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THE INTERMEDIATE PREDATION HYPOTHESIS: SEED DISPERSAL IS MAXIMIZED BY INTERMEDIATE ABUNDANCES OF HOARDERS
Scatter-hoarding rodents can either eat, disperse or ignore encountered seeds. Even after dispersal, hoarders can still retrieve caches and alter seeds' fate. Many factors are known to influence this dynamic, such as seasonality, resource abundance and seeds’ traits. However how hoarder abundance affects cache predation and the seeds’ final fate is rarely explored.
We used the interaction between agoutis (Dasyprocta leporina) and Joannesia princeps seeds as a model to investigate the effects of hoarder abundance and cache predation on seed fate. This interaction serves as a simple straightforward system because agoutis are the only vertebrate species interacting with J. princeps seeds. Camera-traps were used for 30 days to obtain a proxy of agouti abundance in twenty different areas of a forest remnant. Thereafter, we placed seed piles on the same areas and determined their fate using the spool-and-line method to track seeds for over one hundred days.
We found a non-linear relationship between scatter-hoarder abundance and proportion of dispersed seeds. At low abundances of hoarders, proportion of dispersed seeds is low due to low removal. As hoarder abundance increases, cache predation increases as well, which reduces the number of dispersed seeds. At high abundances, low cache survival results in a low proportion of dispersed seeds. As a result, dispersal was maximized in intermediary abundance of scatter-hoarders, where there is a balance between seed removal and survival. Differences in fine-scale scatter-hoarder abundance within the same habitat can largely influence seed fate. Given enough time, predation of buried caches proves to be an important factor affecting seed survival, especially on high abundance of hoarders. Thus using only initially hoarded seeds to assess final rates of dispersal can be misleading. High rates of seed dispersal, combined with low levels of cache predation, maximize the proportion of dispersed seeds in intermediary abundances of hoarders.
Keywords: scatter-hoarding, cache predation, seed dispersal, rodent abundance, Dasyprocta leporina, plant-animal interaction
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação Grupo Boticário de Proteção à Natureza
Pedro Mittelman, Catharina Kreischer, Alexandra Pires, Fernando Antonio dos Santos Fernandez