Drivers of interspecific spatial segregation in two closely-related seabird species at a Pan-Atlantic scale

Aim: Ecologically similar species living in sympatry are expected to segregate to reduce the effects of competition where re-sources are limiting. Segregation from heterospecifics commonly occurs in space, but it is often unknown whether such segregation has underlying environmental causes. Indeed, species could segregate because of different fundamental environmental requirements (i.e., ‘niche divergence’), because competitive exclusion at sympatric sites can force species to either change the habitat use they would have at allopatric sites (i.e., ‘niche displacement’) or to avoid certain areas, independently of habitat (i.e.,‘spatial avoidance’). Testing these hypotheses requires the comparison between sympatric and allopatric sites. Understanding the competitive mechanisms that underlie patterns of spatial segregation could improve predictions of species responses to environmental change, as competition might exacerbate the effects of environmental change. Location: North Atlantic and Arctic. Taxa: Common guillemots Uria aalge and Brünnich's guillemots Uria lomvia.