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

Predation is one of the main barriers that exotic species may face in newly colonized areas and may help stop or control the potential negative impacts of invasive species in the environment. We evaluated if the consumption of an invasive prey (armored catfish: Pterygoplichtys sp.) affects 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 lesser inside the protected area. Finally, the trophic level of otters also showed a reduction related to the occurrence of the armored catfish in their diet.

捕食作用是外来物种在新近定殖区域可能面临的主要阻碍之一，同时也有助于遏制或管控入侵物种在环境中造成的潜在负面影响。本研究以危地马拉北部的本土捕食者新热带河獭（Neotropical river otter: Lontra longicaudis）为研究对象，探究其取食入侵猎物装甲鲶鱼（armored catfish: Pterygoplichtys sp.）是否会影响该獭类的饮食生态位宽度与营养级。我们采集了三条河流的河獭粪便样本：其中两条河流分布有入侵性装甲鲶鱼，另一条则无该入侵鱼类。样本采集时间分别为该区域首次记录装甲鲶鱼后的第2年与第7年。研究中分别采用粪便宏观分析法，以及粪便样本的氮、碳稳定同位素分析法开展检测。在存在入侵性装甲鲶鱼的河流中，该鲶鱼为新热带河獭的主要猎物。尤其在该区域首次记录装甲鲶鱼后的第7年，未受保护区覆盖的河流中，装甲鲶鱼占河獭饮食组成的49%。两种用于评估饮食生态位宽度与营养级的分析方法结果一致性良好。相较于入侵后第2年，两条入侵河流中的河獭在入侵后第7年的饮食生态位宽度均有所收窄，但保护区内的收窄幅度更小。最后，河獭的营养级也因饮食中出现装甲鲶鱼而出现了降低。