非法狩猎威胁热带草原的生态系统

White rhinoceros²（犀牛） may be extinct in twenty years with the current poaching rates. The loss of this megaherbivore is in itself a tragedy, but it may also have tremendous effects on the ecosystems⁴ they now live in. The white rhino¹ (Ceratotherium simum), and other megaherbivores, are key drivers of ecosystem³ functioning because they´re not controlled by predation.   A new study by Joris Cromsigt and Mariska te Beest, published in Journal of Ecology, highlights the role of the white rhino in the savannah ecosystems.   Earlier empirical studies on the ecosystem impact of megaherbivores are strongly biased⁵ to African elephant with very little contemporary evidence for other megaherbivore species. Cromsigt and te Beest quantifies how rhino recolonized Kruger National Park (KNP) following their re-introduction in the 1960s to create a unique 'recolonization experiment' and tests how this megagrazer is affecting the structure of savannah grasslands⁸.   The researchers identified landscapes that rhino recolonized long time ago versus⁹ landscapes that were recolonized more recently. The assumption was that time since colonization⁶ represents a proxy¹⁰ for extent of rhino impact. Grassland⁷ heterogeneity¹¹（异质性，不稳定性） on 40 transects covering a total of 30 kilometer were recorded. Short grass cover was clearly higher in the high rhino impact than low rhino impact landscape. Moreover, they encountered about 20 times more grazing lawns, a specific grassland community, in the high rhino impact landscape. The conclusion is that white rhinoceros may have started to change the structure and composition of KNP's savannah grasslands. The amount of short grass has important consequences for other species, but also components¹² of ecosystem functioning such as fire regimes. The results highlight that this poaching crisis not only affects the species but threatens the potentially key role of this megaherbivore as a driver of savannah functioning.