Optimal initial and adult size in animals

A few weeks ago, Erik picked a classical and highly-cited American Naturalist paper to celebrate the journal’s 150th anniversary. 

For this week’s meeting, we will read a less classical, and much less cited, paper from the treasure trove that is AmNat:

Kozlowski, J. 1996. Optimal Initial Size and Adult Size of Animals: Consequences for Macroevolution and Community Structure. The American Naturalist 147:101–114.

I’ve been reading this paper several times lately as I have been preparing my VR application. Every time, I have found it to be thought-provoking and stimulating. In the paper, Jan Kozlowski asks, using somewhat different terms, the question: what determines the number of unique adaptive peaks for body size on the macroevolutionary adaptive landscape? He does this by combining life history optimization models for optimal age and size at maturity, with models on optimal offspring size, and some really neat ecological reasoning about size-selective interactions. IThe end result is fascinating. Can’t believe this paper has only been cited 41 times! 

/Viktor Nilsson-Örtman

Where? Darwin
When? Tuesday 10.00  

There will be fika!

Abstract

Evolution of adult size and offspring size is considered with the aid of an optimal energy allocation model in which, in contrast to existing allocation models that apply a purely energetic definition of fitness, the amount of energy allocated to reproduction is divided into quanta dependent on offspring size, and net reproductive rate is maximized. This approach enables the connection between adult and offspring size to be identified: larger offspring make it optimal for their mothers to have larger adult size. Optimal offspring size exists in the range of sizes for which the ratio of production rate to mortality rate is concave upward with respect to body size. If such a range does not exist, it is optimal to produce the smallest viable offspring. Optimal adult size exists in the range of sizes for which the ratio of production rate to mortality rate is concave downward. If such a range does not exist, it is optimal to have the largest viable adults. The shape of the function representing the ratio of these two rates changes if a new size-specific predator invades the system: then, a macromutation abruptly changing either initial size or adult size can be preferred by natural selection. Possible mechanisms of such macroevolutionary changes are discussed. In the modern world, in which many small and large species with various offspring sizes exist, replacement of one species by another is expected after invasion by a size-selective predator.