Reduced horn size in two wild trophy‐hunted species of Caprinae

Abstract

Factors affecting horn size in wild Caprinae are of biological and socio-economic interest because several species are selectively harvested on the basis of this heritable character. We analysed temporal trends in horn size in two mountain ungulates from south-eastern Spain, the Iberian wild goat Capra pyrenaica and the aoudad Ammotragus lervia. Trophy harvest is the main way in which these two species are exploited, although 'poor-quality' aoudads are also selectively removed. In recent years, both populations have suffered drastic decreases in number due to outbreaks of sarcoptic mange that led to the suspension of hunting for several years. Horn length in harvested male wild goats and aoudads declined during our study period. Over an 18-year period, the mean age of male goats shot as trophies rose by four years, while the age of trophy-harvested aoudads decreased by around six months over a 9-year period. Age and environmental conditions during the first few years of life explained 20% of variance in horn size in Iberian wild goat and 53% in aoudad. Population density early in life explained much of the reduction in goat horn size over time. Nevertheless, the major fall in population densities after the sarcoptic mange outbreaks did not lead to a recovery in horn size in either species. We suggest that the selective removal of large-horned animals may contribute to a decline in horn size. Other factors that may also explain the observed pattern include changes in interspecific competition, longlasting maternal effects and reduced carrying capacity due to overgrazing during high density periods. Unfortunately, our data sets did not allow us to account for the possible effects of these factors.

When does selective hunting select, how can we tell, and what should we do about it?

“…In Spain, as horn growth of Iberian wild goats Capra hispanica decreased after intense selective harvests, hunters took males that were 4 years older on average, probably because the age at which horns were considered a ‘trophy’ increased over time as growth declined (Pérez et al. ).…”

Inefficiency of evolutionarily relevant selection in ungulate trophy hunting

“…Trait changes consistent with evolutionarily relevant hunter selection are often accompanied by confounding environmental influences (Coltman et al , Coltman , Pérez et al , Pigeon et al ). Clear evidence of negative evolutionary consequences of selective trophy harvest in ungulates is rare (Mysterud , Kuparinen and Festa‐Bianchet ).…”

Demography, not inheritance, drives phenotypic change in hunted bighorn sheep

“…If the trait is heritable, then selection against the character can result in a cross-generational decrease in the character mean (1, 6, 7). Apparent shifts in the distribution of a quantitative character, however, may not occur through genetic mechanisms alone, because hunting can also alter age and sex structure, behavior, and social hierarchies (8-10), which may in turn interact with localized density-dependent and -independent factors to accentuate, or mask, a phenotypic response (6,11,12).To date, there have been some generalizations that hunting management can follow in an attempt to mimic natural mortality and limit selection against desirable traits, such as nose coloration for African lions (13). Where long-term data are available for hunted populations, then a response to unnatural selection can be detected.…”

“…Hunters may target individuals within a population that possess a trait they seek, such as large body or horn size, or a distinct color morph (4)(5)(6). If the trait is heritable, then selection against the character can result in a cross-generational decrease in the character mean (1,6,7).…”

“…Hunters may target individuals within a population that possess a trait they seek, such as large body or horn size, or a distinct color morph (4)(5)(6). If the trait is heritable, then selection against the character can result in a cross-generational decrease in the character mean (1,6,7). Apparent shifts in the distribution of a quantitative character, however, may not occur through genetic mechanisms alone, because hunting can also alter age and sex structure, behavior, and social hierarchies (8)(9)(10), which may in turn interact with localized density-dependent and -independent factors to accentuate, or mask, a phenotypic response (6,11,12).…”