... aspects of the factors contributing species either pollen to a migration may be derived from midden analyses, specifics on the environmental factor(s) influencing the capacity of a species to invade ... and Wullstein, 1985), the absence of summer rain on a predictable basis would then lead a summer to the loss of Q turbinella from the northern habitats if they are not able to maintain summer ... precipitation inputs since the late spring In contrast, the native species, Q gambelii, and the Q gambelii hybrids were albe to maintain higher rates of gas exchange during this summer drought period These...