Invasive plants have different effects on trophic structure of green and brown food webs in terrestrial ecosystems: a meta‐analysis

Abstract

Although invasive plants are a major source of terrestrial ecosystem degradation worldwide, it remains unclear which trophic levels above the base of the food web are most vulnerable to plant invasions. We performed a meta-analysis of 38 independent studies from 32 papers to examine how invasive plants alter major groupings of primary and secondary consumers in three globally distributed ecosystems: wetlands, woodlands and grasslands. Within each ecosystem we examined if green (grazing) food webs are more sensitive to plant invasions compared to brown (detrital) food webs. Invasive plants have strong negative effects on primary consumers (detritivores, bacterivores, fungivores, and/or herbivores) in woodlands and wetlands, which become less abundant in both green and brown food webs in woodlands and green webs in wetlands. Plant invasions increased abundances of secondary consumers (predators and/or parasitoids) only in woodland brown food webs and green webs in wetlands. Effects of invasive plants on grazing and detrital food webs clearly differed between ecosystems. Overall, invasive plants had the most pronounced effects on the trophic structure of wetlands and woodlands, but caused no detectable changes to grassland trophic structure.

Invasive plants negatively impact native, but not exotic, animals

“…Interestingly, we found no evidence that invasive plant impacts on exotic or native animals varied based on trophic level. In contrast, McCary et al () found that invasive plants differentially impacted “green” (e.g., herbivores) and “brown” (e.g., detritivores) food webs. They found that invasive plants decreased primary consumer abundance and increased secondary consumers.…”

“…Previous studies have found differences in invasive plant impacts across ecosystems (e.g., McCary et al, ; Schirmel et al, ); unfortunately, we lacked adequate replication to test for variation among ecosystems. However, we did have studies spanning seven ecosystem types across the globe, which we grouped into “wet” and “dry.” We found that resident animal abundance was reduced by invasive plants in “wet” ecosystems, with no change in abundance in “dry” ecosystems; though there was no evidence that this impact was different for native and exotic animals.…”

“…Invasive plant effects were strongest in riparian systems, while birds and insects were the most strongly impacted animal groups. In a broad comparison of invasive plant effects on trophic levels, McCary, Mores, Farfan, and Wise () found invasive plants to have differential impacts on animal populations in “brown” (i.e., detritivore) and “green” (i.e., herbivore and predator) trophic groups, though this depended strongly on the receiving ecosystem type. Namely, they found that grassland systems host no significant impacts on either food web at any trophic level, while wetlands are host to major impacts on green food webs, and forest invaders host various significant impacts on both green and brown food webs.…”

Invasive plants differentially affect soil biota through litter and rhizosphere pathways: a meta‐analysis

“…This lower sensitivity of the higher trophic groups to plant invasion has previously been documented by McCary et al . () who examined the overall effects of invasive plants on aboveground food web in wetlands. Basal detritus resources can affect predators in the food web through altering the food source via the bottom‐up cascading effect (Pace et al .…”

Impacts of invasive biota in forest ecosystems in an aboveground–belowground context

“…Further, invasive plants that have much higher litter quality than native species can greatly enhance densities of decomposer organisms and processes, and rates of nutrient supply from the soil, as has been shown for invasion of Tradescantia fluminensis into forest understories in New Zealand (Standish et al 2004). Conversely negative belowground effects of invasive plants are also common, and a recent meta-analysis showed a weak overall negative effect of invasive plants on soil detritivores in forests (McCary et al 2016). As such, members of the Northern Hemisphere Pinaceae, which are invasive in many Southern Hemisphere ecosystems (Fig.…”