title: Opportunities drive the global distribution of protected areas.
abstract: BACKGROUND
  Protected areas, regarded today as a cornerstone of nature conservation, result from an array of multiple motivations and opportunities. We explored at global and regional levels the current distribution of protected areas along biophysical, human, and biological gradients, and assessed to what extent protection has pursued (i) a balanced representation of biophysical environments, (ii) a set of preferred conditions (biological, spiritual, economic, or geopolitical), or (iii) existing opportunities for conservation regardless of any representation or preference criteria.
  
  
  METHODS
  We used histograms to describe the distribution of terrestrial protected areas along biophysical, human, and biological independent gradients and linear and non-linear regression and correlation analyses to describe the sign, shape, and strength of the relationships. We used a random forest analysis to rank the importance of different variables related to conservation preferences and opportunity drivers, and an evenness metric to quantify representativeness.
  
  
  RESULTS
  We find that protection at a global level is primarily driven by the opportunities provided by isolation and a low population density (variable importance = 34.6 and 19.9, respectively). Preferences play a secondary role, with a bias towards tourism attractiveness and proximity to international borders (variable importance = 12.7 and 3.4, respectively). Opportunities shape protection strongly in "North America & Australia-NZ" and "Latin America & Caribbean," while the importance of the representativeness of biophysical environments is higher in "Sub-Saharan Africa" (1.3 times the average of other regions).
  
  
  CONCLUSIONS
  Environmental representativeness and biodiversity protection are top priorities in land conservation agendas. However, our results suggest that they have been minor players driving current protection at both global and regional levels. Attempts to increase their relevance will necessarily have to recognize the predominant opportunistic nature that the establishment of protected areas has had until present times.
authors.affiliation: Instituto de Matemática Aplicada San Luis, Universidad Nacional de San Luis & CONICET , San Luis , Argentina.
authors.forename: Germán
authors.initials: G
authors.lastname: Baldi
authors.affiliation: Departamento de Métodos Cuantitativos y Sistemas de Información, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina; Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Universidad de Buenos Aires & CONICET, Buenos Aires, Argentina.
authors.forename: Marcos
authors.initials: M
authors.lastname: Texeira
authors.affiliation: Instituto de Matemática Aplicada San Luis, Universidad Nacional de San Luis & CONICET , San Luis , Argentina.
authors.forename: Osvaldo A
authors.initials: OA
authors.lastname: Martin
authors.affiliation: Instituto de Ecología Regional, Universidad Nacional de Tucumán & CONICET , Horco Molle , Argentina.
authors.forename: H Ricardo
authors.initials: HR
authors.lastname: Grau
authors.affiliation: Instituto de Matemática Aplicada San Luis, Universidad Nacional de San Luis & CONICET , San Luis , Argentina.
authors.forename: Esteban G
authors.initials: EG
authors.lastname: Jobbágy
keywords: Conservation paradigms; National parks; Opportunity; Preferentiality; Protected areas; Representativeness