Diverse effects of the common hippopotamus on plant communities and soil chemistry

Abstract

The ecological importance of the common hippopotamus (Hippopotamus amphibius) in aquatic ecosystems is becoming increasingly well known. These unique megaherbivores are also likely to have a formative influence on the terrestrial ecosystems in which they forage. In this study, we employed a novel exclosure design to exclude H. amphibius from experimental plots on near-river grasslands. Our three-year implementation of this experiment revealed a substantial influence of H. amphibius removal on both plant communities and soil chemistry. H. amphibius significantly reduced grassland canopy height, increased the leafiness of common grasses, reduced woody plant abundance and size, and increased the concentrations of several soil elements. Many of the soil chemistry changes that we experimentally induced by exclusion of H. amphibius were mirrored in the soil chemistry differences between naturally occurring habitats of frequent (grazing lawns) and infrequent (shrub forest) use by H. amphibius and other grazing herbivores. In contrast to existing hypotheses regarding grazing species, we found that H. amphibius had little effect on local plant species richness. Simultaneous observations of exclosures designed to remove all large herbivores revealed that H. amphibius removal had ecologically significant impacts, but that the removal of all species of large herbivores generated more pronounced impacts than the removal of H. amphibius alone. In aggregate, our results suggest that H. amphibius have myriad effects on their terrestrial habitats that likely improve the quality of forage available for other herbivores. We suggest that ongoing losses of this vulnerable megaherbivore are likely to cause significant ecological change.

Fire and grazing determined grasslands of central Madagascar represent ancient assemblages

“…Cattle, hippopotamuses and grazing tortoises share key functional similarities, they prefer highly palatable grasses with high bulk density to maximize intake of nutritious food per bite. McCauley et al [68] showed that a mixture of herbivores (including cattle and hippopotamuses) and removal of hippopotamuses on grazing lawns in East Africa similarly impacted grassland diversity and structure, suggesting some functional equivalence between hippopotamuses and livestock. The replacement of one grazer with another is unlikely to have substantially reshaped diversity where an obligate grazing flora already existed.…”

Spatial ecology of male hippopotamus in a changing watershed

“…This could potentially explain why H. amphibius used many of the available habitats less than expected. Floodplains are a key resource for H. amphibius because they are able to maintain grazing lawns with short-cropped, green foliose, an important resource for H. amphibius 3,26,42 , even at the peak of the dry season (Fig. 1b).…”

“…In African savannas, the common hippopotamus ( Hippopotamus amphibius ) is an important ecosystem engineer because it shapes the physical structure of ecosystems 1 , vegetation communities 2,3 , and biogeochemical cycling 4,5 . These effects are detectable in both aquatic and terrestrial ecosystems.…”

Establishment and characterization of fibroblast cultures derived from a female common hippopotamus (Hippopotamus amphibius) skin biopsy

“…For example, these large grazers directly change the plant communities with respect to grass height and abundance and indirectly affect the abundance and diversity of aquatic animal species (McCauley et al, 2018; Stears et al, 2018). They could also influence the soil and watershed chemistry as well as silicon cycling between these two systems (McCauley et al, 2018; Schoelynck et al, 2019; Stears et al, 2018). Unfortunately, this megaherbivore population has undergone a dramatic decrease in number as a result of illegal hunting and habitat degradation (Lewison & Pluháček, 2017).…”