Browsing by Author "Rotella, Jay J."

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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.
Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high-latitude marine mammal
(2016-02) Rotella, Jay J.; Paterson, J. Terrill; Garrott, Robert A.
Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long-lived mammals, birth dates for different individuals can vary by weeks within a population. A mother\'s birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long-term data for known-age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4-31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother\'s reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother\'s age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime-age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers-Willard sex-allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.
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).
Connectivity between white shark populations off Central California, USA and Guadalupe Island, Mexico
(Frontiers Media SA, 2023-07) Kanive, Paul E.; Rotella, Jay J.; Chapple, Taylor K.; Anderson, Scot D.; Hoyos-Padilla, Mauricio; Klimley, Abbott Peter; Galván-Magaña, Felipe; Andrzejaczek, Samantha; Block, Barbara A.; Jorgensen, Salvador J.
Marine animals often move beyond national borders and exclusive economic zones resulting in a need for trans-boundary management spanning multiple national jurisdictions. Highly migratory fish vulnerable to over-exploitation require protections at international level, as exploitation practices can be disparate between adjacent countries and marine jurisdictions. In this study we collaboratively conducted an analysis of white shark connectivity between two main aggregation regions with independent population assessment and legal protection programs; one off central California, USA and one off Guadalupe Island, Mexico. We acoustically tagged 326 sub-adult and adult white sharks in central California (n=210) and in Guadalupe Island (n=116) with acoustic transmitters between 2008-2019. Of the 326 tagged white sharks, 30 (9.20%) individuals were detected at both regions during the study period. We used a Bayesian implementation of logistic regression with a binomial distribution to estimate the effect of sex, maturity, and tag location to the response variable of probability of moving from one region to the other. While nearly one in ten individuals in our sample were detected in both regions over the study period, the annual rate of trans-regional movement was low (probability of movement = 0.015 yr-1, 95% credible interval = 0.002, 0.061). Sub-adults were more likely than adults to move between regions and sharks were more likely to move from Guadalupe Island to central California, however, sex, and year were not important factors influencing movement. This first estimation of demographic-specific trans-regional movement connecting US and Mexico aggregations with high seasonal site fidelity represents an important step to future international management and assessment of the northeastern Pacific white shark population as a whole.
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, Grant
Extraction 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.
Density-related reproductive costs and natal conditions predict male life history in a highly polygynous mammal
(Elsevier BV, 2023-06) Lloyd, Kyle J.; Oosthuizen, W. Chris; Rotella, Jay J.; Bester, Marthán N.; de Bruyn, P.J. Nico
Polygynous males allocate substantial resources to sexual traits and behaviours to improve their chances of winning competitions for mates often at the cost of body maintenance. However, the degree to which males experience these trade-offs can be influenced by external conditions. Studies are needed that assess whether polygynous male resource allocation decisions about life history traits are density dependent. We tested for an influence of density on age-specific life history traits in male southern elephant seals, Mirounga leonina, using a 34-year data set collected at Marion Island. Specifically, we determine whether life history varied with density-related factors for survival, improved breeding success (measured as social status) and recruitment age. This was done by selecting linear models that tested biological hypotheses about density-dependent covariates related to competition intensity during breeding and natal conditions, while accounting for known intrinsic effects such as age and social status. Baseline mortalities were higher for males that had accumulated above average reproductive costs for their age than males with below average costs. This reproductive cost was determined by the number of females per harem relative to the population average. Thus, males likely allocated more resources to reproduction and less to body maintenance at all ages when defending and servicing relatively large harems, and this cost was compounding for males that dominated large harems at a young age. Males born in years with few pups were more likely to be dominant breeders and recruit at an earlier age than males born in years with many pups. Thus, breeding success and recruitment age likely depended on the population density experienced during early life, suggesting lasting effects of natal conditions in a long-lived animal. We show how density-dependent factors interact with intrinsic determinants of resource allocation to determine variation in polygynous male life history with long-term consequences.
Drivers of Bromus tectorum Abundance in the Western North American Sagebrush Steppe
(2016-09) Brummer, Tyler J.; Taylor, Kimberley T.; Rotella, Jay J.; Maxwell, Bruce D.; Rew, Lisa J.; Lavin, Matthew
Bromus tectorum can transform ecosystems causing negative impacts on the ecological and economic values of sagebrush steppe of the western USA. Although our knowledge of the drivers of the regional distribution of B. tectorum has improved, we have yet to determine the relative importance of climate and local factors causing B. tectorum abundance and impact. To address this, we sampled 555 sites distributed geographically and ecologically throughout the sagebrush steppe. We recorded the canopy cover of B. tectorum, as well as local substrate and vegetation characteristics. Boosted regression tree modeling revealed that climate strongly limits the transformative ability of B. tectorum to a portion of the sagebrush steppe with dry summers (that is, July precipitation <10 mm and the driest annual quarter associated with a mean temperature >15 degrees C) and low native grass canopy cover. This portion includes the Bonneville, Columbia, Lahontan, and lower Snake River basins. These areas are likely to require extreme efforts to reverse B. tectorum transformation. Our predictions, using future climate conditions, suggest that the transformative ability of B. tectorum may not expand geographically and could remain within the same climatically suitable basins. We found B. tectorum in locally disturbed areas within or adjacent to all of our sample sites, but not necessarily within sagebrush steppe vegetation. Conversion of the sagebrush steppe by B. tectorum, therefore, is more likely to occur outside the confines of its current climatically optimal region because of site-specific disturbances, including invasive species control efforts and sagebrush steppe mismanagement, rather than climate change.
Drivers of waterfowl population dynamics: from teal to swans
(2014-12) Koons, David N.; Gunnarsson, G.; Schmutz, J. A.; Rotella, Jay J.
Waterfowl are among the best studied and most extensively monitored species in the world. Given their global importance for sport and subsistence hunting, viewing and ecosystem functioning, great effort has been devoted since the middle part of the 20th century to understanding both the environmental and demographic mechanisms that influence waterfowl population and community dynamics. Here we use comparative approaches to summarise and contrast our understanding of waterfowl population dynamics across species as short-lived as the teal Anas discors and A.crecca to those such as the swans Cygnus sp. which have long life-spans. Specifically, we focus on population responses to vital rate perturbations across life history strategies, discuss bottom-up and top-down responses of waterfowl populations to global change, and summarise our current understanding of density dependence across waterfowl species. We close by identifying research needs and highlight ways to overcome the challenges of sustainably managing waterfowl populations in the 21st century.
Environmental correlates of temporary emigration for female Weddell seals and consequences for recruitment
(Ecological Society of America, 2014) Stauffer, Glenn E.; Rotella, Jay J.; Garrott, Robert A.; Kendall, William
In colonial-breeding species, prebreeders often emigrate temporarily from natal reproductive colonies then subsequently return for one or more years before producing young. Variation in attendance–nonattendance patterns can have implications for subsequent recruitment. We used open robust-design multistate models and 28 years of encounter data for prebreeding female Weddell seals (Leptonychotes weddellii [Lesson]) to evaluate hypotheses about (1) the relationships of temporary emigration (TE) probabilities to environmental and population size covariates and (2) motivations for attendance and consequences of nonattendance for subsequent probability of recruitment to the breeding population. TE probabilities were density dependent (ˆerrors of population size in the previous year) and increased when the fast-ice...
Estimates of regional annual abundance and population growth rates of white sharks off central California
(Elsevier BV, 2021-05) Kanive, Paul E.; Rotella, Jay J.; Chapple, Taylor K.; Anderson, Scot D.; White, Timothy D.; Block, Barbara A.; Jorgensen, Salvador J.
Determining population trends is critical for evaluating management actions and prioritizing species protections. In this study, we used empirical data to produce an estimate of the population trend for sub-adult and adult white sharks in central California. We used the unique dorsal fin morphology to build a mark-recapture data set in a modified Jolly-Seber model (POPAN formulation) to estimate annual abundance and then investigate population growth rates using parametric bootstrapping methods for sub-adult and adult sharks (males and females). For all demographic groups combined, we found equivocal evidence for a positive regional population growth (λ = 1.07 (95% CI = 0.91 to 1.23)). However, sex- and size-specific population growth rate estimates provided some evidence of population increases for reproductively mature males (λ = 1.06 (95% CI = 0.99 to 1.13)) and females (λ = 1.06 (95% CI = 0.95 to 1.17)). For sub-adult male and female white sharks, point estimates of λ were positive but uncertainty prevents strong inference (λ = 1.07 (95% CI = 0.85 to 1.29)) and (λ = 1.08 (95% CI = 0.88 to 1.28)), respectively. Our findings of a potential increase in reproductive-aged white sharks in central California may be a result of regional fluxes in density or attributed in part to current protection efforts and subsequent increase in abundance of pinnipeds as well as reduced gill-net fisheries mortality of juveniles. A trend estimate for the entire northeastern Pacific will require obtaining similar data across known aggregation areas along the west coast of North America.
Estimates of regional annual abundance and population growth rates of white sharks off central California
(2021-05) Kanive, Paul E.; Rotella, Jay J.; Chapple, Taylor K.; Anderson, Scot D.; White, Timothy D.; Block, Barbara A.; Jorgensen, Salvador J.
Determining population trends is critical for evaluating management actions and prioritizing species protections. In this study, we used empirical data to produce an estimate of the population trend for sub-adult and adult white sharks in central California. We used the unique dorsal fin morphology to build a mark-recapture data set in a modified Jolly-Seber model (POPAN formulation) to estimate annual abundance and then investigate population growth rates using parametric bootstrapping methods for sub-adult and adult sharks (males and females). For all demographic groups combined, we found equivocal evidence for a positive regional population growth (λ = 1.07 (95% CI = 0.91 to 1.23)). However, sex- and size-specific population growth rate estimates provided some evidence of population increases for reproductively mature males (λ = 1.06 (95% CI = 0.99 to 1.13)) and females (λ = 1.06 (95% CI = 0.95 to 1.17)). For sub-adult male and female white sharks, point estimates of λ were positive but uncertainty prevents strong inference (λ = 1.07 (95% CI = 0.85 to 1.29)) and (λ = 1.08 (95% CI = 0.88 to 1.28)), respectively. Our findings of a potential increase in reproductive-aged white sharks in central California may be a result of regional fluxes in density or attributed in part to current protection efforts and subsequent increase in abundance of pinnipeds as well as reduced gill-net fisheries mortality of juveniles. A trend estimate for the entire northeastern Pacific will require obtaining similar data across known aggregation areas along the west coast of North America.
Estimating apparent survival of sub-adult and adult white sharks (Carcharodon carcharias) in central California using mark-recapture methods
(2015-04) Kanive, Paul Edward, Jr.; Rotella, Jay J.; Jorgensen, Salvador J.; Chapple, Taylor K.; Anderson, Scot D.; Klimley, A. Peter; Block, Barbara A.
Quantifying life history parameters of marine top predators is challenging, as observations are difficult and uncertainty in sex assignment can confound the determination of sex specific parameters. However, these parameters are critical for accurate population assessments and understanding of population dynamics. Using mark recapture observations at white shark foraging aggregation sites, we tested for differences in survival between sexes and estimated apparent survival for sub-adult and adult white sharks in neritic waters off central California. We used 6 years of mark-recapture data and a model that accounted for imperfect detection and imperfect sex assignment. Empirical information based on direct observations suggests that there are no sex-specific or temporal differences in survival during the study period and that survival was estimated to be 0.90; SE = 0.04. Additionally, after animals whose sex was unknown throughout the study period were probabilistically assigned to sex, the ratio in this sample is estimated to be 2.1 males for every female observed. This estimated ratio is lower than the observed ratio of 3:1. We demonstrate that the estimated capture probability for males was roughly twice as high as that for females (0.41, SE = 0.06 and 0.19, SE = 0.07 respectively). Together these results suggest (1) that the sex ratio is uneven but not as skewed as uncorrected observation data would suggest and (2) that unequal mortality in older age classes are not the cause of the observed sex bias but more likely results from disparate mortality earlier in life or differences in behavior. Future research is needed to explore the potential causes of the observed sex bias.
Estimating nest abundance while accounting for time-to-event processes and imperfect detection
(Ecological Society of America, 2014) Peron, Guillaume; Walker, Johann; Rotella, Jay J.; Hines, James; Nichols, James
Birds and their population dynamics are often used to understand and document anthropogenic effects on biodiversity. Nest success is a critical component of the breeding output of birds in different environments; but to obtain the complete picture of how bird populations respond to perturbations, we also need an estimate of nest abundance or density. The problem is that raw counts generally underestimate actual nest numbers because detection is imperfect and because some nests may fail or fledge before being subjected to detection efforts. Here we develop a state-space superpopulation capture–recapture approach in which inference about detection probability is based on the age at first detection, as opposed to the sequence of re-detections in standard capture–recapture models. We apply the method to ducks in which (1) the age of the nests and their initiation dates can be determined upon detection and (2) the duration of the different stages of the breeding cycle is a priori known. We fit three model variants with or without assumptions about the phenology of nest initiation dates, and use simulations to evaluate the performance of the approach in challenging situations. In an application to Blue-winged Teal Anas discors breeding at study sites in North and South Dakota, USA, nesting stage (egg-laying or incubation) markedly influenced nest survival and detection probabilities. Two individual covariates, one binary covariate (presence of grazing cattle at the nest site), and one continuous covariate (Robel index of vegetation), had only weak effects. We estimated that 5–10% of the total number of nests were available for detection but were missed by field crews. An additional 6–15% were never available for detection. These percentages are expected to be larger in less intense, more typical sampling designs. User-friendly software nestAbund is provided to assist users in implementing the method.
Evaluating the importance of individual heterogeneity in reproduction to Weddell seal population dynamics using integral projection models
(Wiley, 2023-07) Macdonald, Kaitlin R.; Rotella, Jay J.; Paterson, J. Terrill
Identifying and accounting for unobserved individual heterogeneity in vital rates in demographic models is important for estimating population-level vital rates and identifying diverse life-history strategies, but much less is known about how this individual heterogeneity influences population dynamics. We aimed to understand how the distribution of individual heterogeneity in reproductive and survival rates influenced population dynamics using vital rates from a Weddell seal population by altering the distribution of individual heterogeneity in reproduction, which also altered the distribution of individual survival rates through the incorporation of our estimate of the correlation between the two rates and assessing resulting changes in population growth. We constructed an integral projection model (IPM) structured by age and reproductive state using estimates of vital rates for a long-lived mammal that has recently been shown to exhibit large individual heterogeneity in reproduction. Using output from the IPM, we evaluated how population dynamics changed with different underlying distributions of unobserved individual heterogeneity in reproduction. Results indicate that the changes to the underlying distribution of individual heterogeneity in reproduction cause very small changes in the population growth rate and other population metrics. The largest difference in the estimated population growth rate resulting from changes to the underlying distribution of individual heterogeneity was less than 1%. Our work highlights the differing importance of individual heterogeneity at the population level compared to the individual level. Although individual heterogeneity in reproduction may result in large differences in the lifetime fitness of individuals, changing the proportion of above- or below-average breeders in the population results in much smaller differences in annual population growth rate. For a long-lived mammal with stable and high adult-survival that gives birth to a single offspring, individual heterogeneity in reproduction has a limited effect on population dynamics. We posit that the limited effect of individual heterogeneity on population dynamics may be due to canalization of life-history traits.
Evidence of an Absence of Inbreeding Depression in a Wild Population of Weddell Seals (Leptonychotes weddellii)
(MDPI AG, 2023-02) Powell, John H.; Kalinowski, Steven T.; Taper, Mark L.; Rotella, Jay J.; Davis, Corey S.; Garrott, Robert A.
Inbreeding depression can reduce the viability of wild populations. Detecting inbreeding depression in the wild is difficult; developing accurate estimates of inbreeding can be time and labor intensive. In this study, we used a two-step modeling procedure to incorporate uncertainty inherent in estimating individual inbreeding coefficients from multilocus genotypes into estimates of inbreeding depression in a population of Weddell seals (Leptonychotes weddellii). The two-step modeling procedure presented in this paper provides a method for estimating the magnitude of a known source of error, which is assumed absent in classic regression models, and incorporating this error into inferences about inbreeding depression. The method is essentially an errors-in-variables regression with non-normal errors in both the dependent and independent variables. These models, therefore, allow for a better evaluation of the uncertainty surrounding the biological importance of inbreeding depression in non-pedigreed wild populations. For this study we genotyped 154 adult female seals from the population in Erebus Bay, Antarctica, at 29 microsatellite loci, 12 of which are novel. We used a statistical evidence approach to inference rather than hypothesis testing because the discovery of both low and high levels of inbreeding are of scientific interest. We found evidence for an absence of inbreeding depression in lifetime reproductive success, adult survival, age at maturity, and the reproductive interval of female seals in this population.
Female Weddell seals show flexible strategies of colony attendance related to varying environmental conditions
(2015-02) Rotella, Jay J.; Chambert, T. C.; Garrott, Robert A.
Many animal life cycles involve movements among different habitats to fulfill varying resource demands. There are inherent costs associated with such movements, and the decision to leave or stay at a given location ought to be motivated by the benefits associated with potential target habitats. Because movement patterns, especially those associated with reproduction, can have important implications for the success (survival, reproduction) of individual animals, and therefore a population's dynamics, it is important to identify and understand their sources of variation (environmental and individual). Here, using a mark–recapture, multistate modeling approach, we investigated a set of a priori hypotheses regarding sources and patterns of variation in breeding-colony attendance for Weddell seal (Leptonychotes weddellii) females on sabbatical from pup production. For such females, colony attendance might be motivated by predation avoidance and positive social interactions related to reproduction, but some costs, such as reduced foraging opportunities or aggressive interactions with conspecifics, might also exist. We expected these benefits and costs to vary with a female's condition and the environment. Results revealed that the probability of being absent from colonies was higher (1) in years when the extent of local sea ice was larger, (2) for the youngest and oldest individuals, and (3) for females with less reproductive experience. We also found substantial levels of residual individual heterogeneity in these rates. Based on our a priori predictions, we postulate that the decision to attend breeding colonies or not is directly influenced by an individual's physiological condition, as well as by the ice-covered distance to good foraging areas, availability of predator-free haul-out sites, and the level of negative interactions with conspecifics inside colonies. Our results support the idea that in iteroparous species, and colonial animals in particular, seasonal and temporary movements from/to reproductive sites represent flexible behavioral strategies that can play an important role in coping with environmental variability.
Further evidence that Antarctic toothfish are important to Weddell seals
(Cambridge University Press, 2020-09) Ainley, David G.; Cziko, Paul A.; Nur, Nadav; Rotella, Jay J.; Eastman, Joseph T.; Larue, Michelle; Stirling, Ian; Abrams, Peter A.
Antarctic toothfish Dissostichus mawsoni and Weddell seals Leptonychotes weddellii are important mesopredators in the waters of the Antarctic continental shelf. They compete with each other for prey, yet the seals also prey upon toothfish. Such intraguild predation means that prevalence and respective demographic rates may be negatively correlated, but quantification is lacking. Following a review of their natural histories, we initiate an approach to address this deficiency by analysing scientific fishing catch per unit effort (CPUE; 1975–2011 plus sporadic effort to 2018) in conjunction with an annual index of seal abundance in McMurdo Sound, Ross Sea. We correlated annual variation in scientific CPUE to seal numbers over a 43 year period (1975–2018), complementing an earlier study in the same locality showing CPUE to be negatively correlated with spatial proximity to abundant seals. The observed relationship (more seals with lower CPUE, while controlling for annual trends in each) indicates the importance of toothfish as a dietary item to Weddell seals and highlights the probable importance of intra- and inter-specific competition as well as intraguild predation in seal-toothfish dynamics. Ultimately, it may be necessary to supplement fishery management with targeted ecosystem monitoring to prevent the fishery from having adverse effects on dependent species.
An integrated strategy for grassland easement acquisition in the Prairie Pothole Region, USA
(2013-12) Walker, Johann; Rotella, Jay J.; Loesch, C.; Renner, R. W.; Ringelman, J. K.; Lindberg, M. S.; Dell, R.; Doherty, K. E.
Acquisition of perpetual grassland easements is a principal tactic used by the United States Fish and Wildlife Service (USFWS) and its partners to protect nesting habitat for migratory birds in the Prairie Pothole Region of North and South Dakota, USA. This public–private partnership resulted in the conservation of >344,000 ha of grassland during 1998–2012. Past easement acquisition has been targeted to landscapes with greatest expected accessibility to breeding duck pairs without active consideration of probability of conversion or cost of protection. The rising cost of easement acquisition in recent years indicates that re-evaluation and refinement of the easement acquisition strategy could help to improve programmatic outcomes. We assessed regional patterns of easement acquisition during 1998–2012, evaluated the current targeting strategy, and used a combination of publicly available and proprietary geospatial data to develop an easement-targeting Geographic Information System that integrated information about conversion probability and protection cost with current targeting criteria. Our assessment indicated that grassland protection was negatively affected by rising land prices during 1998–2012. In the 5 y between 2008 and 2012, about 100,000 ha of grassland were protected at a cost of $83 million (U.S. dollars). The 2008–2012 acquisitions represented 30% of total protection during 1998–2012 but composed 47% of the total expenditure. We observed strong evidence that easements were targeted to priority landscapes both before and after formalization of the USFWS conservation strategy in 2004. We also found evidence of an opportunity to increase efficiency of future acquisitions. We identified 0.9 million ha of currently unprotected priority grassland in the region with greater than expected conversion risk and smaller than expected protection cost. We suggest that future grassland easement acquisition be refocused on this refined priority area and that an adaptive approach to future easement acquisition (including targeted acquisitions, directed monitoring, and data-based decisions) provides a logical framework for implementation of this new strategy and will facilitate continued conservation success.
Investigating diverse sources of variation in the amount of time Weddell seal ( Leptonychotes weddellii ) pups spend in the water during the lactation period
(Wiley, 2022-07) Petch, Shane M.; Rotella, Jay J.; Link, William A.; Paterson, J. Terrill; Garrott, Robert A.
Field observations suggest that time spent in the water by Weddell seal pups during lactation varies among individuals, which could yield important developmental tradeoffs. We analyzed data from 713 pups born to 419 different mothers over 9 years to evaluate total time in the water, age at first entry, and potential sources of variation using temperature loggers attached to the rear flipper of pups. Pups first entered the water at 11–29 days of age (M = 14.9) and spent 4–204 hr (M = 69.3) in the water by 30 days of age. Age at first entry was earlier for pups with higher birth mass and mothers of above average reproductive experience. Total time in the water was related to maternal identity and greater for female pups and for pups that had higher birth mass, mothers of intermediate age, mothers that skipped reproduction in the previous year, and for pups that first entered the water at younger ages. Phenotypic traits explain observed variation in the development of a key life history behavior in the Weddell seal. Strong individual variation in time spent in metabolically costly swimming and diving might lead to variation in growth, energy stores, and survival and fitness outcomes.
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 (>100â€¯m), rather than next to (1â€¯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.