Relations between species rarity, vulnerability, and range contraction for a beetle group in a densely populated region in the Mediterranean biodiversity hotspot

A Bayesian-weighted approach to predicting the number of newly discovered rare species

In natural ecological communities, most species are rare and thus susceptible to extinction. Consequently, the prediction and identification of rare species are of enormous value for conservation purposes. How many newly found species will be rare in the next field survey? We took a Bayesian viewpoint and used observed species abundance information in an ecological sample to develop an accurate way to estimate the number of new rare species (e.g., singletons, doubletons, and tripletons) in an additional unknown sample. A similar method has been developed for incidence-based data sets. Five seminumerical tests (3 abundance cases and 2 incidence cases) showed that our proposed Bayesian-weight estimator accurately predicted the number of new rare species with low relative bias and low relative root mean squared error and, accordingly, high accuracy. Finally, we applied the proposed estimator to 6 conservation-directed empirical data sets (3 abundance cases and 3 incidence cases) and found the prediction of new rare species was quite accurate; the 95% CI covered the true observed value very well in most cases. Our estimator performed similarly to or better than an unweighted estimator derived from Chao et al. and performed consistently better than the naïve unweighted estimator. We recommend our Bayesian-weight estimator for conservation applications, although the unweighted estimator of Chao et al. may be better under some circumstances. We provide an R package RSE (rare species estimation) at https://github.com/ecomol/RSE for implementation of the estimators.

Uncovering environmental, land-use and fire effects on the distribution of a low-dispersal species, the Hermann’s tortoise Testudo hermanni

Habitat destruction has resulted in the fragmented distribution of numerous terrestrial species, which poses a challenge for conservationists. Furthermore, species management can be further compounded by life history constraints such as low dispersal, hindering the ability of species to recolonize areas they formerly occupied. For these species, a thorough understanding of the local threats and factors that limit their distribution is crucial for effective management. We used occupancy models to examine which factors at landscape and habitat scales (i.e. land uses, fire history, and vegetation structure) explain the presence of terrestrial tortoises within the range of the westernmost isolated population of the endangeredTestudo hermanni hermanniin the Albera Range (NE of the Iberian Peninsula). We randomly surveyed 25 sites (75% of the area known with presence of tortoises) of natural woodlands with 5 to 8 replicates per site in spring 2012-2014. From a sampling effort of 148 hours, we only detected 52 tortoises in 12 of 25 transects. These low numbers are evidence of low population densities. Sites with presence of tortoises were spatially aggregated although the species was absent from apparently adequate sites on the edges of its distribution range. Current and historic land-use primarily explained the presence of tortoises. Besides, wildfires and reduction of habitat complexity also participate to explain the distribution of Hermann’s tortoises. We also discuss some aspects of the conservation ofTestudo hermanniin relation to our results.