Detecting changes in diversity in a fluctuating environment based on simulation of stochastic processes

In this paper, I present a method developed to detect 'extra', or novel, changes in diversity in a naturally fluctuating environment. When comparing samples in order to evaluate changes in community structure, the sampling procedure will inevitably induce randomness in observed species composition and abundance, so two samples may show considerable differences, even if they come from exactly the same community. Sometimes the effort put into the sampling varies as well, leading to the expectation of a further increase in difference. Finally, if there were a temporal distance between the samples, we would like to correct for variations in species abundance occurring naturally due to fluctuating environmental conditions. The test method presented here includes a model of the sampling procedure, and corrects for differential sampling efforts. The population dynamics is modelled by a diffusion process, its variance mimicking the effect a fluctuating environment has on species abundances. We are thereby able to test the null hypothesis of no unnatural change in diversity, against the alternative of additional changes in community structure due to for example human disturbances.Cet article décrit une méthode pour détecter les changements de diversité dans un environnement fluctuant. Dans la comparaison d’échantillons pour évaluer les changements de structure de la communauté, l’échantillonnage induit inévitablement du « hasard » dans la composition des espèces et de leur abondance. Deux échantillons peuvent présenter de fortes différences même s’ils proviennent de la même communauté. Parfois, l’effort déployé dans l’échantillonnage varie également, ce qui conduit à attendre un nouvel accroissement des différences. Finalement, en cas d’intervalle de temps suffisant entre les échantillons, nous proposons de corriger les données des variations d’abondance des espèces dans ces conditions environnementales fluctuantes. La méthode inclut un modèle de méthodologie d’échantillonnage et corrige les différences dans l’effort d’échantillonnage. La dynamique des populations est modélisée par un processus de diffusion, sa variance simulant l’effet d’un environnement fluctuant sur l’abondance spécifique. Nous sommes à même de tester l’hypothèse nulle d’un changement de diversité qui ne serait pas naturel, en face de changements additionnels hypothétiques de la structure de la communauté dus, par exemple, à l’action humaine

Exceptional invertebrate diversity in a scree slope in Eastern Spain

© 2015, Springer International Publishing Switzerland. In this study, the invertebrate fauna of a colluvial Mesovoid Shallow Substratum (MSS) is Eastern Spain was characterized, and the importance of the MSS as refuge for endemic and rare species was assessed. Ten pitfall traps were buried up to 1 m deep inside multiperforated PVC tubes across a stone debris. Several environmental variables were measured in each sampling point. The completeness of the inventory was assessed, and different diversity patterns—variation in abundance, species richness and species composition—were analyzed. 4150 individuals and 164 species were captured, most of them arthropods. The number of individuals and species varied considerably among traps. Half of the species were represented by one or two individuals, and neither the species accumulation curves nor the curves for the non-parametric estimators showed any sign of stabilizing. Individuals of abundant species aggregated in one or a few traps. No consistent diversity patterns were found, except that distance among traps partially explained the similarity in species composition when considering only the most abundant species. This is a very rich but uneven assemblage that shows a high degree of species turnover between traps. One-sixth of the species can be classified as either troglobionts or troglophiles, but there is a significant presence of edaphic species. Obtaining complete fauna inventories in the MSS has proven to be a challenging task. The study of the MSS reveals important faunistic information, providing new taxa to science as well as interesting records of poorly known species.This research Project (CGL2010-19924) was funded by the Spanish Ministry of Science and Innovation. A. J.-V. was supported by the CSIC JAE-Doc Program which is partially financed by the European Social Fund.Peer Reviewe