ESA 2010 Day 4 (August 4th)

J. Nathaniel Holland gave one of the most thought-provoking talks (“Integrating mutualism into food webs through consumer-resource and network theory”) of this fourth day of the ESA meeting. Although I need to do some more reading and thinking on his ideas to fully understand them, Holland seems to be suggesting that the Lotka-Volterra models of mutualism, which predict that mutualisms should not be stable in a network of interactions, should be replaced by integrating mutualisms into our consumer-resource models. In my way of conceptionalizing this, a pair of mutualists are essentially reciprocal parasites, both gaining more from the other than they “give” in return. Even verbalized this way, the essential nature of mutualisms is shed in a different light, with “donations” to the partner more like “tolerated losses”. The currency involved in consumer-resource interactions is pretty straightforward: biomass flows with some efficiency between elements of a food web. How non-biomass benefits conferred on mutualist partners can be accounted for in a consumer-resource framework is still a little unclear to me. Still, Holland’s work is intriguing, as the way that we understand the nature of mutualisms has a big impact on the broader question of ecosystem stability (which was a focus of last year’s symposium on mutualistic networks).

Also in the field of mutualistic interactions was the talk given by Manuel Morales, “Tri-trophic dynamics in an herbivore-protection mutualism”. Morales works in a system with four interacting species: a plant, its herbivore, a mutualist which offers protection to the herbivore, and a predator on the herbivore. He presented a model of this interaction that was parameterized using field observations from his study system: treehoppers who give honeydew and gain protection from ants, and the spiders that prey on the treehoppers. Interestingly, the model predicted unstable interactions in the presence of the mutualist, presumably because the positive feedback between mutualist partners allows for over-exploitation of the basal resource. That is not what Morales finds in his real systems, so some other dynamic must be at work. He suggests that the missing applicable dynamic is female choice of host plant: he has shown that female treehoppers selectively avoid previously-infested host plants, which may dampen the oscillatory dynamics which cause instability in his model. Such an explanation would imply that treehoppers have evolved to perform a kind of crop rotation; I would be interested in how such a coordinated effort could evolve.

I have always enjoyed the diverse work of Brendan Bohannan, and he expanded the breadth of his research further with work presented in his talk “Microbial responses to changes in land use”. We are all familiar with the kinds of biodiversity loss that occurs amongst plant and animal species when pristine land is converted for human use, but what about the diversity of microbes in these areas? As part of a collaborative project called the Amazon Rainforest Microbial Observatory, Bohannan and his colleagues
collected soil samples in primary and secondary forest sites using a nested hierarchical sampling method that allowed them to consider spatial diversity as well as overall diversity. When considering microbial diversity it is impossible to collect, isolate, culture, and identify every strain, so usually diversity is assessed by looking at genetic diversity. DNA present in a sample is amplified at a particular locus and sequenced. A technique called pyrosequencing allows for the identification of up to 40,000 sequences per sample, which makes it possible to look at the multitude of microbes that might be found in a single patch of soil. What initial results from Bohannan’s group suggest is that when considered at this coarse scale of identification, microbial diversity does not decline in areas converted by humans. It seems that human disturbance of soils tends to randomize the microbial community, but not reduce its overall diversity. If further studies bear out this result, this is both interesting and encouraging news: it seems as though the microbial communities upon which so much ecosystem functioning relies are more robust to disturbance than communities of macroscopic organisms.

On this day I also attended the Urban Ecosystem Ecology Section business meeting. urban ecology is a pretty neglected subfield, but in recent time is emerging as a more respected and important area of ecology. This ESA section seems to be at the forefront of this emergence, and a lot of great ideas were tossed around. As more and more colleges and universities are offering courses in urban ecology, the section has provided a really valuable resource outlining where existing programs exist and what they offer. At this point there is no textbook designed to accompany an undergraduate course in urban ecology, and there was some discussion of such a book being worked on by members of the section. Some exciting symposium proposals for next year’s ESA meeting were also discussed. Right now I am what I would call a “benign lurker” at these urban ecology talks and meetings, but eventually my hope is to bring a course in urban ecology to Pratt.

In the evening I attended a special session led by Laurel Anderson entitled “Collaborative Research at Primarily Undergraduate Institutions: Developing the Ecological Research/Education Network (EREN) for PUIs”. The Ecological Research/Education Network (EREN) is a recently-funded inter-institutional project designed to allow for research collaboration between students and faculty at primarily-undergraduate institutions (PUIs). The goal is to involve undergraduate students in authentic research and EREN will attempt to remove one barrier to reaching this goal: the inability of isolated programs to complete sufficiently extensive studies within the biology curriculum. Through pre-planned and coordinated data collection, EREN-affiliated institutions will be able to produce aggregate data that spans large ecological gradients (a feat rarely accomplished even by large research institutions). Well-conceived from the outset, the working group that proposed EREN has established guidelines for publication of collaborative projects, a way for interested faculty members to become involved at various levels, and a series of pilot projects to serve as a model for how EREN should work. I was really impressed by the project already made in the EREN project, and hope to get my students involved in data collection for EREN.