The Laws of Ecology: It is science, honest!

Aug 26, 2006

The Bottom Line The bottom line is quite persistent, isn't it?

I fully intended to finish my series on hermaphroditic sexual selection. Unfortunately, the cosmos appears not to have wanted that to be. Since the last segment, my computer crashed again(!), my flashdrive got fried, and my work PC got formatted. There is no way in hell I’m gonna try and find all that stuff again, no matter how much I love the subject. So instead I’ll treat you to a little lecture on some of the laws of ecology…

That's the thing about being geeky about science - there's always something to say...

What is ecology?
First off, ecology is the study of the interactions and interrelationships between organisms and their environments. The term ecology was coined by the evolutionary biologist (and scoundrel of embryology fraud fame) Ernst Haeckel, from the Greek oikos, for “home”, and logos, “to study”. Ecology is thus the study of our “homes”, or our immediate environment. While Haeckel was the first to formally invoke the field of ecology, the study of organisms and their environment is, of course, far older, and has its roots in natural history – the observation of nature from the earliest times.

What is a law?
A scientific law is a regularity which applies to all members of a broad class of phenomena, or a generalized description of how things behave in nature under a variety of circumstances. Laws are NOT, as is commonly supposed, theories which have reached a high degree of experimental confirmation. Laws are simply statements of a pattern, with no real explanation – that’s where theory comes in. (Newton’s Laws of Gravitation, for example, express mathematically the attractive relationship between bodies, but do not explain them; Einstein’s Theory of Gravitation provides an explanation for the relationship observed.)

Principles of Ecology
Ecology is sometimes perceived by other sciences as being rather messy, and not very rigorous, at least in the mathematical sense. Recently, debate has raged over whether or not there exist any laws of ecology or evolution that might be analogous to the laws of the physical sciences (such as the laws of thermodynamics). Laws, after all, do not have to be exceptionless or inexorable or whatever, but they do have to be pretty damn consistent. As yet, all candidate ecological laws have sufficient exceptions that it might be best to regard them as regularities or principles.

A few of these candidate laws (handily presented in alphabetical order for your enjoyment) are as follows, presented as briefly as I’m able to:

Note: tracking the origin and development of ecological laws is not an easy task, and in most cases the modern expression differs significantly from the original. This just serves as an example of the way science changes as a result of self-examination and criticism, but it does make life a lot less clear-cut...

Allen’s Rule: Originally proposed by Joel Asaph Allen (1877), this rule states that certain extremities of animals are relatively shorter in the cooler parts of a species’ range than in the warmer parts. (The term “extremities” mainly refers to arms, legs, ears and snout/nose).

Bergmann’s Rule: Originally proposed by Christian Bergmann (1847). There have been many formulations of Bergmann’s Rule. One widely-accepted formulation is: within a given species (or species cluster), individuals from higher latitudes will tend to be larger than their lower-latitude counterparts. Several mechanisms have been proposed to explain this rule. Bergmann’s favoured proposal was that this was a result of heat conservation related to cooler temperatures at higher latitudes.

Fisher’s Fundamental Theorem: R.A. Fisher, one of the founders of what has come to be known as the Modern Synthesis of evolutionary biology, showed that natural selection always ensures that a generation is more adapted to the parent generation’s environment than the parent generation was. Note: this does not mean that each generation is more “advanced” than the previous one, nor does it mean that each successive generation would perform better in the former environment. It just means that, of all the factors affecting fitness (genetic drift, for instance), natural selection will always favour increased fitness. Many biologists have been rather blasť about this theorem, while others have enthusiastically embraced it as a “law” of adaptation. I swing to and fro on it from day to day.

Gloger’s Rule: Originally proposed by Constant Wilhelm Lambert Gloger (1883). This rule holds that dark pigments increase in races of animals living in warm and humid habitats. (This rule is sometimes used to explain the original geographic distribution of human races). Dark pigmentation helps protect against ultraviolet radiation, but also has several other effects, many of which have only begun to be investigated recently.

Liebig’s Law: Also called the Law of the Minimum. An early version of this law was formulated by Baron Justus von Liebig (1840). The modern version of the rule holds that, of all the biotic or abiotic factors that control a given population, one or two have to be limiting – that is to say, a change in thee factors produces a change in the average or equilibrium density of the population. These factors could be biotic (e.g. population density of a particular predator species) or abiotic (e.g. amount of nitrogen in the soil).

Lotka-Volterra’s Law: Originally proposed, independently, by Alfred James Lotka (1925) and Vito Volterra (1926). This principle says that when populations are involved in negative feedback with other species, or even components of their environments, cyclical dynamics are likely to be seen. An example of a negative feedback loop: when prey population density increases, predator population density may also increase, which in turn feeds back to reduce the prey population through increased predation-related mortality. Predation then slows as predators starve, allowing the prey to recover, and the cycle continues ad nauseum.

Malthusian Law: Originally proposed by Thomas Malthus (1798), whose Essay on the Principle of Population had some disturbing things to say about the future of humanity. This law holds that, when birth and death rates are constant, a population will grow (or decline) at an exponential rate. It describes the default situation for populations - how they behave in the absence of any disturbing factors (like predation, etc.). The Malthusian law is a fundamental principle of ecology and evolution, underlying the notion of natural selection. (In fact, Charles Darwin’s conception of natural selection was avowedly fuelled by his reading of Malthus.)

Final Thoughts
These rules (or principles, or regularities, or whatever) serve to illustrate the close relationship between ecology and evolution, and theoretical explanations for the observed regularities are usually framed in terms of natural selection and adaptation. The laws may be explicitly ecological, mere statements of regularities, but the explanatory framework behind them is evolutionary – based on descent with modification, just like old Charles Darwin had in mind, only more so. All these ecological laws are aspects of the single core principle underlying biology.

It’s all a bit amazing, really.

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