Wednesday, August 10, 2011

ESA Austin: Day 3

Another great day of talks, and surprisingly so. I went to several talks that were more or less randomly chosen, and was impressed by some of the science that graduate students and younger scientists are doing. While others see a potential decline in ecology, I see a very bright future.

M. Duffy examined how virulence susceptibility and the cost of disease resistance in daphnia and its pathogen (yeast). This talk had one of the best setups I seen, and is based on a trade off between r and resistance. Epidemics result in increased resistance, as one would expect with evolution, but equal number of lakes showed evolution for increased susceptibility because of these tradeoffs. Small epidemics should result in increased susceptibility because of a greater fitness cost from reducing r than from mortality. Large outbreaks should result in greater susceptibility as mortality is high. She also showed that environmental context could alter expectation (e.g., productivity or predation).

In the next talk N. Loeuille examined the heterogeneity of resource dispersal. Classic models assume homogeneity in resources availability for competition. But with different diffusion rates, niche competition may be decoupled from tradeoffs needed for coexistence. He used a model with differential dispersal of resources. Depending on tradeoffs, the model will produce the evolution of diverse strategies of disperal. There will be specialization on single resource if dispersal is symmetric. If dispersal rate is too high or too low, but equal, then the resources support lower diversity. If two resources disperse differentially, creates heterogeneity at different scales and will support higher consumer diversity.

I ran over to Tad Fukami’s talk. He examined phylogenetic patterns in priority effects in the assemblages of yeast that colonize flower nectar. He hypothesized that there should be a strong priority effect with close relatives, since they tend to occupy similar niches. He tested this by Introducing species in different orders and assessed relatedness effects using genetic sequences. The experiment was directed by natural history of the system, like time length of flowers, microbial population dynamics in flowers. If one species colonizes first, he showed that it can reach carrying capacity regardless of the presence of other species. If it arrives second, there are major effects on abundance, but differs between which is first species. Closely related species result in strong priority effect, but weak with distant relatives. Result robust even if you control for differential ability to deal with abiotic conditions. The potential mechanisms include differentially reducing amino acids, and different growth rates on sugars.

Kevin smith gave a great talk on extinctions. He used several large, recently assembled datasets to examine how range size correlates with extinction risk under different scenarios of habitat destruction. Randomly, you would expect that broad species have a low probability of extinction overall and endemics have a high probability. Across the datasets, widespread species are going extinct at higher probabilities then a random model. Land snails conform to random model based on species range. However, for bird and amphibian datasets, the rare species bahave as expected with high extinction risk, but the middle ranged species have higher than expected extinction risk

L. Prevost examined how the theory of Island Biogeography (IBG) explained diversity patterns in fragmented habitats in mid to high elevation habitats in Costa Rica. The short answer is not very well, there were not distance or area effects on plant diversity. Communities have low similarity, no relationship with distance, but are similar according to elevation. It seems as though species responses to heterogeneity drives the system, so she recommends that many small reserves could be valuable.

In a very interesting and stimulating talk, A. Rominger examined fluctuations in evolutionary history. He showed that there are more fluctuations than predicted by various models including random walks (which conforms to a Gaussian distribution). Gaussian is observed in small time slices, but variances change over time. Fluctuations within orders fit Gaussian very well, but different from one another. Volatility itself evolves by gamma distribution. He shows that volatility is inherited within orders, and fascinating and controversial conclusion.

John Parker testing the often assumed, but understudied assumption that exotics differ in advented populations versus native. Basically, is there an away-field advantage? Examined home and away for 1000 worst invaders, across many taxa. Looked at size, reproduction, population growth. None of these were particularly enlightening. For example they are not bigger in away sites, size at home predicts invader size 1:1. There is some variation, but no consistent trend. Fecundity, also no consistent trend, with noninvasive just as likely to increased fecundity. Abundance not consistent but slight trend to be bigger away. Survival, growth, same thing. Overall slightly better away, but not greatly. We need to reexamine our hypotheses.


Juliano "Pqno" van Melis said...

Wait...About L. Prevost seminar:
Did she considered the existence of a very likely resilience of species similarity?

Marc Cadotte said...

I think that was implicit in her data, and would be definitely interesting to work out. Similarity locally but differences among patches at a larger scale.