Food webs & species interactions: A novel twist
It is a widely accepted notion that trophic dynamics have a great impact in determining community structure. The sort of trophic dynamics that one usually thinks about include a predator, a herbivore, and a producer. However, recently, a new level of complexity has been introduced: a combination of competition and predation called Intra-Guild predation. IGP is defined as the killing of potential competitors or species of the same trophic guild. This new twist allows scientists to reconsider some of the traditional food webs because of the dual effect of feeding and eliminating a potential predator and, in turn, has an impact in determining community structure.
Anax nymph by Bruce Lund
When I was initially introduced to this idea, I was up in Koffler Scientific Reserve participating in a Field Research Course. And due to its ecological influences, I decided to make it the subject of my research project. I explored how IGP influences the food web dynamics between Anax and Epitheca dragonfly nymphs. In this context, Anax (Top-predator) and Epitheca (Intermediate-predator) are placed in the same trophic level and are thus considered competitors (they both feed on mosquito larvae among other prey). In my research, I wanted to explore this relationship further and investigate this effect by creating three treatments and controlling for the presence or absence of the IGP participants (top-predator, intermediate predator, prey). My results showed that Anax nymph (top-predator) is more likely to consume Epitheca nymph (intermediate predator) in the absence of the mosquito larvae (shared resource). I attributed these results to interference competition between the competitors, in which one organism interferes with the resources.
Mosquito Larvae by Mark Yokoyama
To understand how communities come about and how they assemble, one must explore how species interact, how some populations rise and others decline, and how the presence of one species affects the existence of another. And when a complex interaction such as IGP comes into play, the intensity of the impact on food web dynamics (and other factors associated with IGP such as interference competition) is significant and worthy of attention due to its overall influence in determining community structure. In terms of management and conservation, this study has shown that different consequences can occur when introducing species from the same trophic level. For example although Anax and Epitheca share many similarities such as being predators, being from the same trophic guild, and sharing a common resource, introducing one to an ecosystem will have substantially different consequences than the other; and similarly, different cascading outcomes will take place in the presence or absence of the shared resource (i.e. mosquito larvae).
By Dalya Al Bassam
References:
Polis, G. and R. Holt. 1992. Intraguild predation: The dynamics of complex trophic interactions. Trends in Ecology & Evolution 7:151-154.
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