Invasive species, and especially omnivorous rodents, are a critical conservation concern for many seabird species and the island ecosystems they call home. For example, eradication of introduced house mice (Mus musculus) has been proposed to protect and restore the native ecosystem of Southeast Farallon Island, California. Southeast Farallon Island is home to 15 breeding seabird species and endemic fauna such the Farallon arboreal salamander (Aneides lugubris farallonensis). However, it is uncertain to what degree mouse removal would aid this island ecosystem because little is known about the diet of invasive house mice on Southeast Farallon Island. This study used stable carbon and nitrogen isotope analysis combined with isotopic niche and dietary mixing model approaches to quantitatively assess the diets and foraging niches of house mice on Southeast Farallon Island to better understand their interactions with native flora and fauna.
Results/Conclusions:
We found that plants are the most important resource for house mice in the spring when plants are most abundant and house mouse populations are low. However, plants decline in importance throughout the summer and fall as mouse populations increase, and seabird and insect resources become relatively more available and important to house mice. In addition, when mouse population are high on Southeast Farallon Island and plant resources are less abundant the isotopic niches of house mice and salamanders overlap significantly indicating the potential for competition, most likely for insect prey. These results indicate how seasonal shifts in both mouse abundance and resource availability are key factors that drive the consumptive and competitive impacts of introduced house mice on this coastal island ecosystem.