Macro-habitat preferences by the African manatee and crocodiles – ecological and conservation implications

摘要

African manatees (Trichechus senegalensis) and crocodiles are threatened species in parts of theirrange. In West Africa, crocodiles may constitute the main predators for manateesapart from humans. Here, we explore the macro-habitat selection of manateesand two species of crocodiles (West African crocodiles Crocodylus suchus and dwarf crocodileOsteolaemus tetraspis) in the Niger Delta (Nigeria), testing the hypotheses that (i) manatees mayavoid crocodiles in order to minimize risks of predation, and (ii) the twocrocodile species do compete. The study was carried out between 1994 and2010 with a suite of different field techniques. We observed that the mainmacro-habitat types were freshwater rivers and coastal lagoons for manatees,mangroves for West African crocodiles, and rivers and creeks fordwarf crocodiles, with (i) the three species differing significantly interms of their macro-habitat type selection, and (ii) significant seasonalinfluence on habitat selection of each species. Null models for nicheoverlap showed a significantly lower overlap in macro-habitat type usebetween manatee and crocodiles, whereas the two crocodiles were relativelysimilar. Null model analyses did not indicate any competitive interactionsbetween crocodiles. On the other hand, manatees avoided macro-habitats wherecrocodiles, and especially West African crocodiles, are abundant.