Abstract
BackgroundTemperature-driven variation in pollinator assemblage and activity are important information, especially at high altitudes, where rising temperature trends exceed global levels. Temporal patterns of pollinators in a flowering season can be used as a proxy to predict the changes of high-altitude plants’ mutualistic relationships. We observed a spring temperature change in one population of a high-altitude endemic species, Megaleranthis saniculifolia on Mt. Sobaeksan, and related it to pollinator assemblage and activity changes.MethodsThis study was conducted at two sites, each facing different slopes (NE and NW), for two times in the spring of 2013 (early-flowering, April 27–28, vs. mid-flowering, May 7–8, 2013). We confirmed that the two sites were comparable in snowmelt regime, composition of flowering plants, and flower density, which could affect pollinator assemblage and activity. Pollinator assemblage and activity were investigated at three quadrats (1 m2 with 5-m distance) for each site, covering a total of 840 min observation for each site. We analyzed correlations between the temperature and visitation frequency.ResultsTwelve pollinator species belonging to four orders were observed for M. saniculifolia at both sites during early- and mid-flowering times. Diptera (five species) and hymenopteran species (four species) were the most abundant pollinators. Pollinator richness increased at both sites toward the mid-flowering time [early vs. mid = 7 (NE) and 3 (NW) vs. 9 (NE) and 5 (NW)]. Compared to the early-flowering time, visitation frequency showed a fourfold increase in the mid-flowering time. With the progression of spring, major pollinators changed from flies to bees. Upon using data pooled over both sites and flowering times, hourly visitation frequency was strongly positively correlated with hourly mean air temperature.ConclusionsThe spring temperature change over a relatively brief flowering period of M. saniculifolia at high altitudes can alter pollinator assemblages through pollinator dominance and visitation frequency changes. Thus, this study emphasizes information on intra- and inter-annual variations in the mutualistic relationship between pollinators and M. saniculifolia to further assess the warming impacts on M. saniculifolia’s reproductive fitness.
Highlights
Temperature-driven variation in pollinator assemblage and activity are important information, especially at high altitudes, where rising temperature trends exceed global levels
Insect visitors of M. saniculifolia foraged for pollen or flower nectar, and nectar was detected at the base of the nectariferous petal (Fig. 2)
The two sites did not differ in mean air temperature, snowmelt regime, composition of flowering plants, and flower density at the community level, they differed in pollinator assemblages
Summary
Temperature-driven variation in pollinator assemblage and activity are important information, especially at high altitudes, where rising temperature trends exceed global levels. Variation in pollinator assemblage and activity along temperature gradients is important information, especially at high altitudes, where annual mean temperatures increase more rapidly than global levels as seen during the last few decades (IPCC 2013). Such information helps infer possible changes in future pollinator assemblages and activity due to climate change (Hegland et al 2009). Such research is critical to predict the future status of high-altitude plants, especially those being dependent upon activities of pollinators that are sensitive to temperature changes in early spring (e.g., Totland 1994a; Hirao et al 2006; Thomson 2010; Mizunaga and Kudo 2017)
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