Bahamian rock iguanas (genus Cyclura) are the largest native terrestrial frugivores in the Bahamian archipelago. Iguana-based ecotourism and associated food provisioning have been shown to affect their physiology; but it is unknown whether affiliated differences in their feeding and movement ecology manifest themselves in terms of their seed dispersal effectiveness. Specifically, we sought to quantify whether iguanas on food-provisioned islands (1) consume less native plant fruits and disperse seeds less frequently than those on non-fed islands, and (2) disperse more seeds on feeding beaches, where the probability of seed survival and germination is compromised. We conducted fieldwork in the Exuma island chain in two different seasons (June and September 2018) in which we located fecal samples and attained fecal samples from captured iguanas on food-provisioned islands. We used generalized linear mixed models to test (1) whether the proportion of located fecal samples containing seeds of native plants differed between food-provisioned and unfed populations, (2) whether iguanas captured on beaches or in non-beach locations on food-provisioned islands differed in their likelihood of dispersing seeds of native plants, and (3) whether the number of fecal depositions on food-provisioned islands differed between feeding beach and beaches were food was not provided by ecotourists.
Results/Conclusions
On average, 35-50% of sampled fecal depositions on iguana-inhabited islands in June 2018 contained seeds of native plants, and this proportion did not differ between food-provisioned and unfed islands. On food-provisioned islands in September 2018, fecal samples of iguanas captured from beach and non-beach locations were equally likely to contain seeds of native plant species (> 60% of all fecal samples contained seeds). The number of fecal samples found on feeding beaches of food-provisioned islands were over an order of magnitude higher than those on beaches that were not accessed by ecotourists. In combination, these results suggest that although iguanas on food-provisioned islands consume similar amounts of native fruits and disperse seeds at similar rates as those on unfed islands, food-provisioned iguanas disperse high numbers of seeds to unfavorable beach locations. The observed lower seed dispersal effectiveness of iguanas on food-provisioned islands may be further compromised by documented loose fecal consistency accompanied by lower soil fecal-imparted nutrient benefits for dispersed seeds. We argue that the multi-faceted conservation efforts for endangered Bahamian rock iguanas need to integrate potential differences in seed dispersal effectiveness and their repercussions.