Understanding who feeds on whom and how often is the basis for understanding how nature is built and works. A new study now suggests that the methods used to depict food webs may have a strong impact on how we perceive their makeup.
In order to understand how feeding interactions are structured, researchers from Finland and colleagues here at BIO chose to focus on one of the simplest food webs on Earth: the moths and butterflies of Northeast Greenland, as attacked by their specialist enemies, parasitic wasps and flies developing on their host, killing it in the process. This work is the result of a five-year exploration of insect food webs of Zackenberg in the High Arctic. The beauty of this rather simple system is that one has to keep track of perhaps only a handful of species which provides one with a food web structure of manageable complexity. As a result researchers were much more confident to have captured the full system and to have ruled out interactions that were not part of it.
The researchers supplemented the traditional technique of rearing host larvae until the emergence of either the adult or its enemy with DNA Barcoding. More specifically, they targeted COI regions which differ between the predator and the prey, in order to selectively detect both immature predators from within their prey, and the remains of the larval meal from the stomachs of adult predators. By then comparing the sequences obtained to a reference library of DNA Barcodes of all species in the region, they could determine exactly who had attacked whom. One of the reasons to use this approach was the obscure nature of some species involved. As larvae, some of the predators attack their prey when they are hidden in the ground or vegetation, where they are likely going to missed by any collector. By instead looking for prey remains in the guts of the more easily-detectable adult predators, the scientists were able to establish previously unknown links within the food web.
The new approach changed every measure of the food web structure with three times as many interactions between species as known before. On average, most types of predator proved less specialized than assumed, and most types of prey were attacked by many more predators than previously thought. Furthermore, the comparison of the different techniques with each other revealed that food web structure more among the different techniques than among localities. Thus, whatever we think that we know about food web structure across the globe may be dictated as much by how we have searched as by how species really interact.
Fascinating, one of the simplest food webs we could possible find in the world, and yet it is far more complex that previously thought. I cannot say I am surprised as all the years in the trade have taught me that relationships and interactions in nature are more intertwined as humans were able to fathom so far. Maybe we are getting a little closer to a deeper understanding now.
In conclusion, our results show how the information provided by molecular techniques can surpass that recovered by traditional techniques, but also that different types of molecular information are complementary, revealing different features in the emergent architecture of ecological interaction webs. By resolving more interactions than traditional techniques, by revealing interactions of species with a cryptic lifestyle, and by revising our impression of emergent food web structure, such combinations have the potential to revamp our impression of local food web structure, and how biotic interactions are patterned across the globe.