WILLIAMSON, C.A.*; MARKS, J.C.; HENDRICKSON, D.A.; SWANSON, B.O.: Aliens invade Mexico: proof of their impact on native cichlids

The basin of Cuatro Ciénegas, with over 200 springs and pools, lies in the Chihuahuan desert of northern Mexico. The area is a high priority conservation site with many endemic fishes and mollusks. Although geographically isolated, the basin’s fauna is threatened by invading species. Stable isotope studies using ¹³C and ¹⁵N revealed dietary overlap between juveniles of the endemic cichlid, Herichthys minckleyi, and the invasive cichlid, Hemichromis guttatus. We conducted a field enclosure experiment to examine this interaction using growth rates as the dependent variable. Results showed H. minckleyi juveniles lost weight in the presence of H. guttatus. In contrast, H. guttatus gained weight in the presence of H. minckleyi indicating that H. guttatus could out compete H. minckleyi juveniles. These results provide strong evidence that juvenile H. minckleyi found in habitats with H. guttatus will be negatively affected potentially leading to increased juvenile mortality for H. minckleyi.