Relationships of autecology and synecology on the shortgrass steppe

Background/Question/Methods

Understanding the community dynamics of ecosystems aids land stewardship. However, communities are not true entities; contrarily, species respond individualistically to environmental gradients, biotic interactions, and disturbances. Thus, an understanding of population processes is necessary for predicting shortgrass steppe community response to disturbances ranging from climate change or oil drilling, but such specific data are often lacking. By examining individual responses based on functional groups, a convergence of autecology and synecology, an approximate prediction of community response may be modeled. We examined 18 species distributions from the Pawnee National Grasslands (CO). Data were taken from 19 sites using the Carolina Vegetation Survey protocol; median values were used for cover that was estimated using a modified Daubenmire cover scale. Sample sites were ordinated based on environmental factors using PCA followed by a permutation test (n=999) of significance. Average species cover was subsequently plotted along the complex environmental gradient to elucidate ecological distributions (a coenocline). We grouped species by functional group (C3 grass, C4 grass, CAM, forb) and hypothesized that C3 grasses and forbs would have the narrowest distributions and exotic species would have the widest distributions.

Results/Conclusions

The first axis of the PCA analysis was significant (Eigenvalue = 2.78, p=0.004) and accounted for 44% of the environmental variance. Longitude, aspect and elevation were positively related to axis 1 while slope position and soil type were negatively related. Thus, the complex gradient generally runs from more moist conditions to less moist conditions. Several taxa were found throughout the gradient: as expected, C4 grasses (Bouteloua gracilis and B. dactylis) were widespread. Contrarily, the C3 grass Elymus elymoides and the CAM Opuntia polyacantha were more restricted in their distribution to more moist and more xeric conditions, respectively. Also matching predictions, the forb Artemisia frigida and shrub Rhus trilobata were restricted in distribution. The results suggest that functional groups follow theorized distributions, and that community response may be predicted using functional groups. The more restricted distributions of some functional groups may inhibit their ability to respond to changes unless the changes result in more area of favorable conditions.