Abstract:
Santa Rosa Nat ional Park is an arbitrarily defined 108 km1 patch of
dry fo rest in the northwestern Pacific coastal lowlands of Costa Rica. It
has a saturniid moth fau na of 30 breeding species (and 5 waif species)
and a sphingid moth fauna of 64 regularty breeding species, 10
occasional breeding species, and 9 waifs (83 species in tota l). There is
one endemic saturniid and no endemic sph ingids. Furthermore, near ly
all of the saturniids and sphingids of Santa Rosa have very broad
geographic and ecological ranges. The saturniids are dormant during
the six month dry season and all survive the dry season within the Park.
More than half of the sphingids migrate out of the Park during the dry
season or even the second ha lf of the rainy season. This migration is
an integral part of Santa Rosa's interdependency with the rainforest
parts of Costa Rica (and vice versa).
What determines the ceiling to the number of species of saturniids and
sphingids in Santa Rosa? The Park is not isolated. There are no in·
hos pitab le barriers to potential colonizing species in the immediately
adjacent rainforest (10·15 km to the east). This rainforest is occupied
by at least 25 spec ies of saturniids and 52 species of sphingids that also
breed in Santa Rosa. Why don 't the other rainforest saturniids and
sphingids move into Santa Rosa, at least during the rainy season? There
is no suggestion that direct competitive interactions prevent the 31st or
65th species of saturniid or sphingid from moving into Santa Rosa.
likewise, there appears to be a sufficient array of food plant species
for the potential invader to find food . However, Santa Rosa supports a
formidable array of predators and parasitoids that eat saturniid and
sphingid caterpillars. On the one hand, this array is sufficiently
depressed by the dry season that the breed ing saturn iids and sphinqids can produce 1-2 generations_ It is probably to make use of the relatively
carnivore-free early wet season that so many sphingids migrate into the
park at the start of the rains. On the other hand, the carnivore array
contains enough specialist and semi-special ist parasitoids to provide the
density-dependent mortality that co uld be regulating the overall species
richness of saturn iids and sphingids. There are numerous species of
parasitoids whose density or foraging intensity could increase were a
31st saturniid or 65th sphingid to be added to the Santa. &esa breeding
array of moths_ This increase cou ld prevent the moth's entry or
elim inate a resident
Santa Rosa is to be viewed as being in a biologically interdependent
state with other habitats in Costa Rica, to say nothing of the adjacent
dry forest. If for example, Costa Rican rainforests are no longer present
to generate and absorb migrants from Santa Rosa, there will be second
and third order impacts on the year-round resident fauna and the
ecological structure of the Park.
