The western thatch ant, Formica obscuripes, is an abundant, generalist predator in coastal dune ecosystems of northern California. This ant tends several aphid species (Aphis farinosa in video) for their honeydew and aphids are protected from predators while they are being tended. These ant-aphid mutualisms may influence the rest of the arthropod community associated with the host plant where the mutualism is occurring in two ways: (1) directly through antagonistic behaviour of ants toward other arthropods, and (2) indirectly by increasing aphid abundance, which damages the host plant and influences the abundance of other arthropods. These mutualisms can be common on the willow, Salix hookeriana, but whether they form likely depends on the distance between S. hookeriana and ant colonies.
In May 2012, I set up an experiment at Lanphere Dunes to examine these spatial effects of thatch-ant colonies on S. hookeriana genotypes as well as its associated arthropod food web. Thus far, I’ve collected a field season worth of data on willow phenotypic traits (e.g. specific leaf area, water content, growth, etc.) and I’m developing a quantitative food web of herbivore-parasitoid interactions on willows in these experimental populations.