Wednesday, August 8, 2012

ESA Portland day 2: march of the phylogeny

The day phylogenies took over. This is how I would describe the talks I attended on day two. There was a palpable collective enthusiasm for what phylogenies can bring to understanding ecological patterns. It seemed like every session I went to there were several talks that test for phylogenetic patterns and it will be interesting to see where this all goes in the future. For me, this phylogenetic onslaught was heralded by the very first talk I went to by Jeannine Cavender-Bares. She spoke about how phylogenetic relatedness and species traits can provide important insights into community patterns and ecosystem function. She ask some of the most pertinent questions such as: how do evolutionary processes affect ecological processes; and how deep in the phylogeny is the evolutionary signal in community assembly. This last question is interesting because it can potentially tell us about past environments when certain lineages evolved. Her talk was divided into three parts. In the first part, she discussed how certain plant traits, like specific leaf area (SLA), were correlated with fire frequency. At extremely low and high fire frequencies, there is a strong trait pattern associated with communtiy membership, and with a strong phylogenetic pattern as well. But this wasn't the case with intermediate fire frequencies. In the second part, she discussed plant community patterns across an urban to natural gradient. There were important trait differences, with species having smaller seeds and higher specific leaf area in urban areas. There were more species in urban areas, but they represented less phylogenetic diversity than in natural areas -meaning that there is an environmental filter selecting for similar species. In the third part, she investigated oak adaptive radiations in North America and the resulting biogeographical patterns. There we differences in diversity across latitude, with high diversity regions also have more close relatives.

The were a number of other very interesting talks, and I spent the day fluttering from room to room, like a confused butterfly in search of sweet rewards. And rewarded I was. There were handful of very memorable talks. By both young graduate students and established researchers. Christina Lamanna gave a nice talk about phylogenetic and functional diversity (PD and FD, respectively) across an elevation gradient, which in part she used to highlight a new measure of species functional overlap. Richness and FD peak at intermediate elevation. She also examined the turnover in FD and PD and that both of these show decreasing turnover at higher elevations. At high elevations, PD was found to be overdispersed as were some of the traits, but other traits appeared underdispersed, indicating the combination of traits under very different selective regimes.

In a session on ecosystem function Jane Cowles told us how diversity and warming interact to shape patterns of ecosystem function. The experiment was great, and they overlaid warming arrays on some of the plots at the classic biodiversity experiment at Cedar Creek, Minnesota. The arrays warmed 1.5 and 3 degrees on 1, 4 and 16 spp plots and they measured aboveground and belowground biomass. More aboveground biomass was observed with warming, but not for belowground, except for deeper roots. Dominant species increased the most in aboveground biomass, seeming to respond to large pools of nitrogen available in early spring. 

One of the two best talks I saw today was given by Amelia Wolf. She constructed a biodiversity-ecosystem function experiment based on realistic scenarios of species loss. Whereas most experiments randomly assemble species together, realistic species loss selects species with certain traits, and once they are lost, those species are not part of the system at lower diversity. She used 20 years of observational data to select those species most susceptible to extinction and then created a series of plots where diversity was based on removing susceptible species. These plots were nested in that when a species was excluded from say the highest to next highest treatment, it could not be included in a lower diversity treatment. She compared this to random diversity treatments and found that the realistic species loss had a stronger effect on ecosystem function. But she suggested that this could be due to the nested structure and not the realistic scenario. So, to cover all her bases, she created 32 different nested loss regimes that were not the realistic one, and found that they were no different than random. Thus species identity and susceptibility really matter for ecosystem function decline with species extinction, as most susceptible species are often from the same functional group.

The other superb talk was from Jay Stachowicz on the influence of eelgrass genotypic richness, relatedness and trait diversity on productivity. Genotypes interact though a number of mechanisms including competition, cooperation, interbreeding, and so there are complex possibilities for the influence of genotype on productivity. From experimental combinations, he found that, counter to his expectations, plots with closer relatives had higher productivity. Further these plots with close relatives also had greater trait diversity, highlighting the complex nature of species interactions and differentiation.

Andrew Siefert gave a talk on disentangling multiple drivers on species turnover in space. Betadiversity is driven by both niche based decay of environmental similarity and stochastic due to dispersal limitation. Both generate similar patterns. But if one uses functional traits, then you can see higher or lower functional turnover than expected from chance, which indicates niche based turnover. He reported the results from 1500 forest plots across eastern USA,  with climate data and data on four functional traits. He found high turnover in soils and species, lower for climate and functional diversity. Both taxonomic and functional betadiversity best explained by climate. Close sites have high taxonomic turnover, but low functional turnover, thus climate filtering.

Finally, Elizabeth Boyle exmined arthropod phylogenetic community patterns in near arctic aquatic systems (ponds, streams, rivers, etc.). These habitats harbor an amazing diversity of insects and Elizabeth collected data from dozens of habitats over a large area, for hundreds of species and constructed a molecular phylogeny based on her own genetic work. An amazing effort for a masters project! She resampled the habitats through the summer and found that many of the habitats started off as phylogenetically clustered but became overdispersed through time. But not all habitats showed the same response, and she found that some environmental variables seemed to be strongly correlated with relatedness patterns. She also questioned whether the emergence of adults caused some of these patterns as the timing of emergence is phylogenetically nonrandom, which to me is a new explanation of potential phylogenetic patterns.

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