Print PageFossorial mammals modify plant composition and structure and are one of the groups consistently discussed within the framework of the “keystone species” concept. However, the mechanisms underlying these keystone effects are not well understood and different mechanisms may function at multiple scales. At Carrizo Plain National Monument in California, the burrows of the endangered Giant Kangaroo Rat (Dipodomys ingens) have significantly higher cover of invasive annual grasses than in the intervening areas. One theory proposes that a mutualism exists where D. ingens inadvertently “farm” the exotic species by preferentially caching their seeds and forgetting to recover them. This has lead to concern that invasive plant control and native plant restoration may be impossible where D. ingens is present. We tracked the fate of cached seeds through the season, monitored plant cover inside and outside of D. ingens exclosures, and sampled soil on and off burrows in order to fully understand the mechanisms underlying the perceived keystone effect of D. ingens on the plant community.
Results/Conclusions
Our preliminary results suggest that biotic soil disturbance trumps foraging behavior as the primary mechanism explaining the localized abundance of invasive grasses on D. ingens burrows. Despite these localized effects, we have found that at the landscape scale, D. ingens actually suppress the abundance of invasive grasses by preferentially consuming invasive grass seeds. This study demonstrates an under-appreciated ecosystem service (invasive plant control) provided by an endangered species, and highlights the importance of understanding the mechanisms underlying keystone effects at multiple scales in order to inform best management practices.
