| Humboldt marten (Martes caurina humboldtensis) research has focused on direct effects of habitat to meet daily needs (rest structures) and annual needs (home ranges). However, indirect effects influencing sensitive demographic characteristics can affect populations. Bobcats are an important marten predator, and survival most influences marten population growth. Using multiple lines of evidence, I retrospectively evaluated the role habitat plays in indirectly mediating marten-bobcat interactions. Important marten prey such as chipmunks and tree squirrels are associated more with mature, late seral forests with dense shrub cover, whereas important bobcat prey such as woodrats and rabbits are associated with early seral forests. Martens select large patches of late seral forest or serpentine habitat with dense shrub layers. Bobcats select for early seral forests (<30 years old) and are nearly absent in landscapes where early seral habitat in lacking. Where martens and bobcats co-occur, and where ~25% of the landscape consisted of early seral forest, bobcats killed 45% of martens monitored over a two-year period. Where early seral stands increased to >50% of the landscape over time, marten distribution contracted. These results suggest landscape composition mediates interactions between these species by affecting their distributions, increasing marten predation when bobcats are present, and reducing marten survival and distribution in landscapes increasingly composed of younger stands. |