Foraging segregation between spotted (Stenella attenuata) and spinner (Stenella longirostris) dolphins in the Mexican South Pacific

Abstract

Coexistence among sympatric species requires a certain degree of resource partitioning. In the Mexican South Pacific, information regarding the coexistence of Stenella attenuata (SA) and Stenella longirostris (SL) is lacking. Stable isotope analyses (δ15N and δ13C) were conducted to assess the differences in feeding habits to infer trophic position and amplitude as well as habitat use, based on Bayesian inference and a random forest (RF) classifier. Potential trophic relationships with other species were assessed by Bayesian mixing models. Feeding segregation between species was mainly based on carbon sources (δ13C: p(SA > SL) = 100%, RF Gini Impurity = 80%). Moreover, SA (n = 22) presented a broader isotopic niche than that of SL (n = 25; SIBER Bayesian Standard Ellipse areas = 0.91‰2 vs. 0.77‰2) with a 33% overlap, suggesting that SA uses more coastal habitats than SL. The most relevant prey species were the mesopelagic fish Benthosema panamense and the epipelagic fish Hyporhamphus naos (~50%), although B. panamense was more related to SL than SA: p(%SL > %SA) = 76.6%. The trophic positions were 4.0 (SA) and 3.8 (SL). Our results provide evidence of resource partitioning within a potential foraging ground for both dolphin species.

Priorities for ecological research on cetaceans in the Galápagos Islands

“…Long-term data on biochemical tracers will provide a unique opportunity for assessing trends in resource use over time and space, and for relating these trends to environmental variation (e.g., El Niño Southern Oscillation; Arneś-Urgelleś et al, 2021). Beyond contributing to mapping the local Galaṕagos food webs (e.g., Okey et al, 2004;Alava, 2009), this approach will also allow us to quantify trophic niche overlap between and within species (Enrıquez-Garcıá et al, 2022), and investigate individual and ontogenetic variation in foraging, and the extent to which such variation is driven by resource partitioning and intra-and interspecific competition (e.g., Teixeira et al, 2022).…”