Research shows size matters
We now have the data to prove it. Mark Bruer reports.
Ecologists may need to rethink their understanding of why living organisms – from beetles to blue whales – grow the sizes that they do, according to new research.
An international team of scientists has compiled more than 22,000 bits of data from 2800 sources to look for patterns in the sizes of eukaryotes – living creatures whose cells contain a nucleus surrounded by a membrane. That includes all plants, animals, fungi and protozoa.
What they wanted to explore was the relationship between the abundance, growth, metabolism and mortality of organisms, and how these affect body size.
For example, would an abundant bug with rapid growth and a high metabolic rate be smaller or larger than other species, and could this be predicted mathematically?
Understanding the interplay between these four variables is important. Their relationship is increasingly used to understand and make large-scale predictions of the effects of critical global environmental problems.
What the team found by analysing their mountain of data was that underlying the endless variety of living things, many of the most important features of life appear to follow universal laws.
The findings show how metabolism, abundance, growth and mortality all follow strikingly consistent relationships with body size, from the tiniest bug to the largest mammal.
And yes, these relationships can be expressed in mathematical formulae, which the researchers present in a paper published in the journal Proceedings of the National Academy of Sciences. Intriguingly, the formula for predicting growth appeared to be ubiquitous across species, the researchers write.
"The fact that we find these simple mathematical relationships that span all life, points to some fundamental process at the heart of living systems that we don't yet fully understand," explains team leader Ian Hatton from the Universitat Autonoma de Barcelona in Spain.
The study also presents evidence that suggests one of ecology's most prominent theories, called the Metabolic Theory of Ecology, needs to be re-examined.
This theory has played a significant role in ecological thinking, based on the idea that an organism's metabolic rate is the principal limit on many other vital traits, including how quickly it can grow.
"One of our key findings is that limits to the rate at which an organism can grow seems to put the brakes on metabolism, rather than the other way around," says co-author Eric Galbraith.
"This puts growth in the driver's seat for understanding these large-scale patterns."
Given that growth underlies everything from juvenile development to cancer, and from resource productivity to global carbon cycling, understanding growth more generally could prove very important.
"What is so astounding is that no matter where you look, no matter what kind of living system, everything seems to follow the same growth law,” says Hatton.
"We can't yet explain it, but we know it has deep implications".