Morphospace disparity and species diversity in Sri Lankan phytophagous scarab beetles—A comparison by forest types, altitude and sites

Abstract Species diversity and morphological disparity are often linked, especially in lineages with evolutionary success. For invertebrates, their relation is poorly investigated, particularly under various ecochorological scales. Here, we explore thirteen assemblages of phytophagous scarab beetles (Coleoptera: Scarabaeidae) in Sri Lanka and infer patterns of morphospace and species diversity along forest types, elevation zones and sampling sites. Disparity of body size and shape was analysed based on 20 linear measurements, considering separately three major lineages: the entire assemblage and their two sister subclades, Sericini and Pleurosticts excluding Sericini. Diversity and disparity were investigated in three sets of landscape partitioning, from regional to local scale: forest type, elevation zone and locality. Results showed divergent patterns of lineages at different geographical scales. Morphospace divergence and occupancy exhibited two distinct patterns. For the entire assemblage and Pleurosticts excluding Sericini, the morphospace volume expressed by median centroid size decreased with increasing altitude. In contrast, Sericini demonstrated a more confined morphospace across different forest types and elevation zones. However, similar patterns were not found for the Shannon diversity. Disparity of morphological shape was significantly correlated with species diversity in all three chorological categories only for the entire assemblage, while in Sericini this correlation was recovered only at locality‐scale. Our results indicate that small changes in diversity are linked to small alterations in disparity, although significant shifts in diversity do not necessarily correspond to substantial disparity change. Future research exploring the genealogical aspect of morphospace divergence should incorporate a phylogenetic framework, especially when comparing different systematic levels.