Reintroductions may play an important role in re-establishing key ecosystem functions. We focused on the role of reintroduced ungulates as internal seeds dispersers (endozoochory). In a comparative study we investigated which plant species are dispersed by Arabian oryx (Oryx leucoryx) a medium sized (65-75 kg) bulk feeder ruminant, Asiatic wild ass (Equus hemionus) a large (160-260 kg) hindgut fermenter, and dorcas gazelle (Gazella dorcas) a small concentrate selector ruminant (15-20 kg), in the Negev desert, Israel. The oryx and wild ass were locally extirpated during the 19th century and recently reintroduced, while the gazelles are the only wide-ranging ungulate that existed continuously in the region. We collected 1-3% of the volume of clearly delineated fresh dung piles in dry stream beds where all species co-occur, and germinated them in sterile soil.
Results/Conclusions
We found that each species dispersed a unique plant community with little overlap. Specifically, oryx, wild-ass and gazelle transported a total of 12, 15 and 4 plant species of which 7, 8, and 1 were unique species, respectively. However, randomization tests of re-sampling showed that the probability of obtaining this number of unique species due to random sampling is below 5% only for the wild ass. The area’s keystone plant species, Acacia raddiana and Acacia tortolis, were overwhelmingly transported by the two reintroduced ungulates, especially the oryx. Germination of A. raddiana from dung collected in the summer occurred in 51, 30 and 7.5% of the samples from oryx, wild-ass, and gazelles (n=49, 37, and 40). Seed dispersal profiles of the three ungulates studied differed and were consistent with the digestion characteristics of each: wild ass being the largest and a hindgut fermenter consumes the greatest amount of dry matter with a low retention time and thus transports the highest number of plant species. The oryx being a large ruminant has the longest gut retention time and thus is an important transporter of the keystone Acacia species that have seeds with a hard protective shell and evidently require long retention time to increase germination probability. The gazelle, a small ruminant, consumes a relatively small amounts of dry matter, has a short retention time, and probably fine-grinds its forage destroying many of the seed, and consequently successfully transporting only few viable seeds from few species. Reintroduced large ungulates may facilitate the restoration of key ecosystem functions and contribute to restoring biodiversity well beyond the preservation of the reintroduced species itself.
