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An Investigation of Frog Density in Ponds with Different Structural and Biotic
Characteristics on the Grand Valley State University, Allendale Campus
Introduction
Near the Calder Arts Center on Grand Valley State Universitys’ Allendale Campus there are two
different sized retention ponds (Figure 1). A retention pond helps improve water quality and
prevent flooding by holding large or small pools of water by draining excess water to a different
location. These drains help the pond to maintain a specific water level (Jordan, 2002).
Figure 1. Aerial view of large and small ponds near Calder Arts Center.
Of the two ponds, the surrounding vegetation, air temperature and locations of the ponds are
similar, but the aquatic vegetation, predation, size, and sun exposure are different. The large
pond had less overhead canopy from beech and maple trees than the small pond. The large
pond’s outer bank is mostly composed of rushes, followed by grasses, and then sedges. Rush
species include Eleocharis palustris (creeping spike rush), Scirpus validus (soft- stem bulrush),
and Juncus effuses (soft rush), with creeping spike rush being the most abundant. Iris
pseudacorus (yellow flag iris) and algae such as duckweed was present. More species around the
large pond include Mentha sp. (mint), Asclepias incarnata (swamp milkweed), Phleum pratense
(timothy grass), Typha sp. (cattails), Alisma sp. (water plantains), Solidago sp. (goldenrod), and
Trifolium sp. (clover) (Vendittelli, Von Maur, West and Westerman). There is a Beech-Maple
forest starting about four meters from the bank and surround about one half of the pond. The sun
exposure was great because of the lack of overhead canopy cover. Figure 2 shows the different
vegetation around and in the large pond.
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Figure 2. Vegetation around large pond.
Pdiastrum sp.
Pdiastrum sp.
Iris pseudacorus
Phleum pratense
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Surrounding about three quarters of the small pond there are beech and maple trees, which
provide a large overhead canopy preventing little sun exposure to the pond (Figure 3).The trees
in the area were less than two meters from the water’s edge. The amount of common duckweed
in the small pond was clearly more than that in the large pond.
Figure 3. Vegetation around small pond.
Salix sp.
Acer sp.
Lemnaceae wolffia
.
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The large retention pond has many frogs croaking and several visible frogs poking out of the
water. In the small pond there are not as many frogs visible and much less noise coming from the
area, yet many tadpoles are seen under water. Frog species in the ponds include bullfrogs (Rana
catesbeiana), green frogs (Rana clamitans melanota) and northern spring peepers (Pseudacris
crucifer crucifer) (Harding and Holman, 1992). Images of frogs are shown in Figures 4, 5 and 6.
Figure 4. Bullfrog.
(Rana catesbeiana)
Figure 5. Green frog.
(Rana clamitans melanota)
Figure 6. Northern spring peeper.
(Pseudacris crusifer crucifer)
The largest species of frogs in North America is the bullfrog. They reside in permanent water
that is deep and has cover such as aquatic vegetation per Kim Long in Frogs: A Wildlife
Handbook (1999). Bullfrogs are very territorial, mostly living alone and only meet to fight or
mate during breeding season resembling a wrestling match (Harding and Holman, 1992). They
lay a substantial amount of eggs and attach them to aquatic plants; bullfrog eggs survive
predators because of their bad taste. Adult bullfrogs tend to stay in the water where resources are
available and food source is plentiful. Their overall diet includes smaller frogs, aquatic
hemiptera, adult odonates, bullfrog tadpoles, algae and plant tissue (Werner, Wellborn and
McPeek, 1995). Bullfrog predators include snakes, turtles, fish, birds and mammals (Harding and
Holman, 1992).
Green frogs are semi-terrestrial, where land is available and temporary water is nearby (Werner,
Wellborn and McPeek, 1995). Adults spend most of their time in water where they breed, while
juvenile green frogs venture to wet woodlands (Harding and Holman, 1992). During mating
season they are attracted to shallow, weedy ponds with vegetation along the shores. They also
look for available food supply, moderate temperatures, and protective covering. Males are
territorial, defending prime mating areas by wrestling with other males. A female chooses her
mate based on the territory he is defending. The territory must be desirable for egg laying where
the eggs can be attach to underwater vegetation (Harding and Holman, 1992). Green frogs eat
insects, including spiders, and other frogs. Tadpoles mostly eat algae and small plant tissue
(Werner, Wellborn and McPeek, 1995). Green frog and tadpole predators are fish, snakes, turtles
and small mammals, some leeches and insects (Harding and Holman, 1992).
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Northern spring peepers are a smaller species of frogs, usually found by natural ponds or
temporary pools where there are no fish. Their primary habitat is wooded areas near water
(Harding and Holman, 1992). Northern spring peepers breed in temporary and permanent ponds,
marshes, and ditches (Parris, 2002). Their eggs are generally laid in temporary pools and attach
to underwater vegetation (Harding and Holman, 1992). Peeper tadpoles eat algae and small
organisms in the water. Adult northern spring peepers feed on small insects like beetles, spiders,
and flies (Harding and Holman, 1992). Northern spring peeper predators include fish, insects,
turtles, snakes, birds, small mammals, and other frogs, particularly bullfrogs (Harding and
Holman, 1992).
Predators around the ponds are mostly large northern water snakes, which prey on frogs,
mammals, turtles, and tadpoles by hunting among plants at the water’s edge. They are a
freshwater species and bask in the sun in order to regulate body temperature (Michigan DNR
2010). There were many snakes around the large pond and few around the small pond, most
likely due to the difference in the overhead canopy cover of beech and maple trees surrounding
the two ponds.
There is an apparent difference between the structural and biotic characteristics of the two ponds
near the Calder Arts Center. These characteristics play a role in how frogs chose their habitats
which led us to ask these questions:





Is there a difference in the mean density of all frogs, regardless of species, between the
large and small pond?
Is there a difference in the mean density of all tadpoles, regardless of species, between
the large and small pond?
Is there a difference in the mean density of frogs by species in the large and small pond?
Is there a difference in the mean density of tadpoles by species in the large and small
pond?
Is there a difference in the mean water temperature between the large and small pond?
We expect to find that the small pond will have a greater mean density of frogs and tadpoles,
regardless of species, due to smaller pond size, more vegetation, and less predation. We also
expect to find a greater mean density of frogs and tadpoles by species, due to more vegetation
and less predation. We expect the temperature in the small pond to be greater due to its smaller
size.
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Methods
We collected data over three consecutive days to help answer our questions. We first measured
the volume of the small and large pond. To estimate the volume of each pond, we measured the
length, width, and depth in meters. We also measured the abundance of total frogs, regardless of
species, in both the small and large pond. To do this, we systematically surveyed each pond and
counted all the visible frogs. We also identified each frog by species to later determine species
density. To collect data we divided the small and large pond into six different plots as seen in
figure 7 and figure 8.
Figure 7. Plots of the small pond.
D
E
C
F
A
B
Figure 8. Plots of the large pond.
E
D
C
F
A
B
We also measured total tadpole density, regardless of species, in both the small and large pond
by a series of dip tests. In our tadpole count we considered frogs with tails to be tadpoles. The
dip test consisted of sweeping a net through each plot, deep enough to collect pond sediment. To
keep the dips consistent, we had the same person perform the dip tests for each pond. We
performed two dips in the middle of each plot. After each dip, we counted the tadpoles, recorded
the species and returned them back to the pond.
To calculate frog and tadpole density, we took the total number of frogs and tadpoles and divided
each by the volume of that specific pond. We also measured the water temperature in degrees
Celsius at each pond. Each day temperature was measured in two random plots at two different
times to get an accurate mean water temperature.
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We used a t-Test to determine the statistical significance in total frog density, total tadpole
density, density of frogs and tadpoles by species, and mean water temperature. For a t-Test to be
considered statistically significant the p-value must be less than or equal to 0.05.
Results
The volume of the small pond was 42.3 m3 and the volume of the large pond was 169.2m3 which
is 4 times as large as the small pond.
169.2 𝑚3
42.3 𝑚3
= 4.00 𝑚3
The total frog abundance in both ponds is shown in Table 1. The large pond contained more
frogs but the density of frogs was greater in the small pond (Table 2).
Table 1. Total frog abundance in the small and large ponds.
Sample
Small pond abundance
Large pond abundance
Day 1
24
53
Day 2
24
50
Day 3
33
62
Total
81
165
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Table 2. Total frog density (frogs/m3) in the small and large ponds.
Sample
Small pond density
Large pond density
Day 1
0.57
0.31
Day 2
0.57
0.30
Day 3
0.78
0.37
Mean
0.64
0.33
There was not a significant difference in the mean frog density between the ponds (p-value =
0.052). If more data had been collected we may have found that there was a significant
difference, as the p-value is very close to being significant.
Tadpole abundance is shown in Table 3. We found a higher abundance of tadpoles in the small
pond as well as a larger density of tadpoles in the small pond (Table 4).
Table 3. Total tadpole abundance in the small and large ponds.
Sample
Small pond abundance
Large pond abundance
Day 1
23
2
Day 2
34
4
Day 3
49
0
Total
106
6
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Table 4. Total tadpole density (frogs/m3) in the small and large ponds.
Sample
Small pond density
Large pond density
Day 1
0.54
0.01
Day 2
0.80
0.02
Day 3
1.16
0.00
Mean
0.83
0.01
There was a significant difference in mean total tadpole densities between the ponds (p-value =
0.044).
The northern spring peepers had the greatest abundance in the small pond while the bullfrogs had
the greatest abundance in the large pond (Table 5 and 6).
Table 5. Frog abundance by species in the small pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
1
2
21
Day 2
2
8
14
Day 3
6
12
15
Total
9
22
50
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Table 6. Frog abundance by species in the large pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
25
5
23
Day 2
19
15
16
Day 3
25
27
10
Total
69
47
49
The density of bullfrogs was greater in the large pond and the density of northern spring peepers
was greater in the small pond (Table 7 and 8).
Table 7. Frog density (frogs/m3) by species in the small pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
0.02
0.05
0.50
Day 2
0.05
0.19
0.33
Day 3
0.14
0.28
0.35
Mean
0.07
0.17
0.39
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Table 8. Frog density (frogs/m3) by species in the large pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
0.15
0.03
0.14
Day 2
0.11
0.09
0.09
Day 3
0.15
0.16
0.06
Mean
0.14
0.09
0.10
There was not a significant difference in mean density of bullfrog frogs (p-value = 0.229) or
green-frog frogs (p-value = 0.379) between the two ponds. There was a significant difference in
northern spring peeper frogs (p-value = 0.013).
Abundance of bullfrog tadpoles and green frog tadpoles was greater in both ponds (Table 9 and
10).
Table 9. Tadpole abundance by species in the small pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
18
5
0
Day 2
27
7
0
Day 3
27
22
0
Total
72
34
0
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Table 10. Tadpole abundance by species in the large pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
2
0
0
Day 2
1
3
0
Day 3
0
0
0
Total
3
3
0
Density of bullfrog and green frog tadpoles was greatest in the small pond (Table 11 and 12).
Table 11. Tadpole density (frogs/m3) by species in the small pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
0.43
0.12
0.00
Day 2
0.64
0.17
0.00
Day 3
0.64
0.52
0.00
Mean
0.57
0.27
0.00
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Table 12. Tadpole density (frogs/m3) by species in the large pond.
Sample
Bullfrog
Green frog
Northern spring
peeper
Day 1
0.01
0.00
0.00
Day 2
0.01
0.02
0.00
Day 3
0.00
0.00
0.00
Mean
0.01
0.01
0.00
There was a significant difference in mean density of bullfrog tadpoles (p-value = 0.016), but
there was not a significant difference in mean density of green frog tadpoles (p-value = 0.175).
There was not a significant difference in mean density of peeper tadpoles because we did not
collect any peeper tadpoles.
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Table 13. Water temperatures of small and large pond.
Water Temp
Day 1
Day 2
Day 3
Mean
Small Pond
Large Pond
18.5
18.5
17.6
20.1
14.5
16.2
14.3
17.6
16.1
18.2
14.8
17.1
15.97
17.95
There was not a significant difference in mean temperature between the ponds (p-value = 0.054).
The mean water temperature for the small pond was 15.97°C and 17.95°C for the large pond.
The standard deviation for the small pond was 1.75°C and 1.33°C for the large pond. The range
for the small pond was 4.20°C and 3.90°C for the large pond.
Conclusion
By conducting statistical tests, we can support only some of our predictions. These are supported
by looking at the structural and biotic characteristics of the small and large ponds. We found a
greater mean density of total frogs in the small pond as seen in table 2. We believe this is due to
the shallow depth of the pond, the numerous amounts of aquatic vegetation, and lack of predators
seen around the pond.
We found that there was a significant difference in mean total tadpole densities between the
ponds, regardless of species. The small pond had a higher density of tadpoles compared to the
large pond. Tadpoles prefer areas where there is a great amount of aquatic vegetation available,
for their food source and protection from predators (Harding, 1992).
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We expected to find a greater mean density of bullfrogs, green frogs and northern spring peepers
in the small pond and our data partially supported this. In the small pond there was a greater
mean density of northern spring peepers (Table 7). There was a significant difference in northern
spring peepers between the two ponds because the large pond has a greater mean density of
bullfrogs which eat smaller species of frogs (Werner, et al. 1995). This would force the northern
spring peepers to live in the small pond where there was not as large of a density of bullfrog
predators
We also found a greater mean density of tadpoles in the small pond specifically with bullfrog and
green frog tadpoles as seen in table 4. We did not see any northern spring peeper tadpoles so we
were unable to perform any statistical tests on their density. We think that there is a higher mean
density of total tadpoles in the small pond based on greater vegetation in the water. As stated by
Harding (1992) eggs are attached to underwater vegetation and the more vegetation seen the
more tadpoles we expect to find. According to the Michigan DNR, most Michigan species of
frogs breed and lay their eggs in smaller ponds because of the lack of predators, which also leads
to a greater mean density of tadpoles in the small pond.
We expected to find a greater mean temperature in the small pond, however the data did not
support this. As seen in table 13, the water temperatures were about the same therefore we
cannot conclude that this affects densities of frogs and tadpoles. Canopy cover and pond size
influence water temperature. The large pond receives more sunlight because there is less canopy
cover but because it has a large volume, it takes longer to warm up. The small pond receives less
sunlight due to greater canopy cover, creating shade, but it has a smaller volume so it can warm
up in a shorter period of time.
From our observations, we came up with a few new questions that could be investigated. We
found new structural and biotic factors that could have been investigated further to see how they
affect the density of frogs in the small and large pond. One structural characteristic that could
have been investigated further was the pond sediment. A biotic factor we could have investigated
further is competition. Does competition affect whether frogs will stay in the small or large pond
and further affect frog density? Lastly, we encountered frog predators while collecting data.
There are more predators in the large pond versus the small pond. We wonder if predators affect
the frog density in the small and large pond. We also wondered about abiotic factors such as air
temperature ranges that influence frogs to be out of the water or in the water affecting frog
density.
If we were to perform this study again, we would do some things differently. We would count
frogs we see and record the number of each species to see if there is an abundance of them in
specific plots. We also would strategically walk around several times instead of just once each
day to obtain a larger sample size, reducing bias. We could also try collect data over a longer
period of time taking into account different temperature. We also wondered if light intensity
affected the density of frogs and tadpoles. We also may have tested the pH of the ponds to see
which pH range creates a suitable habitat for frogs and tadpoles. Another investigation that could
be performed would be to observe the frogs’ behavior in both ponds and why the behavior is
different in each pond to see if this relates to the density differences in the ponds.
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References
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ml
Harding, James H., and J. Alan Holman. Michigan frogs, toads, and salamanders: a field guide
and pocket reference. East Lansing, MI: Cooperative Extension Service, Michigan State
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bullfrogs and green frogs: Implications for Interspecific predation and competition.
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