Muddy waters: Mega‐herbivores as agents of change in African shallow freshwaters

Large herbivores have been described as agents of change in terrestrial habitats. Their effect on aquatic ecosystems are, however, underexplored. We raise the question whether elephants and hippopotamus potential to significantly alter limnological properties and, indirectly, primary secondary productivity within small shallow freshwaters arid semi-arid African landscapes. In this note we discuss hypothetical means by which freshwater bodies. further assimilate with known ways these mega-herbivores environments giving an overview their functional role structuring Les grands ont été décrits comme des de changement dans les habitats terrestres. Leurs effets sur écosystèmes aquatiques sont toutefois peu étudiés. Nous nous demandons si éléphants et hippopotames le potentiel modifier manière significative propriétés limnologiques et, indirectement, la productivité primaire secondaire eaux douces petites profondes paysages africains arides semi-arides. Dans cette note, discutons moyens hypothétiques par lesquels modifient masses d'eau douce profondes. assimilons ensuite ces résultats aux méthodes connues lesquelles méga-herbivores environnements aquatiques, ce qui donne un aperçu leur rôle fonctionnel structuration aquatiques. Disturbance plays a central (Sousa, 1984). can be disturbance, altering through both foraging non-foraging activities (Haynes, 2012; McCarthy al., 1998; Mosepele 2009; Ripple 2015). Such altered are particularly evident many regions Africa given presence so-called mega-herbivores, such (Hippopotamus amphibious), elephant (Loxodonta africana) black rhinoceros (Diceros bicornis) (Ripple Given conspicuous charismatic nature animals, recognised importance ecosystem engineers, roles well studied 2015 references therein). What is less known, effects certain ecosystems. While catchment will certainly indirect implications for ecosystems, processes erosion, animals also often direct association water Semi-arid continent typically characterised smaller, shallower permanent that may susceptible mega-herbivore mediated activities. protected areas region, numbers burgeoning (e.g. Gough & Kerley, 2006), scarce communities bodies they frequent. Africa, among largest species differ considerably behaviour, feeding landscape exploitation, similar affinity (Mosepele Owen-Smith, 1992). Hippopotamus considered semi-aquatic diurnally, spend time rivers, lakes impoundments, thus utilise not only drinking purposes but habitat (Coughlin Fish, Field, 1970; 1998). At night, leave forage surrounding (Field, 1970). primarily hydration purposes, exploit extensively non-drinking mud-bathing swimming 1992; Vanschoenwinkel 2011). As such, regularly move between (Loarie McCauley 2015; 2009). research could limnology ecology theoretical information environments, creating conceptual model (Figure 1). models highly useful conservation planning (Margoluis result size, much column submerged benthos. Movement involves contact bottom water-bodies. walk or bounce along rarely swim 2009), while substratum largely restricted (Owen-Smith, Wright Luck, likely contribute resuspension silt, nutrients organic material homogenisation stratified waters. Since localised increases turbidity nutrient availability column, activity pans, river pools reservoirs consequences productivity. Although present untested hypothesis, homogenisation, increased plankton, macroinvertebrates fishes (Arruda 1983; Henley 2000). The facilitators is, unexplored. has observed movement alters emergent riparian vegetation (McCarthy It shown transport propagules, form dormant cysts, (Vanschoenwinkel 2011) potentially harmful microbes associated faecal matter, into (Ndlovu 2018). These physically shape habitats, forming deepening channels Certain facilitate cross-ecosystem subsidies introduction dung, origin, animal-mediated allochthonous input cycling, dissolved oxygen levels, food-web dynamics (Marcarelli 2011; Stears 2018; McCauley, Vanni, 2002). systems physical activity- raised study, propose play shallow-water communities. hypothesise augmented practice enclosing fence Packer 2013; Slotow, 2012). This ultimately limits large boundaries (Gough 2006; 2012) population higher than recommended maintenance ecological integrity (Maciejewski 2014). issues documented context 2014; 2012), characteristic regions, yet adequately explored. recommend future address specific aspects outlined model, attempt better quantify understand how unknown components interact. vital management disturbance at level. Ryan J. Wasserman: Conceptualization (equal); Writing – original draft review editing (equal). Tatenda Dalu: editor two reviewers thanked contributions revised version manuscript. acknowledge South Institute Aquatic Biodiversity financial support authors. Rhodes University Mpumalanga supporting RJW TD, respectively. No conflicts interest. Data sharing applicable article no new data were created analyzed study.