Biodiversity is governed by organismal trade-offs, but a commonly assumed trade-off, the gleaner-exploiter trade-off, does not exist. This is demonstrated in a new paper published online today in PNAS analyzing data from more than 500 species, aquatic and terrestrial, and from single celled organisms to birds and mammals.
No organism performs optimally with respect to all traits. Peak performance in one trait is typically at the cost of the performance of another trait. Such trade-offs are what generates biodiversity. One commonly assumed trade-off is that between the ability to search for food when resources are scarce versus the ability to process large amounts of food when resources are abundant. Organisms living in nutritionally dilute environments are thought to optimize their food searching ability, while organisms adapted to living in nutrient rich environments are rather adapted assimilate large amounts of food. This would be equivalent to the concepts of ‘gleaners ‘and exploiters’ or the distinction between oligotrophs vs. copiotrophs, and implies a negative relation between maximum clearance rate (search ability) and maximum ingestion and assimilation rate (food processing capacity).
Analyzing observations of consumption rate as a function of resource concentration has allowed us to estimate these two parameters for more than 500 heterotrophic eukaryotes. Rather than the expected negative relation, we find a positive relation between the two parameters. That applies across all taxonomic groups examined, and to aquatic as well as terrestrial organisms. This means that organisms that have high clearance rates also have high maximum ingestion rates (also when accounting for differences in sizes).
Our finding places organism on a slow-fast gradient in the ‘pace-of-life’, which is the result of a fundamental trade-off between current versus future reproduction. We speculate that this pattern is governed by the trade-off between resource acquisition and predation risk. ‘Bold’ organisms acquire resources at high rate but also expose themselves to high predation risk, while organisms with stealth behavior also get access to fewer resources. A high predation risk can also be compensated by investment in defenses, which is at the cost of a high growth rate. At the Centre for Ocean Life we have quantified the resource acquisition/predation risk/defense trade-offs for a large range of pelagic organism, and these trade-offs are built into many of our models. The results of the present study confirms that we have focused on the most fundamental taxa-transcending organismal trade-off in our construction of trait-based models of marine ecosystems.
Read the paper here: 10.1073/pnas.2008370117
Kiørboe T, Thomas MK (2020) Heterotrophic eukaryotes show a slow-fast continuum, not a gleaner-exploiter trade-off. PNAS. DOI: 10.1073/pnas.2008370117
Image credit: Erik Selander