Modelling the functional dynamics of Carabid assemblages as indicators of agroecosystem stability.

Abstract

Carabid beetles (Coleoptera: Carabidae) are ubiquitous and critically important in agroecosystems. Their rapid response to anthropogenic disturbances has been proposed as a practical and realistic tool for monitoring the sustainability of agricultural management practices. Carabid beetles significantly control pest populations, thereby aiding the regulation of harmful insects in agroecosystems. Recognizing their significance in this context highlights the potential of natural pest control strategies that can decrease reliance on chemical pesticides. Despite their potential importance, the impact of agricultural management practices on the diversity patterns and functionality of carabid beetles, specifically in South Africa, remains largely unexplored. Addressing this research gap is imperative to understand the complex association between agroecosystem management practices and carabid beetle populations in this region. This study aimed to advance knowledge about the ecological stability of diversely managed agroecosystems under conventional tillage, semi-natural grassland, conservation grazing, and semi-conservation agriculture by documenting and assessing the status of carabid beetle biodiversity and utilizing their functionality. This was done by (1) systematically reviewing literature on carabids as indicators of sustainability in agroecosystems, (2) assessing the diversity and community structure of carabid beetles in response to contrasting agroecosystem management, (3) investigating carabid beetle concordance with the selected epigeic arthropod taxa (ground spiders, ants, and rove beetles), and (4) characterizing carabid functional diversity (body size, feeding preference/guilds, and wing morphology). I achieved the aims by sampling over a two-year period, from 2020 to 2021, in the Free State province of South Africa using pitfall traps and active search methods. Carabid beetles were classified into morphospecies, and their functional diversity was determined using existing literature on carabid beetles. Data were analyzed with a sequence of multivariate and spatial statistical methods using the R software version 3.4.2. Carabid taxonomic and functional diversity patterns were significantly supported in conservation grazing compared with conventional tillage, semi-natural grassland, and semi-conservation agroecosystems. Notably, the conservation grazing-associated species included large flightless predators from the genera Calosoma and Scarites. Large, immobile, and specialized carabid beetles are sensitive indicators of management intensity in agricultural landscapes. However, not all carabid species are vulnerable to disturbances; some are eurytopic, occurring across all agroecosystems, such as the carabid genus Pterostichus, which are generalists and exhibit tolerance to disturbances. There was a high degree of congruence between the species richness and composition of carabid beetles and the overall epigeic arthropod taxa, indicating the efficacy of using carabid beetles as proxies for predicting the arthropod diversity patterns of epigeic taxa and identifying farms with conservation significance. The use of carabid beetles as model organisms in agroecosystems serves as a reliable proxy for assessing the impact of management practices on agroecosystems, enabling the ranking of disturbance, recovery, and stability levels. This knowledge will facilitate informed decision making and the implementation of effective conservation and sustainable management practices.