The nature of threat category changes in three Mediterranean biodiversity hotspots

Abstract

Step changes in threat category can be quantified and analyzed in relation to reasons for the change or threat intensity in Red List classifications. First, we studied the reasons contributing to changes in the conservation status of more than 2800 threatened plants in California, Spain, and Western Australia over a 10 year period. Second, we investigated the reported threats to these species and their association with particular step changes in the Red List categories. Results indicated that the reasons for step changes are varied and not necessarily linked to the types of threat processes affecting the species, nor actual conservation outcomes. In fact, increasing knowledge about a species from one listing date to the next is the most frequent cause of change in all studied territories, with all regions showing a general upgrading (more threatened) trend in threat category. Threats originating from human activities represent more than 80% of all threat types. The most frequently reported threats in California and Spain are related to population density, whereas in Western Australia threat types are modulated by human presence rather than human abundance. A strong relationship between increasing risk (upgrading in threat categories) and threats derived from human activities was found only for Spanish plants. Nevertheless, when conservation reasons are the cause for a category to change, they are associated with direct upgrading of species in Spain and Western Australia.