Redundancy in seed dispersal by three sympatric ungulates: A reintroduction perspective

Reintroductions may play an important role in re-establishing key ecosystem functions and are potentially a valuable ecosystem-restoration tool. Here, we focus on the role of reintroduced ungulates as seeds dispersers - a key process in shaping plant community structure and dynamics. In a comparative study, we investigated which plant species are dispersed by three sympatric ungulates in the Negev desert, Israel: Arabian oryx Oryx leucoryx, Asiatic wild ass Equus hemionus and dorcas gazelle Gazella dorcas. The oryx and wild ass were locally extirpated and recently reintroduced while the gazelle is the only wide-ranging ungulate that has existed continuously in the region. We hypothesized that although all three species are ungulates, because of expected differences in diet resulting from the differences in their size and digestive characteristics, there will be little overlap in their role as seed dispersers. In addition, we experimentally tested the importance of ingestion of the seeds of the keystone acacia Acacia raddiana and the presence of dung on germination success and seedlings growth. We found that each of the ungulates dispersed a different assemblage of plant species with little overlap, highlighting the importance of the reintroduction of both species in ecosystem restoration. Oryx were the key dispersers of acacia seeds, and oryx-ingested seeds planted with oryx pellets had a germination success 250 times higher than non-ingested seeds planted without pellets. Seedlings from ingested seeds also grew faster than seedlings from non-ingested seeds. We found little redundancy between ungulates as seed dispersers in this region, highlighting the importance of reintroductions as a restorative process even when other species from the same guild still exist in the wild.