Durango Nature Studies
Amphibian population estimates and
ecosystem assessment on the Durango
Nature Studies property
Introduction
Durango Nature Studies (DNS) has been a safe habitat for wild animals for
as long as 18 years, and was founded in 1994. Located in Colorado, about 13
miles from the town of Durango, DNS is a 140 acre piece of land that has been
set aside as a home for many species native to Colorado. Some of these species
include leopard frogs (Rana
pipiens), mountain lions, horny toads, mule deer, and Great Blue Herons.
Many species of plants and trees grow on the DNS property, and create a diverse
environment of vegetation. Down a winding trail below the entrance to the
property, lies a small pond stocked with bluegill, where bullfrogs (Rana
catesbeiana) have been spotted in recent years.
A few steps away the
Florida River cuts through the property carrying many species of
macro-invertebrates, and fish, and providing water for the area. “DNS is a
non-profit organization that has brought hands-on nature, science, and
environmental education to the Four Corners, in the classroom.”(Durango 2012).
The land is open to schools and students of all ages wishing to learn about
nature, while being in nature.
Leopard frogs are small
green or brown frogs with dark spots. Leopard frogs are a state species of
special concern and there has been recent petition to list them as endangered,
as they are becoming very rare in Colorado. At this particular pond, bullfrogs
(exceptionally large green or brown frogs) have been spotted on site. Because
bullfrogs are large, aggressive, generalist predators it is possible that they
are eating the already threatened leopard frogs. Bullfrogs, in the state of
Colorado are an invasive species. This is a species inhabiting an area they are
not originally from, either brought in by people or other means of
transportation, existing in an area and disrupting the balance of the ecosystem
by out-competing native species for resources. These Rana catesbeiana are
drastically changing the DNS pond and are throwing it out of rhythm by devouring
the considerably smaller leopard frogs, which, when alive, eat small insects
that the bullfrogs do not. The bullfrogs are decreasing the number of leopard
frogs exponentially, and are creating an unstable environment in the pond at
DNS.
Natural
History
Leopard frogs start their lives out as eggs, close to 20,000 eggs can be
laid by one adult frog. They then hatch and turn to tadpoles (fish-like, young
frogs, long bodies with a flat tail) after 5-7 days of being an egg. After 12-16
weeks the small frogs have turned into froglets (half matured frog with small
arms and legs, still with a tail), and then on to adults where they will eat
small insects and grow to be between 100-300 mm long. To survive, Rana pipiens
need water and food, the same as most animals. However they need water to swim
in to keep their skin moist, to keep the frogs from drying out and dying. These
frogs need non-polluted water, as ponds, lakes, or streams with many pollutants
may stunt the growth of, or kill the threatened leopard frog.
Bullfrogs like leopard frogs start out their lives as eggs. Up to 25,000
eggs can be laid by one adult bullfrog. After a close to 5 days, the eggs will
hatch and let out small tadpoles. These tadpoles will turn into what is known as
froglets after they have spent time eating specifically water and plants. It may
take up to 2-3 years before a bullfrog is fully matured, however along this
stage, the frog will grow back and front legs, and its long tail will start to
shrink as it matures more. Rana catesbeiana will eat anything from snakes and
(leopard frogs) to small rats and mice, as well as other bullfrogs, (almost
anything they can fit in their mouths.) Rana catesbeiana are very large, they
grow on average to be close to six inches long, however, many have surpassed
this rate and have gotten as big as 12 inches or larger. Using this information,
it was decided that the DNS pond needed a change, therefore, tests were
conducted to learn the situation at the Pond, and to eventually help the
threatened leopard frogs inhabiting that
area.
Methods
and Materials:
To estimate the number of Rana pipiens and Rana catesbeiana inhabiting
the DNS pond and river, three field techniques were used; pitfall traps,
mark-recapture, and visual encounter surveys. Four 5-gallon pitfall traps were
set up around the pond and river, and checked daily (for four days) for frogs
trapped inside that could be marked and counted. Visual encounter surveys were
performed for four days around the pond. By walking around the DNS pond, frogs
were spotted and counted to find an estimate of the number of species living in
the area. A mark session was conducted for an hour, where leopard frogs were
caught and marked using a harmless, temporary injection so the frogs could be
seen as already caught and counted, or not caught and counted, during the next
recapture session. After the one hour marking session was completed, a 1 hour
recapture session took place in the same area. During this time, more frogs
would be caught and counted (but not marked) or counted as already marked and
counted. This would give an idea as to the number of species there are living in
the ecosystem.
Water chemistry tests were taken from the DNS pond after the hour long
capture and mark sessions. The pond water was tested for nitrates, phosphates,
dissolved oxygen, pH, and the temperature. These tests were conducted through
obtaining the DNS pond water and adding pills, drops of chemicals, or using a
thermometer to test the DNS water in a controlled environment as to not affect
the stability of the Pond (except for the temperature, it was tested straight
from the pond as to not affect the temperature of the water, and get incorrect
results.) Then, using a colored code to estimate the concentrations of the water
chemistry. Finally, macro-invertebrates (Invertebrates living in aquatic
ecosystems that are large enough to be seen without the use of a microscope)
were captured from the Florida River, and the DNS pond. Macro-invertebrates
would give an approximation of diversity (Variation or difference) and pollution
amounts in the two bodies of water. In the Florida River, the kick method (a
method used to capture macro-invertebrates by kicking loose rocks and sand from
upstream into a large net, causing macro-invertebrates to float down the river
into captivity) was performed to capture macro-invertebrates living in this
waterway. The dip method (a method used to capture macro-invertebrates in a
non-moving body of water, by dipping a large net into the rocks and sand at the
bottom of the lake or pond) was used to capture macro-invertebrates in the DNS
pond. The Florida River and DNS pond were thoroughly tested in many ways, to
find information on diversity, species number, and water
chemistry.
Results:
Based on the Shannon-Weiner index, it was determined that the diversity
index of the pond was 0.99 in 2011 and 1.2 in 2012.
The biodiversity for the Florida River was 1.03 in 2011 and in 2012 was
0.78. The pH in the DNS Pond and the Florida River was alkaline (non-acidic or
basic). The nitrates (nitrogen) and phosphates (phosphorus, it helps plants to
grow) was high in both the Pond and River. In the DNS Pond, the amount of
dissolved oxygen (oxygen in water) was low. However in the Florida River, the
dissolved oxygen levels were normal. Based on frog recapture data from the pond,
the estimated leopard frog population is 15. The estimated bullfrog population
in the DNS pond is 1.
Conclusion
& Discussion
Based on population estimates, it can be concluded that the amount of
leopard frogs to bullfrogs is very high. There is a larger amount of Rana
pipiens than Rana catesbeiana in the DNS pond. Based on the fact that bullfrogs
eat leopard frogs, there is a possibility that leopard frog population could
decrease exponentially as they may be eaten by bullfrogs inhabiting the pond.
The DNS pond is estimated to be close to 200 square feet, this means that the
pond can hold up to 550 leopard frogs. However, populations of fewer than 60
leopard frogs are less likely to
survive in a drought resistant environment. If the population of leopard frogs
in an area is more than 60, the frogs are more likely to survive in the long
term. Considering this, the population of leopard must be increased or the
population may completely die out of the DNS Pond.
An algal bloom is caused by high levels of phosphates and nitrates in a
body of water that can cause a spike in plant growth.
Water chemistry tests
suggest that the pond is at risk for an algal bloom based on the fact that the
DNS pond has high levels of nitrates and phosphates. When an algal bloom is
caused, it affects the body of water a great deal. Algal blooms can cause a
drastic surge in plant growth; this causes plants living near the bottom of the
body of water to die due to lack of sunlight. The increased rate in dead plants
causes an increase in decomposers; these decomposers use oxygen and immensely
lower the dissolved oxygen amounts in the water which eventually causes every
living organism to die due to lack of dissolved oxygen. Considering that algal
blooms are caused by great increases in nitrates and phosphates, and these can
be increased by manure entering the water, also that both the Florida River and
DNS Pond tested positive for coliform(waste from animals), it can be concluded
that the high amounts of nitrates and phosphates may be caused by cow, (and
other feral animals) dung entering the water. The Florida River is fed by Lemon
Reservoir, during the summer and fall months, the reservoir can empty partially
of water, during this time herds of cows move in to graze, and leave behind
excrement which, when the water level rises again in the spring, gets washed
down into rivers and ponds filled by the reservoir. Based on this evidence, the
high levels of nitrates and phosphates can be reduced by decreasing the number
of animals pooping in Lemon Reservoir and any body of water.
By doing this, coliform would not test positive, the high levels of
nitrates and phosphates would decrease exponentially in the DNS Pond, Florida
River, and other bodies of water waste has stopped being dumped into, which
would ultimately destroy plant growth surges, and decrease the chance for an
algal bloom, but help keep a healthy amount of plant growth in the bodies of
water.
Improvements to the amphibian study can be made for the capture and
recapture hours. It was brought to attention that during these times, scientists
were left without a specific goal in mind. There were young scientists wandering
because a specific job was not given. Frog capture and recapture was successful
during the time periods laid out, however only some were included in the act of
frog catching. Also, the pitfall traps set up around the pond and river were
unsuccessful, as in they did not succeed in capturing any amphibians. In the
future, more traps should be set to hopefully increase the frogs caught, and to
include more data to be used as evidence in making the DNS area more successful
in increasing the population of leopard frogs, and decreasing the amount of
bullfrogs. This study that has been conducted was very successful; much was
learned from the results found, and the DNS Pond and Florida River will most
likely benefit from these tests if they are used correctly. Based on the fact
that bullfrogs inhabiting the DNS Pond eat leopard frogs living in the same
area, the leopard frogs would benefit greatly from the bullfrogs being removed
for the ecosystem. This would decrease the amount of frogs dying each day, and
would create a more stable, unchanging environment for the DNS Pond. The leopard
frog population would be stabilized as well as the amounts of small bugs eaten
by the Rana pipiens. Bullfrogs are an invasive species; therefore they do not
belong in a habitat they have invaded. It throws off the balance of every
organism when an invasive species moves into the area. Removing all Rana
catesbeiana from the area would be the most direct, successful way of improving
the stability of the DNS pond amphibian
population.
ecosystem assessment on the Durango
Nature Studies property
Introduction
Durango Nature Studies (DNS) has been a safe habitat for wild animals for
as long as 18 years, and was founded in 1994. Located in Colorado, about 13
miles from the town of Durango, DNS is a 140 acre piece of land that has been
set aside as a home for many species native to Colorado. Some of these species
include leopard frogs (Rana
pipiens), mountain lions, horny toads, mule deer, and Great Blue Herons.
Many species of plants and trees grow on the DNS property, and create a diverse
environment of vegetation. Down a winding trail below the entrance to the
property, lies a small pond stocked with bluegill, where bullfrogs (Rana
catesbeiana) have been spotted in recent years.
A few steps away the
Florida River cuts through the property carrying many species of
macro-invertebrates, and fish, and providing water for the area. “DNS is a
non-profit organization that has brought hands-on nature, science, and
environmental education to the Four Corners, in the classroom.”(Durango 2012).
The land is open to schools and students of all ages wishing to learn about
nature, while being in nature.
Leopard frogs are small
green or brown frogs with dark spots. Leopard frogs are a state species of
special concern and there has been recent petition to list them as endangered,
as they are becoming very rare in Colorado. At this particular pond, bullfrogs
(exceptionally large green or brown frogs) have been spotted on site. Because
bullfrogs are large, aggressive, generalist predators it is possible that they
are eating the already threatened leopard frogs. Bullfrogs, in the state of
Colorado are an invasive species. This is a species inhabiting an area they are
not originally from, either brought in by people or other means of
transportation, existing in an area and disrupting the balance of the ecosystem
by out-competing native species for resources. These Rana catesbeiana are
drastically changing the DNS pond and are throwing it out of rhythm by devouring
the considerably smaller leopard frogs, which, when alive, eat small insects
that the bullfrogs do not. The bullfrogs are decreasing the number of leopard
frogs exponentially, and are creating an unstable environment in the pond at
DNS.
Natural
History
Leopard frogs start their lives out as eggs, close to 20,000 eggs can be
laid by one adult frog. They then hatch and turn to tadpoles (fish-like, young
frogs, long bodies with a flat tail) after 5-7 days of being an egg. After 12-16
weeks the small frogs have turned into froglets (half matured frog with small
arms and legs, still with a tail), and then on to adults where they will eat
small insects and grow to be between 100-300 mm long. To survive, Rana pipiens
need water and food, the same as most animals. However they need water to swim
in to keep their skin moist, to keep the frogs from drying out and dying. These
frogs need non-polluted water, as ponds, lakes, or streams with many pollutants
may stunt the growth of, or kill the threatened leopard frog.
Bullfrogs like leopard frogs start out their lives as eggs. Up to 25,000
eggs can be laid by one adult bullfrog. After a close to 5 days, the eggs will
hatch and let out small tadpoles. These tadpoles will turn into what is known as
froglets after they have spent time eating specifically water and plants. It may
take up to 2-3 years before a bullfrog is fully matured, however along this
stage, the frog will grow back and front legs, and its long tail will start to
shrink as it matures more. Rana catesbeiana will eat anything from snakes and
(leopard frogs) to small rats and mice, as well as other bullfrogs, (almost
anything they can fit in their mouths.) Rana catesbeiana are very large, they
grow on average to be close to six inches long, however, many have surpassed
this rate and have gotten as big as 12 inches or larger. Using this information,
it was decided that the DNS pond needed a change, therefore, tests were
conducted to learn the situation at the Pond, and to eventually help the
threatened leopard frogs inhabiting that
area.
Methods
and Materials:
To estimate the number of Rana pipiens and Rana catesbeiana inhabiting
the DNS pond and river, three field techniques were used; pitfall traps,
mark-recapture, and visual encounter surveys. Four 5-gallon pitfall traps were
set up around the pond and river, and checked daily (for four days) for frogs
trapped inside that could be marked and counted. Visual encounter surveys were
performed for four days around the pond. By walking around the DNS pond, frogs
were spotted and counted to find an estimate of the number of species living in
the area. A mark session was conducted for an hour, where leopard frogs were
caught and marked using a harmless, temporary injection so the frogs could be
seen as already caught and counted, or not caught and counted, during the next
recapture session. After the one hour marking session was completed, a 1 hour
recapture session took place in the same area. During this time, more frogs
would be caught and counted (but not marked) or counted as already marked and
counted. This would give an idea as to the number of species there are living in
the ecosystem.
Water chemistry tests were taken from the DNS pond after the hour long
capture and mark sessions. The pond water was tested for nitrates, phosphates,
dissolved oxygen, pH, and the temperature. These tests were conducted through
obtaining the DNS pond water and adding pills, drops of chemicals, or using a
thermometer to test the DNS water in a controlled environment as to not affect
the stability of the Pond (except for the temperature, it was tested straight
from the pond as to not affect the temperature of the water, and get incorrect
results.) Then, using a colored code to estimate the concentrations of the water
chemistry. Finally, macro-invertebrates (Invertebrates living in aquatic
ecosystems that are large enough to be seen without the use of a microscope)
were captured from the Florida River, and the DNS pond. Macro-invertebrates
would give an approximation of diversity (Variation or difference) and pollution
amounts in the two bodies of water. In the Florida River, the kick method (a
method used to capture macro-invertebrates by kicking loose rocks and sand from
upstream into a large net, causing macro-invertebrates to float down the river
into captivity) was performed to capture macro-invertebrates living in this
waterway. The dip method (a method used to capture macro-invertebrates in a
non-moving body of water, by dipping a large net into the rocks and sand at the
bottom of the lake or pond) was used to capture macro-invertebrates in the DNS
pond. The Florida River and DNS pond were thoroughly tested in many ways, to
find information on diversity, species number, and water
chemistry.
Results:
Based on the Shannon-Weiner index, it was determined that the diversity
index of the pond was 0.99 in 2011 and 1.2 in 2012.
The biodiversity for the Florida River was 1.03 in 2011 and in 2012 was
0.78. The pH in the DNS Pond and the Florida River was alkaline (non-acidic or
basic). The nitrates (nitrogen) and phosphates (phosphorus, it helps plants to
grow) was high in both the Pond and River. In the DNS Pond, the amount of
dissolved oxygen (oxygen in water) was low. However in the Florida River, the
dissolved oxygen levels were normal. Based on frog recapture data from the pond,
the estimated leopard frog population is 15. The estimated bullfrog population
in the DNS pond is 1.
Conclusion
& Discussion
Based on population estimates, it can be concluded that the amount of
leopard frogs to bullfrogs is very high. There is a larger amount of Rana
pipiens than Rana catesbeiana in the DNS pond. Based on the fact that bullfrogs
eat leopard frogs, there is a possibility that leopard frog population could
decrease exponentially as they may be eaten by bullfrogs inhabiting the pond.
The DNS pond is estimated to be close to 200 square feet, this means that the
pond can hold up to 550 leopard frogs. However, populations of fewer than 60
leopard frogs are less likely to
survive in a drought resistant environment. If the population of leopard frogs
in an area is more than 60, the frogs are more likely to survive in the long
term. Considering this, the population of leopard must be increased or the
population may completely die out of the DNS Pond.
An algal bloom is caused by high levels of phosphates and nitrates in a
body of water that can cause a spike in plant growth.
Water chemistry tests
suggest that the pond is at risk for an algal bloom based on the fact that the
DNS pond has high levels of nitrates and phosphates. When an algal bloom is
caused, it affects the body of water a great deal. Algal blooms can cause a
drastic surge in plant growth; this causes plants living near the bottom of the
body of water to die due to lack of sunlight. The increased rate in dead plants
causes an increase in decomposers; these decomposers use oxygen and immensely
lower the dissolved oxygen amounts in the water which eventually causes every
living organism to die due to lack of dissolved oxygen. Considering that algal
blooms are caused by great increases in nitrates and phosphates, and these can
be increased by manure entering the water, also that both the Florida River and
DNS Pond tested positive for coliform(waste from animals), it can be concluded
that the high amounts of nitrates and phosphates may be caused by cow, (and
other feral animals) dung entering the water. The Florida River is fed by Lemon
Reservoir, during the summer and fall months, the reservoir can empty partially
of water, during this time herds of cows move in to graze, and leave behind
excrement which, when the water level rises again in the spring, gets washed
down into rivers and ponds filled by the reservoir. Based on this evidence, the
high levels of nitrates and phosphates can be reduced by decreasing the number
of animals pooping in Lemon Reservoir and any body of water.
By doing this, coliform would not test positive, the high levels of
nitrates and phosphates would decrease exponentially in the DNS Pond, Florida
River, and other bodies of water waste has stopped being dumped into, which
would ultimately destroy plant growth surges, and decrease the chance for an
algal bloom, but help keep a healthy amount of plant growth in the bodies of
water.
Improvements to the amphibian study can be made for the capture and
recapture hours. It was brought to attention that during these times, scientists
were left without a specific goal in mind. There were young scientists wandering
because a specific job was not given. Frog capture and recapture was successful
during the time periods laid out, however only some were included in the act of
frog catching. Also, the pitfall traps set up around the pond and river were
unsuccessful, as in they did not succeed in capturing any amphibians. In the
future, more traps should be set to hopefully increase the frogs caught, and to
include more data to be used as evidence in making the DNS area more successful
in increasing the population of leopard frogs, and decreasing the amount of
bullfrogs. This study that has been conducted was very successful; much was
learned from the results found, and the DNS Pond and Florida River will most
likely benefit from these tests if they are used correctly. Based on the fact
that bullfrogs inhabiting the DNS Pond eat leopard frogs living in the same
area, the leopard frogs would benefit greatly from the bullfrogs being removed
for the ecosystem. This would decrease the amount of frogs dying each day, and
would create a more stable, unchanging environment for the DNS Pond. The leopard
frog population would be stabilized as well as the amounts of small bugs eaten
by the Rana pipiens. Bullfrogs are an invasive species; therefore they do not
belong in a habitat they have invaded. It throws off the balance of every
organism when an invasive species moves into the area. Removing all Rana
catesbeiana from the area would be the most direct, successful way of improving
the stability of the DNS pond amphibian
population.