Consequences of microclimate variation on insect pollinator visitation in two species of Chaetanthera (Asteraceae) in the central Chilean Andes

Insect pollinator activity can be influenced by biotic (e.g., patch floral density and floral display) or by abiotic factors (e.g., temperature, wind velocity, cloudiness). In spite of microsite, seasonal and interannual variation in temperature in the alpine zone, the consequences of local microclimatic variation on pollinator activity has been rarely studied in high mountain ecosystems. In this study we compared flower visitation rates on a north-facing slope and a west-facing slope in Chaetanthera apiculata (3,100 m of altitude) and on an east-facing slope and a west-facing slope in Chaetanthera lycopodioides (3,300 m of altitude). We studied the breeding system in each species in order to determine level of dependence on external pollinators. While the north-facing slope inhabited by C. apiculata was warmer (1.8 degrees C) and visited (7.8-fold) more frequently than the west-facing slope, in C. lycopodioides the east-facing slope was warmer (3 degrees C) and visited more frequently (4-fold) than the west-facing slope. In C. apiculata only Faunula leucoglene (Lepidoptera: Satyridae) showed higher activity in the warmer population. In C. lycopodioides, F. leucoglene and Liphantus sp. (Himenoptera:Andrenidae) showed higher activity rates in the warmer population. Flower visitation rate in Faunula leucoglene was correlated with temperature in C. apiculata and C. lycopodioides. Both C. apiculata and C. lycopodioides are partially self-compatible, and thus require exogenous pollen for maximum seed set. Our results show that in high elevation environments flower visitation rates can be highly variable and that microclimatic conditions can be more important for pollinator variation among populations than head density. Our results offer valuable insights on the potential consequences of global warming on plant pollination at high elevation.