Showing papers by "Pasquale Raia published in 2007"

Effect of predation on prey abundance and survival in Plio-Pleistocene mammalian communities

Abstract: Question: Does predatory pressure affect the abundance and survival of prey species in extinct communities? Data studied: Presence–absence data and body sizes of large mammals (partitioned into predators and prey) in Plio-Pleistocene Italian PaleoCommunities (PCOMs). Transformed variables: (1) Species’ occupancy: number of presences/number of sites. (2) ADI: the index of disparity (ADI) reflects the relative abundance of a prey species in a PCOM. (3) Predatory pressure on a prey species: the proportion of predators in a given PCOM that are expected to feed on it. (4) Nestedness: the extent to which rare species occur only in the species-rich sites of a PCOM. Search method: For each PCOM, the effect of preservation biases on species’ occupancy was assessed by a nestedness analysis. The ADI was computed for each prey species in each PCOM. Predatory pressure was calculated for each prey species. We used linear regression to test the effect of predatory pressure on ADI. Non-parametric correlation was performed to determine the effect of ADI on species survival. Results: Species prone to greater pressure appear at fewer sites than would be expected for their size alone. The relationship is limited to rare species only. Taphonomy does not explain this disparity. Abundant species survive longer than rare species. Conclusion: Predation controls abundance and local survival of rare species. In contrast, it does not affect abundant species.

Fractal analysis of ostracod shell variability: A comparison with geometric and classic morphometrics

Abstract: Aiello, G., Barattolo, F., Barra, D., Fiorito, G., Mazzarella, A., Raia, P., and Viola, R. 2007. Fractal analysis of ostracod shell variability: A comparison with geometric and classic morphometrics. Acta Palaeontologica Polonica 52 (3): 563–573. Two statistical methods, fractal geometry and geometric morphometrics, are tested for their applicability to ostracod sys− tematics. For this comparison, two morphologically similar ostracod species (Krithe compressa and Krithe iniqua) whose genus−level systematics is still incompletely resolved, are selected. Twenty−nine right valves of each species were col− lected from the upper Pliocene samples at the Monte San Nicola section in southern Italy. Statistical analyses (MANOVA on morphometric shape variables, and D values) were utilized to test if geometric morphometrics and fractal analysis are appropriate into discriminating between the two species. Both methods succeeded in distinguishing the species statisti− cally. The fractal analysis of the two ostracod species shows D values centered on 1.31±0.02 for Krithe iniqua and on 1.40±0.02 for Krithe compressa. Geometric morphometric analysis indicates significant differences between the two spe− cies and allows studying intra−populational variability as well as. The most variable traits indicated by geometric morpho− metrics are vestibular area and posterior outline of the shell, indicating that these traits are the most relevant for the sys− tematics of the species analyzed. Both fractal geometry and geometric morphometrics provide a measure of population variability. Fractal analysis has the advantage of being free from any subjectivity in the selection of characters and could be most appropriate to use for analysis of complex ornamentation for systematic purposes. However, a possible advantage of geometric morphometrics over fractal analysis is its ability to indicate where statistically significant variations in shape occur on the shell.