Wednesday, July 17, 2013

Fruit-eating in crocodilians

Reptile roles in ecosystems are frequently acknowledged as predators, scavengers and prey but their role as pollinators and seed dispersal agents are often overlooked.  In a forthcoming paper in the Journal of Zoology Platt et al (2013) report on the evidence that crocodilians disperse seeds.

The authors ask the questions: (1) Do crocodilians consume fruit and if so, how widespread is this behavior among the order Crocodylia? (2) If fruits are present in the diet, are these ingested incidental to prey capture, consumed as gastroliths, derived secondarily from ingested prey or deliberately ingested as food? (3) Does fruit consumption yield a nutritional reward for crocodilians? (4) What is the fate of fruits and seeds ingested by crocodilians? (5) Are movement patterns of crocodiles likely to extend the seed shadow much beyond the parent plant? (6) What are the ecological implications of this plant–animal interaction; that is, do crocodilians function as seed dispersers?

The authors find  frugivory is widespread among the Crocodylia and while some frugivory is certainly accidental, but the literature leaves little doubt that on occasion, crocodilians deliberately eat fruit. Crocodilians are probably best considered occasional frugivores that is, generalist predators that complement an otherwise carnivorous diet with fruit, which is consumed infrequently and usually, but not always in small quantities.

Although fruit seems of limited importance in crocodilian diets, nutritional benefits are likely. The diversity of fruit types consumed by crocodilians seems to preclude the existence of a specific crocodilian dispersal syndrome similar to that described for other reptiles (aromatic, colorful fruits, borne at ground level or dropped at maturity) . Nonetheless, several lines of evidence strongly suggest that crocodilians potentially function as effective agents of seed dispersal. They  are capable of ingesting large numbers of fruits and seeds, and because these are swallowed without mastication, seeds are likely to escape damage during ingestion. Also, the large gape capacity of crocodilians permits the ingestion of large    fruits. Once ingested, the fate of seeds is less clear; while digestive predation of some seeds undoubtedly occurs, most are probably regurgitated or excreted in the feces. Because crocodilians have large territories and frequently undertake lengthy movements, they are capable of generating extensive seed shadows; seeds are transported well beyond the parent plant before being voided. Although little is known about the ultimate deposition of seeds ingested by crocodilians, the few available reports suggest that defecation sites could prove suitable for seed germination. The authors conclude that it likely that crocodilians function as significant seed dispersal agents in many freshwater ecosystems.

Citation
Platt, S. G., Elsey, R. M., Liu, H., Rainwater, T. R., Nifong, J. C., Rosenblatt, A. E., Heithaus, M. R. and Mazzotti, F. J. (2013), Frugivory and seed dispersal by crocodilians: an overlooked form of saurochory?. Journal of Zoology. doi: 10.1111/jzo.12052

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