Abstract
ABSTRACTThe importance of trophic linkages between aquatic and terrestrial ecosystems is predicted to vary as a function of subsidy quantity and quality relative to in situ resources. To test this prediction, I used multi-year diet data from Bonneville cutthroat trout Oncorhynchus clarki Utah in spring-fed and snowmelt-driven streams in the high desert of western North America. I documented that trout in spring-fed streams consumed more (number and weight) aquatic than terrestrial invertebrates, while trout in snowmelt-driven streams consumed a similar number of both prey types but consumed more terrestrial than aquatic invertebrates by weight. Trout in spring-fed streams consumed more aquatic invertebrates than trout in snowmelt streams and trout consumed more terrestrial invertebrates in snowmelt than in spring-fed streams. Up to 93% of trout production in spring-fed streams and 60% in snowmelt streams was fueled by aquatic invertebrates, while the remainder of trout production in each stream type was from terrestrial production. I found that the biomass and occurrence of consumed terrestrial invertebrates were not related to our measures of in situ resource quality or quantity in either stream type. These empirical data highlight the importance of autotrophic-derived production to trout in xeric regions.
Highlights
Trophic linkages between aquatic and terrestrial ecosystems are ubiquitous, but the relative importance of these linkages can vary across space (Marczak et al 2007; Marcarelli et al 2011)
I found that aquatic and terrestrial invertebrates both contributed to trout trophic basis of production (TBP) in spring and snowmelt streams, though the importance of aquatic invertebrates relative to terrestrial invertebrates was much greater in spring streams
Terrestrial invertebrate inputs were greater in spring streams, yet terrestrial invertebrates, especially oligochaetes, made larger contributions to trout TBP and diets in snowmelt streams
Summary
Trophic linkages between aquatic and terrestrial ecosystems are ubiquitous, but the relative importance of these linkages can vary across space (Marczak et al 2007; Marcarelli et al 2011). Terrestrial subsidies dominate the diets of aquatic consumers even when terrestrial subsidies are rare The relative importance of trophic linkages in recipient habitats is predicted to be a function of the quantity and quality of the subsidy relative to in situ resources (Marczak et al 2007; Marcarelli et al 2011). Recipient consumers select trophic subsidies when they are more abundant, energetically greater, or easier to capture and assimilate than ambient resources (Wipfli 1997; Nakano, Kawaguchi, et al 1999; Wilson et al 2014).
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