#42: New study confirms broad-scale fish distribution shifts associated with climate change
Dan Isaak
Hi Everyone,
It had to happen sooner or later and now it has. A new study (attached) published in Ecography by Lise Comte and Gael Grenouillet, entitled “Do stream fish track climate change? Assessing distribution shifts in recent decades” provides strong empirical evidence for broad-scale distribution shifts in dozens of stream fish species across France. The study used a BIG DATA approach (Blog #’s 39 and 40) wherein 3,500+ sites were sampled to determine species distributions in an early period (1980’s) and a more recent period (2000’s). Distribution models were developed from data for each period separately, then comparisons made between periods for the locations of upstream and downstream distributional boundaries (Graphic 1). Of the 32 species assessed, 25 showed evidence of upstream distribution shifts (Graphic 2) as per the general predictions from the bioclimatic models (Blog #33). The shifts were not monotonic in nature although some types of shifts were much more common than others (Graphic 3). The average rate of distribution shift at range center (0.6 km/decade) also lagged the average climate velocity in streams across France (14.2 km/decade; Blog #36), which means that species are often moving more slowly than their thermal niches (Graphic 4). Even in streams without barriers to impede dispersal, therefore, some species and populations could well be overcome by shifting isotherms in future decades and lose the climate race.
Comte & Grenouillet’s study is a watershed event because it provides biological evidence in support of the basic predictions made by some 20+ fish bioclimatic models in previous decades (Blog #33). The fact that most fish species are behaving like their terrestrial brethren and shifting to higher elevations & cooler areas as the climate warms appears now to be largely corroborated. Climate change is real & is having real effects on something as fundamental as the distribution of species across river networks and regional/national river drainages. There’s nuance and detail, of course, which have yet to be resolved, & we need scientists to replicate these results in other parts of the world, but this study should stimulate those efforts and add impetus to our actions as we grapple with the phenomenon of climate change and its effect on aquatic ecosystems.
So congratulations to Lise & Gael for being the global fish-X prize winners (Graphic 5). As per earlier contest disclaimers, recall that there is no monetary remuneration accompanying this silly prize, just the eternal esteem of, and recognition by, the global fish community for providing an answer to one of the day’s most pressing questions. You are now two famously fishy people. To further spread your fame, I’d direct interested readers to some of Lise & Gael’s previous research on this topic that helped lay the foundation for this signature achievement (http://gael.grenouillet.free.fr/grenouillet_publications.html).
Next time out, we’ll resume our regularly scheduled programming with part 2 of the “mechanisms” blog module.
Until then, best regards,
Dan