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22001155 SOUTHEASTERN NATURALIST 1V4o(2l.) :1342,9 N–3o4. 12
Structure and Dynamics of Lithobates sylvaticus (Wood
Frog) at the Periphery of its Range in Missouri
Raymond D. Semlitsch1,* and Dana L. Drake1
Abstract - Lithobates (Rana) sylvaticus (Wood Frog) has an extensive distribution primarily
in the Appalachian Mountains in the eastern US and throughout Canada and Alaska.
However, peripheral populations exist along the southern edge of its range, including in the
Ozark regions of Missouri and Arkansas. We present results on the structure and dynamics
of 5 Wood Frog populations studied over 4 years (2004–2007) at the edge of the species’
range in central Missouri. We used drift fences and pitfall traps surrounding breeding ponds
to sample adults and metamorphosing juveniles. We captured breeding males between 7
February and 13 March, and females between 28 February and 16 March. The sex ratio was
male-biased (M:F = 2.4), females were larger than males (mean SVL = 61.3 and 52.3 mm,
respectively), and the larval period averaged 14 weeks. The metamorphs had a mean SVL
of 18.1 mm and varied in number from 0 to 400 individuals per pond per year. The mean
juvenile production per female was 8.7 (range = 0–52), and mean survival from egg to
juvenile was 1.28% (range = 0–6.08%). Land managers should consider the species’ small
population sizes, low recruitment, survival rates of terrestrial stages, and the interaction of
population dynamics with changing climate conditions when planning for conservation of
Wood Frog populations at the periphery of the species’ range.
Introduction
Information on the structure and dynamics of populations is fundamental to understanding
how species persist in various locations across their range. Populations
at the range periphery can have very different attributes than populations near the
range center that can make peripheral populations more susceptible to demographic
stochasticity and local extinction (Lesica and Allendorf 1995, Vucetich and Waite
2003). Environmental conditions might be especially limiting outside the center of
a species’ distribution (Gaston 1990). Management and conservation decisions are
made at landscape and regional levels; thus, an understanding of population dynamics
in all parts of a species’ range should inform those decisions. This need may be
greatest for conservation in areas at the periphery of species’ ranges where anthropogenic
factors such as land use, fragmentation, and climate change might interact
with marginal environmental conditions to strongly impact population persistence
(Semlitsch 2000).
Rana sylvatica LeConte (= Lithobates sylvaticus, Wood Frog) is a widely distributed
pond-breeding species that occurs from northern Georgia to Nova Scotia and
from Missouri to Alaska (Lannoo 2005, LeConte 1825). Disjunct populations occur
along the southern and western edge of its range in Alabama, Arkansas, Colorado,
1Division of Biological Sciences, University of Missouri, Columbia, MO 65211. *Corresponding
author - SemlitschR@missouri.edu.
Manuscript Editor: Will Selman
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Missouri, Wyoming, Idaho, and possibly South Dakota (Fig. 1; Muths et al. 2005,
Trauth et al. 2004). Wood Frogs are typically one of the first species to breed in early
spring, are explosive breeders, and use a range of fish-free, seasonal ponds for oviposition
(Trauth et al. 2004). Like many other pond-breeding anurans, Wood Frog
tadpoles grow rapidly, and juveniles metamorphose during the summer. Both juveniles
and adults reside in forested terrestrial habitats surrounding breeding ponds
(Rittenhouse and Semlitsch 2007). Although a large number of studies have been
conducted on Wood Frogs (cited in Lannoo 2005, Martof and Humphries 1959,
Muths et al. 2005), including perhaps the best demographic studies of any amphibian
(e.g., Berven 1990, 2009), population studies at the periphery of the species’ range
are lacking. Further, a recent study of genetic diversity at the southwestern edge of
its range in Missouri indicated that populations of Wood Frogs in a series of isolated
conservation areas have reduced genetic variation (Peterman et al. 2013a).
Here, we add to knowledge of Wood Frog population biology by providing
a detailed account of the structure and dynamics of 5 populations in Missouri
studied over a 4-year period. Our objective was to provide information on annual
breeding phenology, breeding-population size, sex ratio, adult body size, juvenile
emigration, numbers of metamorphosing juveniles, and juvenile body size. We then
qualitatively compared our results with those from studies conducted in other parts
of the Wood Frog’s range to better understand geographic variation, especially at
southern extremes, and to discuss any differences we found in Missouri.
Methods
Study area
We conducted our study within the 1424.5-ha Daniel Boone Conservation Area
(DBCA) in the upper Ozark Highlands in Warren County, MO (Fig. 1; Semlitsch
et al. 2014). We selected for study 5 breeding ponds located 0.38–1.35 km apart
from among >40 available ponds. The 5 ponds we chose are representative and did
not differ in obvious ways from all available ponds at DBCA (Fig. 1). The focal
ponds were located in mature (80–100 years old), second-growth forest of Quercus
sp. (oak) and Carya sp. (hickory) overstory, with varying amounts of Acer saccharum
Marsh. (Sugar Maple) in the understory (Semlitsch et al. 2008, 2009, 2014).
Approximately equal portions of the forest surrounding each pond were subject to
similar levels of timber harvest and subsequently allowed to undergo natural succession
(Semlitsch et al. 2009). Our focal ponds were similar in size (high-water
area = 160–330 m2), <1.2 m deep, and 27–47 years old. All ponds at DBCA were
originally constructed for other wildlife (e.g., Meleagris gallopavo L. [Wild Turkey]
and Odocoileus virginianus Zimmermann [White-tailed Deer]) and have been
naturally colonized by up to 16 species of amphibians (Hocking et al. 2008). Our 5
study ponds were nearly permanent, fishless, and contained water for the duration
of our study except for a short period during a drought late in the summer of 2005.
Drift fences and monitoring
We completely encircled each breeding pond with a drift fence and pitfall
traps during October–December 2003. The drift fences enabled us to sample the
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breeding populations and metamorphosing juveniles each year. We constructed
the drift fences of aluminum flashing buried ~30 cm into the ground and extending
60 cm above ground (Gibbons and Semlitsch 1982). Pitfall traps consisted of
plastic plant pots (23 cm diameter, 45 cm deep) buried so that the top was flush
with the ground and the edge was against the fence. Traps were paired along
both sides of the fence every 3.0 m. We suspended a wooden board 4 cm above
each trap atop metal stakes to reduce predation, and placed a moist sponge in the
bottom of each trap to reduce desiccation of trapped animals. Adult Wood Frogs
can climb out of pitfall traps (R.D. Semlitsch, pers. observ.), so we assume that
we did not detect all individuals. We checked traps every 1–3 days from February
to November depending on season of activity and rainfall during 2004, 2005,
2006, and 2007. We recorded trap location, date, sex, age class, and migration
direction for all Wood Frogs captured in our traps and released them on the opposite
side of the fence. Each year, we also subsampled individuals at each pond and
measured body size (snout–vent length [SVL]; mm).
Figure 1. Inset map of North America showing the range of Wood Frogs (shaded with open
dots) with the position of Daniel Boone Conservation Area (DBCA), Warren County, MO,
noted by a black dot. DCBA map showing topographic features and scale is shown with
delineated boundary lines in black and a wavy black line through the center showing the
only gravel road. All wildlife ponds are indicated with black circles and our study ponds are
indicated with X’s in the open circles and labeled as ponds 1–5.
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Our relatively small dataset had substantial variability and was not normally
distributed; thus, we performed Kruskal-Wallis tests for all analyses. We tested
whether the total number of adults, the number of males, and the number of females
varied by pond or year. We also tested whether the mean date of breeding
immigration varied by pond or year, as well as whether there was a difference in
mean arrival time of males and females. We analyzed whether body size varied
between the sexes, whether metamorph number and the mean date of emigration
varied among ponds or years, and whether the body size of metamorphs varied with
date of emigration. Finally, we correlated the total number of adults captured each
year with cumulative rainfall during March as reported for the area in the National
Oceanic and Atmospheric Administration climate database, and the total number
of metamorphs captured each year with cumulative rainfall during the period 15
May–15 July. All analyses were performed in program R (R Core Team 2013).
Results
Breeding migrations
Male Wood Frogs typically arrived at the ponds earlier than the females, but the
date of first capture varied by year (Table 1). The earliest first date of capture for
males was 7 February (2005, 2006). The mean first immigration date for males was
Table 1. Immigration dates of Wood Frog adults into 5 breeding ponds in Missouri during 2004–2007.
A dash (-) indicates no captures were recorded, (n/a) indicates data were not available.
Female captures Male captures Juvenile captures
Year Pond First Last First Last First Last
2004 1 - - - - - -
2 4 Mar 4 Mar 4 Mar 4 Mar 10 Jun 16 Jun
3 4 Mar 22 Mar 28 Feb 7 Mar 9 Jun 26 Jun
4 - - 3 Mar 8 Mar - -
5 5 Mar 24 Mar 4 Mar 5 Mar - -
2005 1 7 Mar 10 Mar 7 Feb 7 Mar - -
2 28 Feb 7 Mar 7 Feb 7 Mar - -
3 28 Feb 22 Mar 28 Feb 22 Mar 9 Jun 14 Aug
4 8 Mar 31 Mar 28 Feb 12 Apr 15 Jul 15 Jul
5 28 Feb 7 Mar 7 Feb 7 Mar 13 Jul 13 Jul
2006 1 6 Mar 12 Mar 4 Mar 12 Mar - -
2 4 Mar 10 Mar 4 Mar 10 Mar - -
3 6 Mar 12 Mar 6 Mar 6 Mar 30 May 11 Jul
4 6 Mar 12 Mar 4 Mar 10 Mar 12 Jun 12 Jun
5 6 Mar 12 Mar 4 Mar 10 Mar - -
2007 1 - - 1 Mar - - -
2 13 Mar n/a 10 Mar n/a 25 May 31 May
3 10 Mar n/a 1 Mar n/a 23 May 20 Jul
4 16 Mar n/a 10 Mar n/a 31 May 20 Jun
5 - n/a 13 Mar n/a - -
Mean 4 Mar 28 Feb 12 Jun
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28 February, which was also the earliest first date of capture for females (2005).
For Wood Frog females, the mean first date of immigration to the breeding ponds
was 4 March, which was significantly later than males (χ2 = 6.51, df =1, P = 0.01).
The mean date of immigration of all adults varied significantly between years
(χ2 = 12.66, df = 3, P = 0.005), but not between ponds (χ2 = 1.01, df =4, P = 0.91).
Mean male immigration date also varied significantly by year (χ2 = 12.85, df = 3,
P =0.005), but female immigration rate did not vary by year (χ2 = 4.29, df = 3, P =
0.23). The latest a female and male were captured entering a breeding pond in the
spring was 31 March and 12 April 2005, respectively. Although Wood Frogs breed
in spring, we captured adult females entering the breeding ponds on 5 October 2004
(n = 1), 24 September 2005 (n = 2), and 1 November 2005 (n = 1). We captured 3
adult males entering breeding ponds on 7 November 2005. However, we found no
eggs or tadpoles during the fall.
Breeding populations
We recorded a total of 116 adult female and 249 adult male Wood Frogs during
the 2004–2007 surveys. The number of adults captured varied by pond, sex, and
year (Table 2), but the only statistical difference was in the number of males among
years (χ2 = 14.41, df = 3, P = 0.002) and the number of adults by year (χ2 = 11.97,
df = 3, P = 0.007). Other comparisons of adults included total number (χ2 = 0.37,
df = 4, P = 0.98), number of males (chi-square = 0.313, df =4, P = 0.99), and
Table 2. Breeding-population sizes for females and males, sex ratios, the number of emigrating juveniles
(metamorphs), ratios of juveniles to females, and egg to metamorphosis survival of Wood Frogs
at 5 breeding ponds in Missouri during 2004–2007. Egg to metamorphosis survival (survival/egg) was
calculated using a mean clutch size of 850 eggs per female Wood Frog (Trauth et al. 2004).
Year Pond Females (n) Males (n) Ratio (M:F) Metamorphs Meta: Female Survival/egg
2004 1 0 0 0.00 0 0.00 0.0000
2 3 5 1.67 7 2.33 0.0027
3 9 9 1.00 195 21.67 0.0250
4 0 2 0.00 0 0.00 0.0000
5 3 4 1.33 0 0.00 0.0000
2005 1 4 14 3.50 0 0.00 0.0000
2 29 42 1.45 0 0.00 0.0000
3 11 24 2.18 218 19.82 0.0229
4 1 7 7.00 3 3.00 0.0035
5 30 40 1.33 1 0.03 0.0000
2006 1 9 13 1.44 0 0.00 0.0000
2 17 32 1.88 0 0.00 0.0000
3 10 3 0.30 400 40.00 0.0461
4 6 13 2.17 1 0.17 0.0002
5 14 18 1.29 0 0.00 0.0000
2007 1 0 8 0.00 0 0.00 0.0000
2 2 19 9.50 41 20.50 0.0236
3 9 24 2.67 314 34.89 0.0402
4 4 14 3.50 4 1.00 0.0012
5 0 5 0.00 0 0.00 0.0000
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number of females (χ2 = 1.77, df = 4, P = 0.78), none of which showed statistically
significant differences among ponds. Annual differences in the number of females
also did not differ (χ2 = 5.57, df =3, P = 0.13). Ponds 1 and 4 had the fewest adults
during our study (n = 36 and 74, respectively), and ponds 2 and 5 had the most
(n = 88 each), with ranges as low as 0 (pond 1 in 2004) and as high as 57 (pond 5
in 2005) total adults at a pond. We captured a mean of 7.25 (range = 0–22) female
Wood Frogs and a mean of 13.1 (range = 0–35) male Wood Frogs per pond over
the 4 years. We captured the fewest adult Wood Frogs (n = 24) during the first year
of sampling (2004), but then collected the most (n = 190) in 2005, with numbers
decreasing in subsequent years. We captured no females or males at pond 1 in 2004
and no females at ponds 1 and 4 in 2004 or ponds 1 and 5 in 2007. The total number
of adults captured in drift fences was negatively correlated with the cumulative
amount of rainfall during March (Spearman’s rho = -0.79, P < 0.001).
We detected sexual dimorphism in SVL between breeding adults: females were
larger than males (mean SVL = 61.3 mm ± 6.6 SD [n = 102] and 52.3 mm ± 3.7
SD [n = 221], respectively; Kruskal-Wallis chi-square = 180.1, df = 1, P < 0.0001;
Fig. 2). The smallest breeding female was 42 mm SVL, and the smallest breeding
male was 41 mm SVL. The sex ratio of females to males was primarily male biased,
with the exception of pond 3 in 2004 and 2006 (Table 2). The mean ratio of males
to females at all ponds over all years was 2.4 to 1.
Juveniles emigrating
We captured a total of 1184 juvenile Wood Frogs emigrating from all ponds
during all years. The number of metamorphs varied significantly among ponds
(χ2 = 8.05, df = 3, P = 0.045), but not among years (χ2 = 0.48, df = 3, P = 0.92).
The total number of metamorphs captured in drift fences was not correlated with
cumulative rainfall during 15 May–15 July (Spearman’s rho = 0.04, P = 0.84).
The earliest capture of emigrating juveniles occurred on 23 May 2007, and the average
date of emigration was 12 June. Differences in the average date of juvenile
emigration were not statistically significant among ponds (χ2 = 2.30, df = 3, P =
0.51) but were significant among years (χ2 = 8.00, df = 3, P = 0.046). Based on the
average date of arrival of breeding females at the ponds and the average date of
juvenile emigration, we calculated the larval period to be ~14 weeks. We captured
a few juveniles leaving the ponds in July and August, with a latest date of capture
on 14 August (2005).
We measured the body size of 609 metamorphs during the survey period. The
smallest metamorph was 14 mm SVL (pond 3, 31 May 2006, n = 2), and the largest
2 metamorphs were 29 and 26 mm SVL (9 June 2004 and 11 July 2006, respectively).
The total mean SVL of all metamorphs measured was 18.1 mm ± 1.43 SD
(Fig. 3). The size at metamorphosis was largest in 2007 and smallest in 2006 (mean
SVL of 20 mm and 17.8 mm, respectively). The mean metamorph size was highest
at pond 2 (21.3 mm SVL) and lowest at pond 3 (18 mm SVL). The body size of
metamorphs was slightly larger the later in the summer they emigrated from ponds
(Spearman’s rho = 0.069, P = 0.0001).
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Juveniles metamorphosed out of 4 of the 5 ponds; we captured only one metamorph
in pond 5 in all years (Table 2). Pond 3 had the highest juvenile output of
all of the ponds sampled (95.2% of total coming out of all ponds), but was not the
pond with the highest number of breeding adults captured. Juvenile production was
higher for all ponds in 2006 and 2007 than in 2004 or 2005. Calculating survival
through metamorphosis based on average clutch-size per female (850 eggs; Trauth
et al. 2004) revealed that over 4 years, ponds had a mean larval survival of 1.28%
and a maximum survival of only 6.07% (Table 2).
Discussion
The Wood Frog is one of the most widely distributed amphibian species in
North America, with a range covering the northeastern US, and most of Canada
Figure 2. Size-frequency distribution of snout–vent length (SVL) of adult Wood Frogs
captured at 5 breeding ponds in Missouri during 2004–2007.
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and Alaska (Lannoo 2005). Although large populations can be found in the northern
portion of its range (Berven 2009, Egan and Paton 2004), populations along
the southern and western edges are small and fragmented, which makes them more
susceptible to habitat loss and fragmentation due to altered land use (Muths et al.
2005). Wood Frogs in Missouri have a basic life history similar to that observed in
most other regions across its range; however, because their populations there are
isolated and considered vulnerable, the species is listed as being of conservation
concern (Missouri Natural Heritage Program 2007).
We found that breeding migrations started in late February and ended by the
middle of March each year, typically lasting no more than 2 weeks. Males usually
arrived earlier than females, with the onset of breeding for males among the earliest
reported (7 February) compared to other southern regions (Maryland: 15 February
[Berven 1982], Tennessee: 22 February [Meeks and Nagel 1973], eastern Missouri:
Figure 3. Size-frequency distribution of snout–vent length (SVL) of Wood Frog metamorphs
captured leaving 5 ponds in Missouri during 2004–2007.
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26 February [Guttman et al. 1991]). The onset of breeding is largely determined by
rainfall and increasing spring temperatures; thus, annual variation of environmental
factors in Missouri likely accounts for these differences. Meeks and Nagel (1973)
noted that temperatures that trigger breeding migrations (>5–6 °C) appeared to be
similar across the Wood Frog’s range, suggesting that breeding period varies with
the date at which critical temperatures are reached at each population location.
The breeding-population sizes of Wood Frogs were small at our study sites in Missouri
compared to populations in the central portion of the species’ range. In other
regions, breeding population sizes were >500 adult frogs in most years in Maryland
(Berven 1990), up to 1033 females in Rhode Island (Egan and Paton 2004), and in
some years exceeded 6000 adults in Michigan (Berven 2009). However, we found
only a few males and females in some years and at most just 30 females and 42 males.
The number of breeding adults fluctuated greatly, and in 2004 and 2007, we collected
no females at 2 different ponds. We likely did not detect all Wood Frogs because they
are known to escape from pitfall traps (R.D. Semlitsch, pers. observ.), so the actual
number of adults present may have been higher. However, egg-mass counts at these
ponds in subsequent years and at the other surrounding ponds at DBCA also indicated
low numbers of females (Peterman et al. 2013b). In addition, we found that the number
of adults we captured was negatively correlated with cumulative rainfall during
the breeding period. Although this is counter-intuitive, we suggest that moisture for
terrestrial migration in the spring is not limiting, so more rainfall would unlikely
cause more frogs to breed. Therefore, we posit that more rainfall may create additional
temporary pools (in road ruts and ditches) that draw adults away from the more
permanent wildlife ponds.
We found that adult body size averaged 52.3 mm and 61.3 mm for males and
females, respectively, and their size was very similar to results reported in another
study in eastern Missouri (51.1 mm and 60.3 mm for males and females, respectively;
Guttman et al. 1991). The smallest Wood Frog body sizes were reported
in Canada, averaging 37.7 mm for males and females combined in Manitoba
and Saskachewan (Martof and Humphries 1959) and 47.1 mm and 50.9 mm for
males and females, respectively, in northern Quebec (LeClair et al. 2000). Some
of the largest Wood Frogs were found in the mountains of Virginia (55.3 mm and
64.4 mm for males and females, respectively; Berven 1982) and in the mountains
of Georgia and North Carolina (54.8 mm and 66.8 mm for males and females,
respectively; Martof and Humphries 1959). Thus, the number of females contributing
to reproduction was likely limited rather than the absolute contribution per
female, which is determined primarily by body size (i.e., larger females produce
more eggs; Berven 1990).
Our results showed that the number of metamorphosing juveniles also fluctuated
widely among ponds and years, with most ponds producing no metamorphs,
while 1 pond produced at least 400 metamorphs. Rainfall during the period of
emigration had no apparent correlation with the number of metamorphs captured
at our drift fences. At our sample ponds, survival rate from the egg stage to metamorphosis
averaged 1.28% among years with the most successful pond having
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6.07% survival to metamorphosis in one year. This single pond produced 195–400
metamorphs each year and contributed 95% of all the metamorphs that had the
potential to be recruited into adult breeding populations. Berven (1990) reported
larval survival from Maryland ponds averaged 0.95–4.5% with a maximum
survival rate of 8% in one year. Most ponds at the DBCA are small and nearly
permanent, seldom drying seasonally. These permanent ponds are numerically
dominated by 4 predatory salamander species (Drake et al. 2015, Hocking et al.
2008), including Ambystoma opacum (Gravenhorst) (Marbled Salamander) and
A. annulatum (Cope) (Ringed Salamander). Larvae of salamanders that breed in
the fall likely prey heavily on newly hatched, spring-breeding Wood Frogs. Adult
Notophthalmus viridescens (Rafinesque) (Eastern Newt) are also present in early
spring (R.D. Semlitsch, pers. observ.; Trauth et al. 2004) and may prey heavily on
hatchling Wood Frogs. More-permanent ponds also have a high density and diversity
of invertebrate predators that prey on tadpoles (Shulse et al. 2013). Therefore,
predation and quality of the aquatic habitat in permanent wildlife ponds may be
important for predicting Wood Frog success at our study sites.
We found that the body size of metamorphosing juveniles in our study averaged
18.1 mm and was comparable to the larger metamorphs observed in Virginia.
Berven (1982) found that metamorphosing juveniles were larger in mountain
ponds of Virginia (averaged 17.8, 19.3, and 19.4 mm across 3 years) than in lowland
ponds of Maryland (averaged 14.9, 14.2, and 15.6 mm). Further, the larval
period for tadpoles in Missouri is approximately 98 days and falls in the middle of
development times reported across the species’ range (60–120 days; Martof and
Humphries 1959). Therefore, the metamorphs leaving our ponds appeared to attain
a comparatively large body size in a moderate period of time, both of which
are traits that should favor higher survival in the terrestrial habitat (Berven 1982,
1990; Harper 2007).
We found small population sizes at our 5 study ponds and believe these ponds
were representative of others in the DBCA. Peterman et al. (2013a) found low
numbers (mean = 10 ± 5.12 clutches per pond per year) of Wood Frog egg masses
during 6 years of surveys in all 34 ponds occupied at DBCA. These results indicate
that breeding-population sizes at DBCA are consistently small, a finding in line
with observations from 2 adjacent conservations areas (Peterman et al. 2013b) and
thus suggests this is a general trend at the southwest edge of the species’ range in
Missouri. No data are available from other peripheral Wood Frog populations to
make more quantitative comparisons. It is unclear whether small population size
is due to low production of metamorphosing juveniles and predation in permanent
ponds or low juvenile and adult survival in terrestrial habitat or both. The habitat
at DBCA is high-quality mature forest and very suitable for other species like fossorial
Ringed Salamanders (e.g., Semlitsch et al. 2014); however, rainfall in the
upper mid-western US is relatively low and results in occasional droughts that can
significantly affect survival of the terrestrial stages primarily due to physiological
stress (Harper 2007, Rittenhouse et al. 2009). The ecological drivers of terrestrial
survival warrant future study.
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Our findings highlight the need to develop a management plan to ensure the
long-term persistence of Wood Frogs in Missouri. Although several areas within
Missouri have remnant Wood Frog populations (including conservation areas in the
Riverhills Region east of DBCA and further southwest in the Ozark Highlands of
Missouri and northwestern Arkansas), these areas are disjunct from the major portion
of the species’ range east of the Mississippi River (Fig. 1). Further, although
they were not documented, historical Wood Frog breeding sites were likely in
locations along the bluffs of the Missouri River floodplain that have largely been
converted to agriculture. Thus, to maintain remnant populations in Missouri, we
suggest that further habitat analyses are needed to understand how aquatic pond
habitats and the terrestrial habitat surrounding ponds can be improved to increase
survival in each Wood Frog life-history stage (Semlitsch 2000). The addition of
seasonal ponds that dry each year and reduce the risk of predation by predatory
salamanders seen in most permanent ponds at DBCA may be necessary to increase
production of juveniles. New ponds should be interspersed among existing ponds
that already produce good numbers of egg clutches to promote colonization by
adults (Peterman et al. 2013b). Maintaining adequate terrestrial core habitat of
mature forest surrounding each breeding pond (~300–500-m radius) that also includes
ravines for over-summer habitat would help protect juveniles and adults,
especially in drought years (Harper et al. 2008, Rittenhouse and Semlitsch 2007:fig.
2C, Rittenhouse et al. 2009). Further, considering that low genetic variation has
been documented at 1 of the most-distant conservation areas occupied by Wood
Frogs (Danville Conservation Area ~10–12 km northwest of DBCA; Peterman et
al. 2013a), it seems important to incorporate plans to increase connectivity and
re-establish gene flow across the region and among adjacent conservation areas
inhabited by Wood Frogs. If peripheral populations of species such as Wood Frogs
are to be maintained, then development of effective plans and active management
are likely needed to keep potentially important populations such as these from going
locally extinct.
Acknowledgments
We thank S. Altnether, T. Altnether, C. Conner, J. Earl, E. Harper, D. Hocking, M.
Osbourn, D. Patrick, L. Rehard, T. Rittenhouse, B. Scheffers, J. Sias, and E. Wengert for
building drift fences and checking pitfall traps; T. Anderson for analyses; and J. Briggler
and G. Raeker of the Missouri Department of Conservation for permits and logistical
support. This research was supported by a collaborative grant from the National Science
Foundation DEB 0239943 and from the Department of Defense SERDP grant RC-2155 to
R.D. Semslitsch. Animals were sampled under University of Missouri Animal Care and Use
Protocol 3368.
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Berven, K.A. 2009. Density dependence in the terrestrial stage of Wood Frogs: Evidence
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