Linking Wildlife Nutrition with Population Productivity

Symposium

SESSION NUMBER: 16

Symposia will be available on-demand on their scheduled date, then again at the conclusion of the conference.

 
Nutrition is fundamentally important to life, with influences on biological processes from cell signaling to growth and reproduction. Although nutrition operates initially at the level of the individual, through decisions about where, when, what, and how much to eat, nutrition can scale up to have population-level effects that are relevant to conservation and management. In this symposium, we explore the myriad ways through which thousands of small decisions about bites of food compound to influence demographic rates and productivity of wildlife populations and discuss best practices for wildlife managers interested in incorporating nutritional ecology into their wildlife management programs. Our symposium begins with a new look into how population productivity can be limited through density-dependent and density-independent pathways and demonstrate several real-world examples of these limitations to population productivity. We then discuss the concepts of animal-indicated nutritional carrying capacity and ?foodscapes? as complementary approaches to understand the nutritional environment in which animals live. We also examine how climate change and associated changes in the phenology of the foodscape have predictable influences on demographic rates. Further, we demonstrate how an individual?s nutritional state influences its perception of the foodscape and how that can interact with behavior to influence survival and susceptibility to non-nutritional causes of mortality, including predation. Finally, we end with best practices for linking nutrition with population productivity and provide managers with a framework for incorporating nutritional ecology into wildlife management programs.

From the Bite to the Biome: Monitoring and Managing the Foodscape for Vertebrate Herbivores
Jennifer S. Forbey; Peter Olsoy; Lisa Shipley; Gail Patricelli; Brecken Robb; Nielsen Olafur; Kristinn Magnusson; Virve Ravolainen; Clara Buchholtz; Carolyn Dadabay; Rongsong Liu; Ethan Ellsworth; John Connelly
Herbivores interact with a diversity of nutrients and toxins in plants that comprise the foodscape. Concentrations of specific components of the foodscape alter the physiology, foraging behavior, and population demographics of herbivores. However, much of what we know about the consequences of vertebrate herbivores interacting with foodscapes is limited to specific biological, temporal, or spatial scales. We demonstrate how recent advances in genomics, chemistry, remote sensing, and modeling can be used to link consequences of foodscapes from what individual herbivores consume (the bite) to how populations fluctuate over time across the landscape (the biome). We use collaborative data from pygmy rabbits and greater sage-grouse in Idaho and Wyoming in the USA, from moose in Isle Royale National Park, Michigan, USA, and from ptarmigan in Iceland, Sweden, and Norway to identify consequences of foodscapes at different biological scales. We show how diet composition and quality consumed and digested are linked to the physiological condition of individual herbivores. We also show how the availability, composition, and quality of foodscapes across landscapes are linked to behavioral and demographic traits of herbivores. This multi-scale and multi-disciplinary effort show how monitoring foodscapes from the bite to the biome can help manage healthy populations of vertebrate herbivores.
Influence of Plant Phenology on Mule Deer Population Performance
Mark A. Hurley; Joseph St. Peter; Mark Hebblewhite; Scott Bergen; Erin Roche; Shane Roberts; Brendan Oates; Paul Atwood
Understanding the relationship between the nutritional quality of a landscape and mule deer (Odocoileus hemionus) vital rates is often compromised by the annual variation in plant phenology, especially in dry seasonal habitats. The nutritional quality of habitat with known plant composition will change within and between seasons relative to the phenology of individual plants. Although, many research projects use remotely sensed NDVI from MODIS as a surrogate for nutrition, the true nutritional quality related to plant structure is largely unknown. We used digital cameras to provide a consistent view of vegetation phenology at fine spatial and temporal scales and linked phenology data from these cameras to greenness indices derived from 16-day MODIS NDVI. To estimate phenological variation in nutrition, we documented the growth cycle and nutritional quality of plants within each MODIS window using plant composition transects. We initiated vegetation phenology plots within mule deer summer range and measured each between 3 and 5 times per summer to link vegetation phenology, pseudo-NDVI from cameras, and NDVI from MODIS to mule deer population performance. We mapped forage species within fawn rearing habitat of GPS collared adult females using a 1m resolution vegetation map. The fine-scale vegetation map consisted of overstory structural components derived from NAIP imagery, and modeled understory species based on > 3000 ground plots, overstory classification, physiological, and environmental covariates. We estimated annual nutritional quality of maternal home ranges as a function of plant composition and duration of nutritional quality throughout the growing season. We used discrete-time, known fate modeling to determine winter fawn survival, and estimated December fawn/female ratios from aerial surveys. To test the influence of summer nutritional quality on population performance, we then linked the estimate of nutritional quality on summer range to fawn weight and ratios during early winter, and overwinter fawn survival.
Nutritional Allee Effects in the Recovery of Endangered Species
Kristin Denryter; Tom R. Stephenson; Mary M. Conner; David W. German; Kevin L. Monteith
Endangered species may experience an unexpected influence of Allee effects on nutritional condition. For group-living animals, nutritional Allee effects may arise when populations sizes are too small for benefits of group living to be realized (e.g., vigilance). In small or reintroduced populations, individuals may have reduced knowledge of the nutritional landscape and migration routes, which may result in suboptimal patterns of habitat use that limit nutrient acquisition. We tested the hypothesis that differences in nutrient acquisition, as indexed by nutritional condition, resulted in Allee effects in populations of endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae). Using data on nutritional condition, vital rates, and migration strategies of Sierra Nevada bighorn sheep collected since their listing as federally endangered in 1999, we evaluated effects of nutrient acquisition on vital rates at different population sizes. We also examined the influence of nutritional condition and seasonal carryover effects of nutrition on migration strategies, seasonal movements, and energy expenditures. Nutritional condition strongly influenced key vital rates of populations of Sierra Nevada bighorn sheep, including pregnancy rates, adult survival, and finite rate of population increase and relationships between nutritional condition and adult survival varied by sex and migration strategy. We discuss our findings in the context of nutritional Allee effects as they relate to population recovery and recovery actions, including quantifying potential population size; determining translocation strategies (i.e., identifying when, where, how many, and what sexes of individuals to translocate); and identification and conservation of seasonally important ranges and migration routes. Lastly, we discuss strategies to mitigate potential Allee effects that may limit population vital rates and hence population productivity.
Forage Quality, Nutritional Stochasticity, and Density Dependence in White-Tailed Deer
David G. Hewitt; Charles A. DeYoung; Timothy E. Fulbright; David B. Wester; Don A. Draeger
Cervid management is underpinned by an assumption of density-dependent population behavior. Density dependence is likely mediated through changes in forage quantity and quality but no studies have explicitly linked deer density, vegetation, and nutrition in a manipulative study to understand density dependent mechanisms. We conducted such a study on white-tailed deer (Odocoileus virginianus) in semi-arid rangelands of western South Texas, an area where past research has suggested weak density dependence. Our replicated, 9-year study had 3 deer densities (13, 31, and 50 deer/km2) and 2 nutrition treatments (absence and presence of pelleted feed) in 12, 80-ha enclosures. Our nutrition treatment demonstrated that deer in this region are limited by nutrition because all morphologic and demographic parameters increased with improved nutrition from pelleted feed. Despite nutritional limitation, deer without pelleted feed showed only weak density dependence. Cover of palatable forbs increased in all density treatments but more so in the low density treatment. Cover of shrubs was not influenced by deer density. Observing habituated deer in the low and high density treatments, we detected no differences in diet composition, diet quality, or foraging behavior. An abundance of maintenance-quality forage, primarily shrubs, enables adult deer to persist across a broad range of deer densities. Forbs, which are probably necessary for reproduction, are absent in this highly variable environment during drought and are abundant during wet periods. Thus, reproduction is much more heavily influenced by precipitation than deer density. Increasing density did cause a decline in home range size and we hypothesize that some deer were forced into smaller, poorer-quality home ranges as density increased. Without supplemental nutrition, deer harvest in this environment should be conservative because compensatory responses will be weak. High adult survival is critical to population persistence, making these populations susceptible to overharvest and diseases that increase mortality.
Nutritional Ecology of North American Bears: Studies to Inform Population Management, Guide Resource Development, and Predict Adaptability to Change
Grant V. Hilderbrand
The three species of North American bears: black, brown, and polar bears span the continent and occupy tremendously diverse ecosystems. Though they have a relatively simple digestive system, their life history is complex and includes a multi-annual strategy of cub production and rearing, a period of winter dormancy and fasting, and delayed implantation and birth occurring while denning. Further, the management goals and conservation challenges related to bears include endangered species recovery, reduction of predation impacts on ungulates, trophy harvest, and impacts of climate change. Over the past thirty years, numerous basic knowledge gaps have been filled and a variety of tools have been developed related to physiology, diet, energetics, body composition, and habitat requirements. We continue to work to refine existing and develop new tools to better understand bears’ unique physiology and how they can successfully use the resources available within a wildly diverse and changing suite of environments.
Nutritional Ecology of Mountain Goats in Coastal Alaska
Kevin White
Mountain ungulates endure extreme climatic conditions and typically exhibit conservative life-history strategies to cope with nutritionally mediated trade-offs associated with reproduction and survival. In this study, field data collected from mountain goats in coastal Alaska (n = 479, 2005-2019) is used to examine relationships between nutritional ecology, life-history strategies and reproductive trade-offs. Specifically, data from individually marked animals is used to characterize nutritional composition of diets, body fat reserves, body mass and reproductive histories across multiple studies areas. Overall, mountain goat diets were comprised of low-quality forage items during winter but switched to high-quality sedge (Carex sp.) dominated diets during the summer growing season. During summer, mountain goats gained body mass at a rapid rate (males: 0.58 lbs/day; females: 0.40 lbs/day) relative to overall body mass (body mass on August 1st: males, mean = 260 lbs; females, mean = 160 lbs) suggesting the importance of summer range conditions in the annual nutritional cycle of mountain goats. Within this context, female mountain goats experience a significant nutritional cost of reproduction such that females with kids at heel were both lighter and had less rump fat than those without kids at heel. Overall, annual kid production ranged between 55-88% for adult females; animals less than 4-years old rarely had young. When comparing females for which kid production was determined during subsequent years, reproductive pauses were observed in 60% of cases. In a broad context, these findings provide an overview of the nutritional ecology, life-history characteristics and reproductive trade-offs of mountain goats in coastal Alaska. Specifically, these data offer insight into the linkage between nutrition and reproduction in alpine ungulates and pose important questions about the importance of summer range conditions and reproductive costs on population productivity and resilience.
Influence of Nutrition on Ungulate Recruitment in Idaho
Jon Horne; Mark Hurley; Erin Roche
Elk (Cervus canadensis) and mule deer (Odocoileus hemionus) are high‐profile game animals in the western United States, yet over the past several decades some populations have experienced a persistent and broad‐scale declines in recruitment. While the effect of predation has garnered much recent attention, there are several direct and indirect ways that the nutritional landscape can affect ungulate recruitment and these nutritional effects can often be mitigated or exacerbated by weather conditions. To investigate the potential influence of nutrition on recruitment, we modeled risk of elk and mule deer young (~6 months old to 1 year old) mortality and cause of death as a function of chest girth or weight, winter snow conditions, and predator presence using 806 monitored calves and 5500 fawns. Changes in chest girth or weight had the largest effect on risk of mortality followed by snow conditions and predators present. For elk, an approximate 20% decrease in the size of calves (130 cm to 110 cm) translated to an approximate doubling of the mortality risk (0.28 to 0.53), an effect size similar in magnitude to the combined effects of deep snow and increased predator presence. Smaller calves and fawns were likely more vulnerable to mortality because of a decreased ability to tolerate nutritional deficiencies and winter weather or because they were more susceptible to predation. Because of the importance of this covariate in explaining risk of mortality, we discuss the environmental and management conditions that affect the size of young entering winter including parturition date, summer-autumn nutritional resources, and an interaction between these variables.
Confronting Slippery Shibboleths in Ungulate Ecology Through the Lens of Nutrition
Kevin L. Monteith; Vern C. Bleich; R. Terry Bowyer; Tom R. Stephenson
Density dependence is an essential component for understanding the ecology of many species, especially K-selected large mammals. Misunderstandings, however, abound from failing to recognize that density dependence is both a life-history characteristic of a species, and a functioning attribute of populations. Despite methodological advances, interactions among predation, climate, and density dependence continue to obscure factors ultimately responsible for regulating population growth. Through long-term, individual-based monitoring of demography and nutritional condition, my colleagues and I have revealed the importance of nutrition for understanding life-history characteristics and population regulation of large herbivores. Nutritional condition is a product of an individual’s environment because it integrates nutrient intake and demands, which are a function of habitat, density dependence, and reproduction. Nutritional reserves are preferentially used to support survival and secondly to support reproduction in long-lived herbivores, thereby creating important links from habitat to nutrition to population dynamics. Nutritional condition in turn indicates the relative position of a population to its annual food supply (i.e., nutritional carrying capacity), and can yield a practical measure of the potential for population growth. Furthermore, nutrition illuminates the consequences of mortality, because it ultimately determines the baseline potential for survival and recruitment of young—mortality up to this baseline is imminent and irrespective of the proximal cause. In summary, we contend that coupling nutritional ecology with life-history theory provides a fruitful avenue to restore slippery shibboleths to their rightful place in ungulate ecology and management.
Nutritional Limitations in Ungulates: Linking Plants to Performance
Rachel C. Cook; John G. Cook; Mary M. Rowland; Michael J. Wisdom; Larry L. Irwin
Nutrition has quantifiable cause-and-effect influences on nearly every measure of ungulate performance (e.g., reproduction, growth, and survival). Nutritional ecology, then, offers a quantitative basis for linking plant community attributes and other habitat components to populations – a basis required for holistic landscape assessments and resource planning on behalf of ungulates. While many approaches have been used to quantify nutritional resources for ungulates, most have not been validated, and considerable uncertainty exists regarding the relevance and rigor of these measures. Captive animal trials, by contrast, measure nutritional response in a way that is meaningful to a ruminant herbivore and as such help explain why certain plant communities are more nutritionally valuable in summer than others and why certain ungulate herds experience more severe nutritional limitations than others. We present results from a study combining data from captive feeding trials with elk (bite count methodology and diet selection), extensive sampling of forage biomass from two vastly different ecoregions in the Northwest, spatial analyses to predict and map digestible energy levels in elk diets across the landscape, and performance data from 13 wild elk herds. Predictions of nutritional resources (i.e., foodscape maps) from fine-scale data explained >75% of the variation in autumn body fat and pregnancy of lactating elk in wild herds, showing that nutrition data collected at fine scales can be used to predict nutritional resources at large scales. Results show important similarities and differences across different ecological settings and demonstrate that nutrition models should reflect influences of disturbance, succession, and ecological context. For the first time, managers in those ecosystems have a validated nutritional basis to link landscape characteristics and habitat improvement to animal and population performance.
Study Designs for Using Nutritional Condition to Assess Populations
Tom Stephenson; Rachel C. Cook; Kristin Denryter; David W. German; Kevin L. Monteith
Nutritional condition provides a means of assessing the nutritional status of individuals within populations. Measurement of body mass and estimation of body fat are routinely sampled to quantify somatic reserves. Yet a lack of adequate understanding of the physiology of the species of interest in relation to nutrition often hampers appropriate data collection and interpretation of data. Condition data that are collected with consideration for seasonal variation and in conjunction with other covariates such as reproductive status will ensure more robust statistical designs. Currently, too many studies collect data on nutritional condition opportunistically rather than planning capture efforts around good study design. Estimates of body fat sampled within populations over short time intervals often exhibit low standard errors and require relatively low sample sizes, particularly when accounting for reproductive status. Thoughtful study designs and statistical power analysis used in conjunction with hypothesis testing will increase our likelihood of gaining reliable knowledge. Data that is poorly collected or analyzed is often incorrectly interpreted and may hamper scientific progress. In addition, training in the use of ultrasonography and body condition scoring is an essestial prerequisite for sound data collection. We elaborate on a framework for incorporating nutrition into wildlife management programs and linking nutrition with population productivity. We provide examples of well designed studies with sound conclusions.

 
Organizers: Kristin Denryter, California Department of Fish and Wildlife, West Sacramento, CA; Tom Stephenson, California Department of Fish and Wildlife, Bishop, CA; Mark Hurley, Idaho Department of Fish and Game, Boise, ID; Grant Hilderbrand, United States Geological Survey Alaska Science Center, Anchorage, AK
 
Supported by: Nutritional Ecology Working Group

Symposium
Location: Virtual Date: September 30, 2020 Time: -