Scholarly Work - Ecology
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Item Size-specific apparent survival rate estimates of white sharks using mark–recapture models(Canadian Science Publishing, 2019-02) Kanive, Paul E.; Rotella, Jay J.; Jorgensen, Salvador J.; Chapple, Taylor K.; HInes, James E.; Anderson, Scot D.; Block, Barbara A.Abstract: For species that exist at low abundance or are otherwise difficult to study, it is challenging to estimate vital rates such as survival and fecundity and common to assume that survival rates are constant across ages and sexes. Population assessments based on overly simplistic vital rates can lead to erroneous conclusions. We estimated sex- and length-based annual apparent survival rates for white sharks (Carcharodon carcharias). We found evidence that annual apparent survival differed over ontogeny in a system with competitive foraging aggregations, from 0.63 (standard error (SE) = 0.08) for newly recruiting subadults to 0.95 (SE = 0.02) for the largest sharks. Our results reveal a potential challenge to ontogenetic recruitment in a long-lived, highly mobile top marine predator, as survival rates for subadult white sharks may be lower than previously assumed. Alternatively, younger and competitively inferior individuals may be forced to permanently emigrate from primary foraging sites. This study provides new methodology for estimating apparent survival as a function of diverse covariates by capture–recapture study, including when sex assignment is uncertain. Résumé : Pour les espèces qui existent en faible abondance ou dont l’étude présente par ailleurs un défi, il est difficile d’estimer des indices vitaux comme la survie et la fécondité et il est couramment présumé que les taux de survie ne varient pas selon le sexe et le groupe d’âge. Des évaluations de populations reposant sur des indices vitaux trop simplistes peuvent mener à des conclusions erronées. Nous avons estimé les taux de survie annuels apparents en fonction du sexe et de la longueur pour de grands requins blancs (Carcharodon carcharias). Nous avons relevé des preuves de variation du taux de survie annuel apparent au fil de l’ontogénie dans un système caractérisé par des regroupements concurrents d’individus en quête de nourriture, ce taux allant de 0,63 (l’écart-type (ÉT) = 0,08) pour les individus subadultes récemment recrutés à 0,95 (ÉT = 0,02) pour les requins les plus grands. Nos résultats révèlent une difficulté potentielle en ce qui concerne le recrutement ontogénique chez un prédateur marin de niveau trophique supérieur très mobile et longévif, puisque les taux de survie de grands requins blancs subadultes pourraient être plus faibles que présumés auparavant. Une autre explication est que les individus plus jeunes ou moins concurrentiels pourraient être forcés d’émigrer des meilleurs sites d’approvisionnement de manière permanente. L’étude présente une nou-velle méthodologie pour estimer la survie apparente en fonction de différentes variables reliées, par une approche de capture–recapture, y compris pour les cas où l’affectation du sexe est incertaine. [Traduit par la Rédaction]Item Simulation-based validation of spatial capture-recapture models: A case study using mountain lions(2019-04) Paterson, J. Terrill; Proffitt, Kelly M.; Jimenez, Ben; Rotella, Jay J.; Garrott, Robert A.Spatial capture-recapture (SCR) models have improved the ability to estimate densities of rare and elusive animals. However, SCR models have seldom been validated even as model formulations diversify and expand to incorporate new sampling methods and/or additional sources of information on model parameters. Information on the relationship between encounter probabilities, sources of additional information, and the reliability of density estimates, is rare but crucial to assessing reliability of SCR-based estimates. We used a simulation-based approach that incorporated prior empirical work to assess the accuracy and precision of density estimates from SCR models using spatially unstructured sampling. To assess the consequences of sparse data and potential sources of bias, we simulated data under six scenarios corresponding to three different levels of search effort and two levels of correlation between search effort and animal density. We then estimated density for each scenario using four models that included increasing amounts of information from harvested individuals and telemetry to evaluate the impact of additional sources of information. Model results were sensitive to the quantity of available information: density estimates based on low search effort were biased high and imprecise, whereas estimates based on high search effort were unbiased and precise. A correlation between search effort and animal density resulted in a positive bias in density estimates, though the bias decreased with increasingly informative datasets. Adding information from harvested individuals and telemetered individuals improved density estimates based on low and moderate effort but had negligible impact for datasets resulting from high effort. We demonstrated that density estimates from SCR models using spatially unstructured sampling are reliable when sufficient information is provided. Accurate density estimates can result if empirical-based simulations such as those presented here are used to develop study designs with appropriate amounts of effort and information sources.Item Maladaptive nest-site selection by a sagebrush dependent species in a grazing-modified landscape(2019-04) Cutting, Kyle A.; Rotella, Jay J.; Schroff, Sean R.; Frisina, Michael R.; Waxe, James A.; Nunlist, Erika; Sowell, Bok F.Animals are expected to select habitats that maximize their fitness over evolutionary time scales. Yet in human-modified landscapes, habitat selection might not always lead to increased fitness because animals undervalue high-quality resources that appear less attractive than those of lower quality. In the American West, agriculture has modified landscapes, yet little is known about whether agricultural changes alter the reliability of the cues animals use to identify habitat quality; ultimately forming maladaptive breeding strategies where behavioral cues are mismatched with survival outcomes. Using the greater sage-grouse, a species highly dependent upon sagebrush landscapes, we (1) evaluated how females select nesting habitats based on sagebrush type, along with livestock grazing related linear and point features, and other biotic, abiotic characteristics, given hypothesized influences on hiding cover, microclimate and predator travel routes and perches, (2) compared habitat selection information with results for nest survival estimates to evaluate if selection appears to be adaptive or not, and (3) used our results to evaluate the most appropriate strategies for this species in a grazing-modified landscape. Nest-site selection for sagebrush type appears to be maladaptive: in the most-preferred sagebrush type, nest survival rate was one-fourth the rate realized by females nesting in the sagebrush type avoided. Nest survival was four times higher for nests placed away from (>100 m), rather than next to (1 m), the nearest fence, and survival was lower within sites with higher cow pie density (a proxy for previous grazing intensity). Live and dead grasses influenced selection and survival in opposing ways such that dead grass was selected for but resulted in reduced survival while live grass was avoided but resulted in increased survival. Results collectively provide the first empirical evidence that a specific type of sagebrush acts as an ecological trap while another sagebrush type is undervalued. These results also suggest that adding more fences to control livestock grazing systems will likely reduce sage-grouse nest survival.Item Variation in the vital rates of an Antarctic marine predator: the role of individual heterogeneity(2018-10) Paterson, J. Terrill; Rotella, Jay J.; Link, William A.; Garrott, Robert A.Variation in life-history traits such as lifespan and lifetime reproductive output is thought to arise, in part, due to among-individual differences in the underlying probabilities of survival and reproduction. However, the stochastic nature of demographic processes can also generate considerable variation in fitness-related traits among otherwise-identical individuals. An improved understanding of life-history evolution and population dynamics therefore depends on evaluating the relative role of each of these processes. Here, we used a 33-yr data set with reproductive histories for 1,274 female Weddell seals from Erebus Bay, Antarctica, to assess the strength of evidence for among-individual heterogeneity in the probabilities of survival and reproduction, while accounting for multiple other sources of variation in vital rates. Our analysis used recent advances in Bayesian model selection techniques and diagnostics to directly compare model fit and predictive power between models that included individual effects on survival and reproduction to those that did not. We found strong evidence for costs of reproduction to both survival and future reproduction, with breeders having rates of survival and subsequent reproduction that were 3% and 6% lower than rates for non-breeders. We detected age-related changes in the rates of survival and reproduction, but the patterns differed for the two rates. Survival rates steadily declined from 0.92 at age 7 to 0.56 at the maximal age of 31yr. In contrast, reproductive rates increased from 0.68 at age 7 to 0.79 at age 16 and then steadily declined to 0.37 for the oldest females. Models that included individual effects explained more variation in observed life histories and had better estimated predictive power than those that did not, indicating their importance in understanding sources of variation among individuals in life-history traits. We found that among-individual heterogeneity in survival was small relative to that for reproduction. Our study, which found patterns of variation in vital rates that are consistent with a series of predictionsfrom life-history theory, is the first to provide a thorough assessment of variation in important vital rates for a long-lived, high-latitude marine mammal while taking full advantage of recent developments in model evaluation.Item Respiratory pathogens and their association with population performance in Montana and Wyoming bighorn sheep populations(2018-11) Butler, Carson J.; Edwards, William H.; Paterson, J. Terrill; Proffitt, Kelly M.; Jennings-Gaines, Jessica E.; Killion, Halcyon J.; Wood, Mary E.; Ramsey, Jennifer M.; Almberg, Emily S.; Dewey, Sarah R.; McWhirter, Douglas E.; Courtemanch, Alyson B.; White, Patrick J.; Rotella, Jay J.; Garrott, Robert A.At the request of National Park Service resource managers, we began a study in 2000 to evaluate causes for the decline of the bighorn sheep (Ovis canadensis) population inhabiting Bighorn Canyon National Recreation Area (BICA), the Pryor Mountain Wild Horse Range, and surrounding state and U.S. Forest Service lands in Montana and Wyoming. Our study consisted of radio-collaring adult rams and ewes with mortality sensors to monitor adult mortalities, tracking ewes to determine pregnancy and lambing rates, habitat assessments to determine why the population was not expanding into what had been modeled using GIS methodology as suitable bighorn sheep habitat, measuring ungulate herbaceous consumption rates and herbaceous production to determine plant responses, and aerial and boat surveys to determine bighorn sheep population range and population dynamics (Schoenecker and others, this report). Two habitat suitability models were created and conducted (Gudorf, this report; Wockner and others, this report) using different methodologies, and comparisons made between the two. Herd population dynamics were modeled using the POP-II and POP-III programs (Roelle, this report), and a reassessment of ungulate exclosures that were established 8–10 years ago was conducted (Gerhardt, this report). The bighorn sheep population of the greater Bighorn Canyon National Recreation Area (BICA) was extirpated in the 1800s, and then reintroduced in 1973. The herd increased to a peak population of about 211 animals (Kissell and others, 1996), but then declined sharply in 1995 and 1996. Causes for the decline were unknown. Numbers have remained around 100 ± 20 animals since 1998. Previous modeling efforts determined what areas were suitable bighorn sheep habitat (Gudorf and others, 1996). We tried to determine why sheep were not using areas that were modeled as suitable or acceptable habitat, and to evaluate population dynamics of the herd.Item Assessing respiratory pathogen communities in bighorn sheep populations: Sampling realities, challenges, and improvements(2017-07) Butler, Carson J.; Edwards, William H.; Jennings-Gaines, Jessica E.; Killion, Halcyon J.; Wood, Mary E.; McWhirter, Douglas E.; Paterson, J. Terrill; Proffitt, Kelly M.; Almberg, Emily S.; White, Patrick J.; Rotella, Jay J.; Garrott, Robert A.Respiratory disease has been a persistent problem for the recovery of bighorn sheep (Ovis canadensis), but has uncertain etiology. The disease has been attributed to several bacterial pathogens including Mycoplasma ovipneumoniae and Pasteurellaceae pathogens belonging to the Mannheimia, Bibersteinia, and Pasteurella genera. We estimated detection probability for these pathogens using protocols with diagnostic tests offered by a fee-for-service laboratory and not offered by a fee-for-service laboratory. We conducted 2861 diagnostic tests on swab samples collected from 476 bighorn sheep captured across Montana and Wyoming to gain inferences regarding detection probability, pathogen prevalence, and the power of different sampling methodologies to detect pathogens in bighorn sheep populations. Estimated detection probability using fee-for-service protocols was less than 0.50 for all Pasteurellaceae and 0.73 for Mycoplasma ovipneumoniae. Non-fee-for-service Pasteurellaceae protocols had higher detection probabilities, but no single protocol increased detection probability of all Pasteurellaceae pathogens to greater than 0.50. At least one protocol resulted in an estimated detection probability of 0.80 for each pathogen except Mannheimia haemolytica, for which the highest detection probability was 0.45. In general, the power to detect Pasteurellaceae pathogens at low prevalence in populations was low unless many animals were sampled or replicate samples were collected per animal. Imperfect detection also resulted in low precision when estimating prevalence for any pathogen. Low and variable detection probabilities for respiratory pathogens using live-sampling protocols may lead to inaccurate conclusions regarding pathogen community dynamics and causes of bighorn sheep respiratory disease epizootics. We recommend that agencies collect multiples samples per animal for Pasteurellaceae detection, and one sample for Mycoplasma ovipneumoniae detection from at least 30 individuals to reliably detect both Pasteurellaceae and Mycoplasma ovipneumoniae at the population-level. Availability of PCR diagnostic tests to wildlife management agencies would improve the ability to reliably detect Pasteurellaceae in bighorn sheep populations.Item Security Areas for Elk During Archery and Rifle Hunting Seasons(2017-07) Ranglack, Dustin H.; Proffitt, Kelly M.; Canfield, Jodie E.; Gude, Justin A.; Rotella, Jay J.; Garrott, Robert A.Fall elk (Cervus canadensis) habitat management on public lands provides security areas for reasonable elk survival and hunter opportunity. The management focus of maintaining or improving security areas, combined with conservative harvest regulations, may explain why some elk populations have increased in the western United States. However, in areas that include lands that restrict public hunter access, elk may alter their space use patterns during the hunting season by increasing use of areas that restrict public hunter access rather than using security areas on adjacent public lands. We used global positioning system location data from 325 adult female elk in 9 southwest Montana populations to determine resource selection during the archery and rifle hunting seasons. We found that during the archery season, in order of decreasing strength of selection, elk selected for areas that restricted access to public hunters, had greater time-integrated normalized difference vegetation index values, had higher canopy cover, were farther from motorized routes, and had lower hunter effort. During the rifle season, in order of decreasing strength of selection, elk selected for areas that restricted access to public hunters, were farther from motorized routes, had higher canopy cover, and had higher hunter effort. Interactions among several covariates revealed dependencies in elk resource selection patterns. Further, cross-population analyses revealed increased elk avoidance of motorized routes with increasing hunter effort during both the archery and rifle hunting seasons. We recommend managing for areas with 13% canopy cover that are 2,760m from motorized routes, and identifying and managing for areas of high nutritional resources within these areas to create security areas on public lands during archery season. During the rifle season, we recommend managing for areas with 9% canopy cover that are 1,535m from motorized routes, and are 20.23km(2). Lastly, given increased elk avoidance of motorized routes with higher hunter effort, we recommend that to maintain elk on public lands, managers consider increasing the amount of security in areas that receive high hunter effort, or hunting seasons that limit hunter effort in areas of high motorized route densities.Item Breeding season occupancy of long-billed curlews and sandhill cranes in grazed habitats at Red Rock Lakes National Wildlife Refuge, Montana.(2015-12) Stadum, Jennifer; Warren, Jeffrey M.; Rotella, Jay J.Long-billed curlew (Numenius americanus) and sandhill crane (Grus canadensis) are species of concern at state and federal levels. The concern is largely due to declines in population resulting from loss and degradation of wetland and grassland habitats that have reduced the amount of available breeding habitat for both species. Red Rock Lakes National Wildlife Refuge (RRLNWR) in southwestern Montana encompasses one of the largest wetland complexes in the Intermountain West, providing important breeding habitat for cranes and curlews in the region. We explored landscape- and plot-scale drivers of curlew and crane breeding-season occupancy ([psi]) in grazed grassland and wet meadow habitats at RRLNWR. Distance to palustrine emergent marsh was the best landscape-scale predictor of curlew and crane occupancy. Mean breeding season occupancy of curlews across sites was 0.68 (95% CI = 0.39-0.87) and increased with distance from emergent marsh, ranging from 0.37 (95% CI = 0.24-0.52) to 0.80 (95% CI = 0.56-0.93) as distance to emergent marsh went from 64 in to 629 in. Conversely, crane mean breeding season occupancy was 0.38 (95% CI = 0.17-0.64) and decreased as distance from emergent marsh increased, ranging from 0.58 (95% CI = 0.27-0.58) to 0.28 (95% CI = 0.11-0.56) as distance to emergent marsh went from 64 in to 629 m. Plot-scale vegetation characteristics available from a reduced data set indicated curlew occupancy was positively related to the ratio of vegetation 5-15 cm tall to vegetation >15cm (([beta]) over cap =4.92, SE = 2.53).Item Patterns of age-related change in reproductive effort differ in the pre-natal and post-natal periods in a long-lived mammal.(2016-09) Paterson, J. Terrill; Rotella, Jay J.; Mannas, Jennifer M.; Garrott, Robert A.Age-related changes in maternal reproductive allocation for long-lived species are a key prediction from life-history theory. Theoretical and empirical work suggests that allocation may increase with age due to constraint (increases with experience) or restraint (increases with age in the face of declining residual reproductive value), and may decrease among the oldest aged animals due to senescence in reproductive function. Here, we use a hierarchical modelling approach to investigate the age-related patterns of change in maternal reproductive effort in the Weddell seal, a long-lived marine mammal with a protracted period of maternal care during which mothers allocate a large proportion of body mass while feeding little. We find that maternal allocation increases with age for young mothers during both the pre-natal and post-natal periods. In contrast, older mothers demonstrate a senescent decline in pre-natal allocation but allocate more of their declining resources to their offspring during the post-natal period. We also find strong evidence for the importance of individual effects in reproductive allocation among mothers: some mothers consistently produce heavier (or lighter) pups than expected. Our results indicate that maternal allocation changes over a mother\'s reproductive life span and that age-specific differences differ in notable ways in pre-natal and post-natal periods.Item Coping with the loss of large, energy-dense prey: a potential bottleneck for Weddell Seals in the Ross Sea(2017-01) Leo, Salas; Nur, Nadav; Ainley, David; Burns, Jennifer; Rotella, Jay J.; Ballard, GrantExtraction of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea began in 1997, following a management plan that targets the largest fish with a goal of reducing the spawning biomass by 50% over 35 yr. We investigate the potential long-term consequences of the reduced availability of this prey for Weddell seals (Leptonychotes weddellii). Energy -demands in seals are acute, especially immediately following lactation, when females must -recover substantial mass and cope with molting costs. We tested the hypothesis that toothfish are critically important for adult female seals during this period. Toothfish body mass is three orders of magnitude greater, and its energy density nearly double that of the most common seal prey, Antarctic silverfish (Pleuragramma antarcticum). Reduction or elimination of toothfish consumption could impair a female's ability to sufficiently recover and successfully produce a pup in the following pupping season. Our goals are to (1) illustrate mechanisms and conditions whereby toothfish depletion might plausibly affect seal population trends; (2) identify measurable parameters of the seals' ecology that may help better understand the potential negative impact of toothfish depletion on seal populations; and (3) promote a precautionary management approach for the fishery that includes monitoring of seal populations We constructed a set of inter-linked models of seal diving behavior, physiological condition, and demography based on existing information. We evaluate the effect of the following factors on seal mass recovery and intrinsic population growth rates: fishery depletion rate, daily diving limits, probability of a successful dive, and body mass recovery target. We show that loss of toothfish has the greatest potential impact on seal populations' growth rate. Under some scenarios, populations may decrease at > 10% per year. Critical parameters to better understand fishery impacts include prevalence and size of toothfish in the seals' diet; the relationship between diet and the rate of mass recovery; and female breeding propensity in relation to body condition at the end of the molting period. Our results lend support to concerns about the potential negative impact of toothfish extraction in the Ross Sea; and to advocate for a precautionary management approach by the fishery.
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