Response of Grasshoppers to the Agricultural Mosaics of the Cape Floristic Region Biodiversity Hotspot in South Africa

Abstract

Agricultural production is one of the main drivers of the on-going biodiversity crisis. This has resulted in research on the impact of agriculture on biodiversity being at an all-time high. This is critical given that the world must produce food for the ever-growing human population. This growing demand for food often demands increasing production areas at the expense of protected ones. Such trade-offs can potentially lead to dire consequences on biodiversity and its associated ecosystem function. In an attempt to minimise this potential negative impact, and also to conserve biodiversity and its associated ecosystem function, scientists and producers have developed a system that integrates natural with production patches as part of making agriculture more sustainable. In most instances, decisions on agro-natural schemes for sustainable food production are based on research conducted on larger animals at the expense of smaller ones, especially arthropods, even though they constitute the largest group of animals. If humans are to achieve the aim of producing food to meet the growing demand at minimum cost to the environment and biodiversity, studies on smaller animals such as insects, which constitute more than 75% of all animals, and are also major contributors of terrestrial ecosystem function in the terrestrial world, must be considered a high priority. An insect group that has much value for the purpose of designing agro-natural schemes is grasshoppers (Orthoptera, Acridoidea). This is because they show high sensitivity to changes in vegetation type and structure, and have high potential for expressing changes in environmental conditions and vegetation. This is even more important in a biodiversity hotspot which is also known for intensive agricultural production, such as the Cape Floristic Region (CFR). In view of that, I embarked on a study to document the footprint of agricultural production types on biodiversity using grasshoppers as keystone species in four studies making up my four core chapters. Firstly, I compared species richness, abundance, composition, diversity and evenness of grasshoppers among 46 sites in four geographical areas in the CFR. Here, I investigated three land-use types: fynbos, vineyards and deciduous fruit orchards, the main production types in the region. Results showed that grasshopper abundance were significantly higher in vineyards than in fynbos or orchards. Species richness, diversity, and evenness were highest in fynbos followed by vineyards and then orchards. There was overall high species similarity among all three land-use types, with high species assemblage similarities between vineyards and orchards. Species that preferred fynbos were mostly flightless and endemic to the CFR. In the second chapter, grasshopper abundance was studied under agricultural land-use (vineyards) and in natural vegetation (fynbos) across two peak seasons (spring vs. summer). This study aimed at quantifying the level at which different grasshopper species utilise the different aspects of the landscape and how this range of utilisation among species relates to certain species’ traits. My results showed that species traits play a major role in grasshoppers’ ability to move between patches, and which also affects how they utilize various different patches on the landscape. Highly mobile, generalist species are able to utilise more aspects of the landscape. And depending on seasonality, these species will inhabit either vineyards or fynbos aided by their high ability to move between patches. On the other hand, low mobility, specialists lack the ability to move readily between patches, and as a result, they are confined to one or a few patches across the seasons. In the third chapter, I developed species distribution models for four localized, CFR endemic flightless grasshopper species, Euloryma larsenorum and E. lapollai, E. umoja and E. ottei. The first two are associated with fynbos only, while E. umoja and E. ottei, the second two, are both associated with both fynbos and vineyards. I used the Maximum Entropy algorithm, which showed that vegetation type and soil characteristics were the most important environmental factors affecting local distribution of Euloryma species in the CFR. My models also showed that Euloryma species have very narrow, predicted, suitable habitats in the CFR. I also showed that there are no significant differences in the distribution of species associated with fynbos only as well as those associated with both fynbos and vineyards. Lastly, in the fourth chapter, I investigated grasshopper species assemblage composition on three land-uses across the agro-natural mosaic landscape of CFR. This study documented species’ level of occupancy and abundances in relation to their life history traits in order to assess the amount of change occurring on the landscape in the CFR. My results show that very few species, and mostly from Acrididae, dominated the landscape. It also shows that the species that dominated the transformed landscape were generalists. There was also a high correlation between generalists, high to medium mobility and widespread species on one hand, and specialists, low in mobility, and localised species on the other.