Present and Future Taxonomic Selectivity in Bird and Mammal Extinctions

Abstract

We compared the distribution of historical bird and mammal species extinctions across genera and families with the distribution we would expect if these extinctions had occurred at random with respect to taxonomy. We then repeated the comparison for species listed in various categories of threat according to the 1996 Red List of the World Conservation Union. We found the distributions of extinctions and threat classifications to be almost always nonrandom-"selective"-with clustering in certain genera and families. Furthermore, extinctions tended to be clustered in taxa that contain few species; species in smaller genera tended to have higher probabilities of extinction. This tendency was strong for historical extinctions but was reduced or absent for some categories of threat. We attribute this to a change in the causes of extinction whereby predation and introduced species have been joined or superseded by widespread habitat loss. We then assessed the implications of this variable selectivity for the past and likely future losses of genera and families. In most cases, the number of lost taxa rises. Finally, we made predictions about minimum losses of taxa at specific dates in the future and showed that, despite the reduction in some forms of selectivity, we will still lose more taxa than if species extinctions were random. Selectividad Taxonómica Presente y Futura Extinciones de Aves y MamíferosResumen: Se comparó la distribución de las extinciones históricas de especies de aves y mamíferos con la distribución que se esperaría si las extinciones hubieran ocurrido al azar con respecto a la taxonomía. La comparación fue repetida para las especies incluidas en distintas categorías de riesgo en la Lista Roja de la UICN. En casi todos los casos se encontró que las distribuciones de las extinciones y de las categorías de riesgo no estaban distribuidas al azar, sin que fueron 'selectivas,' con distribución agrupada en ciertos géneros y familias. Se observó, además, que las extinciones tendieron a estar agrupadas en taxones que contienen pocas especies; las especies en géneros más pequeños tienden a tener mayores probabilidades de extinción. Esta tendencia fue fuerte para las extinciones históricas, pero reducida o ausente para algunas categorías de riesgo. Esto se atribuyó a un cambio en las causas de extinción, donde la predación y las especies introducidas se han sumado o han sido reemplazadas por la gran destrucción de hábitat. Se evaluaron luego las consecuencias de esta selectividad variable para las extinciones de géneros y familias en el pasado y en un futuro probable. En la mayoría de los casos el número de taxones extinguidos aumenta. Finalmente, se hicieron predicciones acerca de las extinciones mínimas de taxones en el futuro, demostrándose que, a pesar de la reducción en algunas formas de selectividad, se extinguirán más taxones que si las extinciones fueran al azar.

Reconsidering the Loss of Evolutionary History: How Does Non-random Extinction Prune the Tree-of-Life?

“…Across studies, high extinction risk is generally associated with large body size, long generation times and small geographic range sizes (Bennett and Owens 1997 ;Russell et al 1998 ;Purvis et al 2000a ;Cardillo 2003 ;Fisher and Owens 2004 ;Cooper et al 2008 ). Conversely, species at low risk of extinction are small, reproduce rapidly, and have a wide niche breadth.…”

“…First, they assumed extinction events were random -the fi eld-of-bullets model, in which extinction is independent of species' traits and thus also phylogeny. If extinctions are clustered on a phylogeny, we might also lose the internal branches of the tree that connect them, and thus experience a greater overall loss of phylogenetic diversity (Russell et al 1998 ;Purvis et al 2000a ). Second, their expectation was derived assuming a phylogeny based on a coalescent model, which generates a highly unrealistic distribution of branching times, with most branches clustered towards the present (see Fig.…”

“…In mammals, it has been suggested that species subtending from longer phylogenetic branches, and thus representing greater unique evolutionary history, are at higher risk of extinction (Russell et al 1998 ;Purvis et al 2000a ). This pattern matches to Wilson's ( 1961 ) 'taxon cycle', which predicts that older species would have higher extinction probabilities as species expand and contract in their geographical distributions over their evolutionary lifetimes.…”

“…Correlates of extinction risk in animal kingdom have been explored extensively using data from the IUCN Red List (Bennett and Owens 1997 ;Russell et al 1998 ;Purvis et al 2000a , b ;Cardillo 2003 ;Cooper et al 2008 ) with particular attention to mammals (Russell et al 1998 ;Cardillo et al 2005Cardillo et al , 2008Isaac et al 2007 ;Huang et al 2012 ), perhaps the best-studied higher taxonomic group. Across studies, high extinction risk is generally associated with large body size, long generation times and small geographic range sizes (Bennett and Owens 1997 ;Russell et al 1998 ;Purvis et al 2000a ;Cardillo 2003 ;Fisher and Owens 2004 ;Cooper et al 2008 ).…”

Diversity, distribution, and conservation of endemic island rodents

“…We level a special focus on the genus rank in regional and other comparisons of rodents. When applied consistently and in a phylogenetic framework, as we feel is generally done appropriately across Rodentia, the genus represents a convenient means for measuring biodiversity (Williams and Gaston, 1994), and can be very useful in conservation planning aimed at establishing the most pressing priorities (Russell et al, 1998). Moreover, this taxonomic rank is useful in broadscale comparisons because, though always dynamic (e.g.…”