Human land-use changes the diets of sympatric native and invasive mammal species.

The consequences of biological invasions and habitat degradation for native biodiversity depend on how species cope with the individual and synergetic challenges these processes present. To assess the impact of anthropogenic land-use on the food web architecture of an invaded community, we examine the diets of nine native and two highly invasive mammal species at different trophic levels, inhabiting different land-uses across six biogeographic regions in Tasmania, Australia. We use two complementary methods, environmental DNA metabarcoding analysis (eDNA) of faeces and stable isotope analysis (SIA) of nitrogen (N) and carbon (C) in whole blood, to account for the high interindividual and temporal variability in the diets of multiple species simultaneously. eDNA showed regionalisation in the diet of smaller species, with land-use further defining dietary taxa within each region. SIA revealed that bioregion and land-use influence the δ13C values of all carnivore species and omnivores, whereas the δ15N values of these species are influenced only by land-use and not bioregion. Including multiple species showed that native rats are changing their diet in response to the presence of invasive rats, an impact that would have otherwise been attributed to land-use. Our findings demonstrate that human activities and invasive species are moulding the diets of invaded communities, raising questions about the potential impacts that dietary modifications will have on the life-history traits and the evolutionary consequences these modifications might have on the survival of native species. This highlights the urgency of including human activities in ecological studies and the importance of targeting multispecies assemblages to gain a better understanding of synergetic impacts on native biodiversity.

Las consecuencias de invasiones biológicas y degradación de hábitat en la biodiversidad nativa de un lugar dependen de las respuestas de las especies a los desafíos individuales y conjuntos que estos procesos les presentan. En este estudio examinamos la dieta de nueve mamíferos nativos y dos mamíferos altamente invasivos, pertenecientes a diferentes niveles tróficos, y que habitan diferentes usos de suelo en seis regiones bioclimáticas en Tasmania, Australia con el fin de examinar el impacto de diferentes usos de suelo en la estructura de una red trófica en una comunidad invadida. Para ello utilizamos dos métodos complementarios: ADN ambiental (eDNA) en heces y análisis de isótopos estables (SIA) de nitrógeno (N) y carbono (C) en sangre para dar cuenta, respectivamente, de la alta variabilidad interindividual y temporal en la dieta de estos animales. Los resultados de eDNA mostraron una regionalización en la dieta de las especies más pequeñas, y que el uso de suelo define aún más los taxa dietéticos dentro de cada región. El SIA reveló que los valores de δ13C de todas las especies de carnívoros y omnívoros están influenciadas por biorregiones y uso de suelo, mientras que los valores de δ15N de carnívoros y omnívoros sólo son influenciadas por el uso de suelo. Nuestros hallazgos demuestran que las actividades humanas y las especies invasoras están moldeando las dietas en comunidades invadidas generando preguntas sobre los potenciales impactos que las modificaciones dietéticas puedan tener sobre las características de las historias de vida de especies nativas y las consecuencias evolutivas que a su vez estas puedan tener en la sobrevivencia de estas especies. Así, este estudio demuestra la urgencia de incluir actividades humanas en los estudios ecológicos y la importancia de enfocarse en ensamblajes de múltiples especies para obtener un mejor entendimiento de los impactos sinérgicos sobre la biodiversidad nativa.

Inter-annual isotopic niche segregation of wild humboldt penguins through years of different El Niño intensities.

The Humboldt Current System presents high interannual variability, influenced by the El Niño Southern Oscillation (ENSO), whose implications in wildlife are not fully understood. We studied the isotopic niche of wild Humboldt penguins at Punta San Juan (Peru) during the pre-moult foraging trip in 4 consecutive years (2008-2011) under known oceanographic (ENSO) conditions. Our results show that there is a clear isotopic niche segregation (on both δ13C and δ15N values) of wild Humboldt penguins among all years. Besides isotopic niche segregation, niche width also varied significantly among years. The larger isotopic niche displayed in 2008 reflected the opportunistic feeding behaviour of Humboldt penguins when oceanographic conditions were unfavourable (i.e. El Niño of strong intensity). In contrast, and despite strong segregation, penguins displayed a more specialist behaviour in years of mild environmental conditions (i.e. 2009 "warm-weak", 2010 "neutral" and 2011 "warm-moderate"). No evidence of sexual segregation in wild Humboldt penguins during the pre-moulting foraging trip was found. This study highlights the coping mechanisms of an endangered species to changes in environmental conditions (i.e. overall, from strong to neutral El Niño events), which should have important ramifications in the management of the marine ecosystem in Peru, particularly the one related to the anchovy industry.