Biotic responses to shifting ecological drivers in a desert community

Background/Question/Methods

Ecological forecasting depends critically on understanding the temporal dynamics of ecological systems. Decades of long-term research have helped us to map out the range of dynamics ecological systems can express, but a framework for understanding these dynamics still eludes us. Predicting temporal dynamics is challenging because many ecological changes can be traced to complex responses to underlying changes in ecological drivers. Since most ecological theory either explicitly or implicitly assumes drivers are in steady state, the ability to apply theory to nature is currently limited. However, both short-term and long-term shifts in ecological drivers can generate important biotic responses that can change the expected trajectory of an ecosystem. Understanding the biotic consequences of short-term and long-term changes in ecological drivers is an important step for predicting ecological dynamics.

For thirty six years, experimental and observational research has been conducted at a study site near Portal, AZ. Experimental manipulation of desert rodents has highlighted the role of granivory and competition as important drivers structuring the plant and animal communities. Additionally, precipitation is an important climate driver in desert ecosystems and regional changes in precipitation patterns have had dramatic and complex impacts at this long-term study site. Here I will use this study system to examine the important role shifting drivers play in ecological dynamics and highlight two theories - niche opportunities and regime shifts - that show promise for linking shifting ecological drivers with biotic responses.

Results/Conclusions

At this study site, both short-term and long-term shifts in drivers have had important and long-lasting impacts on the structure of this desert ecosystem. Short-term fluctuations in biotic and climatic drivers created a window of opportunity that resulted in the rapid increase in the abundance of an invasive plant species that quickly became a dominant species. These dynamics were consistent with the concept of niche opportunities, which posits that invasion success is a function of the abundance of resources and enemies.  Long-term shifts in precipitation resulted in reorganization of plant and rodent communities. This created long-term shifts in community structures and changed the dynamics of ecosystem responses to the underlying climate driver. While currently focused on non-linear responses of ecosystems to small changes in drivers, concepts from regime shift theory may be useful for understanding ecosystem dynamics in response to long-term shifts in ecosystem drivers.