scaling

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Competitive advantages of colonies: size, shape and energy

Competitive advantages of colonial living in marine organisms may relate to the increasing gap between energy acquisition and expenditure as colonies grow.

The Centre for Geometric Biology is very interested in how size and shape affect an organism’s ability to acquire and utilise energy.  Researchers at the Centre also investigate factors that might affect the balance between energy acquisition and energy expenditure and the consequences of this for survival, growth and reproduction.

New research by Diego Barneche, Craig White and Dustin Marshall demonstrates how colonial marine organisms can be used to explore these issues. This research found that the relationship between size and metabolic rate (a measure of energy use) will change with temperature in some species of colonial marine organisms but not others.  This means that the way organisms use energy might vary for the same species in different environments which could then affect their ultimate colonisation success and abundance.

A colonial marine organism; Bugula neritina, one of the species Diego Barneche and colleagues manipulated in their study.
A colonial marine organism, Bugula neritina, one of the species Diego Barneche and colleagues manipulated in their study.

The advantage of using colonial organisms in this type of research is that size can be manipulated by dissecting the colonies and allowing a comparison of size without typically confounding factors such as age (older individuals are usually bigger) and nutrition (‘wellfed’ individuals are usually larger). Diego and his colleagues were able to adjust the size of colonies in a way that mimicked predation or physical disturbance in natural situations and measure metabolic rate at two temperatures in four species, two of which had a tree-like growth form and two of which were encrusting species.

Interestingly, while feeding rate has been shown to increase in proportion to size in certain colonial taxa, Diego and his colleagues found that increases in size resulted in a less than proportional increase in metabolic rate. This means that as colonies get bigger, their capacity to capture food increases more quickly than the rate at which they expend energy. This contrasts to what has been found in unitary or ‘solitary’ organisms and may explain why colonial organisms are often competitively superior to unitary organisms; the difference between energy intake and expenditure increases more strongly with size in colonial organisms.

This research was published in the journal Ecology.

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Temperature effects on mass-scaling exponents in colonial animals: a manipulative test

Authors: Diego R Barneche, Craig R White and Dustin J Marshall

Published in: Ecology, volume 98, issue 1 (January 2017)

Abstract

Body size and temperature are fundamental drivers of ecological processes because they determine metabolic rates at the individual level. Whether these drivers act independently on individual-level metabolic rates remains uncertain.

Most studies of intraspecic scaling of unitary organisms must rely on pre-existing differences in size to examine its relationship with metabolic rate, thereby potentially confounding size-correlated traits (e.g., age, nutrition) with size, which can affect metabolic rate.

Here, we use a size manipulation approach to test whether metabolic mass scaling and temperature dependence interact in four species (two phyla) of colonial marine invertebrates. Size manipulation in colonial organisms allows tests of how ecological processes (e.g., predation) affect individual physiology and consequently population- and community-level energy flux.

Body mass and temperature interacted in two species, with one species exhibiting decreased and the other increased mass-scaling exponents with increasing temperature.

The allometric scaling of metabolic rate that we observe in three species contrasts with the isometric scaling of ingestion rates observed in some colonial marine invertebrates.

Thus, we suggest that the often observed competitive superiority of colonial over unitary organisms may arise because the difference between energy intake and expenditure increases more strongly with size in colonial organisms.

Barneche DR, White CR, Marshall DJ (2017) Temperature effects on mass-scaling exponents in colonial animals: a manipulative test, Ecology, PDF  DOI