Ecological invasions provide a unique opportunity to study basic ecology. By definition, invasive species move into ecosystems displacing native species and form high density populations. Invasions result in a shift in the dominant species within a particular habitat and, in some cases, are associated with a diverse community becoming a quasi-monoculture. This is the case in some portions of the Eastern Deciduous Forest of North America where Amur honeysuckle (Lonicera maackii) is extremely effective at colonizing and growing at high densities. This invasion is particularly prevalent in the riparian zones of headwater streams in the Ohio Valley where L. maackii forms near monocultures. This invasion results in a shift in dominant traits of the riparian vegetation and has the opportunity to substantially impact the biology of headwater streams, which is tightly linked to allochthonous inputs. Here we present results from a sequence of experiments that seek to understand how this invasion influences stream biology across varying levels of aquatic trophic structure.
Ecological invasion of the terrestrial habitat, by definition, includes the replacement of native biomass with that of the invading species. In most cases, invasion results in a simplification of the community and a contraction of the total trait space maintained by the system. In headwater streams in temperate forests, this results in an alteration of the composition and chemistry allochthonous materials that are vital to the biology of the aquatic system. In-situ studies indicate that the invasion of L. maackii is associated with a substantial and statistically significant decline the stream biofilm community as measured by both chlorophyll-a and total biomass (AFDM). Laboratory microcosm assays indicate that L. maackii foliar leachates have a highly toxic effect on aquatic macroinvetebrates and that the effect varies through the year indicating a phytochemical origin for this effect. Ongoing work seeks to understand how this invasion may influence stream predators (salamander larvae) across a range of invasion intensity. In summary, our results support the hypothesis that terrestrial invasion can result in the introduction of novel subsides, toxic in some cases, and these subsidies are related to shifts in the aquatic community.