Networks Unit
IMT School
for Advanced Studies
Lucca (Italy)


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Different living systems, the same rules

Our earth is a beautiful place to be, with a huge diversity of life forms spread across all environments. Despite this huge diversity of sizes and body plans, all living organisms rely on the same building blocks (e.g. metabolic pathways for photosynthesis and respiration) and are subject to similar evolutionary constraints on the way how they acquire and use energy.
As a result, we often observe clear patterns whereby life-diversity varies hugely along some dimension, but is heavily contrained along some other dimension, possibly reflecting the fact that living organisms can only take a limited range of forms and body plans, squeezed in-between the inefficient and the unattainable.

Many small and few large individuals

Living organisms can take a huge range of different sizes: over 11 orders of magnitude in body mass separate unicellular algae from trees, and bacteria from blue whales.
However, we often observe clear patterns in this diversity of sizes: first, small organisms are much more abundant than large ones. But not only, the abundance of organisms of a given size often follows a very consistent pattern across different ecological communities, which appears as a straight line in a log-log plot (a power-law).
Understanding the slope of that relation (the number λ in the figure) is one step towards understanding why these patterns emerge.

Size-abundance scaling of trees

Related scientific publications