L'altitude et la concurrence (Altitude and Competition)

Yesterday, I accompanied a small team of researchers from the project INTERREG POCTEFA ECTOPYR (Les ECTOthermes PYRénéens bio-indicateurs du changement climatique). This project is a broad international collaboration, including both research and extensive outreach, seeking to understand and explain the potential effects of climate change on a variety of reptile and amphibian species living in the Pyrénées (and is coordinated by Fabien Aubret, my mentor and collaborator here at the SETE in Moulis). I am very grateful that, from what I have seen, using the term ‘global warming’ (réchauffement climatique) is not in the least controversial here in France. ECOTPYR is a multi-year project involving researchers from three countries (France, Spain, Andorra) – they have a very nice website here: http://poctefa-ectopyr.com.

Rock outcrops provide great habitat for rock lizards near Étang d'Eychelle.

Our goal yesterday was to collect data from a higher-elevation population of Aran Rock Lizards (Iberolacerta aranica; more about these guys below). We drove up winding mountain roads for about 20 minutes past the town of Castillon and parked the car at a small overpass. From there, we hiked quickly (this was no leisurely stroll!) for 2 hours, gaining 500 m in elevation until we reached our target of 1900 m. At Étang d’Eychelle (Eychelle’s Pond), we spent the afternoon catching and collecting data on the rock lizards in this area. The activity pattern of these lizards, especially at high altitudes, is highly dependent on the amount of available sunlight so that they can bask and bring their bodies up to active temperatures. Since the day was on-and-off cloudy, we had mixed luck and ended one lizard shy of our goal. Amazingly, there are a number of other reptile and amphibian species that live at these altitudes high in the Pyrénées. We had the good fortune of seeing a few of these: the Common Frog (Rana temporaria), the Spiny Toad (Bufo spinosus), and the Viviparous Lizard (Zootoca vivipara). While this is impressive in itself, there are some reptiles and amphibians that live in remarkably extreme conditions. For example, a couple species of Toad-Headed Lizards (Phrynocephalus erythrurus and Phrynocephalus vlangalii) in Tibet possess some physiological adaptations allowing it to live at elevations up to nearly 5000 m above sea level (see papers by Tanget al., 2013 and He et al., 2013). Closer to home, the European Adder (Vipera berus) is widespread across the continent and possess behavioural and physiological adaptations that allow it to live well north of the Arctic Circle (for example, see Lourdaiset al., 2013).

A lovely example of Iberolacerta aranica.

So why are Iberolacerta aranica interesting? There are three species in this genus that are endemic to very small areas of the Pyrénées, generally restricted to higher altitudes (I mentioned seeing Iberolacerta bonnali in my first visit to Pic-du-Midi). As the climate continues to warm, it is predicted that many organisms at lower elevations might track their preferred temperatures and move upward in elevation. This creates two important problems for Iberolacerta lizards: 1) living at the tops of the mountains, they simply can’t migrate any higher, and 2) other lizard species now living at lower elevations, such as Podarcis muralis, might migrate upward in elevation and may cause problems for the Iberolacerta species. Recent work suggests some ambiguity about what might happen if climate warming brings these species into contract more often. On one hand, Podarcis is generally larger and can out-compete Iberolacerta in direct interactions, owing largely to its stronger bite force. On the other hand, Iberolacerta are able to more precisely thermoregulate and have a metabolism more suited to higher elevations (see a couple great papers by Žagaret et al., 2015 and Žagar et al., 2017). This is where we come in! Until we have a better idea of how Podarcis might be able to physiologically and behaviourally adjust to higher elevations (and especially lower oxygen levels), the effects of climate change on these species, and their interactions, is uncertain.

Ranges of three endemic rock lizard species in the Pyrénées. Image taken from the indispensable Field Guide to the Amphibians & Reptiles of Britain and Europe.

After a long afternoon of catching lizards and data collection, the weather began to change rapidly so we immediately began our hike back down to the car. Wisps of cloud suddenly appeared, emerging from the lower elevations and moving with an eerie quiet into the small valley where we were working. We packed and left quickly, descending at an all-out run at times, but still found ourselves in a dangerous position (i.e., carrying metal poles on the side of a mountain during a thunderstorm). Fortunately, there are small stone cabins scattered throughout the area, equipped with a small wood-stove, table, and a sleeping loft – perfect for a week-end in the hills or a research team dodging lightening! We took shelter for a short while, as the the clouds moved not only overhead but right at our level. The storm passed quickly, and we returned safely, if not a bit wet, a bit late, and with some very sore legs.

Watching the storm pass from the little cabin.