Population‐specific vital rate contributions influence management of an endangered ungulate

Abstract

To develop effective management strategies for the recovery of threatened and endangered species, it is critical to identify those vital rates (survival and reproductive parameters) responsible for poor population performance and those whose increase will most efficiently change a population's trajectory. In actual application, however, approaches identifying key vital rates are often limited by inadequate demographic data, by unrealistic assumptions of asymptotic population dynamics, and of equal, infinitesimal changes in mean vital rates. We evaluated the consequences of these limitations in an analysis of vital rates most important in the dynamics of federally endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae). Based on data collected from 1980 to 2007, we estimated vital rates in three isolated populations, accounting for sampling error, variance, and covariance. We used analytical sensitivity analysis, life-stage simulation analysis, and a novel non-asymptotic simulation approach to (1) identify vital rates that should be targeted for subspecies recovery; (2) assess vital rate patterns of endangered bighorn sheep relative to other ungulate populations; (3) evaluate the performance of asymptotic vs. non-asymptotic models for meeting short-term management objectives; and (4) simulate management scenarios for boosting bighorn sheep population growth rates. We found wide spatial and temporal variation in bighorn sheep vital rates, causing rates to vary in their importance to different populations. As a result, Sierra Nevada bighorn sheep exhibited population-specific dynamics that did not follow theoretical expectations or those observed in other ungulates. Our study suggests that vital rate inferences from large, increasing, or healthy populations may not be applicable to those that are small, declining, or endangered. We also found that, while asymptotic approaches were generally applicable to bighorn sheep conservation planning; our non-asymptotic population models yielded unexpected results of importance to managers. Finally, extreme differences in the dynamics of individual bighorn sheep populations imply that effective management strategies for endangered species recovery may often need to be population-specific.

Short-term vegetation response to wildfire in the eastern Sierra Nevada: Implications for recovering an endangered ungulate

“…In addition, the benefit of improving winter ranges should be compared to the relative benefit of other management actions including disease prevention, predator control and augmentation (Johnson et al, 2010). Although we found no difference in nonnative plant biomass between burned and unburned sites, this may be a result of the limited timeframe and area sampled.…”

Seeking sanctuary: the neonatal calving period among central mountain woodland caribou (Rangifer tarandus caribou)

“…Predation is the main natural cause of calf mortality (Linnell et al 1995;Gustine et al 2006). Research suggests calf predation is probably most important for population growth during the calf's first winter (6-12 months) prior to recruitment into the population as a yearling (Hebblewhite et al 2007a;Johnson et al 2010;DeCesare et al 2012a). However, the neonatal period is an especially vulnerable time for predation (Adams et al 1995;Gustine et al 2006), and there is limited information available on the neonatal period of a calf's life (0-4 weeks of age), including parturition rates, neonatal calf survival, adult female habitat selection, and calving-range fidelity (Rettie and Messier 1998;Wittmer et al 2005a;Pinard et al 2012).…”

Declining recruitment of Gunnison Sage-Grouse highlights the need to monitor juvenile survival

“…However, this relationship also may vary among different populations within the same species (Johnson et al 2010). These varying relationships might indicate that different management strategies are necessary to most efficiently manage separate populations (Johnson et al 2010). Under these conditions, evaluating vital rates, such as recruitment in birds, for different populations within a species is necessary.…”