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COMPLEX TIME: Adaptation, Aging, & Arrow of Time

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Irreversible Processes in Ecological Evolution/AnnetteOstling

From Complex Time

Notes by user Annette Ostling (Univ. Michigan) for Irreversible Processes in Ecological Evolution

Post-meeting Reflection

1+ paragraphs on any combination of the following:

  • Presentation highlights
  • Open questions that came up
  • How your perspective changed
  • Impact on your own work
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Darwin's arrow of time versus the 2nd law

Life on earth is subject to constant energy input from the sun. The 2nd law of thermodynamics, that entropy should increase, is for a closed system. So it seems it is not even really relevant for thinking about life on earth.

Definitions of irreversibility

One key def of irreversibility we discussed is that if you reversed time the process would look strange—abiological. Can we make that definition more quantitative? Perhaps we mean simply that it would be going against changes predicted by the selective regime or expected population dynamics? Can we make that definition accommodate degrees of irreversibility, e.g. looking backwards involves changes less likely to happen? This fits in with what Priyanga talked about with adaptation to colder being easier than adaptation to warmer.

BUT is this definition too broad? Any system with an equilibrium point is irreversible in this sense, because if you reversed time series of it approaching equilibrium it would not make sense?

So do we really need to add something more to that definition, perhaps to include the idea that some environmental variable is being changed in time and we are watching the response to it, and asking if the system would go back if we changed the environment back? In that case our definition of irreversibility is the presence of hysteresis?

And is another definition of irreversibility that the system changes in a way that impacts its future potential changes or response to change in the environment? Or maybe this is just something often associated eith irreversibility, as it is not the same as asking about a reversal of time, but instead whether there is path dependency in the system. But this is then more Gould’s question about replaying the tape of life than it is about irreversibility?

In the case of competitive cluster formation, if one assembles the community under one environmental filter, and then environmental filter changes, community biomass may go down and never achieve what it was before or could have been under new environmental regime if assembled that way in the first place? Have in mind that environmental filter effects may not be strong enough to overcome competitive footholds. 

Drift and selection and is drift reversible?

Two key processes in ecology and evolution are drift and selection (among species or among alleles). Corner more disordering perhaps? So would think it would increase entropy in a sense and lead to irreversible changes? But we think of it here as reversible. Can we be more quantitative about why we think about it that way? Is it really?

In a sense drift can irreversibly prevent a system from reaching another fitness peak, by causing loss of even an advantageous allele. It can also be involved in the somewhat irreversible process of competitive cluster formation. A particular species may gain high abundance by chance and then have a stronger influence on the the competition landscape for other species and become abundant in its cluster. Actually if there are no edges and no environmental filter, drift is a potential key ingredient in cluster formation (along with initial conditions).

Questions I raised in my talk

In my talk I highlighted that the formation of clusters on trait axes has some degree of irreversibility, in the sense that under strong competitive sorting, once a species dominates a particular cluster it is unlikely to loose its foothold. It would take a strong perturbation in species' abundances, or a change in which species are favored by the environment, to change which species would dominate in each cluster. Further, once certain species have gained a foothold in each cluster, this influence any subsequent assembly or evolution (selection, speciation, extinction) in the community.

The questions I posed about this particular phenomenon of irreversibility are:

1) How is the rate of competitive sorting, i.e. the strength of cluster formation, and hence degree of irreversibility, shaped by the mechanisms of competition? Do clusters emerge for all realistic competition mechanisms?

2) How will cluster formation depend on spatial scale, and how will this be influenced by the strength and scale of dispersal, relative to the scale of any heterogeneity involved in niche differentiation mechanisms?

3) Is the irreversibility of community pattern formation a particular concern for communities that may become isolated? These communities will experience extinction debt, and afterwards their resilience to environmental change may be low (the species that may be favored by the new environment may be gone).

Reference material notes

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  • Here is [A] database on [B] that I pull data from to do [C] analysis that might be of interest to this group (insert link).
  • Here is a free tool for calculating [ABC] (insert link)
  • This painting/sculpture/forms of artwork is emblematic to our discussion on [X]!
  • Schwartz et al. 2017 offers a review on [ABC] migration as relate to climatic factors (add the reference as well).

Reference Materials

Title Author name Source name Year Citation count From Scopus. Refreshed every 5 days. Page views Related file
The application of statistical physics to evolutionary biology Guy Sella, Aaron E. Hirsh PNAS 2005 0 5

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Emergent structure and dynamics in stochastic, open, competitive communities

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