Climate-induced variation in vital rates of an unharvested large-herbivore population

Abstract

Variation in vital rates of an unharvested elk (Cervus elaphus) population was studied using telemetry for 7 consecutive years, 1991–1998. We found pronounced senescence in survival rates, but no evidence for reproductive senescence. Prime-age females (<10 years old) experienced very high annual survival rates (mean = 0.97, SE = 0.02), with lower survival rates for senescent animals ([Formula: see text]10 years old; mean = 0.79, SE = 0.06). There was evidence that the severity of snowpack conditions had little effect on survival of prime-age animals except during the most extreme winter, while survival of senescent animals was progressively depressed as the severity of snowpack conditions increased. Reproductive rates remained essentially constant, near their biological maxima (mean = 0.91, SE = 0.02). Annual re cruitment was highly variable. Snowpack had a pronounced effect on recruitment (r2 = 0.91), the most severe snowpack conditions resulting in the virtual elimination of a juvenile cohort. Population estimates and recruitment rates obtained during this investigation and historic data collected from 1965 to 1980 support the premise that the population has been maintained in a dynamic equilibrium for at least three decades despite the stochastic effects of climate variation on vital rates. We conclude that the population is resource-limited, with variation about the equilibrium caused primarily by variable recruitment driven by stochastic annual snowpack.

Body condition and pregnancy in northern Yellowstone elk: Evidence for predation risk effects?

“…However, subsequent assays of feces collected from this elk herd in some pre-and post-wolf years revealed substantial errors of misclassifying pregnant animals as nonpregnant based on observations of calves with marked females and population measures of calf production (Garrott et al 2003. Many of these fecal samples were assayed in the same laboratory and frequently intermixed with the fecal samples reported in Creel et al (2007).…”

“…21, No. 1 not recognized in the radio and enzyme immunoassays (Garrott et al 2003, Hamlin et al 2009). However, we have been unable to explain the aberrant fecal steroid results despite additional assay work and numerous consultations with biologists and reproductive endocrinologists (S. Creel and J. Berardinelli, Montana State University; S. Monfort, Smithsonian Institution).…”

Assessing Timing and Causes of Neonatal Lamb Losses in a Bighorn Sheep (Ovis canadensis canadensis) Herd via Use of Vaginal Implant Transmitters

“…Together, birth rate and juvenile survival constitute recruitment. Recruitment in ungulates can be driven by many factors such as disease (Douglas 2001, Monello et al 2001, Cassirer and Sinclair 2007, Cassirer et al 2013), habitat quality (Langvatn et al 1996), density dependence (Douglas and Leslie Jr. 1986, Portier et al 1998, Forchhammer et al 1998), predation (Festa-Bianchet et al 1994, Wehausen 1996, White and Garrott 2005, and climate (Owen-Smith 1990, Langvatn et al 1996, Garrott et al 2003, Brown 2011.…”

Trophic interactions and dynamic herbivore responses to snowpack

“…But their occurrence drops much more rapidly in response to increasing snowpack depth, suggesting either that they die off rapidly or else move to lower elevations, such as outside the national park, as snow accumulation increases. It is unlikely that females are dying off faster; elk survival studies show higher survival for females than males [27,28], though juvenile survival rates are lower than those of adults [29,30]. Because over-winter mortality of 1st-year juveniles is higher than that of adult females [30], the individual abundance of adult females + juveniles is likely to decline over the course of many winters.…”

“…It is unlikely that females are dying off faster; elk survival studies show higher survival for females than males [27,28], though juvenile survival rates are lower than those of adults [29,30]. Because over-winter mortality of 1st-year juveniles is higher than that of adult females [30], the individual abundance of adult females + juveniles is likely to decline over the course of many winters. Our study, however, assessed occurrence rates of groups rather than abundance of individuals.…”