Social organization and food resources availability in primates: a socio-bioenergetic analysis of diet and disease hypotheses.

Data obtained during a field study of two species of nonhuman primates (Alouatta villosa and Ateles geoffroyi) living in the Tikal National Park in Guatemala are used to suggest an answer to the question: To what extent is the existence of a particular form of social organization (group size, structure, and composition) an indication of the amount of energy in the form of food resources available to animals in a particular habitat? Seven researchers working in teams spent 2,318 hours in the field, 1,145 hours of which were in contact with the monkeys. Comparisons of dietary data, estimated energy expenditures, and habitat productivity provide indications of the degree to which a habitat is capable of supporting the energy and other nutritional requirements of howler and spider monkeys living within the study area. These data suggest that much larger populations and different forms of social organizations can be supported by resources available within the habitat.     

黑龙江凤凰山国家级自然保护区野猪冬季容纳量及最适种群密度

近年黑龙江省凤凰山国家级自然保护区野猪数量不断增长,人猪冲突加剧,保护区资源保护管理工作面临较大管理压力.为确定野猪种群的实际数量,同时评估该保护区的野猪的容纳量水平,以便为保护区管理局针对野猪的管理提供相关指导意见.2009-2010年冬季,在保护区采用样带调查、雪地足迹链跟踪和观察食痕的方法,并结合已有野猪生态研究确定野猪食性.野猪主要食物种类包括:木贼(Equisetum hiemale)、红松(Pinus koraiensis)果实松籽、胡桃楸(Juglans mandshurica)果实核桃、蒙古栎(Quecusmongolica)果实橡子、稠李(Padus racemosa)、榛子(Corylus heterophlla)、苔草(Carex spp.)、辽东葱木(Aralia elata).研究期间共布设长3-5km、单侧宽度50m、总长134 km的样带30条.调查中,每隔200 m布设10 m×10 m的大样方,并在每个大样方中央及四角布设1 m×1 m的小样方,共布设大样方350个,小样方1 750个.通过样方调查,统计野猪栖息生境当年可食植物枝条及其食物种类,然后计算其食物的总供给量,再结合食物营养成分,通过粗蛋白、粗纤维、粗脂肪的能量转换,按照每克粗蛋白和粗纤维的能量转换系数为16.74kJ、每克粗脂肪的能量转换系数为37.66 kJ,确定野外生境食物总能量供给.结合野猪冬季日营养需求,以能量为基础估算保护区野猪的营养容纳量.在种群密度调查过程中,通过足迹链判断个体方法为:单一清晰足迹链确定为一个体所留,30m内多条足迹穿越同一样带被认为是一个野猪群所留,调查中根据个体分开时的足迹链数确定野猪个体数,同时将粪便、卧迹、啃食痕迹作为个体判断的辅助信息.研究结果表明:凤凰山保护区内能够提供的总能量为7.375 ×107MJ,冬季平均每头野猪生存所需能量为(14 677.698±409.92) MJ,野猪营养容纳量为(1 006±28)头,种群密度为(3.79±0.11)头/km2.此外,调查中发现30余个野猪套及2头野猪被猎杀现场,反应出当地的人猪冲突较为严重.结合调查中发现的野猪套数量及野猪被猎杀概率,对野猪种群数量引入20％的死亡风险系数.最终确定凤凰山野猪种群的最适数量在(603±17)头左右,最适密度为(2.27±0.06)头/km2.通过样带法调查得出凤凰山自然保护区实际野猪种群数量为(596±155)头,密度(2.24±0.58)头/km2,已趋近营养容纳量.因此,野猪并未过量,不能采取狩猎等降低种群数量的措施,同时保护区也应对野猪种群进行持续监控,防止野猪种群过度繁殖以至成灾.     

Determination of Foraging Thresholds and Effects of Application on Energetic Carrying Capacity for Waterfowl

Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts. However, carrying capacity can be difficult to estimate accurately and simplified models often depend on many assumptions and few estimated parameters. We demonstrate the complex nature of parameterizing energetic carrying capacity models and use an experimental approach to describe a necessary parameter, a foraging threshold (i.e., density of food at which animals no longer can efficiently forage and acquire energy), for a guild of migratory birds. We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter. Dabbling ducks (Anatini) fed extensively in plots and all initial densities of supplemented seed were rapidly reduced to 10 kg/ha and other natural seeds and tubers combined to 170 kg/ha, despite different starting densities. However, ducks did not abandon or stop foraging in wetlands when seed reduction ceased approximately two weeks into the winter-long experiment nor did they consistently distribute according to ideal-free predictions during this period. Dabbling duck use of experimental plots was not related to initial seed density, and residual seed and tuber densities varied among plant taxa and wetlands but not plots. Herein, we reached several conclusions: 1) foraging effort and numerical responses of dabbling ducks in winter were likely influenced by factors other than total food densities (e.g., predation risk, opportunity costs, forager condition), 2) foraging thresholds may vary among foraging locations, and 3) the numerical response of dabbling ducks may be an inconsistent predictor of habitat quality relative to seed and tuber density. We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.     

Opportunity costs influence food selection and giving‐up density of dabbling ducks

The interaction of animals with their food can yield insights into habitat characteristics, such as perceived predation risk and relative quality. We deployed experimental foraging patches in wetlands used by migrating dabbling ducks Anas spp. in the central Illinois River Valley to estimate variation in seed removal and giving‐up density (GUD; i.e. density of food remaining in patches following abandonment) with respect to seed density, seed size, seed depth in the substrate, substrate firmness, perceived predation risk, and an energetic profitability threshold (i.e. critical food density). Seed depth and the density of naturally‐occurring seeds outside of experimental plots affected seed removal and GUD in experimental patches more than perceived predation risk, seed density, seed size or substrate firmness. The greatest seed removal and lowest GUDs in experimental patches occurred when food resources in alternative foraging locations outside of plots (i.e. opportunity costs) appeared to be near or below a critical food density (i.e. 119–181 kg ha^–1). Giving‐up densities varied substantially from a critical food density across a range of food densities in alternative foraging locations suggesting that fixed GUDs should not be used as surrogates for critical food densities in energetic carrying capacity models. Foraging and resting rates in and near experimental foraging patches did not reflect patterns of seed removal and were poor predictors of GUD and foraging habitat quality. Our results demonstrated the usefulness of GUDs as indicators of habitat quality for subsurface, benthic foragers relative to other available foraging patches and suggested that food may be limited for dabbling ducks during spring migration in some years in the midwestern USA.     

Biomechanics and foraging profitability: an approach to assessing trophic needs and impacts of diving ducks

A biomechanical model of underwater locomotion is described, and data required by the model presented for 3 species of diving duck (Aythya spp.). Based on field observations of behavior and foods consumed, the model is used to estimate energy costs of foraging and minimum food intake rates of canvasbacks (Aythya valisineria) in two habitats in North Carolina. Increased water depth from 0.5 m in Lake Mattamuskeet to 1.5 m in Pamlico Sound increased the net cost of time spent foraging at the bottom by 43%. Biomechanical calculations are combined with data on intake rates at different food densities (Takekawa, 1987) to determine minimum food densities for profitable foraging in Lake Mattamuskeet. Field observations of behavior are used to adjust minimum intake per dive for unsuccessful dives spent locating food patches. Density and dispersion of plant tuber foods in Lake Mattamuskeet, before and after the fall staging period, suggest that the fraction of habitat with tuber densities above a profitability threshold is more critical to canvasbacks than average tuber density. Such factors are important in relating bird energy requirements and benthic sampling data to carrying capacity and total area of usable habitat. The proportion of foods that can be fed upon profitably also determines the fraction of food organisms subject to depletion as components of trophic pathways.     

The Influence of Water Depth on Energy Availability for Ducks

Habitat management and planning strategies for nonbreeding ducks are focused on providing enough energy to support a desired number of individuals. Therefore, regional estimates of energy availability for nonbreeding ducks are required to determine if sufficient habitat exists for them. I used core sampling to estimate food and energy density in 6 types of water bodies (i.e., actively and passively managed emergent wetlands, playas, small and large reservoirs, and sloughs) in northeastern Colorado, USA, during 3 sampling occasions throughout 2 nonbreeding seasons, 2015–2016 and 2016–2017. Also, I used precise depth measurements to estimate the percentage of each site that was shallow enough to facilitate feeding by dabbling ducks as a way to correct overall energy density to reflect availability to ducks. Emergent wetlands contained the greatest food and energy density, followed by playas and sloughs, and reservoirs contained little food or energy. Fall depletion of food was greatest in actively managed emergent wetlands and spring depletion was greatest in sloughs and passively managed emergent wetlands. Mean percentage of passively managed emergent wetlands, actively managed emergent wetlands, small reservoirs, large reservoirs, and sloughs shallower than 50 cm was 37%, 77%, 10%, 4%, and 83%, respectively. Incorporating these estimates into the energetic carrying capacity model developed by the Playa Lakes Joint Venture for eastern Colorado resulted in a 54% decrease in overall duck energy day estimates, which is below what is needed to support population goals. This research identifies the need for additional wetland restoration in eastern Colorado to meet energy requirements of nonbreeding ducks and provides information to conservation planners to make more informed decisions about the extent and location of wetland restoration activities. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.     

Assessing Nutritional Parameters of Brown Bear Diets among Ecosystems Gives Insight into Differences among Populations

Food habit studies are among the first steps used to understand wildlife-habitat relationships. However, these studies are in themselves insufficient to understand differences in population productivity and life histories, because they do not provide a direct measure of the energetic value or nutritional composition of the complete diet. Here, we developed a dynamic model integrating food habits and nutritional information to assess nutritional parameters of brown bear (Ursus arctos) diets among three interior ecosystems of North America. Specifically, we estimate the average amount of digestible energy and protein (per kilogram fresh diet) content in the diet and across the active season by bears living in western Alberta, the Flathead River (FR) drainage of southeast British Columbia, and the Greater Yellowstone Ecosystem (GYE). As well, we estimate the proportion of energy and protein in the diet contributed by different food items, thereby highlighting important food resources in each ecosystem. Bear diets in Alberta had the lowest levels of digestible protein and energy through all seasons, which might help explain the low reproductive rates of this population. The FR diet had protein levels similar to the recent male diet in the GYE during spring, but energy levels were lower during late summer and fall. Historic and recent diets in GYE had the most energy and protein, which is consistent with their larger body sizes and higher population productivity. However, a recent decrease in consumption of trout (Oncorhynchus clarki), whitebark pine nuts (Pinus albicaulis), and ungulates, particularly elk (Cervus elaphus), in GYE bears has decreased the energy and protein content of their diet. The patterns observed suggest that bear body size and population densities are influenced by seasonal availability of protein an energy, likely due in part to nutritional influences on mass gain and reproductive success.     

Habitat carrying capacity is reached for the European eel in a small coastal catchment: evidence and implications for managing eel stocks

1. Despite carrying capacity being one of the most important parameters in population management and modelling, we lack substantial evidence for habitat limitations on freshwater species. Here we tested the ideal free distribution (IFD) hypothesis using an indirect behaviour‐based method for small closed populations assuming that animals can effectively estimate habitat suitability and distribute themselves accordingly in time and space. 2. We analysed spatiotemporal variations in the density of the European eel Anguilla, a catadromous species with good colonisation abilities in a small coastal catchment in France. The general linear model used enabled us to test simultaneously the effect of temporal, macro‐ and meso‐scale habitat factors on the presence and abundance of eels at 30 sites over an 8‐year period. 3. Almost every site sampled had eels, whatever its location on the catchment and its habitat characteristics. Density estimates (overall mean ± SD of 0.40 ± 0.48 m^?2) were at the upper range of other values for European catchments. Moreover, eel densities were mainly influenced by the availability of suitable habitats (rocky substratum and instream cover), which suggests that their distribution reflects an IFD. 4. Despite marked variability in recruitment, the density of the oldest size‐class remained stable over the study, suggesting that density‐dependent mortality occurred, probably due to intraspecific competition for space and food and to predation. 5. These findings suggest that eel habitats are saturated in the Frémur. Therefore, we suggest that the mean abundance of eels observed could serve as a threshold value for other male‐dominated river stocks (provided they have a similar overall percentage of suitable habitats) that are common in small, low gradient streams on the north‐Atlantic coast of Europe.     

Food resource availability for American black ducks wintering in southern New Jersey

Midwinter waterfowl survey data indicates a long-term decline in the number of wintering American black ducks (Anas rubripes), potentially due to habitat limitations. In order for future estimates of carrying capacity to be determined, it is critical that regional food availability is estimated. We collected pairs of habitat core samples (n = 510) from 5 habitat types in southern New Jersey, USA, during October, January, and April 2006–2008 to estimate resource availability and variability. We collected upper gastrointestinal tracts from hunter-killed birds (n = 45) and late season collections (n = 19) to identify food items and limited our estimates of resource availability to only winter food items; thereby reducing the availability of seed foods found in our core samples by 38% and animal foods by 96%. We did not detect differences in years or sampling period, but did between habitat types. Mudflat habitat had the greatest availability of invertebrate and vertebrate food items and appeared to supply the bulk of energy to black ducks wintering in southern New Jersey. We suggest conservation efforts to be focused on restoring or enhancing mudflat habitat as an integral component of an ecologically functioning salt marsh to increase food availability. © 2011 The Wildlife Society.     

Energy limitation of hummingbird populations in tropical and temperate communities

Summary Regular censuses were conducted at both a temperate alpine and a tropical lowland site to determine seasonal changes in the composition of hummingbird communities and the availability of their food. From these data we calculated the total daily energy demand by the hummingbirds (Daily Energy Expenditure; DEE) and the daily energy supply available from floral nectar (Daily Energy Production; DEP) for each community census. Despite differences in habitat type and hummingbird community structure between these two sites, the hummingbird populations were often at or near carrying capacity. On average, all of the daily nectar production was cropped by the birds. We suggest that the supply/demand economics of coevolved mutualisms favour the evolution of complete resource use.     

Food and density limitations of the Seychelles Magpie Robin,Copsychus sechellarum,on Cousine Island

The critically endangered Seychelles Magpie Robin, Copsychus sechellarum, is one of the rarest birds in the world. At the end of December 1999, there were 88 individuals distributed on four small granite islands: Fregate, Aride, Cousin and Cousine. Little is known of Magpie Robin ecology in its natural habitat. Studies carried out on Aride, Cousin and Cousine are therefore valuable as each island is dominated by native woodland. The composition of Magpie Robin diet was compared between Fregate and Cousine. An exotic species of cockroach, Pycnoscelus indicus, and dropped fish were found to be considerably more important prey items on Cousine. Observations of chick food provisioning indicated habitat quality differences between the territories. Invertebrate and vertebrate food resources available to the Magpie Robin were sampled on Cousine between 1997 and 1998. Fourteen sites were sampled for invertebrates and fifty-two species from fifteen taxa were identified. There were significant differences between the mean number of species recorded per site and the mean number of animals found at each site. Skink density was estimated at between 1219-1516/ha and 354-538/ha for Mabuya sechellensis and Mabuya wrightii respectively. Invertebrate diversity and abundance was greatest in areas dominated by closed-canopy woodland on or near the coastal plain. These results explained the current distribution of Magpie Robin territories. The invertebrate abundance data were used to estimate the carrying capacity of the island for the Magpie Robin. Cousine could theoretically support up to six breeding pairs but it is questionable that a population of this size could be self-sustaining in the long-term.     

Effects of Snow on Sitka Black-Tailed Deer Browse Availability and Nutritional Carrying Capacity in Southeastern Alaska

ABSTRACT Snow affects the nutritional ecology of northern ungulates during winter through burial of important winter forages. We used nonlinear regression analyses to model snow-burial dynamics of blueberry (Vaccinium spp.) browse biomass, a key winter food item of Sitka black-tailed deer (Odocoileus hemionus sitchensis) in southeastern Alaska, USA. During November 2003—March 2004 we collected data from 546 individually marked twigs located on 100 plants of differing sizes and architectures across a range of snow depths. In general, browse biomass became buried and unavailable to deer at snow depths substantially lower than prewinter twig heights. Plant architecture and plant height were related to the probability of a twig being buried. Probability of twig burial was higher on plants with lateral than on those with erect architectures. Twig height also affected the probability of burial by snow but the relationship was complex. For twigs located on erect plants, probability of burial was greatest for twigs near the bottom and top of the plant due to ground-up burial and bending of flexible apex stems, respectively. We used estimated nonlinear equations to model blueberry browse availability in a simulated upland old-growth habitat patch subject to a range of snow depths. We then compared subsequent estimates of deer winter nutritional carrying capacity for this habitat patch to findings derived using an alternative, simple linear (ground-up) model of winter-browse burial by snow. Comparisons indicated that ground-up models of browse burial overestimated browse availability and nutritional carrying capacity for most snow depths. Our findings demonstrate the importance of applying detailed snow-burial models when characterizing nutritional landscape of northern ungulates during winter.     

Estimate of population extinction risk and its application to ecological risk management

Environmental threats, such as habitat size reduction or environmental pollution, may not cause immediate extinction of a population but may shorten the expected time to extinction. We developed a method to estimate the mean time to extinction for a density-dependent population with environmental fluctuation and to compare the impacts of different risk factors. We first derived a formula of the mean extinction time for a population with logistic growth and environmental and demographic stochasticities expressed as a stochastic differential equation model (canonical model). The relative importance of different risk factors is evaluated by the decrease in the mean extinction time. We studied an approximated formula for the reduction in habitat size that enhances extinction risk by the same magnitude as a given decrease in survivorship caused by toxic chemical exposure. In a large population (large K) or in a slowly growing population (small r), a small decrease in survivorship can cause the extinction risk to increase, corresponding to a significant reduction in the habitat size. Finally, we studied an approximate maximum likelihood estimate of three parameters (intrinsic growth rate r, carrying capacity K, and environmental stochasticity σ ² _e ) from time series data. By Monte Carlo sampling, we can remove the bias very effectively and determine the confidence interval. We discuss here how the reliability of the estimate changes with the length of time series. If we know the intrinsic rate of population growth r, the mean extinction time is estimated quite accurately even when only a short time series is available for parameter estimation. Received: March 31, 1999 / Accepted: November 9, 1999     

Population survey of the spider monkeyAteles geoffroyi at Tikal,Guatemala

Intensive strip census methods were used to estimate population density and age-sex composition of a natural population of the spider monkeyAteles geoffroyi, in seasonally dry forest at Tikal, Guatemala. An objective procedure for determining effective strip width is discussed, and various census methods, including direct count and strip census, are evaluated as to merits and disadvantages     

Allometry of territory size and metabolic rate as predictors of self-thinning in young-of-the-year Atlantic salmon

1. Self-thinning is a progressive decline in population density caused by competitively induced losses in a cohort of growing individuals and can be depicted as: log₁₀ (density) = c − β log₁₀ (body mass).
2. In mobile animals, two mechanisms for self-thinning have been proposed: (i) the space hypothesis predicts that maximum population density for a given body size is the inverse of territory size, and hence, the self-thinning slope is the negative of the slope of the allometric territory-size relationship; (ii) the energetic equivalence hypothesis predicts that the self-thinning slope is the negative of the slope of the allometric metabolic rate relationship, assuming a constant supply of energy for the cohort.
3. Both hypotheses were tested by monitoring body size, population density, food availability and habitat for young-of-the-year Atlantic salmon ( Salmo salar ) in Catamaran Brook, New Brunswick. The results were consistent with the predictions of the space hypothesis. Observed densities did not exceed the maximum densities predicted and the observed self-thinning slope of −1·16 was not significantly different from the slope of −1·12, predicted by the allometry of territory size for the population under study.
4. The observed self-thinning slope was significantly steeper than −0·87, predicted by the allometry of metabolic rate, perhaps because of a gradual decline in food abundance over the study period. The decline in density was more rapid in very shallow sites and may have been partly caused by a seasonal change in water depth and an ontogenetic habitat shift rather than solely by competition for food or space.
5. The allometry of territory size may be a useful predictor of self-thinning in populations of mobile animals competing for food and space.     

Estimating Carrying Capacity for Sea Otters in British Columbia

ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km² and 2.53 otters/km² for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km²) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.     

Ecology of the Zanzibar Red Colobus Monkey: Demographic Variability and Habitat Stability

We examined the Zanzibar red colobus' (Procolobus kirkii) social structure and population dynamics in relation to the density, diversity and dispersion of food resources in ground-water forest and agricultural land, which we characterized in terms of red colobus food species density, diversity, basal area and dispersion. We used transect sampling and group follows to describe population dynamics and social systems. Two agricultural areas, SJF Shamba and Pete Village, had higher densities and more uniformly dispersed red colobus food tree species than those of the ground-water forest. Red colobus at these two sites had greater population densities and natality, and smaller home ranges than red colobus in the ground-water forest. However, these findings apply to a very small area of agricultural land (approximately 18 ha) that is contiguous with an area of the forest reserve having a high density of red colobus. It is not representative of agricultural areas elsewhere on Zanzibar which support much lower densities or no red colobus. Although agricultural areas contiguous with the forest reserve had high densities of red colobus, they appear to be very unstable. Within the agricultural areas, we observed higher intergroup variation in group size and composition, study groups that decreased dramatically in size and disappeared from the study site, significantly lower levels of juvenile recruitment, and red colobus food trees that exhibited definite signs of overbrowsing. This apparent instability in the subpopulation of red colobus utilizing agricultural systems probably reflects the lower basal area of food trees and the greater fragmentation of suitable habitat and floristic dynamics due to human activities in these areas. A fusion-fission social system occurred only in the ground-water forest subpopulation, which we hypothesize to be due to highly clumped food resources.     

Inferring the temperature dependence of population parameters: the effects of experimental design and inference algorithm

Understanding and quantifying the temperature dependence of population parameters, such as intrinsic growth rate and carrying capacity, is critical for predicting the ecological responses to environmental change. Many studies provide empirical estimates of such temperature dependencies, but a thorough investigation of the methods used to infer them has not been performed yet. We created artificial population time series using a stochastic logistic model parameterized with the Arrhenius equation, so that activation energy drives the temperature dependence of population parameters. We simulated different experimental designs and used different inference methods, varying the likelihood functions and other aspects of the parameter estimation methods. Finally, we applied the best performing inference methods to real data for the species Paramecium caudatum. The relative error of the estimates of activation energy varied between 5% and 30%. The fraction of habitat sampled played the most important role in determining the relative error; sampling at least 1% of the habitat kept it below 50%. We found that methods that simultaneously use all time series data (direct methods) and methods that estimate population parameters separately for each temperature (indirect methods) are complementary. Indirect methods provide a clearer insight into the shape of the functional form describing the temperature dependence of population parameters; direct methods enable a more accurate estimation of the parameters of such functional forms. Using both methods, we found that growth rate and carrying capacity of Paramecium caudatum scale with temperature according to different activation energies. Our study shows how careful choice of experimental design and inference methods can increase the accuracy of the inferred relationships between temperature and population parameters. The comparison of estimation methods provided here can increase the accuracy of model predictions, with important implications in understanding and predicting the effects of temperature on the dynamics of populations.     

Prediction of bird-day carrying capacity on a staging site: a test of depletion models

1. The carrying capacity of a site for migratory water birds, expressed in bird-days, can be of particular conservation value. Several attempts have been made to model this carrying capacity using ideal free distribution models such as, for instance, depletion models, in which the distribution is fully determined by exploitative competition. 2. In the tests of depletion models carried out so far, no alternative models were compared; rather, one specific model was tested. We tested whether bird-days were more in accordance with birds depleting the food resource (a1) until a critical food density which just enabled survival or (a2) until a threshold food density which renders the site as profitable as an alternative site; and birds (b1) satisfying their daily requirements or (b2) maximizing daily intake. 3. We studied Bewick's swans feeding on below-ground tubers of fennel pondweed in one part of an autumn staging site. In most years between 1995 and 2005, we measured tuber biomass densities around September, November and March, and counted swans daily during their stopover in October. 4. The best fit between observed and predicted bird-days was obtained by assuming that the swans were maximizing their daily intake and depleting the tubers until a threshold biomass density (which yielded the same energetic return as the alternative food source after accounting for a small part of the initial tuber biomass being out of reach of the swans). Also in line with daily intake maximization, the daily feeding time did not differ from 10 h day(-1), the value predicted for Bewick's swans based on their feeding costs. 5. Our results suggests that the applicable model to calculate carrying capacity may depend strongly on whether birds use a site to stopover or to winter, because it determines whether the birds are more likely to use a threshold or critical food density, and to behave as energy maximizers or satisficers.     

Multi-scale species density model for conserving an endangered songbird

Habitat modeling across a landscape that has gradients of habitat conditions requires potential predictor data that can be quantified at biologically relevant scales. We used remotely sensed data to develop a multi-scale density model in 2018 for the golden-cheeked warbler (Setophaga chrysoparia; warbler), a species that breeds in Ashe juniper (Juniperus ashei)-oak (Quercus spp.) woodlands in central Texas, USA. We first classified Ashe juniper and broadleaf tree cover at a 1-m resolution and used this to map potential habitat across the warbler's >67,000-km² breeding range. We then designed a survey for estimating warbler density based on hierarchical distance sampling. We used stratified random sampling to survey for male warblers at 1,804 points across the continuum of tree canopy cover and composition and detected 810 warblers during our surveys. We developed a suite of potential predictor variables for modeling warbler density that reflected vegetation, topography, climate, and anthropogenic land use conditions across the breeding range and developed these at 3 scales representing the territory, site, and landscape. We modeled warbler density and used the best fit model to produce a spatially explicit estimate. Predicted warbler density was influenced by tree canopy cover and canopy height at the territory scale (100-m radius); tree canopy cover, percent of the canopy comprised of juniper, and an interaction between canopy cover and compound topographic index at the site scale (1-km radius); and annual temperature range at the landscape scale (5-km radius). We estimated a population size of 217,444 male warblers (95% CI = 153,917–311,965) and >3,000 males in each recovery unit. After controlling for the duration of point count surveys, our estimate of population size was similar to that reported from the only previous breeding range survey conducted in 2008–2009. Our model results indicated that management activities to increase warbler density should promote woodlands with high tree canopy cover, approximately 60–80% Ashe juniper composition, and tree heights >3 m. In contrast to a patch-based approach, our treatment of habitat variables as continuous helped to credibly map the warbler distribution across areas with broad transitions from woodlands to shrublands. By measuring these predictor variables at biologically relevant scales, we allowed the warbler survey data to define habitat relationships instead of using anthropogenically defined habitat patches. Outcomes from our study show the benefits of developing spatial products tailored to individual species of interest for conservation and management decisions.