Amphibian body size and species richness as a proxy for primary productivity and climate: The Orce wetlands (Early Pleistocene, Guadix-Baza Basin, SE Spain)

Abstract

Amphibians are considered excellent indicators of ecological and climatic changes with a remarkable phenotypic plasticity. The study of such adaptative capacities is central to understanding the climate and environmental changes that occurred during the Early-Middle Pleistocene Transition, at around 1.2 Ma, when the persistence of subtropical ecosystems in Europe came to an end, and several reptile and tree taxa were extirpated. The SE Spain sites in the Guadix-Baza Basin offer an exceptional opportunity for studying this change, in addition to the significant findings made in this area in the field of human evolution. We have analysed the body size of the most well-represented amphibian species in the sites, the Iberian waterfrog, Pelophylax perezi . In order to reconstruct past body sizes from fossil samples, a regression model from current osteological collections has been generated. Also, diversity of the herpetofauna community was studied at different levels as richness or species number. Finally, to study the relationships between body size, richness, climate and productivity, OLS regression models and Pearson correlations were applied. Also for this purpose, a productivity indicator was designed based on the addition of the two most productive ecosystems from previous habitat reconstruction. Amphibian body size appears to be negatively associated with primary productivity, reaching minimum values during the interglacial stages, when species richness increased. In contrast, during glacial periods characterised by greater aridity and fewer resources, amphibian body size increased while species richness decreased. Main explanations proposed to justify this pattern are the “water-availability hypothesis” and a trade-off between somatic growth and reproductive opportunities for females. The study of herpetofaunal diversity shows a clear correlation to regional plant diversity and primary productivity. The results of this work indicate that species richness and amphibian body size are valuable proxies that can complement current environmental and climate reconstruction methods. • Somatic growth and reproduction: the trade-off which determines amphibian body size. • Amphibian body size decreases towards more productive ecosystems. • Primary productivity determines species richness. • Frog body size is defined as a new indicator of Pleistocene ecosystem conditions.