Effects of plant defenses and water availability on seasonal foraging preferences of the Nubian Ibex (Capra nubiana)

Abstract

The study of herbivore patch use has implications for herbivore habitat quality assessment, foraging behaviors, species interactions, and coexistence in patchy environments. This research focuses on the comparison of the effects of two qualitatively different plant defenses, mechanical (thorns) and chemical (tannins), on ibex foraging preferences during different seasons of the year. The occurrence of both chemical and mechanical plant defenses were experimentally manipulated in artificial resource patches, in addition to water availability. Ibex foraging preferences were quantified using giving-up densities during four separate fieldwork sessions in each of the seasons of the year at cliff sites overlooking the Zin Valley of the Negev Highlands. Both mechanical and chemical plant defenses significantly hindered ibex food intake overall. Mechanical and chemical defenses acted as substitutable defenses, meaning that their combined effects were not greater than additive. There were strong seasonal patterns of the amount of food consumed by ibex, further corroborated by comparison to rainfall levels. Seasonality also interacted with the effectiveness of plant defenses. Thorns were especially ineffective in summer, whereas tannins were most effective in spring. Decreases in seasonal food availability and increased marginal value of energy for ibex may have resulted in thorn ineffectiveness, while seasonal changes in the emergence of young foliage may have resulted in the greater springtime tannin effectiveness. Water was not found to mitigate the detrimental effects of tannins through dilution. The implications for decreased constraints on selective pressures on ibex due to the substitutability of plant defenses are discussed.

Keywords:

• foraging behavior
• herbivore patch use
• Nubian Ibex
• giving-up density
• plant defenses
• resource complementarity

Acknowledgements

We owe Keren Embar our deepest gratitude for her invaluable assistance with fieldwork, statistics, protocols, translation, and excellent ideas. We greatly appreciate our colleagues for suggestions and advice: Solomon Tadesse, Ikram Salah, Stuart Summerfield, Sonny Bleicher, and Justin St. Juliana. We thank Professors David Saltz, Ofer Ovadia and Yael Lubin for the helpful comments and review. Thanks also to Joel Brown for help with statistics, to Marc Goldberg and Ishai Hoffmann for technical assistance, and to the Israel National Parks Authority for allowing us to conduct experiments at the cliffs of Midreshet Ben-Gurion. The study was conducted under permit 3425301 of the Israel National Parks Authority and permit IL-70-12-2010 of the BGU Animal Ethics Committee. The study was carried out in the Mitrani Department for Desert Ecology of the Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the United States-Israel Binational Science Foundation [grant number 2008163] and by the Israeli Science Foundation [grant number 804/09]. Financial support was also provided by a scholarship made available through the Albert Katz International School for Desert Studies, Ben-Gurion University of the Negev.