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A
survey of anuran breeding activity in Illinois, 1986-1989
Justin Florey and Stephen J. Mullin
Department of Biological Sciences, Eastern Illinois University.
Abstract
Amphibian populations have been declining worldwide, with several documented
species extinctions in the past two decades. Although monitoring population
health can present challenges, surveys of breeding choruses are relatively
effective methods for assessing populations and population trends of many frog
and toad species. We analyzed data from breeding chorus surveys conducted
throughout Illinois from 1986 to 1989. Of the twenty species native to Illinois,
nine
were stable or increasing during the survey period whereas the trends for other
species were either inconsistent or indicated a decline in population size. To
better assess population trends for Illinois frogs, we advocate re-establishment
and regular monitoring of choruses, and improved training for volunteers who
conduct the surveys.
Introduction
Amphibian populations have declined worldwide [1,3], even in natural areas
[2].
Long-term monitoring is crucial to the understanding of both pattern and process
in population decline [4].
We assessed population trends for Illinois frog species using historical data
from breeding chorus surveys conducted between 1986-1989 (Figure 1).
Methods
Surveyors completed three runs during early spring, late spring, and
summer. Sixty five routes were surveyed, each having twenty sampling points spaced 0.8 km apart.
We plotted population trends for each species for all years and calculated
coefficients of correlation.
Results
Of the toad species populations of
Bufo fowleri increased,
whereas no trends were apparent for either
B. americanus or
Gastrophryne carolinensis. (Figure 2).
Scaphiopus holbrooki was not reported.
Of the four smaller hylid species Pseudacris crucifer and
Acris crepitans
increased,
P. triseriata decreased, but no trend was apparent for P. streckeri
illinoiensis (Figure 3).
Of the four Hyla species, H. cinerea and H. chrysoscelis increased, whereas
H. versicolor and H. avivoca were not apparent. (Figure 4).
Populations of
Rana blairi,
R. areolata,
R. sphenocephala and
R. catsbeiana
increased during the study period. (Figure 5).
Population trends for
R. pipiens,
R. clamitans,
R. sylvatica, and
R. palustris
were not apparent. (Figure 6).
Definitive assessment of Illinois frog populations is lacking for several
species because of inconsistent route coverage.
Future survey efforts in Illinois could be improved with more intensive training
of volunteers to properly identify breeding sites and species.
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Figure 1. Map of Illinois counties,
with the number of survey routes identified. Values of 0.5 denote a
route that overlapped between counties. |
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Figure 2. Percent of routes
reporting breeding calls of three anuran species between 1986-1989. |
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Figure 3. Percent of routes
reporting breeding calls of four small hylid species between
1986-1989. |
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Figure 4. Percent of routes
reporting breeding calls of four treefrog species between 1986-1989. |
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Figure 5. Percent of routes reporting
breeding calls of leopard and crayfish species between 1986-1989. |
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Figure 6. Percent of routes reporting
breeding calls of four ranid species between 1986-1989. |
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Literature cited
[1]
Blaustein & Kiesecker, 2002. Ecol. Letters 5:597-608.
[2]
Collins & Storfer, 2003. Diversity & Distributions 9:89-98.
[3]
Guerry & Hunter, 2002. Conservat. Biol. 16:745-754.
[4]
Semlitsch et al., 1996. Pp. 217-248 in Long-Term Studies of Vertebrate
Communities (ed. Cody & Smallwood), Academic Press, San Diego, Calif.
Acknowledgements
We are grateful to Robert Szafoni and the Illinois Department of Natural Resources
for providing the opportunity to examine the data set generated during the study
period. Partial funding for this study was provided by the Undergraduate
Research Council of Eastern Illinois University and The Nature Conservancy,
Illinois Chapter.
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