Effect of Adult Sex Ratio on Mule Deer and Elk Productivity in Colorado

White, Gary C.; Freddy, David J.; Gill, R. Bruce; Ellenberger, John H.

doi:10.2307/3803107

Cited by 45 publications

(41 citation statements)

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“…Although this is natural, widespread use of maleselective harvesting strategies is increasing the sex ratio skew in many such populations (Milner et al 2007). There is some evidence that decreasing the proportion of males in these systems can have negative effects on female reproduction (Bergerud 1974;Aitken and Child 1992;White et al 2001;Solberg et al 2002). Such effects can, for example, be caused by changes in the timing and synchrony of breeding at skewed sex ratios (Markgren 1974;CluttonBrock et al 1983CluttonBrock et al , 1987CluttonBrock et al , 1988Schwarz et al 1994;Taquet et al 1999;Mysterud et al 2002;Holand et al 2003;, a tendency among females to delay or even avoid breeding when they do not have access to preferred males (Komers et al 1999;Møller and Legendre 2001), or problems with mate finding (Berec et al 2001;Rankin and Kokko 2007).…”

Section: Discussionmentioning

confidence: 98%

Demographic Stochasticity, Allee Effects, and Extinction: The Influence of Mating System and Sex Ratio

Lee

Sæther

Engen

2011

The American Naturalist

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Demographic stochasticity has a substantial influence on the growth of small populations and consequently on their extinction risk. Mating system is one of several population characteristics that may affect this. We use a stochastic pair-formation model to investigate the combined effects of mating system, sex ratio, and population size on demographic stochasticity and thus on extinction risk. Our model is designed to accommodate a continuous range of mating systems and sex ratios as well as several levels of stochasticity. We show that it is not mating system alone but combinations of mating system and sex ratio that are important in shaping the stochastic dynamics of populations. Specifically, polygyny has the potential to give a high demographic variance and to lower the stochastic population growth rate substantially, thus also shortening the time to extinction, but the outcome is highly dependent on the sex ratio. In addition, population size is shown to be important. We find a stochastic Allee effect that is amplified by polygyny. Our results demonstrate that both mating system and sex ratio must be considered in conservation planning and that appreciating the role of stochasticity is key to understanding their effects.

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Section: Discussionmentioning

confidence: 98%

Demographic Stochasticity, Allee Effects, and Extinction: The Influence of Mating System and Sex Ratio

Lee

Sæther

Engen

2011

The American Naturalist

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“…This effect can be compounded, if there is an additional age bias in the harvest where hunters are removing large numbers of older males that typically do most of the breeding. The negative effects can be caused by changes in the timing and synchrony of breeding (White et al, 2001;Solberg et al, 2002), or females delaying or avoiding breeding because they are not able to find enough suitable mates (Ginsberg and Milner-Gulland, 1994;Komers et al, 1999;Møller and Legendre, 2001;Milner-Gulland et al, 2003).…”

Section: Discussionmentioning

confidence: 99%

“…Skewed ASRs have been linked to breeding behavior, social status, and the reproductive success of individuals (Murray, 1991;Clutton-Brock et al, 1997;Castro et al, 2004). ASRs are important indicators of a population's status and are a commonly used index for population management (White et al, 2001;Clutton-Brock et al, 2002;McLoughlin et al, 2005;Solberg et al, 2005). However for most species, little is known of the specific causes of annual variation in ASRs and the impacts they have on population dynamics (Le Galliard et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Examination of Annual Variation in the Adult Sex Ratio of Pronghorn (Antilocapra americana)

Hoffman

Genoways

2012

The American Midland Naturalist

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ABSTRACT.-The adult sex ratio (ASR) is an important component of a population's demographics and can be used as an indicator of a population's status. However, the causes of annual variation in ASRs are unknown for many species. Fluctuations in ASR can arise through demographic stochasticity and intense selective harvesting. In this study we investigate the longterm patterns of variation in the ASRs (bucks: 100 does) for four populations of pronghorn (Antilocapra americana) in western Nebraska. We used multiple variables in a model selection process to predict annual fluctuation of pronghorn ASRs. We found that the number of bucks: 100 does significantly varied over the four populations. The best predictors of annual variation in pronghorn ASRs were variable across all populations. The number of pronghorn bucks harvested in the previous year's hunting season and the previous year's density of pronghorn were the most common predictors of ASR fluctuation. Buck harvest was an important predictor variable in only two of the four populations. Variation of harvest strategies within the populations could account for the lack of importance of buck harvest in half of the populations. The relationship between density and ASR is novel but difficult to interpret due to lack of data on birth sex ratios and fawn survival. More data on pronghorn demographics are needed in order to better explain the connection between density and ASR.

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“…These strategies frequently result in skewed sex and age ratios at the population level [2]. Research on cervid species including moose ( Alces alces ) [3], [4] and mule deer ( Odocoileus hemionus ) [5], [6] has found little evidence to suggest that these reductions affect productivity, despite large changes to overall population composition. However, exceedingly female-biased sex ratios can have long term demographic and genetic effects on populations [7], [8], [9], [10], [11], and in some circumstances these effects can lead to declines in reproductive success [2], [8], [12] or calf survival and recruitment [7], [13], [14].…”

Section: Introductionmentioning

confidence: 99%

Possible Secondary Population-Level Effects of Selective Harvest of Adult Male Muskoxen

Schmidt

Gorn

2013

PLoS ONE

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Selective harvest regimes are often focused on males resulting in skewed sex-ratios, and for many ungulate species this strategy is sustainable. However, muskoxen (Ovibos moschatus) are very social and mature bulls (≥4 years old), particularly prime-age bulls (6–10 years old), play important roles in predator defense and recruitment. A year-round social structure incorporating large males into mixed-sex groups could make this species more susceptible to the effects of selective harvest if population composition and sex-ratios influence overall survival and reproductive success. Using detailed data collected on the muskox population occupying the Seward Peninsula, Alaska during 2002–2012, we formulated the hypothesis that the selective harvest of mature bulls may be related to documented changes in population composition and growth rates in this species. In addition, we reviewed existing published information from two other populations in Alaska, the Cape Thompson and Northeastern populations, to compare population growth rates among the three areas under differential harvest rates relative to our hypothesis. We found that on the Seward Peninsula, mature bull:adult cow ratios declined 4–12%/year and short-yearling:adult cow ratios (i.e., recruitment) declined 8–9%/year in the most heavily harvested areas. Growth rates in all 3 populations decreased disproportionately after increases in the number of bulls harvested, and calf:cow ratios declined in the Northeastern population as harvest increased. While lack of appropriate data prevented us from excluding other potential causes such as density dependent effects and changes in predator densities, our results did align with our hypothesis, suggesting that in the interest of conservation, harvest of mature males should be restricted until causal factors can be more definitively identified. If confirmed by additional research, our findings would have important implications for harvest management and conservation of muskoxen and other ungulate species with similar life-histories.

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Effect of Adult Sex Ratio on Mule Deer and Elk Productivity in Colorado

Cited by 45 publications

References 0 publications

Demographic Stochasticity, Allee Effects, and Extinction: The Influence of Mating System and Sex Ratio

Demographic Stochasticity, Allee Effects, and Extinction: The Influence of Mating System and Sex Ratio

Examination of Annual Variation in the Adult Sex Ratio of Pronghorn (Antilocapra americana)

Possible Secondary Population-Level Effects of Selective Harvest of Adult Male Muskoxen

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