Introduction to Anolis Carolinensis
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A green anole. |
The green anole, Anolis carolinensis, is the only anole species of this large iguanid group native to southern Florida. They are small lizards, characterized by a brightly colored dewlap (more prominent in males). These can be seen being extended during displays of courtship or aggression. Green anoles also have the ability to change color to brown for camouflage purposes. Color is related to temperature, with brown coloration associated with lower temperatures. Green coloration also signifies dominance over competitors, while brownness is correlated with submissive behavior . With the exception of during egg-laying, green anoles spend little time on the ground. They prefer foliage, tree trunks, and basking surfaces such as walls and fences (Carmichael and Williams). They feed mainly on insects, especially larval forms and crickets (Stranger-Hall et al 2001). Most members of this species only live one or two years in the wild, due to heavy predation . They lay one egg every two weeks from early spring to early fall, with eggs hatching after five to seven weeks. This is a slower rate of reproduction then that of the Cuban brown anole (Anolis sagrei) which is now out competing the green anoles throughout southern Florida (Behler and King 1979). Both male and female green anoles are territorial lizards (although this quality is reduced in females because of few reproductive benefits)(Jenssen et al. 2000). Anoles are capable of recognizing newcomer to their area, which may result in aggression towards new males or courtship displays towards females (Orell et al. 2002). Aggression between strangers is maintains the territory of individuals (Stamps et al. 1979). In addition, anoles have many requirements (access to food, heat and shelter) that determine where they live. As a result, some degree of spacing between individuals could be expected. The main purpose of this study was to determine the factors influencing where green anoles were found.
Materials and Methods
Most sample specimens were caught between 9:00 and 11:30 am between the dates of May 4th and 14th (with four days without collecting). Weather conditions were clear and the temperature approximately eighty degrees Fahrenheit. Two samples were caught during the evening at approximately 7:30 pm. Other attempts at collecting in the evening were made, but they proved much less fruitful then morning collecting. Between one and five collectors were present at all times, with three being the most common number. All collecting was done at Buck Island Ranch in wooded thicket known as Owl Hammock. Owl Hammock is dominated by sable and saw palmetto, and is surrounded by enclosed cattle pastures. The ground is covered with dense underbrush. The study area is surrounded on two sides by a barb wire fence interspersed by wooden poles. There is another fence across the road from the main site that also provided specimens. The first fence is 320 meters long (where it contacts the study site). The second is 206.5 meters long at the site. The site itself is 105.6 meters east to west when measured at the midsection. Measured on a north-south diagonal, the site is 150 meters across. The Owl Hammock site has a latitude of 27"0911 North and a longitude of 81"1151 West. It is 11.8n meters above sea level. There is a residential house at the center of the Hammock, dividing it into north and south clusters. Most collecting was done by hand and using and nets. A Raytek Mini-temp instrument was used to measure body temperature on the animals' ventral surface. Anoles were weighed using a Pasola instrument and a weighing bag. The weight of the bag (1.3 grams) was subtracted to find the weight of the animal in grams. A Dialmax measuring instrument was used to determine snout/ventral length, head length, and head width in millimeters. The specimen was then marked with either a fine point black marker or a red or white enamel paint marker in the event of recapture. A red plastic ribbon was tied at the site of capture and marked with the number and gender of the animal. The anole was released at or near the site of its capture. In all, forty-six anolis carolinensis specimens were caught, measured, marked and released. The body temperature of recaptured animals was measured and their place of capture recorded.
Results
An analysis of the capture sites showed a bias towards the northern cluster of vegetation, or that located left of the house. Of the forty-six anoles captured, twenty-six were found within this section or on its perimeter, ten were found in the southern or "right" section, and ten were caught open areas not considered to be part of either section. Twenty-seven anoles were captured in shaded or partially shaded areas, while only seventeen were caught in open sunlight. (Two anoles are not included here because their capture sites were not described in sufficient detail). Forty individuals were caught in vegetation, on fence posts, or otherwise elevated off the ground. Only six were captured from the ground, and three of these were found in brush piles. Statistical analysis of the anoles' body measurements revealed an average weight of 3 grams, an average snout/ventral length of 48 millimeters, an average head length of 12.5 millimeters, and an average head width of 5.9 millimeters. The average body temperature taken from the ventral surface was 32.4 degrees Celsius. The average distance between individuals (found using a GPS map of the section with capture sites) was 45.4 meters.
Discussion
It should first be noted that the body temperature data should not be considered reliable. The readings were often taken after the animals had been hand-held or kept in snake bags to to await measuring. It is likely that this had the effect of raising the body temperature above that which is normal in the wild. The fact that the average body temperature was 32.4 degrees Celsius, while data collected on a separate anole species showed an average body temperature of 27.7 degrees Celsius supports the possibility that the body temperatures are artificially high (Vitt et al. 2001).
There are three likely contributors to the higher concentration of anoles on the northern side of the hammock. One is the fact that the southern section is larger and more thickly wooded, with more areas blocked from sunlight. Anoles living in this area would have to move a greater distance from the center of the the thicket to reach areas with partial or full sunlight. Another factor is that the northern section was searched more extensively. This is due to the fact that the northern section has more open areas, making to easier for collectors to find and capture anoles. In addition, the measuring equipment was kept in a clearing on the north side, so attempts to catch anoles were concentrated in that area. A third possible factor is heavier predation in the south section. During evenings, a barred owl was frequently seen or heard in the southern thicket. There is a red-shouldered hawk's nest near the center of the south hammock, and numerous scrub jay sightings suggest a possible nesting area for them as well. As discussed in the introduction, bird predation accounts for the high mortality of anoles, so it is possible that they reduce the numbers in this area.
The data collected regarding the specific places where green anoles were found corresponds with previous knowledge about their behavior. Relatively few anoles were found in open sunlight, while many were found in the shade or partial shade. This has the effect of allowing the animals access to warmth (the Hammock is filled with clearings) while giving them easy cover from predation or excessive sunlight. It is also a well-established fact that green anoles tend to avoid the ground except during egg-laying (Carmichael and Williams 1991). At the Owl Hammock site, only six of the forty-six captured anoles were found on the ground, and three of these were found in brush piles, which mimic a raised vegetation habitat.
