It took me about three months to get through this book, but I remain somewhat näive as to the whole debate about constant vs inertial growth. I am convinced the inertial model is elegant and simple and potentially extremely applicable, but I haven’t read any other research on “frictional forces” (i.e. density-dependent effects) affecting population growth.

Chapter 2: Does ecology have laws?

What conditions must a set of relationships meet before they can be considered a natural law? In other words, what is the definition of natural law? To the point, if ecology can even be considered to have laws, you must logically show that ecological relationships are not inherently barred from forming a law.

Best candidates for law: allometries

• “remarkable statistical regularities that hold between various biological and ecological quantities”
• Often it isn’t surprising that certain relationships between such quantities exist, rather that they hold across species. In addition often the particular details of the relationship appear arbitrary, e.g. why metabolic rate should be proportional to 3/4 power of body mass.
• Examples
  • Kleiber allometry between mass and metabolic rate
  • Bonner’s Generation-time allometry
  • Fenchel allometry between mass and reproduction rate
  • Damuth allometry between mass per capita and metabolic rate per habitable unit
  • Calder allometry between mass and period of population size oscillation
• “Holy grail” of ecology
  • What is the explanation of these allometries?
  • Why the recurring theme of 1/4 and 3/4 powers?

What is a law of nature? Are there necessary conditions?

• A natural law need not be without exceptions: cf. law of conservation of momentum or Kepler’s laws of planetary motion / Newton’s law of universal gravitation
  • These idealized models are limit myths because they are impossibly real
  • Perhaps limit myths are important for our understanding of laws of nature because they describe some basic systemic disposition that is followed in real data
• A natural law need not make precise predictions: i.e a law need not be falsifiable. e.g. a law is falsified if it says P should be seen from condition, and this is not observed. Under this definition most laws are false.
• A natural law cannot easily be distinguished from mere regularity: One attempt is to show a law has explanatory power, in addition to having predictive power. However deep down laws exist simply to reveal the underlying assumptions of a model of reality and do not necessarily distinguish cause and effect. To some extent physics isn’t held to this notion, since the physical laws “are where explanation might be thought to end”.
• When choosing between two comparable models, appeal to parsimony.

Laws in ecology

• So in physics we are considering the fundamental laws of nature, so further causal explanation may not be expected (unless you delve into cosmology). In biology, ecology, etc, i.e. the other branches of science, we expect these laws to boil down to chemistry and then to physics in the end. That is to say, we expect biology to reduce to physics.
  • The authors don’t think this should be the goal, as it probably isn’t useful or possible
  • They do claim however that questions of causality end in physics, if they end at all.

Summary

There are good candidates for laws in ecology. If you deny this then perhaps you have some misconceptions about the definition of natural law in other fields and in general. Physics are ecology are similar in that many fundamental relationships have exceptions, may not be explanatory or predictive, and often invoke an idealized situation.

Ideas having finished the book

Ginsberg proposes that lots of research be done to determine the ecological relevance of the inertial (i.e. maternal effect) model of growth. I wonder whether yeast would be a suitable organism in which to study this model.

Specifically do yeast growth dynamics exhibit periodicity under certain conditions (which are not interaction-dependent)?

• At what point do haploid cells die so that periodicity can be measured?
• What approaches offer a glimpse into mechanisms of yeast maternal effects and their effect on population growth? What are the molecular mechanisms?
• Does maternal effect affect cell size? I think reasonably this is true, in that larger mother cells spawn larger daughters. What data is there on this? Is there any evidence that a more efficient mother produces a larger sized daughter?