Above-below ground interactions

Because herbivory often elicits systemic changes in plant traits (e.g., secondary chemistry), indirect herbivore interactions via induced plant responses may be a pervasive feature structuring herbivore communities. Although the ecological importance of this phenomenon has recently been emphasized and described for herbivorous insects, it is unknown if and how induced responses contribute to the organization of other major phytoparasitic taxa. In collaboration with Bob Denno and Sandy Sardanelli I have been investigating the role of plants in linking foliar-feeding insects and root-feeding nematodes on tobacco (Nicotiana tabacum).

Plant-parasitic nematodes and phytophagous insects comprise a large proportion of the biodiversity and abundance of multi-cellular animal life on earth. Nematodes dominate the belowground herbivore community (attaining densities >1,000,000 individuals/m2) on many plant species where they impair the translocation of water/nutrients and thus limit primary production. In North American grasslands, for example, nematodes have been identified as the key consumer (either above- or belowground) controlling plant productivity. Moreover, the role of nematodes in reducing agricultural yield has been well-documented, with annual losses estimated at >$100 billion worldwide. Phytophagous insects are the aboveground counterparts to nematodes where they are well-recognized for their detrimental effects on plants in natural and managed habitats. Both nematodes and insects are present (and typically abundant) in virtually all terrestrial ecosystems, yet potential interactions between these two dominant groups of plant parasites are poorly described.


As depicted in the above interaction web, diverse mechanisms lead to indirect interactions between above- and belowground herbivores on tobacco. Most notably, resistance and tolerance mechanisms facilitate positive associations between foliar-feeding insects and root-feeding nematodes. This lends support to the growing perception that plants play a critical role in propagating indirect effects among a diverse assemblage of consumers.