Puzzles Sexual Dimorphism Delayed Implantation and Coexistence among Weasel Species

to specialize in hunting small rodents, a successful predator must have not only obvious characteristics, such as the ability to enter very small spaces, but also less obvious ones, such as some means of surviving and breeding year after year despite huge variations in food supply. Weasels have in fact evolved a whole set of special adaptations to deal with these conditions, which make the weasel way of life possible. Most of these adaptations have been introduced in the preceding chapters.

Of course, no one means to imply that animals are capable of sitting down and thinking out a plan for survival. It is just that certain sets of characteristics are likely to favor the animals that happen to have them in a given set of conditions. Over the long term, only the favorable sets of characteristics survive to be observed.

Some of the adaptations of weasels are long term, involving physical characteristics unchangeable in an individual's lifetime, such as the long thin shape of the weasel body or the details of the reproductive cycle. Some are short term, including the flexibility of behavior and reproductive response appropriate to different and changeable circumstances. And some (such as delayed implantation) have caused biologists considerable consternation, because it is not obvious how certain weasel characters could have evolved or what adaptive value they now have.

To understand the ways in which weasels have evolved to deal with the hazards of their lives, and to understand the puzzles they still present to us, we must draw on practically everything we know about weasels discussed in this book so far.

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