Inefficiency of evolutionarily relevant selection in ungulate trophy hunting

Abstract

Differentially harvesting individual animals with specific traits has led some to argue that such selection can cause evolutionary change that may be detrimental to the species, especially if those traits are related positively to individual fitness. Most hunters are not selective in the type of animal they take, satisfied instead to harvest any legal animal. In a few exceptions, however, regulations may limit hunters to harvest animals of a minimum size or age regardless of their personal choice. Using information from a broad range of aquatic and terrestrial systems exposed to a myriad of potential and operational selective pressures, several authors have made expansive generalizations about selective harvest and its applicability to ungulates. Harvest-based selection can potentially be intensive enough to be relevant in an evolutionary sense, but phenotypic changes consistent with hunter selection are otherwise confounded with multiple environmental influences. Factors such as age, genetic contribution of females, nutrition, maternal effects, epigenetics, patterns of mating success, gene linkage, gene flow, refugia, date of birth, and other factors affecting selection interact with harvest to impede unidirectional evolution of a trait. The intensity of selection determines potential for evolutionary change in a meaningful temporal framework. Indeed, only under severe intensity, and strict selection on a trait, could human harvest prompt evolutionary changes in that trait. Broad generalizations across populations or ecological systems can yield erroneous extrapolations and inappropriate assumptions. Removal of males expressing a variety of horn or antler sizes, including some very large males, does not inevitably represent directional artificial selection unless the selective pressures are intensive enough to cause a unidirectional shift in allele frequencies that may act on some relevant life-history trait or process. Here I review the topic of harvest-based selection in male ungulates and discuss the inefficiency of trophy hunting in changing genetic expression of phenotype. Ó 2017 The Wildlife Society.

Predicting the evolutionary effects of hunting requires an understanding of genetics

“…The relaxin‐like receptor 2 ( RXFP2 ) gene referred to by Heffelfinger () appears to be pleiotropic in Soay sheep because variation at this locus is associated with horn morphology and survival (Johnston et al ). The alternative alleles at RXFP2 appear to be maintained by balancing selection, where 1 allele confers larger horns and increased reproductive success of males, and the other confers smaller horns and increased survival, resulting in net heterozygous advantage at the locus (Johnston et al ).…”

“…Heffelfinger () did not consider the effects of genetic drift due to small effective population size ( N e ), which can reduce to the evolutionary response to selective hunting. The response to selection is less predictable in small populations because genetic drift generates random changes in allele frequency, whereas positive selection increases the frequency of a favorable allele (Robertson , Coltman ).…”

Obstacles to evolutionary consequences of ungulate trophy hunting: Reply to Kardos et al

“…Heffelfinger () provided a poor example of linked loci confounding an evolutionary response to selection, but Kardos et al () acknowledged this concept is correct and well supported by theoretical and empirical genetics research. The point remains valid even if the empirical example provided was not.…”

“…Kardos et al () helped clarify details of the mechanisms behind selective harvest and evolutionary effect. This dialogue is important but does not alter the primary premise of Heffelfinger (), which was to call attention to the multitude of previously neglected genetic and nongenetic factors that make hunter selection inefficient and uncommon in wild ungulates, and to warn against generalizing the results from specific studies. Kardos et al () misrepresent my paper by repeatedly creating a false argument that the factors I discuss do not preclude rapid evolution in response to selective hunting.…”

“…Artificial selection through trophy hunting was more likely at Ram Mountain than elsewhere because of its isolation and the intensity of selection exerted (Festa‐Bianchet ). Heffelfinger () provides a detailed discussion of the inappropriateness of applying results from Ram Mountain widely to other wild sheep (and other ungulate) populations under different management paradigms and selection intensities.…”