In ungulates, parturition is correlated with a reduction in movement rate. With advances in movement-based technologies comes an opportunity to develop new techniques to assess reproduction in wild ...ungulates that are less invasive and reduce biases. DeMars et al. (2013, Ecology and Evolution 3:4149-4160) proposed two promising new methods (individual- and population-based; the DeMars model) that use GPS inter-fix step length of adult female caribou (Rangifer tarandus caribou) to infer parturition and neonate survival. Our objective was to apply the DeMars model to caribou populations that may violate model assumptions for retrospective analysis of parturition and calf survival. We extended the use of the DeMars model after assigning parturition and calf mortality status by examining herd-wide distributions of parturition date, calf mortality date, and survival. We used the DeMars model to estimate parturition and calf mortality events and compared them with the known parturition and calf mortality events from collared adult females (n = 19). We also used the DeMars model to estimate parturition and calf mortality events for collared female caribou with unknown parturition and calf mortality events (n = 43) and instead derived herd-wide estimates of calf survival as well as distributions of parturition and calf mortality dates and compared them to herd-wide estimates generated from calves fitted with VHF collars (n = 134). For our data, the individual-based method was effective at predicting calf mortality, but was not effective at predicting parturition. The population-based method was more effective at predicting parturition but was not effective at predicting calf mortality. At the herd-level, the predicted distributions of parturition date from both methods differed from each other and from the distribution derived from the parturition dates of VHF-collared calves (log-ranked test: χ2 = 40.5, df = 2, p < 0.01). The predicted distributions of calf mortality dates from both methods were similar to the observed distribution derived from VHF-collared calves. Both methods underestimated herd-wide calf survival based on VHF-collared calves, however, a combination of the individual- and population-based methods produced herd-wide survival estimates similar to estimates generated from collared calves. The limitations we experienced when applying the DeMars model could result from the shortcomings in our data violating model assumptions. However despite the differences in our caribou systems, with proper validation techniques the framework in the DeMars model is sufficient to make inferences on parturition and calf mortality.
Abstract
Scale remains a foundational concept in ecology. Spatial scale, for instance, has become a central consideration in the way we understand landscape ecology and animal space use. Meanwhile, ...scale-dependent social processes can range from fine-scale interactions to co-occurrence and overlapping home ranges. Furthermore, sociality can vary within and across seasons. Multilayer networks promise the explicit integration of the social, spatial, and temporal contexts. Given the complex interplay of sociality and animal space use in heterogeneous landscapes, there remains an important gap in our understanding of the influence of scale on animal social networks. Using an empirical case study, we discuss ways of considering social, spatial, and temporal scale in the context of multilayer caribou social networks. Effective integration of social and spatial processes, including biologically meaningful scales, within the context of animal social networks is an emerging area of research. We incorporate perspectives that link the social environment to spatial processes across scales in a multilayer context.
1. Describing distribution and abundance is requisite to exploring interactions between organisms and their environment. Recently, the resource selection function (RSF) has emerged to replace many of ...the statistical procedures used to quantify resource selection by animals. 2. A RSF is defined by characteristics measured on resource units such that its value for a unit is proportional to the probability of that unit being used by an organism. It is solved using a variety of techniques, particularly the binomial generalized linear model. 3. Observing dynamics in a RSF - obtaining substantially different functions at different times or places for the same species - alerts us to the varying ecological processes that underlie resource selection. 4. We believe that there is a need for us to reacquaint ourselves with ecological theory when interpreting RSF models. We outline a suite of factors likely to govern ecologically based variation in a RSF. In particular, we draw attention to competition and density-dependent habitat selection, the role of predation, longitudinal changes in resource availability and functional responses in resource use. 5. How best to incorporate governing factors in a RSF is currently in a state of development; however, we see promise in the inclusion of random as well as fixed effects in resource selection models, and matched case-control logistic regression. 6. Investigating the basis of ecological dynamics in a RSF will allow us to develop more robust models when applied to forecasting the spatial distribution of animals. It may also further our understanding of the relative importance of ecological interactions on the distribution and abundance of species.
In Focus: Formica, V., Donald, H., Marti, H., Irgebay, Z., Brodie III, E. Social network position experiences more variable selection than weaponry in wild subpopulations of forked fungus beetles. ...Journal of Animal Ecology, 90, 168–182, https://doi.org/10.1111/1365‐2656.13322. That social network traits can exhibit consistent‐individual differences among individuals and confer a fitness benefit or cost is increasingly well‐established. However, how selection—natural or sexual—affects those social traits and at what scale remains an open question. In this Special Feature, Formica and colleagues employ a meta‐population of forked fungus beetles to test and contrast whether sexual selection on social network traits contrasted to morphological traits occurs at the local (soft) or global (hard) scales. The authors demonstrate that morphological traits are largely under hard directional positive selection, whereas social traits are under soft and variable selection. The findings are compelling and raise interesting discussion of multi‐level selection and the evolution of social traits in a meta‐population.
Selection on social network derived traits is hypothesized to occur at local, rather than global, scales and the adaptive values of these traits at the meta‐population scale (a) may differ among sub‐populations (b–e), which are connected in landscapes that vary in their resistance to demographic exchange (grey shading).
Sociality is poorly understood in the context of population processes. We used wild, female elk (Cervus canadensis) equipped with proximity-logging radio collars (n = 62) from Manitoba, Canada ...(2007–2009), to test for modifying effects of population density (two areas: 0.42 and 0.22 animals/km²) on the relationship between two measures of sociality. This included the rate at which collared individuals encountered one another per year (encounters logged as animals ranging to within 1.4 m of each other) and the extent to which animals overlapped in annual home range (proportion of shared minimum convex polygon ranges). Overlap was significantly greater in the high density area compared to that of the low, but not if we only considered individuals that directly encountered each other, implying that familiar individuals will maintain a constant degree of range overlap regardless of density. Encounter rate was nonlinearly related to home range overlap. This relationship was also density-dependent, exhibiting negative density dependence at high proportions of overlap, primarily in the high density subpopulation. Sociality, as defined by two interacting measures of behaviour—encounter rate and home range overlap—exhibits a complex nonlinear relationship; we discuss the implications of these results as they pertain to sociobiology, resource competition, and pathogen transmission.
Nutritional ecologists aim to predict population or landscape-level effects of food availability, but the tools to extrapolate nutrition from small to large extents are often lacking. The appropriate ...nutritional ecology currencies should be able to represent consumer responses to food while simultaneously be simple enough to expand such responses to large spatial extents and link them to ecosystem functioning. Ecological stoichiometry (ES), a framework of nutritional ecology, can meet these demands, but it is typically associated with ecosystem ecology and nutrient cycling, and less often used to study wildlife nutrition. Despite the emerging zoogeochemical evidence that animals, and thus their diets, play critical roles in nutrient movement, wildlife nutritional ecology has not fully embraced ES, and ES has not incorporated nutrition in many wildlife studies. Here, we discuss how elemental currencies are “nutritionally, organismally, and ecologically explicit” in the context of terrestrial herbivore nutritional ecology. We add that ES and elemental currencies offer a means to measure resource quality across landscapes and compare nutrient availability among regions. Further, we discuss ES shortcomings and solutions, and list future directions to advance the field. As ecological studies increasingly grow in spatial extent, and attempt to link multiple levels of biological organization, integrating more simple and unifying currencies into nutritional studies, like elements, is necessary for nutritional ecology to predict herbivore occurrences and abundances across regions.
Theory on density-dependent habitat selection predicts that as population density of a species increases, use of higher quality (primary) habitat by individuals declines while use of lower quality ...(secondary) habitat rises. Habitat partitioning is often considered the primary mechanism for coexistence between similar species, but how this process evolves with changes in population density remains to be empirically tested for free-ranging ungulates. We used resource-selection functions to quantify density effects on landscape-scale habitat selection of two sympatric species of ungulates moose (Alces alces) and elk (Cervus canadensis manitobensis) in Riding Mountain National Park, Manitoba, Canada (2000–2011). The density of elk was actively reduced from 1.2 to 0.4 elk km⁻² through increased hunting effort during the period of study, while moose density decreased without additional human influence from 1.6–0.7 moose km⁻². Patterns of habitat selection during winter by both species changed in accordance to expectations from density-dependent habitat-selection theory. At low intraspecific density, moose and elk did not partition habitat, as both species selected strongly for mixed forest (primary habitat providing both food and cover), but did so in different areas segregated across an elevational gradient. As intraspecific density increased, selection for primary habitat by both species decreased, while selection for secondary, lower quality habitat such as agricultural fields (for elk) and built-up areas (for moose) increased. We show that habitat-selection strategies during winter for moose and elk, and subsequent effects on habitat partitioning, depend heavily on the position in state space (density) of both species.
Home range size of consumers varies with food quality, but the many ways of defining food quality hamper comparisons across studies. Ecological stoichiometry studies the elemental balance of ...ecological processes and offers a uniquely quantitative, transferrable way to assess food quality using elemental ratios, e.g., carbon (C):nitrogen (N). Here, we test whether snowshoe hares (
Lepus americanus
) vary their home range size in response to spatial patterns of C:N, C:phosphorus (P), and N:P ratios of two preferred boreal forage species, lowbush blueberry (
Vaccinium angustifolium
) and red maple (
Acer rubrum
), in summer months. Boreal forests are N- and P-limited ecosystems and access to N- and P-rich forage is paramount to snowshoe hares’ survival. Accordingly, we consider forage with higher C content relative to N and P to be lower quality than forage with lower relative C content. We combine elemental distribution models with summer home range size estimates to test the hypothesis that home range size will be smaller in areas with access to high, homogeneous food quality compared to areas of low, heterogeneous food quality. Our results show snowshoe hares had smaller home ranges in areas where lowbush blueberry foliage quality was higher or more spatially homogenous than in areas of lower, more heterogeneous food quality. By responding to spatial patterns of food quality, consumers may influence community and ecosystem processes by, for example, varying nutrient recycling rates. Our reductionist biogeochemical approach to viewing resources leads us to holistic insights into consumer spatial ecology.
Foragers must balance the costs and gains inherent in the pursuit of their next meal. Classical functional response formulations describe consumption rates driven by prey density and are naive to ...predator foraging costs. Here, we integrated foraging costs into functional responses to add mechanism and precision to foundational ideas. Specifically, using a model system with a single predator and two prey, we express a functional response emerging from variable energy and time costs of each predation phase: searching, attacking, or consuming prey. The utility of our model is explored through a focused example where prey can exert variable influence on predator foraging costs through antipredator traits. Dissimilarity between prey in their foraging costs influence the energy gain rate of the predator through optimal prey switching. We found that a small subset of prey antipredator traits and density conditions generated a stabilizing Type III (sigmoidal) functional response—the pattern often thought to typify a generalist predator switching between prey species. The sigmoid functional response occurred for highly profitable prey only when the costly prey (1) were at a high density and (2) their antipredator traits increased energy or time costs following an encounter. We outline testable predictions regarding foraging costs from our model. We provide guidance on how to apply optimal foraging theory to empirical scenarios where predator foraging costs vary due to prey type, predator type, or environmental conditions. Our framework represents a synergy of foundational and contemporary theory across disciplines, facilitating the discovery of shared principles and context‐dependent variation across varied predator–prey systems.
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