OOS 46-3 - More than the textbook food web: The complexity of trophic interaction effects on and with abiotic characteristics in plant community structure and function

Background/Question/Methods
Many of us have learned at some point a classic terrestrial food chain with arrows depicting trophic levels with a plant, eaten by a rabbit, who is then eaten by a wolf. We then tried increasing complexity by adding more herbivores and carnivores, creating a textbook food web. But what happens to those trophic interactions when arrows begin to change direction because of global changes? Global changes in climate, plant invasions, and wildfire regimes are not fitting into a linear path determining plant community structure. For example, the direct effect of wildfire may not be as critical as the potential indirect effects such as altering the behavior of consumers, who then affect soil moisture availability. Therefore, we experimentally analyzed how the interactions between wildfire and changes in precipitation lead to cascading effects, both bottom-up and top-down, in structuring plant communities in the Mojave and Great Basin deserts. We have asked questions across multiple studies such as: What role do consumers play in regulating plant communities after fire with changing precipitation regimes? How do fire and consumer interactions alter the consumer community composition which could then alter plant communities? Does repetitive disturbance change the expected outcomes from single disturbance events?

Results/Conclusions
We found that interactions of precipitation, single and repeated fire events, and consumer communities can be linked (directly or indirectly) to changes in soil moisture, plant communities, and consumer community composition. Wildfire reduces rodent diversity and abundance which can release top-down pressure (biotic resistance) on invasive plants. Subsequently, the invasive plant propagule pressure can overcome the biotic resistance from the native plant community, and invasion persists into unburned environments. Rodent diversity decreases in heavily invaded environments, therefore rodents' changed behavior in burned environments indirectly changes their behavior in neighboring habitat by restructuring plant communities. We also found the interaction between changes in precipitation timing, the loss of rodent consumers, and repeat fire events changes soil water potential which is linked to increased invasion potential.

We must not lose sight of the desert for the shrub and continue to experiment and collect data on interactive effects of global change drivers and biotic communities. Top-down and bottom-up interactive processes are critical to synthesize with the wealth of data drylands are accumulating through careful study of the scientific community. We hope our results will provide insight into how consumers affect both biotic and abiotic interactions and shape our dryland ecosystems.