Frugivore Declines Across Taxa Affect Forest Biomass

ABSTRACT Widespread disturbance to frugivory networks endangers ecosystem functioning. Carbon‐rich tropical forests are particularly vulnerable to seed dispersal limitation from frugivore declines. However, understanding the ecological consequences of frugivore declines in tropical forests is challenging due to incomplete knowledge of existing frugivore‐plant interaction networks. Here, we assessed the impact of frugivore loss on aboveground biomass (AGB) across 260 tropical forest plots in Gabon, using imputed interaction networks between 122 frugivore species and 99,349 individual trees. We investigated (1) how faunal degradation of frugivores affects AGB, (2) the relative importance of different vertebrate taxa to AGB maintenance, (3) the role of dietary redundancy and seed dispersal compensation in AGB change, and (4) geographic patterns in AGB change. Simulated degradation of endangered frugivores reduced AGB, but results varied by taxon: simulated degradation of elephants, apes, monkeys, ungulates, and bats decreased AGB, but degradation of carnivores and birds increased AGB. Results were sensitive to imputed interaction failing to account for unobserved interactions may underestimate future AGB storage. Results were also sensitive to compensatory effects: assuming seed dispersal compensation due to dietary redundancy dampened, and in some cases reversed, the magnitude of AGB change. Anthropogenic and environmental plot characteristics predicted vulnerability to AGB change. AGB loss tended to occur in forests at low latitudes, low elevation, low precipitation, and farther from villages. Primary forests were more vulnerable to AGB loss than secondary forests. Accounting for ecological interactions across broad taxonomic groups and spatial scales—not just charismatic taxa and in well‐studied areas—is critical for understanding the nuanced effects of frugivore declines on ecosystem functioning.