Variation in neotropical river otter (Lontra longicaudis) diet: Effects of an invasive prey species.

Due to human activities, some species have expanded their distribution into areas that were historically difficult or impossible to reach by natural dispersal. Such species may become invasive if they successfully establish reproductive populations. Predation is one of the main barriers that exotic species may face in newly colonized areas. We evaluated the effect of an invasive prey (armored catfish: Pterygoplichtys sp.) on the dietary niche breadth and trophic level of a native predator (Neotropical river otter: Lontra longicaudis) in northern Guatemala. We examined otter scats from three rivers: two where the invasive armored catfish occurred and one without the invasive fish. Samples were collected two and seven years after the first report of the catfish in the area. We performed gross scat analysis and stable isotope analyses of nitrogen and carbon of fecal matter. Where the invasive armored catfish occurred, it was the main prey item for L. longicaudis. Particularly in the river outside of protected areas seven years after the first report of the catfish, where it accounted for 49% of the otter diet. Concordance was found between the two techniques to estimate dietary niche breadth and trophic level. The dietary niche breath of otters was narrower seven years after the invasion in comparison to two years after the invasion in both invaded rivers, but, the extent of the reduction was less inside the protected area. Finally, the trophic level of otters also showed a reduction related to the occurrence of the armored catfish on their diet.