The Demography and Determinants of Population Growth in Utah Moose (\u3ci\u3eAlces alces shirasi\u3c/i\u3e)

Moose in Utah represent the southernmost naturally occurring populations of moose in the world. Concerns over possible numeric declines and a paucity of baseline data on moose in the state prompted the Utah Division of Wildlife Resources to initiate a study of moose demography in collaboration with Utah State University. The objectives of this study were to 1) determine reproductive rates of moose in Utah and the factors which influence them, and 2) combine aerial count data from multiple management units within the state to identify factors which influence interannual variation in population growth rates. We constructed generalized linear models to relate maternal body condition and age to reproductive success. We found that body condition (P = 0.01) and age (P = 0.02) contributed significantly to the probability of pregnancy and the best model describing this relationship was nonlinear. Body condition also related positively to subsequent calving (P = 0.08) and recruitment (P = 0.05), but model selection suggested the relationship for these metrics was best described by linear models. A meta-analysis of moose reproductive rates in North America suggested that reproductive rates declined significantly with latitude (P ≤ 0.01), i.e. as populations approached their southern range limit. We used Bayesian state-space models to combine moose count data from different management units to estimate statewide population dynamics between 1958 and 2013. This approach incorporated uncertainty in population counts arising from observation error. Population density and warm winter temperatures negatively influenced population growth rate with a high degree of confidence; 95% Bayesian Credible Intervals for these variables did not overlap zero. Short-term projections of moose abundance in the state suggested that the population will likely remain stable despite projected increases in winter temperature. Results from this study will aid managers in achieving management objectives as well as future decision making. The unique characteristics of the population also have application toward understanding the dynamics of populations of cold-adapted species at their southern range limit

Spatial Ecology and Species Interactions among Predators and their Prey

Carnivores have disproportionate effects in ecological systems but understanding their exact influences on ecosystems is a matter of great complexity and debate. Predators directly impact prey by killing them, and indirectly by modifying their behavior in response to predation risk. Yet how species interact, both among members of a carnivore guild and between predators and prey, is still a frontier in the field of ecology. Using cougars, coyotes, black bears, and bobcats as model species, I tested methods to estimate carnivore population densities most efficiently, disentangled the intraguild dynamics and species interactions within a terrestrial carnivore community, and studied the spatial response of carnivores to an ephemeral resource pulse of large herbivore neonates. Between 2016 and 2019 I collected data on the four carnivore species at the Starkey Experimental Forest and Range in northeast Oregon. I collected over 1,200 carnivore scats, deployed nearly 100 remote cameras over 3 field seasons, and captured and GPS-collared over 50 individuals encompassing the four study species. I tested a suite of models for density estimation that utilized images of carnivores from remote cameras, individual genotypes determined from scats, capture-recapture data from the effort to capture and collar carnivores, and GPS data from collared individuals. I found that spatial capture-recapture models using genetic data performed the best, but that spatial mark-resight models based on resighting GPS-collared animals using remote cameras were generally in agreement but with lower precision. Methods consisting of photos of unmarked animals from remote cameras performed poorly and generated misleading estimates of population densities for all species. Finally, I developed a novel method to combine data from genetic sources, remote cameras, the physical capture process, and GPS collars into a hybrid model that provided the most precise estimates of animal abundance. I next studied the intraguild interactions between members of the carnivore community. Resource provisioning from competitively-dominant cougars to coyotes through scavenging was so prolific as to be an overwhelming determinant of coyote behavior, space use, and resource acquisition. This was evident via strong attraction of coyotes to cougar kill sites, frequent scavenging of cougar-killed prey, and coyote diets that nearly matched cougars in the magnitude of ungulate consumption. Yet coyotes were often killed by cougars and used space to minimize encounters, complicating the fitness benefits gained from scavenging. I estimated that 23% (95% CI: 8–55%) of the coyote population in our study area was killed by cougars annually suggesting that coyote interactions with cougars are a complex behavioral game of risk and reward. In contrast, I found no indication that bobcat space use or diet was influenced by cougars. Black bears avoided cougars, but there was no evidence of attraction to cougar kill sites, and much lower levels of ungulate consumption and carcass visitation than for coyotes. Finally, I studied the spatial response of the four carnivore species to the seasonal pulse of two large herbivore species using simultaneous GPS locations of the predators and prey. I used step-selection functions to assess whether coyotes, cougars, black bears, and bobcats actively searched for parturient females in a low-density mule deer population and a high-density elk population. I found that none of the four carnivore species encountered parturient mule deer more often than expected by chance suggesting that predation on fawns resulted from incidental encounters. By contrast, I determined that cougar and bear movements positioned them in proximity of parturient elk with male bears driving the observed pattern. In a subsequent analysis, I found that use of parturition habitat dynamically tracked the phenology of the elk birth pulse for bears, but not cougars. These results suggest that of the species studied, only bears shifted habitat use to maximize encounters with elk calves, and in doing so, caused them to encounter elk calves more often than expected by chance. These results contribute to a better understanding of the multitude of effects carnivores have in ecological communities

Fluctuations in age structure and their variable influence on population growth

Temporal fluctuations in growth rates can arise from both variation in age‐specific vital rates and temporal fluctuations in age structure (i.e. the relative abundance of individuals in each age‐class). However, empirical assessments of temporal fluctuations in age structure and their effects on population growth rate are relatively rare. Most research has focused on understanding the contribution of changing vital rates to population growth rates and these analyses routinely assume that: (a) populations have stable age distributions, (b) environmental influences on vital rates and age structure are stationary (i.e. the mean and/or variance of these processes does not change over time), and (c) dynamics are independent of density. Here we quantified fluctuations in age structure and assessed whether they were stationary for four populations of free‐ranging vertebrates: moose (observed for 48 years), elk (15 years), tawny owls (15 years) and grey wolves (17 years). We also assessed the extent that fluctuations in age structure were useful for predicting annual population growth rates using models which account for density dependence. Fluctuations in age structure were of a similar magnitude to fluctuations in abundance. For three populations (moose, elk, owls), the mean and the skew of the age distribution fluctuated without stabilizing over the observed time periods. More precisely, the sample variance (interannual variance) of age structure indices increased with the length of the study period, which suggests that fluctuations in age structure were non‐stationary for these populations – at least over the 15‐ to 48‐year periods analysed. Fluctuations in age structure were associated with population growth rate for two populations. In particular, population growth varied from positive to negative for moose and from near zero to negative for elk as the average age of adults increased over its observed range. Non‐stationarity in age structure may represent an important mechanism by which abundance becomes non‐stationary – and therefore difficult to forecast – over time‐scales of concern to wildlife managers. Overall, our results emphasize the need for vertebrate populations to be modelled using approaches that consider transient dynamics and density dependence and that do not rely on the assumption that environmental processes are stationary

Extensive aquatic subsidies lead to territorial breakdown and high density of an apex predator

Energetic subsidies between terrestrial and aquatic ecosystems can strongly influence food webs and population dynamics. Our objective was to study how aquatic subsidies affected jaguar (Panthera onca) diet, sociality, and population density in a seasonally flooded protected area in the Brazilian Pantanal. The diet (n = 138 scats) was dominated by fish (46%) and aquatic reptiles (55%), representing the first jaguar population known to feed extensively on fish and to minimally consume mammals (11%). These aquatic subsidies supported the highest jaguar population density estimate to date (12.4 jaguars/100 km²) derived from camera traps (8,065 trap nights) and GPS collars (n = 13). Contrary to their mostly solitary behavior elsewhere, we documented social interactions previously unobserved between same-sex adults including cooperative fishing, co-traveling, and play. Our study demonstrates that aquatic subsidies, frequently described in omnivores, can also transform the ecology and behavior of obligate carnivores