University of St Andrews-Led Study Reveals Global Trend of Organism Size Reduction

Image of Butterfly fish by Maria Dornelas.
Issued by the University of St Andrews Communications Office.

(IN BRIEF) New research, led by the University of St Andrews and published in Science, reveals that organisms worldwide are shrinking in size due to a combination of species replacement and changes within species. The study, conducted by an international team of scientists from 17 universities, spanning six decades of data, found that the phenomenon is most common among fish but varies among other groups of organisms. Interestingly, ecosystems tend to maintain a balance in total life volume (biomass) despite these changes, indicating an intriguing adaptability. This research sheds light on how organisms are responding to challenges in the Anthropocene era.

(PRESS RELEASE) ST ANDREWS, Scotland, 8-Sep-2023 — /EuropaWire/ — The University of St Andrews, founded in the early 15th century, is Scotland’s first university and the third oldest in the English speaking world, announces a groundbreaking study led by the University has uncovered a compelling trend: organisms worldwide are experiencing a reduction in size due to a combination of species replacement and intraspecies changes. This transformative research, published in the journal Science, draws on data spanning six decades and encompasses diverse animal and plant species.

Conducted by an international consortium of scientists hailing from 17 renowned universities, this research initiative received critical support from the German Centre for Integrative Biodiversity Research (iDiv). The study was spearheaded by scientists from the University of St Andrews’ Centre for Biological Diversity and School of Biology in collaboration with the University of Nottingham.

While previous studies hinted at diminishing sizes, such as the decrease in trophy fish size in fishing competitions and the vulnerability of larger species, this new investigation connects the dots comprehensively. It demonstrates that the decline in organism size results from not only individuals within species becoming smaller but also from the replacement of larger species by smaller ones.

Lead author Dr Inês Martins, from the University of St Andrews, said: “In some locations, for example, smaller and smaller individuals of thorny skate are being observed, while smaller-bodied species like mackerel are increasing in abundance.

“Whether it’s because of what humans prefer to eat, or their habitats getting warmer, big fish just can’t seem to catch a break.”

The phenomenon of shrinking is most prevalent among fish, though for various groups of organisms, including plants and invertebrates, the changes are more multifaceted. Examining a broad spectrum of species reveals a nuanced pattern, with some organisms growing larger while others undergo reduction.

Senior author of the paper, Professor Maria Dornelas of the University of St Andrews, said: “We think this suggests that, when large organisms disappear, other ones try to take up their place and use up the resources that become available.”

Reflecting on the importance of these results Dr Martins added: “Recognizing and exploring this complexity is imperative if we want to understand the mechanisms involved in how body size is changing through time.”

Remarkably, the study identifies the substitution of a few large organisms with numerous smaller ones while maintaining consistent biomass—the total life volume—within ecosystems. This intriguing finding supports the hypothesis that ecosystems adapt to change by balancing reductions in body size with corresponding increases in organism abundance. This equilibrium highlights the remarkable resilience of ecosystems in maintaining the overall quantity of life within specific habitats.

The implications of these findings extend far and wide, offering fresh insights into how diverse organisms are adapting to the challenges posed by the Anthropocene era.

Professor Dornelas said: “It’s clear the widespread species replacement we see around the world is having measurable consequences. Organisms becoming smaller has important effects as the size of animals mediates their contribution to how ecosystems function, and how humans benefit from them. Bigger fish can usually feed more people than smaller fish.”

Working group co-lead Dr Franziska Schrodt, from the University of Nottingham, said: “Our study highlights the importance of considering changes in species’ characteristics at both the individual level and across species if we want to understand the effects of environmental change and human influences on biodiversity globally.

“Unfortunately, we currently lack data on many organisms other than fish to draw clear conclusions – future research will benefit from a greater investment in these kinds of measurements, particularly when exploring food webs and other species interactions.”

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SOURCE: The University of St Andrews