Heated rivalries: Phenological variation modifies competition for pollinators among arctic plants

Abstract

When plant species compete for pollinators, climate warming may cause directional change in flowering overlap, thereby shifting the strength of pollinator‐mediated plant–plant interactions. Such shifts are likely accentuated in the rapidly warming Arctic. Targeting a plant community in Northeast Greenland, we asked (a) whether the relative phenology of plants is shifting with spatial variation in temperature, (b) whether local plants compete for pollination, and (c) whether shifts in climatic conditions are likely to affect this competition. We first searched for climatic imprints on relative species phenology along an elevational gradient. We then tested for signs of competition with increasing flower densities: reduced pollinator visits, reduced representation of plant species in pollen loads, and reduced seed production. Finally, we evaluated how climate change may affect this competition. Compared to a dominant species, Dryas integrifolia × octopetala, the relative timing of other species shifted along the environmental gradient, with Silene acaulis and Papaver radicatum flowering earlier toward higher elevation. This shift resulted in larger niche overlap, allowing for an increased potential for competition for pollination. Meanwhile, Dryas emerged as a superior competitor by attracting 97.2% of flower visits. Higher Dryas density resulted in reduced insect visits and less pollen of S. acaulis being carried by pollinators, causing reduced seed set by S. acaulis. Our results show that current variation in climate shifts the timing and flowering overlap between dominant and less‐competitive plant species. With climate warming, such shifts in phenology within trophic levels may ultimately affect interactions between them, changing the strength of competition among plants.

Ecological Niche and Interspecific Association of Plant Communities in Alpine Desertification Grasslands: A Case Study of Qinghai Lake Basin

“…Competition among plant communities has become a consensus of most scientists [ 31 , 32 , 33 , 34 ]. Classical niche theory suggests that each species can survive under limited conditions, and that a large overlap of limiting factors prevents a species from gaining a foothold in a community [ 35 ].…”

Diverging trends and drivers of Arctic flower production over space and time

“…In a resource-limited ecosystem such as the Arctic, this resource availability change can directly affect diversity and community structure. For plants, an increase in flower production could, for example, directly affect competition for pollinators (Hocking 1968; Tiusanen et al 2020). Adding to this are changes in the relative phenology of plants, which may either increase or decrease competition, depending on how changes affect the temporal overlap between more and less- attractive plant species (Tiusanen et al 2020).…”

“…For plants, an increase in flower production could, for example, directly affect competition for pollinators (Hocking 1968; Tiusanen et al 2020). Adding to this are changes in the relative phenology of plants, which may either increase or decrease competition, depending on how changes affect the temporal overlap between more and less- attractive plant species (Tiusanen et al 2020). Overall, a potential future decrease in flower production, as observed for Saxifraga and Papaver in the high Arctic, has the potential to affect the long-term recruitment of new individuals (Inouye 2008) and long-distance dispersal.…”

“…For example, many arctic insects depend on flowers for food, providing pollination services for plants in return (Kevan 1972). Thus, changes in the dynamics of flower production or in the composition of plant communities can profoundly affect local ecological networks and ecosystem functioning (Schmidt et al 2016; Tiusanen et al 2020). Given the recent and rapid environmental changes in the Arctic (Robinson 2022), a better understanding of the mechanisms determining flower production is fundamental for quantifying and predicting population, community, and ecosystem dynamics of both plants and their associated taxa.…”

Disorder or a new order: how climate change affects phenological variability

“…An increase in phenological variability may hamper the ability of dependent species to track the moving target of other species' changing phenology if the species track different climatic cues or have different sensitivities to the same cues. Variation in phenological overlap affects the strength of interactions between co-occurring species (Tiusanen et al, 2020), so there might be immediate consequences for species' fitness and coexistence. Extreme inter-annual phenological variation in the overlap of interacting species may even lead to local extirpation (Patterson et al, 2020).…”