Do Pipevine Swallowtails need Malthus or movement?

[Patrick Foley]

Dear Lepsters,

It seems a standard field-guide fact of Pipevine Swallowtail behavior,
that unlike the widespread populations of the eastern version, the
central California Battus philenor butterflies tend not to migrate. Is
this true? Is there any movement up the Sierra Nevda as the spring
season progresses?

My ecology class is monitoring a "population" of about 200 adults
hanging around one small patch (about 10 m2, 20% coverage) of  the host
plant Aristolochia californica. 90% of these swallowtails are males
along the American River in Sacramento, CA.

Where are the females? One hypothesis is that mated females are moving
around between host plant patches (perhaps hundreds of meters away)
while the males hope to get new females as they emerge at the patch they

know. Females may even be moving upstream (American River), following
the spring.

Anybody know anything about this?

Malthus would be pleased to note that even though near-predation is
common (most of the butterflies lose their tales over a couple of
weeks), and the on-again-off-again weather introduces
density-independent environmental stochasticity, that the host plant is
pretty thoroughly attacked by the helpfully (to my ecology class)
diurnal caterpillars. Resources do appear to be limiting for the
pipevine swallowtails. But you Alaskans may be amused by the apparent
lack of resource limitation by the Western Tiger Swallowtail, Papilio
rutulus, who fly in far fewer numbers than Battus, despite the far more
common willows along the American River. Do you northern folk ever see
willows denuded by Tiger swallowtails? I don't.

Maybe Malthus was wrong! ... at least about the details (In defense of
my claim, see Hanski, I. , P. Foley and M. Hassell 1996. Random walks in

a metapopulation: how much density dependence is necessary for long term

persistence? J. Animal Ecology 65: 274-282, which clearly shows that
even when lots of environmental stochasticity occurs, and lots of local
extinctions, that populations hit their resource limits a predictable
fraction of the time. Peace Andrewartha and Birch.)

Patrick Foley
patfoley at csus.edu


 
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