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Irreversible Processes in Ecological Evolution/Natural selection, population cycles, and climate change in forest insects

From Complex Time

January 29, 2019
1:30 pm - 2:30 pm


Greg Dwyer (Univ. Chicago)


Cyclic outbreaks of forest insects devastate forests, leading to widespread defoliation and tree death. Outbreaks would be far worse if not for epidemics of fatal virus diseases, which decimate outbreaking insect populations. The selection pressure imposed by these diseases suggests that natural selection may affect outbreaks, but understanding such effects is impossible with data alone. My lab has therefore used a combination of field experiments and models to test for effects of selection on outbreaks. Our work shows that both heritable host resistance and variation in viral virulence strongly affect outbreaks of the the gypsy moth, Lymantria dispar, an introduced pest of eastern hardwood forests in North America. Over the last few decades, however, an introduced fungal pathogen has competitively displaced the virus. The fungus provides better control, but its survival is much higher when the weather is cool and wet, whereas climate change is likely to cause weather conditions in the range of the gypsy moth to become increasingly hot and dry. By again combining models and data, we have shown that climate change will have a strong negative effect on the gypsy moth fungus, which may lead to the devastation of hardwood forests in North America. A key question is therefore, can the virus make a comeback? Our answers to this question are as yet incomplete, but provide initial chapters in an interesting story about the ecological effects of climate change.    

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Post-meeting Reflection

Greg Dwyer (Univ. Chicago) Link to the source page

Pamela's presentation reminded me of the importance of basic competition theory in understanding competition between pathogen strains, specifically in terms of the interplay between frequency-dependent and density-dependent selection in the insect pathogens that I study. That has in turn helped me to begin to see how theory of pathogen competition is related to more general theories of competition, as Priyanga pointed out, and as became clear from seeing Annette's and Otto's and Bobby's presentations.

Something I am unclear on, however, is how and whether such theory of such generality has practical implications for pest control. Those comments apply even more strongly to the whole idea of irreversibility. I can see what Dervis and Jacopo mean by "ecological irreversibility", but I can't see the practical applications. Meanwhile, I can't see what David Krakauer's ideas have to do with killing pests in any way. That said, I can appreciate that I may need to think about all these ideas quite a bit more.

My first 2 paragraphs were based on the first day of talks. Now that the meeting is done, I have 2 more thoughts. Off and on during the meeting, we had long rambling discussions about the semantics of irreversibility. I found much of that discussion to be a waste of time. After the meeting was over, however, we were able to identify metrics of irreversibility, and those metrics will be directly useful in work in my lab.

Questions I would like to know the answer to, and that are motivated by the talks I've listened to:

Is the outcome of pathogen competition irreversible, or can it be reversed by climate change?

To what extent are high-level abstractions useful in understanding ecological problems, and in applied ecology more specifically?

Are statistically robust tests of ecological theory necessary for the theory to be useful?

Reference Material

Paez et al. (2017) and Fleming-Davies et al. (2015) represent about 2/3's of the results that I presented in my talk.

Title Author name Source name Year Citation count From Scopus. Refreshed every 5 days. Page views Related file
Eco-Evolutionary Theory and Insect Outbreaks The American Naturalist 2017 0 0
Effects of host heterogeneity on pathogen diversity and evolution Ecology Letters 2015 0 2