Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv Evidence of browsing pressure on the critically endangered Acacia gazelle (Gazella acaciae) Benjamin Breslau a,b,* , Tal Polak c , Benny Shalmon c , Elli Groner d,e a Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, 06269, USA b Arava Institute for Environmental Studies, Kibbutz Ketura, D.N, Hevel Eilot, 88840, Israel c Israel Nature and Parks Authority, Yotam 3, Eilat, 88000, Israel d The Dead-Sea and Arava Science Center, Tamar Regional Council, Dead-Sea Mobile Post, 86910, Israel e Eilat Campus, Ben-Gurion University of the Negev, Hatmarim Blv, Eilat, 8855630 Israel ARTICLE INFO Keywords: Acacia gazelle Acacia tree Arabian gazelle Arava Browsing line Competition Dorcas gazelle Lowest leaf ABSTRACT The Arabian Gazelle (Gazella arabica) is vulnerable throughout its range. Israel's population, known locally as the Acacia gazelle (G. acaciae), is critically endangered. The entire 22-individual population inhabits a 3.5 km 2 enclosure and, at the time of the experiment, shared the space with over 120 dorcas gazelles (G. dorcas). This study investigated whether the Acacia gazelles faced significant browsing pressure in their enclosure by com- paring the browsing line and lowest leaf of Acacia trees in the Acacia gazelle enclosure to those of dorcas gazelle habitats in Evrona, Yotvata Hai Bar, Shezaf, and Wadi Shita. We discovered a significantly higher browsing line in the Acacia Gazelle Enclosure than in the other gazelle habitats, implying that the Acacia gazelles faced high browsing pressure that may affect their survival. Our study will inform the way that Israel's Acacia gazelle reintroduction program manages the population, and will influence the determination of locations and condi- tions for future reintroductions. 1. Introduction The Arabian Gazelle (Gazella arabica) is listed as “vulnerable” by the IUCN, and is declining throughout its range (IUCN, 2018). The Israeli population, known colloquially as Acacia gazelles (Gazella acaciae), is critically endangered (IUCN, 2018). At the time of the study, Israel's population consisted of a single group of approximately 22 individuals, all concentrated in a 3.5 km 2 enclosure in the Acacia Gazelle Enclosure at the Western Yotvata Nature Reserve in the Arava Valley. This po- pulation faces many pressures. First, there is minimal genetic diversity among individuals, which threatens to create inbreeding depression (Hadas et al., 2015). Secondly, such small numbers may result in sto- chastic fluctuations that can lead to extinction due to random processes (Reed et al., 2003). Israel's Acacia gazelles also face external threats such as predation and, as this study will address, potential significant browsing pressure within the enclosure due to the presence of a larger population of the sympatric dorcas gazelles (Gazella dorcas)(IUCN, 2018). Israel's Acacia gazelles are a unique taxon on which to focus con- servation efforts. This population was originally classified as Gazella gazella acaciae, a subspecies of mountain gazelle (Gazella gazella) (Mendelssohn et al., 1997). More recently, researchers genetically dis- tinguished the mountain gazelle from the Arabian Gazelle (Gazella arabica) and included Israel's Acacia gazelle in the latter clade (Wronski et al., 2010; Lerp et al., 2013; Bärmann et al., 2013; Hadas et al., 2015). Morphologically, Israel's Acacia gazelles are distinguishable from sympatric gazelle species (e.g. dorcas gazelles) by their more pro- nounced coloration, horn shape, and body shape. Hadas et al. (2015) stated that genetic divergence is significant enough – with Israel's po- pulation bearing unique haplotypes from all other Gazella arabica po- pulations – that they should be treated as a unique conservation unit (Ryder, 1986). In this study we will refer to Acacia gazelles as Gazella acaciae, in accordance with Groves and Grubb (2011). The control of population size by a limited resource has been shown to be an important dynamic in deserts (Tilman, 1982; Kotler et al., 1993; Goldberg and Novoplansky, 1997; Chesson, 2000), contrary to the older concept that density-dependent processes are of minor im- portance in determining abundance (Andrewartha and Birch (1954), especially in deserts (Shreve, 1942; Noy-Meir, 1973; Grime, 1977). Hence, it is now understood that depletion of food can significantly https://doi.org/10.1016/j.jaridenv.2019.104019 Received 9 October 2018; Received in revised form 23 July 2019; Accepted 26 August 2019 * Corresponding author. Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, 06269, USA. E-mail addresses: benjamin.breslau@uconn.edu (B. Breslau), TalP@npa.org.il (T. Polak), benny.shalmon072@gmail.com (B. Shalmon), elligroner@gmail.com (E. Groner). Journal of Arid Environments 173 (2020) 104019 Available online 11 September 2019 0140-1963/ © 2019 Elsevier Ltd. All rights reserved. T