Issue 101:6 of Journal of Ecology is now online. The Editor’s Choice paper from the final issue of 2013 is “Waiting for Gajah: an elephant mutualist’s contingency plan for an endangered megafaunal disperser” by Sekar & Sukumar. Read Associate Editor Michelle Leishman’s commentary on the paper below.

Editor’s Choice 101:6

What are the flow-on effects to ecosystems when a megaherbivore is lost from the system? There is increasing interest in understanding the impact of the loss of top predators such as wolves from ecosystems. But the effect of the loss of large herbivores is less well understood, particularly on ecosystem processes such as seed dispersal.  Megaherbivores such as elephants can be highly effective seed dispersers: they swallow large amounts of fruits, transport them kilometres across the landscape, and pass them out unscathed to germinate. So what may happen to those plant species that rely on a threatened and declining megaherbivore to disperse their seeds?

Sekar & Sukumar studied the dispersal of Dillenia indica, an Asian tree species commonly known as ‘elephant wood apple’ or ‘chalta’ that produces large hard fruit, thought to be inaccessible to smaller frugivores. Asian elephants appear to have a particular fondness for the fruits of D. indica, with 90% of elephant dung piles in the Buxa Tiger Reserve in India containing chalta seeds during the fruiting season.

Using a variety of approaches, including camera trapping, fruit aging trials, seed counts of dung and germination trials, Sekar & Sukumar built up a fascinating picture of the natural history of this species and its relationship to elephants as a disperser of its seeds.

Elephants in the Buxa Reserve were found to be the most important disperser of chalta fruits, responsible for more than 63% of seed removal by frugivores. The seeds inside the hard fruits could then be dispersed by the elephants over large distances to germinate and establish; nearly 80% of dung piles examined contained chalta seeds. However, the fate of chalta plants is not uniquely tied to the fate of the elephants and other megaherbivores. Instead the chalta has developed a back-up system, whereby its hard fruits that are only accessible to megaherbivores, slowly soften on the forest floor through the dry season to allow access to successively smaller animals such as macacques, rodents and squirrels. Seeds from both old and soft fruits are able to germinate well, enabling the persistence of chalta to be independent of the survival of its major megaherbivore disperser.

Natural history studies such as this can provide important insights for conservation management. In the short to medium-term, the research by Sekar & Sukumar provides good news for the chalta. However, who knows what the long-term genetic and evolutionary consequences of the loss of its most effective long-distance disperser will be for the chalta?

Michelle Leishman
Associate Editor, Journal of Ecology