Rarity, Fragmentation, and Extinction Risk in Desert Fishes

Abstract

Theoretical efforts and small‐scale experiments have given rise to the widespread belief that the fewer occurrences a species has or the more fragmented its distribution is, the more vulnerable that species should be to extinction. Lacking, however, are large‐scale multi‐species studies exploring the connection between rarity and local extinction risk. Here we present a landscape‐level biogeographic test of this widely assumed linkage. Using a unique data set detailing the occurrence patterns of freshwater fishes of the Sonoran Desert (a gravely endangered fauna) we obtained for each of 25 species a measure of rarity that was independent of spatial scale. We found that fragmentation was consistently associated with elevated extinction risk, whereas the number of occurrences exerted a significant effect only if fragmentation had not already been accounted for. Specifically, desert fish species with the most fragmented historic distributions were nearly five times more likely to suffer local extirpations (since 1980) than were species with more continuous distributions. These findings underscore what a strong link exists between spatial distribution and vulnerability to extinction, clarifying that the link exists even at the landscape level and across an entire biogeographic fauna.

Detecting range shifts among Australian fishes in response to climate change

“…Other potential changes to habitat include, at a very fine scale, the loss of aquatic plants, which provide important structural habitat in rivers and wetlands (Balcombe et al 2011), and at much larger scales, levels of connection among habitat patches containing local populations (Labbe and Fausch 2000). Thus, at larger spatial scales, changes in connectivity among local populations may increase overall extinction risk of local and regional populations, as has been previously predicted and documented for fragmented fish populations in desert streams (see Fagan 2002;Fagan et al 2002).…”

Body size-independent safety margins for gas exchange across grasshopper species

“…For relationships between family, subfamily and tribe, we used Otte and Nasrecki (Otte and Nasrecki, 1997), and for species relationships we used published molecular studies (Chapco et al, 1997;Chapco et al, 1999;Knowles and Otte, 2000). Then, we counted the number of branches at the level of family, subfamily, tribe, genus and species between each species pair as a measure of the distance between species (Fagan et al, 2002;Woods et al, 2004). These distance measures were compiled into a matrix, which was held constant, while we compared matrices created for the differences in body mass between each species pair to the differences in respiratory parameters between the same pairs, using partial Mantel tests (PASSAGE software) (Rosenberg, 2001).…”

A new measure of longitudinal connectivity for stream networks

“…However, little of this work has been translated into aquatic systems, despite the fact that landscape and riverine ecology share many attributes and organizing principles (Benda et al 2004), including the concept of connectivity (Wiens 5 2002). The degree of connectivity or isolation of a watershed is reflected in the productivity (Dryden and Stein 1975;Baker and Votapka 1990;Stanford et al 1996), species composition (Sheldon 1987(Sheldon , 1988Spens et al 2007), extinction risk (Dunham et al 1997;Fagan et al 2002;Morita and Yamamoto 2002), population size (Preston 1962a, b), genetic stability (Morita and Yamamoto 2002;Wofford et al 2005), morphological characteristics (Reznick 1982;Crossin et 10 al. 2004), life history (Dingle 1996), and ability of the biota to recover from disturbance (Stanford et al 1996).…”