The role of demography and grazing in the patterns of endangerment of threatened plants

Abstract

This study explores the effect of two types of threat on a group of rare plants at risk of extinction in Spain, distributed across altitudinal and latitudinal gradients, under a scenario of rapid changes in land use. On the one hand, we focused on livestock herbivory as one source of risk for these plants, also taking into account factors such as altitude and the protection status of the area. On the other hand, we explored a threat which has been little documented so far, namely, rapid changes of the dynamics of plant communities.

Field data from 54 populations of 37 different threatened plant species were analyzed using contingency tables and linear models (ANCOVA and GLM) to study the effect of livestock and herbivory. In addition, we used an asymmetry index of population structure to look for deviations and asynchronies with respect to general vegetation dynamics.

Our results point to an overestimation of grazing as a threat to these plants, its effect having declined as a result of rapid changes in land use. Altitude was found to provide a dual conservation shield, preventing grazing for different reasons. Hence, we recommend that herbivory to threatened plants should be reported by accurately quantifying individual losses and damage. We found no relationship between population structure and plant conservation status. In addition, we detected no asynchronies between threatened plant population structure and community dynamics.

New indicators related to size and distance between populations as well as density distribution within patches should be explored.

En el artículo mostramos, entre otras cosas, como la amenaza del ganado (doméstico y silvestre) sobre las plantas en peligro de extinción ha podido ser sobrevalorada en España, puesto que en las plantas incluidas en el artículo, todas con una alta categoría de amenaza, el ganado no tiene un efecto negativo determinante. Además, la estructura poblacional de dichas plantas no es indicadora de problemas demográficos, y sugerimos otras formas de descubrir cuál es el estado real de conservación cuando de plantas amenazadas se trata.