Paper 13 - R. Kiat

Paper 13 – R. Kiat

Fenchel, T. 1974. Intrinsic rate of natural increase: the relationship with body size. Oecologia 14:317-326.

Commentary -- Richard M. Sibly

Tom Fenchel

-        Professor Emeritus at the University of Copenhagen , Marine Biology

-        PhD from the University of Copenhagen

-        Research Interests: Microbial Ecology and physiology, Marine Biology, Evolutionary Biology

Richard M. Sibly

-        Professor at the University of Reading, School of Biological Sciences

-        Research Interests: Integrating Life History Theory with the new theory of Metabolic Ecology. Using Agent Based Models (ABMs) to develop new methods in Population Ecology applicable to real landscapes.

Summary:

How fast can a species increase its population size and how might this be related to its body size? In this paper, Fenchel demonstrates a relationship between “the intrinsic rate of natural increase” of a species (r_m – also commonly known as population growth rate and in this instance measured in days) and a species body weight by looking at 42 different species from literature. His results show that smaller species (with lighter weight measured grams) have a higher population growth rate than bigger species.

By viewing r_m as a form of productivity, Fenchel then makes a connection of body size and metabolic rate. In Figure 2, Fenchel highlights the previously found relationship between the two which shows that smaller animals have a higher metabolic rate, which he says can be viewed as a measure of how much energy an organism uses for productivity e.g. reproduction vs. maintenance. By comparing organisms based upon ‘complexity’, Fenchel argues that move evolved organisms had a higher metabolic rate per unit weight, which might be explained energetically by higher maintenance in the organism – proportionally more energy is allocated to maintenance.

On a broader context, Fenchel’s paper and his framing is important in light of viewing population growth rate and body size in terms of energetics – which is still a topic of wide interest (as Sibly mentioned in the commentary).

Note: Fenchel notes that the 42 species he selected which included rats and microorganisms, were mainly limited to laboratory studies (which he suggests might be a bias selection for certain type of species).

Questions:

What other constrains might there be that relate to a species body size? Thoughts on Fenchel’s law? Figure 3? Are there other ecological concepts previously discussed that we might be able to talk about in terms of energetics?