The role of large herbivores in recruitment of Acacia trees via endozoochory in the Arava Valley, Israel

Abstract

Acacia trees are keystone species of drylands. The recruitment of Acacia seedlings is regulated by large herbivores. The study objective was to investigate the effect of several large herbivore species on Acacia germination and recruitment. These species include the addax (Addax nasomaculatus), Arabian oryx (Oryx leucoryx), Asiatic wild ass (Equus hemionus), African wild ass (Equus africanus), and dorcas gazelle (Gazella dorcas). Feces of these herbivore species were collected in a safari reservation in the hyper-arid Arava Valley, where Acacia raddiana and Acacia tortilis trees are widespread. The study was implemented in a net house, where the feces were laid in small piles on the ground and irrigated. Two batches of the feces were studied: one in the winter and one in the spring of 2012. The winter batch encompassed only the feces of the addax, oryx, and Asiatic ass, and it was found that the addax feces generated a significantly greater number of seedlings than the feces of other species. Of this batch, only 13 % of seedlings were alive ∼250 days later. The spring batch encompassed all five species and revealed a germination rate in the feces according to the following order: addax > oryx > Asiatic ass > gazelle > African ass. Of this batch, 46 % of seedlings were alive ∼200 days later. This study provides new knowledge regarding the effect of each of the ungulate species on recruitment capacity of new trees to the Acacia population. The results propose that the two most significant factors affecting recruitment are rumination and size of herbivores.