Long Ryan A, Wambua Alois, Goheen Jacob R, Palmer Todd M, Pringle Robert M
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, 08544, USA.
Mpala Research Centre, PO Box 555 Rumuruti Road, Nanyuki, Kenya.
J Anim Ecol. 2017 Jul;86(4):739-748. doi: 10.1111/1365-2656.12669. Epub 2017 May 2.
Large mammalian herbivores (LMH) strongly shape the composition and architecture of plant communities. A growing literature shows that negative direct effects of LMH on vegetation frequently propagate to suppress the abundance of smaller consumers. Indirect effects of LMH on the behaviour of these consumers, however, have received comparatively little attention despite their potential ecological significance. We sought to understand (i) how LMH indirectly shape small-mammal habitat use by altering the density and distribution of understorey plants; (ii) how these effects vary with climatic context (here, seasonality in rainfall); and (iii) the extent to which behavioural responses of small mammals are contingent upon small-mammal density. We tested the effects of a diverse LMH community on small-mammal habitat use using 4 years of spatially explicit small-mammal trapping and vegetation data from the UHURU Experiment, a replicated set of LMH exclosures in semi-arid Kenyan savanna. Small-mammal habitat use was positively associated with tree density and negatively associated with bare (unvegetated) patches in all plots and seasons. In the presence of LMH, and especially during the dry season, small mammals consistently selected tree cover and avoided bare patches. In contrast, when LMH were excluded, small mammals were weakly associated with tree cover and did not avoid bare patches as strongly. These behavioural responses of small mammals were largely unaffected by changes in small-mammal density associated with LMH exclusion. Our results show that LMH indirectly affect small-mammal behaviour, and that these effects are influenced by climate and can arise via density-independent mechanisms. This raises the possibility that anthropogenic LMH declines might interact with changing patterns of rainfall to alter small-mammal distribution and behaviour, independent of numerical responses by small mammals to these perturbations. For example, increased rainfall in East Africa (as predicted in many recent climate-model simulations) may relax constraints on small-mammal distribution where LMH are rare or absent, whereas increased aridity and/or drought frequency may tighten them.
大型哺乳动物食草动物（LMH）对植物群落的组成和结构有着强烈的塑造作用。越来越多的文献表明，LMH对植被的负面直接影响常常会扩散，抑制小型消费者的数量。然而，尽管LMH对这些消费者行为的间接影响具有潜在的生态意义，但受到的关注相对较少。我们试图了解：（i）LMH如何通过改变林下植物的密度和分布来间接塑造小型哺乳动物的栖息地利用；（ii）这些影响如何随气候背景（这里指降雨的季节性）而变化；（iii）小型哺乳动物的行为反应在多大程度上取决于小型哺乳动物的密度。我们利用来自乌胡鲁实验（UHURU Experiment）的4年空间明确的小型哺乳动物诱捕和植被数据，测试了多样化的LMH群落对小型哺乳动物栖息地利用的影响，该实验是在肯尼亚半干旱稀树草原上一组重复设置的LMH围栏。在所有样地和季节中，小型哺乳动物的栖息地利用与树木密度呈正相关，与裸露（无植被）斑块呈负相关。在有LMH存在的情况下，尤其是在旱季，小型哺乳动物始终选择树木覆盖区域并避开裸露斑块。相比之下，当排除LMH时，小型哺乳动物与树木覆盖的关联较弱，并且对裸露斑块的回避程度也没那么强。小型哺乳动物的这些行为反应在很大程度上不受与排除LMH相关的小型哺乳动物密度变化的影响。我们的结果表明，LMH间接影响小型哺乳动物的行为，并且这些影响受到气候的影响，并且可以通过密度独立机制产生。这增加了一种可能性，即人为导致的LMH数量下降可能与降雨模式的变化相互作用，从而改变小型哺乳动物的分布和行为，而与小型哺乳动物对这些干扰的数量反应无关。例如，东非降雨量的增加（正如许多近期气候模型模拟所预测的那样）可能会放宽对小型哺乳动物分布的限制，在LMH稀少或不存在的地方；而干旱加剧和/或干旱频率增加可能会收紧这些限制。
