This study examined whether non-native plants in residential Washington DC limited the presence of the Carolina chickadee, a local breeding insectivore.
We predicted that areas with more native plants would support more chickadees, and chickadees would forage more often in the most insect-producing native plants [Narango 2017: 43].
The authors had also considered the possibility that non-native plants could promote increases in other food items (e.g. non-native arthropods), keeping overall prey biomass similar between native and non-native plants. What they found, though, affirmed their prediction: native plants produce more caterpillars, which in turn support more chickadees. In fact, the birds avoided foraging in non-native plants, including non-native species of the same tree genera: the chickadees preferred maples native to the eastern US compared to European-origin maples.
Native plants produce more caterpillars, which in turn support more chickadees.
Native plants were more likely to host a higher biomass of caterpillars compared to non-native plants, and chickadees strongly preferred to forage in native plants that supported the most caterpillars. In addition, chickadees were less likely to breed in yards as the dominance of non-native plants increased [Narango 2017: 42].
Also unique to our study is that we measured the probability of caterpillar occurrence between congeneric species (e.g. native vs. non-native Acer [maple]). This is particularly important considering the popularity and invasive qualities of congeneric species in this region such as Acer platanoides and Quercus acutissima. Although non-native congeners support more caterpillars in comparison to plants unrelated to any native species, congeners had a 47% (CI: 34%–59%) lower probability of having caterpillars compared to native species [Narango 2017: 47].
The authors state that local insects are adapted to local plants, presumably due to their shared co-evolutionary history.
This occurs in part because herbivorous insects have adapted to circumvent the phytochemical defenses of particular plant lineages, resulting in a radiation of specialized plant-insect associations. During urban conversion, native plants are replaced by non-native species with novel chemical, physical, and phenological features for which native herbivorous arthropods have few physiological or behavioral adaptations [Narango 2017: 42].
Narango, Desiree L., D. W. Tallamy, P. P. Marra, 2017, Native plants improve breeding and foraging habitat for an insectivorous bird, Biological Conservation 213, https://www.sciencedirect.com/science/article/abs/pii/S0006320717305153