Scale dependence in the species‐discharge relationship for fishes of the southeastern U.S.A.

Abstract

1. Species-discharge relationships (SDR) are aquatic analogues of species-area relationships, and are increasingly used in both basic research and conservation planning. SDR studies are often limited, however, by two shortcomings. First, they do not determine whether reported SDRs, which normally use complete drainage basins as sampling units, are scale dependent. Second, they do not account for the effects of habitat diversity within or among samples. 2. We addressed both problems by using discrete fish zones as sampling units in a SDR analysis. To do so, we first tested for longitudinal zonation in three rivers in the southeastern U.S.A. In each river, we detected successive 'lower', 'middle', and 'upper' fish zones, which were characterized by distinct fish assemblages with predictable habitat requirements. Because our analyses combined fish data from multiple sources, we also used rarefaction and Monte Carlo simulation to ensure that our zonation results were robust to spurious sampling effects. 3. Next, we estimated the average discharge within each zone, and plotted these estimates against the respective species richness within each zone (log 10 data). This revealed a significant, linear SDR (r 2 = 0.83; P < 0.01). Notably, this zonal SDR fit the empirical data better than a comparable SDR that did not discriminate among longitudinal zones. We therefore conclude that the southeastern fish SDR is scale dependent, and that accounting for within-basin habitat diversity is an important step in explaining the high diversity of southeastern fishes. 4. We then discuss how our zonal SDR can be used to improve conservation planning. Specifically, we show how the slope of the SDR can be used to forecast potential extinction rates, and how the zonal data can be used to identify species of greatest concern.

Site length for biological assessment of boatable rivers

“…Although much of this heterogeneity in terms of fish species richness can be captured by patterns in species-discharge relationships as long as the sample sites are of sufficient size and number (McGarvey and Hughes, 2008;McGarvey and Ward, 2008), biological interactions and movement patterns also contribute to heterogeneity at multiple levels (May, 1975;Crowl et al, 1997). To understand individual, population, metapopulation and assemblage responses to the environmental template, persons conducting surveys of river assemblages must take into account these multiple geographic extents (Norris, 1995;Fausch et al, 2002;LaVigne et al, 2008b).…”

Moving beyond species–discharge relationships to a flow-mediated, macroecological theory of fish species richness

“…The rationale for using the speciesdischarge relationship as a predictive tool stems directly from efforts to predict changes in terrestrial biodiversity from traditional species-area relationships (Rosenzweig 1999, Thomas et al 2004. Thus, the predictive speciesdischarge method has many of the same problems and limitations as the predictive species-area method (see Botkin et al 2007, McGarvey andWard 2008). Nevertheless, it is an important starting point in the effort to antici-E-mail address: 2 djmcgarvey@vcu.edu pate changes in aquatic biodiversity in response to altered hydrology .…”

Longitudinal variation in community structure of floodplain fishes along two rivers of the southeastern USA

“…Understanding how fish and other biotic communities change among floodplains along the length of a river system is of importance in terms of conservation (McGarvey and Ward 2008). Over half of the world's large river systems have been modified by dams and other water diversions (Nilsson et al 2005).…”