Climate change is introducing new competitors into existing communities of Alpine plants, and these new rivals are impacting their growth and survival, according to findings published in Nature Communications this week. 

When species migrate to different habitats to keep up with changes in climate, they encounter new competitors and bring new interactions to ecological communities. However, there’s been little observational or experimental evidence for the effects of these sorts of novel interspecies interactions. Most studies have focused on the shifting interactions among co-existing competitors today. 

So, a trio led by Jake Alexander of ETH Zurich wanted to replicate the effects of rising temperatures on different species interactions by transplanting alpine plants and whole plant communities to different elevations along a mountain slope in the Swiss Alps. Then, over the course of two years, the researchers studied the plants’ survival, biomass, and flowering performance.

Their migration scenarios focused on four focal alpine species: the alpine kidney vetch (Anthyllis vulneraria ssp. alpestris), black plantain (Plantago atrata), spring pasqueflower (Pulsatilla vernalis, pictured above), and glossy scabious (Scabiosa lucida).

To similate a scenario in which the plants remain in their current location as the climate warms, they were moved from an alpine meadow to a new spot 600 meters (2,000 feet) lower down, which is 3 degrees Celsius warmer – the rise expected in Switzerland over the next 50-100 years. The plants were either transplanted into vegetation native to the low elevation site (novel competitors, which in the future might extend their range upwards) or into vegetation brought down from their alpine home (current competitors). 

For those plants grown with their current competitors, the higher temperature did have a slight effect on competition, but nowhere near as significantly as for the plants transplanted with new competitors. For these plants novel competition strongly reduced performance and impacted dramatically on survival rates, which decreased by more than half. This suggests that competition, not temperature, is the key factor.

"Finding out that it is competition from lower-elevation flora that serves as the decisive effect, and not higher temperatures as previously assumed, is a very valuable discovery," says Alexander in a statement.

"Our study provides one of the first empirical indications that competition with new 'range expanders' has to be taken into account when forecasting species' responses to climate change," Alexander added. For example, plants from lower elevations are typically taller with bigger leaves, so in a competition for light, they might beat out the smaller alpine species.

^{Experimental site at 2,000 meters above sea level where indigenous alpine plants face migrant plant competitors. ETH Zurich/Peter Rüegg}

Image in text: Alpine flowers at the 2000-meter field site. Jonathan Levine