Distinguishing between Invasions and Habitat Changes as Drivers of Diversity Loss among California's Freshwater Fishes

Abstract

Many of California's native populations of freshwater fish are in serious decline, as are freshwater faunas worldwide. Habitat loss and alteration, hydrologic modification, water pollution, and invasions have been identified as major drivers of these losses. Because these potential causes of decline are frequently correlated, it is difficult to separate direct from indirect effects of each factor and to appropriately rank their importance for conservation action. Recently a few authors have questioned the conservation significance of invasions, suggesting that they are "passengers" rather than "drivers" of ecological change. We compiled an extensive, watershed-level data set of fish presence and conservation status, land uses, and hydrologic modifications in California and used an information theoretic approach (Akaike's information criterion, AIC) and path analysis to evaluate competing models of native fish declines. Hydrologic modification (impoundments and diversions), invasions, and proportion of developed land were all predictive of the number of extinct and at-risk native fishes in California watersheds in the AIC analysis. Although nonindigenous fish richness was the best single predictor (after native richness) of fishes of conservation concern, the combined ranking of models containing hydrologic modification variables was slightly higher than that of models containing nonindigenous richness. Nevertheless, the path analysis indicated that the effects of both hydrologic modification and development on fishes of conservation concern were largely indirect, through their positive effects on nonindigenous fish richness. The best-fitting path model was the driver model, which included no direct effects of abiotic disturbance on native fish declines. Our results suggest that, for California freshwater fishes, invasions are the primary direct driver of extinctions and population declines, whereas the most damaging effect of habitat alteration is the tendency of altered habitats to support nonindigenous fishes.

Addressing longitudinal connectivity in the systematic conservation planning of fresh waters

“…Instead of using just reference site distributions (Linke et al 2007), our present distribution models were built on the whole datasetusing even sites with perturbed fish communities and including human-influenced C o p y f o r R e v i e w environmental variables as predictors. Potential distributions can be unrealistic, since some species may have been pushed out to marginal areas within their original distribution or displaced to new areas due to human impairment (Kouamélan et al, 2003;Light & Marchetti, 2007). In this sense, Araújo, Williams & Fuller (2002) showed how the probability of persistence increases if reserve selection algorithms maximize the probability of the current occurrence instead of using a hypothetical niche model.…”

First record of Amatitlania nigrofasciata (Günther, 1867) (Cichliformes: Cichlidae) as introduced species in natural freshwaters of Colombia

“…This suggests that habitat degradation could be contributing to the loss of native species, and possibly facilitating the establishment of non-native species. Habitat degradation by human intervention has been shown to be a factor strongly related to establishment of non-native fishes in natural freshwaters (Light and Marchetti 2007;Leprieur et al 2008).…”

Size matters: predation of fish eggs and larvae by native and invasive amphipods

“…Invasive species are one of the primary threats to freshwater biodiversity, reflecting the globally extensive but locally intensive use of fresh waters by humans (Richter et al 1997;Sala et al 2000;Millennium Ecosystem Assessment 2005;Dextrase and Mandrak 2006;Light and Marchetti 2007). Moreover, introduced predators in freshwaters have particularly severe impacts relative to those in terrestrial or marine systems (Sala et al 2000;Cox and Lima 2006).…”