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Remarkable Amphibian Biomass and Abundance in an Isolated Wetland: Implications for Wetland Conservation


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Despite the continuing loss of wetland habitats and associated declines in amphibian populations, attempts to translate wetland losses into measurable losses to ecosystems have been lacking. We estimated the potential productivity from the amphibian community that would be compromised by the loss of a single isolated wetland that has been protected from most industrial, agricultural, and urban impacts for the past 54 years. We used a continuous drift fence at Ellenton Bay, a 10-ha freshwater wetland on the Savannah River Site, near Aiken, South Carolina (U.S.A.), to sample all amphibians for 1 year following a prolonged drought. Despite intensive agricultural use of the land surrounding Ellenton Bay prior to 1951, we documented 24 species and remarkably high numbers and biomass of juvenile amphibians (>360,000 individuals; >1,400 kg) produced during one breeding season. Anurans (17 species) were more abundant than salamanders (7 species), comprising 96.4% of individual captures. Most (95.9%) of the amphibian biomass came from 232095 individuals of a single species of anuran (southern leopard frog[Rana sphenocephala]). Our results revealed the resilience of an amphibian community to natural stressors and historical habitat alteration and the potential magnitude of biomass and energy transfer from isolated wetlands to surrounding terrestrial habitat. We attributed the postdrought success of amphibians to a combination of adult longevity (often >5 years), a reduction in predator abundance, and an abundance of larval food resources. Likewise, the increase of forest cover around Ellenton Bay from <20% in 1951 to >60% in 2001 probably contributed to the long-term persistence of amphibians at this site. Our findings provide an optimistic counterpoint to the issue of the global decline of biological diversity by demonstrating that conservation efforts can mitigate historical habitat degradation.
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Remarkable Amphibian Biomass and Abundance in an
Isolated Wetland: Implications for Wetland
Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, U.S.A.
†Institute of Ecology, University of Georgia, Athens, GA 30608, U.S.A.
‡University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154–4004, U.S.A.
§Partners in Amphibian and Reptile Conservation, 2221 West Greenway Road, Phoenix, AZ 85023, U.S.A.
∗∗Wayland Baptist University, 5530 E. Northern Lights Boulevard, Suite 24, Anchorage, AK 99504, U.S.A.
††Department of Biology, Davidson College, Davidson, NC 28035–7118, U.S.A.
‡‡Department of Biology, Southern Utah University, Cedar City, UT 84720, U.S.A.
§§Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148–0001, U.S.A.
Abstract: Despite the continuing loss of wetland habitats and associated declines in amphibian populations,
attempts to translate wetland losses into measurable losses to ecosystems have been lacking. We estimated
the potential productivity from the amphibian community that would be compromised by the loss of a single
isolated wetland that has been protected from most industrial, agricultural, and urban impacts for the past
54 years. We used a continuous drift fence at Ellenton Bay, a 10-ha freshwater wetland on the Savannah River
Site, near Aiken, South Carolina (U.S.A.), to sample all amphibians for 1 year following a prolonged drought.
Despite intensive agricultural use of the land surrounding Ellenton Bay prior to 1951, we documented 24
species and remarkably high numbers and biomass of juvenile amphibians (>360,000 individuals; >1,400
kg) produced during one breeding season. Anurans (17 species) were more abundant than salamanders
(7 species), comprising 96.4% of individual captures. Most (95.9%) of the amphibian biomass came from
232095 individuals of a single species of anuran (southern leopard frog [Rana sphenocephala]). Our results
revealed the resilience of an amphibian community to natural stressors and historical habitat alteration and
the potential magnitude of biomass and energy transfer from isolated wetlands to surrounding terrestrial
habitat. We attributed the postdrought success of amphibians to a combination of adult longevity (often >5
years), a reduction in predator abundance, and an abundance of larval food resources. Likewise, the increase
of forest cover around Ellenton Bay from <20% in 1951 to >60% in 2001 probably contributed to the long-
term persistence of amphibians at this site. Our findings provide an optimistic counterpoint to the issue of the
global decline of biological diversity by demonstrating that conservation efforts can mitigate historical habitat
Keywords: amphibian decline, biodiversity, drought, land use, wetland recovery
Paper submitted June 7, 2005; revised manuscript accepted November 7, 2005.
Conservation Biology Volume 20, No. 5, 1457–1465
2006 Society for Conservation Biology
DOI: 10.1111/j.1523-1739.2006.00443.x
1458 Amphibian Biomass and Abundance Gibbons et al.
Biomasa y Abundancia de Anfibios Extraordinaria en un Humedal Aislado: Implicaciones para la Conservaci´on de
Resumen: A pesar de la p´
erdida de h´
abitats de humedales y las declinaciones asociadas de poblaciones de
anfibios, se han realizado pocos intentos para traducir las p´
erdidas de humedales en p´
erdidas mensurables
en los ecosistemas. Estimamos la productividad potencial de la comunidad de anfibios que se afectar´
ıa por
la p´
erdida de un humedal aislado que ha estado protegido de los impactos industriales, agr´
ıcolas y urbanos
durante los ´
ultimos 54 a˜
nos. Utilizamos un cerco de desv´
ıo en la Bah´
ıa Ellentonn, un humedal dulceacu´
ıcola de
10 ha en el R´
ıo Savannah, cerca de Aiken, Carolina del Sur (E.U.A.), para muestrear todos los anfibios durante
no despu´
es de una sequ´
ıa prolongada. A pesar del intensivo uso agr´
ıcola del suelo alrededor de la Bah´
Ellenton antes de 1951, documentamos 24 especies y n´
umeros y biomasa de anfibios juveniles notablemente
altos (>360,000 individuos; >1,400 kg) en una temporada reproductiva. Los anuros (17 especies) fueron m´
abundantes que las salamandras (7 especies), y comprendieron 96.4% de las capturas individuales. La mayor
parte (95.9%) de la biomasa provino de 232095 individuos de una sola especie de anuro (Rana sphenocephala).
Nuestros resultados revelaron que la resiliencia de la comunidad de anfibios a los estresantes naturales y a
la alteraci´
on hist´
orica del h´
abitat y la magnitud potencial de la transferencia de biomasa y energ´
ıa desde los
humedales aislados hacia el h´
abitat terrestre circundante. Atribuimos el ´
exito post-sequ´
ıa de los anfibios a una
on de longevidad de adultos (a menudo >5a
nos), la reducci´
on de la abundancia de depredadores
y la abundancia de recursos alimenticios para las larvas. Asimismo, el incremento de la cobertura forestal
alrededor de la Bah´
ıa Ellerton de <20% en 1951 a >60% en 2001 probablemente contribuy´
o a la persistencia
de los anfibios a largo plazo en este sitio. Nuestros hallazgos proporcionan un contrapunto optimista al tema
de la declinaci´
on global de la diversidad biol´
ogica al demostrar que los esfuerzos de conservaci´
on pueden
mitigar a la degradaci´
on hist´
orica del h´
Palabras Clave: biodiversidad,declinaci´on de anfibios, recuperaci´on de humedales sequ´ıa, uso de suelo
Isolated wetlands, which support high species diversities
and serve as essential habitat for many groups of organ-
isms, are under increased threat of destruction. In the
United States, the ongoing decline in numbers of iso-
lated and other palustrine wetlands due to agricultural
and commercial development since European settlement
is well documented (Dahl 1990, 2000). At least 87% of
the original 1.2 million ha of shrub bog pocosins (see de-
scription in Sharitz & Gibbons 1982) in the southeastern
United States have been destroyed or altered (Richardson
1983). Similarly, 69% of playas >4 ha in the Southern Great
Plains have been modified by cultivation, grazing, and
other activities (Guthery & Bryant 1982). The Solid Waste
Agency of Northern Cook County v. U.S. Army Corps of
Engineers (2000) decision by the U.S. Supreme Court has
weakened federal jurisdiction over isolated wetlands, ef-
fectively leaving freshwater wetlands unprotected when
they lack a permanent surface-water connection to navi-
gable waterways and have no link to interstate commerce
(Zedler et al. 2001; Downing et al. 2003). The loss and
degradation of numerous wetlands have presumably re-
sulted in a concomitant loss of species abundance and
diversity, with ramifications for ecosystem functioning.
Despite the ecological value of isolated wetlands to re-
gional biodiversity (Whigham 1999) and their importance
for maintaining metapopulation connectivity for semi-
aquatic species (Gibbs 1993; Semlitsch & Bodie 1998),
few researchers have quantified the productivity achiev-
able within a taxonomic group from a single isolated
wetland over a well-defined time frame. Moreover, al-
though surrounding terrestrial habitats are critical for
the integrity of wetland ecosystems (Gibbons 2003), few
researchers have enumerated the potential transfer of
biomass and energy from wetlands to surrounding ter-
restrial ecosystems.
Our study was undertaken to document the potential
contribution of amphibians to secondary production and
to the transfer of matter and energy between aquatic and
terrestrial habitats. Although the global decline of am-
phibians has been confirmed repeatedly (Stokstad 2004;
Stuart et al. 2004), attempts to translate wetland losses
into tangible effects on ecosystems due to the loss of
amphibian productivity have been lacking. Our results
demonstrate the levels of amphibian abundance and di-
versity that contribute to habitat interconnectivity and
that could potentially be lost by the elimination of a single
isolated wetland. We also addressed the critical question
of how rapidly and successfully amphibian populations
inhabiting ephemeral wetlands in a historically agricul-
tural landscape can recover from multiyear droughts.
Study Site
Ellenton Bay (Gibbons 1990) is an isolated freshwater wet-
land, typical of Carolina bays (see descriptions in Sharitz
& Gibbons 1982; Sharitz 2003), and within a 202-ha
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Volume 20, No. 5, October 2006
Gibbons et al. Amphibian Biomass and Abundance 1459
Figure1. Aerial photos from (a) 1951 and (b) 2001 of land cover surrounding Ellenton Bay (arrows) and (c)
relationship between distance from Ellenton Bay and the proportion of the landscape within 2 km of the periphery
of Ellenton Bay classified as upland forest in 1951 and in 2001. In 1951 Ellenton Bay was within a 202-ha
agricultural field planted in cotton and corn. By 2001 natural succession had restored the landscape to primarily
pine and mixed pine–hardwood forest.
formerly agricultural field that was planted in cotton,
peanuts, and corn from the 1870s through 1951 (Fig. 1;
Davis & Janecek 1997). The fish-free wetland is in South
Carolina on the U.S. Department of Energy’s (DOE) Savan-
nah River Site (SRS), a national environmental research
park (Shearer & Frazer 1997). Wetlands on the SRS have
been protected since 1951 from most of the environmen-
tal perturbations typically resulting from agricultural, ur-
ban, and industrial alterations in the region. Ellenton Bay
and surrounding uplands have received special protec-
tion as part of the DOE Set-Aside Program, which was
established to protect habitats and facilitate long-term re-
search. No herpetofaunal diversity or population data are
available for Ellenton Bay and surrounding areas before
establishment of the SRS. Because of the historical empha-
sis on clearing and preparing lands for agricultural pur-
poses, we presume that species diversity and abundance
at the wetland in the first half of the twentieth century
were reduced from historical levels. Nonetheless, long-
term (since 1968) herpetological studies conducted at
Ellenton Bay suggest that the amphibian species richness
characteristic of the region (Gibbons & Semlitsch 1991)
had recovered within 25 years. After 1951, Ellenton Bay
and other wetlands on the SRS returned to more natu-
ral conditions as a consequence of secondary succession
coupled with limited forest management activities.
The closest isolated wetland to Ellenton Bay is 200
m away, and Ellenton Bay has the longest hydroperiod
of the nonpermanent wetlands in the region. The only
wetland within 1.4 km of Ellenton Bay that holds water
during multiyear droughts is a small, human-made pond
0.5 km from the bay. The areal extent of the Ellenton Bay
basin when full is approximately 10 ha. A dike 5 to 6 m
wide divides the bay completely and creates two distinct
aquatic areas when water depth is <1.5 m. Water surface
area and depth are extremely variable, with a maximum
depth of approximately 2 m. During periods of drought,
subsurface moisture normally remains beneath the thick
organic crust that covers the entire basin up to 0.5 m
deep (Gibbons 1990). Parts of the basin remain mucky
during some dry periods, with up to 1 ha of viscous mud
surrounding small areas of open water, but no standing
water remained during the 2000–2003 drought. Two ma-
jor multiyear droughts have occurred at Ellenton Bay dur-
ing the last 29 years (Willson et al., 2006), the first from
October 1987 through August 1990, and the second from
August 2000 to February 2003. We initiated the current
study in February 2003 at the end of the second drought.
Historical Changes in Land Use
We used object-based classification of aerial photographs
to quantify the change in land cover between 1951 and
2001. We classified groups of pixels, rather than individ-
ual pixels, which allowed us to incorporate both spec-
tral (i.e., red–green–blue [RGB] values) and contextual
information (i.e., spatial configuration) of objects (Walter
2004). To define our area of interest, we used a bounding
rectangle that fully encompassed the 2-km radius from the
edge of Ellenton Bay. Panchromatic aerial photographs,
with an on-ground resolution of 2 m, were taken in 1951
in conjunction with the establishment of the DOE facil-
ity. False-color, infrared, aerial photographs were taken in
2001. We resampled from 0.3 to2mtoprovide a consis-
tent on-ground resolution between time periods. We used
filters and advanced learning algorithms incorporated in
Feature Analyst (version 3.4, Visual Learning Systems, Mis-
soula, Montana), an extension of ArcGIS (version 8.3,
Conservation Biology
Volume 20, No. 5, October 2006
1460 Amphibian Biomass and Abundance Gibbons et al.
Environmental Systems Research Institute [ESRI], Red-
lands, California), to conduct supervised classifications.
We segmented images and extracted general types of land
cover that were easily recognized (i.e., Anderson level 1
classes of urban, agricultural, forest, water, wetland, and
barren) for both time periods. We generated summary
statistics of classified maps for discrete 200-m-wide buffer
intervals radiating out from the perimeter of Ellenton Bay.
Collection Techniques
In February 2003, we re-erected a terrestrial drift fence
(Gibbons & Semlitsch 1981; Semlitsch et al. 1996) that
had been used in studies at Ellenton Bay for all or part
of 19 of the 28 years from 1968 to 1994 (Gibbons 1990;
Seigel et al. 1995). The continuous drift fence completely
encircled the wetland and was equipped with pitfall and
funnel traps, which allowed us to capture most of the
amphibians entering and exiting the wetland. Serendipi-
tously, we began monitoring the fence and traps 3 days
before the start of a long period of rain that began to
refill the wetland, after 2.5 years of drought. We moni-
tored the fence from 1 February 2003 to 31 January 2004
and therefore were able to document the abundance and
productivity of amphibians throughout the first wet year
following the drought.
The drift fence was constructed of aluminum flashing
(1230 m long, 40 cm high) and buried several cm into
the soil (Gibbons & Semlitsch 1981). The distance of the
fence from the margin of the water varied with water level
but was <10 m in many places when the bay reached its
maximum water level in August 2003. We placed 164
traps in pairs on opposite sides of the fence, with half of
the traps on each side of the fence, allowing individual
amphibians to be categorized as entering or leaving the
bay (Gibbons & Semlitsch 1981). Of these, 41 pairs of
19-L pitfall traps (plastic buckets), spaced approximately
every 30 m along the fence, were in place on 1 February
2003. On 24 February 2003, we installed 21 pairs of 2.3-L
pitfall traps (metal coffee cans) between every other pair
of buckets along the fence (60 m apart). On 27 February
2003, we installed 20 pairs of wooden box funnel traps
(Himes 2000; Zappalorti & Torocco 2002) along the fence
(60 m apart) between bucket pairs where cans had not
been placed. Thus, bucket pairs were followed alternately
by cans and funnel traps.
Pitfall and funnel traps were checked a minimum of
once daily (0700–0900 hours). During warm months,
traps were checked again in the late afternoon (1700–
2000 hours). Sponges were placed in the bottom of buck-
ets and cans, providing moisture during dry conditions
or a “raft” if water collected in buckets between checks;
however, standing water was bailed from buckets and
cans daily as needed. We classified captured amphib-
ians as recently metamorphosed individuals or adults (see
“Productivity and Biomass”) and released them approxi-
mately 10 m away on the opposite side of the fence.
During peak emigrations of recently metamorphosed
amphibians (e.g., 7,000 to 41,000 individuals per
night), special procedures were needed to reduce mortal-
ity associated with predation and overcrowding in traps.
Box traps were not deployed at night, and in addition
to morning and afternoon checks, all other traps were
checked multiple times during the night to aid emigra-
tion of recently metamorphosed individuals. On a few
occasions, we did not use box traps during the day to re-
duce the possibility of heat-related mortality of amphib-
ians. During peak emigrations involving thousands of ani-
mals, counting all individuals of some species would have
resulted in unnecessary mortality due to prolonged reten-
tion of animals in traps. Consequently, we estimated the
number of captured animals by counting the number of
animals contained in a handful or one sweep of a dipnet
and the number necessary to empty the trap. During mass
emigrations, animals were released approximately 30 m
on the outside of the fence to discourage immediate re-
capture. Recently metamorphosed amphibians captured
entering the wetland during peak emigrations were as-
sumed to have been emigrants that had been captured
and released earlier, rather than being immigrants from
other wetlands; therefore, they were re-released on the
outside of the fence and not included in capture totals.
Productivity and Biomass
To determine amphibian productivity at Ellenton Bay, we
estimated the number of emigrating young of year of all
species. Because the wetland was dry during the previous
2.5 years, recently metamorphosed amphibians captured
leaving Ellenton Bay during this study could be catego-
rized unambiguously as having been produced during the
2003 breeding season. One or more of three criteria were
used to classify amphibians emigrating from the wetland
as recently metamorphosed: (1) similar in size to pub-
lished data on size at metamorphosis for the particular
species from this region, (2) incomplete resorption of the
tail in anurans or of the gills in salamanders, (3) species-
specific attributes indicating recent metamorphosis (e.g.,
a distinct ventral stripe in A. talpoideum; scars at base of
forearms in anurans).
To estimate body size at metamorphosis, we haphaz-
ardly collected subsamples of newly metamorphosed
individuals (n=1–148) for focal species and measured
snout-vent length (SVL; ±0.5 mm) and wet body mass
(±0.01 g). We used the mean wet mass to estimate the
total biomass for each species produced at Ellenton Bay
during 2003. Individuals that were part of the 2003 juve-
nile cohort but were older juveniles at the time of capture
(i.e., likely had experienced significant postmetamorphic
growth while still inside the fence) were not used for
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Volume 20, No. 5, October 2006
Gibbons et al. Amphibian Biomass and Abundance 1461
estimates of body size at metamorphosis, but their counts
were used in estimating total biomass.
At Ellenton Bay, the mole salamander (A. talpoideum)
is the only species that undergoes facultative paedomor-
phosis (Patterson 1978; Semlitsch et al. 1990). Thus, we
subsampled metamorphosed individuals of this species in
two different seasons (spring and fall) to generate sepa-
rate estimates of body size at metamorphosis and biomass.
By January 2004 it became difficult to distinguish whether
emigrating animals were large, newly metamorphosed in-
dividuals from breeding that occurred in 2003 (and there-
fore should have been tallied for the biomass estimate) or
were postbreeding adults from the 2003–2004 season. Al-
though some of these salamanders were no doubt part of
the 2003 cohort, we did not count them as such. Conse-
quently, our total biomass estimate for A. talpoideum is
a highly conservative one.
To convert amphibian abundance to density estimates,
we first had to calculate the maximum area of the wetland.
We used global positioning system technology (Trimble
Pro-XR, Sunnyvale, California, with submeter accuracy) to
map the perimeter of the Ellenton Bay basin. We defined
the perimeter of the maximum waterline as the bound-
ary between emergent grasses (predominantly Panicum
spp.) in the bay’s basin and the surrounding pine (Pinus
spp.) forest. We used ArcView (version 3.3, ESRI) to cal-
culate the area of the resulting polygon.
Table 1. Total number of young-of-year amphibian emigrants at a single isolated wetland, Ellenton Bay, in South Carolina (U.S.A.).a
Total Aquatic
biomass Number of Mean density Production
Scientific name Common name (kg) individuals mass (g) (animals/ha) (kg/ha/year)
Ambystoma opacum marbled salamander 0.35 104 3.33 11 0.04
Ambystoma tigrinum tiger salamander 25 1,171 21.21 125 3
Ambystoma talpoideum mole salamander—late 14 2,412 5.91 257 2
summer metamorphosis
Ambystoma talpoideum mole salamander—spring 29 6,046 4.87 643 3
total 68.35 9,733 — 1036 8.04
Hyla chrysoscelisbgray treefrog 1 0.1—
Hyla squirellabsquirrel treefrog 10 1
Hyla cinereabgreen treefrog 15 2
Acris gryllus southern cricket frog 56 6
Scaphiopus holbrookii eastern spadefoot toad 0.17 316 0.55 34 —
Pseudacris crucifer spring peeper 0.89 1,970 0.45 210 0.09
Rana clamitans green frog (bronze frog) 1 216 5.63 23 0.13
Hyla gratiosabbarking treefrog 1 362 3.88 39 0.15
Pseudacris ornata ornate chorus frog 4 3,126 1.20 333 0.40
Bufo terrestris southern toad 48 115,056 0.42 12,240 5
Rana sphenocephalabsouthern leopard frog 1307 232,095 5.63 24,691 139
total 1421 353,223 — 37,577 151
Amphibian total 1490 362,956 — 38,612 159
aSecondary production during the 1-year study period was estimated as the number of young of year captured leaving the wetland, minus the
number of young of year captured entering the wetland.
bTotal captures were likely significantly underestimated due to the species’ ability to climb or jump over the drift fence. Estimates of biomass
are the number of young-of-year emigrants multiplied by the mean individual mass of 1–135 haphazardly selected individuals. The individual
mass used for R. clamitans was estimated from the mass of similarly sized R. sphenocephala.
Historical Changes in Land Use
Historical accounts from inhabitants of the area suggest
that intensive agriculture began in the 1800s, and agri-
cultural alteration of the landscape was conspicuous in
1951, at which time forested habitat comprised <20% of
the area within 1 km of Ellenton Bay (Fig. 1). The last row
of crops—primarily corn, cotton, and peanuts—were har-
vested from fields adjacent to Ellenton Bay in 1951 (Davis
& Janecek 1997). In 1957 pine trees were planted within
80 m of the south end of the wetland, and natural estab-
lishment of pines adjacent to the bay began to occur by
the mid-1960s. Since that time, Ellenton Bay and most of
the surrounding fields have undergone natural vegetation
succession, with forest coverage within 1 km of the bay
increasing to 60–75% by 2001 (Fig. 1).
Productivity and Biomass
During the single year of drift-fence sampling at Ellen-
ton Bay, we captured 408,220 amphibians representing
24 species. Of the individual captures, 96.4% were anu-
rans (17 species) and the remainder were salamanders (7
species). Most (n=21) of the amphibian species at El-
lenton Bay were captured by April 2003, and all had been
captured by 19 August 2003. At least 362,956 recently
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Volume 20, No. 5, October 2006
1462 Amphibian Biomass and Abundance Gibbons et al.
metamorphosed amphibians produced at Ellenton Bay
emigrated to the surrounding terrestrial habitat (Table
1). Most (95.9%) of the amphibian biomass came from
232095 individuals (1307 kg) of a single species of anuran
(southern leopard frog [R. sphenocephala]; Table 1). Two
species of salamanders (mole salamander [Ambystoma
talpoideum] and tiger salamander [A. tigrinum]) and one
species of anuran (southern toad [Bufo terrestris]) each
produced more than 24 kg of biomass during the year and
collectively produced more than 115 kg (Table 1). Mini-
mum estimates of larval amphibian density and biomass
for the aquatic portion of Ellenton Bay were 38612 indi-
viduals/ha and 159 kg/ha/year, based on the maximum
area inundated and numbers of emigrating young of year
(Table 1). Productivity of R. sphenocephala alone was at
least 139 kg/ha/year (Table 1). Young-of-year densities (in-
dividuals per ha) for the two most abundant species were
24,691 (R. sphenocephala) and 12240 (B. terrestris;Table
1). The productivity levels we observed for most amphib-
ian species are likely substantial underestimates, because
individuals were recorded only terrestrially when they
departed from the aquatic area of the wetland.
Our findings on biomass and density demonstrate that
amphibians are key components of wetland ecosystems
and can potentially supply an appreciable portion of the
energy transferred between aquatic and terrestrial habi-
tats. Although high, our estimates of individual numbers
and biomass of amphibians from a single natural wetland
are conservative because of sampling protocols. For ex-
ample, many individuals of some amphibian species did
not leave the aquatic habitat during the study owing to de-
layed metamorphosis. Some species also tend to remain
within or near aquatic areas following metamorphosis,
making them less likely to emigrate as far as the drift
fence. In addition, some climbing species of anurans (e.g.,
hylid treefrogs [Dodd 1991]; Table 1) are capable of sur-
mounting drift fences, leading to an underestimation of
abundance and young-of-year biomass for these species.
Thus, the actual contribution of the amphibian commu-
nity to secondary productivity at Ellenton Bay during a
single year was appreciably higher than observed.
Previous estimates of wetland productivity have typi-
cally focused on primary production. Estimates of wet-
land primary productivity for vascular plants and algae
(e.g., Barker & Fulton 1979; Neckles 1984; Hooper &
Robinson 1976; Brinson et al. 1981) vary by an order
of magnitude, depending on factors such as hydrology,
timing and duration of inundation, latitude, and domi-
nant plant species (Brinson et al. 1981). Net primary pro-
duction of three depressional wetlands in South Carolina
ranged from 564 to 774 g/m2/year as measured by stem
production and litterfall (Busbee et al. 2003).
Secondary production in freshwater wetlands has been
measured less often than primary production and most es-
timates are of invertebrate production (e.g., White 1985;
Plante & Downing 1989; Leeper & Taylor 1998; Taylor
et al. 1989). Information on productivity or biomass of
vertebrates in aquatic systems, other than amphibians, is
limited and includes studies on fish (e.g., Lawler et al.
1974), turtles (e.g., Iverson 1982; Congdon et al. 1986),
and snakes (e.g., Godley 1980; Shine 1986). We did not
determine terrestrial densities of the Ellenton Bay amphib-
ian species. However, our density estimate of 38612 indi-
viduals/ha in the aquatic habitat is consistent with results
of previous studies indicating that amphibians are among
the most abundant vertebrates in aquatic and terrestrial
systems. For example, terrestrial plethodontid salaman-
ders reached densities of 2000–2500 individuals/ha in a
New Hampshire forest (Burton & Likens 1975) and at
least 18486 individuals/ha in a streamside habitat in the
Southern Appalachians (Petranka & Murray 2001). Maxi-
mum biomass and numbers of larval tiger salamanders (A.
tigrinum) were estimated to be 180 kg/ha and 5000 indi-
viduals/ha in prairie ponds of the western United States
(Deutschman & Peterka 1988). Our productivity estimate
(159 kg/ha/year) of amphibians that successfully emi-
grated from the aquatic habitat demonstrates that isolated
wetlands contributed substantially to the overall produc-
tivity of the surrounding landscape.
The numbers of individuals and species of amphibians
we observed, considering both the immediate drought
and history of intensive agricultural use of the Ellenton
Bay study site, demonstrate that wetland functions can re-
cover from both natural and anthropogenic disturbances
under some circumstances. During drought years in the
Coastal Plain of the southeastern United States, when
isolated wetlands either do not fill or have extremely
short hydroperiods, amphibian populations can expe-
rience complete reproductive failure (i.e., zero recruit-
ment). Ellenton Bay presumably had minimal amphibian
productivity during the 3 years preceding the 2003 study,
based on known responses of amphibians to drought and
extrapolation from observations at Rainbow Bay, a Car-
olina bay wetland located 11.5 km from Ellenton Bay
(Semlitsch et al. 1996). Continuous long-term data (1978–
2004) for 13 amphibian species at Rainbow Bay indicate
that all species suffered virtually complete reproductive
failures for 4 of the first 16 years of study owing to short-
ened hydroperiods (Semlitsch et al. 1996). From 2000
to 2003, when both the Rainbow Bay and Ellenton Bay
breeding sites remained dry for all or most of each year,
limited or no juvenile recruitment occurred at Rainbow
Bay (D.E.S., J.L.G. & B.S.M., unpublished data).
The continued presence and productivity of amphib-
ians at Ellenton Bay in 2003–2004, despite prolonged
drought, was due in part to an extensive storage compo-
nent of long-lived individuals in habitats outside the wet-
land and a reduction in predators and increase in prey
Conservation Biology
Volume 20, No. 5, October 2006
Gibbons et al. Amphibian Biomass and Abundance 1463
within the wetland. Evidence suggests that most of the
breeding adults that repopulated Ellenton Bay in 2003
were individuals that had persisted in the surrounding
terrestrial habitat rather than being dispersers from other
wetlands. A capture–recapture study at Rainbow Bay doc-
umented longevities of >5–10 years for individuals of
at least seven of the species that occur at Ellenton Bay,
and some of these species (e.g., Ambystoma spp., B. ter-
restris) are known to abide drought in terrestrial habitats
adjacent to the wetland (D.E.S., unpublished data).
Although the persistence of many amphibian popula-
tions at the landscape level depends on dispersal and re-
colonization from other wetlands (Semlitsch 2000), most
amphibians arriving at Ellenton Bay did not immigrate
from the direction of the only nearby permanent water
body, but instead arrived at the drift fence from all direc-
tions. All ephemeral wetlands within 2 km of Ellenton Bay
have shorter hydroperiods and would not have served as a
refuge for amphibians during the preceding drought. Fol-
lowing droughts, when adult amphibians return to Ellen-
ton Bay to breed, their larvae benefit both from a reduced
abundance of predators (e.g., aquatic snakes, turtles, and
predatory insects; Gibbons et al. 1983; Seigel et al. 1995;
Taylor et al. 1999; Willson et al. 2006) and from enhanced
nutrient levels that support primary production (i.e., al-
gae) and invertebrate prey (e.g., copepods and cladocer-
ans; Taylor et al. 1988; Taylor & Mahoney 1990). Such
years of strong recruitment are in effect “stored” in the
population because the persistence and staggered repro-
duction of long-lived adults buffer against fluctuations in
juvenile recruitment from the aquatic stage (Warner &
Chesson 1985; Taylor et al. 2006).
Studies of the relationship between landscape charac-
teristics and amphibian distribution patterns have gen-
erally found positive associations between amphibians
and forested habitat (e.g., Hecnar & M’Closkey 1996;
Gibbs 1998; Willson & Dorcas 2003; Porej et al. 2004).
Assessing the effects of previous agricultural activities
on amphibians is often equivocal, however, because of
limited historical information and because associations
between amphibians and agriculture vary regionally ac-
cording to landscape context and species composition.
Some researchers have detected decreases in amphibian
diversity in landscapes with intensive agriculture (Bonin
et al. 1997; Hecnar 1997). However, results of a study
in Iowa and Wisconsin showed little effect or slightly
positive effects of agriculture on amphibian richness and
abundance in Wisconsin and more negative associations
in Iowa (Knutson et al. 1999). Both the extent and prox-
imity of forested lands to wetland breeding habitat in-
fluence amphibian species occurrence and abundance.
Results of a study of forest extent and adjacency around
116 breeding ponds in Maine showed that five of nine
amphibian species (three of which were woodland sala-
manders) were positively associated with forest area in
the surrounding landscape (Guerry & Hunter 2002). Sim-
ilarly, Gibbs (1998) noted that two species of woodland
salamanders do not persist once forest cover is reduced
below a threshold level (30–50%).
In 1951 forest comprised <20% of the area within 1 km
of Ellenton Bay, and it is likely that the salamander com-
ponent of the amphibian fauna (Ambystoma opacum
[marbled salamander], A. talpoideum,A. tigrinum)was
reduced relative to current population sizes. In general,
from 1951 to 2004, both the forest extent and adjacency
increased dramatically (Fig. 1), which likely promoted in-
creased salamander diversity and numbers. For anuran
species, the impressive numbers of B. terrestris and R.
sphenocephala witnessed in 2003 as the wetland refilled
after drought may have occurred under similar conditions
prior to 1951, although no earlier records are available.
Nonetheless, it is reasonable to assume that many of the
amphibian species, particularly the forest-dependent sala-
manders, that use Ellenton Bay as a breeding site would
not have persisted if the wetland had remained embedded
in an agricultural landscape without forested peripheral
Our findings highlight the key role of small, isolated
wetlands in amphibian productivity and in maintaining
community dynamics by coupling aquatic habitats with
adjacent terrestrial habitats via transfer of biomass and
energy. Although the observed numbers and biomasses
of amphibians we report are very high, we suspect these
results are typical responses to postdrought conditions,
rather than a one-time occurrence. Our findings offer
hope that even moderate conservation efforts that pro-
tect wetlands and allow surrounding terrestrial habitat
to recover from prior disturbance can promote a diverse
amphibian community. Our results also suggest that cur-
rent U.S. wetland regulations that do not offer protection
to isolated wetlands will jeopardize conservation efforts
to preserve the contribution of amphibian biodiversity to
ecosystem productivity on a landscape level.
We thank R. D. Semlitsch, P. Mason, E. E. Clark, and G. J.
Graeter for providing comments on the manuscript and
the following individuals for field assistance: M. Aresco,
V. Burke, T. Carroll, E. Clark, J. Clark, K. Clark, J. Cole, L.
Cook, H. Dessauer, D. DiIullo, G. Edwards, S. Fedewa, B.
Fokidis, M. Gibbons, K. Grayson, V. Guy, W. Guthrie, I. Ha-
gen, P. Hill, W. Johnson, B. Lawrence, P. Mason, M. Mills,
T. Mills, S. Murray, B. Nelson, A. Newman, M. O’Neill, J.
Perry, A. Pickens, M. Pilgrim, S. Poppy, S. Reichbach, T.
Robison, L. Ruyle, M. Salmi, R. Semlitsch, M. Slinkard, C.
Thawley, R. Thomasson, J. Van Dyke, J. Williams, and A.
Young. We thank P. Mason, T. Mills, and S. Poppy for drift-
fence construction and repair. Research and manuscript
Conservation Biology
Volume 20, No. 5, October 2006
1464 Amphibian Biomass and Abundance Gibbons et al.
preparation were aided by the Environmental Remedia-
tion Sciences Division of the Office of Biological and Envi-
ronmental Research, U.S. Department of Energy through
Financial Assistance Award no. DE-FC09–96SR18546 to
the University of Georgia Research Foundation. Fund-
ing for M.E.D. was partially provided by National Sci-
ence Foundation grant DUE-9980743 and The Duke En-
ergy Foundation. D.A.C. was supported by a Board of Re-
gents Superior Graduate Fellowship from the University
of New Orleans. The procedures used in this study were
approved by the University of Georgia animal care and
use committee (A2003–10024, “Reptile and Amphibian
Research–General Field Studies”) and the South Carolina
Department of Natural Resources (collection permits 56–
2003, 07–2004).
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... Phenology has a key role in amphibian lives, chiefly in species living in temperate regions where many activity cycles are determined by seasonality 17,18 . For instance, climatic features such as temperature and precipitation play a central role in determining breeding migrations and changes in phenology 19 , especially for species that rely on ephemeral waterbodies for reproduction and larval development 20,21 . Adults must use environmental cues to time their movements with seasonal precipitation events that fill wetlands to allow larvae to have enough time to develop before water levels recede. ...
... and females at the start of the breeding season appears to be a common feature for ephemeral pond breeders that expect a high probability of reproductive failure 44,45 . Indeed, as reproduction takes place only once a year for explosive breeders, the timing of the arrival at the breeding sites is fundamental to ensure high reproductive success and full larval development 21 . ...
... prolactin), which normally are themselves triggered by temperature changes and photoperiod 51 . At the same time, moving at too hot external temperatures can be dangerous for amphibians as they can increase the risk of death by desiccation 21 . ...
Full-text available
In the last century, a plethora of species have shown rapid phenological changes in response to climate change. Among animals, amphibians exhibit some of the greatest responses since their activity strongly depends on temperature and rainfall regimes. These shifts in phenology can have negative consequences for amphibian fitness. Thus, understanding phenological changes in amphibians is pivotal to design conservation actions to mitigate climate change effects. We used data on Common Spadefoot Toad (Pelobates fuscus) reproductive migration to wetlands over a period of 8 years in Italy to (i) identify the factors related to breeding migrations, (ii) assess potential phenological shifts in the breeding period, and (iii) determine which climatic factors are related to the observed phenological shifts. Our results showed that toads migrate to spawning sites preferably in early spring, on rainy days with temperatures of 9–14 °C, and with high humidity. Furthermore, despite an increase in average temperature across the study period, we observed a delay in the start of breeding migrations of 12.4 days over 8 years. This counterintuitive pattern was the result of a succession of hot and dry years that occurred in the study area, highlighting that for ephemeral pond breeders, precipitation could have a larger impact than temperature on phenology. Our results belie the strong presumption that climate change will shift amphibian phenology toward an earlier breeding migration and underline the importance of closely investigating the environmental factors related to species phenology.
... The timing and sequence of vertebrate colonisation events affects community composition within aquatic habitats by changing the presence and/or abundance of predators and resources. For example, amphibians with terrestrial adults that immediately recolonise water bodies after dry down and refill may benefit from lack of potential predators or interspecific competitors, which can lead to high amphibian abundance and biomass (Gibbons et al., 2006;Wells, 2010). Amphibians, however, often avoid ovipositing in pools with fish present because fish have strong negative effects on larval survival (Amburgey et al., 2014;Mas-Martí et al., 2010;Petranka et al., 1987;Pilliod et al., 2010). ...
... Previous observational studies (e.g., Gibbons et al., 2006) have hypothesised drying and refilling could lead to more juvenile anurans emigrating into the terrestrial landscape because of drying-induced reduction in predation. However, our study suggests that the mechanisms involved (top-down and bottom-up) and the valuation of quantity versus individual fitness (e.g., size-dependent survival rates) of juveniles leaving refilled systems are nuanced. ...
1. Intermittent streams are hydrologically dynamic within and among years, leading to episodic bouts of local extirpations and subsequent recolonisation of vertebrate groups such as fish and larval amphibians. As these aquatic habitats undergo drying and enter states of incomplete recovery, their ecosystem functionality is impacted. We investigated the legacy effects of drying and refilling of wetlands via mesocosms on growth and survival of recolonising aquatic vertebrates and their subsequent effects on ecological function. Specifically, we tested the effects of prior drying on anuran and fish growth and survival (using Gompertz growth curves), the joint effects of vertebrates and drying on periphyton biomass, and whole‐system gross primary productivity. 2. Using 64 1000‐L hard plastic cattle tanks to create replicate aquatic mesocosms, four trophic treatments (no vertebrate control, larval anurans, fish, larval anurans and fish) were crossed with two drying treatments (undried and dried–refilled) to simulate different outcomes of colonisation by two common vertebrate guilds and drying/refilling cycles. Mesocosms with anuran treatments received 50 Lithobates blairi tadpoles (1600 total) and mesocosms with fish treatments received one Lepomis cyanellus juvenile (32 total). We recorded anuran growth rates, survival and time/size at metamorphosis, fish growth, gross primary productivit, and periphyton biomass over 12 weeks from 9 May 2021 to 1 August 2021. 3. Prior drying strongly reduced L . blairi growth rate by 38.2% but increased survival from 48.5 to 75%, resulting in relatively equal emergent anuran biomass between the two drying treatments. No L . blairi survived to metamorphosis when co‐occurring with fish (i.e., larval anurans and fish treatment). On average, prior drying reduced the size at metamorphosis by 35.5%, delayed time to metamorphosis by 4 days, and increased the range of metamorphosis days by 10 days. Fish growth and survival were unaffected by trophic or drying treatments. Gross primary production and periphyton biomass decreased in response to prior drying and the presence of larval anurans, but these effects were non‐constant over time. 4. The effects of short‐term drying were not immediately reversed by refilling and were still perceivable across nearly all trophic levels several months post‐refill. However, for generalist colonisers such as L . cyanellus , optimal habitat is minimally impacted by drying history of the aquatic habitat and depends primarily on the presence of water and connection to source populations. Colonisation by fish removed an entire consumer guild (anuran larvae) and an aquatic–terrestrial flow of resources (anuran juveniles). 5. Climate change is increasing the frequency and severity of droughts and drying events around the world, and increasingly leaving ecosystems in an incomplete state of recovery. Intermittent streams are particularly well‐suited for studying dry–refill cycles as they are one of the most common global freshwater systems. While several studies have investigated the contemporary effects of drying on aquatic systems (i.e., what happens to organisms when a pool dries), this study addresses gaps in our understanding of legacy effects of prior drying on aquatic organisms and ecosystem processes after water returns. Here we clearly show that even short‐term drying has pervasive effects on aquatic ecosystem function following refill.
... Через екологічні та фізіологічні особливості амфібії мають обмеження у просторовому розподілі в екосистемах і пересуванні. Після метаморфозу земноводні пов'язані з наземними та водними біотопами (Gibbons et al., 2006;Goldspiel et al., 2019). ...
Agricultural activity in the global world is accompanied by the use of a significant number of synthetic insecticides for the control of insect pests. Pyrethroid and neonicotinoid insecticides are among the widely used insecticides in many countries for the control of crop pests. They are a generation of synthetic insecticides that have replaced the more environmentally stable organophosphorus and organochlorine compounds. Pyrethroid and neonicotinoid insecticides were thought to have low toxicity to vertebrates, leading to their widespread use and increased production. However, many studies have emerged in recent decades that have shown that, under certain conditions, these substances can cause significant damage to the internal systems of amphibians. Recently, special studies have also revealed the toxic effects of pyrethroids and neonicotinoids on the post-metamorphic stages of amphibians, which had previously been ignored. It has also been noted that abnormalities in gastrointestinal tract functions occur, leading to abnormalities in the digestive system. Pyrethroid and neonicotinoid insecticides have been shown to affect the biochemical and histological parameters of amphibians. The possible genotoxicity of these insecticides resulted in producing erythrocytes with abnormal nuclei and an increased number of micronuclei in amphibian cells. Meanwhile, changes in the activity of antioxidant enzymes and increases in lipid peroxidation products could be used as biomarkers of oxidative stress in amphibians under the influence of pyrethroid and neonicotinoid insecticides. The available literature also indicates that these insecticides appear to affect the nervous system of amphibians and induce changes in their behaviour. At the same time, our data suggest that it is neuromolecular biomarkers that can be practised to determine the toxic effects of insecticides on non-target species. Such biomarkers can be used in the context of the low-dose influence of insecticides, which however requires additional research on amphibians.
... Amphibians are regarded as a key component of wetland ecosystems (Gibbons et al., 2006). The results obtained in our study demonstrate that amphibians can make a considerable qualitative contribution to trophic webs of a certain riparian ecosystems. ...
The transfer of biomass and polyunsaturated fatty acids by the spadefoot P. vespertinus (previously subspecies of P. fuscus) from aquatic to terrestrial ecosystems was studied for five years in small floodplain water bodies of a forest-steppe zone. Average emergence of metamorphs from unit of water area, wet mass was 6.7 g m-2 year-1. A ratio of the emergence to biomass was calculated and represented as E/B coefficient (an analog of P/B production/biomass coefficient). The average E/B was found to be 0.038 year-1. The introduced coefficient can be used for a coarse estimation of the emergence on the basis of tadpole biomass measurements. A considerable partitioning of tadpoles and metamorphs in the composition of fatty acids in their biomass was revealed. Tadpoles had significantly higher mean levels (percent of total fatty acids) of 16:0, 16:1n-9, 18:0, 20:5n-3 and 22:5n-3, while metamorphs had significantly higher levels of 14:0, 15:0, 17:0, 17:1n-8, 18:2n-6, 20:2n-6, 20:4n-6 and 22:5n-6, likely due to the shifting to terrestrial food. Metamorphs had significantly higher content of total fatty acids, mg g-1 of wet weight, and, in spite of lower level, they had significantly higher content of eicosapentaenoic acid (20:5n-3, EPA) than tadpoles. Metamorphs also had significantly higher content of docosahexaenoic acid (22:6n-3, DHA) and sum of EPA + DHA than tadpoles. Average flux of EPA + DHA from unit of water area with metamorphs was 3.27 mg m-2 year-1. The metamorphs appeared to be qualitatively and quantitatively prominent prey for a number of terrestrial consumers.
... Determining amphibian population trends, requires multi-year studies that ideally include population turnover, that is immigration and emigration, as well as multiple generations (Connell & Sousa 1983;Semlitsch 2002;Adams et al. 2013). Such long-term monitoring provides valuable insights to decline stressors, population responses to environmental variation, and population resilience to perturbations and habitat change for at-risk species (Gibbons et al. 2006;Homyack & Hass 2009). It is also necessary in order to determine if populations are in decline or exhibiting natural fluctuations, and to identify proximate causes (Pechmann et al. 1991;Lips et al. 2003;Storfer 2003). ...
Technical Report
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This report covers the fourth consecutive year (2013-2016) of research on the population dynamics, ecology, and conservation status of the Arizona Toad (Anaxyrus microscaphus) in New Mexico. The year 2016 represented the rare opportunity to study the effects of El Niño, which typically brings above average precipitation to New Mexico, on the breeding behavior and ecology of the Arizona toad. We expected that the El Niño-driven above average precipitation during the winter of 2015 and spring of 2016 would result in increased detection of toads at breeding sites, especially those sites that were dry in 2013, 2014, and 2015. Furthermore, we expected to observe a decrease of tadpole mortality at breeding sites caused by streams and tanks drying before tadpole metamorphosis. These expectations were based on observations of Arizona Toad's breeding success in Arizona during El Niño years. In addition to breeding surveys, we continued monitoring Arizona toad populations for the amphibian fungal disease Batrachochytrium dendrobatidis and chigger skin parasites, which may cause toad mortality. Herein we also model stream environmental factors that regulate toad breeding and success and summarize disease prevalence in the region.
... To determine amphibian population trends, whether in abundance or occurrence, requires multi-year studies that ideally cover population turnover (Connell & Sousa 1983;Semlitsch 2002;Adams et al. 2013). Such long-term monitoring provides valuable insights to decline stressors, population responses to environmental variation, and population resilience to perturbations and habitat change for at-risk species (Gibbons et al. 2006;Homyack & Hass 2009). ...
... The biomass amphibians export to terrestrial systems can be substantial: one wetland had greater than 220,000 frog metamorphs in a single year. 68 More studies are needed to fully understand how pondbreeding complex life cycle species affect biologically driven movement of Hg across the landscape. ...
Quantifying how contaminants change across life cycles of species that undergo metamorphosis is critical to assessing organismal risk, particularly for consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as juveniles and adults. Thus, amphibians can be vectors of mercury exposure in both aquatic and terrestrial food webs. However, it is still unclear how mercury concentrations are affected by exogenous (e.g., habitat or diet) vs endogenous factors (e.g., catabolism during hibernation) as amphibians undergo large diet shifts and periods of fasting during ontogeny. We measured total mercury (THg), methylmercury (MeHg), and isotopic compositions (δ 13C, δ15N) in boreal chorus frogs (Pseudacris maculata) across five life stages in two Colorado (USA) metapopulations. We found large differences in concentrations and percent MeHg (of THg) among life stages. Frog MeHg concentrations peaked during metamorphosis and hibernation coinciding with the most energetically demanding life cycle stages. Indeed, life history transitions involving periods of fasting coupled with high metabolic demands led to large increases in mercury concentrations. The endogenous processes of metamorphosis and hibernation resulted in MeHg bioamplification, thus decoupling it from the light isotopic proxies of diet and trophic position. These step changes are not often considered in conventional expectations of how MeHg concentrations within organisms are assessed.
Ephemeral wetlands are globally important systems that are regulated by regular cycles of wetting and drying, which are primarily controlled by responses to relatively short-term weather events ( e.g. , precipitation and evapotranspiration). Climate change is predicted to have significant effects on many ephemeral wetland systems and the organisms that depend on them through altered filling or drying dates that impact hydroperiod. To examine the potential effects of climate change on pine flatwoods wetlands in the southeastern United States, we created statistical models describing wetland hydrologic regime using an approximately 8-year history of water level monitoring and a variety of climate data inputs. We then assessed how hydrology may change in the future by projecting models forward (2025–2100) under six future climate scenarios (three climate models each with two emission scenarios). We used the model results to assess future breeding conditions for the imperiled Reticulated Flatwoods Salamander ( Ambystoma bishopi ), which breeds in many of the study wetlands. We found that models generally fit the data well and had good predictability across both training and testing data. Across all models and climate scenarios, there was substantial variation in the predicted suitability for flatwoods salamander reproduction. However, wetlands with longer hydroperiods tended to have fewer model iterations that predicted at least five consecutive years of reproductive failure (an important metric for population persistence). Understanding potential future risk to flatwoods salamander populations can be used to guide conservation and management actions for this imperiled species.
Coastal wetlands provide critical habitat for aquatic organisms and important ecosystem services for the terrestrial and aquatic landscapes that they bridge, but increasingly common invasive macrophytes disrupt plant communities, food webs, habitat structure and littoral–pelagic linkages. In Laurentian Great Lakes coastal wetlands, invasive cattails ( Typha × glauca and T. angustifolia , hereafter Typha ) homogenise ecosystem structure and reduce nearshore dissolved oxygen, and plant, fish and macroinvertebrate diversity. We hypothesised that management treatments which reduce Typha and its abundant litter promote structural heterogeneity and mitigate physicochemical and biodiversity impacts. To test this hypothesis, we implemented a large‐scale (2,048 m ² treatment units), multi‐site (four coastal wetlands) experiment in northern Michigan (U.S.A.) to examine how invasive Typha mechanical harvesting treatments (biomass harvest, aquatic connectivity channels, Typha‐ dominated control) altered fish, macroinvertebrate, plant, larval amphibian abundance and diversity, and water quality for 2‐year post‐treatment. Both harvest and channel treatments reduced Typha biomass, cover and dominance; harvest increased multi‐taxa species richness, fish diversity and abundance; and channels altered plant, fish, and macroinvertebrate community structures. Dissolved oxygen was greater and litter was reduced by both treatments, indicating likely mechanisms for shifts in fish and macroinvertebrate use. Our results suggest that harvesting invasive macrophytes can ameliorate biodiversity impacts and improve habitat quality, and that adding aquatic connectivity channels can increase community complexity. Typha management that incorporates both harvesting and aquatic connectivity channels appears to provide the greatest benefit to several taxonomic groups, likely by reducing Typha and its litter, increasing dissolved oxygen availability, and increasing the connection between open water and wetland interiors. Increasing habitat complexity and aquatic connectivity of invaded wetlands can promote biodiversity and provides a more realistic management goal than the complete elimination of invasive macrophytes.
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Direct, indirect, and cumulative impact of the use of the biopesticides Bacillus thuringiensis israelensis (Bti) et du Lysinibacillus (Bacillus) sphaericus (Ls, Bsph) for the control of biting insects on non-target species, food webs and ecosystems. Literature Review.
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This chapter describes a 16-year study, in which it has been found that pond hydroperiod is a primary source of variation in community structure for a natural community of pond-breeding amphibians. Larval competition and predation form other axes that are positioned along a continuum of hydroperiod, and the strength of their influence on the success of species is mediated by pond hydroperiod. Although hydroperiod, competition, and predation had a detectable influence on the amphibian community at Rainbow Bay, the effects of these factors were often difficult to separate. Correlative analyses are less powerful for sorting out confounding factors than manipulative experiments in replicated artificial ponds. The predictor variables used are often themselves correlated. Nevertheless, in many cases, a good year for a species is also a good year for its competitors and predators. Juvenile recruitment of all species is limited by a short hydroperiod in the driest years. In years with longer hydroperiods, the density of competitors affected the number of metamorphosing juveniles per breeding females for some species. The density of salamander larvae is also a significant predictor of per-capita juvenile recruitment for anurans. A significant negative relationship is detected for two of four anuran species analyzed, most likely due to predation by the salamander larvae on the anuran tadpoles. These results indicate that community structure, at least in terms of relative abundances, varied continuously. However, regulation of community structure within a pond occurs through the predictable interaction of rainfall, hydroperiod, competition, and predation.
A "common garden" experiment using artifical ponds was performed to test if differences in frequency of paedomorphosis and metamorphosis among six natural populations of the salamander Ambystoma talpoideum resulted from the drying regime of the aquatic habitat acting as an agent of selection. Our experiment supports the hypothesis of genetic differentiation in the propensity to metamorphose among the populations, but gave mixed evidence that pond-drying regime is the selective force directing evolution of this trait. Some populations appear to have evolved phenotypic plasticity whereas others may have a genetic polymorphism in their propensity to metamorphose as ponds dry.
The abundance, biomass and production of aquatic invertebrates were determined for 1992 and 1993 at Rainbow Bay, a small (maximum inundated area ~1.5 ha), shallow (maximum depth ~1m) depression wetland in South Carolina, USA, which dries annually. Estimates were based on invertebrates collected from benthic substrates and the water column, including those associated with macrophytes. Mean invertebrate density during the periods of inundation was 7.1 x 105 animals/m2 in 1992 and 7.7 x 105 animals/m2 in 1993. Small taxa, including nematodes, rotifers and microcrustaceans dominated numerically. Biomass, was 2.1 g dry mass/m2 in 1992, and 0.9 g/m2 in 1993. Oligochaetes, insects (mostly chironomids) and crustaceans dominated the biomass. The lower biomass in 1993 was the result of significant reductions in the biomass of oligochaetes and benthic chironomids. Laboratory-derived daily growth rates of oligochaetes and chironomids collected from Rainbow Bay, along with daily production rates for crustaceans and rotifers derived from other studies were used to estimate secondary production. Production in 1993 (14.7g dry mass/m2) was less than in 1992 (36.7g/m2), due primarily to lower biomass of oligochaetes and chironomids in 1993. Differences between years in abundance, biomass and production were associated with differences in hydrology of the wetland, including duration of inundation, and abundances of salamanders.
Coordinated efforts by ecologists and natural resource managers are necessary to balance the conservation of biological diversity with the potential for sustained economic development. Because some amphibians have suffered world-wide declines during the last 20 years, it is important to consider biologically based management strategies that will preserve local and regional populations. This paper provides a brief overview of potential threats to local and regional populations, the state of knowledge on population and landscape processes, and the critical elements needed for an effective management plan for amphibians. Local population dynamics and ecological connectivity of amphibian metapopulations must be considered in effective management plans. There are 3 critical factors to consider in a management plan (1) the number or density of individuals dispersing from individual wetlands, (2) the diversity of wetlands with regard to hydroperiod, and (3) the probability of dispersal among adjacent wetlands or the rescue and recolonization of local populations. Wetland losses reduce the total number of sites where pond-breeding amphibians can reproduce and recruit juveniles into the breeding population. Loss of small, temporary wetlands (
We surveyed a streamside community in a southern Appalachian old-growth forest to determine the feasibility of using removal sampling to estimate salamander density and biomass. We removed salamanders during 21 nightly searches of two 30 x 30 m plots from 29 June to 20 July 1999. Despite the removal of 2433 animals and a lack of evidence for significant trespass onto plots, there was no overall decline in total catch per night Moisture levels associated with recent rainfall history strongly influenced the surface activity of small species (Desmognathus carolinensis, Desmognathus wrighti Eurycea bislineata wilderae) but not large species (Plethodon jordani, Plethodon glutinosus, Plethodon yonahlossee). More refined analyses of individual species using either regression analysis (large species) or covariance analysis (small species adjusted for moisture conditions) indicate that the catch of all species except D. wrighti declined with time. The estimated number of consecutive nights required to remove 70% of the population varied from eight (P. yonahlossee) to 32 (D. carolinensis) and tended to be inversely related to the body size of the species. Conservative estimates of total salamander density and wet biomass in streamside habitats at this site are 18,486 individuals and 16.53 kg per hectare. These values are seven and 14 times greater than those reported for the Hubbard Brook Experimental Forest in New Hampshire and underscore the importance of salamanders in riparian zone communities of southern Appalachian forests.
Under the hypothesis that low metabolic rates are adaptations to low rates of energy throughput, taxa with unusually low metabolic rates-such as acrochordid snakes-might be expected to show unusually low rates of feeding, growing, maturing and reproducing. Field studies of Acrochordus arafurae in the Alligator Rivers Region of tropical Australia show that these aquatic snakes feed and reproduce less frequently than do most other snake species studied previously. Published data on other acrochordids suggest similarly low rates. A. arafurae feeds exclusively on fishes, including carrion. Live prey are subdued by constriction. The proportion of freshly-captured snakes containing food (5%) is lower in this species than in most other snakes. Feeding frequency may be very low and digestive efficiency may be unusually high in A. arafurae. Reproduction is seasonal, with an average litter of about 17 young (11-25) depending upon maternal body size. Neonates are large (360 mm, 31 g) and relative clutch mass is high (0.53). However, the proportion of adult-sized females that are reproductive (7%) is lower than in any previously studied snake species, suggesting a low frequency of reproduction in individual females. Population densities and biomass of A. arafurae vary among billabongs, but may reach extraordinarily high levels (100 snakes per hectare, > 50 kg per hectare).
A "common garden" experiment using artifical ponds was performed to test if differences in frequency of paedomorphosis and metamorphosis among six natural populations of the salamander Ambystoma talpoideum resulted from the drying regime of the aquatic habitat acting as an agent of selection. Our experiment supports the hypothesis of genetic differentiation in the propensity to metamorphose among the populations, but gave mixed evidence that pond-drying regime is the selective force directing evolution of this trait. Some populations appear to have evolved phenotypic plasticity whereas others may have a genetic polymorphism in their propensity to metamorphose as ponds dry.
Increasing attention is being devoted to the dynamics of interacting local populations of species, especially the role of changes in incidence that affect regional persistence. The status of species in a regional context may be determined more by metapopulation dynamics than by purely demographic birth and death processes. The contrast between local and regional views of species' persistence is illustrated today by discussion of the status of amphibians. The amphibian fauna may provide an important indicator of the impact of anthropogenic disturbance to wetland ecosystems. We assessed the status of 11 amphibian species in southwestern Ontario, Canada, by estimating species richness, changes in presence and absence, and incidence at 97 ponds from 1992 to 1994. We detected a significant reduction in amphibian species richness in one of three regions. This loss of diversity relative to the historical species complement is a consequence of the land use history. We observed surprisingly high turnover of species at ponds, with increased incidence varying from 0.07 to 0.29 species per pond per year, and decreased incidence ranging from 0.16 to 0.30 species per pond per year. The incidence of common species across years included both declines (leopard frog, Rana pipiens) and increases (American toad, Bufo americanus). For eight relatively rare species, losses exceeded gains between 1992 and 1993, but this pattern was reversed between 1993 and 1994. Understanding environmental factors that determine the status of species will require an expanded, large-scale view of groups of populations (metapopulations) and their spatial dynamics.