Decline in Bee Diversity and Abundance from 1972-2004 on a Flowering Leguminous Tree, Andira inermis in Costa Rica at the Interface of Disturbed Dry Forest and the Urban Environment

Long-term monitoring of bees in specific sites provides information on changes in species diversity and abundance, especially in areas close to human habitation. Evaluations of this monitoring data combined with relevant measures of anthropogenic activity can aide in interpreting emerging patterns of bee pollinators. In 1972, we sampled bees visiting flowers of a population of the leguminous tree, Andira inermis (W. Wright) DC in a dry forest site adjacent to the town of Liberia, Guanacaste Province, Costa Rica. Slightly more than 800 bees were recorded on the average per tree site, with an overall bee diversity among the trees of approximately 70 species. Standardized bee samples were taken again from the same population of A. inermis in 1996, 1999, and 2004. In each of these years average abundance level per tree was greatly reduced, as was overall species diversity. Andira inermis trees were also observed to have variable attraction for large anthophorid bees versus honey bees. Some trees attracted significantly more anthophorids than honey bees, whereas other trees attracted the opposite. Since 1972 there were many changes in land use that were directly related to a rapidly growing human population in Liberia. These changes, which greatly modified the natural landscape and vegetation, are believed to have caused a major decline in species diversity and abundance of bees to a low but consistent level. Concurrently, increased urban growth has resulted in many more residential neighborhoods that have a wide variety of ornamental flowering plant species, many of which are native to Costa Rica, that attract a wide variety of native bee species. Evidence is offered to suggest that urban residential areas represent a source of bees that continue to visit A. inermis at low levels in and immediately around Liberia.