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Eco Evolution Land Use By Zebras

Most large-bodied wildlife populations in sub-Saharan Africa only survive in spatially contained protected regions (Newmark 1996). However, many are still declining because external changes influence ecological processes within conservation areas, leading to a lack of functionality (Western et al. 2009; Fynn and Bonyongo 2010). Wetland ecosystems are particularly vulnerable to external land use changes (Turner et al. 2000). The Okavango Delta, an inland wetland covering 15,000 km2 in north-west Botswana, southern Africa, is a RAMSAR site with high densities of large herbivores (Bonyongo and Harris 2007) that typifies
many of these problems.

The Okavango Delta’s catchment basin covers circa 350,000 km2 across Angola, Botswana and Namibia (Mbaiwa 2004), making sustainable management of the entire basin practically and politically complicated. The Okavango Delta floods annually, with flood water arriving in the north-west in March and reaching the south-eastern Delta by July (McCarthy and Ellery 1998). The duration of inundation and extent of the seasonal floodplains vary with local topography, and amount and progression of the flood water (Mendelsohn et al. 2010). However, currently proposed water extraction and hydroelectric schemes outside Botswana would, if implemented, have a significant impact on water flow into the Delta. An estimated 95 km2 of wetland, mainly seasonal
floodplains, would be lost for every 100 million m3 of water extracted (Gumbricht et al. 2004). Climatic variation also plays an important role in yearly flood variation (Gumbricht et al. 2004), and climate change is likely to lead to increased climatic variability and reduced rainfall (Hulme et al. 2001), potentially decreasing Okavango flood levels (Wolski and Murray-Hudson 2008). While the combined effects of climatic variation and anthropogenic disturbances could lead to significant loss of seasonal wetlands in the Okavango Delta, how such landscape scale changes influence ecological processes is poorly understood, and so limits our ability to manage protected areas (Hansen and DeFries 2007).

Flooding variation is one of the principal factors driving habitat heterogeneity in the Okavango Delta (McCarthy et al. 2000), creating a temporally and spatially shifting mosaic of habitat patches across the landscape. Despite little change in elevation and a homogeneous sand substrate, the Okavango Delta is a highly heterogeneous, dynamic system, with substantial small-scale spatial variation in vegetation structure dependent on flooding characteristics (Ramberg et al. 2006; Bartlam 2010). Variation in the density and distribution of key resources within a landscape influence animal distribution (Whittaker and Levin 1977), and the shape and complexity of habitat patches and their relative juxtaposition and fragmentation within a landscape influence the shape and size of home ranges (e.g., Tufto et al. 1996; Anderson et al. 2005) and animal movements (Wheatley and Johnson 2009).

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