Alpine Plants May Struggle for Pollination as Climate Warms

Featured Image Caption: Clover is a common plant across a wide range of elevations in the Swiss Alps. Image Source: Free to use under the Pixabay license. No attribution required

Source Article: Richman, SK, Levine, JM, Stefan, L, Johnson, CA. Asynchronous range shifts drive alpine plant–pollinator interactions and reduce plant fitness. Glob Change Biol. 2020; 26: 3052– 3064.

Mountain Life is Tough, and Now This?

For plants living on mountains, survival can be a struggle. Depending on the elevation and region, mountain plants experience harsh winds, cold temperatures, and dry, infertile soil. These mountain plants are called “alpine,” and are especially resilient to tough conditions. Now, climate warming may bring these plants additional challenges in the form of new interactions with unfamiliar species.

Many flowering plants depend on pollinators for reproduction, one example of an essential interaction between species. Pollinator and plant species have certain ranges that they survive in year after year, and climate warming could shift these ranges. In mountains, many species’ ranges are specific to certain elevations defined by usual temperatures; for example, low elevations might be home to certain plants and pollinators that prefer warmer temperatures while high elevations are home to different plants and pollinators that prefer cooler temperatures.

Pollinators like bumble bees and flies can quickly move up mountains to higher elevations when temperatures warm, but plant species cannot spread as quickly. As a result, a pollinator journeying uphill to keep up with warming temperature will encounter different communities of plants. This raises a big question: Will these traveling pollinators interact with the unfamiliar plants they encounter at higher elevations? Over time, plants originally from low elevations are also expected to move slowly up the mountain, and when they do, they will also encounter unfamiliar plant communities uphill. This raises a second big question: How might the uphill-traveling plants compete with plants local to higher elevations? To see how these new interactions among pollinators and plants might play out on mountain slopes as the climate warms, researchers designed a clever experiment.

The Old Switcheroo

Because lower elevations are warmer, researchers decided to simulate climate warming on alpine plants and pollinators by moving high-elevation plants to lower, warmer locations in the Swiss Alps. At these lower elevations, the high-elevation plants were exposed to the warmer climate and low-elevation pollinators, as though the pollinators made their expected move uphill due to climate warming.

Researchers moved plants from high on mountains to lower elevations to simulate the effects of climate warming for alpine pollinators and plants. Image Source: Self, Julia Bebout, Based on methods of Richman et al. 2020

To do this, researchers took square turfs of alpine plants, including their roots and soil, from an elevation of 2000 meters (m) above sea level and moved them to three lower elevation sites (1800 m, 1600 m, and 1400 m). These elevations reflect three scenarios of climate warming: minor, moderate, and severe. In the most minor warming case, the ranges of insects and plants would not be expected to move much. High-elevation plants would interact with the pollinators and plants from a just slightly lower elevation. In the most severe case, high-elevation plants would interact with the pollinators and plants originating from far down the mountain. Local areas of land with the typical plant community at each elevation were designated to compare the pollinators in the relocated alpine turfs to the pollinators in the local plant community. High-elevation turfs were also relocated at their local elevation of 2000 meters to ensure that just moving the turfs alone did not affect the plants.

Throughout the growing season, the researchers visited the relocated turfs and local plant communities at each elevation and watched how often different types of pollinators visited the various plants. Researchers also counted the seeds of three common alpine plant species in each relocated turf: red clover, bellflowers, and dwarf eyebright.

The common alpine plant species monitored in the relocated turf at each elevation: red clover (Trifolium pratense), bellflowers (Campanula scheuchzeri), and dwarf eyebright (Euphrasia minima). Sources: Wikipedia Commons 1, 2 by Benjamin Zwittnig, 3 by user Tigerente
George Chernilevsky, Public domain, via Wikimedia Commons
Benjamin Zwittnig, CC BY 2.5 SI, via Wikimedia Commons
User:Tigerente, CC BY-SA 3.0, via Wikimedia Commons
Picky Pollinators

Different pollinators were found at the four experimental elevations, and even at the same elevation, the relocated turfs and local communities were visited by different pollinators. Pollinators seemed to have preferences for certain plant communities. Relocated turfs received more pollinator visits than local communities at 1800 m, the simulated minor warming scenario, mostly from flies. These flies seemingly preferred the high-elevation, relocated plant community. Contrastingly, local communities received almost all the bumble bee attention, meaning that bumble bees strongly preferred the plants that were local to lower elevations. If pollinators have preferences for certain plant communities, this could create competition for pollinators as low-elevation plant communities move uphill in a warming climate.

While the number of dwarf eyebright seeds produced depended on the number of pollinator visits, the bellflowers and clover reproduced best when visited by certain types of pollinators. Pollinator type was perhaps even more important than the number of visits, making competition for pollinators even higher stakes for these species. The pollinators needed most by high-elevation plants, like bellflowers and clover, might strongly prefer visiting the low-elevation plants that are likely to invade uphill, leaving the high-elevation plants high and dry.

What Should We Expect?

Climate change is likely to have a complicated impact on life on Earth. While warming temperatures will directly affect how plants and animals behave and survive, the interactions between species could be indirectly affected in complex ways that may benefit some at the expense of others. If we want to understand how climate change will affect the world’s natural communities, we will need further research on how climate change will affect the interactions between species.

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Julia Bebout

Julia Bebout

I am a PhD student at the University of California San Diego studying how the timing of germination and flowering shapes plant communities. I'm fascinated by how past environments can affect present and future ecosystems, especially faced with climate change. My favorite things to write about are community ecology, wetland and alpine ecosystems, and regenerative agriculture. I also love hiking, climbing, baking, and dancing! Twitter: @BeboutJulia

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