Intra-population isotopic niche variation in common bottlenose dolphins (Tursiops truncatus) from the northern Adriatic Sea

Among-individual variability in animal behaviour and diet leads to a plethora of mini-niches within a population's general niche. Such variability is directly or indirectly linked to inter- and intra-specific competition, behavioural adaptation and variation in foraging tactics, which may lead to evolutionary divergence and speciation but is also relevant to population resilience and conservation. We used boat surveys, photo-identification techniques, biopsy sampling and stable isotope analysis (δ¹³C, δ¹⁵N) to study the intra-population isotopic niche variation in an apex predator, the common bottlenose dolphin (Tursiops truncatus), in the northern Adriatic Sea. We integrated this information with various demographic, behavioural, social and temporal parameters from long-term re-sighting histories of photo-identified individuals, as well as with information on persistent organic pollutant concentrations (PCB and DDE). Despite overlap, we found marked differences in overall isotopic niche among different social groups within the same population, consistent with differences in behaviour. However, interestingly, differences in δ¹⁵N values, a proxy for trophic level, did not correlate with persistent pollutant concentrations. This study provides new insight into fine-scale variability and drivers of intra-population partitioning in an apex predator, which may be relevant when evaluating multiple and cumulative impacts affecting marine conservation.