Effects of disturbances by forest elephants on diversity of trees and insects in tropical rainforests on Mount Cameroon

Abstract

Natural disturbances are essential for tropical forests biodiversity. In the Afrotropics, megaherbivores have played a key role before their recent decline. Contrastingly to savanna elephants, forest elephants’ impact on ecosystems remains poorly studied. Few decades ago, forests on Mount Cameroon were divided by lava flows, not being crossed by a local population of forest elephants until now. We assessed communities of trees, butterflies and two guilds of moths in the disturbed and undisturbed forests split by the longest lava flow. We surveyed 32 plots, recording 2025 trees of 97 species, and 7853 insects of 437 species. The disturbed forests differed in reduced tree density, height, and high canopy cover, and in increased DBH. Forest elephants’ selective browsing and foraging also decreased tree species richness and altered their composition. The elephant disturbance increased butterfly species richness and had various effects on species richness and composition of the insect groups. These changes were likely caused by disturbance-driven alterations of habitats and species composition of trees. Moreover, the abandonment of forests by elephants led to local declines of range-restricted butterflies. The recent declines of forest elephants across the Afrotropics probably caused similar changes in forest biodiversity and should be reflected by conservation actions.

Elevational distribution of montane Afrotropical butterflies is influenced by seasonality and habitat structure

“…Habitat structure has also been shown to influence elevational and non-elevational patterns of species richness and abundance of Lepidoptera in previous studies in the Afrotropics [ 17 , 30 , 56 ]. Along an elevational gradient on Mount Kilimanjaro Axmacher & Fiedler (2008) [ 57 ] reported that geometrid moth diversity (Fisher’s α) was higher in open than closed habitats, which is consistent with our findings from the Uluguru Mountains.…”

“…Along an elevational gradient on Mount Kilimanjaro Axmacher & Fiedler (2008) [ 57 ] reported that geometrid moth diversity (Fisher’s α) was higher in open than closed habitats, which is consistent with our findings from the Uluguru Mountains. Maicher et al [ 17 ] also have recently reported a significant interaction between elevation and elephant-caused habitat disturbance on Mount Cameroon with higher butterfly species richness in more disturbed or open sites on Mount Cameroon at lower (1100 m) elevations than at higher (1850 m) elevations. We hypothesize that higher butterfly species richness and abundance in open than in closed habitats along an elevational gradient in the Uluguru Mountains may be a result of higher light intensity and thus abundance of food resources and/or host plants for larval and adult stages.…”

“…Both abiotic and biotic factors influence species richness and abundance of tropical Lepidoptera along elevational gradients. Of these factors seasonality [ 14 , 15 ] and habitat structure [ 16 , 17 ] have been shown to influence elevational distributions of Afrotropical Lepidoptera species richness and abundance. However, the combined effects of seasonality and habitat structure and their interaction on the elevational distribution of butterflies have not been examined, as per out knowledge, in the tropics unlike in the subtropics [ 18 , 19 ].…”

“…Habitat structure has also been shown to influence elevational patterns of species richness and abundance in Afrotropical Lepidoptera [ 17 , 30 ]. Patchiness of habitat can increase niche availability for specialized species, and thus alter species richness and abundance along an elevational gradient [ 31 ].…”

The challenging coexistence of forest elephants Loxodonta cyclotis and timber concessions in central Africa

“…via trampling damage; Terborgh et al 2015, Rosin et al 2017). Forest elephants induce a reduction in stem density, resulting in reduced competition amongst trees and the development of larger trees with higher wood density, positively impacting carbon sequestration (Berzaghi et al 2019, Maicher et al 2020). They also preserve the forest richness and diversity by dispersing the seeds of many species (Campos‐Arceiz & Blake 2011).…”