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.
Highlights
Successful seedling recruitment represents a bottleneck for tropical trees (Whitmore, 1996) and recruitment greatly benefits from effective seed dispersal (Janzen, 1970; Levey et al, 2002; Forget and Janzen, 2007)
O. oniscus was captured throughout the Coimbra forest including forest edges (76 captures, 29% of capture success) and interior areas (67 captures, 30.3%)
Seed predation by any vertebrate varied from 3.5% (L. lurida) to 13.6% (V. gardneri), whereas predation by small rodents varied between 4.7% (H. courbaril) and 26.6% (L. lurida). These figures represented an elevated rate of predation for a 24-hour period of seed exposition, and during the 120 hours of focal observation, only O. oniscus was visually recorded as a seed predator, including seed predation within the exclosures for medium-sized and large vertebrates
Summary
Successful seedling recruitment represents a bottleneck for tropical trees (Whitmore, 1996) and recruitment greatly benefits from effective seed dispersal (Janzen, 1970; Levey et al, 2002; Forget and Janzen, 2007). Benefits of seed dispersal include reduced seed predation and seedling mortality – escape hypothesis sensu Howe and Smallwood (1982); colonisation of new habitats (Redford, 1992; Corlett and Turner, 1997); seed release from fruits (Asquith et al, 1997); seed discarding in microhabitats suitable for seed germination (Howe and Smallwood, 1982; Hoch and Adler, 1997); seed burial (Forget, 1990); and enhanced seed-mediated gene flow (Jordano et al, 2007). Plant recruitment does not exclusively result from mortality driven by density-dependent factors, as recruitment is expected to occur where seed/seedling face suitable conditions in terms of soil nutrients, water supply and light availability as well (Turner, 2001)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
