Glucocorticoids are often associated with stressful environments, but they are also thought to drive the best strategies to improve fitness in stressful environments. Glucocorticoids improve fitness ...in part by regulating foraging behaviours in response to daily and seasonal energy requirements. However, many studies demonstrating relationships between foraging behaviour and glucocorticoids are experimental, and few observational studies conducted under natural conditions have tested whether changing glucocorticoid levels are related to daily and seasonal changes in energy requirements.
We integrated glucocorticoids into habitat selection models to test for relationships between foraging behaviour and glucocorticoid levels in elk (Cervus canadensis) as their daily and seasonal energy requirements changed. Using integrated step selection analysis, we tested whether elevated glucocorticoid levels were related to foraging habitat selection on a daily scale and whether that relationship became stronger during lactation, one of the greatest seasonal periods of energy requirement for female mammals.
We found stronger selection of foraging habitat by female elk with elevated glucocorticoids (e
= 1.44 95% CI 1.01, 2.04). We found no difference in overall glucocorticoid levels after calving, nor a significant change in the relationship between glucocorticoids and foraging habitat selection at the time of calving. However, we found a gradual increase in the relationship between glucocorticoids and habitat selection by female elk as their calves grew over the next few months (e
= 1.01, 95% CI 1.00, 1.02), suggesting a potentially stronger physiological effect of glucocorticoids for elk with increasing energy requirements.
We suggest glucocorticoid-integrated habitat selection models demonstrate the role of glucocorticoids in regulating foraging responses to daily and seasonal energy requirements. Ultimately, this integration will help elucidate the implications of elevated glucocorticoids under natural conditions.
The concept of ecotypes is complex, partly because of its interdisciplinary nature, but the idea is intrinsically valuable for evolutionary biology and applied conservation. The complex nature of ...ecotypes has spurred some confusion and inconsistencies in the literature, thereby limiting broader theoretical development and practical application. We provide suggestions for how incorporating genetic analyses can ease confusion and help define ecotypes. We approach this by systematically reviewing 112 publications across taxa that simultaneously mention the terms ecotype, conservation and management, to examine the current use of the term in the context of conservation and management. We found that most ecotype studies involve fish, mammals and plants with a focus on habitat use, which at 60% was the most common criterion used for categorization of ecotypes. Only 53% of the studies incorporated genetic analyses, and major discrepancies in available genomic resources among taxa could have contributed to confusion about the role of genetic structure in delineating ecotypes. Our results show that the rapid advances in genetic methods, also for nonmodel organisms, can help clarify the spatiotemporal distribution of adaptive and neutral genetic variation and their relevance to ecotype designations. Genetic analyses can offer empirical support for the ecotype concept and provide a timely measure of evolutionary potential, especially in changing environmental conditions. Genetic variation that is often difficult to detect, including polygenic traits influenced by small contributions from several genes, can be vital for adaptation to rapidly changing environments. Emerging ecotypes may signal speciation in progress, and findings from genome‐enabled organisms can help clarify important selective factors driving ecotype development and persistence, and thereby improve preservation of interspecific genetic diversity. Incorporation of genetic analyses in ecotype studies will help connect evolutionary biology and applied conservation, including that of problematic groups such as natural hybrid organisms and urban or anthropogenic ecotypes.
Abstract
Aims
Intraspecific variation in plant traits has important consequences for individual fitness and herbivore foraging. For plants, trait variability across spatial dimensions is well ...documented. However, temporal dimensions of trait variability are less well known, and may be influenced by seasonal differences in growing degree days (GDD), temperature and precipitation. Here, we aim to quantify intraspecific temporal variation in traits and the underlying drivers for four commonly occurring boreal plant species.
Methods
We sampled the elemental and stoichiometric traits (%C, %N, %P, C:N, C:P, N:P) of four common browse species’ foliage across 2 years. Using a two-step approach, we first fitted generalized linear models (GzLM, n = 24) to the species’ elemental and stoichiometric traits, and tested if they varied across years. When we observed evidence for temporal variability, we fitted a second set of GzLMs (n = 8) with temperature, productivity and moisture as explanatory variables.
Important Findings
We found no evidence of temporal variation for most of the elemental and stoichiometric traits of our four boreal plants, with two exceptions. Year was an important predictor for percent carbon across all four species (R2 = 0.47–0.67) and for multiple elemental and stoichiometric traits in balsam fir (5/8, R2 = 0.29–0.67). Thus, variation in percent carbon was related to interannual differences, more so than nitrogen and phosphorus, which are limiting nutrients in the boreal forest. These results also indicate that year may explain more variation in conifers’ stoichiometry than for deciduous plants due to life history differences. GDD was the most frequently occurring variable in the second round of models (8/8 times, R2 = 0.21–0.41), suggesting that temperature is an important driver of temporal variation in these traits.
In many taxa, individual social traits appear to be consistent across time and context, thus meeting the criteria for animal personality. How these differences are maintained in response to changes ...in population density is unknown, particularly in large mammals, such as ungulates. Using a behavioral reaction norm (BRN) framework, we examined how among- and within-individual variation in social connectedness, measured using social network analyses, change as a function of population density. We studied a captive herd of elk (Cervus canadensis) separated into a group of male elk and a group of female elk. Males and females were exposed to three different density treatments and we recorded social associations between individuals with proximity-detecting radio-collars fitted to elk. We constructed social networks using dyadic association data and calculated three social network metrics reflective of social connectedness: eigenvector centrality, graph strength, and degree. Elk exhibited consistent individual differences in social connectedness across densities; however, they showed little individual variation in their response to changes in density, i.e., individuals oftentimes responded plastically, but in the same manner to changes in density. Female elk had highest connectedness at an intermediate density. In contrast, male elk increased connectedness with increasing density. Whereas this may suggest that the benefits of social connectedness outweigh the costs of increased competition at higher density for males, females appear to exhibit a threshold in social benefits (e.g. predator detection and forage information). Our study illustrates the importance of viewing social connectedness as a density-dependent trait, particularly in the context of plasticity. Moreover, we highlight the need to revisit our understanding of density dependence as a population-level phenomenon by accounting for consistent individual differences not only in social connectedness, but likely in other ecological processes (e.g., predator-prey dynamics, mate choice, disease transfer).
The increased popularity and accessibility of social network analysis has improved our ability to test hypotheses about complex animal social structures. To gain a deeper understanding of the use and ...application of animal social network analysis, we systematically surveyed the literature and extracted information on publication trends from articles using social network analysis. We synthesize trends in social network research over time and highlight variation in the use of different aspects of social network analysis. The use of social network analysis in empirical articles has increased over time. In the context of social network methods, we found that many studies did not use an association index to account for missing individuals or observations of individuals; that the number and type of social network metrics calculated in a given study varied substantially (median=2); and that focal observation was by far the most common method used to generate social networks, although the use of biologging devices increased over time. We also observed that most species studied using social networks are mammals (55%) or birds (23%), and that the majority are species of least concern (59%; International Union for the Conservation of Nature, IUCN, www.iucn.org). Based on our findings, we highlight four key recommendations for future studies: (1) the use of association indices is almost always necessary; (2) the a priori selection of specific network metrics and associated hypotheses increases transparency; (3) combination of focal observation with biologging devices could improve our understanding of remotely sensed behaviours; and (4) because most studies rarely study species of conservation concern, it may be practical to generate networks for similar species or populations, which could help inform management decisions. We highlight emerging trends in social network research that may be valuable for distinct groups of social network researchers: students new to social network analysis, experienced behavioural ecologists interested in using social network analysis and advanced social network users interested in trends of social network research. Our findings also shed light on past research and provide guidance for future studies using social network analysis.
•Social network analysis has increased in popularity in the last two decades.•The majority of empirical social network articles use focal observation methods.•Mammals and birds are the most commonly studied species in social network articles.•The majority of species studied are listed by the IUCN as least concern.
Animals use a variety of proximate cues to assess habitat quality when resources vary spatiotemporally. Two nonmutually exclusive strategies to assess habitat quality involve either direct assessment ...of landscape features or observation of social cues from conspecifics as a form of information transfer about forage resources. The conspecific attraction hypothesis proposes that individual space use is dependent on the distribution of conspecifics rather than the location of resource patches, whereas the resource dispersion hypothesis proposes that individual space use and social association are driven by the abundance and distribution of resources. We tested the conspecific attraction and the resource dispersion hypotheses as two nonmutually exclusive hypotheses explaining social association and of adult female caribou (Rangifer tarandus). We used location data from GPS collars to estimate interannual site fidelity and networks representing home range overlap and social associations among individual caribou. We found that home range overlap and social associations were correlated with resource distribution in summer and conspecific attraction in winter. In summer, when resources were distributed relatively homogeneously, interannual site fidelity was high and home range overlap and social associations were low. Conversely, in winter when resources were distributed relatively heterogeneously, interannual site fidelity was low and home range overlap and social associations were high. As access to resources changes across seasons, caribou appear to alter social behavior and space use. In summer, caribou may use cues associated with the distribution of forage, and in winter caribou may use cues from conspecifics to access forage. Our results have broad implications for our understanding of caribou socioecology, suggesting that caribou use season‐specific strategies to locate forage. Caribou populations continue to decline globally, and our finding that conspecific attraction is likely related to access to forage suggests that further fragmentation of caribou habitat could limit social association among caribou, particularly in winter when access to resources may be limited.
Using individual caribou fit with GPS biotelemetry collars, we quantified inter‐annual site‐fidelity for individual caribou (Rangifer tarandus) and constructed social and spatial networks based on social associations and home‐range overlap for 187 animal years in both summer and winter. With close attention to caribou natural history, we considered winter and summer as relative proxies for heterogeneous and homogeneous distribution of forage resources, respectfully, and we compared site‐fidelity, social association, and home range overlap across seasons to test the RDH and the CAH. In summer, when forage resources are relatively homogeneously distributed, caribou use spatial cues to access forage (supporting the RDH in summer), while in winter, when forage resources are relatively heterogeneously distributed, caribou use social cues to access forage (supporting the CAH in winter).
Human-driven environmental changes affect behavior, morphology, life history, and population dynamics of wild species. Artificial food sources in anthropogenic environments benefit some species and ...may lead to faster somatic growth and larger body size, which affects survival and reproduction, thus contributing to a species’ success in modified environments. Using raccoons (Procyon lotor (L., 1758)) as a model, we documented age-specific body-mass pattern and evaluated the influence of human activities (human density, area with artificial food sources, edges of forested area bordering corn (Zea mays L.) fields) and weather (index of winter severity and mean annual precipitation) on body-mass variation at multiple spatial scales. The effect of human-driven changes on raccoon mass varied with age, sex, and spatial scale, suggesting that anthropogenic changes affect raccoons differentially according to gender and life stages. Human activity had consistently opposing effects between the sexes. Weather covariates represented >50% of the total variance in body mass explained by our models. Previous winter severity and mean annual precipitation affected body mass negatively and positively, respectively. Our results emphasize the importance of multiscale, sex- and age-specific analyses when studying influences of human activity on wildlife.
Age at primiparity is a flexible life-history trait that purportedly responds to changing population dynamics and variable resource abundance. We examined placental scars in yearling Canada lynx ...(Lynx canadensis (Kerr, 1792)) from the island of Newfoundland and used pregnancy rates and litter sizes to indicate primiparity. We modelled these lynx productivity data with snowshoe hare (Lepus americanus Erxleben, 1777) population attributes using seven multiple a priori competing hypotheses. Hare abundance showed peak, decline, and increase phases, and densities based on capture–mark–recapture estimates ranged from 0.11 to 1.19 hares·ha
−1
. Overall, yearling pregnancy rate was 23.5% and the model with hare abundance fitted alone had the most support. However, surprisingly hare abundance explained little (6%) variation in yearling pregnancy rate. Mean (±SE) litter size was 3.51 ± 0.27. None of our covariate models provided unequivocal support for predicting yearling litter size. We speculate that individuals may exhibit behavioural plasticity such that they can dampen the impact of primary prey abundance on yearling pregnancy rate by exploiting alternate prey. Furthermore, intraspecific social interactions may provide additional insight into the determinants of pregnancy rate in yearling lynx.
Endemic and emerging diseases are rarely uniform in their spatial distribution or prevalence among cohorts of wildlife. Spatial models that quantify risk‐driven differences in resource selection and ...hunter mortality of animals at fine spatial scales can assist disease management by identifying high‐risk areas and individuals. We used resource selection functions (RSFs) and selection ratios (SRs) to quantify sex‐ and age‐specific resource selection patterns of collared (n = 67) and hunter‐killed (n = 796) nonmigratory elk (Cervus canadensis manitobensis) during the hunting season between 2002 and 2012, in southwestern Manitoba, Canada. Distance to protected area was the most important covariate influencing resource selection and hunter‐kill sites of elk (AICw = 1.00). Collared adult males (which are most likely to be infected with bovine tuberculosis (Mycobacterium bovis) and chronic wasting disease) rarely selected for sites outside of parks during the hunting season in contrast to adult females and juvenile males. The RSFs showed selection by adult females and juvenile males to be negatively associated with landscape‐level forest cover, high road density, and water cover, whereas hunter‐kill sites of these cohorts were positively associated with landscape‐level forest cover and increasing distance to streams and negatively associated with high road density. Local‐level forest was positively associated with collared animal locations and hunter‐kill sites; however, selection was stronger for collared juvenile males and hunter‐killed adult females. In instances where disease infects a metapopulation and eradication is infeasible, a principle goal of management is to limit the spread of disease among infected animals. We map high‐risk areas that are regularly used by potentially infectious hosts but currently underrepresented in the distribution of kill sites. We present a novel application of widely available data to target hunter distribution based on host resource selection and kill sites as a promising tool for applying selective hunting to the management of transmissible diseases in a game species.
In this study, we present an analytical approach to quantify high‐risk areas for disease transmission based on sex‐ and age‐specific tracking data of nonmigratory elk and hunter‐kill sites using resource selection functions and selection ratios. We present a novel application of widely available data to target the distribution of hunters based on host demography and distribution, and map areas that are regularly used by potentially infectious hosts but currently underrepresented in the distribution of kill sites. Our disease risk management maps provide a complementary tool that allows managers to precisely evaluate hunter success, which creates opportunities to redirect hunters and improve disease monitoring and control.
Changes in foliar elemental niche properties, defined by axes of carbon (C), nitrogen (N), and phosphorus (P) concentrations, reflect how species allocate resources under different environmental ...conditions. For instance, elemental niches may differ in response to large‐scale latitudinal temperature and precipitation regimes that occur between ecoregions and small‐scale differences in nutrient dynamics based on species co‐occurrences at a community level. At a species level, we compared foliar elemental niche hypervolumes for balsam fir (Abies balsamea (L.) Mill.) and white birch (Betula papyrifera Marshall) between a northern and southern ecoregion. At a community level, we grouped our focal species using plot data into conspecific (i.e., only one focal species is present) and heterospecific groups (i.e., both focal species are present) and compared their foliar elemental concentrations under these community conditions across, within, and between these ecoregions. Between ecoregions at the species and community level, we expected niche hypervolumes to be different and driven by regional biophysical effects on foliar N and P concentrations. At the community level, we expected niche hypervolume displacement and expansion patterns for fir and birch, respectively—patterns that reflect their resource strategy. At the species level, foliar elemental niche hypervolumes between ecoregions differed significantly for fir (F = 14.591, p‐value = .001) and birch (F = 75.998, p‐value = .001) with higher foliar N and P in the northern ecoregion. At the community level, across ecoregions, the foliar elemental niche hypervolume of birch differed significantly between heterospecific and conspecific groups (F = 4.075, p‐value = .021) but not for fir. However, both species displayed niche expansion patterns, indicated by niche hypervolume increases of 35.49% for fir and 68.92% for birch. Within the northern ecoregion, heterospecific conditions elicited niche expansion responses, indicated by niche hypervolume increases for fir of 29.04% and birch of 66.48%. In the southern ecoregion, we observed a contraction response for birch (niche hypervolume decreased by 3.66%) and no changes for fir niche hypervolume. Conspecific niche hypervolume comparisons between ecoregions yielded significant differences for fir and birch (F = 7.581, p‐value = .005 and F = 8.038, p‐value = .001) as did heterospecific comparisons (F = 6.943, p‐value = .004, and F = 68.702, p‐value = .001, respectively). Our results suggest species may exhibit biogeographical specific elemental niches—driven by biophysical differences such as those used to describe ecoregion characteristics. We also demonstrate how a species resource strategy may inform niche shift patterns in response to different community settings. Our study highlights how biogeographical differences may influence foliar elemental traits and how this may link to concepts of ecosystem and landscape functionality.
Foliar elemental niches, defined by axes of carbon (C), nitrogen (N), and phosphorus (P), reveal the ecophysiological responses of species to environmental conditions at regional and local scales. Our study shows that species exhibit biogeographical specific elemental niches likely driven by biophysical ecoregion differences as well as how changes in niche structure occur in response to different community types across scales. Our study highlights biogeographical differences relating to foliar elemental traits linking concepts of ecosystem and landscape ecology.
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