The Little Guy Wins

The Little Guy Wins

We would generally predict that if the big fellas defend a territory to exclude other males and to attract females, it is worth their while in terms of reproductive success. Territorial defence can be costly, increasing predation risk and the possibility of injury, but when sexual selection is strong, those that can, do. Those that can't either disperse or pursue an alternative tactic. In the case of collared lizards, Crotaphytus collaris, large males, those 2 years old and older, do defend territories that overlap with home ranges of up to eight females. These males must patrol frequently, perform broadcast push-up displays, chase off and even fight other males to defend these territories. The courtship displays ( Fig. 1) they perform to females can also be costly, or at least time consuming as they may last up to 30 minutes. First-year males are smaller and can't hope to outcompete these dominant males. They don't defend territories and try to remain as inconspicuous as possible. Normally we would predict that they would achieve few matings.

Joshua York, Troy Baird and Michelle Haynie of the University of Central Oklahoma tested the prediction that territory defence by the dominant males did allow them to monopolize females and that females should preferentially mate with males that defend areas that overlap with their home ranges. However, these researchers worked on a site that had unusual characteristics compared with the usual habitat of collared lizards. More commonly, collared lizard habitat consists of small discontinuous patches of rocks with few crevices for hiding and these patches are separated by expanses of prairie grass. Travel between patches is fraught with risk from predators. Here territory owners have small, easily defended territories and subordinates cannot easily hide. On the other hand, the site where this work was done was a dam flood control spillway characterized by large, homogeneous patches of rock with almost unlimited crevices. All males and females in the population were marked and their ages and sizes known.

Figure 1.
A courtship encounter between a territorial male (foreground) and female collared lizard. Photo: Teresa D. Baird.


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