Lucía Gálvez-Bravo

Comments on Bartolino et al. (2011): limits of cumulative relative frequency distribution curves for hotspot identification

The recent paper by Bartolino et al. (Popul Ecol 53:351–359, 2011) presents a new method to objectively select hotspots using cumulative relative frequency distribution (CRFD) curves. This method is presented as being independent from the selection of any threshold and, therefore, less arbitrary than traditional approaches. We argue that this method, albeit mathematically sound, is based on likewise arbitrary decisions regarding threshold selection. Specifically, the use of the CRFD curve approach requires the occurrence of two criteria for the method to be applied correctly: the selection of a 45° tangent to the curve, and the need to consider the highest relative value of the study parameter corresponding to a 45° slope tangent to the curve. Using two case studies (dealing with species richness and abundance of a particular species), we demonstrate that these two criteria are really unrelated to the underlying causes that shape the spatial pattern of the phenomena under study, but rather related to sampling design and spatial scale; hence, one could likewise use different but valid criteria. Consequently, the CRFD curve approach is based on the selection of a pre-defined threshold that has little, if any, ecological justification, and that heavily influences the final hotspot selection. Therefore, we conclude that the CRFD curve approach itself is not necessarily better and more objective than any of the global methods typically used for hotspot identification. Indeed, mathematical and/or statistical approaches should not be viewed as a panacea to solve conservation problems, but rather used in combination with biological, practical, economic and social considerations.

Contrasting feeding patterns of native red deer and two exotic ungulates in a Mediterranean ecosystem

Abstract Context. Ungulates have been widely introduced in multiple ecosystems throughout the world due to their value as food and for sport hunting. The identification of foraging preferences of exotic and native ungulates living in sympatry is, therefore, becoming increasingly important in order to assess potential impacts of introduced animals on the host ecosystem. Aims. To describe species-specific foraging strategies and infer resource selection overlap between native and exotic ungulates. Methods. We compared the trophic ecology of three sympatric ungulate species living in a Mediterranean landscape: the native Iberian red deer Cervus elaphus hispanicus, and two exotic bovids, the European mouflon Ovis orientalis musimon and the aoudad Ammotragus lervia. We simultaneously determined herbivore diet through analyses of botanical content in faeces and assessed the nutritional content of these diets. Key results. Higher selection of shrubs by deer was sustained throughout the year, while bovids showed seasonal shifts in forage selection. Both bovids displayed a selective dietary strategy directed towards a higher overall nutritional quality than that of deer. Divergent exploitation patterns between the studied cervid and bovids might be related to body mass and physiological adaptations to overcome secondary defence compounds of shrubs, and were largely affected by seasonal changes in the nutritional value of available vegetation. Ecological theory suggests that diet overlap should be greater between similar-sized species. Indeed, both exotics showed similar, sometimes overlapping, dietary patterns that could lead to potential competition in the use of resources. Native red deer preferences only showed some overlap with those of exotic mouflon under constrained summer conditions. Conclusions. Dietary overlap between deer and mouflon and between aoudad and mouflon during limiting summer conditions could entail a potential competitive interaction under more even densities of the study species, since a concurrent habitat overlap between those pairs of species has previously been reported. Implications. The outcomes of our study suggest the need for an integration of habitat and ungulate management. Management actions in Mediterranean rangelands should be directed towards protecting habitat conditions so that biodiversity is enhanced along with the presence of sustainable communities of large herbivores. Management directed towards ungulates should maintain moderate stocking rates and monitor and control introduced and native populations.