RESUMO
Parallel studies of nesting colonies in Mexico and the United States show that Elegant Terns (Thalasseus elegans) have expanded from the Gulf of California Midriff Island Region into Southern California, but the expansion fluctuates from year to year. A strong inverse relationship between nesting pairs in three Southern California nesting areas [San Diego saltworks, Bolsa Chica Ecological Reserve, and Los Angeles Harbor (1991 to 2014)] and Isla Rasa in the Midriff (1980 to 2014) shows that terns migrate northward when confronting warm oceanographic anomalies (>1.0°C), which may decrease fish availability and hamper nesting success. Migration pulses are triggered by sea surface temperature anomalies localized in the Midriff and, secondarily, by reductions in the sardine population as a result of intensive fishing. This behavior is new; before year 2000, the terns stayed in the Midriff even when oceanographic conditions were adverse. Our results show that terns are responding dynamically to rapidly changing oceanographic conditions and fish availability by migrating 600 km northwest in search of more productive waters.
RESUMO
Studies were conducted at the La Selva Biological Station in the Atlantic lowlands of Costa Rica and in a greenhouse in California to assess the potential role of a Neotropical fish in dispersing the seeds of a rain forest tree. Feeding experiments showed that the seeds of Ficus glabrata H. B. K., a major, canopy-forming riparian tree, require approximately 18-36â h to pass through the digestive tract of Brycon guatemalensis Regan, an abundant riverine fish whose adult diet consists largely of leaves and fruits of this fig tree. The seeds were still viable after passing through the fish's gut but germinated somewhat more slowly than seeds that had been left in the fig exposed to air or floated in water. Stem elongation of seedlings from seeds that had passed through the fish's gut was faster than that of seeds in the other two treatments. Placement of seeds upstream may be more important than enhanced germination for plants such as Ficus that produce large numbers of seeds. Radio telemetry showed that five of six tagged fish had moved distances of 0.1-1â km upstream; seven other fish with transmitters, including three large males, were not relocated and may have moved into tributary streams for spawning or feeding. These findings suggest that Brycon can disperse large numbers of Ficus seeds and help maintain the upstream populations of the tree.