Trophic levels and trophic tangles: The prevalence of omnivory in real food webs

R.M. Thompson, M. Hemberg, B.M. Starzomski, J.B. Shurin

    Research output: Contribution to journalArticle

    177 Citations (Scopus)

    Abstract

    The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top‐down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4%) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic‐level‐based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.

    Original languageEnglish
    Pages (from-to)612-617
    Number of pages6
    JournalEcology
    Volume88
    Issue number3
    DOIs
    Publication statusPublished - 2007

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    omnivory
    omnivores
    trophic level
    food webs
    food web
    food chain
    herbivores
    herbivore
    soil food webs
    energy flow
    trophic cascade
    habitat type
    trophic levels
    ecology
    lakes
    habitats
    lake

    Cite this

    Thompson, R.M. ; Hemberg, M. ; Starzomski, B.M. ; Shurin, J.B. / Trophic levels and trophic tangles: The prevalence of omnivory in real food webs. In: Ecology. 2007 ; Vol. 88, No. 3. pp. 612-617.
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    abstract = "The concept of trophic levels is one of the oldest in ecology and informs our understanding of energy flow and top‐down control within food webs, but it has been criticized for ignoring omnivory. We tested whether trophic levels were apparent in 58 real food webs in four habitat types by examining patterns of trophic position. A large proportion of taxa (64.4{\%}) occupied integer trophic positions, suggesting that discrete trophic levels do exist. Importantly however, the majority of those trophic positions were aggregated around integer values of 0 and 1, representing plants and herbivores. For the majority of the real food webs considered here, secondary consumers were no more likely to occupy an integer trophic position than in randomized food webs. This means that, above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Omnivory was most common in marine systems, rarest in streams, and intermediate in lakes and terrestrial food webs. Trophic‐level‐based concepts such as trophic cascades may apply to systems with short food chains, but they become less valid as food chains lengthen.",
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    Trophic levels and trophic tangles: The prevalence of omnivory in real food webs. / Thompson, R.M.; Hemberg, M.; Starzomski, B.M.; Shurin, J.B.

    In: Ecology, Vol. 88, No. 3, 2007, p. 612-617.

    Research output: Contribution to journalArticle

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