus, should not be viewed as a stark dichotomy.
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