#49: Part 9, Mechanisms of change in fish populations: Non-native species invasions
Dan Isaak
There’s a war going
on out there…
Hi Everyone,
As if there weren’t enough complexities already in figuring out how BIDE processes in many native fish populations will adjust to climate-induced changes in the physical (Blog #41) and food environments (Blog #48), what if these populations also had to contend with alien invaders? Not the sort from space, but the sort that humans, both intentionally & unintentionally, have long been moving around the planet. In the literature, these are now usually referred to as non-native invasive species and we’re presently in the middle of a global invasion pandemic. Once a non-native species is established in a stream or lake, there are many pathways, both direct and indirect, by which the local ecosystem can be affected (graphic 1; Cucherousset and Olden provide a good review hyperlinked here: http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2013/03/Fisheries_2011c_Inv.pdf). Not all are negative, or even noticeable, but many are and it can be a real bugger to control or eliminate an invasive species when they are problematic.
Human mediated species invasions have no doubt been happening for 10,000s of years, back to when our species first dispersed out of Africa to colonize other parts of the Earth & brought along a few favorite critters & pesky tag-alongs. But in recent times these invasions have accelerated to where they’re now orders of magnitude more common that was previously the case. The emergence of a global, hyper-connected economy means that humans and our goods move around so much that there are endless opportunities for invasive tag-alongs to make it into new environments. In fact, some now talk of a new Pangaea—reference to the supercontinent 200 million years ago when the land mass of the 7 continents was merged into one and species could more easily disperse across broad areas.
Compounding the pandemic of panmixing in the putative Pangaea is the possibility that environmental trends associated with climate change will facilitate the expansion of many invasive species into areas that were not previously suitable habitats (graphic 2; Rahel and Olden provide a good review hyperlinked here: http://www.uwyo.edu/frahel/pdfs/rahel-2008-1.pdf). Perhaps the best examples of this were the fishes comprising the first big wave of invasives (what we’ll call the ‘old-invasives’) that were purposely trucked around from the late-1800’s to mid-1900’s, often to supplement existing fisheries or develop new ones. Some of the old-invasives have been parts of riverscapes long enough that they’d likely expanded to reach a quasi-equilibrium with their environmental niche. But just as distributions of native fishes are shifting in response to climate change (blog #’s 32, 34, 35, 42), the old-invasives are likely to be on the march in places where climatic constraints were previously limiting. Only this time, unfortunately, their like will be accompanied by a legion of new-invasive species that our species is spreading willy-nilly across the Earth.
It all portends a sort of global fish gladiator contest this century in which many native fishes, and even the old-invasives we’ve grown accustomed to, are going to have to vie & compete for survival in the new Pangaea. Understanding how and where it all goes, and what we can do about it is going to be a huge, costly, and ongoing challenge. Some monetary estimates already put the disruptions caused by non-native species at many millions & billions of $’s annually. And in some places, invasive fishes are so prevalent that they’re directly impacting humans (graphic 3). Witness this video of the hazards that high flying invasive fish can cause your health (http://www.youtube.com/watch?v=rPeg1tbBt0A). A war of the worlds indeed.
Until next time, best regards,
Dan