| 
  • If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!

View
 

Rana catesbeiana, Bullfrog

Page history last edited by PBworks 15 years, 6 months ago

Rana catesbeiana

 The American Bullfrog

 

Figure 1

 

 Image Provided by Wikipedia Commons.  Photographer: Carl D. Howe   http://en.wikipedia.org/wiki/Image:North-American-bullfrog1.jpg

 

Figure 1 depicts a typical male bullfrog.  Note the characteristic yellow throat patch and tympanum significantly larger than the eye.

 

 

Taxonomy

            Kingdom:  Animalia

            Phylum:  Chordata

            Superclass:  Tetrapoda

            Class:  Amphibia

            Subclass:  Lissamphibia

Order:  Anura

Suborder:  Neobatrachia

            Family:  Ranidae

            Genus:  Rana

Species:  catesbeiana

 

 

Taxonomic notes

Some information sources may recognize a new name, Lithobates catesbeianus, however, the name is not yet standard.[3]

 

 

 


Identification

 

The American bullfrog is the largest of the ranid species, or true frogs, native to North America.[6]  The species may appear in varying shades of green and brown with a transition to lighter green on the head.  Individuals may be relatively solid in color above or have dark spots and blotches.[3]  Their underside is mostly white but may also have blotches and a dark banding appearance may be present on the hindlegs.[4]  The absence of dorsolateral folds can be used to distinguish this species from a look-alike relative, the green frog (Rana clamitans).[3]  A fold of skin extending from the eye around the tympanum down toward the base of the forearm is a characteristic unique to this species (this can be seen in figure 1).[5]

 

 

Adults may range from 3.5 to eight inches in length when measured from snout to vent.  Young are also quite large (up to six inches long) when compared to tadpoles of other frog species.[4]  Females are typically slightly larger than males and can be distinguished from one another by the size of the tympanum (a round structure where the eardrum is found behind the eye).[5]  In females the tympanum is nearly the same size in diameter as the eye whereas in males the tympanum is considerably larger.[5]  Males may also have a yellow throat patch as shown in figure 1. 

 

 

 


Distribution

 

Nationwide Distribution

 

 Image provided by Wikimedia Commons  http://en.wikipedia.org/wiki/Image:Bullfrog_range.gif

 

 

The American bullfrog is widely distributed across the lower 48 states of the US and into southeastern Canada.[6]  Most bullfrog populations found in the western states are a result of introduced frogs.  Bullfrogs have also been introduced to regions of Asia, Europe, British Columbia, Mexico, Brazil, the Caribbean Islands, and Hawaii.[2]

 

Distribution within Idaho    

 

Image by Stephen Burton, ©1999.

 

 


Habitat

 

Bullfrogs are most commonly found near larger bodies of water such as rivers, lakes, ponds, and swamps where they can be found along the water’s edge.  Individuals may venture overland during periods of rain.  Although the species thrives in most wetland habitats, it is limited to lower to moderate elevations.[4]  Preference is also given to lentic, warmer water habitats but with a temperature no greater than 32ºC.[2]  Tadpoles select for habitat with thick vegetation which can offer adequate protection from predators.[2]

 

 


Behavior

 

This species is highly aquatic and active both day and night.  Often emits a chirp or squawk when startled and then quickly jumps into the water.[5]  Males call and defend territories which most commonly range from 2-5 meters in diameter.[2]  The primary call, intended to attract females, sounds reminiscent to the roar of a bull and may be written as jug-o-rum.[5]  Males also recognize the calls of local individuals and respond more strongly to the calls of strangers.[2]  If a male is unable to hold a territory or attract females it may resort to male parasitism or opportunism as mating strategies, essentially intercepting females heading toward higher quality males.[2]

 

Feeding Behavior

Adults are opportunistic predators and readily attack nearly any insect or animal they encounter which is smaller in size.[2]  Cannibalism is also well documented.  Studies have found in some instances conspecifics may comprise up to 80% of the diet for mature bullfrogs.[2]

 

 

 


Reproduction

 

Breeding typically begins in late spring and lasts through much of the summer.[4]  Fertilization is external as is the case in other ranid frogs.  During fertilization the male grasps the female by the back, an action sometimes referred to as amplexus, and then the eggs and sperm are emitted into the water in unison.  Females may produce up to 20,000 eggs in a single clutch.[2]  The eggs normally hatch within 3-5 days and the new young may take as little as only a few months in their southern range to up to 3 years in northern locations to metamorphose into an adult.[6] 

 

 

 


Scientific Study

Adams, M.J., Bury, R.B., McCreary, B., and Pearl, C.A.  2004.  Asymmetrical Effects of Introduced Bullfrogs (Rana catesbeiana) on Native Ranid Frogs in Oregon.  Copeia 1: 11-20.

 

 

The negative effects of introduced bullfrogs on native amphibian species have been well documented in recent years.  A study published in 2004 by Adams et al. provides one such testimony of support to the claim that some amphibian declines can be attributed to the introduction of bullfrogs.  The study investigated the effects of introduced bullfrogs on native Oregon spotted frogs (Rana pretiosa) and northern red-legged frogs (Rana aurora aurora).

 

Twelve livestock watering tanks were arranged linearly and tilted such that the water/land interface would divide each tank into approximately half water and half land.  Eggs were then collected for both R. pretiosa and R. a. aurora from locations where no bullfrogs existed. Adult bullfrogs were also collected from two distant wetlands near Corvallis, OR. 

 

Experiment 1—Rana catesbeiana Microhabitat Selection

 Six bullfrogs were selected and randomly placed in separate water tanks.  Each frog was monitored for 3.75 hours after being allowed to acclimate for 45 minutes.  Parallel lines were drawn at 10 cm intervals from the water/land interface so each frog’s location could be classified every 15 minutes.  A total of 10 locations were recorded for each of the six frogs.

 

            Results…

Of six bullfrogs that were monitored, 73 percent of their recorded locations were locations found on the aquatic side of the tank.  The mean distance was 15.1 centimeters from the water/land interface.

 

 

Experiment 2—Native Anuran Microhabitat Selection in the Nonlethal Presence of Rana catesbeiana

Seven juveniles of each R. a. aurora and R. pretiosa were added to six separate tanks, each of which contained a single caged R. catesbeiana.  The bullfrogs were each enclosed within a clear plastic container that allowed both visual and chemical predator cues to the juvenile frogs in the tanks.  The bullfrog containers were located 15.1 cm on the aquatic side of the land/water interface as determined by the mean of the results from experiment 1.  After adding the 14 juveniles to each tank, they were allowed a 45 minute acclimation period before their locations were recorded at 20 minute intervals. 

 

            Results…

A total of 194 observations were made for juvenile R. a. aurora and 185 for R. pretiosa.  Both species spent the majority of their time in terrestrial microhabitats (58.8% and 61.6% respectively) but a greater proportion of time was spent in fully aquatic microhabitats for R. pretiosa.  This is believed to result in R. pretiosa encountering R. catesbeiana more frequently than R. a. aurora. 

 

 

Experiment 3—Rana catesbeiana Predation on Native Anurans

Seven juveniles of each of the before mentioned native species were added to twelve different experimental tanks and allowed to acclimate for 50-70 minutes.  One R. catesbeiana was then introduced into the tanks and predation was measured by counting the remaining native juveniles at the end of approximately seven hours.  The experiment was performed twice and no juvenile survivors were used twice.

 

Results…

Rana pretiosa juveniles were consumed significantly more than R. a. aurora juveniles.  In 10 of the 24 observations more R. pretiosa juveniles were consumed, in 10 others equal amounts of juveniles of both species were consumed and in only four of the observations were more R. a. aurora juveniles predated.  Further analysis of the data revealed smaller R. catesbeiana consumed a greater amount per bodyweight than larger individuals and all sizes of bullfrogs consumed more Oregon spotted frogs than northern red-legged frogs.  This demonstrates the potential of introduced bullfrogs to have a detrimental effect on local amphibian populations where bullfrogs are not native.

 

 

 


References

 

[1]Adams, M.J., Bury, R.B., McCreary, B., and Pearl, C.A.  2004.  Asymmetrical Effects of Introduced Bullfrogs (Rana catesbeiana) on Native Ranid Frogs in Oregon.  Copeia 1: 11-20. 

http://www.bioone.org/archive/0045-8511/2004/1/pdf/i0045-8511-2004-1-11.pdf

 

[2]AmphibiaWeb: Information on amphibian biology and conservation. [web application]. 2008. Berkeley, California: AmphibiaWeb. Available: http://amphibiaweb.org/ (Accessed: 30 September 2008). 

 

[3]California Reptiles and Amphibians.  Rana catesbeiana-American Bullfrog.  http://www.californiaherps.com/frogs/pages/r.catesbeiana.html (Accessed: 30 September 2008)

 

[4]Digital Atlas of Idaho: Rana catesbeiana. Idaho State University. 1997.  Available: http://inmh.isu.edu/digitalatlas/bio/amph/main/amphmnfr.htm (Accessed: 30 September 2008)

 

[5]Stebbins, R.C.  2003.  A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company.

 

[6]Wikipedia, The Free Encyclopedia.  Bullfrog.  http://en.wikipedia.org/wiki/Bullfrog (Accessed: 30 September 2008)

 

 

 

             This page was created by Levi Horrell

 

 

Comments (0)

You don't have permission to comment on this page.