Community Structure and Functioning of Soil-dwelling Macro-invertebrates in Cocoa Plantations Invaded by the Little Fire Ant and Neighboring Secondary Forest in Mbalmayo Reserve Forest (Centre-Cameroon)

Abstract

Agroforestry leads to the degradation of natural forests, floral and faunal biodiversity. Little information exists on faunal functioning in agroforestry environments invaded by exotic pests compared to natural environments. Ecological survey was conducted from September to November 2023 in Mbalmayo Reserve Forest (Centre-Cameroon), the community structure and functioning of macro-invertebrates in cocoa plantations invaded by the little fire ant, were compared to the situation in neighboring secondary forest. Baits, pitfall, and quadrats allowed collection of 129,916 specimens of seven classes, 18 orders, 39 families, and 82 species. Insecta was mostly abundant (cocoa plantations: 92.7%, secondary forest: 6.97%, pooled sites: 99.7%), as well as Hymenoptera (cocoa plantations: 92.6%, secondary forest: 6.80% of 13 species, pooled sites: 99.4% of 14 species). Cocoa plantations and secondary forest presented each low species richness, diversity, and evenness, and a high dominance by a few species. Cocoa plantations presented more exotic species (92.9%, 25 species) while secondary forest showed mostly natives of unknown pest status and few native pests. The little fire ant was abundant (92.6%) and dominant exclusively in cocoa plantations. In secondary forest, Myrmicaria opaciventris, Crematogaster gabonensis, and Pheidole megacephala were abundant in the dry season, the two former being co-dominants while in the rainy season Cr. gabonensis, Cr. striatula, Craspedophorus bonvouloirii, My. opaciventris, Ph. speculifera, and Paltothyreus tarsatus were abundant, the four former being co-dominants. A low dissimilarity was noted between the two sites. The change in species composition from cocoa plantations to secondary forest was relatively large. Armadillidium vulgare Latreille, 1804 (Armadillidiidae) and Wasmannia auropunctata Roger, 1863 (Formicidae) were good indicators of disturbed environments. Assemblage functioned on the basis of maintaining a multi-species network developed in time and space for the circulation of the information, but with a weak force of regeneration. The secondary forest undergrowth was unfavorable for exotics and in-depth studies would be conducted on the behavior of natives in relation to the progression of invasions, since cases of repellency have been recorded. Policy makers responsible for green space management should take effective measures to prohibit the transfer of plants infested with exotic pest species between invaded and non-invaded areas when creating agroforestry areas.