Opportunities drive the global distribution of protected areas

Background. The establishment of protected areas, regarded today as a cornerstone of nature conservation, resulted from a multiple array of motivations and opportunities. We explore at global and regional levels, the current distribution of protected areas along biophysical, human, and biological gradients, and assess to what extent protection pursued (i) a balanced representation of biophysical environments, (ii) a set of preferred conditions (biological, spiritual, economical, or geopolitical) or (iii) lands where conservation opportunities exist. Methods. We described with histograms the distribution of terrestrial protected areas along physical, human, and biological independent gradients. Linear and non-linear regressions and correlations led to a general description of sign, shape, and strength of the relationships; a random forest analysis led to a importance ranking of the variables related to individual preferential motivations and opportunistic forces; and an evenness metric seized the strength of variables related to individual representative motivations. Results. We found that globally protection was primarily driven by the opportunities provided by isolation and a low population density (variable importance = 34.6 and 19.9, respectively). Preferences played a secondary role, with a bias towards tourist attractions and international borders (variable importance = 12.7 and 3.4, respectively). Opportunities shaped protection strongly in North America & Australia–NZ and Latin America & Caribbean, while the representativeness of biophysical environments was higher in Sub-Saharan Africa (1.3 times the average of other regions). Discussion. Our results suggest that in spite of being a top priority in land conservation agendas, environmental representativeness and biodiversity protection are still minor players driving protection at global and regional levels, and that the attempts to increase their relevance will necessarily have to recognize the predominant weight that other drivers are playing in the protected areas deployment.