El rompecabezas de las extinciones

Con seis mil millones de seres humanos y que siguen aumentando, como también nuestro consumo individual, afrontamos dificultades enormes con vistas a la utilización sostenible de nuestros recursos naturales y disponemos de una medida clara de nuestro desempeño en relación con esa tarea: las tasas de extinciones. Por esa razón, algunos colegas y yo hemos calculado la tasa de extinción de especies de aves habidas en el pasado reciente y la que probablemente habrá en el futuro.

Las extinciones de aves son la mejor ventana por la que observar las repercusiones medioambientales irreversibles y en gran escala provocadas por la Humanidad. Por cada una de las 10.000 especies de aves del mundo, puede haber diez o incluso tal vez cien especies desconocidas más de animales, plantas u hongos. Gracias a su popularidad, las aves brindan una fuente inigualable de información sobre las especies que viven en lugares determinados y sobre cómo les va.

Los cálculos aproximados del numero de extinciones han solido variar mucho por las diferencias en el hipotético número total de especies, que oscila entre un millón de especies que tienen nombres científicos y un poco probable cálculo por lo alto de cien millones de especies. Para evitar esas incertidumbres, mis colegas y yo introdujimos la tasa de extinciones: el número de extinciones por año y por especie o, para que los números fueran menos elevados, de extinciones por millón de años y por especie (E/MSY). Exceptuados los cincos episodios de extinciones en gran escala del pasado, los cálculos aproximados que se desprenden de los registros de fósiles indican que una tasa de fondo aproximada es una extinción por millón de años y por especie (1 E/MSY). En el caso de las 10.000 especies de aves, sólo debería haber una extinción en cada siglo.

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