Pringle Robert M, Goheen Jacob R, Palmer Todd M, Charles Grace K, DeFranco Elyse, Hohbein Rhianna, Ford Adam T, Tarnita Corina E
Department of Ecology and Evolutionary Biology, Princeton University, , Princeton, NJ 08544, USA, Department of Zoology and Physiology, University of Wyoming, , Laramie, WY 82070, USA, Department of Biology, University of Florida, , Gainesville, FL 32611, USA, Department of Plant Sciences, University of California, , Davis, CA 95616, USA, Mpala Research Centre, , Nanyuki, Kenya, Department of Zoology, University of British Columbia, , Vancouver, BC V6T 1Z4, USA.
Proc Biol Sci. 2014 Apr 30;281(1785):20140390. doi: 10.1098/rspb.2014.0390. Print 2014 Jun 22.
Large herbivorous mammals play an important role in structuring African savannahs and are undergoing widespread population declines and local extinctions, with the largest species being the most vulnerable. The impact of these declines on key ecological processes hinges on the degree of functional redundancy within large-herbivore assemblages, a subject that has received little study. We experimentally quantified the effects of three browser species (elephant, impala and dik-dik) on individual- and population-level attributes of Solanum campylacanthum (Solanum incanum sensu lato), an encroaching woody shrub, using semi-permeable exclosures that selectively removed different-sized herbivores. After nearly 5 years, shrub abundance was lowest where all browser species were present and increased with each successive species deletion. Different browsers ate the same plant species in different ways, thereby exerting distinct suites of direct and indirect effects on plant performance and density. Not all of these effects were negative: elephants and impala also dispersed viable seeds and indirectly reduced seed predation by rodents and insects. We integrated these diffuse positive effects with the direct negative effects of folivory using a simple population model, which reinforced the conclusion that different browsers have complementary net effects on plant populations, and further suggested that under some conditions, these net effects may even differ in direction.
大型食草哺乳动物在构建非洲大草原生态系统中发挥着重要作用，但其种群数量正在普遍下降，局部灭绝现象也屡见不鲜，其中体型最大的物种最为脆弱。这些种群数量下降对关键生态过程的影响程度取决于大型食草动物群落内部功能冗余的程度，而这一主题此前鲜有研究。我们通过实验量化了三种食叶动物（大象、黑斑羚和犬羚）对茄属弯曲茄（狭义的刺天茄）个体和种群水平属性的影响，茄属弯曲茄是一种不断扩张的木本灌木。我们使用半透性围栏选择性地排除不同体型的食草动物。近5年后，在所有食叶动物都存在的地方，灌木数量最少，且随着每种食叶动物的相继排除，灌木数量增加。不同的食叶动物以不同方式啃食同一植物物种，从而对植物的生长和密度产生一系列不同的直接和间接影响。并非所有这些影响都是负面的：大象和黑斑羚还传播了有活力的种子，并间接减少了啮齿动物和昆虫对种子的捕食。我们使用一个简单的种群模型将这些扩散的积极影响与啃食的直接负面影响结合起来，这进一步证明了不同食叶动物对植物种群具有互补的净效应这一结论，并且还表明在某些情况下，这些净效应甚至可能在方向上有所不同。
