Habitat preferences depend on substrate quality in a cooperative breeder

15 Background : The evolution of complex social organization is mediated by diverse environmental 16 constraints, including predation risk and the availability and distribution of food resources, mating 17 partners, and breeding habitats. The cooperatively breeding cichlid Neolamprologus pulcher inhabits 18 highly distinct habitats ranging from sheer rock face to gastropod shells, rubble and sandy bottoms with 19 dispersed stones. Physical habitat characteristics influence predator abundance and consequently the 20 social system and reproductive performance of this species. Under natural conditions, habitat 21 preferences should allow for optimizing the territory position within a colony. 22 Question : If given the choice, does N. pulcher distinguish between environments differing in 23 structural complexity and the presence of sand? 24 Method : We created breeding groups consisting of a dominant pair and two subordinates. We 25 manipulated structural complexity (low vs. high stone cover) and sandy environments (present vs. 26 absent). We measured habitat preference using a four-factorial design with binary choice options. 27 Predictions : We predicted that groups prefer to settle in a highly structured environment 28 providing many possibilities to hide from potential predators. We further predicted a preference for 29 sandy bottom, especially in environments with low structural complexity, because sand allows for 30 digging out shelters. 31 Results and Conclusion : N. pulcher favored more complex over less complex habitats, 32 independently of the presence of sand. When fish faced low structural complexity in both experimental 33 compartments, sand presence became a critical factor. Choosing appropriate habitats may contribute to 34 effectively reduce predation risk.