Abstract
Food webs are known to have myriad trophic links between resource and consumer species. While herbivores have well-understood trophic tendencies, the difficulties associated with characterizing the trophic positions of higher-order consumers have remained a major problem in food web ecology. To better understand trophic linkages in food webs, analysis of the stable nitrogen isotopic composition of amino acids has been introduced as a potential means of providing accurate trophic position estimates. In the present study, we employ this method to estimate the trophic positions of 200 free-roaming organisms, representing 39 species in coastal marine (a stony shore) and 38 species in terrestrial (a fruit farm) environments. Based on the trophic positions from the isotopic composition of amino acids, we are able to resolve the trophic structure of these complex food webs. Our approach reveals a high degree of trophic omnivory (i.e., noninteger trophic positions) among carnivorous species such as marine fish and terrestrial hornets.This information not only clarifies the trophic tendencies of species within their respective communities, but also suggests that trophic omnivory may be common in these webs.
Highlights
Recent studies have emphasized the importance of functional diversity in the provision of ecosystem services (Duffy et al 2007; Griffin et al 2008)
Ecology and Evolution published by John Wiley & Sons Ltd
Carbon and nitrogen isotopic compositions are reported in the standard delta (d) notation relative to the Vienna Peedee Belemnite (VPDB) and to atmospheric nitrogen (AIR), respectively
Summary
Recent studies have emphasized the importance of functional diversity in the provision of ecosystem services (Duffy et al 2007; Griffin et al 2008). Analysis of the stable nitrogen isotopic composition (d15N) of amino acids represents a relatively new method that has been shown to provide accurate and precise estimates of the trophic position of organisms in aquatic and terrestrial systems (e.g., McClelland and Montoya 2002; McCarthy et al 2007; Popp et al 2007; Chikaraishi et al 2009; Steffan et al 2013).
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