Publications by Colleges and Departments (MSU - Bozeman)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/3
Browse
7 results
Search Results
Item 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.Item 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.Item 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.Item 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.Item Meta-analysis of relationships between human offtake, total mortality and population dynamics of gray wolves (Canis lupus)(2010-09) Creel, Scott; Rotella, Jay J.Following the growth and geographic expansion of wolf (Canis lupus) populations reintroduced to Yellowstone National Park and central Idaho in 1995–1996, Rocky Mountain wolves were removed from the endangered species list in May 2009. Idaho and Montana immediately established hunting seasons with quotas equaling 20% of the regional wolf population. Combining hunting with predator control, 37.1% of Montana and Idaho wolves were killed in the year of delisting. Hunting and predator control are well-established methods to broaden societal acceptance of large carnivores, but it is unprecedented for a species to move so rapidly from protection under the Endangered Species Act to heavy direct harvest, and it is important to use all available data to assess the likely consequences of these changes in policy. For wolves, it is widely argued that human offtake has little effect on total mortality rates, so that a harvest of 28–50% per year can be sustained. Using previously published data from 21 North American wolf populations, we related total annual mortality and population growth to annual human offtake. Contrary to current conventional wisdom, there was a strong association between human offtake and total mortality rates across North American wolf populations. Human offtake was associated with a strongly additive or super-additive increase in total mortality. Population growth declined as human offtake increased, even at low rates of offtake. Finally, wolf populations declined with harvests substantially lower than the thresholds identified in current state and federal policies. These results should help to inform management of Rocky Mountain wolves.Item Time-lagged variation in pond density and primary productivity affects duck nest survival in the Prairie Pothole Region(2013-07) Walker, Johann; Rotella, Jay J.; Stephens, Scott E.; Lindberg, M. S.; Ringelman, J. K.; Hunter, C. M.; Smith, A. J.The Prairie Pothole Region (PPR) is the primary breeding region for most species of North American dabbling ducks (Anas spp.). Conservation of these species is guided in part by knowledge of relationships between nest survival probability and habitat features. Positive relationships between duck nest survival and amount and configuration of herbaceous perennial vegetation have been observed in previous studies, but these 2- to 4-year studies might not have adequately characterized the temporal effect of wet–dry episodes on nest survival. Over an eight-year period, we studied nest survival of five species of ducks in the PPR relative to spatial and temporal variation in pond density, primary productivity, and hydrologic status of wetlands, soil, and vegetation on 52 study sites selected to span a gradient of spatial variation in proportion of herbaceous perennial vegetation and in number of wetland basins. We observed the fate of 12 754 nests. Consistent with past studies, 90% of nests that failed to hatch were destroyed by predators. Nest survival probability was positively related to current-year pond density and primary productivity, negatively related to pond density and primary productivity during the previous two years, and positively related to the number of wetland basins on the study site. Predicted relationships between nest survival and proportion or configuration of herbaceous perennial vegetation in the surrounding landscape were not supported. For mallard (Anas platyrhynchos), median estimated nest survival probability ranged from 0.02 (SE = 0.01) to 0.22 (SE = 0.02). Estimated nest survival was greatest on sites with numerous wetland basins that had transitioned from dry, unproductive conditions to wet, productive conditions in the previous 1–2 years. Our results were consistent with time-lagged responses of food webs to resource pulses in a broad array of ecosystems. Our study highlighted the importance of wetland basins and wet–dry episodes to duck nest survival in the PPR. Current habitat conservation efforts focus on landscapes with numerous wetland basins and a high proportion of herbaceous perennial vegetation. Our results suggest that future conservation efforts should focus on preserving high-density wetland complexes across as large a geographic extent as possible even in cropland-dominated landscapes.Item 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, WilliamIn 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...