Land Stewardship
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Land Stewardship

Limiting Factors

This story was originally published at wild-wonderings.blogspot.com in November 2014. For the most up-to-date information, please visit our website at nri.tamu.edu.

Many land owners spend a lot of time and money on improving wildlife habitat in order to increase low population numbers or maintain stable populations. It is important that land owners understand what the local game population’s limiting factor is in order to effectively and efficiently use their resources to improve the habitat. All wildlife species require four main habitat components: food, water, cover, and space. The limiting factor is the habitat component that is insufficient to the point that it prevents the population from growing, or that causes a population to decline. More than one of the four main habitat components may be deficient; however the limiting factor is the most severe. Improving the other habitat components may lead to slight population increases, but only improving the limiting factor will significantly improve the population. In areas with good habitats the limiting factor may be something such as disease or predation, however these two examples could also be related to insufficient space (high population densities are more prone to disease outbreaks) or cover (not enough cover can lead to more predation).

Managing for quail is a good example of how important it is to determine the limiting factor. Many land owners provide supplemental feed for quail in an attempt to increase populations. However, nesting and escape cover tend to be limiting factors in quail populations, not food. If that is the case on your property, then supplemental feeding will have little or no effect on the population, but improving cover through grazing management and brush sculpting will have a better chance of increasing the population. There may be instances on certain ranches with great cover where food is in fact the limiting factor.

Predator control is another common practice attempted by land owners to help increase the populations of many different game animals. The problem with predator control is that new predators will always be attracted to land with an abundant population of easily accessible prey. Shooting and trapping predators may help reduce predation in the short term, but a more long term solution to predation is to increase cover so that game animals can elude predators. For quail this would mean increasing both nesting and loafing cover. Recent research in the Rolling Plains of Texas shows that quail use a variety of cover types to escape different predator threats. It was found that quail prefer large, dense woody coverts when escaping from avian predators (Perkins et al.2014). Keep in mind that reducing predation will increase your game population significantly only if predation mortality is the limiting factor. If food, water, or space is significantly insufficient then reducing predation will not make a huge population difference.

One limiting factor that many people don’t think about is space. If food, water, and cover are all sufficient then space becomes the limiting factor. Extremely high population densities are highly conducive to disease transmission. Populations of animals can also get so dense that even with supplemental food and water there is simply not enough space for all the resources necessary to increase the population. Behavioral traits such as territoriality can also put a ceiling on how dense the population of a certain species can get in an area. Some species simply will not live in dense populations, even if a certain area has plenty of resources to go around. If space has become the limiting factor on your land then the only thing that can be managed may be your own expectations. At some point no amount of supplemental food, water, and cover will increase the population.

There are several ways to go about determining the limiting factor for a certain species on your property. Simple trial and error combined with good population records can rule out what isn’t the limiting factor, or may confirm that you’ve been managing for the limiting factor all along. For instance, if you’ve been providing supplemental feed for years but haven’t seen any appreciable population improvement then it’s probably safe to say that food isn’t the limiting factor. If you are already implementing management practices then you should step back and evaluate whether you are actually improving the limiting factor.

Another way to determine the limiting factor is to conduct a habitat evaluation, either by yourself or with the help of a wildlife professional. AgriLife Extension publications such as B-6172: “Habitat Monitoring for Quail on Texas Rangelands,” SP-317: “Habitat Appraisal Guide for Rio Grande Wild Turkey”, or “Deer Range Appraisal for East Texas Forests” can be used as guides if conducting the evaluation yourself.

The best approach would be to combine habitat evaluations with trial and error. First, conduct a habitat evaluation to get an overall estimation of the insufficient habitat components on your property. If multiple habitat components are deemed insufficient then trial and error with different management techniques can narrow down which is the most limiting factor. If you have the time and money to correct all the insufficient components then by all means do so. However, if funds are limited then focusing on the most limiting factor will yield the best returns.

Keep in mind that the limiting factor is not concrete, it will change over time. As you work on managing the habitat to correct the limiting factor you will cause the limiting factor to change. For instance, if the limiting factor had been water, but you added a stock tank to correct this then the new limiting factor may become food. Ideally a property will get to the point where the limiting factor is space, meaning the habitat is sufficient to sustain and grow the populations but for a simple lack of space for any additional animals. As mentioned before, this is now the time to manage your own expectations.

Works Cited

  • Perkins, R., C. Boal, D. Rollins, and R. M. Perez. 2014 Northern bobwhite predator avoidance behavior in response to varying types of threat. The Journal of Wildlife Management 78: 1272–1281

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Texas A&M Natural Resources Institute

Texas A&M Natural Resources Institute

At the Texas A&M Natural Resources Institute, our work improves the conservation and management of natural resources through applied research. nri.tamu.edu