Roland, J., N. Keyghobadi & S. Fownes. (in press)Alpine Parnassius butterfly dispersal: effects of landscape and population size. Ecology


We use mark-recapture methods to estimate the number of Parnassius smintheus (Paplionidae) butterflies moving among 20 alpine meadows separated by varying amounts of forest along the east slope of the Rocky Mountains in Alberta, Canada. We combine generalized additive models and generalized linear models to estimate the effects of intervening habitat type and of population size on butterfly movement. By incorporating habitat-specific distances between patches, we are better able to estimate movement compared to a strictly isolation-by-distance model. Our analysis estimates that butterflies move readily through open meadow but that forests are twice as resistant to butterfly movement. Butterflies also tend to stay at sites with high numbers of butterflies, but readily emigrate from sites with small populations. We show that P. smintheus are highly restricted in their movement at even a fine spatial scale, a pattern reflected in concurrent studies of population genetic structure. As an example of the utility of our approach, we use these statistical models, in combination with aerial photographs of the same area taken in 1952, to estimate the degree to which landscape change over a 43 year interval has reduced movement of butterflies among sub-populations. At these sites, alpine meadow habitat has declined in area by 78 percent, whereas the estimated effect of fragmentation has been to reduce butterfly movement by 41 percent.