Selective harvest focused on sexual signal traits can lead to extinction under directional environmental change

Abstract

Humans commonly harvest animals based on their expression of secondary sexual traits such as horns or antlers. This selective harvest is thought to have little effect on harvested populations because offtake rates are low and usually only the males are targeted. These arguments do not, however, take the relationship between secondary sexual trait expression and animal condition into account: there is increasing evidence that in many cases the degree of expression of such traits is correlated with an animal's overall well-being, which is partly determined by their genetic match to the environment. Using an individual-based model, we find that when there is directional environmental change, selective harvest of males with the largest secondary sexual traits can lead to extinction in otherwise resilient populations. When harvest is not selective, the males best suited to a new environment gain the majority of matings and beneficial alleles spread rapidly. When these best-adapted males are removed, however, their beneficial alleles are lost, leading to extinction. Given the current changes happening globally, these results suggest that trophy hunting and other cases of selective harvest (such as certain types of insect collection) should be managed with extreme care whenever populations are faced with changing conditions.

Hunting and evolution: theory, evidence, and unknowns

“…Sustainability is a fundamental principle underlying any harvest. Clearly, if intense selective hunting had consequences for fitness and population dynamics beyond just some evolutionary shrinking of weapons, it would be a more serious conservation issue (Knell & Martinez-Ruiz 2017). Our review highlights the current limitations of the empirical evidence and suggest new research towards determining whether harvesting practices are evolutionary sustainable (Ashley et al 2003) and not just ecologically sustainable.…”

“…That possibility rests largely on the assumption of a genetic correlation between fitness and male trophy size. While theory shows that such a correlation could have important consequences for population dynamics (Knell & Martinez-Ruiz 2017), evidence supporting it in large mammals is limited so far. That is partly because this subject has received little attention, making it another area ripe for additional investigation (Table 4).…”

“…Here, we argue that many current hunting management systems likely have no detectable evolutionary impacts on weapon size or shape. Results suggesting evolution of smaller horn size of male bighorn sheep (Ovis canadensis) due to selective hunting (Pigeon et al 2016), and model simulations underlying the possible effects of a covariance between trophy size and fitness (Knell & Martinez-Ruiz 2017) have been misrepresented in popular media, making hunting appear to have a much stronger evolutionary effect than what is supported by data. Another reason for the controversial nature of this subject is the difficulty of distinguishing evolution from phenotypic plasticity.…”

Divergent density feedback control of migratory predator recovery following sex-biased perturbations

“…Sexual dimorphism, for example, is prevalent in natural populations (Fairbairn 1997), 54 often leading to sex-biased pressure (Coltman et al 2003). As stress becomes intensified, these 55 sources of intraspecific variation in fitness may emerge as a directional shift in demographic 56 rates (Wedekind 2017), diminishing reproductive output (Knell & Martínez-Ruiz 2017). Because 57 of sex-dependent differential investment in reproduction, sex-biased stresses may pose a 58 unpredictable threat to persistence of wild populations (Coltman et al 2003).…”

Testing the importance of harvest refuges for phenotypic rescue of trophy‐hunted populations

“…Selective harvesting may reduce population growth if alleles associated with trophy size also affect life-history traits (Coltman, O'Donoghue, Hogg, & Festa-Bianchet, 2005;Knell & Martínez-Ruiz, 2017). Rates of phenotypic change due to anthropogenic selective pressures are higher than those induced by natural selection (Darimont et al, 2009) because harvest-induced selective pressures are often stronger than natural selection (Conover, Munch, & Arnott, 2009).…”