2025/06/30 by Emil Ellegaard Thomassen, Kent Olsen, Morten D. D. Hansen +2 · 1 voice · 2 citations
Environmental Science · Agricultural and Biological Sciences · #Environmental DNA in Biodiversity Studies #Forest Ecology and Biodiversity Studies #Species Distribution and Climate Change
paper · pdf · doi:10.1111/1365-2664.70082
Abstract Reintroducing megafauna to reinstate missing top‐down trophic interactions (trophic rewilding) is increasingly being applied as a tool to promote self‐regulating, biodiverse ecosystems. Even though the theoretical background is clear, and megafauna effects are documented from prehistorical ecosystems, the effects of reintroduced herbivores in contemporary ecosystems remain understudied. This not only includes how reintroduced megafauna interact with each other and the ecosystem, but also how current management practices affect the processes they provide. In this study, we investigated the effects of proactive health management, that is, winter feeding and anti‐parasitic treatments on the ecosystem by examining diets of large herbivores and dung‐associated invertebrate communities. We used environmental DNA metabarcoding to yield community compositions of plants and invertebrates in dung from cattle and horses from five comparable nature sites in Denmark, which differed in management and site/population‐specific properties such as availability of woody plant species, herbivore densities and provision of winter feeding and anti‐parasitic treatments. We found different diet compositions between cattle and horses, highlighting their functional differences. For example, horse samples had higher relative read abundances of graminoid and tree DNA. Supplementary feeding affected diets by decreasing consumption of graminoids and tree species relative to forbs and legumes, probably originating from fodder, and intense feeding seemed to almost eliminate consumption of local vegetation. However, more studies are needed to generalize these findings. Several invertebrate families were associated with either cattle or horse dung, suggesting complementary effects on dung‐associated invertebrate biodiversity by these large grazers. The taxa that responded negatively to anti‐parasitic treatments were mainly parasitic nematodes (e.g. the families Ancylostomatidae, Cooperidae and Strongylidae), suggesting that the applied treatments work as intended, but these results should be interpreted with caution due to methodological limitations. Synthesis and application . Our findings demonstrate functional differences between cattle and horses, which suggest complementary effects on vegetation development and consequently biodiversity. Also, our results indicate that this functionality is impacted by proactive health management actions. We suggest that potential effects on herbivory and biodiversity are carefully considered before supplementary feeding, or anti‐parasitic treatments are provided in year‐round grazing systems and avoided if possible.