Thursday, August 11, 2011

Day 4

As the fourth day of ESA sessions began, it was clear that many attendees’ (including my own) energy was flagging, and 8:00 am talks were more sparsely attended. However, this didn’t mean that the presentations were of any less quality or interest. In the face of so many competing talks, I took the path of least resistance, in that I chose an interesting-sounding session, and stayed put. Today, that meant that I saw much of the Community Pattern and Dynamics IV session, and some talks in the Invasion: Invasibility, Stability, and Diversity session.

Thursday poster session

The early morning portion of Community Patterns and Dynamics provided some interesting talks focused on diversity in aquatic ecosystems, in particular ponds. Schalk et al. examined how the community structure of tadpoles related to environmental gradients in Bolivia, in particular how tradeoffs in pond permanency, predation, and canopy cover determine the tadpole species present. This talk proved that frog ovipositing behaviour can be fascinating, and provided the first example I've seen of a mule-aided sampling strategy (the mule transported supplies).

Jamie Kneitel reminded us that aquatic ecosystems, and the functions and services they provide, are under threat. One issue is human-driven increases in turbidity. To examine the impacts of turbidity, and how these impacts may differ depending on the underlying cause – turbidity may be cause by input of resource, leading to eutrophication, or directly, such as via cattle trampling in pools—Kneitel used experimental mesocosms meant to simulate vernal pools. He showed that different causes of turbidity conferred different types of changes in water chemistry, and that turbidity had different effects on vegetation and invertebrate communities.

Moving to the Invasion: Invasibility, Stability, and Diversity session, Jiaqui Tan from Lin Jiang’s lab gave a very interesting talk about the oft-observed negative relationship between invasibility and diversity. In particular he connected the suggested explanation for this pattern (the sampling effect and the niche complementarity effect) to phylogenetic patterns of relationship between species. He predicted that increasing phylogenetic relatedness would increase the sampling effect, while increasing phylogenetic diversity would increase niche complementarity. Using microcosms of aquatic bacteria, in which Serratia marcesens acted as the invader, he looked at how a factorial design of low, medium, and high phylogenetic relatedness and phylogenetic diversity effected invasibility of the bacterial communities. Perhaps surprisingly, phylogenetic diversity had only a little effect on the degree of invasibility, but phylogenetic relatedness strongly decreased invasibility. However, an explanation for these results was made more difficult by the fact that the 57 traits he measured for the bacteria showed little evidence of niche conservation.

At the same session, Karen Alofs shared some preliminary analysis of a fantastic dataset showing changes in the presence of introduced smallmouth bass over 30 years in Ontario, Canada. Ontario is a place where southern and northern range limits of many fish species occur, and ranges are limited by temperature. Smallmouth bass is an invasive species originally introduced for sport, and Karen examined how changes through time in the bass’ range related to species composition, environmental characteristics and predator presence. She found that abiotic and biotic variables were correlated with invasion probability, but made the important conclusion that community composition affects invasibility, but the reverse—invasion alters community composition—is also true.

Finally, Galen Holt from Peter Chesson’s lab gave a great talk about fitness-density covariance as a possible mechanism of coexistence, and the interaction of dispersal with it. He examined water invertebrate species in a stream, in which both symmetrical dispersal and asymmetric dispersal (i.e. stream flow) could affect the strength of this mechanism. In fact, he found that dispersal weakens fitness-density covariance since species are less likely to stay where environment is best, as is required by this mechanism.

An unidentified University of Toronto student,
letting loose after a long day of talks

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