Studies in Mutualism: The Senita Moth

Science News Daily has an interesting story about the mutualism between the senita moth and the senita cactus. At least that’s what the title of the piece proclaims. The article is actually about the struggle of one scientist to make sense of the phenomena.


Here is the problem:

The problem is that the moths lay their eggs inside the cacti’s flowers immediately after pollination, and when the eggs hatch the moth larvae eat the fruit, destroying the flowers’ chances to produce seeds. Historic theory predicts extreme ecological instability for this relationship; as moth populations increase, more flowers are destroyed, fewer new cacti appear, and the spiral continues until both species disappear.

In the this case that hasn’t happened. Moth and cactus are doing fine. The question, then, is why? At this point the answer to that question is unknown. This is where the Science News Daily article gets really interesting, so pardon the long excerpt:

“I develop theoretical models, equations that attempt to explain mutualistic relationships like the one between the moth and the cactus, and I take those models into the field and examine them empirically to find out how well they predict what really happens,” Holland said.
Traditional theory of such mutualistic interactions leads to predictions of unbounded population growth or instability and eventual doom due to one species overexploiting another. These predictions clearly don’t square with what Holland and his students see happening in the Sonoran Desert, where both species thrive. Holland’s models differ from traditional theory, suggesting that one mutualist may exert some control over the other’s population increases, such that neither unbounded growth nor overexploitation ensue.
“I have always been interested in the community ecology of mutualism — the larger puzzle — and this moth-cactus relationship is just one piece of that,” Holland said. “When we discovered the relationship in 1995, I immediately thought of using it to look at the bigger picture. But in aiming to do that, I wound up spending a decade working on the population ecology of mutualisms, a prerequisite for then understanding this larger puzzle.”
Having made some progress on the population ecology of mutualism, some of Holland’s current work, which is slated for publication later this year, returns to his earlier interests in community ecology. “We want to understand how the structure of mutualistic communities influences their stability and dynamics, both of individual species and of whole networks of species.” The results suggest that the structures of mutualistic communities compliment those of predator-prey food webs, a finding that presents the tantalizing possibility of developing an overarching scheme that incorporates elements of both.

An interesting example of the way science progresses. You start out looking at one problem and are detoured into something else in order to understand the original problem. The end result is something new that explains your original problem plus some other stuff you hadn’t thought of…

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One Response

  1. An interesting and obvious use of modeling too. Most AGW deniers think of the models of climate researchers as being unconnected to reality because they are called models and exist only in computers. They are not aware of the connection between modeling, hypothesis, theory, successive refinement – etc., etc. Not that I’m aware of all the subtleties either….
    One DOES wonder tho. Can you model a real life system, successively refine it until it is very good at predicting the real life system and still be totally wrong about the variables you’ve used to create the model?
    Suppose you use a superposition of sine waves to create a formula that very accurately describes some natural phenomena you’ve measured – say the Dow Jones. Does the amplitude of each wave used in the equation give you some idea of the importance of individual variables and the number of important variables and how do you connect those amplitudes to real variables?
    Sorry to have rambled on so.

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