An introduction to the concept of Zoohydrology – the interactions between hydrological processes and wild animals

Ecohydrology describes the effects of hydrological processes on ecosystem structure and functioning and the effects of biotic processes on hydrological processes. Recently, there is an increasing emphasis on the role of megafauna, large mammals and birds, on earth system processes, such as nutrient cycling, energy flows and vegetation patterns. Ecohydrology as a field, however, has not yet considered megafauna as central drivers of hydrological processes but focused strongly on the interactions between hydrological processes and plants and soils. Here, we introduce zoohydrology to emphasize the importance of considering the interactions between wild animals and hydrological processes. This includes both the effects of hydrological processes on the occurrence, behavior and life history of animals as well as the effects animals have on hydrology. In this introductory talk, we will outline different pathways through which hydrology affects megafauna and through which megafauna affect hydrological processes using a systems approach. We will illustrate these pathways with concrete examples from different parts of the world and on different species. For example, the importance of hydrological processes and hydromorpho-dynamics for shaping habitats of endangered species, such as the Ganges freshwater dolphin and Bengal tigers in northern India and Nepal, but also for structuring megafauna community dynamics, such as the example of Gorongosa National Park in Mozambique. We will also exemplify how wild animals can affect central hydrological processes in diverse ways; directly (e.g., species such as beaver and hippo as ecosystem engineers of aquatic systems) and indirectly (e.g., elephants that reduce woody cover at large scales, affecting evapotranspiration). Many effects of animals on hydrological processes remain understudied and are often lacking from hydrological models. By introducing the concept of zoohydrology, we stress the potentially pivotal interactions between central hydrological processes, wild animals and their habitats. To unravel the full complexity of these interactions and assess their true importance, zoohydrology must be advocated among scientists, policy makers and practitioners in order to better address biodiversity conservation and restoration, make the concept of environmental flow needs more concrete, and investigate the consequences of biodiversity restoration on hydrological systems.