Cool, cold or colder? Spatial segregation of prions and blue petrels is explained by differences in preferred sea surface temperatures
Résumé
The Southern Ocean provides one of the largest environmental gradients on
Earth that lacks geographical barriers, and small but highly mobile petrels
living theremay offer finemodels of evolution of diversity along environmental
gradients. Using geolocation devices,we investigated thewinter distribution of
closely related petrel species breeding sympatrically in the southern Indian
Ocean, and applied ecological niche models to compare environmental conditions
in the habitat used. We show that thin-billed prions (Pachyptila
belcheri), Antarctic prions (Pachyptila desolata) and blue petrels (Halobaena
caerulea) from the Kerguelen archipelago in the southern Indian Ocean segregate
latitudinally, sea surface temperature being the most important variable
separating the distribution of the species. Antarctic prions spent the winter
north of the Polar Front in temperate waters, whereas blue petrels were
found south of the Polar Front in Antarcticwaters. Thin-billed prions preferred
intermediate latitudes and temperatures. Stable isotope values of feathers
reflected this near complete niche separation across an ecological gradient
that spans large scales, and suggest evolutionary isolation by environment.
In pelagic seabirds that exploit large areas of ocean, spatial niche partitioning
may not only facilitate coexistence among ecologically similar species, but
may also have driven their evolution in the absence of geographical barriers.
1. Introduction
Individualmovements and behaviour are inextricably linked to habitat characteristics,
which determine the distribution and availability of trophic resources.
In the oceans, the more productive areas are often in cold-water or upwelling
regions where higher nutrient availability sustains productive foodwebs. Seabird
species often breed in large communities and target productive areas within their
foraging range, leading to intense competition for resources [1] and reduced foraging
efficiency [2]. Seabirds can avoid interspecific competition at least partially
by ecological segregation in foraging areas [3,4], diving depths [4,5] or diet
choice [6,7]. However, little is known from pelagic birds during the non-breeding
season, when seabirds forage over much larger spatial scales. Among the most
abundant small seabirds worldwide, prions (Pachyptila spp.) and closely related
blue petrels (Halobaena caerulea) inhabit the open waters of the Southern Ocean.
As these small petrels are very similar in size, foraging techniques and diet
during the breeding season, it has been suggested that they may be suitable
model species in the context of niche partitioning and community assembly
rules [8,9]. In the southwest Atlantic Ocean, thin-billed and Antarctic prions
had divergent patterns of migration, resulting in nearly complete spatial segregation
(0–5% overlap by month, [10]). Consistent foraging in different water
& 2015 The Author(s) Published by the Royal Society. All rights reserved.