Seed predation by rodents and safe sites for large-seeded trees in a fragment of the Brazilian Atlantic forest

Abstract

Seed predation by small rodents is an emerging theme in the ecology of modified landscapes. Here we investigate the role played by the small rodent Oryzomys oniscus as a seed predator of large-seeded trees in a large remnant of the Atlantic forest -the Coimbra forest (3,500 ha), Alagoas state, northeastern Brazil. O. oniscus was captured and identified by setting twenty 500 m long transects, each one composed of 25 traps 20 m apart. This procedure resulted in 483 trap-nights set during a 20-mo period. We used 692 seeds (>15 mm length) from ten local large-seeded tree species for the seed predation trials that basically consisted of three treatments: one seed on the ground freely accessed by vertebrates (unprotected seed), one seed totally protected by an exclosure, and one partially-protected seed (exclosure just for medium-sized and large vertebrates). O. oniscus was captured throughout the Coimbra forest including forest edges (76 captures) and interior areas (67), and this small rodent was responsible for all seed predation visually documented inside exclosures. A 24 hours period of seed exposition permitted elevated rates of seed removal and predation. Seeds were much more removed/predated beneath fruiting trees, but rates varied according to the level of seed protection -26.3% of predation among partially-protected versus 19.2% among unprotected seeds. Seeds suffered higher levels of seed predation/removal at the forest edge as well (up to 90%). In both habitats, most seeds (>84%) remained intact beneath trees without fruits, regardless of the level of seed protection. Our results suggest that O. oniscus may operate as an effective large-seed predator in forest fragments, in which adult trees without fruits constitute low resource spots and thereby provide, at least temporarily, safe sites for large seeds.Keywords: frugivory, Janzen-Connell model, Oryzomys oniscus, seed dispersal, tropical forest. Predação de sementes por roedores e sítios seguros para árvores com grandes sementes em um fragmento de floresta Atlântica brasileira ResumoPredação de sementes por pequenos roedores é um tema emergente na ecologia de paisagens modificadas. Nesse estudo foi investigado o papel desempenhado pelo pequeno roedor Oryzomys oniscus como predador de grandes sementes de árvores em um grande fragmento de floresta Atlântica -mata de Coimbra (3.500 ha), Estado de Alagoas, Nordeste do Brasil. O. oniscus foi capturado e identificado usando-se 20 transectos com 500 m de comprimento, cada um composto por 25 armadilhas espaçadas a cada 20 m. Esse procedimento resultou em um esforço total de captura de 483 armadilhas-noites, durante um período de 20 meses. Foram utilizadas 692 grandes sementes (>15 mm de comprimento), provenientes de dez espécies de árvores para as sessões de predação, as quais consistiram basicamente de três tratamentos: uma semente no solo com acesso livre para vertebrados (semente desprotegida), uma semente totalmente protegida e uma semente parcialmente protegida (exclusão apenas para médios e grandes ...

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Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

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Seed removal of Dipteryx alata Vog. (Leguminosae: Faboidae) in the edge and interior of Cerrado

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