Ecosystems grow independently of the body size of the organisms that compose them
A recent study, published in Nature Communications and led by Lorenzo Fant from OGS and Giulia Ghedini from the Instituto Gulbenkian de Ciência (Lisbon), offers a new perspective on how individual organisms and entire ecosystems grow and metabolize energy.
The study begins with observations of the developmental dynamics of marine phytoplankton in laboratory settings. These tiny organisms, thanks to their wide range of sizes, provide an ideal model for understanding the link between individual metabolism and ecosystem growth.
The research demonstrated that, even though the individual species populating an ecosystem vary greatly in size, the metabolism of the entire living system remains unaffected. Instead, the total metabolic activity and growth of the ecosystem depend almost exclusively on the total biomass, the available resources, and interspecific competition. This finding applies to both monocultures (single species) and communities of different organisms.
The research is based on the sublinear relationship between metabolism, growth, and individual size. According to this observation, larger organisms proportionally use less energy per unit of mass compared to smaller ones. A similar relationship is observed when comparing growth rates, where smaller organisms grow proportionally faster than larger ones.
Although organisms of different sizes exhibit varying metabolic rates, these differences seem to vanish at the ecosystem level, where energy consumption appears to be independent of the size of the individuals within it.
The study reveals that the metabolic rate of an ecosystem does not change drastically with variations in the composition and size of the species present within it. On the contrary, ecosystems maintain similar consumption and growth rates, even when the sizes of the organisms composing them differ significantly.
The authors of the study argue that this is possible due to interspecies competition, which helps regulate and balance the overall metabolism of an ecosystem. As biomass increases, competition for available resources and interactions among individuals slow the overall metabolism, eliminating differences between individuals. This is the main reason why the metabolic rate of ecosystems remains relatively stable despite variations in species composition.