Biodiversity across a Rural Land-Use Gradient

Private lands in the American West are undergoing a land-use conversion from agriculture to ex- urban development, although little is known about the ecological consequences of this change. Some nongov- ernmental organizations are working with ranchers to keep their lands out of development and in ranching, ostensibly because they believe biodiversity is better protected on ranches than on exurban developments. However, there are several assumptions underlying this approach that have not been tested. To better inform conservation efforts, we compared avian, mesopredator, and plant communities across the gradient of inten- sifying human uses from nature reserves to cattle ranches to exurban developments. We conducted surveys at randomly selected points on each type of land use in one Colorado watershed between May and August of 2000 and 2001. Seven bird species, characterized as human commensals or tree nesters, reached higher den- sities (all p � 0.02) on exurban developments than on either ranches or reserves. Six bird species, character- ized as ground and shrub nesters, reached greater densities (all p � 0.015) on ranches, reserves, or both of these types of land use than on exurban developments. Domestic dogs ( Canis familiaris ) and house cats ( Felis catus ) were encountered almost exclusively on exurban developments, whereas coyotes ( Canis latrans ) were detected more frequently ( p � 0.047) on ranchlands than exurban developments. Ranches had plant com- munities with higher native species richness and lower non-native species richness and cover than did the other types of land use (all p � 0.10). Our results support the notion that ranches are important for protect- ing biodiversity and suggest that future conservation efforts may require less reliance on reserves and a greater focus on private lands. Biodiversidad a lo largo de un Gradiente de Uso de Suelo Rural Resumen: Los terrenos privados del oeste de America estan experimentando una conversion del suelo de un uso agricola a un uso urbano, aunque se conoce poco acerca de las consecuencias ecologicas de este cambio. Algunas organizaciones no gubernamentales estan trabajando con granjeros para que sus tierras permanez- can sin urbanizar, ostensiblemente porque piensan que la biodiversidad se protege mejor en tierras rurales que en urbanizaciones. Sin embargo, hay varios supuestos subyacentes a este modelo que no han sido com- probadas. Para informarnos mejor sobre los esfuerzos de conservacion, comparamos comunidades de aves, mesodepredadores y plantas a lo largo del gradiente de intensidad de uso humano de reservas naturales, granjas y zonas de urbanizacion. Realizamos muestreos en sitios seleccionados aleatoriamente en cada uso de suelo en una cuenca del Colorado entre mayo y agosto de 2000 y 2001. Siete especies de aves, caracteriza- das como comensales humanos o nidificantes arboreos, alcanzaron densidades mas altas (todas p � 0.02) en urbanizaciones nuevas que en granjas o reservas. Seis especies de aves, caracterizadas como nidificantes de suelo y arbustos, alcanzaron densidades mayores (todas p � 0.015) en granjas, reservas o usos mixtos del suelo que en las nuevas urbanizaciones. Se encontraron perros ( Canis familiaris ) y gatos ( Felis catus ) domes- ticos casi exclusivamente en nuevas urbanizaciones, mientras que se detectaron coyotes ( Canis latrans ) mas frecuentemente ( p � 0.047) en granjas que en nuevas urbanizaciones. Las granjas tenian comunidades de plantas con mayor riqueza de especies nativas y menor riqueza y cobertura de especies no nativas que en to- dos los demas usos de suelo (todas p � 0.10). Nuestros resultados apoyan la nocion de que las granjas son im-