Monday, June 12, 2017

Trilobite pelotons and the variation range hypothesis

Our new paper on "Trilobite pelotons" published by the journal, Paleontology, is now out.

Although it remains a hypothesis, the findings of the paper support the "variation range hypothesis", the notion that there is a relationship between the energy saving quantity and the size range among a group of organisms where there is an energy saving mechanism. I first explored this (with Matjaz Perc) across a range of organisms in our paper "Energy saving mechanisms in biological systems".

The variation range hypothesis is simple and intuitive. Weaker individuals can sustain speeds set by stronger individuals by exploiting the available energy saving mechanism. So, these individuals can be weaker to a degree that is roughly proportionate to the energy saving quantity.  In the paper, we summarize it this way:

"The variation range hypothesis posits that the size range among individuals in groups corresponds proportionately to the energy saving quantity (as a per cent) because weaker, smaller, individuals sustain speeds of stronger, larger, individuals by exploiting the energy saving mechanism. We determine size range by

SR = [(BLmax – BLmin) / BLmax] * 100,                      (1)

where SR is size range, and BL is body-length. As discussed further, this allows comparisons between size ranges and energy saving as a per cent, shown as equation (8). Individuals too small to fit within this range become isolated from the group and may perish, or form sub-groups of narrower size ranges, as has been modelled by Trenchard et al. (2015) in the context of bicycle pelotons.

In the wider context of migration as a factor that drives speciation (Winker 2000), we consider the possibility that this form of group-sorting may contribute to migratory divergence and to reproductive isolation, as proposed by Delmore et al. (2012). Speyer & Brett (1985) reported that individuals within trilobite groups generally fall within a rather narrow size range, a finding which tends to support the variation range hypothesis. Moreover, the presence of any similarly sized trilobites of other species mixed with clusters of another species also tends to support the variation range hypothesis, since such individuals would likely have possessed similar power and speed capacities."

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