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

Vincent Maicher,Eric B Fokam,Mercy Murkwe,Jiří Doležal,Julie Desmist,Ishmeal N Kobe,Jan Altman,Robert Tropek,Tomasz Pyrcz,Sylvain Delabye

doi:10.1038/s41598-020-78659-7

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.

Highlights

Natural disturbances are key drivers of biodiversity in many terrestrial ecosystems[1], including tropical forests despite their traditional view as highly stable e cosystems[2,3]
The consequent cascade effects on forest biodiversity have not been studied yet, effects of elephant disturbances on other tropical forest organisms can be expected as well[24,25]
2025 trees were identified to 97 species and 7853 butterflies and moths were identified to 437 species in all sampled forest plots (Supplementary Table S1)

Summary

Introduction

Natural disturbances are key drivers of biodiversity in many terrestrial ecosystems[1], including tropical forests despite their traditional view as highly stable e cosystems[2,3]. The consequent changes in plant communities cause cascade effects on higher trophic levels (herbivores, predators, parasites), expanding the impact of disturbances on the entire ecosystem Such increase of heterogeneity of habitats and species communities substantially contribute to maintaining the overall biodiversity of tropical forest e cosystems[5,6]. Savanna elephants are best known to alter their h abitats[8,10] Besides their important roles of seed dispersers or nutrient cyclers[8], they directly impact savanna ecosystems through disturbing vegetation, especially by increasing tree mortality by browsing, trampling, and d ebarking[10]. Such habitat alterations substantially affect diversity of many organism g roups[11], including insects. We focus on species’ distribution ranges in both types of forests, with no a priori hypothesis on the direction of the changes

Methods

Results

Conclusion