Hello Cable.
Populations that are not isolated from other populations have little or no problem with gene flow. Horned lizards that are in areas of little or no human disturbance have small home ranges because of sufficient resources to maintain population. Hatchlings tend to disperse rather rapidly out into surrounding areas once they are capable. This usually occurs with 4 to 6 days after hatching. Adult males tend to be the ones that leave an area and have a greater home range in the spring. The males are searching for females. Once mating occurs, males will again establish smaller home ranges if the resources allow. Females will maintain their normal home range to nest and lay eggs. Females tend to not leave an area or home range unless the resources decline due to environmental stresses, i.e. drought or increase in predators. There may be some inbreeding that occurs in these areas, but that still may not have an effect on the popuation unless a negative trait is expressed right away in the hatchlings. Some negative traits may be a recessive trait and may not ever show unless there is a high rate of the recessive trait within the populations.

In closed populations, habitats that lack any open corridors to outside populations, there may be problems right away but that would depend on the population demogaphics and the resources available. Typically, the smaller the habitat, the less available resources, the sooner the carrying capacity is reached and the sooner the population will decline. The gene flow will depend on the population demographics. One adult male and three adult females with overlapping and shared home ranges with ample resources could survive for several generations. The assumption would be that the population was clear of any previous inbreeding and there is no environmental stress on resources.

One of my study sites was a 647 acre site with a population count of 237 adults. There were 83 males and 154 females when I started my studies in the area 20 years ago. It was a locked habitat with no corridors, but it had ample resources. the population remained very stable. Predators helped maintain the carrying capacity of the site. The damage began with increased activity, i.e. illegal dumping and ORV use. The habitat was finally lost due to development. I watched the population decline from 632 to 0 in less than 3 years. I could never identify any problem with gene flow within the population.

Hope that gives you insight.

Best to you
Lester G. Milroy III
Conservation Biologist

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