Defaunation shadow on mutualistic interactions

Tregidgo et al. (1) show that size-selective overfishing has drastically depleted and downsized populations of tambaqui ( Colossoma macropomum ) along the Purus River, Amazonia. Because fishers have historically targeted the largest individuals, tambaqui ∼1,000 km upriver are twofold larger than those near the Manaus rainforest metropolis (1). Here, we demonstrate that this overfishing shadow has cascading consequences, reaching beyond the sustainability of this fishery. By effectively dispersing seeds of >100 species, tambaqui plays a major role in the natural regeneration of Amazonian floodplain forests (2⇓⇓–5). However, due to gape limitation, only large-bodied tambaqui can disperse large-seeded fruits (3). Thus, we hypothesize that the tambaqui’s key ecological function as a seed disperser is diminished by the striking fisheries-induced downsize. We constructed a niche model of food web structure (6), using the statistical relationship between tambaqui body size and fruit size, to infer losses in seed dispersal potential. First, we measured the fruit or seed (for dehiscent species) size of 264 species … [↵][1]1To whom correspondence should be addressed. Email: raulcpereira{at}gmail.com. [1]: #xref-corresp-1-1