Ecology Primer Laws of Ecology An Optional Graphic

Ecology Primer: Laws of Ecology An Optional Graphic can go here l l l Nicklaus Kruger NISL nicklaus@webmail. co. za Available at http: //planet. uwc. ac. za/nisl/Eco_people/Presentations /

What is a scientific law? 1, 2 q A scientific law is a regularity that applies to all members of a broad class of phenomena q Laws are NOT theories that have been confirmed to a very high degree q Laws are statements of patterns observed in nature q Theories are explanatory frameworks for those patterns q Hypotheses have the potential to develop into either theories or laws, depending on their nature

Newton’s Law of Gravitation 3 q The classic example of a scientific law is Newton’s Law of Gravitation q Newton’s Law of Gravitation was proposed by Isaac Newton in 1687 q It quantifies the gravitational attraction between two bodies q It does not provide an explanation for this attraction q It’s merely a statement of the pattern displayed

Principles of Ecology 2, 4 q Ecology is a messy, complicated affair q It’s not as mathematically rigorous or precise as physics q Still, many candidate ecological laws have been proposed q As yet, these proposed laws have enough exceptions that it might be best to term them regularities or principles, rather than laws

Allen’s Rule 5 q Originally proposed by Joel Asaph Allen in 1877 q This rule holds that body shape varies within an animal species – certain extremities are shorter in those individuals found in the colder parts of the species’ range q This is related to heat conservation

Bergmann’s Rule 6 q Originally proposed by Christian Bergmann in 1847 q There have been many formulations of this rule since then q Within a given species, individuals from higher latitudes will tend to be larger than their lower-latitude counterparts q Several mechanisms have been proposed to explain Bergmann’s Rule

Bergmann’s Rule (cont) q The favoured explanation comes in terms of heat conservation 1) Heat exchange is related to surface area rather than volume. (2) Larger animals tend to have a smaller surface area to volume ratio. (3) Higher latitudes tend to have cooler temperatures than lower latitudes. (4) Therefore, larger animals are selected for in higher latitudes. )

Fisher’s Fundamental Theorem 7 q Originally proposed by Ronald Fisher in 1930 q This theorem shows that “the rate of increase in fitness of any organism at any time is equal to its genetic variance at that time”

Fisher’s Fundamental Theorem q According to FFT, adaptation is a function of genetic variation q Fisher thought this was fundamental because his equations showed that natural selection will always act to ensure that offspring are better adapted to the parent generation’s environment than their parents were q NOTE: other factors, such as genetic drift, can still negatively affect the fitness of the filial generation

Gloger’s Rule 8 q Originally proposed by Constant Lambert Gloger in 1883 q This rule holds that dark pigments increase in races of a species living in warm and humid environments q The pattern of this rule is similar to the pattern for Bergmann’s Rule

Liebig’s Law 9 q Originally formulated by Justus von Liebig in 1840 q The modern version of this rule holds that, of all the biotic or abiotic factors that affect a population, one or two have to be limiting q That means that a change in these factors produces a change in the average or equilibrium density of the population q These factors could be biotic or abiotic

Liebig’s Law q That means that a change in these factors produces a change in the average or equilibrium density of the population q These factors could be biotic or abiotic q For example, Nitrogen limitation is a common problem for oceanic phytoplankton

Lotka-Volterra Law 10, 11 q Originally proposed, independently, by Alfred James Lotka (1925) and Vito Volterra (1926) q This principle holds that when populations are involved in negative feedback interactions with other components of their environments, cyclical dynamics are likely to be seen

Lotka-Volterra Law 10, 11 q The classic example of such a cyclical dynamic is found in predator/prey relations q When prey population density increases, predator population density may also increase, which in turn leads to a drop in prey populations density

Malthusian Law 12 q Originally proposed by Thomas Malthus in 1798 q This law holds that, when birth and death rates are constant, a population will grow (or decline) at an exponential rate q This law is a fundamental principle of both ecology and evolution q Both Charles Darwin and Alfred Russel Wallace were inspired by Malthus to create their principle of Natural Selection

Evolution and Ecological Laws q Ecological rules serve to show the close relationship between ecology and evolution q The rules themselves may be mere statements of regularities, but their theoretical underpinning is evolutionary q As Theodosius Dobzhansky said: “Nothing in biology makes sense except in the light of evolution”

References 1. Krebs R. E. (2001) Scientific laws, principles and theories. Greenwood Press, Westport, Connecticut 2. Colyvan, M. and Ginzburg, L. R. (2003) Laws of nature and laws of ecology. Oikos 101: 649 -653 3. Newton, I. (1687) Philosophiae Naturalis Principia Mathematica 4. Turchin P. (2001) Does population ecology have general laws? Oikos 94: 17 -26 5. Allen, J. A. (1877) The influence of Physical conditions in the genesis of species. Radical Review 1: 108 -140. 6. Bergmann, C. (1847) Über die Verhältnisse der wärmeökonomie der Thiere zu ihrer Grösse. Göttinger Studien, Göttingen 3(1): 595 -708. 7. Fisher, R. A. (1930) The Genetical Theory of Natural Selection. Oxford. Clarendon Press 8. Gloger, C. L. (1833) Das Abändern der Vögel durch Einfluss des Klimas. August Schulz, Breslau. 9. Liebig J. (1840) Chemistry and its application to agriculture and physiology. Taylor and Walton, London 10. Lotka A. J. (1925) Elements of Physical Biology. Williams & Wilkens, Baltimore, USA 11. Volterra, V. (1926) Variazioni e fluttuazioni del numero d'individui in specie animali conviventi. Mem. R. Accad. Naz. dei Lincei 2: 31– 113. 12. Malthus T. R. (1798) An Essay on the Principle of Population. J Johnson, London