Is It Possible to Estimate Time-Specific m2 Values?

[HC]

Hi all,

I’d like to ask whether it's possible in BioGeoBEARS to calculate how the m2 value of a trait changes across different time periods during evolution, in order to reflect the changing importance of that trait over time?

I understand that the time-stratification model can divide the analysis into different time slices, but the model still only produces a single m2 value for the entire timeframe. It seems this only allows us to assess whether paleogeographic changes (e.g., tectonic plate movements) influence overall dispersal patterns, but not whether the importance of a specific trait varies across different time periods — is that correct?

Or, is it the case that currently there's no way to statistically assess changes in the influence of traits across time periods, and the best approach is still to visualize the timing of trait emergence on a phylogenetic tree and discuss it qualitatively?

Thank you very much!
Hsuan

[Nick Matzke]

Hi! Great question!  Having an m2 that varies by time-slice is an imaginable model, but it is not one that is currently programmed and it would take some serious work to do so. 

You might, though, get some sense of it by using one of the dispersal multiplier/distance matrices, and having say:

1 1 1

1 1 1

1 1 1

0.1 0.1 0.1

0.1 0.1 0.1

0.1 0.1 0.1

and then taking this to the power ^n (the +n model variant, using the "envdistances" matrix).

If n=1, then overall dispersal rate was 10 times lower in the older time period.  If n=0, there is no difference.  If n=-1, then dispersal rate was 10 times higher in the older time period.

This is a bit crude, but would give you an idea of changes in overall dispersal rates, then you could multiply through by any other multipliers to get specific dispersal rates.

Cheers!

Nick

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