Abstract
The reconstruction of deep-time diversity trends is key to understanding current and future species richness. Studies that statistically evaluate potential factors affecting paleodiversity have focused on continental and global, clade-wide datasets, and thus we ignore how community species richness build-up to generate large-scale patterns over geological timescales. If community diversity is shaped by biotic interactions and continental and global diversities are governed by abiotic events, which are the modulators of diversity in subcontinental regions? To address this question, we model Iberian mammalian species richness over 13 million years (15 to 2 Ma) using exhaustive fossil evidence for subcontinental species’ ecomorphology, environmental context, and biogeographic affinities, and quantitatively evaluate their impact on species richness. We find that the diversity of large Iberian mammals has been limited over time, with species richness showing marked fluctuations, undergoing substantial depletions as diversity surpasses a critical limit where a significant part of the niches is unviable. The strength of such diversity-dependence has also shifted. Large faunal dispersals and environmental heterogeneity increased the system’s critical diversity limit. Diversity growth rate (net migration and diversification) also oscillated, mainly modulated by functional saturation, patchiness of canopy cover, and local temperature and aridity. Our study provides quantitative support for subcontinental species pools being complex and dynamic systems where diversity is perpetually imbalanced over geological timescales. Subcontinental diversity-dependence dynamics are mainly modulated by a multi-scale interplay of biotic and abiotic factors, with abiotic factors playing a more relevant role.
Highlights
Because unveiling past diversification processes is fundamental to understanding current and future diversity patterns[1,2,3], the study of deep-time diversity trends —and its drivers and limiters— is a major task in paleobiology and macroecology
Models derived from the TRiPS diversity curve are more clearly discriminated according to their fit
Saw-like diversity profiles like these are common in paleontological literature and have been used to argue in favor of unbounded diversity dynamics[22]
Summary
We use two different methods for estimating biodiversity through time while controlling for sampling: a maximum likelihood method (True Richness estimated using a Poisson Sampling, or TRiPS23), and a subsampling method (the Shareholder Quorum Subsampling method, or SQS24) (see supplementary methods and Fig. S1). In TRiPS-derived models the similarity of Iberian faunas with those from Europe and the Middle East (EME) appears as the main factor controlling K (73% of the support) followed by changes in the canopy cover, based on δ13C isotopes (11%; Fig. 3A,D). According to the TRiPS-derived models, the isolation of Iberian faunas from the EME region translates into a smaller carrying capacity and less precited diversity than expected under the pure DD scenarios where K is constant (Fig. 3). The rate of species accumulation (diversity growth, DG) in EME-modulated K models is slower than expected when diversity is low (Fig. 3D) These findings indicate that during geographic isolation and higher endemism, the Iberian mammalian faunas were not as rich as the system would have allowed, with local speciation never contributing to the species packing as dispersals from the main continent did. Did African connections increase Iberian diversity limit beyond
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