Modelling ungulate dependence on higher quality forage under large trees in African savannahs |
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| Authors: | Anna C Treydte Ignas MA Heitkönig Fulco Ludwig |
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| Institution: | 1. Plant Ecology and Nature Conservation, Potsdam University, Maulbeerallee 2, 14469 Potsdam, Germany;2. Resource Ecology Group, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, The Netherlands;1. Agroecology in the Tropics and Subtropics, University of Hohenheim, Germany;2. Nelson Mandela African Institution of Science and Technology, Arusha, Tanzania;3. Veterinary Medicine and Agriculture, Addis Ababa University, Ethiopia;4. Werer Agricultural Research Center, EIAR Addis Ababa, Ethiopia;1. Instituto de Investigaciones Biológicas y Tecnológicas, Centro de Ecología y Recursos Naturales Renovables (CONICET – Universidad Nacional de Córdoba), Av. Vélez Sarsfield 1611, X5016GCA Córdoba, Argentina;2. NGO Ecosistemas Argentinos, Argentina;1. Université de Tunis El Manar, Faculté des Sciences de Tunis, UR11-ES11 Unité de Recherche de Bio-Ecologie Animale et Systématique Evolutive, 2092 Tunis, Tunisia;2. Département de Biologie, Université de Moncton, Moncton, NB E1A 3E9, Canada;1. Department of Electrical Engineering, University of California Los Angeles, 63-134 Engr IV, Los Angeles, CA 90095-1594, United States;2. Department of Head and Neck Surgery, University of California Los Angeles, School of Medicine, 31-24 Rehab Center, Los Angeles, CA 90095-1794, United States;3. Department of Electrical Engineering, University of California Los Angeles, 66-147G Engr IV, Los Angeles, CA 90095-1594, United States |
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| Abstract: | In African savannahs, large trees improve grass quality, particularly in dry and nutrient poor areas. Enhanced below-canopy grass nutrients, such as nitrogen and phosphorus contents should therefore attract and benefit grazers. To predict whether ungulates really need these forage quality islands we focused on four grazer species, i.e., zebra, buffalo, wildebeest, and warthog, differing in body size and digestive system. We confronted literature estimations of their feeding requirements with forage availability and quality, observed in three South African savannah systems, through linear modelling. The model predicted the proportion of below-canopy grass that grazers should include in their diet to meet their nutritional requirements.During the wet season, the model predicted that all animals could satisfy their daily nutrient requirements when feeding on a combination of below- and outside-canopy grasses. However, wildebeest, having relatively high nutrient demands, could meet their nutrient requirements only by feeding almost exclusively below canopies.During the dry season, all animals could gain almost twice as much digestible protein when feeding on below – compared to outside-canopy forage. Nonetheless, only warthogs could satisfy their nutrient requirements – when feeding almost exclusively on below-canopy grasses. The other ungulate species could not meet their phosphorus demands by feeding at either site without exceeding their maximum fibre intake, indicating the unfavourable conditions during the dry season.We conclude that grazing ungulates, particularly warthog, zebra, and buffalo, actually depend on the available below-canopy grass resources. Our model therefore helps to quantify the importance of higher quality forage patches beneath savannah trees. The composition of grazer communities depending on below-canopy grasses can be anticipated if grazer food requirements and the abundance of large trees in savannahs are known. The model suggests that the conservation of large single-standing trees in savannahs is crucial for maintenance of locally grazing herbivores. |
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