Factors affecting millipede, centipede and scorpion diversity in a savanna environment.

Abstract

Millipedes, centipedes and scorpions are an important component of the ground-dwelling invertebrate fauna, and may have value as bioindicators of ground-dwelling invertebrate diversity. However, some level of understanding of which factors influence patterns of their distribution and diversity is necessary prior to any investigation of their use in conservation planning and as bioindicators. This project was undertaken in the Greater Makalali Conservancy in the Northern Province. Many methods have been used to sample millipedes, centipedes and scorpions but the efficiency of these in savanna has not been investigated. One aim was to determine a method for quantitatively sampling these invertebrates in this environment. Six sampling methods were tested during the study. Millipedes were found to be efficiently sampled by active searching 9m2 quadrats and drive transects, centipedes by actively searching 25m2 plots and scorpions by pitfall traps. The other methods tested were wet cloths and cryptozoan traps. Another aim was to determine spatial and temporal variation in millipede, centipede and scorpion diversity in the range of habitat types present in the Conservancy. 45 sites within five habitat types were sampled during three different sampling periods. The highest diversity for each study group was recorded in the most heterogeneous habitat, with the lowest being recorded in more homogeneous habitat types. Millipede and centipede diversity was significantly influenced by habitat type, while sampling period had a significant effect on millipede and scorpion diversity. Quantifying the effect of various environmental factors on the diversity of these invertebrates was a further aim. Maps of various Conservancy wide variables as well as micro-habitat variables were created, including an accurate vegetation map, maps of soil characteristics, rainfall and temperature. Micro-habitat characteristics were also recorded within each of the sample sites. Diversity of the three study groups was related to specific micro-habitat variables. A Geographic Information Systems (GIS) model was created, predicting millipede, centipede and scorpion diversity in areas of the Conservancy not sampled. Three undescribed millipede and one centipede species were found and a new distribution record for a scorpion species was documented. These results emphasise the importance of invertebrate biodiversity studies in the savanna environment.