Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities, Burghardt et al. 2010

This research evaluates the impact of the invasion of non-native plants in the distribution of lepidopteran (butterfly, skipper, and moth) communities. The authors assert that although the introduction of non-native plants has not resulted in a “global extinction”, they have had a considerable impact on how ecosystems function—they often result in significant bottom-up reductions of energy available in local food webs.

The experiment established four gardens near mature woodlots containing most, if not all, of the native species planted within the treatment. The richness and abundance were then compared for lepidopteran communities found on native versus corresponding non-native congener^[4] species of 13 woody plant genera. For example, the genus Acer (maple) was selected for this study because the native and non-native maples were widespread in that area. In separate plots, the researchers also compared native plants and unrelated (non-congeneric) non-native plants for lepidopteran richness and abundance.

The study found that lepidopterans suffer from the replacement of native plants by non-natives, especially when those non-natives are unrelated to any native plant species. The authors explain that “insect herbivores adapted to the chemical challenges [toxic plant defenses] of particular native hosts may be able to adopt a novel plant species as a host if its phytochemistry is sufficiently similar to the original hosts” [Burghardt 2010: 10]. Over the two-year study, lepidopteran abundance and richness were depressed both on congener and (unrelated) non-congener non-native plants, but especially on the latter.

Specialist lepidopteran species, which require specific diet and habitat conditions to survive, fared worse on non-natives than did generalists, which can eat a variety of foods and survive in many different habitats. The authors note, for example, that “geographically novel congeners were acceptable hosts to less than half of the generalists and only one fourth of the specialists that we found on native congeners in 2009” [Burghardt 2010: 11]. Only 7% of specialist species used non-congener non-natives as hosts.

The authors argue that the loss of lepidopteran diversity and abundance due to the displacement of native plant species with non-natives can ripple up the food chain, reducing diversity at higher trophic levels. Reduced diversity leads to lower ecosystem productivity and stability, thus disrupting the whole system.

Because insect herbivores are near the hub of most terrestrial food webs, comprising essential food stuffs for an incredible diversity of insect predators and parasitoids, spiders, amphibians, lizards, rodents, bats, birds, and even higher predators such as foxes and bears, it is particularly important to understand changes wrought by non-native plants on this critical taxon [Burghardt 2010: 13].