Species Succession

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Biologists calculate richness and rarity in amphibians and reptiles as they do for plants and other animal life. Finding these species to count them

 

 

presents a challenge, however, because they have evolved superb methods of going undetectable to predators: camouflage; ability to stay completely still; ability to hide underwater, in soils, and in mud; or the preference for staying under rocks and tree trunks or in trees. Ecology research uses two monitoring methods for amphibians and reptiles—visual counting and capture—but it also requires scientists to have a good sense of where to find these animals.

Two common visual methods for monitoring amphibians are migration counts and sit counts. Migration counts involve monitoring a location at night during migration season and recording the number of animals that pass through a counting area, for instance, animals
crossing a road. The second method—equally as tedious—involves sitting in a single location and recording each species seen in a set time period.

Some species have characteristics that make counting them, if not easier, more fun. One example is the frog call survey. In this method a biologist drives along a route in the evening and stops the engine every half mile to listen for five minutes to frog calls. Volunteers become fairly good at telling how many frogs or toads they hear calling in
the woods. Geckos provide a second specialized monitoring method. Some geckos fluoresce in ultraviolet light, so biologists take advantage of this feature when tramping through the woods with an ultraviolet lamp in hand.

Capturing amphibians and reptiles makes monitoring easier than stalking them in the night. Commonly used capture methods are the following: hand-capture, trapping, artificial refuges, and markingrecapture.

Hand-capture is useful in reptile surveys involving snakes, lizards, tortoises, and aquatic turtles and terrapins. Biologists may capture reptiles hiding under logs, rocks, scrap metals, and derelict cars, or they can use mirrors attached to long sticks for checking into cracks and holes. Reptile capture requires a modest amount of training to avoid bites and to handle properly species that exhibit tail autonomy, meaning they can drop their tail if caught. It helps also to remember a cautionary rhyme when catching snakes, “Red and yellow kill a fellow. Red and black, venom lack.”

 

Biologists capture crocodiles, alligators, and large lizards by noosing. Noosing involves a long, stout stick with a noose at one end. Once the animal is snared, the noose can be operated to create a tight hold on the animal, which can be counted on to put up a fight. Biologists use dip nets rather than nooses for capturing aquatic species such as terrapins and turtles.

Two types of traps can collect amphibians and reptiles without the biologist being present. The first, a pitfall trap, is simply a bucket dug into the ground so its mouth is even with the surface and covered with camouflage twigs, sticks, or leaves. Funnel traps are the second method in which an aboveground funnel-shaped container collects the animals. Short-drift fences aid both methods by providing a barrier that guides the animals toward the trap. Trapping does not harm the animal and scientists release the trapped individuals after the counting period ends.

Artificial refuges also collect animals, but they do not usually trap them. Any open-ended canopy made of a sheet of wood or metal provides a shady, dark habitat that attracts amphibians and reptiles. Well- constructed artificial habitats allow scientists to count and study the animals but not affect their behavior.

The marking-recapture method uses special, nonpainful techniques for marking individual animals so that they are recognized if recaptured. Common marking methods are  toe-clipping (for species that do not climb trees), scale removal, painting, or passive  integrated transponder (PIT) tags placed under the skin and monitored with a handheld scanner. Statistical calculations result in data containing the following two components: the number of animals in an area, based on the number of animals captured, and the number of times the same animal has been captured.