Fire alters top-down effects of small mammal granivores on Mojave Desert plant communities

Background/Question/Methods

In arid systems, small mammal granivores can have top-down effects on plant community structure through seed consumption and dispersal. Recent invasions of exotic grasses (e.g. Bromus rubens) have resulted in increased frequency of large fires in the Mojave Desert that may alter feedbacks of small mammals on plant community characteristics. Granivores consume invasive seeds but may have a preference for native seeds when they are available. We hypothesize that fire alters small mammal community structure in ways that changes seed consumption in burned landscapes.  We tested our hypotheses on seeds of three native plant species (Encelia farinosa, Ambrosia dumosa, and Larrea tridentata) and a single exotic species (Bromus rubens) by placing trays of seeds in soil, along burned and unburned landscapes and across burn transitions.  Seeds were made available for 7 days after which seed removal was assessed.

Results/Conclusions

The results indicate that removal of the native seeds was on average 40% higher in burned landscapes compared to paired unburned transects, while invasive seeds showed the opposite trend. This phenomenon may be due to apparent competition where granivore populations that are being maintained by exotic seeds are capable of rapidly consuming native seeds when they are available.  More intense removal of native seed on burned landscapes may contribute shifts in plant community composition driven by slow re-establishment of the native plant community and higher regeneration of red brome.