Chapter 14 Demography of Central Yellowstone Bison: Effects of Climate, Density, and Disease

Geremia, Chris; White, P. J.; Garrott, Robert A.; Wallen, Rick L.; Aune, Keith; Treanor, John J.; Fuller, Julie A.

doi:10.1016/s1936-7961(08)00214-5

Cited by 9 publications

(22 citation statements)

References 65 publications

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“…By our estimation, this would suggest that seropositive elk produce approximately 24% fewer calves than seronegative elk (see ). Similar reductions in pregnancy and recruitment attributable to brucellosis have been found for bison in Yellowstone, which lend additional support to our findings (Fuller et al., ; Geremia et al., ). This indicates the potential for the disease to have as much of an effect on reducing pregnancy as severe winters or droughts.…”

Section: Discussionsupporting

confidence: 91%

Hidden cost of disease in a free‐ranging ungulate: brucellosis reduces mid‐winter pregnancy in elk

Cotterill

Cross

Middleton

et al. 2018

Ecology and Evolution

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Demonstrating disease impacts on the vital rates of free‐ranging mammalian hosts typically requires intensive, long‐term study. Evidence for chronic pathogens affecting reproduction but not survival is rare, but has the potential for wide‐ranging effects. Accurately quantifying disease‐associated reductions in fecundity is important for advancing theory, generating accurate predictive models, and achieving effective management. We investigated the impacts of brucellosis (Brucella abortus) on elk (Cervus canadensis) productivity using serological data from over 6,000 captures since 1990 in the Greater Yellowstone Ecosystem, USA. Over 1,000 of these records included known age and pregnancy status. Using Bayesian multilevel models, we estimated the age‐specific pregnancy probabilities of exposed and naïve elk. We then used repeat‐capture data to investigate the full effects of the disease on life history. Brucellosis exposure reduced pregnancy rates of elk captured in mid‐ and late‐winter. In an average year, we found 60% of exposed 2‐year‐old elk were pregnant compared to 91% of their naïve counterparts (a 31 percentage point reduction, 89% HPDI = 20%–42%), whereas exposed 3‐ to 9‐year‐olds were 7 percentage points less likely to be pregnant than naïve elk of their same age (89% HPDI = 2%–11%). We found these reduced rates of pregnancy to be independent from disease‐induced abortions, which afflict a portion of exposed elk. We estimate that the combination of reduced pregnancy by mid‐winter and the abortions following mid‐winter reduces the reproductive output of exposed female elk by 24%, which affects population dynamics to a similar extent as severe winters or droughts. Exposing hidden reproductive costs of disease is essential to avoid conflating them with the effects of climate and predation. Such reproductive costs cause complex population dynamics, and the magnitude of the effect we found should drive a strong selection gradient if there is heritable resistance.

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Section: Discussionsupporting

confidence: 91%

Hidden cost of disease in a free‐ranging ungulate: brucellosis reduces mid‐winter pregnancy in elk

Cotterill

Cross

Middleton

et al. 2018

Ecology and Evolution

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“…Despite these criticisms and disparate findings, we encourage continued site-specific investigations of the relative influences of habitat conditions and antipredator responses on the body condition and probability of pregnancy in elk because, theoretically, the consequences of antipredator responses that carry nutritional costs could approach the consequences of direct predation Christianson 2008, Peckarsky et al 2008). Future studies should consider factors in addition to predation that could lower pregnancy rates in elk, including climate and forage conditions (Peckarsky et al 2008), an aging population (White and Garrott 2005), interactions among nutrition, condition, and lactation (Cook et al 2004a, b), low breeding bull : female ratios (Raedeke et al 2002), and diseases such as brucellosis (Geremia et al 2009, Rhyan et al 2009) that are increasing in prevalence in some areas (Cross et al 2010). The Yellowstone wolf saga has become an exemplar of the ecological consequences of large predator restoration, which is likely to guide science and policy regarding such intentional introductions.…”

Section: P J White Et Al 6 Ecological Applicationsmentioning

confidence: 99%

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

White

Garrott

Hamlin

et al. 2011

Ecological Applications

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Abstract. S. Creel et al. reported a negative correlation between fecal progesterone concentrations and elk : wolf ratios in greater Yellowstone elk (Cervus elaphus) herds and interpreted this correlation as evidence that pregnancy rates of elk decreased substantially in the presence of wolves (Canis lupus). Apparently, the hypothesized mechanism is that decreased forage intake reduces body condition and either results in elk failing to conceive during the autumn rut or elk losing the fetus during winter. We tested this hypothesis by comparing age-specific body condition (percentage ingesta-free body fat) and pregnancy rates for northern Yellowstone elk, one of the herds sampled by Creel et al., before (1962Creel et al., before ( -1968 and after (2000)(2001)(2002)(2003)(2004)(2005)(2006) wolf restoration using indices developed and calibrated for Rocky Mountain elk. Mean age-adjusted percentage body fat of female elk was similarly high in both periods (9.0% 6 0.9% pre-wolf; 8.9% 6 0.8% post-wolf). Estimated pregnancy rates (proportion of females that were pregnant) were 0.91 pre-wolf and 0.87 post-wolf for 4-9 year-old elk (95% CI on difference ¼ À0.15 to 0.03, P ¼ 0.46) and 0.64 pre-wolf and 0.78 post-wolf for elk .9 years old (95% CI on difference ¼ À0.01 to 0.27, P ¼ 0.06). Thus, there was little evidence in these data to support strong effects of wolf presence on elk pregnancy. We caution that multiple lines of evidence and/or strong validation should be brought to bear before relying on indirect measures of how predators affect pregnancy rates.

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“…Through nutritional and thermoregulatory mechanisms, a warming climate (see Fig. 1 Larter et al 2000, Fuller et al 2007a, Geremia et al 2009). The high rates of extraction (up to 32%) that keep the HM population below its carrying capacity undoubtedly diminish intrinsic feedbacks, but the relative lack of disease and severe winter snowpack might also be contributing factors (Geremia et al 2009, Plumb et al 2009).…”

Section: Discussionmentioning

confidence: 99%

“…1 Larter et al 2000, Fuller et al 2007a, Geremia et al 2009). The high rates of extraction (up to 32%) that keep the HM population below its carrying capacity undoubtedly diminish intrinsic feedbacks, but the relative lack of disease and severe winter snowpack might also be contributing factors (Geremia et al 2009, Plumb et al 2009). Although it was once thought that large animals like bison should experience strong density dependence because of K-selection (Pianka 1970), these ideas have since been replaced (see Reznick et al 2002), and recent evidence suggests that long-lived species actually tend to experience weaker density dependence than short-lived species (Herrando-Pe´rez et al 2012).…”

Section: Discussionmentioning

confidence: 99%

“…In conclusion, climate likely has its strongest effect on bison populations during early life-cycle stages (Koons et al 2012), as in large mammals, juveniles tend to be more responsive and susceptible to environmental variation than adults (Gaillard et al 1998). However, the impacts of climate and density dependence across the age-and sex-structured life cycle will need to be estimated in order to better understand how these mechanisms affect HM bison population dynamics (e.g., Geremia et al 2009). Moreover, our unstructured statespace model may have attributed too much of the variation in population dynamics to demographic processes rather than observation error, sometimes resulting in predicted rates of growth that may be unrealistically high (e.g., !40% growth in 1977, 1978, 1990, 1993, 2007Fig.…”

Section: Discussionmentioning

confidence: 99%

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Disentangling the effects of climate, density dependence, and harvest on an iconic large herbivore's population dynamics

Koons

Colchero

Hersey

et al. 2015

Ecological Applications

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Understanding the relative effects of climate, harvest, and density dependence on population dynamics is critical for guiding sound population management, especially for ungulates in arid and semiarid environments experiencing climate change. To address these issues for bison in southern Utah, USA, we applied a Bayesian state-space model to a 72-yr time series of abundance counts. While accounting for known harvest (as well as live removal) from the population, we found that the bison population in southern Utah exhibited a strong potential to grow from low density (β0 = 0.26; Bayesian credible interval based on 95% of the highest posterior density [BCI] = 0.19-0.33), and weak but statistically significant density dependence (β1 = -0.02, BCI = -0.04 to -0.004). Early spring temperatures also had strong positive effects on population growth (Pfat1 = 0.09, BCI = 0.04-0.14), much more so than precipitation and other temperature-related variables (model weight > three times more than that for other climate variables). Although we hypothesized that harvest is the primary driving force of bison population dynamics in southern Utah, our elasticity analysis indicated that changes in early spring temperature could have a greater relative effect on equilibrium abundance than either harvest or. the strength of density dependence. Our findings highlight the utility of incorporating elasticity analyses into state-space population models, and the need to include climatic processes in wildlife management policies and planning.

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Chapter 14 Demography of Central Yellowstone Bison: Effects of Climate, Density, and Disease

Cited by 9 publications

References 65 publications

Hidden cost of disease in a free‐ranging ungulate: brucellosis reduces mid‐winter pregnancy in elk

Hidden cost of disease in a free‐ranging ungulate: brucellosis reduces mid‐winter pregnancy in elk

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

Disentangling the effects of climate, density dependence, and harvest on an iconic large herbivore's population dynamics

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