| Spatial and temporal heterogeneity in the environment are ubiquitous in ecological systems. Community dynamics are regulated through processes that are affected by this variability and are mediated through species specific responses. Woody perennials dominate the cold deserts of the arid southwest, but herbaceous perennials remain an important biodiversity component. However, there is limited information on the traits that enable herbaceous perennials to persist in such communities. In these chapters, I manipulated spatial variability in soil nitrogen, mimicking Mule deer excretions, over three different growing seasons to examine the interactions between temporal changes in precipitation and soil nutrient heterogeneity on the individual and population performance of an herbaceous aridland perennial, Cryptantha flava . In chapter I, I demonstrate that a one-time application of urea derived N results in a rapid acquisition and allocation of N to above ground tissues. In Chapter II, I measured the lateral root foraging distance of two size classes of C. flava, and demonstrated that all size classes have a minimum lateral root distribution of 1 m from the edge of the canopy area. In Chapter III, I examined the allocation patterns of small and large, and reproductive and non-reproductive plants and found that small plants have less flexible allocation patterns, yet reproductive efforts are similar to those of large reproductive plants. In Chapter IV, I examined the differential responses of open plants to plants growing under the dominant shrub species in the community. I found that the interaction between shrubs and C. flava ranges from competition for light in times of adequate resources, to facilitation of survival in periods of below average precipitation. Finally, in Chapter V, I modeled populations of C. flava with and with-out a mule deer N input in a year of average and below average precipitation. Nitrogen inputs enhanced population growth under above average precipitation, but resulted in greater plant mortality and reduced population growth in years of below average precipitation. The persistence of this subordinate can be attributed to an highly effective root system whose foraging ability allows indirect positive interactions with mule deer, high allocation to reproduction, and high adult survival. |
