Habitat mediates coevolved but not novel species interactions

Ongoing recovery of native predators has the potential to alter species interactions, with community and ecosystem wide implications. We estimated the co-occurrence of three species of conservation and management interest from a multi-species citizen science camera trap survey. We demonstrate fundamental differences in novel and coevolved predator–prey interactions that are mediated by habitat. Specifically, we demonstrate that anthropogenic habitat modification had no influence on the expansion of the recovering native pine marten in Ireland, nor does it affect the predator's suppressive influence on an invasive prey species, the grey squirrel. By contrast, the direction of the interaction between the pine marten and a native prey species, the red squirrel, is dependent on habitat. Pine martens had a positive influence on red squirrel occurrence at a landscape scale, especially in native broadleaf woodlands. However, in areas dominated by non-native conifer plantations, the pine marten reduced red squirrel occurrence. These findings suggest that following the recovery of a native predator, the benefits of competitive release are spatially structured and habitat-specific. The potential for past and future landscape modification to alter established interactions between predators and prey has global implications in the context of the ongoing recovery of predator populations in human-modified landscapes.

Predators learning to avoid toxic invasive prey: a study on individual variation among free-ranging lizards

Within all wild populations, individuals vary in ways that affect their vulnerability to threatening processes. Understanding that variation may clarify mechanisms of population persistence and/or evolution. In Australia, Yellow-spotted Monitors (Varanus panoptes), decline by >90% when toxic Cane Toads (Rhinella marina) invade an area. Taste-aversion training (exposing animals to non-lethal toads) can buffer impacts; but does pre-existing behavioural variation also influence survival? An individual’s fate can be predicted from its behaviour during aversion-training trials. Lizards presented with small toads either consumed them, rejected them, or fled. When Cane Toads invaded our study site, mortality was lower in lizards that ‘consumed’ (aversion-trained) than in those that ‘fled’ (untrained), but even lower in lizards that ‘rejected’ toads outright. Thus, animals reluctant to consume toads in trials survived despite never being aversion-trained. In this system, lizard vulnerability is driven by boldness, behavioural responses to novel prey types, and the opportunity to learn aversion.

Limpkin, Aramus guarauna (L., 1766) (Gruiformes, Aramidae), extralimital breeding in Louisiana is associated with availability of the invasive Giant Apple Snail, Pomacea maculata Perry, 1810 (Caenogastropoda, Ampullariidae)

We document the first breeding record of Limpkin, Aramus guarauna (Linnaeus, 1766) (Gruiformes, Aramidae), for Louisiana, describe an additional unpublished breeding record from Georgia, as well as a possible record from Alabama, and associate these patterns with the concurrent establishment of the invasive Giant Apple Snail, Pomacea maculata Perry, 1810 (Caenogastropoda, Ampullariidae). We predict that an invasive prey species may facilitate range expansion by native predator species, which has ramifications for conservation and management.

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:Pterygoplichtyssp.) 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 forL. 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.ResumenComo producto de las actividades humanas algunas especies han expandido su distribución hacia áreas que históricamente eran difícil o imposible de alcanzar mediante de dispersión natural. Estas especies pueden convertirse en invasoras si establecen exitosamente poblaciones reproductivas. La depredación es una de las principales barreras que las especies exóticas deben afrontar en las áreas recientemente colonizadas. Evaluamos los efectos de una especie invasora (el pez diablo:Pterygoplichtyssp.) sobre la amplitud de nicho alimenticio y el nivel trófico de un depredador nativo (la nutria de rio Neo-tropical:Lontra longicaudis) en el norte de Guatemala. Examinamos las excretas de nutrias provenientes de tres ríos: dos donde el pez diablo se encuentra presente y uno donde este invasor aún está ausente. Las muestras fueron colectadas dos y siete años después del primer reporte de del pez diablo en le área. Realizamos un análisis macroscópico de las excretas y análisis de isotopos estables de nitrógeno y carbono de la materia fecal. Donde el pez diablo invasor estaba presente, fue el principal ítem alimenticio deL. longicaudis. Particularmente en el río ubicado fuera de áreas protegidas siete años después del primer reporte del pez diablo, donde este consistió en el 49% de la dieta de la nutria. Encontramos concordancia entre las dos técnicas para estimar la amplitud de nicho dietario y nivel trófico. La amplitud de nicho dietario de las nutrias fue más angosto siete años después de la invasión en comparación con dos años luego de la invasión en ambos ríos invadidos, pero la magnitud de la reducción fue inferior dentro del área protegida. Finalmente, observamos una reducción en el nivel trófico de las nutrias relacionada con la ocurrencia del pez diablo en su dieta.

Eastern Fence Lizards (Sceloporus undulatus) display an ontogenetic shift in relative consumption of native and invasive prey

Interactions between invasive prey and native predators can provide an opportunity to better understand predator–prey dynamics and how these may change through ontogeny. Eastern Fence Lizards (Sceloporus undulatus (Bosc and Daudin in Sonnini and Latreille, 1801)) are ant specialist, particularly as juveniles. Invasive red imported fire ants (Solenopsis invicta Buren, 1972) pose a lethal risk to S. undulatus that eat them, especially smaller-bodied juveniles. We examine ontogenetic shifts in S. undulatus consumption of toxic invasive fire ants versus palatable native pyramid ants (Dorymyrmex bureni (Trager, 1988)). We predicted that hatchlings should avoid eating fire ants in favor of native ants, whereas less-vulnerable adults should take advantage of both prey sources. However, when given the choice between fire ants and native ants, hatchlings consumed similar numbers of these species, whereas adults consumed nearly three times as many native ants as invasive fire ants. Increased consumption of fire ants in adulthood could be the result of lifetime experience, strategies to safely consume fire ants, ontogenetic shifts in the ability to distinguish between ants, or reduced costs to adults of eating venomous ants. Future research should aim to distinguish these alternative mechanisms and examine the long-term consequences of native species incorporating toxic invasive prey into their diets.