Microhabitat segregation and fine ecomorphological dissimilarity between two closely phylogenetically related grazer fishes in an Atlantic Forest stream, Brazil

Abstract

Habitat segregation is considered the mostprevalent resource-partitioning mechanism for streamfishes and the species morphology can be a strongpredictor of their spatial distribution. However, moststudies addressing morphology-habitat relationshipshave defined the space in physiognomically homoge-neous units (i.e., mesohabitat), probably not detectingsegregation among several closely related species. Herewe investigated the ecomorphology and the use of hab-itat in a fine spatial scale (i.e., microhabitat) by twoclosely phylogenetically related grazer fishes (theloricariidsParotocinclus maculicaudaandHisonotusnotatus), syntopic in an Atlantic Forest stream. Weconducted standardized underwater observations intwo 50 m long stream sections differing in canopycondition, totaling 273 individual microhabitat records.We clearly detected microhabitat segregation betweenthe species. In both sample sites,H. notatusremainednear the stream banks and closer to shelters, whileP. maculicaudapredominantly occurred in more hydro-dynamic microhabitats, facing higher focal current ve-locities and water turbulence. Differences in focal ele-vation and water depth (i.e., vertical segregation) wereexclusively detected in the deforested site. The spatialsegregation was congruent with slight interspecific mor-phological differences, being in accordance with hy-potheses about form-function relationships previouslyreported for fishes. Given that the diel activity and dietof these grazer species were strongly overlapping, webelieve that the observed microhabitat segregation fa-vors resource partitioning betweenP. m a c u l i c a u d aandH. notatus, facilitating their coexistence in high abun-dances in the studied system. This study illustrates howthe assessment of fine-tuned ecological processes canprovide subsidy to management strategies aiming theconservation of tropical stream biodiversity.