One Fish, Two Fish

               Chances are you wouldn’t be happy if someone broke into your house and started eating all your food, and just generally trashing the place. So you can see why invasive species are such a pressing issue in ecology. Invasive species are species that have been introduced or have found their way somewhere they didn’t originally live, and can sustain a population. In many populations of invasive species, they do quite well for themselves. There are many historical cases of invasive species taking over an area and drastically changing the environment and trophic webs of that area. For instance, rabbits were introduced into Australia in the 18^th century and experienced a massive population boom. They quickly became pests, eating all of the crops grown in the area and generally messing things up. So it is clearly important to have methods in place to deal with possible invasive species. But how do we know where we need to be vigilant? From what? This issue is addressed in a research article by Poulos et al.

Image of a Northern Snakehead
http://upload.wikimedia.org/wikipedia/commons/f/f8/Snakehead_-_Channa_argus_2.jpg

               They set out to find out what factors influence the distribution of three invasive fish species, the northern snakehead (Channa argus), round goby (Neogobius melanostomus), and silver carp (Hypophthalmichthys molitrix). In order to do this, they used a modeling tool called species distribution modeling (SDM). SDM is used to generate a map of potential habitat for a species based on presence or presence/absence (abundance) data, as well as environmental factors. There are many different types of species distribution models, and to get a more accurate read the authors decided to use ensemble modeling. This type of modeling uses multiple models, and combines them to see where all of them are in agreement. The authors use data gathered from the Nonindigenous Aquatic Species (NAS) Database for their species presence data, and data gathered from several other databases for their environmental variables. Then, using the appropriate software, they ran their models. This generated their habitat predictor maps, which they combined for each species of fish. They found that for northern snakeheads, the best habitats for invasion were those with low elevation, slow-flowing waters, with emergent vegetation (plants that live in water but grow partly out of the water). The most ideal habitats for round goby populations to invade were areas in higher latitudes with high canopy cover and forested shorelines. Lastly, they found that silver carp liked areas with slow-flowing water, low sand content, and not very much vegetation.

               So how do we use this information to better the field of ecology? What purpose do these maps serve? Well, with home-burglarizing fish swimming around we really have to be careful about what types of fish we release into new habitats. Having maps of possible habitats of these fish lets us devise strategies for protecting areas of high risk for invasion. Without them these fish may just be running around, so to speak, wherever they want. If we want to preserve what’s left of the natural ecosystems around us, a good place to start is with preventing harmful invasive species from setting up shop.

Reference:

Poulos, H., Chernoff, B., Fuller, P., & Butman, D. (2011). Ensemble forecasting of potential habitat for three invasive fishes. Aquatic Invasions, 7(1), 59-72. http://www.aquaticinvasions.net/2012/AI_2012_1_Poulos_etal.pdf