Native and introduced megafauna have convergent effects on animals and ecosystems: a meta-analysis

Introduced large herbivores (henceforth megafauna) are thought to have 'harmful' effects on ecosystems by disrupting coevolutionary dynamics. If this is the case, their effects should be distinct from those of native megafauna. We use a systematic meta-analytic dataset of 3,532 observations from 235 articles to test whether there is any difference between the effects of native, introduced, and invasive megafauna on animals, soil, and a variety of ecosystem processes. Among 32 ecological responses, we only find moderate evidence that invasive megafauna have more neutral effects on soil compaction than native megafauna. We then compare the effects of introduced megafauna to intact African megafauna assemblages, the closest proxies for the communities that dominated Earth's continents for millions of years. We find moderate evidence that introduced megafauna reduces soil magnesium more than African megafauna, but no differences among the other responses. Our results suggest that nativeness is unlikely to be a biological attribute of megafauna. While the effects of introduced megafauna may seem unusual in reference to modern defaunated baselines, we suggest that broader lenses-and objective research across the cascading indirect effects of megafauna-will help us better understand the role of introduced megafauna in a time of rising global novelty.