Abstract:
The foliage of 80 species common in the Santa Rosa National Park, Costa Rica, has been analysed
for content of total phenolics, condensed tannins, acid detergent fibre and water. Wherever possible
analyses were performed at three stages in the life cycle of the leaf: young but fully expanded
(coinciding with the beginning of the rainy season); middle-aged (two months later); and old (six
months later). A comparison of the three age classes showed no significant change in the levels of
phenolics or fibre as leaves aged but water content decreased significantly. A comparison of
deciduous and evergreen species in the sample showed that the latter group had leaves with a
significantly higher fibre content at all three sampling times, most particularly at the beginning of
the rainy season, but other measures were not significantly different. Alkaloids were much more
common in the foliage of deciduous species and it was observed that their distribution differed
significantly from that of total phenolics and condensed tannins. It is suggested that the interaction
that occurs between many tannins and alkaloids would be liable to reduce the defence capability of
both classes of compounds if they occurred together.
High levels of defoliation occur in the early rainy season (third to tenth weeks) due to larvae of
moths of theSphingidae and Saturniidae. A comparison of investigated tree species that host larvae
of these two taxa shows a striking dichotomy. Species that are selected by Sphingidae'\fI1d to be
relatively deficient in levels of phenolics but are more likely to contain alkaloids, and probably
other small toxic molecules. Saturniidae, on the other hand, appear to prefer host-species rich in
phenolics but poor in alkaloids.
