Climate change versus biotic interaction: a case study of large mammal faunal complexes on the Italian Peninsula from the Pliocene to the Late Pleistocene. New methodological approaches

Changes in mammal faunal complexes over time have often been considered the result of bioevents linked to major climatic changes though some authors claimed that environmental factors such as impacts, eruptions, and climatic change have a minimal effect, and intrinsic biotic controls may be essential in affecting taxonomic diversity and changing community structure. To contribute to the debate, Italian faunal complexes (FCs) have been analysed in order to correlate diversity trends and structural dynamics with the extensive Middle Pliocene to Late Pleistocene environmental changes. Three main aspects have been considered for exploring the palaeoclimatic significance of faunal evolutionary changes: shifts in diversity; shifts in origination/immigration and extinction rates (turnover, dispersal, extinction phases); shifts in relative abundance of ecological categories defined herein. Two major structural reconstructions occurred in the FCs at the early/middle Villafranchian transition (from the Middle to the Late Pliocene, around 2.6 Ma) and from the early to middle Galerian (from the Early to the Middle Pleistocene, i.e., from about 1.2 to 0.7 Ma). The Villafranchian turnover phase corresponds to the Middle Pliocene climate deterioration, and can be considered a starting point for the Late Pliocene dispersal phases. The Early to Middle Pleistocene turnover represents the major reorganization (dispersal and successive turnover) in the large mammal complexes of the Italian peninsula, and occurred in successive phases during the period of palaeoenvironmental changes at the onset of 100 ka climate cyclicity. Accordingly, the results of this study confirm that the most important renewals in the Italian large mammalian faunas (due both to originations/immigrations and extinctions) are connected to major global climatic changes. Nonetheless, there is no or minor evidence of cyclical, climatically-driven turnovers matching “glacial/interglacial” alternations. The Late Villafranchian (latest Pliocene and Early Pleistocene partim) and middle/late Galerian FCs (early Middle Pleistocene), for instance, present only minor phyletic adjustments and their evolutionary patterns support a model of protracted minor faunal change which seems driven by more complex forcing factors rather than climate alone. All in all, patterns of Italian faunal complexes indicate that climatic changes act in driving faunal structural changes in a rather complex way and intrinsic biotic controls may also be essential in determining faunal complex evolution: major climate change (changes of climate cyclicity), via migrations and dispersal events, allowed diversity to increase and altered palaeocommunity equilibria, leading to new intra- and inter-guild dynamics. The new internal competition caused the disappearances of some species through time and led to a new equilibrium within reconstructed FCs. The results obtained indicate that, at least in Italy, climatic changes are a forcing factor, especially in large mammal first appearances, whereas the global reconstruction of the structure of the FCs has been also influenced by the internal dynamics, not necessarily predicting strict dependence on major climatic changes.