Microhabitat Selection and Agonistic Interactions Determine Habitat Partitioning in Sympatric Territorial Damselfish

Abstract

Habitat partitioning reduces competition among ecologically similar species and promotes their coexistence within the same environment. In this study, we evaluated the abundance, microhabitat use, reef occupancy, spatial overlap, and agonistic interactions of the sympatric territorial damselfishes Stegastes acapulcoensis and Stegastes flavilatus at La Entrega reef, Oaxaca, Mexico. Using visual censuses, habitat characterizations, in situ observations, and non-invasive video recordings, we found that S. acapulcoensis exhibited higher abundance than S. flavilatus across all reef zones. Both species exhibited clear habitat partitioning along the reef zones, with S. acapulcoensis occupying sites with high percentages of live coral and algae, as well as large shelters, while S. flavilatus used sites characterized by high rugosity and the presence of rock, sand, and rubble. Although S. flavilatus defended larger territories than S. acapulcoensis (6.6 ± 4.9 m² vs. 4.5 ± 1.5 m², respectively), S. acapulcoensis occupied a greater proportion of the reef area (58% vs. 18%). Spatial overlap between species was limited (10%–25%) but increased up to 40% among individuals of size class III in the deep zone, where the availability of preferred microhabitats for both species was substantially lower. Both species displayed a higher frequency of agonistic interactions toward conspecifics; however, interspecific interactions increased in the deep zone. Our results suggest that the spatial partitioning of S. acapulcoensis and S. flavilatus is driven by differences in microhabitat selection, resulting in relatively low spatial overlap and predominantly intraspecific aggression. Our findings show that the fine-scale selection of species-specific microhabitats and interspecific agonistic interactions drive spatial segregation and maintain ecological differentiation between S. acapulcoensis and S. flavilatus, thereby promoting their coexistence even in overlapping reef zones within structurally complex systems.