NULL MODELS FOR ASSESSING ECOSYSTEM CONSERVATION PRIORITIES - THREATENED BIRDS AS TITERS OF THREATENED ECOSYSTEMS IN SOUTH-AMERICA

We set ecosystem conservation priorities based on a comparison of obse rved levels of threat and protection versus expected levels derived fr om the use of null models. We used differences in the proportion of th reatened and nonthreatened bird species among ecosystems to assess lev els of threat and differences in the coverage of parks and protected a reas relative to land area to assess levels of protection. We applied this approach to terrestrial biomes of continental South America and d etermined where recommendations for species and ecosystem conservation converge and diverge. We calculated the percentage of range in each b iome for 132 bird species threatened by habitat destruction and 288 no nthreatened bird species. Three biomes (evergreen forest, broadleaf fo rest, and cold desert) were not included because few bird ranges fell primarily within them. Tropical humid forest and mountain biomes suppo rted the greatest levels of avian species diversity. But only subtropi cal and temperate rainforests and tropical dry forests supported a hig her proportion of threatened bird species than expected, making them e cosystem destruction hotspots. Tropical humid forests and tropical and temperate grasslands supported lesser proportions of threatened bird species than expected (i.e., coldspots), whereas mountain and warm des erts supported similar proportions of threatened and nonthreatened bir d species (i.e., neutral). These patterns were corroborated by the app ortionment of human population densities among biomes. Highest densiti es (>25 per km(2)) occurred in subtropical and temperate rainforests a nd tropical dry forests, whereas tropical humid forests and warm deser ts supported the lowest human densities (<1 per km(2)). The largest pr oportions of protected areas were in tropical humid forest and mountai n biomes, which is in accord with the distribution of avian diversity but not with our assessment of habitat destruction. Protected areas we re especially underrepresented in tropical dry forests, making them th e most threatened biome.