Carmela Barbera

The fast life of a dwarfed giant

In the first half of the 1960s, a rich paleontological site was discovered at Spinagallo caves (Eastern Sicily, Southern Italy). A very abundant fossil population (at least 104 specimens) of the dwarf elephant Elephas falconeri, the smallest elephant that ever lived, was recovered. We computed the survivorship curve for this fossil population in order to investigate both the great juvenile abundance and high calf mortality which it shows. Through the analysis of E. falconeri survivorship, of some reconstructed life-history traits, and of its ecology, and taking into account the Island rule (Foster, 1964), we concluded that E. falconeri moved somewhat toward the ‘fast’ extreme of the slow-fast continuum in life-history traits in regards to its mainland ancestor E. antiquus, that is, it was somehow r-selected. In keeping with our findings, we propose a new explanation for the common occurrence of dwarfism in large mammals living on islands. We suggest the interplay of competition, resource allocation shift and feeding niche width could successfully explain this pattern.

Occupancy, range size, and phylogeny in Eurasian Pliocene to Recent large mammals

Abstract Temporal patterns in species occupancy and geographic range size are a major topic in evolutionary ecology research. Here we investigate these patterns in Pliocene to Recent large mammal species and genera in Western Eurasia. By using an extensively sampled fossil record including some 700 fossil localities, we found occupancy and range size trajectories over time to be predominantly peaked among both species and genera, meaning that occupancy and range size reached their maxima midway along taxon existence. These metrics are strongly correlated with each other and to body size, after phylogeny is accounted for by using two different phylogenetic topologies for both species and genera. Phylogenetic signal is strong in body size, and weaker but significant in both occupancy and range size mean values among genera, indicating that these variables are heritable. The intensity of phylogenetic signal is much weaker and often not significant at the species level. This suggests that within genera, occupancy and range size are somewhat variable. However, sister taxa inherit geographic position (the center of their geographic distribution). Taken together, the latter two results indicate that sister species occupy similar positions on the earths surface, and that the expansion of the geographic range during the existence of a given genus is driven by range expansion of one or more of the species it includes, rather than simply being the summation of these species ranges.

Species accumulation over space and time in European Plio-Holocene mammals

The rate of increase in species number with sampled area is one issue of major interest in ecology. Species number increases with sampled time as well, though this kind of analysis is much rarer in literature. Species-area and species-time relationships have been recently integrated in a single model, which allows studying how time and area interact with each other in determining the cumulative increase in species richness. Here we studied species-area, species-time, and species-time-area relationships in Plio-Holocene large mammals of Western Eurasia, by using an extensive database including 184 species distributed in 685 fossil sites. We found that the increase of species number with time is much higher than with area. When sampling inequality of fossil localities in time and space is accounted for, time and area interact with each other in a negative, though non-linear fashion. The intense climatic changes that characterized the Plio-Holocene period apparently affected both species-area and species-time relationships in large mammals, by increasing the slope of the former during the Pliocene and middle Pleistocene, and of the latter during younger, climatically harsher, late Pleistocene times. This study emphasizes the importance of accounting for time and space in tracing paleodiversity curves.