Introduced Species Summary
Project
North American
Bullfrog (Rana castesbeiana)
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Common Name: (North American) Bullfrog
Scientific Name: Rana catesbeiana
Classification:
Kingdom: Animalia
Phylum or Division: Chordata
Class: Amphibia Linnaeus
Order: Anura
Family: Ranidae
Subfamily: Rafinesque
Identification: The North American bullfrog is the largest frog in
Figure 2: Green frog with dorsolateral folds
Original Distribution: The North American bullfrog is native to the central
and eastern
Current Distribution: North American bullfrogs are now found from
Figure 3:
Site and Date of Introduction: Several theories exist, but it is believed to be
introduced from its original habitat in
Mode(s) of Introduction: There seem to be several modes of introduction. Its original invasion appears to have been through accidental introduction to trout streams and lakes during the Colorado Divisions of Wildlife fish stocking operations in the early 1900s. Bullfrogs occasionally invade fish hatchery ponds and their larvae are caught along with fishes routinely stocked in ponds and reservoirs. Other modes of introduction include: (1) via the aquarium trade: as released pets no longer suitable for home aquariums; (2) landscape/fauna “improvement”: bullfrogs are deliberately introduced as a harvestable game animal (frogs legs) or aesthetically pleasing wildlife; (3) pest control: bullfrogs have been deliberately introduced to control agricultural pests; (4) self-propelled: bullfrogs are capable of considerable overland travel and are known to disperse throughout entire watersheds, provided they have interspersed patches of suitable habitat (similar to the corridor concept); and (5) aquaculture: bullfrogs are often imported into a country or area for commercial production as food (frog legs), and as noted above can inadvertently be introduced along with fishes raised in hatcheries where bullfrog larvae are abundant.
Reason(s) Why it has Become Established: Most fish appear to be averse to
eating bullfrog tadpoles because of their undesirable taste, so the bullfrog
has been able to thrive in freshwater lakes and rivers without these fish
predators. Bullfrogs are predators and
usually feed on snakes, worms, insects, crustaceans, frogs, and tadpoles,
so it has a varied menu and diet. They are also cannibalistic
and will not hesitate to eat their own kind. Bullfrogs
easily adapt to environments modified by human beings.
For example, increased water temperatures and
resulting aquatic vegetation, which are common factors in lakes polluted
by humans, favor bullfrogs by providing suitable habitats for growth, reproduction
and escape from predators. Bullfrogs also
have a longer breeding season and a higher rate of “pre-metamorphic survivorship”
(tadpoles), which also allows them to be more
successful than other frogs. One possible reason
the bullfrog has thrived in
Ecological Role: As it consumes a wide variety of animals and insects, its main ecological role is in controlling populations of insect pests and, where abundant, other animals such as snakes and mice to control their populations.
Benefit(s): North American bullfrogs help to control insect pests and are important for medical research because their skeletal, muscle, digestive, and nervous systems are similar to those of higher animals. They are often hunted or bred for meat (frog legs).
Threat(s): They
may be driving native frog populations and species to extinction in some
areas in the
Control Level Diagnosis: Medium Priority: although the population may
be increasing in some regions, it may actually be declining or sustainable
in others, particularly where it is regularly harvested as game (e.g.,
Control Method: In
References:
1. Global Invasive Species Database, Rana catesbeiana (amphibian), www.issg.org/database/species/ecology.
2. Invasivespecies.gov, Species Profile, Bullfrog, www.invasivespecies.gov/profiles.
3. Integrated Taxonomic Information System (ITIS) Report, Rana catesbeiana, www.itis.usda.gov.
4. United States Department of Agriculture (USDA), Forest Service, www.fs.fed.us/r4/amphibians/bullfrog/htm.
5.
United States Department of Agriculture
(USDA) Southern
6.
United States Geological Survey,
7.
8.
Photos and Map: From
U.S. Geological Survey,
Author: Martin Murphy
Last Edited:
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