Mesoherbivores alter their activity levels with elephant-induced habitat modifications and behavioral cues

Abstract

The largest herbivore species are declining across the world, threatening the structure and function of ecosystems. While the effects of megaherbivores (herbivores with a body mass over 1000 kg) on vegetation structure and composition have been studied extensively, megaherbivores may also influence other taxa, including smaller herbivores with which they share dietary overlap. In African savannas, megaherbivores, particularly African elephants Loxodonta africana, may influence mesoherbivores in two different ways: 1) indirectly through changes in vegetation structure that shape forage availability and predation risk, and 2) directly through their presence, which may elicit fear responses due to a risk of antagonistic interactions from these dominant competitors. However, these mechanisms have yet to be isolated, and thus their relative impact on mesoherbivores is unknown. We conducted a field experiment to test the effects of both of these mechanisms on mesoherbivore activity by emulating elephant-induced habitat alterations and behavioral cues (vocalizations) related to their presence in a savanna in Mlawula Nature Reserve, Eswatini, a protected area where elephants are absent. We found that, overall, mesoherbivores limited their activity in areas with either type of elephant impact. However, individual species exhibited large variation in the magnitude and direction of their responses to elephant impacts, with smaller species typically exhibiting stronger avoidance of elephant-impacted areas. Furthermore, combination of both types of elephant impacts tended to influence mesoherbivores more strongly than habitat alterations or vocalizations alone, emphasizing the complex roles that megaherbivores play in these communities. These results provide new insights into the consequences of megaherbivore loss, an issue of high conservation concern, and can inform efforts to restore megaherbivores' roles in savannas. Such efforts could include both recreating the impacts of elephants on vegetation structure and behavioral cues like vocalizations to move mesoherbivores around the landscape, potentially altering the effects of herbivory on savanna vegetation.