The effects of wild ungulates on small mammals: a systematic review and meta-analysis

Wild ungulates are increasing in several regions of the world, recolonizing the empty niche left by previous livestock systems. Due to their important role as ecosystem engineers, wild ungulates can modify and change vegetation structure, as well as modulate soil ecological processes, affecting the remaining components of communities and posing new management challenges. Several studies have evaluated the effects of wild ungulates on other guilds, but the results are taxonomically biased. Thus, our goal is to synthesise the overall effects of wild ungulates on smaller mammals on a broad scale.Due to the complexity of assessing these impacts throughout the ecological network, we focused on mammals since they occupy different trophic levels and are key taxa in food webs. We conducted a review of the documented effects of wild ungulates on the guild's abundance of mammals with less than 10 kg, which revealed a gap in the literature regarding how higher trophic levels respond to wild ungulate disturbances. Using a hierarchical meta-analytic approach, we assessed, on a subset of articles, whether the presence of wild ungulates affects the guild of small mammals and whether these effects were associated with biome, wild ungulates' body mass and foraging strategy, and small mammals' body mass.A quantitative meta-analysis was possible only for small mammals (Rodentia/Soricomorpha/Macroscelidea <1 kg) and revealed that their abundance tended to decrease with increasing abundance of wild ungulates. The magnitude of this impact, however, was modulated by body mass, being greater for larger small mammals than for smaller ones.The impacts of wild ungulates might result in changes in the abundance of small mammals through direct and indirect pathways. Our results motivate a more holistic evaluation of rewilding projects and the correct assessment of the effects concerning wild ungulates' reintroductions.