Rewilded horses in European nature conservation - a genetics, ethics, and welfare perspective.

In recent decades, the integration of horses (Equus ferus) in European rewilding initiatives has gained widespread popularity due to their potential for regulating vegetation and restoring natural ecosystems. However, employing horses in conservation efforts presents important challenges, which we here explore and discuss. These challenges encompass the lack of consensus on key terms inherent to conservation and rewilding, the entrenched culture and strong emotions associated with horses, low genetic diversity and high susceptibility to hereditary diseases in animals under human selection, as well as insufficient consideration for the social behaviour of horses in wild-living populations. In addition, management of wild-living horses involves intricate welfare, ethics and legislative dimensions. Anthropocentric population-control initiatives may be detrimental to horse group structures since they tend to prioritise individual welfare over the health of populations and ecosystems. To overcome these challenges, we provide comprehensive recommendations. These involve a systematic acquisition of genetic information, a focus on genetic diversity rather than breed purity and minimal veterinary intervention in wild-living populations. Further, we advise allowing for natural top-down and bottom-up control - or, if impossible, simulating this by culling or non-lethal removal of horses - instead of using fertility control for population management. We advocate for intensified collaboration between conservation biologists and practitioners and enhanced communication with the general public. Decision-making should be informed by a thorough understanding of the genetic makeup, common health issues and dynamics, and social behaviour in wild-living horse populations. Such a holistic approach is essential to reconcile human emotions associated with horses with the implementation of conservation practices that are not only effective but also sustainable for the long-term viability of functional, biodiverse ecosystems, while rehabilitating the horse as a widespread wild-living species in Europe.

Worldwide Late Pleistocene and Early Holocene population declines in extant megafauna are associated with Homo sapiens expansion rather than climate change.

The worldwide extinction of megafauna during the Late Pleistocene and Early Holocene is evident from the fossil record, with dominant theories suggesting a climate, human or combined impact cause. Consequently, two disparate scenarios are possible for the surviving megafauna during this time period - they could have declined due to similar pressures, or increased in population size due to reductions in competition or other biotic pressures. We therefore infer population histories of 139 extant megafauna species using genomic data which reveal population declines in 91% of species throughout the Quaternary period, with larger species experiencing the strongest decreases. Declines become ubiquitous 32-76 kya across all landmasses, a pattern better explained by worldwide Homo sapiens expansion than by changes in climate. We estimate that, in consequence, total megafauna abundance, biomass, and energy turnover decreased by 92-95% over the past 50,000 years, implying major human-driven ecosystem restructuring at a global scale.