photo courtesy of The Sean and Laura Spectacular
It is hypothesized that large seeds produced by a number of tropical trees were once dispersed by giant mammals, similar to today’s elephants, called gomphotheres. Gomphotheres would have ingested and defecated the seeds, dispersing them across large distances; however, the last gomphotheres are believed to have gone extinct approximately 10,000 years ago. The dispersal of oversized seeds since the extinction of gomphotheres has been a mystery, however, researchers have recently discovered that a group of species of rodents, known as agoutis (including the common agoutis, genus Dasyprocta), are responsible for this dispersal.
Seed dispersal within rainforests is of imperative importance for tree survival. If seeds are not dispersed then trees become isolated from the rest of their species, meaning there is no opportunity for genes to mix. This would eventually lead to extinction. Early studies of agoutis suggested that they were unable to replace the gomphoteres’ role because of their small home ranges, meaning seeds would not be dispersed far enough. However, this theory was overruled when scientist Joe Wright had the idea of radio tagging seeds as well as the animals. Camera traps were also used to study the burial of the seeds. Both of these methods identified that seeds were being further dispersed by rival agoutis that were digging them up and stealing them. One seed was recorded to pass between 36 agoutis, with the average seed ending up 68m away from its parent tree as a result of repeated burial and disinterment.
However, the survival of trees such as the Astrocarymu standleyanum palms, which rely on this dispersal method, could still become threatened. Firstly agoutis only cache seeds and nuts during times of plenty, typically eating them straight away when food is scarce. Secondly, in some areas of tropical forest agoutis are copiously hunted, raising the question are there any other species able to take on this pivotal role?
If you would like to help conduct tropical forest research in countries including Madagascar, Costa Rica and Cambodia then information on our volunteering projects can be found on the Frontier website.
By Julia Crabbe