Food Web Implications of δ¹³C and δ¹⁵N Variability over 370 km of the Regulated Colorado River USA

Abstract

Dual stable isotope analysis in the regulated Colorado River through Grand Canyon National Park, USA, revealed a food web that varied spatially through this arid biome. Down-river enrichment of delta13C data was detected across three trophic levels resulting in shifted food webs. Humpack chub delta13C and delta15N values from muscle plugs and fin clips did not differ significantly. Humpback chub and rainbow trout trophic position is positively correlated with standard length indicating an increase in piscivory by larger fishes. Recovery of the aquatic community from impoundment by Glen Canyon Dam and collecting refinements for stable isotope analysis within large rivers are discussed.

The effects of dams on longitudinal variation in river food webs

“…The minimal influence of dams on the d 13 C values of potential food sources and biota in this study is in contrast to other studies that have demonstrated enrichment or depletion of 13 C in biota downstream of dams (Angradi 1993(Angradi , 1994Shannon et al 2001;Doi et al 2008). The influence of the Lostock and Chichester dams on downstream d…”

“…In contrast, Angradi (1994) observed depletion of 13 C and 15 N in seston in a downstream direction and no longitudinal variation in the isotopic composition of amphipods or fish for 25 km. Shannon et al (2001) observed enrichment of 13 C in benthic algae, macroinvertebrates and fish up to 350 km downstream of Glen Canyon Dam but no longitudinal trends in d 15 N for the same groups. Doi et al (2008) used isotope signatures of phytoplankton to suggest that they contributed to the downstream food webs for up to 10 km.…”

Trophic dynamics in a relatively pristine subtropical fringing mangrove community

“…Many studies suggested widespread correlations between fish size and habitat use and feeding (e.g. Minns 1995, Gu et al 1996, Shannon et al 2001, Barnes et al 2008, Chassot et al 2008), but fish size was not a major influence in our study. The influence of size may decline with increasing complexity of food webs where body size of primary consumer taxa is highly variable (Layman et al 2005).…”

“…Stable isotopic values often vary with body size (Gu et al 1996, Shannon et al 2001, Barnes et al 2008, so log transformed length was included as a covariate in tests for site differences in δ N stable isotope values between sites were evaluated using circular statistics with Oriana (Schmidt et al 2007). Such analysis uses Rayleigh's Z statistic.…”

Realistic Fasting Does Not Affect Stable Isotope Levels of a Metabolically Efficient Salamander

“…The method of comparing non-destructive and destructive tissue in animals for stable isotope research has yielded successful results with fish (Shannon et al 2001;Johnson et al 2002;Jardine et al 2005;Kelly et al 2006;Sanderson et al 2009), birds , and sea turtles (Seminoff et al 2006), and this study shows this method can work well with other ectothermic vertebrates. Though our results suggest species-specific differences in stable isotope relationships among tissues, we caution that our study cannot resolve whether there were truly species-specific differences.…”