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¹ Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas

Bottlenose dolphins (Tursiops truncatus) and pantropical spotted dolphins (Stenella attenuata) co-occur in GolfoDulce, a fjord-like embayment located in the southern Pacific coast of Costa Rica. We evaluated if spatial overlapby these dolphin species is associated with similar environmental requirements. Presence-only models based onniche theory were constructed by contrasting a set of spatial locations with the responses of the target speciesto abiotic ecogeographical variables (EGVs: depth, slope, distance to rivers, distance to 200 m isobath, meansea surface temperature, and variation in sea surface temperature). Models were cross-validated with levels ofdiscrimination that ranged from acceptable to excellent based on the area under the curve assessment (T. truncatus,rainy season: 0.76, dry season: 0.83; S. attenuata, rainy season: 0.84, dry season: 0.89). Both dolphin speciesoccur in Golfo Dulce year-round; the lack of seasonality documented previously was supported by the models.Species distribution models showed no spatial overlap, with differences in EGVs affecting their distribution(T. truncatus: distance to river + distance to 200 m isobath, S. attenuata: depth + sea surface temperature). Weargue that the coexistence of both predators in Golfo Dulce is linked to habitat heterogeneity, where criticalhabitats are spatially differentiated. The lack of fine-scale spatial overlap, along with influential abiotic variables,highlights a process of coexistence for dolphins that are sympatric at the scale of Golfo Dulce, but within the Gulfthere is fine-scale allopatry.

Palabras clave: Coexistence; Costa Rica; Ecological niche modeling

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