Experimental Test of the Combined Effects of Water Availability and Flowering Time on Pollinator Visitation and Seed Set

Abstract

Climate change is likely to alter both flowering phenology and water availability for plants. Either of these changes alone can affect pollinator visitation and plant reproductive success. The relative impacts of phenology and water, and whether they interact in their impacts on plant reproductive success remain, however, largely unexplored. We manipulated flowering phenology and soil moisture in a factorial experiment with the subalpine perennial Mertensia ciliata (Boraginaceae). We examined responses of floral traits, floral abundance, pollinator visitation, and composition of visits by bumblebees vs. other pollinators. To determine the net effects on plant reproductive success, we also measured seed production and seed mass. Reduced water led to shorter, narrower flowers that produced less nectar. Late flowering plants produced fewer and shorter flowers. Both flowering phenology and water availability influenced pollination and reproductive success. Differences in flowering phenology had greater effects on pollinator visitation than did changes in water availability, but the reverse was true for seed production and mass, which were enhanced by greater water availability. The probability of receiving a flower visit declined over the season, coinciding with a decline in floral abundance in the arrays. Among plants receiving visits, both the visitation rate and percent of non-bumblebee visitors declined after the first week and remained low until the final week. We detected interactions of phenology and water on pollinator visitor composition, in which plants subject to drought were the only group to experience a late-season resurgence in visits by solitary bees and flies. Despite that interaction, net reproductive success measured as seed production responded additively to the two manipulations of water and phenology. Commonly observed declines in flower size and reward due to drought or shifts in phenology may not necessarily result in reduced plant reproductive success, which in M. ciliata responded more directly to water availability. The results highlight the need to go beyond studying single responses to climate changes, such as either phenology of a single species or how it experiences an abiotic factor, in order to understand how climate change may affect plant reproductive success.

Evaluation of Native and Nonnative Ornamentals as Pollinator Plants in Florida: II. Floral Resource Value

“…In this study, plants were irrigated sufficiently to avoid drought stress. Under drought stress, the results may have been different because nectar production generally decreases during periods of drought, but the magnitude of this effect can vary across plant species (Carroll et al, 2001;Gallagher and Campbell 2021;Kuppler and Kotowska 2021;Rering et al, 2020). Our results further highlight the need to sample nectar across seasons as nectar production, and relative differences across taxa, can vary over time.…”

Climate driven disruption of transitional alpine bumble bee communities

“…Specifically, spring warming coincides with emergence from torpor and colony initiation for bumble bee queens (Szabo & Pengelly, 1973) and onset of new growth in their host plants (Gezon et al, 2016). Summer maximum temperatures and summer precipitation (respectively, mean of monthly diurnal high temperatures and sum of June, July, and August precipitation) were used as they influence accumulation of energy resources in the nest via production and activity of foraging workers (Maebe et al, 2021) and duration of flowering in host plants via soil and plant water budgets (Galen, 2000; Gallagher & Campbell, 2021; Olliff‐Yang & Mesler, 2018).…”

“…Observations of bumble bees (queens [Q], workers [W]) and their host plants were made at several geographically isolated sites and altitudinal zones, over varying time scales to probe effects of climate change on community dynamics. Because not all species were found in all zones, total replication was reduced in some cases budgets (Galen, 2000;Gallagher & Campbell, 2021;Olliff-Yang & Mesler, 2018).…”

“…Extreme temperatures, early snow melt, and summer drought advance the seasonal activity of plants and pollinators by about 4 days per °C (Abrol, 2012) and impact phenological resource partitioning among consumer species (Duchenne et al, 2020). For plants, phenological advancement generates pollination deficits and shifts in pollinator composition (Gallagher & Campbell, 2021). Warming reduces abiotic barriers to colonization, functioning as an ecological rachet for movement of warm‐adapted pollinator taxa into historically colder environments (Biella et al, 2017; Marshall et al, 2020; Osland et al, 2021; Rafferty, 2017; Shah et al, 2020; Suzuki‐Ohno et al, 2020).…”

Not just flowering time: a resurrection approach shows floral attraction traits are changing over time

“…These changes include altered temperature, precipitation, photoperiod, and CO 2 and N 2 O levels, many of which display seasonally and geographically distinct patterns, and all of which together form a complex and multifactorial suite of selective pressures ( IPCC, 2022 ). For most species, we have very little understanding of which traits may underlie adaptive responses when exposed to the multivariate selective pressures typical of global change ( Abatzoglou et al, 2020 ; Gallagher & Campbell, 2021 ). In plant systems, the potential that climate or land use changes may disrupt plant-pollinator interactions is of particular concern.…”