JAMESON, ANNEMARIE. Department of Biology, University of Miami, P.O. Box 249118, Coral Gables, FL 33124-0421. - Spatial pattern analysis of Torchwood in south Florida.
In order to further our understanding of the habitat requirements an
endangered butterfly, I undertook a study to determine the spatial
patterning of a Rutaceous tree with a neotropical distribution.
Torchwood, Amyris elemifera L., is considered to be the
primary larval food plant of an endangered butterfly subspecies with
an Antillean distribution, the Schaus swallowtail, Heraclides
(=Papilio) aristodemus ponceanus . Patchiness in plant communities
can provide the underlying habitat structure for a specialist
herbivore on both a landscape and population level. Determining the
scale of the spatial patterning for torchwood can aid us in
determining the minimum scale at which models of the butterfly's
habitat must be based, as well as providing a cell size for
multivariate models of both butterfly and host plant habitat. Two
term local quadrat variance (TTLQV) as described by Dale (1999) in
Spatial Pattern Analysis in Plant Ecology was used to address the
question, at what scale(s) is torchwood aggregated in the tropical
hardwood hammocks of south Florida? The unit measured was contiguous 5
meter square quadrats. The data recorded is mapped locations of stems
at each of two life stages, seedlings (< breast height) and
reproductive individuals (>breast height). In TTLQV, the average
squared difference between a block and the adjacent block is
calculated for a range of block sizes, b . Peaks in the plot
of the variance, V3 (b) against block size are indicative of
scales at which the species is aggregated. Preliminary results
collected in Crocodile Lakes National Wildlife Refuge, North Key Largo
Florida, indicate that Amyris elemifera is strongly
aggregated at distances between 20 and 25 meters.
Key words: Amyris elemifera , spatial pattern analysis, specialist herbivore, Torchwood, tropical dry forest, two term local quadrat variance