Eco-evolutionary dynamics and food webs

A news article in Science about eco-evolutionary dynamics surrounding various alewife (Alosa pseudoharengus) populations caught my eye the other day. The idea of feedbacks between ecology and evolution has been around for quite some time, but the notion that they can occur over relatively short timescales is much more recent. The example cited in the article is research by David Post, investigating how alewife populations impact their environment, and how that environment can, in turn, impact the evolution of the alewife population.

Normally anadromous populations of alewives have, in some areas been trapped in lakes by dams. Before the dams were put in, these populations would swim upstream to reproduce and are voracious consumers of Daphnia to the point where Daphnia populations do not recover until the alewives return to the ocean, and juveniles hatch. For those areas with alewives trapped upstream, however, the Daphnia populations are unable to recover. This has lead to some interesting dynamics in terms of the evolution of both alewives and Daphnia. Specifically alewives, having depleted their environment of larger zooplankton, have developed smaller mouths and gill rakers that allow them to more efficiently consume smaller prey. On the other side, Daphnia from areas that still have anadromous alewives exhibit faster growth, earlier maturation, and have more offspring.

This marks yet another fascinating discovery in the field of evolutionary ecology in my opinion. Of course, if you find this stuff as exciting as I do you may also enjoy papers by Yoshida et al. as well as this excellent review by Post and Palkovacs. The 2003 Yoshida et al. paper is a great example of experimental evolutionary ecology. They examined a predator-prey system involving rotifers and algae and found that predator-prey cycling was in part mediated to changes in prey genotype frequency (where the genotype was basically responsible for how nutritious the algae was for the rotifer). This research, along with that of the alewives, Trinidadian guppies (studied by David Reznick), as well as several other empirical examples of eco-evolutionary feedbacks are summarized in the review by Post and Palkovacs.

To me, the most interesting part about the alewife research highlighted in the Science article, was that Post and his colleagues have expanded their search for eco-evolutionary effects rippling through the food chain. Looking up the food chain they are investigating changes in pickerel life history, noticing differences between lakes with trapped alewives versus those without. Moving the other direction Matthew Walsh is investigating the impacts on the prey of Daphnia and how that affects ecosystem function. I think that research such as this is absolutely critical.

Throughout much of the history of ecology a great deal of emphasis has been placed on studying pairwise interactions. I think that this type of research is an excellent example of how we, as a field, can begin to move away from that viewpoint and towards a better understanding the dynamics of complex systems. Furthermore, while I think that the fields of ecology and evolution have prospered relatively independent of one another, I think that we can learn a great deal about the world by bringing these two disciplines together.

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