Abstract
Efficient allocation of conservation resources will be achieved only if the priorities for biodiversity conservation are correctly defined. Area, energy available and latitude are thought to be the most important determinants of species richness.
Area is clearly the most important, but the relative importance of the other two is uncertain. To test the relative importance of energy available and latitude, data on the species richness of orchids was collected for 67 countries from 5 continents, the influence of area factored out and the residuals correlated with energy available and with latitude.
We show that area is always very important, latitude is more important than energy available and the size of the protected areas gives a better fit than the total area of the country. This implies that conservation efforts should be directed to maximizing the size of the protected areas in each country.