Undesirable Evolutionary Consequences of Trophy Hunting

Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.
Nature (Impact Factor: 41.46). 01/2004; 426(6967):655-8. DOI: 10.1038/nature02177
Source: PubMed


Phenotype-based selective harvests, including trophy hunting, can have important implications for sustainable wildlife management if they target heritable traits. Here we show that in an evolutionary response to sport hunting of bighorn trophy rams (Ovis canadensis) body weight and horn size have declined significantly over time. We used quantitative genetic analyses, based on a partly genetically reconstructed pedigree from a 30-year study of a wild population in which trophy hunting targeted rams with rapidly growing horns, to explore the evolutionary response to hunter selection on ram weight and horn size. Both traits were highly heritable, and trophy-harvested rams were of significantly higher genetic 'breeding value' for weight and horn size than rams that were not harvested. Rams of high breeding value were also shot at an early age, and thus did not achieve high reproductive success. Declines in mean breeding values for weight and horn size therefore occurred in response to unrestricted trophy hunting, resulting in the production of smaller-horned, lighter rams, and fewer trophies.

    • "A skewed sex ratio may create long-term problems for the maintenance of genetic diversity and population health of species. Selective hunting could also cause species decline and possible local extirpation (e.g., Tuyttens and MacDonald, 2000; Frank and Woodroffe, 2001; Harris et al., 2002; Coltman et al., 2003; Adams, 2004; Lindsey et al., 2007; Caro et al., 2009). "
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    ABSTRACT: ABSTRACT Dhorpatan Hunting Reserve (DHR) of Nepal, the only hunting reserve in the country, is famous for trophy hunting of bharal or ‘blue sheep’ (Pseudois nayaur) and Himalayan tahr (Hemitragus jemlahicus). Although trophy hunting has been occurring in DHR since 1987, its’ ecological consequence is poorly known. We assessed the ecological consequences of bharal and the Himalayan tahr hunting in DHR and measured the economic contribution of hunting to the government and local communities based on the revenue data. The bharal population increased significantly from 1990 to 2011, but the sex ratio was skewed from male-biased (129Male:100Female) in 1990 to female-biased (82Male:100Female) in 2011. Similarly, the recent survey of Himalayan tahr in DHR showed that there was a total of 285 individuals with a sex ratio of 60 Male: 100 Female. Bharal and Himalayan tahr trophy hunting have generated economic benefits through local employment generation and direct income of US$364,072 during the last five years. Government revenue collected from 2007-08 to 2011-12 totalled US$184,372 from hunting of bharal and Himalayan tahr. Male-focused trophy hunting as practiced in DHR may not be an ecologically sustainable practice due to its effect on the sex ratio that may lead negative consequences to the genetic structure of the population in a long term. Therefore, bharal and tahr population dynamics and sex ratios must be considered while setting harvest quotas in DHR. KEYWORDS: bharal, Himalayan tahr, hunting, conservation, local community, revenue, sex ratio, population,
    Hystrix 11/2015; 26(2):XX. DOI:10.4404/hystrix-26.2-11210 · 2.86 Impact Factor
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    • " , Gaillard et al . 2004 ) in Alberta , we produced a simple model where the average horn length of 4 - year - old males in fictitious populations was stable , declined by 1% / year , or increased by 1% / year over 50 years . This yearly change is realistic : the study population showed a decline in horn length of approximately 31% over 28 years ( Coltman et al . 2003 ) . Although changes in horn length of 4 - year olds translated to changes at the population level , their magnitude varied . For example , when horns of 4 - year olds were simulated to increase by 1% annually , the average population horn length only increased by approximately 36% over 50 years despite the 63% increase of horn length o"
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    ABSTRACT: Many agencies and researchers use data from harvested animals to study temporal trends in phenotype. For large mammals, complete harvest records are typically only available for the past few decades, but records of the largest trophies have been collected for over a century. To examine whether record books and data from male bighorn sheep (Ovis canadensis) harvested under a minimum-curl regulation could detect temporal trends in horn length, we simulated populations of trophy-harvested male bighorn sheep where horn length was modeled to increase, remain stable, and decrease over time. All populations experienced a simulated harvest based on a minimum horn length, but only horns in the longest 5% of the initial distribution were entered in a fictional record book. We then assessed whether monitoring of harvested and “record” males detected temporal trends. Data from selective harvest underestimated declines and initially underestimated increases, but qualitatively detected both trends. Record-book entries, however, severely underestimated increases and did not detect declines, suggesting that they should not be used to monitor population trends. When these biases are taken into account, complete trophy harvest records can provide useful biological information.
    Wildlife Society Bulletin 10/2015; DOI:10.1002/wsb.597 · 1.27 Impact Factor
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    • "In those models which also exhibit the greatest evolutionary change, we also impose selection that is stronger than typically observed in the field. We consequently caution against claims of evolution in a generation or two (Coltman et al. 2003) as likely being flawed given our results suggest a few tens of generations are required before compelling evidence of evolution is likely to be detectable (see also Hadfield et al. (2010)). "
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    ABSTRACT: 1) Micro-evolutionary predictions are complicated by ecological feedbacks like density dependence, while ecological predictions can be complicated by evolutionary change. A widely used approach in micro-evolution, quantitative genetics, struggles to incorporate ecological processes into predictive models, while structured population modelling, a tool widely used in ecology, rarely incorporates evolution explicitly. 2) In this paper we develop a flexible, general framework that links quantitative genetics and structured population models. We use the quantitative genetic approach to write down the phenotype as an additive map. We then construct integral projection models for each component of the phenotype. The dynamics of the distribution of the phenotype are generated by combining distributions of each of its components. Population projection models can be formulated on per generation or on shorter time steps. 3) We introduce the framework before developing example models with parameters chosen to exhibit specific dynamics. These models reveal (i) how evolution of a phenotype can cause populations to move from one dynamical regime to another (e.g. from stationarity to cycles), (ii) how additive genetic variances and covariances (the G matrix) are expected to evolve over multiple generations, (iii) how changing heritability with age can maintain additive genetic variation in the face of selection and (iii) life history, population dynamics, phenotypic characters and parameters in ecological models will change as adaptation occurs. 4) Our approach unifies population ecology and evolutionary biology providing a framework allowing a very wide range of questions to be addressed. The next step is to apply the approach to a variety of laboratory and field systems. Once this is done we will have a much deeper understanding of eco-evolutionary dynamics and feedbacks.
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