Middleton A.D.,University of Wyoming |
Kauffman M.J.,University of Wyoming |
Kauffman M.J.,U.S. Geological Survey |
Jimenez M.D.,U.S. Fish and Wildlife Service |
And 6 more authors.
Ecology Letters | Year: 2013
Ecological theory predicts that the diffuse risk cues generated by wide-ranging, active predators should induce prey behavioural responses but not major, population- or community-level consequences. We evaluated the non-consumptive effects (NCEs) of an active predator, the grey wolf (Canis lupus), by simultaneously tracking wolves and the behaviour, body fat, and pregnancy of elk (Cervus elaphus), their primary prey in the Greater Yellowstone Ecosystem. When wolves approached within 1 km, elk increased their rates of movement, displacement and vigilance. Even in high-risk areas, however, these encounters occurred only once every 9 days. Ultimately, despite 20-fold variation in the frequency of encounters between wolves and individual elk, the risk of predation was not associated with elk body fat or pregnancy. Our findings suggest that the ecological consequences of actively hunting large carnivores, such as the wolf, are more likely transmitted by consumptive effects on prey survival than NCEs on prey behaviour. © 2013 John Wiley & Sons Ltd/CNRS.
Osorio I.,University of Kansas Medical Center |
Osorio I.,Flint Hills Scientific LLC |
Manly B.,Western EcoSystems Technology Inc. |
Sunderam S.,University of Kentucky
Epilepsy and Behavior | Year: 2010
Seizure frequency is the only variable used for assessing therapeutic efficacy. Advances in quantitative analyses allow measurement of intensity, duration, spread, and time between seizures (TBS). These variables are used here to investigate the efficacy of brain electrical stimulation in humans with pharmacoresistant seizures. The results of a trial of contingent high-frequency electrical stimulation (HFES) for abatement of clinical and subclinical seizures are examined using principal component analysis (PCA) and regression models. HFES significantly: (1) Decreased seizure severity in two of eight and increased TBS in one of eight subjects; (2) decreased seizure severity in the primary epileptogenic zone of one subject but increased it in the secondary zones; (3) had both a beneficial and detrimental effect on severity and/or TBS (increase). These effects were immediate and also outlasted the duration of stimulation ("carryover"). Contingent HFES has multifarious and complex effects, intra- and interindividually, on seizure severity and TBS. Two inferences, at once promising and sobering may be drawn from these results: one, that contingent electrical stimulation deserves a place in the armamentarium of therapies for pharmacoresistant seizures, and the other, that its apparently narrow therapeutic ratio calls for careful implementation and multivariate quantification of its effects. © 2010 Elsevier Inc.
Sawyer H.,University of Wyoming |
Sawyer H.,Western Ecosystems Technology Inc. |
Kauffman M.J.,University of Wyoming
Journal of Animal Ecology | Year: 2011
Birds that migrate long distances use stopover sites to optimize fuel loads and complete migration as quickly as possible. Stopover use has been predicted to facilitate a time-minimization strategy in land migrants as well, but empirical tests have been lacking, and alternative migration strategies have not been considered. We used fine-scale movement data to evaluate the ecological role of stopovers in migratory mule deer Odocoileus hemionus- a land migrant whose fitness is strongly influenced by energy intake rather than migration speed. Although deer could easily complete migrations (range 18-144km) in several days, they took an average of 3weeks and spent 95% of that time in a series of stopover sites that had higher forage quality than movement corridors. Forage quality of stopovers increased with elevation and distance from winter range. Mule deer use of stopovers corresponded with a narrow phenological range, such that deer occupied stopovers 44days prior to peak green-up, when forage quality was presumed to be highest. Mule deer used one stopover for every 5·3 and 6·7km travelled during spring and autumn migrations, respectively, and used the same stopovers in consecutive years. Study findings indicate that stopovers play a key role in the migration strategy of mule deer by allowing individuals to migrate in concert with plant phenology and maximize energy intake rather than speed. Our results suggest that stopover use may be more common among non-avian taxa than previously thought and, although the underlying migration strategies of temperate ungulates and birds are quite different, stopover use is important to both. Exploring the role of stopovers in land migrants broadens the scope of stopover ecology and recognizes that the applied and theoretical benefits of stopover ecology need not be limited to avian taxa. © 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.
Nielson R.M.,Western EcoSystems Technology Inc. |
Sawyer H.,Western EcoSystems Technology Inc.
Ecology and Evolution | Year: 2013
Resource selection functions (RSFs) are typically estimated by comparing covariates at a discrete set of "used" locations to those from an "available" set of locations. This RSF approach treats the response as binary and does not account for intensity of use among habitat units where locations were recorded. Advances in global positioning system (GPS) technology allow animal location data to be collected at fine spatiotemporal scales and have increased the size and correlation of data used in RSF analyses. We suggest that a more contemporary approach to analyzing such data is to model intensity of use, which can be estimated for one or more animals by relating the relative frequency of locations in a set of sampling units to the habitat characteristics of those units with count-based regression and, in particular, negative binomial (NB) regression. We demonstrate this NB RSF approach with location data collected from 10 GPS-collared Rocky Mountain elk (Cervus elaphus) in the Starkey Experimental Forest and Range enclosure. We discuss modeling assumptions and show how RSF estimation with NB regression can easily accommodate contemporary research needs, including: analysis of large GPS data sets, computational ease, accounting for among-animal variation, and interpretation of model covariates. We recommend the NB approach because of its conceptual and computational simplicity, and the fact that estimates of intensity of use are unbiased in the face of temporally correlated animal location data. © 2013 The Authors. Ecology and Evolution.
Manly B.F.J.,Western Eco Systems Technology Inc.
Journal of Biopharmaceutical Statistics | Year: 2011
Two methods of bootstrap resampling are discussed with log-linear models for count data. The first involves the resampling of observations and the second involves the resampling of Pearson residuals taking into account changes in the distribution of residuals associated with the expected values of counts. The use of both methods is illustrated on two data sets; one data set concerns the number of ear infections of swimmers related to whether they are frequent swimmers or not and three other variables, and the other data set concerns the number of visits to a doctor made in the last 2 weeks related to the age of subjects and 10 other variables. A third data set on the number of marine mammal interactions in different years and fishing areas is also used as an example. In this case only the second bootstrap method can be used because the nature of the data allows the bootstrap resampling of observations to produce sets of data that could not have occurred in practice. Simulation results indicate that the bootstrap results are slightly better than the results from a conventional analysis for the first data set, and much better than the results from a conventional analysis for the second data set, but a conventional analysis works well for the third data set while there are problems with bootstrap analyses. © Taylor & Francis Group, LLC.
Castellon T.D.,Archbold Biological Station |
Rothermel B.B.,Archbold Biological Station |
Nomani S.Z.,Western EcoSystems Technology Inc
Chelonian Conservation and Biology | Year: 2012
Gopher tortoises (Gopherus polyphemus) occur in a variety of habitats, but are primarily associated with sandhill communities. In peninsular Florida, however, mesic flatwoods make up the largest area of habitat, and scrub often replaces sandhill on inland ridges. Tortoise ecology is poorly understood in these habitats and few data are available to guide management. We surveyed tortoise burrows and assessed vegetation in scrub, flatwoods, and pine plantations on flatwoods soils at Avon Park Air Force Range in south-central Florida. Densities of noncollapsed burrows in scrub (1.93/ha) and flatwoods/plantations (1.42/ha) were generally lower than is typical for sandhill (3.25-9.95/ha), although total abundance was high (>20,000) because of the large habitat area. In scrub, low burrow densities may be due to low abundance of food plants. Nonetheless, the burrow density in scrub was significantly higher than in flatwoods/plantations, where food was abundant but soils were poorly drained and burrows were often flooded. The percentage of collapsed burrows was significantly higher in scrub (53%) than in flatwoods/plantations (35%), although a higher percentage of the remaining (noncollapsed) burrows were active in scrub (23%) than in flatwoods/plantations (16%). These patterns (and data from a subsequent radiotelemetry study) suggest that tortoises in scrub maintain strong fidelity to individual burrows, and frequently abandon others, whereas tortoises in flatwoods share burrows and move among them regularly, but rarely abandon them. This sharing and continual reuse of available burrows suggests a possible limitation on suitable conditions for burrow construction in flatwoods, probably related to the high water table. We suggest that scrub and flatwoods may constitute suboptimal habitats for gopher tortoises, due to low abundance of food in scrub and poorly drained soils in flatwoods. Nonetheless, large numbers of tortoises may occupy scrub and flatwoods, necessitating better understanding of their ecology in these habitats. © 2012 Chelonian Research Foundation.
Mcdonald T.L.,Western EcoSystems Technology Inc.
Journal of Animal Ecology | Year: 2013
Summary: Use-availability and presence-only analyses are synonyms. Both require two samples (one containing known locations, one containing potential locations), both estimate the same parameters, and both use the same fundamental likelihood. Use-availability and presence-only designs compare characteristics of points where an organism was located to those where the organism could have been located. These designs can be generalized to estimate the relative probability that any event occurred at a set of locations. This article generalizes the use-availability likelihood given in Johnson et al. (Resource selection functions based on use-availability data: theoretical motivation and evaluation methods, Journal of Wildlife Management, 2006) to point locations. This derivation arrives at the same likelihood as Fithian & Hastie (Statistical Models for Presence-Only Data: Finite-Sample Equivalence and Addressing Observer Bias, 2012) but uses a different technique and allows a more general link function. Fithian & Hastie (2012) use a case-control argument and Bayes theorem to derive the likelihood. This article uses Lagrangian multipliers to maximize the two-sample likelihood. Resource selection functions (RSF) defined here are ratios of density functions. RSFs must be positive and unbounded. Proper link functions must provide proportionality over their entire range. Given these conditions, the exponential link is the most logical and appropriate link function for RSFs. These conditions exclude the logistic link. This article affirms that estimation of a RSF does not involve 'running logistic regression'. By assigning 0 and 1 (pseudo-)responses to vectors of covariates associated with locations in the used and available sample, it is possible to 'trick' logistic regression software into maximizing the use-availability likelihood. Representing the analysis as 'logistic regression' is misleading because that implies use of the logistic link, which is inappropriate for RSF's. It is more accurate to state that the 'use-availability likelihood was maximized'. RSFs are more general, intuitive and useful than resource selection probability functions (RSPF). RSPFs depend heavily on sampling mechanisms and the number of used and available locations selected. Consequently, the objective of estimation in use-availability studies should be the RSF, not the RSPF. Two simple examples and R code in the Supporting Information illustrate computations. These examples maximize the general log likelihood without the aid of logistic regression software. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.
Osorio I.,University of Kansas Medical Center |
Manly B.F.J.,Western EcoSystems Technology Inc.
Clinical Neurophysiology | Year: 2014
Objective: Real-time EKG-based automated seizure detection is emerging as a complement or supplement to that based on cortical signals, but its value is unproven. This study assesses the clinically relevance of EKG-based seizure detection by comparing the information content in EKG and ECoG. Methods: ECoGs (6935 h; 241 clinical and 4311 sub-clinical seizures) with simultaneous EKG from 81 subjects undergoing surgical evaluation were used in these analyses. Differences, if any, between clinical and sub-clinical seizures in variables such as intensity, duration and their product severity, were investigated with a multi-variate regression model. Results: Highly statistically significant differences in severity between clinical and sub-clinical seizures were discerned with EKG and ECoG. Furthermore, EKG-based seizure severity was linearly correlated with that estimated using ECoG. Conclusions: These findings support the notion that EKG-based seizure detection is clinically relevant in certain localization-related epilepsies, providing similar information to that yielded by neuronal electrical signals. Significance: The information content equivalence between EKG and ECoG would enable automated seizure detection, quantification and therapy delivery, without resorting to cortical monitoring. The considerably higher S/N and ease of acquisition and processing of EKG compared to ECoG/EEG may foster widespread clinical applications of this novel detection approach. © 2014 International Federation of Clinical Neurophysiology.
Robertson B.L.,University of Canterbury |
Brown J.A.,University of Canterbury |
Mcdonald T.,Western EcoSystems Technology Inc. |
Jaksons P.,University of Canterbury
Biometrics | Year: 2013
To design an efficient survey or monitoring program for a natural resource it is important to consider the spatial distribution of the resource. Generally, sample designs that are spatially balanced are more efficient than designs which are not. A spatially balanced design selects a sample that is evenly distributed over the extent of the resource. In this article we present a new spatially balanced design that can be used to select a sample from discrete and continuous populations in multi-dimensional space. The design, which we call balanced acceptance sampling, utilizes the Halton sequence to assure spatial diversity of selected locations. Targeted inclusion probabilities are achieved by acceptance sampling. The BAS design is conceptually simpler than competing spatially balanced designs, executes faster, and achieves better spatial balance as measured by a number of quantities. The algorithm has been programed in an R package freely available for download. © 2013, The International Biometric Society.
Lebeau C.W.,Western EcoSystems Technology Inc. |
Beck J.L.,University of Wyoming |
Johnson G.D.,Western EcoSystems Technology Inc. |
Holloran M.J.,Wyoming Wildlife Consultants LLC
Journal of Wildlife Management | Year: 2014
Greater sage-grouse (Centrocercus urophasianus) are experiencing population declines across much of their current range. Population declines are directly related to changes in greater sage-grouse fitness parameters including nest and brood success, and female survival. Reduced fitness in greater sage-grouse populations has been attributed to a decrease in habitat suitability caused by anthropogenic disturbance factors including energy extraction activities. The increased demand for renewable energy has raised concerns about the impacts of infrastructure associated with wind energy development on greater sage-grouse populations. We hypothesized that greater sage-grouse nest, brood, and adult survival would decrease with increasing proximity to wind energy infrastructure, particularly wind turbines. We monitored 95 nests, 31 broods, and identified 45 mortalities from 116 female greater sage-grouse from 2009 to 2010 at a wind energy facility in south-central Wyoming, USA. We used Cox proportional hazards regression to model nest survival and used the Andersen-Gill survival model to estimate female and brood survival relative to vegetation cover, topography, and distance to wind turbines and other anthropogenic features on the landscape. Results from our survival analysis indicated that the risk of a nest or brood failing decreased by 7.1% and 38.1%, respectively, with every 1.0km increase in distance from nearest turbine. We detected no variation in female survival relative to wind energy infrastructure. Decreased nest and brood survival was likely the result of increased predation, which may have been a product of anthropogenic development and habitat fragmentation. Future wind energy developments should consider the increased risk of nest and brood failure within habitats of close proximity to turbines. Identifying nesting and brood-rearing habitats within close proximity to proposed wind energy developments is critical when estimating potential impacts to overall population fitness. © 2014 The Wildlife Society.