Ecological Interactions Involving Feral Horses and Predators: Review with Implications for Biodiversity Conservation

Abstract

For many ecosystems, feral horses are increasingly becoming an important if not dominant component of ungulate biomass and hence influence on community dynamics. Yet we still know little of how horses contribute to key ecological interactions including predator-prey and indirect competitive relationships at a community level. Notably, feral species like horses can exhibit life-history traits that differ from that of native (mainly artiodactyl) herbivore competitors. Artificial selection for traits like increased, early, or extended reproduction that have yet to be reversed by natural selection, coupled with naturally selected differences in anatomy and behavior, in addition to unique management objectives for horses compared to other species, means that the dynamics of feral horse populations are not likely to align with what might be expected of other large herbivores. Unexpected population dynamics and inherent biological asymmetries between native ungulates and feral horses may therefore influence the former via direct competition for shared resources and through enemy-mediated interactions like apparent competition. In several localities feral horses now co-exist with multiple native prey species, some of which are in decline or are species at risk. Compounding risks to native species from direct or indirect competitive exclusion by horses is the unique nature and socio-political context of feral horse management, which tends towards allowing horse populations to be limited largely by natural, density-dependent factors. We summarize the inherent asymmetries between feral horse biology and that of other ungulate prey species with consequences for conservation, focusing on predator-prey and emerging indirect interactions in multi-prey systems, and highlight future directions to address key knowledge gaps in our understanding of how feral horses may now be contributing to the (re)structuring of food webs. Observations of patterns of rapid growth and decline, and associated skews in sex ratios of feral horse populations, indicate a heightened potential for indirect interactions among large ungulate prey species, where there is a prevalence of feral horses as preferred prey, particularly where native prey are declining. In places like western North America, we expect predator-prey interactions involving feral horses to become an increasingly important factor in the conservation of wildlife. This applies not only to economically or culturally important game species but also at-risk species, both predators (e.g., wolves [Canis lupus], grizzly bears [Ursus arctos]) and prey (e.g., woodland caribou [Rangifer tarandus caribou]), necessitating an ecological understanding of the role of horses in natural environments that goes beyond that of population control.

Nutritional Quality and Socio-Ecological Benefits of Mare Milk Produced under Grazing Management

“…In the context of climate change, autochthonous horse breeds offer opportunities for sustainable agricultural production in less favored [135] and extensive areas [136] as they can survive extreme environmental conditions like prolonged droughts or severe snowing episodes that cause the death of most free-ranging livestock [137]. Moreover, horses are easy to manage and have been reported to face lower vulnerability to predation compared to other large herbivores [138].…”

Gray Wolves (<i>Canis lupus</i>) consume free-ranging horses (<i>Equus ferus caballus</i>) on the Chilcotin plateau, British Columbia

“…While acknowledging that concerns have been raised about the ecological interactions involving free-ranging horses and predators and the potential implications for biodiversity conservation (Boyce and McLoughlin 2021), namely through indirect compet-itive relationships (Wittmer et al 2013;Gooch et al 2017;Hall et al 2018;Boyce and McLoughlin 2021), Duncan (1992) suggests that predation and horse social dynamics may be more important factors in regulating free-ranging horse populations than food supply. Based on our scat findings and given the minimum 300+ years that horses have been in this area (Storrar et al 1977;McCrory 2002;Bhattacharyya et al 2011;Bhattacharyya and Larson 2014; G. Cothran and W.P.M.…”

The Wildlife Profession's Duty in Achieving Science‐Based Sustainable Management of Free‐Roaming Equids

“…In most places they have effectively few or no predators, circumstances requiring the need for management to control population growth and protect limited resources, similar to management of other large ungulates. Domestic horses, like other domesticated ungulates, have undergone thousands of years of artificial selection for high reproductive performance, meaning that feral populations have the potential to grow rapidly because females will sacrifice their own body condition for survival of their offspring (Grange et al 2009) and mortality rates of horses tend to be low for multiple reasons (Garrott 2018, Boyce and McLoughlin 2021). The annual finite rate of increase for feral equids in Australia ranges as high as 1.36 (Dawson and Hone 2012), a remarkable rate of increase (36%) for a large ungulate with only 1 offspring per year.…”

“…In this special section, authors present a broad range of research on feral equids, including estimating space use and population size (Gedir et al 2021, King et al 2021, Schoenecker et al 2021), population control in the absence of co‐evolved predators (Andreasen et al 2021, Boyce and McLoughlin 2021, Hinchcliffe et al 2021), effects of feral equids on wildlife habitat and sympatric species (Burdick et al 2021, Clancy et al 2021, Coates et al 2021, Hennig et al 2021, Scorolli 2021, Stoner et al 2021), and a promising new equid fertility control method (Holyoak et al 2021). Although these papers provide techniques or approaches to manage feral equids, their application will vary by population, political jurisdiction, and country.…”