mmvvmm@mixcom.COM (Daniel Offutt) (06/22/91)
How is the evolutionary "success" of a species measured? The population size alone does not seem a reasonable measure, since typical members from different species may tie up different quantities of resources. The total mass of elephants on earth may be greater, for example, than the total mass of mice, even though there are many fewer elephants than mice. "Biomass" has been proposed as a general method for measuring the relative "success" of different species. But upon closer inspection, the concept of a species' total biomass has some problems. Consider man. Which masses count as part of man's total biomass? All human bodies should be counted, of course. But why wouldn't man's artifacts also be counted as part of man's biomass? Should robins' nests be counted as part of the biomass of robins'? Should the hives bees build be considered part of the biomass of bees? It seems to me that the answer has to be "yes." It also seems that that answer leads to yet other conceptual difficulties. How does one know that a given mass, such as a robin's nest, should be included in the robin's biomass? If the robin uses twigs torn from a living tree, then are the twigs (1) no longer part of the tree's biomass, or (2) part of both the tree's and the robin's biomass? Does it matter which organism has "control" of a given mass? So that when the tree "controls" the mass of the twig, the twig counts as part of the biomass of the species of tree, while when the robin "controls" the twig, the twig is part of the biomass of robins? What exactly does "control" mean in this context? How would a case in which "control" is shared between members of different species be handled? Consider an ant hive, or any other underground tunnel dug by an animal. The tunnel itself has no mass. Yet I feel compelled to say that a species of animal that digs burrows is tying up, and has control of a greater quantity of resources than an otherwise identical species (in size and structure) that does not dig burrows. If you want to count the earth around the burrow as the additional biomass, then how much of it do you count, and where do you draw the boundary? Maybe the answers to these questions have something to do with the amount of "order" created by the members of a species, or the amount of energy expended by the members per units time, on average. Comments and criticism are welcome. Dan Offutt
kpc@pluto.arc.nasa.gov (kpc) (06/22/91)
i don't know for certain about this, and probably you had something in mind, but the first thing that made an impression on me when reading your article was: when you want to measure something, you should have a clear idea of what sort of thing it is that you want to measure. if you have a clear idea, then you probably have a better idea of how to measure it, don't you think? maybe you do have a clear idea, but i'm not sure what you mean by success... if you are trying to define it by finding a measurement, then are you really saying that you would like to find a measurement that has predictive value in approximating our subjective notions of success, is feasible, and is somehow useful as a result? i'm wondering what you mean by success, or, in lieu of a clear meaning for it, what you mean by your question. here are some ideas just for fun. i don't know if any of them will be useful at all, but i'm interested in comments... number of genes expressed. bacteria are successful! amount of information contained in all genes together, or average amount of information expressed. use only encoding genes. humans are successful! i like this one, and have an interest in finding out its implications. is it possible? who else is interested in this? who is studying it, i wonder? what assumptions are made? diversity within species. then again, how do you define a species? longevity of species. then again, there is that coelacanth thread... longevity of individuals. tortoises! average happiness :-). non-stereotyped use of tools. humans! height in the food chain. this has relevance to entropy, which you hinted at. humans and lions! i don't know what the ideas about biomass are all about. now, probably there is a whole established intricate theory of biomass that your article is about and i've stumbled into the thread clumsily... :-) in any case, as i am a newcomer to biology, i welcome comments. of course, i would welcome comments if i weren't a newcomer to biology, also. -- Tweety is a bird. Socrates is a man. John loves Mary. Mary is tall.