Monday, 3 July 2017

Ecological success and dominance

Evolutionary biology's best-known measure of success is fitness. "Fitness" has become a popular term, and as a result of its success it has become overloaded with multiple meanings - e.g. see the 1982 Dawkins book chapter titled: "An agony in five fits". Most definitions share the property that fitness measures whether an entity - or a population of entities - is increasing in number. "Fitness" usually measures the extent of that increase in some way. From the perspective of ecology, fitness isn't the only success metric in town - it just happens to be one that can be easily applied to individuals. If broadening the perspective to include populations, one could also consider the population size, its expected probability of going extinct in some specified time, it rate of throwing off new distinct populations and some measure of how well it is capturing and using resources.

The last concept is the one that this post is about. I think of it as being "ecological success". Kudzu has it. Ants have it. Islam has it. The decimal system has it. I think one reason this type of metric is not more popular and better-known is that there's no consensus regarding the best way to measure it. A thermodynamic metric seems attractive to me: since resources can all (in principle) be manufactured from available energy. Another possible metric involves weighing the systems involved - to measure their mass. This is sometimes done when measuring the extent to which humans have conquered the globe, for example.

A sister concept is "ecological dominance". It refers to extreme levels of success - where competitors are either obliterated or marginalized.

These concepts can also be applied within particular niches. Entities which are doing badly overall may be succeeding in or dominating their particular niche.

If anything, attempting to apply these concepts to cultural evolution is even harder than with organic systems. Gene-meme coevolution results in entanglement in terms of gene and meme products, which makes weighing them and calculating the energy flux through them more challenging. The most common metrics used in cultural evolution are a bit different. "Mindshare" is a common concept which is used to measure cultural popularity within a cultural niche. Assuming that a meme is either possessed by a host, or not, and assuming whether they have it or not is measurable, the mindshare of a meme can be measured for a given population. Another common metric that is used is US dollars. Cultural products sometimes have monetary value, and sometimes that can be calculated or estimated. However, some of the most common memes are free. It seems as though these memes would be unfairly disadvantaged by value-based metrics of popularity. The internet has brought with it some other common popularity metrics: views, links, clicks and likes. Unfortunately the supporting data is not always publicly available. This data is beginning to be used by scientists.

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