DBSCAN and GIE, Two Density-Based "Grid-Free" Methods for Finding Areas of Endemism: A Case Study of Flea Beetles (Coleoptera, Chrysomelidae) in the Afrotropical Region

Up and down from North to South: Latitudinal Distribution of Flea Beetle Genera in Continental Africa (Coleoptera, Chrysomelidae, Galerucinae, Alticini)

The distribution of global biodiversity can be investigated based on comprehensive datasets and many methods to process them. The taxonomic diversity of phytophagous insects is typically linked to plant diversity, which increases from temperate to tropical latitudes. In this paper, we explored the latitudinal distribution of the flea beetle genera (Coleoptera, Chrysomelidae, Galerucinae, Alticini) on the African continent. We divided the area into latitudinal belts and looked for possible correlations with the number and types of vegetational divisions, the area of each belt, and the bioclimatic variables. The number of flea beetle genera is related to the number and types of vegetation divisions rather than the area of each belt. Some bioclimatic variables are highly related to the number of genera, which is higher within those belts where climate factors limit the oscillation of temperature over the year and favor high precipitations, especially in the warmest months. These biotic and abiotic factors lead to a two-peak trend in the taxonomic richness of flea beetle genera from north to south. Genera endemic to restricted areas are linked to the presence of high mountain systems and increase the taxonomic richness of the belt they belong to.

Climatic Niche, Altitudinal Distribution, and Vegetation Type Preference of the Flea Beetle Genus Arsipoda in New Caledonia (Coleoptera Chrysomelidae)

New Caledonia is one of the major biodiversity hotspots. The flea beetle genus Arsipoda (Coleoptera Chrysomelidae) is present with 21 species, all endemic. We investigated, using GIS analyses and ecological niche models, the habitat preferences of these species in terms of vegetation types, altitude, and climate, and assessed the adequacy of knowledge on the spatial parameters affecting the distribution of the genus in New Caledonia. Altitude and geology seem to play an important role in shaping species distribution. Volcanic substrate allows the growth of ultramafic vegetation, which includes most of their host plants. From a biogeographic and conservation perspective, our results report a deep link between Arsipoda species and their habitats, making them particularly sensitive to environmental modifications.

Fine-Tuned Ecological Niche Models Unveil Climatic Suitability and Association with Vegetation Groups for Selected Chaetocnema Species in South Africa (Coleoptera: Chrysomelidae)

Despite beetles (Coleoptera) representing most existing animal species, the ecological and biogeographical factors shaping their distribution are still unclear in many regions. We implemented state-of-the-art ecological niche models (ENMs) and niche overlap analysis to investigate climate–occurrence patterns for five flea beetle species of the genus Chaetocnema in South Africa (C. brincki, C. danielssoni, C. darwini, C. gahani, and C. natalensis). ENMs were fitted through Maxent and Random Forests, testing various parameterizations. For each species, tuned ENMs attaining good discrimination on spatially independent test data were selected to predict suitability across the study region and individuate its main climatic drivers. Percentage coverage of climatically suitable areas by seventeen Afrotropical vegetation formations was also computed. Predicted suitable areas do not extend far away from known presence localities, except for C. brincki and C. gahani in north-eastern South Africa. Temperate grasslands and shrublands cover most of suitable areas for C. brincki and C. gahani, along with warm temperate forests, as well as for C. danielssoni, in this case being followed by tropical flooded and swamp forests. Climatic suitability for C. darwini mainly relates to the Mediterranean grasslands and scrublands of the southern coastal region, while suitable areas for C. natalensis encompass various vegetation formations, coherently with its wide distribution. The environmental niche of C. danielssoni significantly overlaps with those of the wide-ranging C. darwini and C. natalensis, suggesting that historical factors, rather than low climatic tolerance, has determined its restricted distribution in the Western Cape Province. Maxent and Random Forests were confirmed to be of great help in disentangling the environment–occurrence relationships and in predicting suitability for the target species outside their known range, but they need to be properly tuned to perform at their best.