Do alien plants reduce insect biomass?
Tallamy, D. W. (2004). Do alien plants reduce insect biomass?. Conservation Biology, 18(6), 1689-1692. PDF.
Summary
Non-native plants are a common feature of gardens and urban landscapes. Many of these plants are selected specifically because they are unpalatable to insects. But, insects are a critical part of the food chain, supporting a wide variety of birds (particularly nestlings), mammals, reptiles, and amphibians. Tallamy (2004) argues that the widespread planting of non-native species in urban and suburban landscapes is having an insidious and detrimental effect on urban fauna. Why are non-native species likely to be problematic for insects? First, the nursery industry tends to select for ornamental plants that are unpalatable to native species (i.e. pest-free species). While this is beneficial aesthetically, these plants provide little to no resources to the urban ecosystem. Second, many non-native (and invasive) species benefit from 'enemy release', whereby insects from the native range are left behind, and insects from the introduced range are less apt to use novel plants. For example, in Europe over 170 insects feed on Phragmites australis, whereas in the U.S. the species supports only 5 insect species. Lastly, phytophagous ('plant eating') insects tend to be specialists. Indeed, over 90% of phytophagous insects are though to specialize on single species or genera. Thus, the introduction of a novel, non-native species or genus is unlikely to support these insects. Tallamy (2004) concludes that non-native plants are likely altering insect species biomass and assemblages, with these impacts cascading up to affect insectivorous animals.
Take home points
Widespread non-native plants in urban landscapes likely fail to support specialist, plant-eating insects, which could reduce the abundance of insect protein for native fauna
Almost all (96%) of North American birds rear their young on insect protein. Insect protein also supports a range of native mammals, reptiles, and amphibians.
By reducing resources at the bottom of the food chain, non-native plants likely reduce the abundance and prevalence of native fauna.
Management implications
Even 'benign' non-native plants (i.e. those unlikely to become invasive) could still have detrimental effects on fauna by failing to provide food resources for insects.
Keywords
Impact Study; Review; Invasive Plant