Alligators and Crocodiles in South Florida

Posted on by Andrew Furness

A google search for ‘difference between alligator and crocodile’ returns 30 million search results. Physical differences include alligators having round U-shaped snouts and crocodiles pointed V-shaped snouts, alligators being dark green or black and crocodiles generally lighter green or grey in coloration, and alligators having only the upper teeth visible when the mouth is closed but crocodiles having both upper and lower teeth visible. However, unless observed in captivity, geographic location is surely the easiest way to tell whether you are dealing with an alligator or crocodile. This is because there is only one small region on earth where alligators and crocodiles naturally co-occur together in the wild – South Florida. In this post I will give some background on the biology of this fascinating group of ancient predators (the Crocodilians) and then share some natural history information regarding American alligators and crocodiles in South Florida.

Comparison of American alligator (top) and American crocodile (bottom). Photo credits: alligator (The Nature Conservancy), crocodile (Audubon Florida).

The biology of Crocodilia

The Order Crocodilia contains crocodiles (family Crocodylidae), the gharial and false gharial (family Gavialidae), and the alligators and caimans (family Alligatoridae). This group, together referred to as crocodilians, is an ancient group of large, semiaquatic, predatory reptiles that (perhaps surprisingly given physical appearances) are the closest living relatives to birds.

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Phylogenetic tree showing the inferred evolutionary relationships among birds, reptiles, and mammals. Crocodilians are the closest living relatives to birds. Colors indicate the estimated rates of genome evolution; crocodilians exhibit exceptionally slow rates. Figure credit: Green et al. (2014).
Phylogenetic tree depicting the evolutionary relationships between Crocodilian species. Branch lengths are scaled to depict millions of years before present (Scale bar and Geologic Timescale are depicted at the bottom). Alligators and crocodiles diverged (last shared a common ancestor) approximately 80 million years ago, yet look remarkably similar to each other – indicative of morphological conservativism in this group. For reference, dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period). Figure credit: Timetree.org, images Wikimedia Commons.
Examples of some of the 24 species of living crocodilians. Credit: Roger Hall.

Although an ancient group that appears little changed since the age of dinosaurs, there are a limited number of living crocodilians – 24 species to be exact. These 24 species are grouped into three families. In the family Alligatoridae there are 8 species – 6 species of caiman, which are native to Central and South America, and two species of alligator, the American alligator and the smaller Chinese alligator. The family Gavialidae contains 2 species, the Gharial and False Gharial. Both species are found only in Asia, and both are threatened with extinction. They are noted for their long slender snout and specialize in eating fish. Finally, there are 14 species of crocodiles in the family Crocodylidae. Crocodile species are found throughout the tropics.

Geographic range of crocodilian species. In the family Alligatoridae (red on the map), caiman are found in the neotropics and the two alligator species are found in the Southeastern U.S.A. (American alligator) and China (Chinese alligator). The gharial and false gharial are found in Asia (yellow on map). Crocodiles are found throughout the tropics (blue on map) and some species inhabit brackish and salt water, in addition to fresh. Map credit: Lisa R. Ritter

American alligators and crocodiles in South Florida

In South Florida, the American crocodile is at the northernmost limit of its range, and the American alligator the southernmost. It is estimated over 2 million alligators are found in Florida, but only 1,500 crocodiles (ref). Crocodiles inhabit coastal regions, while alligators inhabit inland freshwaters of all types as well as coastal regions.

Range of the American alligator versus the American crocodile. The only place of range overlap is in South Florida. Map credit: Wikimedia commons.

In the Everglades I have observed hundreds of alligators, in all types of freshwater habitat, and about a half dozen crocodiles, in mangrove areas on Virginia Key and the Flamingo marina of the Everglades. Below, I have included some photos I took of American crocodiles and alligators, and give some natural history details about these species.

The teeth of this American crocodile are so long and sharp they have actually created two holes in the upper snout, through which they slot into when the mouth is closed. I photographed this individual swimming in Flamingo marina Everglades, adjacent to mangroves.
Despite seeing a limited number of crocodiles in South Florida, I have seen dozens in Costa Rica (the same species found in South Florida). The American crocodile, likely owing to its tolerance of saltwater and hence ability to disperse throughout the Caribbean Sea, has a wide distribution and is found in northern South America, Central America, parts of Mexico, many Caribbean islands, and South Florida. In Costa Rica, it is quite easy to see large numbers of crocodiles at the ‘Crocodile Bridge’ where the intercoastal highway crosses the River Tarcoles. Here crocodiles concegrate below the bridge because in the past people fed them from here. In this photo, which I took in 2013, a group of hungry crocodiles gathers below the bridge in anticipation of an easy meal.
American alligators provide parental care to their young (i.e. nest guarding, helping hatched young from the nest to the water, and guarding young from predators). While fishing in an Everglades canal I came upon a group of a few dozen baby alligators, each less than a foot in length. The young began ‘yelping’ and a few moments later the mother’s head suddenly emerged amongst her young, and one of them crawled onto her snout.
In the Everglades, alligators have become increasingly accustomed to people, especially in high trafficked areas. While shore fishing I have sometimes had alligators swim up to me and even emerge from the water (as this bold individual did). This undoubtedly stems from having been fed by humans (something which is illegal) or them recognizing that the presence of humans may be associated with an easy meal (for example a fish being reeled in).

Lately I have been thinking about habitat usage and potential interactions between American alligators and crocodiles in South Florida. These two species occupy somewhat differing habitats, with crocodiles primarily found near salt water and alligators fresh, which matches my own observations in the Everglades. Yet, alligators do enter and forage in brackish / estuary habitat (Nifong and Lowers 2017), and in multiple trips to Costa Rica to conduct fieldwork on poeciliid fishes, I have seen American crocodiles dozens of miles upstream in freshwater rivers. So, I was wondering if in South Florida there is a greater degree of habitat segregation (as evidence of competitive exclusion) than when either species occurs alone in all other parts of their geographic ranges (besides South Florida). Put simply, in South Florida are alligators limited primarily to freshwaters so as to avoid competitive / aggressive interactions with crocodiles? Conversely, could crocodiles be limited primarily to brackish and salt waters in South Florida, but elsewhere in their range they also utilize freshwaters to a greater extent? I think this question could be addressed quantitively using occurrence data of both species in South Florida, compared to other parts of their geographic range where they do not co-occur. It might be interesting to combine such a quantitative analysis with whatever anecdotal information is available on (rare) observed interactions between these two species in the wild.

2 thoughts on “Alligators and Crocodiles in South Florida”

  1. GREAT BLOG-POSTING; with GREAT RESEARCH is the REWARD; CONCERNING Alligators and Crocadiles…IN U.S.A. Sincerely Brian CANUCK-THE BREEZE Murza, Niagara Falls, Ontario, Canada. Note: I have had the GREAT CHANCES; of VIEWING ALLIGATORS…IN MANY PARTS OF THE SOUTHERN U.S.A.!!!

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  2. Pingback: Incredible wildlife amongst ruins of an abandoned zoo – Reason and Nature

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