This was my second paper that I wrote during my PhD (2004-2007) with my supervisors (Dr. Francoise Burel & Pr Pierre Auger). At that time I was working on what is called methods of aggregation of variables
. For me the interest of this hierarchical mathematical method was to understand how the life-history traits of a species measured at a habitat scale (i.e., vital rates, movement, life-cycle, etc ... measured at a habitat scale), could be scaled up and understood at the landscape scale (i.e., global survival rate, fecundity, natural selection pressure, etc ... observed at the landscape scale).
For this paper, I used this method to understand how habitat loss and fragmentation was impacting the life-history traits of a #keystone
, aka Abax ater
) in the #bocage
landscapes of the celtic region of #Brittany
(France). Abax is a corridor forest beetle known to be sensitive to forest loss and fragmentation.
We found that the spatial matrix population model that we developed to represent the life-cycle of the species, its vital rates within various habitats (forest, hederows, corn fields) and movements between habitats could be scaled up (i.e., aggregated) almost always into a simple non-spatial version for most landscape configurations that we studied, and this without making significant aggregation errors that would have had affected the mathematical properties of the matrix population model (eigen values, eigen vectors, etc ...). As a consequence, we were confident that we could upscale and understand the demography and life-history traits of the species at the landscape scale, rather than just at a habitat scale. With this aggregated model at the landscape, we could also predict critical threshold of forest loss and fragmentation, and understand their impact on the vital rates and population viability of the species.
I hadn't time during my PhD to extend this paper to show how this method could be used to also upscale natural selection pressure on the vital rates (measured as the sensitivity (= heritability) or elasticity (= evolvability) of the population growth rate to disturbances of the vital rates of the matrix population model) from the habitat to the landscape scale. However I still believe this method could bring fresh new light on this topic. I happy to work on this with some of you guys if you find any interest for your own species.
If you are interested by hierarchical methods, and that you don't care about math (and my poor writing skills at that time ;p), you may find interesting downloading and reading the paper here (http://goo.gl/eYoHJM
). Reference:~ Pichancourt, J. B., Burel, F., & Auger, P. (2006). Assessing the effect of habitat fragmentation on population dynamics: An implicit modelling approach. Ecological Modelling, 192(3), 543-556.