Insect herbivores in Neotropical and Afrotropical wetlands with differing grazing pressure from large mammalian herbivores.

WILLIEMS, FRANK; MURPHY KEVIN; DE WYSIECKI M. LAURA; KENNEDY, MICHAEL; SICHINGABULA, HENRY; MARTINEZ, FEDRA S.; FRANCESCHINI M. CELESTE

Mendoza

Congreso; X Congreso Argentino de Entomología; 2018

Impacts and abundance of herbivores on wetlands have long been considered as largely insignificant. Recent reviews of plant-herbivore interactions in temperate freshwater ecosystems, however, have shown that herbivores (invertebrates and vertebrates) can have quite substantial impacts on aquatic plant populations, though there is much less information available about the importance of such interactions in warm-water aquatic systems of the tropics and sub-tropics. In this study we compare the impacts and abundance of insect and gastropod herbivores when they are accompanied by macro-herbivores (in Africa: Afrotropical) and when there is much less macro-herbivore grazing (in South America: Neotropical). Data collected during 2012-2013 from Zambia and Argentina for 15 aquatic plant species permitted quantification of grazing damage and abundance of insect and gastropod herbivores. The number of leaves damaged by invertebrate herbivory was >70 % for most aquatic plants. Insects were the most abundant invertebrate herbivores. For total numbers of invertebrate herbivores found in the Afrotropical aquatic plants non-herbivorous species were significantly more abundant than herbivores (ANOVA, p=0.036), but for those present in Neotropical plants there was no significant difference between number of herbivore and non-herbivore individual animals present (ANOVA, p=0.5002). In total seven species of large mammalian herbivores, were observed, often in abundance (especially so for Black Lechwe antelope, Kobus leche), grazing aquatic plants in the Afrotropical wetlands. In the Neotropical wetlands, only the much smaller Capybara (Hydrochoerus hydrochaeris) was sporadically observed feeding on wetland grasses and aquatic plants in the study sites. The results obtained to date indicate that invertebrate herbivores, mainly insects, form a numerically-important trophic group feeding in the wetlands examined in both the Afrotropics and Neotropics, causing sufficient damage to influence calculations of aquatic plant biomass and productivity in these wetland systems. We also show that terrestrial and semiaquatic mammalian herbivores, present in large numbers only in the Afrotropical wetlands, also had strong impacts, both on aquatic plants and their associated insect herbivore assemblages.