Experimentally induced helper dispersal in colonially breeding cooperative cichlids |
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Authors: | D Heg Z Heg-Bachar L Brouwer M Taborsky |
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Institution: | (1) Department of Behavioural Ecology, Zoological Institute, University of Bern, CH-3032 Hinterkappelen, Switzerland;(2) Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, 9750AA Haren, The Netherlands |
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Abstract: | The ‘benefits of philopatry’ hypothesis states that helpers in cooperatively breeding species derive higher benefits from
remaining home, instead of dispersing and attempting to breed independently. We tested experimentally whether dispersal options
influence dispersal propensity in the cooperatively breeding Lake Tanganyika cichlids Neolamprologus pulcher and N. savoryi. Cooperative groups of these fishes breed in densely packed colonies, surrounded by unoccupied, but apparently suitable breeding
habitat. Breeding inside colonies and living in groups seems to benefit individuals, for example by early detection and deterrence
of predators. We show that despite a slight preference of both species for habitat with a higher stone cover, 40% of the preferred
habitat remained unoccupied. On average, the colonies contained a higher number of (1) predators of adults, juveniles and
eggs, (2) shelter competitors, and (3) other species including potential food competitors, compared to the outside colony
habitat. Apparently, habitat differences cannot explain why these cichlids breed in colonies. Accordingly, dispersal may not
be limited by a lack of suitable breeding shelters, but by the relatively higher risk of establishing an outside- compared
to a within-colony breeding territory. To test whether cichlids prefer within- to outside-colony breeding territories, we
provided breeding shelters inside the colony and at the colony edge and studied helper dispersal. As expected, significantly
more shelters were occupied within the colony compared to the edge. New breeding pairs with several helpers occupied these
shelters. We conclude that although breeding habitat is plentiful outside the colonies, helpers delay dispersal to obtain
a higher quality breeding position within the group or colony eventually, or they disperse in groups. Our results suggest
that (1) group augmentation and Allee effects are generally important for dispersal decisions in cooperatively breeding cichlids,
consistent with the ‘benefits of philopatry hypothesis’, and (2) habitat saturation cannot fully explain delayed dispersal
in these species. |
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Keywords: | Dispersal Cooperative breeding Habitat saturation Allee effects Cichlidae |
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