Predicting how defaunation-induced changes in seed predation and dispersal will affect tropical tree populations.

The loss of large animals due to overhunting and habitat loss potentially affects tropical tree populations and carbon cycling. Trees reliant on large-bodied seed dispersers are thought to be particularly negatively affected by defaunation. But besides seed dispersal, defaunation can also increase or decrease seed predation. It remains unclear how these different defaunation effects on early life stages ultimately affect tree population dynamics. We review the literature on how tropical animal loss affects different plant life stages, including conducting a meta-analysis of seed predation effects, and use this information to parameterize models assessing how defaunation-caused changes in seed dispersal and predation affect the population growth rates of a suite of tree species. We find that, on average, population-level effects of defaunation are negligible, suggesting that defaunation may not cause the massive reductions in forest carbon storage that have been predicted. In contrast to previous hypotheses, we did not detect an effect of seed size on changes in seed predation rates. We also found that the change in seed predation did not differ significantly between exclosure experiments and observational studies, though the results of observational studies were far more variable. While defaunation will surely affect certain tree taxa, we currently remain unable to predict 'winners', 'losers', or net changes in forest carbon storage based on best available data. Further research on how interactions such as seed predation vary across tree species and defaunation scenarios is necessary for understanding cascading changes in species composition and diversity. This article is protected by copyright. All rights reserved.