Date: June 8, 2017
Source: Michel, N. L., Sherry, T. W., & Carson, W. P. (2013). The omnivorous collared peccary negates an insectivore-generated trophic cascade in Costa Rican wet tropical forest understory. Journal of Tropical Ecology, 30(01), 1-11.
Summary: Leaf-litter disturbance by omnivorous peccaries can reverse trophic cascades.
In tropical forest, insectivores, such as birds and bats, initiate a top-down trophic cascade, unknowingly protecting plants by reducing predation on leaves by arthropods. New research has found that when peccaries (ungulates that consume some plant material, but are predominantly known for trampling and rooting of the forest floor) are present, that trophic cascade can be disturbed. At La Selva Biological Station, Costa Rica the peccary is a common sight. Nicole Michel has researched for several years the interactions between ungulates and leaf litter herpetofauna. Previous studies have found the large peccary population at La Selva has increased the abundance of herpetofauna in the leaf litter of the forest.
Michel and colleagues placed multiple exclosures throughout La Selva, excluding the peccaries and only allowing smaller to mid-sized mammals through their borders. They also excluded birds and bats from some regions but not others by placing nets both within and outside of the peccary exclosures. Visual surveys of all leaves and stems were taken within the enclosures and any arthropods present were also identified and noted. Plant damage was assessed on random plants within in the exclosures and in the control plots, where peccaries were allowed to enter. Arthropod density and leaf damage estimates were averaged across all exclosures and plots. The authors found that peccary exclusion resulted in increased densities of arthropod predators. The plots that excluded birds and bats but included peccaries had constant leaf litter damage present, unlike the exclosures that did not allow birds, bats, or peccaries to enter. This evidence supports Michel’s hypothesis that peccaries not only disturb trophic cascades, but could also negate them completely.
Michel writes, “regardless of the specific mechanism by which peccaries reduced leaf damage in the absence of birds and bats, the finding that an omnivorous ungulate can reverse bird/bat-arthropod-plant trophic cascade is novel, and has important theoretical and conservation implications.” Forests continue to be fragmented causing huge disturbances in the balance; large predators are lost and peccaries continue to flourish at sometimes great numbers. An improved understanding of this subject is needed to better comprehend the complex interactions involving important species and their consequences on diversity in the tropics.