Trophic Cascades in Terrestrial Systems: A Review of the Effects of Carnivore Removals on Plants

Abstract

We present a quantitative synthesis of trophic cascades in terrestrial systems using data from 41 studies, reporting 60 independent tests. The studies covered a wide range of taxa in various terrestrial systems with varying degrees of species diversity. We quantified the average magnitude of direct effects of carnivores on herbivore prey and indirect effects of carnivores on plants. We examined how the effect magnitudes varied with type of carnivores in the study system, food web diversity, and experimental protocol. A metaanalysis of the data revealed that trophic cascades were common among the studies. Exceptions to this general trend did arise. In some cases, trophic cascades were expected not to occur, and they did not. In other cases, the direct effects of carnivores on herbivores were stronger than the indirect effects of carnivores on plants, indicating that top-down effects attenuated. Top-down effects usually attenuated whenever plants contained antiherbivore defenses or when herbivore species diversity was high. Conclusions about the strength of top-down effects of carnivores varied with the type of carnivore and with the plant-response variable measured. Vertebrate carnivores generally had stronger effects than invertebrate carnivores. Carnivores, in general, had stronger effects when the response was measured as plant damage rather than as plant biomass or plant reproductive output. We caution, therefore, that conclusions about the strength of top-down effects could be an artifact of the plant-response variable measured. We also found that mesocosm experiments generally had weaker effect magnitudes than open-plot field experiments or observational experiments. Trophic cascades in terrestrial systems, although not a universal phenomenon, are a consistent response throughout the published studies reviewed here. Our analysis thus suggests that they occur more frequently in terrestrial systems than currently believed. Moreover, the mechanisms and strengths of top-down effects of carnivores are equivalent to those found in other types of systems (e.g., aquatic environments).

Vegetation dynamics of predator‐free land‐bridge islands

“…The matter is trivially simple in principle, but in practice, the challenge of experimentally creating predator-free environments in which herbivores can increase without constraint has proven almost insurmountable (Marquis & Whelan 1994;Schmitz et al 2000;Sinclair et al 2000).…”

“…However, accumulating evidence increasingly underscores the potential of terrestrial systems to undergo trophic cascades (Mclaren & Peterson 1994;Pace et al . 1999;Schmitz et al . 2000;Ripple et al .…”

Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management

“…The term refers to predator-prey interactions whose effects Connell (1990) and Morin (1999). extend (or cascade) down through more than one level in a food web so that plant biomass is ultimately affected by changes in predator abundance, via a series of intermediate links (Paine, 1980 ;Pace et al, 1999 ;Schmitz, Hambäck & Beckerman, 2000) (Fig. 1D).…”

Temporal dynamics of a simple community with intraguild predation: an experimental test

“…Although much theoretical development in ecology has treated the stability and dynamics of predation and interspecific competition separately (e.g., May 1973, Tilman 1982, 1988, Kot 2001, Murdoch et al 2003, it is clear that in nature both processes occur simultaneously, often with strong interaction strengths (e.g., Wooton 1994, Schmitz et al 2000, Hampton et al 2006. Theory that explores the implications of food web complexity for community dynamics has generally been confined to analyses of stability and species persistence (e.g., May 1973, Martinez et al 2006, Allesina and Pascual 2008, and only rarely has the nature of the underlying temporal dynamics been considered (Fussmann and Heber 2002).…”