Scale Example - A Multi-Scale Approach to Lesser Prairie-Chickens
How do landscape patterns affect animals? Do animals respond differently to broad-scale patterns versus fine-scale pattern? How do animals respond to broad-scale land cover change compared to fine-scale changes? These were questions asked in a study of Lesser Prairie-Chickens in Oklahoma and Texas that can help us understand real-world implications of scale (Fuhlendorf et al. 2002).
In their study, the researchers looked at 10 separate populations of Lesser Prairie-Chickens in the panhandles of Oklahoma and Texas. They then classified each population as either “Declining” or “Sustained” based on decades of surveys.
Next, the researchers looked at the land around each population. At multiple scales, the researchers measured how much land consisted of cropland and how tree cover had changed over time. They used the same grain but different spatial extents including 450, 900, 1800, 3600, and 7200 hectares. This allowed them to look for relationships among scale, land cover, and Lesser Prairie-Chickens.
To picture how much land the researchers studied, it is important to know how big a hectare is. One hectare is approximately equivalent to two gridiron football fields. At the smallest scale (450 hectares) the researchers studied an area equivalent to 900 football fields surrounding each population. They scaled this up step-by-step until they reached the broadest scale (7200 hectares), which was the equivalent of 14,400 football fields surrounding each population.
The researchers found several important takeaways from their study (see Figure 1).
- Researchers found that at finer scales (450 ha, 900 ha, and 1800 ha) the sustained populations had slightly higher percentages of cropland surrounding them. But at the broadest scales (3600 ha and 7200 ha) the declining populations had more cropland, while the sustained populations had similarly low cropland cover across all scales. This shows that influence of cropland cover on Lesser Prairie-Chickens is scale dependent. In other words, results from one scale do not match relationships at other scales.
- When studying the effect of changing tree cover on Lesser Prairie-Chickens at various scales, they found that at finer scales (450 ha, 900 ha, and 1800 ha) there was very little difference between declining and sustained populations. However, at the broadest scales (3600 ha and 7200 ha), tree cover changed very little for the sustained populations but increased around the declining populations. This indicates that Lesser Prairie-Chickens respond to increasing tree cover at broad scales. However, this does not mean that Lesser Prairie-Chickens are not sensitive to tree cover at fine scales. Lesser Prairie-Chickens avoid trees at fine scales, thus no populations occurred in areas with large increases in tree cover at fine scales
These findings are important to understand, especially for those who want to help the Lesser Prairie-Chicken, a species that has been in decline across much of its range. Firstly, the results from tree cover change are a warning to land managers who wish to manage for the Lesser Prairie-Chicken. Scale mismatches may occur when managers focus on removing trees at fine scales (i.e. <500 ha), but do not consider tree cover changes at broader scales (>3500 ha). To avoid declining prairie-chicken populations, tree cover must be reduced at broad scales.
In addition, the influence of cropland on Lesser Prairie-Chickens is scale dependent. At fine scales relatively low levels of cropland appears to have little influence on populations but at broad scales greater cropland cover is associated with declining populations. Thus, areas with high levels of cropland at broad scales are poorly suited for Lesser Prairie-Chicken reintroduction or local habitat improvement investments.
In summary, this example illustrates the importance scale in interpreting the influence of land use on wildlife populations. Different implications arise from different scales, thus it is increasingly important that we reconcile management goals with scale.
Fuhlendorf, S. D., Woodward, A. J. W., Leslie Jr., D. M., and J. S. Shackford. “Multi-scale effects of habitat loss and fragmentation on lesser prairie-chicken populations of the US Southern Great Plains.” Landscape Ecology 17 (2002): 617-628.