Paleoecology and the Coarse-Filter Approach to Maintaining Biological Diversity

: The difficulties of saving millions of species from extinction often cause conservationists to focus on a higher level of biological organization, the community. They do so for two reasons: (1) communities are considered important biological entities in their own right; and (2) conserving representative samples of communities is seen as an efficient way to maintain high levels of species diversity. This approach will work if the chosen communities contain almost all species. Because it potentially saves most but not all species, community conservation is a “coarse-filter” approach to the maintenance of biological diversity, and contrasts with the “fine-filter” approach of saving individual species. Paleoecological information on the distribution of plant taxa in North America, however, indicates that most modern plant communities are less than 8,000 years old and therefore are not highly organized units reflecting long-term co-evolution among species. Rather, they are only transitory assemblages or co-occurrences among plant taxa that have changed in abundance, distribution, and association in response to the large climate changes of the past 20,000 years. During periods when climate changes are large, communities are too ephemeral to be considered important biological entities in their own right. Large climatic changes are also likely to occur during the next century because of increased concentrations of CO2, and we therefore propose that the coarse-filter approach to selecting nature reserves should be more strongly influenced by the distribution of physical environments than by the distribution of modern communities. Ideally, nature reserves should also encompass a broad enough range of environments to allow organisms to adjust their local distribution in response to long-term environmental change and should be connected by regional corridors that would allow species to change their geographic distributions. Resumen: Las dificultades en salvar millones de especies de extincion muchas veces lleva a los conservacionistas a enfocarse a un nivel mas alto de organizacion biologica: la comunidad. Ellos lo hacen por dos razones: 1. las communidades son consideradas entidades biologicas importantes en su derecho, y 2. conservando ejemplos representativos de las communidades se considera manera eficiente de mantener niveles altos de diversidad de especies. Esta aproximacion aproche trabaja si las comunidades escogidas contienen casi todas las especies. Al salvar potencialmente la mayoria, pero no todas las especies, la conservacion de comunidades es solo una aproximacion gruesa para el mantenimiento de la diversidad biologica, y contrasta con la mayor resolucion que representa el de salvar especies individuales. Sin embargo, informacion paleoecologico sobre la distribucion de la taxonomia de plantas en Norte America indica que las comunidades mas modernas de plantas tienen menos de 8,000 anos y por eso no son unidades bien organizadas reflejando coevolucion de largo plazo entre las especies. Mas bien, son ensamblajes transitorios o concurrentes entre la taxonomia de plantas que ban cambiado su abundancia, distribucion y asociacion en respuesta a cambios grandes climaticos de los ultimos 20,000 anos. Durante periodos cuando los cambios de clima son grandes, comunidades son muy efimeras para considerarse entidades biologicos importantes Cambios grandes climaticos tambienson probables durante el proximo siglo por las concentraciones crecientes de CO2, y nosotros, por esta razon proponemos que la aproximucion gruesa de seleccionar reservas de la naturaleza debe ser mas influenciada por la distribucion de ambientes fisicos que por la distribucion de comunidades modernas. Idealmente, las reservas de la naturaleza tambien deben considerar un rango suficientemente amplio de ambientes diferentes para permitir a los organismos a ajustar su distribucion local en respuesta a cambios ambientales de largo plazo. Asi mismo las reservas deben, en lo posible, formar corredores regionales que permitan a las especies cambiar su distribucion geograficas.