Thieving rodents as substitute dispersers of megafaunal seeds

Abstract

The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 y without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatterhoarding rodents has facilitated the persistence of these largeseeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35% of seeds for >100 m. An estimated 14% of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other's buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.Pleistocene extinctions | seed predation | cache pilferage | telemetry

Evidence for cache surveillance by a scatter-hoarding rodent

“…Previous studies have shown that seed-caching birds and rodents respond to an increase in cache theft rates by increasing their rate of food caching (Vander Wall & Jenkins 2003;Dally et al 2006;Huang et al 2011; but see Dally et al 2006 for alternate responses to cache theft), suggesting that this information is important to hoarders. It is possible that the agoutis in our study surveyed their caches to assess theft risk, which would allow them to recover caches and move them to safer places if necessary (Hirsch et al 2012a, b;Jansen et al 2012), but whether these activities are a response to perceived theft risk is not known.…”

“…When seeds were buried, the transmitters affixed to the ends of the wire remained above ground, thus allowing us to place the transmitters on top of magnets that deactivated the transmitter and saved battery life. When the seed was moved by an agouti or other animal, the transmitter was activated, allowing us to find the new location of the seed with hand-held radiotelemetry equipment (for full details see: Hirsch et al 2012b;Jansen et al 2012). We covered the transmitter and flagging tape with loose leaf litter to reduce possible visual cues.…”

“…Each seed plot was checked daily and removed seeds were located by sight or with hand-held radiotelemetry equipment (Yaesu-VR500, Cypress, CA, U.S.A.) to determine dispersal distance and seed fate. Individual seeds were frequently removed and recached by agoutis, resulting in stepwise dispersal for most seeds in our study (median number of caches per seed ¼ 8, range 1e36; Jansen et al 2012). …”

Dispersión de semillas de Mauritia flexuosa (Arecaceae) por frugívoros terrestres en Laguna Azul, Beni, Bolivia

“…Sin embargo, esto dependerá de si la depredación de M. flexuosa por brúquidos ocurre antes o después de que las semillas caen de Dispersión de semillas de Mauritia flexuosa (Arecaceae) por frugívoros terrestres en Laguna Azul, Beni, Bolivia ACTA AMAZONICA los árboles. Si los brúquidos ovipositan antes de la caída de los frutos, como en el caso de Astrocaryum standleyanum (Jansen et al 2012), el efecto será insignificante.…”

“…Este comportamiento de acopio esparcido o "scatterhoarding" (Morris 1962) cumple un rol importante en la dispersión de las semillas (Alho 1982;Jansen et al 2004;Jorge y Howe 2009). Jansen et al (2012) reportan que un 14% de las semillas enterradas por D. punctata sobreviven un año; y las semillas enterradas suelen germinar más rápido que las que no se entierran (Forget y Milleron 1991). Dasyprocta dispersa varios géneros de palmeras: Acrocomia, Astrocaryum, Attalea, Mauritia, Oenocarpus, Phytelephas y Syagrus (Silvius y Fragoso 2003;Pires y Galetti 2012;Emsens et al 2013).…”