Invasion risk of a popular aquarium trade fish in an endemic hotspot

Background/Question/Methods

Invasive species are commonly cited as one of the top threats to global biodiversity.  The IUCN Red List database indicated that invasives are contributing threats 292 extinct, extinct in the wild, critically endangered or endangered fishes.  The aquarium trade is one of five main pathways by which aquatic species are introduced to a new location.  Hemichromis guttatus, a popular ornamental cichlid native to West Africa, is one of these species having been introduced into an endemic hotspot in northern Mexico, the desert spring system Cuatro Cienegas, where it has established, is spreading and is in the process of becoming invasive.  This site provides the opportunity to study an invasion in progress and to make predictions about to where H. guttatus may spread, and then to test these predictions.  In this work, we asked what is the invasion risk of currently uninhabited sites within Cuatro Cienegas?  To do this, we conducted a valley-wide survey of H. guttatus and collected data on the environmental characteristics at each trap site.  We then used logistic regression to model which environmental characteristics were related to presence of the exotic and used these results to assign invasion risk to as-of-yet uninhabited sites throughout the valley.  

Results/Conclusions

We found that the model that best predicted Hemichromis guttatus presence included pH, temperature² (indicating a non-linear relationship between temperature and presence), depth and vegetation presence.  However, only pH, temperature² and vegetation presence were significant predictors, indicating a threshold level of depth below which presence is much more probable, yet under which, there is no clear pattern between depth and the probability of presence.  Using these results, we were able to identify sites with a very high, high, moderate and low invasion risk in the valley.  Generally, invasion risk declined as sites were further away from thermal spring inputs i.e., downstream in the large river system, and higher closer to these sites.  Some sites with a high risk of invasion have surface connections to known presences of H. guttatus while others with a high invasion risk are more isolated, thus dispersal limitation could interact with the environmental characteristics of a site to slow unaided invasion into these more isolated sites.  These results will be beneficial to reserve managers in terms of deciding how to prioritize where to use the limited resources available to them to combat the spread of H. guttatus in the valley.