Molecular approach to describing a seed-based food web: the post-dispersal granivore community of an invasive plant

Authors: Lundgren, Jonathan; SASKA, PAVEL - Crop Research Institute - Czech Republic; HONEK, ALOIS - Crop Research Institute - Czech Republic

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2013
Publication Date: 4/28/2013
Citation: Lundgren, J.G., Saska, P., Honek, A. 2013. Molecular approach to describing a seed-based food web: the post-dispersal granivore community of an invasive plant. Ecology and Evolution. 3(6):1642-1652.

Interpretive Summary: Seed-feeding insects are an important source of mortality for weed seeds, but science currently lacks a clear picture of which granivores are important at regulating specific weed species in large part because examples of seed-targeted gut analysis (seeing what seeds are in an insect stomach) are scarce. Dandelion is native to eastern Europe, where its seed predator community has been well described; the plant is invasive in the U.S., and the granivores that eat dandelion seeds are entirely unknown. We marked dandelion seeds with small quantities of a protein marker (Rabbit IgG), and disseminated the seeds into dandelion communities in the Czech Republic (native range) and South Dakota (invaded range). Then we collected insects from these habitats, and analyzed their guts for the presence of the protein to see which insects ate dandelion seeds in these two environments. Using this technique, we discovered a much more diverse granivore community than has ever been described for a seed species before (27 species and 16 species ate dandelion seeds in each of the invaded and native ranges, respectively). The community was dominated by unexpected insects and other arthropods, including isopods, millipedes, crickets, caterpillars, rove beetles, and weevils. We found a much more diverse community consumed dandelion seeds in the invaded range versus the native habitat, also unexpected. This research widens our view of the insect community that affects seed populations, the basis of insect conservation programs to manage weed communities.

Technical Abstract: We adapted protein-marking techniques and gut content analysis to study the relative granivore communities of the invasive plant, dandelion, in its recipient and native ranges. Dandelion seeds marked with Rabbit IgG were disseminated into plots that had high dandelion populations in recipient habitat (South Dakota, U.S.A.) (n = 5) and the native range (Czech Republic) (n = 3). Arthropods were collected in pitfall traps every 12 h for at least 24 h (1,783 specimens from South Dakota and 288 from Czech Republic), and their guts were searched for the protein marker using ELISA. Seed dishes were placed in each plot, and dandelion seed removal rates were measured. The entire experiment was repeated five times in each plot over the dandelion flowering period. Gut analysis revealed approximately 22% of specimens analyzed tested positive for the seed marker. A more diverse seed predator community had trophic linkages to seeds than has previously been realized under field conditions. This community included taxa such as isopods, millipedes, weevils, rove beetles and caterpillars, in addition to the traditionally recognized ants, crickets, and carabid beetles. Rarefaction and Chao analysis estimated a more diverse granivore community in the biota in the recipient range (27 species) versus in the native range (16 species). This diverse and polyphagous arthropod community is clearly important as a form of biotic resistance to invasive plants and they can adapt to new food resources like exotic plant seeds. It is likely that generalist granivore communities are shaped more by biotic and abiotic characteristics of the habitat than by ephemeral influxes of seed resources from invasive plants.