Trophic Levels and Trophic Tangles: The Prevalence of Omnivory in Real Food Webs

Thompson, Ross; Hemberg, Martin; Starzomski, Brian M.; Shurin, Jonathan B.

doi:10.1890/05-1454

Cited by 308 publications

(274 citation statements)

References 38 publications

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“…Certainly, trophic levels are artificial constructions for many arthropods, and there is an increasing recognition that many taxa feed as facultative or obligate omnivores (23). These trophic "tangles," characterized by increasing trophic indeterminacy at higher positions, are prevalent across marine, freshwater, and terrestrial systems (24). Our assignment of all predatory arthropods to a single trophic role almost certainly mischaracterizes some of these omnivores.…”

Section: Resultsmentioning

confidence: 99%

Interactions among predators and the cascading effects of vertebrate insectivores on arthropod communities and plants

Mooney

Gruner

Barber

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

200

251

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Theory on trophic interactions predicts that predators increase plant biomass by feeding on herbivores, an indirect interaction called a trophic cascade. Theory also predicts that predators feeding on predators, or intraguild predation, will weaken trophic cascades. Although past syntheses have confirmed cascading effects of terrestrial arthropod predators, we lack a comprehensive analysis for vertebrate insectivores-which by virtue of their body size and feeding habits are often top predators in these systems-and of how intraguild predation mediates trophic cascade strength. We report here on a meta-analysis of 113 experiments documenting the effects of insectivorous birds, bats, or lizards on predaceous arthropods, herbivorous arthropods, and plants. Although vertebrate insectivores fed as intraguild predators, strongly reducing predaceous arthropods (38%), they nevertheless suppressed herbivores (39%), indirectly reduced plant damage (40%), and increased plant biomass (14%). Furthermore, effects of vertebrate insectivores on predatory and herbivorous arthropods were positively correlated. Effects were strongest on arthropods and plants in communities with abundant predaceous arthropods and strong intraguild predation, but weak in communities depauperate in arthropod predators and intraguild predation. The naturally occurring ratio of arthropod predators relative to herbivores varied tremendously among the studied communities, and the skew to predators increased with site primary productivity and in trees relative to shrubs. Although intraguild predation among arthropod predators has been shown to weaken herbivore suppression, we find this paradigm does not extend to vertebrate insectivores in these communities. Instead, vertebrate intraguild predation is associated with strengthened trophic cascades, and insectivores function as dominant predators in terrestrial plant-arthropod communities.bottom-up and top-down control | intraguild predation | meta-analysis | trophic cascade | vertebrate predator exclusion R esearch demonstrates that predators, by feeding on herbivores, can increase plant biomass via the indirect interaction commonly labeled a trophic cascade (1). In recent years, metaanalyses have quantified trophic cascades separately in terrestrial (2, 3) and aquatic systems (4, 5) and in multiple habitats together to compare the strength of trophic cascades among ecosystem types (6). Although the strengths of trophic cascades vary across ecosystem types, explanations for the significant residual variation within ecosystems remain enigmatic (6-8).Vertebrate insectivores such as birds, bats, and lizards often feed as top predators on terrestrial arthropod communities, but based upon current theory it is unclear whether their effects should cascade down to affect plant biomass. Because of their large body size relative to arthropod prey, vertebrate insectivores can consume both predatory and herbivorous arthropods (9, 10). As a consequence, vertebrate insectivores may feed as so-called intraguild predators ...

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Section: Resultsmentioning

confidence: 99%

Interactions among predators and the cascading effects of vertebrate insectivores on arthropod communities and plants

Mooney

Gruner

Barber

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

200

251

View full text Add to dashboard Cite

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“…We also found that some inhabitants attached to different habitat‐formers and at multiple levels in the habitat cascade, analogous to generalist and omnivorous consumers, respectively, in trophic cascades (Thompson et al., 2007; Williams & Martinez, 2004). For example, Ulva was found attached to all other habitat‐forming species at all levels in the habitat cascade (Figure 5a).…”

Section: Discussionmentioning

confidence: 99%

A sixth‐level habitat cascade increases biodiversity in an intertidal estuary

Thomsen

Hildebrand

South

et al. 2016

Ecology and Evolution

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Many studies have documented habitat cascades where two co‐occurring habitat‐forming species control biodiversity. However, more than two habitat‐formers could theoretically co‐occur. We here documented a sixth‐level habitat cascade from the Avon‐Heathcote Estuary, New Zealand, by correlating counts of attached inhabitants to the size and accumulated biomass of their biogenic hosts. These data revealed predictable sequences of habitat‐formation (=attachment space). First, the bivalve Austrovenus provided habitat for green seaweeds (Ulva) that provided habitat for trochid snails in a typical estuarine habitat cascade. However, the trochids also provided habitat for the nonnative bryozoan Conopeum that provided habitat for the red seaweed Gigartina that provided habitat for more trochids, thereby resetting the sequence of the habitat cascade, theoretically in perpetuity. Austrovenus is here the basal habitat‐former that controls this “long” cascade. The strength of facilitation increased with seaweed frond size, accumulated seaweed biomass, accumulated shell biomass but less with shell size. We also found that Ulva attached to all habitat‐formers, trochids attached to Ulva and Gigartina, and Conopeum and Gigartina predominately attached to trochids. These “affinities” for different habitat‐forming species probably reflect species‐specific traits of juveniles and adults. Finally, manipulative experiments confirmed that the amount of seaweed and trochids was important and consistent regulators of the habitat cascade in different estuarine environments. We also interpreted this cascade as a habitat‐formation network that describes the likelihood of an inhabitant being found attached to a specific habitat‐former. We conclude that the strength of the cascade increased with the amount of higher‐order habitat‐formers, with differences in form and function between higher and lower‐order habitat‐formers, and with the affinity of inhabitants for higher‐order habitat‐formers. We suggest that long habitat cascades are common where species traits allow for physical attachment to other species, such as in marine benthic systems and old forest.

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“…However, omnivorous links are frequently observed in trophic networks [56][57][58]. Therefore, one must look more closely to identify in community matrices a signature of nonadaptive systemic selection through stability constraints.…”

Section: Box 3 Modeling Species Interactionsmentioning

confidence: 99%