Patterns of genetic diversity and biogeographical history of the tropical wetland tree, Pterocarpus officinalis (Jacq.), in the Caribbean basin.

Studies examining intraspecific variation in plant species with widespread distributions and disjunct populations have mainly concentrated on temperate species. Here, we determined the genetic structure of a broadly distributed wetland tropical tree, Pterocarpus officinalis (Jacq.), from eight Neotropical populations using amplified length fragment polymorphisms (AFLP). AFLPs proved highly variable with almost half (48%) of the genetic variation at these loci occurring among individuals within populations. Nonetheless, there was a strong geographical pattern in the distribution of AFLP variation within P. officinalis. Caribbean and continental populations fell into two well-defined genetic clusters supported by the presence of a number of unique AFLP bands. Within these two regions, there were also strong genetic differences among populations, caused mainly by frequency differences in AFLP bands, making it difficult to determine the evolutionary relationships among populations. In addition, our analysis of P. officinalis revealed striking differences in the levels of AFLP variation among the eight populations sampled. In general, Caribbean populations had lower genetic diversity than continental populations. Moreover, there was a clear loss in AFLP diversity with distance from the continent among Caribbean populations. The overall genetic pattern within P. officinalis suggests that past colonization history, coupled with genetic drift within local populations, rather than contemporary gene flow are the major forces shaping variation within this species.

Urban expansion and the loss of prime agricultural lands in Puerto Rico.

In many countries where the economy has shifted from mainly agricultural to industrial, abandoned agricultural lands are lost to urbanization. For more than 4 centuries the Puerto Rican economy depended almost entirely on agriculture, but sociopolitical changes early in the 20th century resulted in a shift to industry. This shift in the economy, and an increase in population, has resulted in an increase in urban areas. This study describes the rate and distribution of urban growth on the island of Puerto Rico from 1977 to 1994 and the resulting influence on potential agricultural lands. Urban extent and growth were determined by interpreting aerial photographs and satellite imagery. The 1994 urban coverage was combined with a soil coverage based on agricultural potential to determine the distribution of urban areas relative to potential farmlands. Analyses showed that in 1977, 11.3% of Puerto Rico was classified as urban. After 17 years, urban areas had increased by 27.4% and urban growth on soils suitable for agriculture had increased by 41.6%. This represents a loss of 6% of potential agricultural lands. If this pattern of encroachment by urban growth into potential farmlands continues, Puerto Rico's potential for food production in the future could be greatly limited.

Synchronous leaf production and herbivory in juveniles of Gustavia superba.

Synchronous leaf production has been proposed as a mechanism to reduce herbivore damage to young leaves by satiating herbivores. To test this hypothesis, I measured leaf production, leaf survivorship, and herbivore damage on juveniles of Gustavia superba (H.B.K.) Berg (Lecythidaceae), in two sites in Central Panama. Leaves were produced throughout the year, but there were peaks in leaf production at the beginning of the wet scason. Plants that produced leaves synchronously with conspecifics received significantly less damage than plants that produced leaves out of synchrony, and high levels of leaf damage were correlated with shorter leaf lifetimes. These data suggest that plant phenology can influence risks of herbivory.