Habitat partitioning mediates the coexistence of sympatric dolphins in a tropical fjord-like embayment

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From: Journal of Mammalogy(Vol. 99, Issue 3)
Publisher: Oxford University Press
Document Type: Author abstract; Report
Length: 540 words

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Abstract :

Bottlenose dolphins (Tursiops truncatus) and pantropical spotted dolphins (Stenella attenuata) co-occur in Golfo Dulce, a fjord-like embayment located in the southern Pacific coast of Costa Rica. We evaluated if spatial overlap by these dolphin species is associated with similar environmental requirements. Presence-only models based on niche theory were constructed by contrasting a set of spatial locations with the responses of the target species to abiotic ecogeographical variables (EGVs: depth, slope, distance to rivers, distance to 200 m isobath, mean sea surface temperature, and variation in sea surface temperature). Models were cross-validated with levels of discrimination that ranged from acceptable to excellent based on the area under the curve assessment (71 truncatus, rainy season: 0.76, dry season: 0.83; S. attenuata, rainy season: 0.84, dry season: 0.89). Both dolphin species occur 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). We argue that the coexistence of both predators in Golfo Dulce is linked to habitat heterogeneity, where critical habitats 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 Gulf there is fine-scale allopatry. El delfin nariz de botella (Tursiops truncatus) y el delfin manchado pantropical (Stenella attenuata) son delfinidos presentes en el Golfo Dulce, una bahia similar a un fiordo, en el litoral del Pacifico Sur de Costa Rica. Este estudio evalua si el traslape espacial en estas especies se asocia a requerimientos ambientales similares. Se hicieron modelos de "solo presencia" basados en la teoria de nichos, que ponderan una muestra de localidades geograficas con la respuesta de las especies evaluadas a variables ecogeograficas abioticas (VEGs: Profundidad, Pendiente, Distancia a Rios, Distancia a la Isobata 200 m, Promedio de la Temperatura Superficial del Mar y Variacion de la Temperatura Superficial del Mar). Los modelos se sometieron a validacion cruzada con niveles de discriminacion en un rango que va desde aceptable a excelente, en base a la medicion del Area Bajo la Curva (T. truncatus, temporada de lluvia: 0.76, temporada seca: 0.83; S. attenuata temporada de lluvia: 0.84, temporada seca: 0.89). Ambas especies de delfines estan presentes todo el ano, los modelos sustentaron la falta de estacionalidad documentada previamente. Los modelos de distribucion de las especies no muestran traslape espacial, estos evidencian diferencias en VEGs que afectan la distribucion de los delfines (T. truncatus. distancia a rios + distancia a isobata de 200 m, 5. attenuata: profundidad + temperatura superficial del mar). La coexistencia de ambos depredadores en el Golfo Dulce esta ligada a la heterogeneidad de habitat, donde los habitats criticos estan espacialmente diferenciados. La falta de traslape en la dimension espacial del habitat, incluyendo la segregacion de las variables abioticas, resaltan un proceso de coexistencia para delfinidos que se caracteriza como una simpatria aparente a la escala del Golfo Dulce con alopatria a escala fina dentro del Golfo. Key words: coexistence, Costa Rica, ecological niche modeling, Golfo Dulce, habitat partitioning, spatial overlap, Stenella attenuata, sympatry, Tursiops truncatus DOI: 10.1093/jmammal/gyy021

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Gale Document Number: GALE|A545566934