Last month I talked about the evolution of body size which, when it comes to the superorganism, translates to the number of cells (workers) making up the body (colony). When it comes to the honey bee superorganism, it’s reasonable to say that big is good. This is true whether you’re talking about a natural colony nesting in trees or a managed colony supered up for a honey flow. True – but only to a point, and this nuance we will return to later in the article. For now let’s stick to the idea that a big population is good.
Now strictly speaking, from an evolutionary point of view we may call an adaptation “good” if it has solved an important environmental problem and contributed to the long-term survival of a species or group. The adaptation doesn’t need to be modern; in fact it may be quite ancient and primitive. That’s why we still see horseshoe crabs washed up on our beaches: this is an extremely ancient group, essentially living fossils, but adaptable and well-fit for survival. It is almost a corollary of evolution that evolutionary failures do not stick around to be noticed by evolutionary biologists. I say all this to reinforce that just because I call big populations “good” doesn’t mean that small populations are “bad.” There are many species of primitively social bees that have small populations – examples include bumble bees and sweat bees – yet they are well adapted to their environments, persistent, and successful. It is more correct to think of late adaptations in evolution as innovations – nature’s experiments to “try out” a new strategy and see if it rewards the genes that code for it with greater occupancy of a habitat’s niches. One clue that an innovation may be on the right track is when it breeds more innovations1; in this way complexity builds and the species becomes extraordinarily fine-tuned to its habitat. But if a fine-tuned adaptation leaves the innovator vulnerable to tiny disturbances in the environment and the species goes extinct, we would be hard-pressed to call that adaptation successful. These natural experiments may take hundreds of thousands or millions of years to play out, and we short-lived humans don’t know where we are along that story line. This is why evolutionary biologists refer to characters as “primitive” or “derived;” it is fairly easy to identify a character that is basic versus one that is an innovation: it doesn’t necessarily follow that the newer one is “better.”
With these caveats aside, we can safely say that big populations have translated into greater layers of complexity in social insect colonies. If I were a betting man, I’d say big populations is a derived character destined for greatness.
Let’s first look at what large populations has done for the western honey bee Apis mellifera and her near ancestors. Readers of last month’s installment will remember that ancestral Apis moved from a primitive habit of nesting on single open combs with a curtain of living bees serving as a proxy shelter to a derived habit of nesting in tree hollows, losing in the process the need for the protective curtain of bees, freeing those bees to contribute more actively in the economy of the colony, promoting the innovation of multiple combs to accommodate the greater capacity for brood rearing, increasing the ratio of brood to foragers, and thus selecting for higher metabolic rate to meet this foraging demand (Fig. 1). This is a beautiful example of how complexity breeds complexity1: once these self-reinforcing dynamics are in motion it becomes difficult to identify what is a cause of bigger populations versus an effect of bigger populations.
It has been settled beyond controversy that large social insect populations promote nest defense, homeostasis, task efficiency, ability to manipulate the environment, predictability of queen production, year to year colony survival rates, and resilience to seasonal climate fluctuations.2 These are formidable advantages, and theorists do in fact predict that social insect evolution pushes species toward ever larger populations and layers of complexity.2 But at the scale of near ecologic time there appear to be environmental constraints that put a limit on unbridled growth. These include seasonal limits to food availability, the size of available nesting cavities, and the possibility of a point of diminishing return in which ever increasing numbers of workers fail to realize a proportional return in efficiency and colony benefit. I personally believe that the spatial limits of hollow trees (roughly 15-80 liters3) have constrained cavity-nesting Apis compared, for example, to soil-nesting ants and termites for which nest size is virtually unbounded. In consideration of this, I’m not surprised that it’s the ants and termites who have the largest population sizes, numbers and variety of castes, and greatest variations of behavior and life history innovations. Big nests and big populations are good for innovation.
If we should be cautious with our value judgments when we’re talking about natural history, remembering that the jury is still out when it comes to time at the scale of millions of years, we can be more liberal when it comes to managed systems in which beekeepers are interested in making a living. On this count we can say with more confidence that bigger is better.
Last month I sang the praises of C.L. Farrar, the USDA scientist who showed that honey hoarding efficiency increases as colony population increases.4 In other words, one colony of 50,000 bees can be expected to make more honey than the sum of two colonies of 25,000 bees. The biggest challenge to this goal is, of course, the one thing a colony of honey bees wants to do most of all, and that’s swarm. Thus, there is a kind of conflict of interests between the bees and the beekeeper. Beekeepers want unnaturally big colony populations; bees want to swarm. A two-year study in Canada showed that honey production was reduced by …