Spatio-temporal dynamics of fruit-feeding butterfly communities across Savanna-forest gradients in a seasonal climate

Abstract

Trapping fruit-feeding butterflies is often used for biodiversity surveys in tropical forests, but only occasionally in more open habitats. Moreover, extending data collection to estimation of, e.g. seasonal colorations and wing damage can improve our understanding of their biology. We aimed to determine how butterfly communities respond to changing seasons across a forest-savannah gradient. We conducted monthly butterfly trapping for one year or more in Limpopo (South Africa) across six sites, with at most sites transects at different altitudes or in different habitats. For each specimen, we measured forewing length, classified it as wet or dry season colour form if appropriate, and scored wing damage and wing wear. We compiled weather data for each site from satellite resources. As of March 2025, we collected 8923 specimens belonging to 49 species. Species richness was higher at the forest sites than in the savannah sites. Generally, throughout the wet season, more species were found than during the dry season. The species composition differed significantly between habitats and among seasons. Species and sites differed in how wing length and the timing of the appearance of dry season forms varied over time. For example, contrary to expectation, dry-season forms were not always larger than wet-season forms, with a weak trend in two species, and sex-specific opposite trends in others, and dry-season forms were considerably smaller in C. zoolina. Furthermore, B. safitza dry-season forms appeared two months later at the wettest forest site than at the driest forest site. Wing wear appeared to track population dynamics, increasing steadily throughout the dry season, and oscillating during the wet season, presumably as new generations emerged. Wing damage tended to be more severe in wet-season forms and in females, and often varied over time, peaking in the wet season. In a few cases, butterflies appeared to change habitat preference seasonally, gathering in the gallery forest during the wet season, and some species appeared completely absent from the savannah sites during the dry season, indicating longer-distance movements. While forests have more diverse fruit-feeding butterfly faunas than savannahs, the latter do host a different set of species. Moreover, as some species utilize both habitats seasonally, conserving both forests and savannahs at the landscape scale may be needed.