Extreme cache theft and re-caching leads to long term seed dispersal by Central American agoutis

Background/Question/Methods

Seed dispersal and the role played by seed dispersers are important factors which affect forest dynamics and species distribution. Large seeded plant species such as Astrocaryum standleyanum are thought to be difficult to disperse effectively because the seeds are too large to be swallowed by most extant mammals. The major disperser of Astrocaryum is a 2.5-3kg rodent, the Central-American agouti (Dasyprocta punctata). Agoutis regularly scatter-hoard seeds in the ground, and then return to eat the seeds during periods of low food availability. It has been hypothesized that the seeds left or forgotten by agoutis are a major source of seeds which reach the germination stage. Alternately, agoutis have relatively small home ranges and high rates of cache recovery, thus may not be very effective dispersers. We tested the role of agoutis and other rodents as seed dispersers in a tropical forest (BCI, Panama). Rates of seed removal, dispersal distances, and seed fate were determined using radio-transmitters attached to seeds, which provided far better results than previous studies. Radio-tagged seeds were monitored with motion sensitive cameras to determine the species which removed the seeds.

Results/Conclusions

We observed and quantified extraordinarily high levels of secondary dispersal. Many seeds were re-cached multiple times (up to 36 times for one seed). Total seed dispersal distances increased with the number of re-caching events, and these distances were sometimes longer (up to 280m) than the average agouti home range diameter (175m). This is partial evidence that seeds were being moved and re-cached by different individuals. This hypothesis was supported by direct camera monitoring of a subset of seed caches. With this subset of camera monitored seeds, we were able to determine that seeds cached by one marked agouti were stolen by other marked agoutis. These results indicate that through multi-step dispersal, agoutis are able to disperse seeds at distances far greater than previously believed. These observations may also explain how large seeded species survive and reproduce in the absence of traditional dispersers.