Gaku Kudo

The resource budget hypothesis is widely accepted as a physiological explanation of masting, which is characterized by highly variable, synchronous reproduction within a population across years. According to the hypothesis, when resources are depleted by a large reproductive output, it takes more than one year to replenish them. This results in intermittent mass flowering and seed production. The key resources depleted by a single reproduction have been identified in several woody species but rarely in herbaceous species. We examined the adequacy of the resource budget hypothesis for masting in the herbaceous species Veratrum album subsp. oxysepalum and identified the key resources. Over an 11‐year period, we investigated stem volume as an indicator of resource storage level and flowering in 61 individuals, each consisting of a single ramet, tagged in the 2013 mast year in a population in northern Japan. We compared the concentrations and masses of carbon and nitrogen in the aboveground and belowground parts of flowering and non‐flowering ramets. Stem volume decreased in the year after reproduction and gradually recovered in subsequent years. Flowering occurred again once the ramet had grown to a large size. These results support the predictions of the resource budget hypothesis. Flowering ramets had greater concentrations and masses of carbon in their aboveground parts than non‐flowering ramets, but smaller concentrations and masses in their belowground parts. Conversely, there were no consistent differences in nitrogen concentration or mass between flowering and non‐flowering ramets. Therefore, carbon is the key limiting factor in reproduction for this species.

To determine the impacts of global warming on pollinator-plant interactions, we recorded phenological variations in alpine flowers and bumble bees during 10–12 years in northern Japan, and analyzed the effects of weather conditions and phenological shift on worker population dynamics of four Bombus species. Flowering patterns of alpine plants were formed by the combination of early-flowering fellfield and late-flowering snowbed communities, where snowbed flowers were important resources for worker bees. The flowering phenology of the fellfield communities was correlated with early season air temperature, whereas that of the snowbed communities was clearly predicted by snowmelt time. It was predicted that 1 °C warming with 10 days earlier snowmelt would advance the peak flowering time of the fellfield and snowbed communities by 3.6 and 9.5 days, respectively, resulting in a 9.2 day shorter flowering period. In contrast, the peak time of worker abundance was consistent between years, independent of temperature and snowmelt time. As a result, the time lag between the peak flowering of snowbed plants and the peak abundance of worker bees, i.e., the phenological mismatch, increased with earlier snowmelt. Mid-summer temperature was negatively correlated with worker abundance for three Bombus species, and the effect of phenological mismatch varied between Bombus species. The abundance of B. hypocrita decreased with increasing phenological mismatch in the previous year, the abundance of B. beaticola and B. yezoensis increased, and B. hypnorum showed no clear response. Therefore, changes in the phenology of alpine plants due to global warming affect pollinators in highly species-specific ways.

Predispersal seed predation could influence the sexual expression of plants with sexually heteromorphic flowers. The timing of snowmelt determines the reproductive phenology of alpine plants at a given site, and it can also cause variation in the intensity of seed predation at a local level in alpine ecosystems. We investigated the associations between predation intensity and the floral sex allocation and fitness in an andromonoecious alpine herb, Peucedanum multivittatum (Apiaceae), along the natural gradient of flowering phenology in northern Japan over 4 years. The developing fruits of the early‐flowering populations were heavily predated by moth caterpillars, whereas seed predation was negligible in the late‐flowering populations because predator moths concentrated their oviposition in early summer. The moths tended to oviposit on umbels with more perfect flowers, fewer male flowers and taller flower stems. Plants with male‐biased umbels predominated in the early‐flowering populations. Selection differential and selection gradient analyses showed that greater production of perfect flowers accelerated seed predation, resulting in lower female fitness as seed producers. In contrast, male flower production contributed to a reduction in predation damage, but this was independent of male fitness as a pollen donor. Therefore, having a male‐biased floral gender is advantageous in minimising seed predation and maintaining the floral display. The proportion of perfect flowers per umbel increased in the late‐snowmelt populations, where higher production of perfect flowers led to greater fruit production due to low levels of seed predation. Along the phenological gradient, natural selection for perfect flower production shifted from negative to positive values, indicating heterogeneous local‐scale selection. Synthesis: Our study shows that spatiotemporal variation in the intensity of seed predation acts as a selective force, promoting the local evolution of floral sex expression in andromonoecious plants.

The persistence of angiosperm communities largely depends on pollinator‐mediated interactions. However, the importance of plant–pollinator interactions has often been overlooked in studies of plant community assembly. This study aims to assess the influence of plant–pollinator interactions on the assembly of plant communities. We compared the distribution of three floral traits (colour, symmetry, and tube length) across approximately 650 animal‐pollinated plant species in six plant communities located in distinct geographical regions: Mongolian grassland, Japanese grassland, Japanese alpine zone, Swedish subalpine zone, Swedish alpine zone, and New Zealand alpine zone. Additionally, we examined the pollinator fauna in each community, focusing on the taxon‐specific usage of floral traits by pollinators. The composition of all floral traits was predictably linked to taxonomic composition of the pollinator fauna and taxon‐specific preferences of pollinators for certain floral traits. Furthermore, the dispersion of floral morphology depends on composition of pollinator fauna, rather than phylogenetic dispersion of plant communities. Interestingly, while composition of flower symmetry was largely linked to plant family composition, compositions of flower colour and tube length were almost independent of plant family composition. Our study suggests that pollinator fauna influences the assembly of floral traits. Analysis considering plant family composition suggests that the assembly process could be either ecological, where plant–pollinator interactions select for specific functional traits from a pre‐existing pool, or evolutionary, where traits evolve in response to the pollinator environment within a community. This highlights the dual pathways through which pollinator fauna influences plant community assemblages.

Plant reproduction is often inhibited by herbivorous leaf damage, which affects the resource pool allocated for reproduction. Rhododendron kaempferi var. kaempferi is a semi‐evergreen shrub widely distributed in Japan, and its leaves are occasionally damaged by sawfly larvae ( Arge similis ). This species is partially self‐compatible, but its selfed seedlings suffer from inbreeding depression. Our study aimed to clarify (1) the magnitude of herbivorous damage under natural conditions, (2) the effects of foliage damage on seed number and mass, and (3) the possibility of selective abortion of selfed seeds to maintain outcrossed seed production under resource limitation. In the 2022 survey, 2 of the 20 ramets observed were collectively parasitized by sawfly larvae, and the most damaged ramet had a 59.6% foliage loss. In contrast, the herbivorous damage in 2023 was consistently low throughout the growing season, averaging a 3.2% loss. Leaf excision reduced the seed number per fruit (i.e., low seed‐set rate) but did not affect the individual seed mass. The outcrossing rate of the excision treatment (81.7%) was significantly higher than that of the control (72.0%). The values of seed‐set rate × outcrossing rate were 0.172 for the excision treatment and 0.171 for the control, nearly equal. Our results indicated that (1) sawfly larvae damage was concentrated on a few specific plants, (2) intense foliage damage reduced seed number but not seed mass, and (3) R. kaempferi mitigated the decline in outcrossed seed production by the abortion of selfed seeds when leaves were intensively damaged.

Pollination success of alpine plants is often restricted by low and unpredictable pollinator activity because of harsh and unstable weather conditions, where nocturnal pollination is rare. The alpine orchid, Platanthera tipuloides (Orchidaceae), has inconspicuous greenish yellow flowers with a sweet scent and a long spur that contains nectar. These floral traits are expected to be related to nocturnal moth pollination. To elucidate the pollination mode and reproductive characteristics of this species, we measured floral traits (spur length, nectar content in the spur, floral scent), documented flower visitors using camera traps, and quantified self‐compatibility and the degree of pollen limitation through controlled pollinations at two study plots in the Taisetsu Mountains, northern Japan. It was revealed that P. tipuloides is self‐incompatible and pollen limitation was absent at one of the study plots. The flowers emitted more volatile substances during the night, including lilac aldehyde isomers, which are known to attract moths. A nocturnal moth, Entephria amplicosta , was observed foraging nectar from the flowers, while no diurnal visitors were observed. The proboscis of E. amplicosta was shorter than the spur length, but it was long enough to access the accumulated nectar in the spurs. These results suggest that nocturnal pollination by moths is possible and can be efficient even in an alpine ecosystem with harsh environmental conditions.

There is wide consensus that climate change will seriously impact flowering plants and their pollinators. Shifts in flowering phenology and insect emergence as well as changes in the functional traits involved can cause alterations in plant-pollinator interactions, pollination success and plant reproductive output. Effects of rising temperatures, advanced snowmelt and altered precipitation patterns are expected to be particularly severe in alpine habitats due to the constrained season and upper range margins. Yet, our understanding of the magnitude and consequences of such changes in life history events and functional diversity in high elevation environments is incomplete.This special issue collects novel insights into the effects of climate change on plant-pollinator interactions in individual plant species and on network structure of entire plant and pollinator communities in alpine ecosystems. Using simulated changes of earlier snowmelt, natural gradients of variation in temperature, precipitation and snowmelt, or a long-term monitoring approach, these studies illustrate how plant species, plant communities, and pollinators respond to variation in environmental conditions associated with scenarios of ongoing climate change.The collection of papers presented here clearly demonstrates how spatial or temporal variation in the environmental climatic context affects flower abundances and plant community composition, and the consequences of these changes for pollinator visitation, pollination network structure, pollen transfer dynamics, or seed production. As changes in the availability of flowers, fruits, and seeds are likely to impact on other trophic levels, the time is ripe and pressing for a holistic multitrophic view of the effects of climate change on biotic interactions in alpine ecological communities.

The great majority of studies on foundation species focused on a single dominant plant in a community, while more than one such species can often coexist and compete for space and limited resources. Morphologically different coexisting foundation species can create diverse niches occupied by different subsets of beneficiary species. To test this hypothesis, we sampled alpine plant communities at exposed fellfields in alpine zone, in the Taisetsu Mountains (Hokkaido, northern Japan), with coexisting putative foundation species Pinus pumila (evergreen shrub) and Diapensia lapponica (evergreen cushion‐forming shrub), and analyzed their spatial relationships with other plants. Preliminary vegetation survey indicated that fruticose lichens and Loiseleuria procumbens (evergreen mat‐forming shrub) might also act as a foundation species; thus, we included them in our analyses. The coexisting foundation species had both general as well as specific effects on plant community structure. Namely, almost all the members of the community aggregated spatially with lichens, while the other foundation species were spatially segregated from each other. These foundation plants associated with different members of the community, thus showing species‐specific effects on the community structure. Blooming species showed even stronger patterns of species‐specific spatial associations, suggesting that foundation species had beneficial effects on their associated species. We conclude that the focus on coexisting foundation species can reveal important details of community structure which would be hidden if we treated all species as equal members of the community. Studying the effects of coexisting foundation species could greatly advance our understanding of how species diversity functions in plant communities.