1- 2 T er~-1L 1.1 ill-/1L-jLiLIi _1_ -A- '1 BUT# I 0 1, h % 0 * 1 . 80 = 1 : of the FLORIDA STATE MUSEUM Biological Sciences Volume 24 1979 Number 3 BEHAVIOR AND ECOLOGY OF THE ROCK IGUANA CYCLURA CARINATA JOHN B. IVERSON 0 . S , ~f,m ' I » ae % 1 4 E % & .4 4:SM> · S#th= ,· 8 4 1 ' ,/ . 1{~'- i -~ , 9 -1 St: ' ; 1 UNIVERSITY OF FLORIDA GAINESVILLE Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. JOHN WILLIAM HARDY , Editor RHODA J . RYBAK , Managing Editor Consultants for this issue: HENRY FITCH ROBERT.W. HENDERSON Communications concerning purchase or exchange of the publications and all manuscripts should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of Florida; Gainesville, Florida 32611. Copyright © 1979 by the Florida State Museum of the University of Florida. This public document was promulgated at an annual cost of $5,607.48, or $5.607 per copy. It makes available to libraries, scholars, and all interested persons the results of researches in the natural sciences, emphasizing the circum-Caribbean region. Publication date: December 20, 1979 Price, $5.65 BEHAVIOR AND ECOLOGY OF THE ROCK IGUANA CYCLURA CARINATA JOHN B. IVERSON' SyNopsis: The natural history and social behavior of the rock iguana, Cyclum carinata, were studied during 25 weeks between September 1973 and June 1976 on several small cays in the Turks and Caicos Islands, British West Indies, and in captive enclosures in Gainesville, Florida. Reproductive cycles were synchronized to climatic cycles: Testes sizes were max- imal in April and May (the end of the dry season). Vitellogenesis began in January (onset of the dry season); ovulation and mating occurred in early May. Courtship was typical of most iguanid lizards; the mating system was probably one of serial polygyny with monogamy among some males. A single annual clutch of 2 to 9 eggs was laid in early Juhe in the terminal portion of the female's retreat burrow. Clutch size was positively correlated with female size. Clutch weight averaged about 25% of preoviposition weight. Females defended their nest burrows for several days to several weeks after nesting, but Were not territorial during the remainder of the year. Hatching occurred after approximately 90 days. Neonates averaged 79.8 mm SVL and 14.6 gm. Juvenile growth rate averaged 19.2 mm SVL/year. Males reachedsexual maturity at approximately 220 mm SVL and 375-475 gm and at an age of about 7 yr; females 185-200 mm, 200-300 gm at 6 to 7 yr. Adult males averaged 276 mm SVL and 935 gm, adult females 225 mm and 475 gm. The largest male measured 360 mm SVL and 1864 gm, largest female 292 mm and 1135 gm. Adults grew between 2 and 17 mm SVL/year. Rock iguanas were primarily herbivorous at all ages and fed arboreally and terres- trially. Five partial septa partition the proximal colon region; this modification presum- ably increases digestive efficiency. Huge oxyurid nematode populations inhabited the colon, and their relationship with the iguana may be mutualistic rather than parasitic. Abdominal fat deposits were negatively correlated with gonadal activity. Home range size was correlated with body size and habitat productivity, averaging 980 m: for females, 1260 mz for subdominant males, and 1590 m' for dominant males. Diurnal activity was bimodal during warmer months; high midday temperatures resulted in reduced activity. Winter activity was generally reduced and peaked at mid- day. Iguanas basked following emergence; most of the remainder of the day was spent feeding, interacting with other lizards, and shuttling in the sun-shade mosaic forther- moregulatory purposes. Basking preceded the termination of daily activity. Rock iguanas performed ritualized "signature" displays or headbobs. Postural ad- justments were among the modifiers producing variation in this display in different behavioral contexts. Displays were important to territory declaration, male challeng- ing, and sex recognition. Males were territorial year-round in the field, but developed dominance hierarchies in captivity. Dominant males displayed less than subordinates. Male territorial defense probably evolved as a mechanism guaranteeing access to food resources and females for breeding. The sex ratio was 1:1 in all age classes. Survivorship was positively correlated with body size. Juvenile densities reached 90.3/ha in optimum habitat, adults exceeded 31.1/ha. Biomass estimates were 5.15 kg/ha for juveniles and 17.01 kg/ha for adults. Life table data indicate replacement rate was near unity, and mean generation time was 14.0 years. In its life history strategy, C carinata is a predominately K-selected species. 'The author is an Assistant Professor of Biology, Earlham College, Richmond Indiana 47374, and an Adjunct Assistant Curator of Herpetology of the Florida State Museum, Gainesville, Florida 32611. IVERSON, JOHN B. 1979. Behavior and ecology of the rock iguana Cyclum carinata. Bull. Florida State Mus., Biol. Sci. Vol. 24(3):175-358. 176 BULLETIN FLORIDA STATE MUSEUM Vol. 24, No. 3 TABLE OF CONTENTS INTRODUCTION. 176 ACKNOWLEDGMENTS . 182 MATERIALS AND METHODS . .. 182 MORPHOLOGY · · 188 HABITAT · · 193 REPRODUCTION .. 204 GROWTH 247 FOOD AND FEEDING 265 ACTIVITY AND MOVEMENT . 285 SOCIALORGAN]ZAT1ON . 299 INTERSPECIFICCOACNONS 318 DENSITY AND DEMOGRAPHY 325 LITERATURE ~1TED . 344 INTRODUCTION PURPOSE The genus Cyclura is one of the most poorly known lizard genera in North America, despite being one of the most conspicuous members of the West Indian fauna. Although a sizable literature exists regarding the genus, most of the references are faunal lists or general works and contain only anetdotal information; no thorough autecological study of any of the species has been made. Few New World lizards have experienced as intimate a relationship with man, and suffered more from the interaction, than Cyclura. Maj or populations have been extirpated within historic times. Probably no presently existing population is entirely free from pressures induced by man and his animals. It is increasingly clear that a thorough knowledge of the habits and adaptations of our fauna is necessary if we are to be able to insure their survival in the face of continuing and in- creasing cohabitation with humans. It was for these reasons that study was begun on a still relatively common species: Cyclura carinata, the Turks Island iguana (Fig. 1). From September 1973 1979 IVERSON: ROCK IGUANA BEHAVIOR-ECOLOGY 177 through June 1976 C carinata was studied both in the field in the Turks and Caicos Islands and in the laboratory. The goals of the study were: (1) to obtain data on the behavior, adaptations, life history, and community role of this species; (2) to determine what factors limit population size; (3) to discover methods by which the species might survive cohabitation with man, without threat of extinction; and (4) to provide an indepth charter study for ex- trapolation to similar investigations of other less common and more endangered species of Cyclura in the West Indies. SYSTEMATIC RELATIONSHIPS AND DISTRIBUTION The genus Cyclura is most closely related to the three largest herbi- vorous iguanine lizard genera inhabiting continental North and Cen- tral America: Ctenosaurg Iguang and Sauromalus. On the basis of myology and osteology Cyclura is most similar to Ctenosaura and next most similar to Iguana (Avery and Tanner 1971). Endemic to the An- tilles and Bahamas, Cyclura apparently evolved from a pre-Ctenosaura stock isolated in the islands. The genera A mblyrhynchus, Brachylophus, Conolophus, Ctenosaura, Cyclura, Dipsosaurus, Enyaliosaurus, Iguana, and Sauromalus constitute the subfamily Iguaninae (Avery and Tanner 1971). Seven extant species constitute the genus Cyclura, distributed from the northern Bahamas through the Greater Antilles (Schwartz and Thomas 1975). Pleistocene remains are known from severalislands within the present range (review in Carey 1975). Cyclura carinata is closely allied to C rileyi (San Salvador, Bahamas). The two species share a number of characters (lack of enlarged, tubercular, median frontal shields; presence of dorsal crest, with elongate spines, interrupted on shoulders and rump; maximum size less than 1 m, etc.) and are both distributed in the southern half of the Bahaman archipelago. The relationship of Cyclura ricordi (Hispaniola) to C carinata deserves additional study despite the larger size (commonly exceeding 1 m total length) of the former. The two species have similar dorsal crests and pigmentation patterns and are the only two species of Cyclura without enlarged supracephalic scales. STUDY AREA The Turks and Caicos Islands lie to the southeast of the Bahama Islands between latitude 21° and 22° N and longitude 71° and 72°31' W (Fig. 2). Although politically distinct from the Bahama Islands, this 178 BULLETIN FLORIDA STATE MUSEUM Vol. 24, No. 3 British Crown Colony is geologically part of the Bahaman archipelago. The islands are situated approximately 150 km north of Hispaniola and 890 km southeast of Miami, Florida. They consist of two groups of islands separated by a 35.5 km wide, deep water ( > 2200 m) channel, the Turks Island Passage. The Turks Islands lie east of the passage, the Caicos to the west. The former consist of two inhabited islands (Grand Turk and Salt Cay), six uninhabited cays, and numerous emergent rocks. The Caicos Islands lie along the perimeter of the Caicos Bank, a northwest-to-southeast-lying triangular shoal with a base and altitude of approximately 125 and 75 km, respectively. Depths frequently ex- ceed 180 m within 2 km of the reefs surrounding the Turks and Caicos banks. Each of the banks is surrounded by depths of at least 1800 m. The highest elevation in the islands barely exceeds 85 m (on Providen- ciales). The present surface area of the islands, as calculated by the Turks and Caicos Survey Department, is approximately 500 km, with only 27 km2 in the Turks Islands group.