Alligator: Alligator mississippiensis
Appearance:
Female alligators rarely exceed 9 feet in length, but males can
grow much larger. The Florida state record for length is a 14 foot
3-1/2 inch male from Lake Washington in Brevard County. The Florida
record for weight is a 1,043 pound (13 feet 10-1/2 inches long)
male from Orange Lake in Alachua County.
The tell-tale eye-shine of an alligator (and other nocturnal
vertebrates) is caused by a layer of cells called the tapetum
lucidum (a Latin phrase meaning "bright carpet"). This structure is
located beneath the photoreceptor cells (rods and cones) in the
retina and reflects light back into these cells to increase the
amount of light detected, which improves an alligator's vision in
low light conditions. In alligators this eye-shine is red, but it
can be different colors in other species. For more information, see
the documents at the links below.
While most reptiles have 3-chambered hearts, the heart of
alligators, and all crocodilians, has 4 chambers, a trait shared
with mammals and birds. The advantage of a 4-chambered heart is
that oxygenated blood and deoxygenated blood are separated, which
results in more efficient respiration needed for the high
metabolism of endothermic (warm-blooded) animals, and enables
different pulmonary (lung) and systemic blood pressures, but is
seemly over-complex for ectothermic (cold-blooded) crocodilians.
The single ventricle of the 3-chambered reptile heart allows some
mixing of oxygenated blood with deoxygenated blood, which may help
regulate their metabolic state. Crocodilians have evolved a shunt
between the left and right aorta (immediately above the ventricles)
to facilitate the mixing of oxygenated and deoxygenated blood.
Crocodilians also have a valve in the pulmonary artery that, when
closed, forces deoxygenated blood to recirculate through the left
aorta, which increases mixing. This increased mixing helps
crocodilians transition to a lower metabolic state, and enables
them to dive for extended periods.
Some scientists have hypothesized that the complex heart structure
of crocodilians might indicate that they evolved from endothermic
ancestors.
Habitat:
Alligators occur from southeast Oklahoma and east Texas on the
western side of their range to North Carolina and Florida in the
east. They prefer fresh water lakes and slow-moving rivers and
their associated wetlands, but they also can be found in brackish
water habitats.
Behavior:
Alligators are opportunistic feeders. Their diets include prey
species that are abundant and easily accessible. Juvenile
alligators eat primarily insects, amphibians, small fish, and other
invertebrates. Adult alligators eat rough fish, snakes, turtles,
small mammals, and birds.
Nearly all alligators become sexually mature by the time they
reach approximately 7 feet in length although females can reach
maturity at 6 feet. A female may require 10-15 years and a male
8-12 years to reach these lengths. Courtship begins in early April,
and mating occurs in May or June. Females build a mound nest of
soil, vegetation, or debris and deposit an average of 32 to 46 eggs
in late June or early July. Incubation requires approximately 60-65
days, and hatching occurs in late August or early September.
The average clutch size of an alligator nest is 35. From this,
an estimated 15 live hatchlings will emerge. Only 6 alligator
hatchlings will live to one year. Of these yearlings, 5 will become
subadults (reach 4 feet in length). The number of subadults that
reach maturity (6 feet in length) is approximately 4. These
estimates are for a growing alligator population. As an alligator
population matures (and has a higher percentage of large animals),
the survival rate would be expected to be lower, in part due to a
higher rate of cannibalism.
Eggs: Alligator eggs are susceptible to drowning, being crushed
by the female, predation, and other less common calamities.
Raccoons are the primary predator, although hogs, otters, and bears
have been reported to depredate nests.
Juveniles: Small alligators are eaten by a variety of predators
including raccoons, otters, wading birds, and fish; however, larger
alligators may be their most significant predator.
Adults: Cannibalism, intraspecific fighting, and hunting by humans
are probably the most significant mortality factors.
Diseases and Parasites: Very little information is available in the
scientific literature on wild alligator diseases and parasites.
They are not believed to be a significant problem for wild
alligators.
Alligators are ectothermic -- they rely on external sources of
heat to regulate their body temperature. Alligators control their
body temperature by basking in the sun, or moving to areas with
warmer or cooler air or water temperatures. Alligators are most
active when temperatures are between 82° to 92° F (28° to 33° C).
They stop feeding when the ambient temperature drops below
approximately 70° F (21° C) and they become dormant below 55° F
(13° C). Alligators are dormant throughout much of the winter
season. During this time, they can be found in burrows (or "dens")
that they construct adjacent to an alligator hole or open water,
but they occasionally emerge to bask in the sun during spells of
warm weather.
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