Abstract
Analyzing plant phenology and plant–animal interaction networks can provide sensitive mechanistic indicators to understand the response of alpine plant communities to climate change. However, monitoring data to analyze these processes is scarce in alpine ecosystems, particularly in the highland tropics. The Andean páramos constitute the coldest biodiversity hotspot on Earth, and their species and ecosystems are among the most exposed and vulnerable to the effects of climate change. Here, we analyze for the first time baseline data for monitoring plant phenological dynamics and plant–pollinator networks along an elevation gradient between 4,200 and 4,600 m asl in three mountain summits of the Venezuelan Andes, which are part of the GLORIA monitoring network. We estimated the presence and density of plants with flowers in all the summits and in permanent plots, every month for 1 year. Additionally, we identified pollinators. We calculated a phenological overlap index between species. We summarized the plant–pollinator interactions as a bipartite matrix and represented a quantitative plant–pollinator network, calculating structural properties (grade, connectance, nestedness, and specialization). We also evaluated whether the overall network structure was influenced by differences in sampling effort, changes in species composition between summits, and phenology of the plant species. Finally, we characterized the pollination syndrome of all species. Flowering showed a marked seasonality, with a peak toward the end of the wet season. The overall phenological overlap index was low (0.32), suggesting little synchrony in flowering among species. Species richness of both plants and pollinators decreased along the elevation gradient. Flies, bumblebees, and hummingbirds were the most frequent pollinators in the network, while entomophily and anemophily were the prevailing pollination syndromes. The interaction network in all summits showed high connectance values, significant specialization (H2), and low nestedness. We did not find a significant effect of sampling effort, summit plant species composition, or plant phenology on network structure. Our results indicate that these high tropical alpine plant communities and their plant-pollination networks could be particularly vulnerable to the loss of species in climate change scenarios, given their low species richness and functional redundancy coupled with a high degree of specialization and endemism.
Highlights
Climate change is accelerating and is having important impacts on species range shifts, which are well documented in cold biomes, where there is increasing evidence that alpine species distributions are shifting upwards (Lenoir and Svenning, 2015; Steinbauer et al, 2019)
In the context of monitoring long-term vegetation dynamics in alpine ecosystems, much less is known about the impacts of climate change on plant reproduction, including phenological responses, changes in plant-pollination, and the possible relation between these two processes
In systems with a high degree of functional redundancy, pollinator species with strong preferences for certain floral traits have less need to synchronize their dynamics with the phenology of particular plant species (Benadi et al, 2014)
Summary
Climate change is accelerating and is having important impacts on species range shifts, which are well documented in cold biomes, where there is increasing evidence that alpine species distributions are shifting upwards (Lenoir and Svenning, 2015; Steinbauer et al, 2019). In the context of monitoring long-term vegetation dynamics in alpine ecosystems, much less is known about the impacts of climate change on plant reproduction (but see Tovar et al, 2020 in the case of plant dispersal strategies), including phenological responses, changes in plant-pollination, and the possible relation between these two processes. In plants and crops from the temperate zone, evidence has shown that increases in temperature in recent years, can have a significant effect on phenological patterns, including the time for the beginning or the amplitude of the flowering or fruiting period, as well as significant disruptions of pollination interactions (Harrison, 2000; Chapman et al, 2005; Inouye, 2008). In systems with less functional redundancy and/or with many specialists, there can be a greater susceptibility to species losses and changes in phenology, resulting in adverse effects on the stability of plant–pollinator networks (Bartomeus et al, 2011, 2013)
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