The impact of megafaunal loss and climate change on ecosystem functions in aridland ephemeral river systems

短暂性河流系统指的是一年中最多只有几个星期看得见水的河流。这通常是因为它们位于炎热干燥的气候中，降雨量很少。因此，它们对人类和野生动物群体来说都是无价的，因为它们可以从其他来源获得的水相对稀缺。纳米比亚有12条这样的短暂河流流经该国，这些河流支持丰富而独特的植被，提供农业服务，并作为大型动物迁徙和地方性种群的绿洲(Jacobson等人，1995)。不幸的是，极具魅力的大型动物(重量超过1000公斤的陆生脊椎动物，Owen-Smith，1988)现在在纳米比亚的大多数河流中很少见，主要是由于狩猎和其他人与野生生物的冲突。从保护的角度来看，这是个坏消息，但从经济的角度来看，这也是一个坏消息，因为野生动物旅游业为纳米比亚的收入贡献了相当大的一部分(Jacobson等人，1995)。然而，它确实为实验提供了一个独特的机会。由于类似的河流系统中有一些大型动物存在，但另一些河流中没有，我们可以比较河流之间生态过程的差异，有相对明确的因果关系。我的博士学位涉及使用遥感数据调查这些河流系统之间的差异。它还应该产生关于使用这些系统的某些大型动物的生态角色的新数据，特别是大象和长颈鹿。气候影响的建模也是这项研究的关键组成部分，原因有两个。第一个问题与旱地短暂河流系统的普遍存在有关，因为气候变化导致的降雨频率和强度的预期变化可能会促使其他临时河流被归类为“短暂河流”(Larned等人，2010年；Tooth和Nanson，2011年)。第二个问题是气候和生态系统之间的关系。预计降雨量的变化如何影响短暂的河流水文可能有所了解，但这种变化如何影响依赖含水层的生态系统内的生态过程尚不清楚(Eamus等人，2006年；Colvin等人，2007年)。因此，研究这些系统中的降雨量变化是该项目的一个组成部分。

Ephemeral river systems refer to rivers that only visibly contain water for a few weeks in a year, at most.This is usually because they are situated in hot, dry climates with very little rainfall. As such they areinvaluable to communities of humans and wildlife alike, because of the relative scarcity of water availableto them from other sources. Namibia has 12 of these ephemeral rivers running through the country, whichsupport rich and unique vegetation, provide agricultural services, and act as an oasis for migrating andendemic megafauna populations (Jacobson et al , 1995).Unfortunately, charismatic megafauna (terrestrial vertebrates heavier than 1000kg, Owen-Smith, 1988) isan uncommon sight in most of the Namibian rivers now, largely due to hunting and other human-wildlifeconflicts. This is bad news from a conservation perspective, but also from an economic perspective, aswildlife tourism contributes a significant amount towards Namibia's revenue (Jacobson et al , 1995). Itdoes provide a unique opportunity for experimentation, however. With similar river systems havingmegafauna persist in some but not others, we can compare the disparity of ecological processes betweenthe rivers, with relatively clear cause and effect.My PhD involves investigating the differences between these river systems using remote sensing data. Itshould also yield new data on the ecological roles of certain large animals using these systems,particularly elephants and giraffes.Modelling of climate effects are also a key component of this study for 2 reasons. The first pertains to theprevalence of ephemeral river systems in drylands, as expected changes to rainfall frequency and intensity,resulting from climate change, may drive other temporary rivers to become classed as 'ephemeral'(Larned et al, 2010; Tooth and Nanson, 2011). The second pertains to the relationship between climateand ecosystem. How the projected rainfall changes influence ephemeral river hydrology may be somewhatunderstood, but how said changes influence ecological processes within aquifer dependent ecosystems arenot (Eamus et al, 2006; Colvin et al, 2007). Thus, investigating rainfall change in these systems is integralto this project.