Range Size and Body Size Variation in Afrotropical Montane Millipedes: Test of Ecogeographical Rules

Several environmental factors influence geographic variation in body size, range size, and distribution of animals along an altitudinal gradient. In this study, we investigated the effects of altitude and temperature on two morphometric characteristics: body length and trunk width. We evaluated also the species distribution and tested several ecogeographical rules in millipede populations collected across three elevation bands (0–400 m, 401–800 m, and 801–1200 m above sea level). Our results revealed a negative correlation between temperature and altitude, with mean body length and mean trunk width of millipede populations exhibiting an increase from lower to higher altitudes, both of which were negatively correlated with temperature. Additionally, many specialist species occurred at higher elevations while generalist species had a broader distribution range. Species richness increased from lower elevations to mid-elevations and peaked at higher elevations. These patterns underscore that both body size and range size increase with elevation, thereby supporting Bergmann and Stevens rules. However, species richness exhibited a more monotonic increase pattern due to higher human activities found at different elevations. These findings suggest that millipede range size and body size are strongly influenced by a complex interplay of biological and environmental factors along elevational gradients within afrotropical montane ecosystems.