Amphibian population estimates and ecosystem assessment on the Durango Nature Studies property
Durango Nature Studies is a piece of property just south of Durango, CO. It is a piece of property around 140 acres in size and it has a hiking trail, pond, and the Florida River is running through it. It is a nature center located at the bottom of Bondad hill just outside of Durango, Colorado. Invasive species are a threat to the global environment because they out compete natives species for resources. The Rana catesbeiana is a good example of an invasive species because it isn’t from south-western Colorado and it is s a generalist predator. They are natively from the eastern part of the US and they were first introduced to the area because of the wildlife preserve introducing more game species. When they were first introduced they weren’t as much of a problem as they have come to be. At this point the Rana catesbeiana eat the macroinvertebrates and don’t leave much of anything for the Rana pipiens to eat. They will eat anything that they can fit in their mouth, meaning that they will eat things like Rana pipiens, macroinvertebrates, mice, and many other species. Another species that could negatively affect the Rana pipiens would be the bluegill fish. The bluegill fish, like the Rana catesbeiana, eats the macroinvertebrates that the Rana pipiens needs to survive. The bluegill fish mainly lives in standing water like a lake or a pond, they tend to avoid rivers with a lot of moving water. Currently in Colorado the Rana pipiens population has decreased from previous years, meaning that they have become a species of concern with wildlife biologists.
The Rana pipiens will eat almost any kind of insect, but they will also eat much more than just an insect. They will also eat things such as spiders, snails, and frogs. Some research suggests that they chose what to eat based on availability, not the type of food. It is suggested that staples in their diet are beetles. In 1967 it was determined that the Rana pipiens diet also consists of vegetable matter, around 10 – 20%. For the Rana pipiens to survive it needs clean water and an abundance of food, which is difficult because the Rana Catesbeiana eats most of its food. When the Rana pipiens is born it is first an egg, but it then hatches into an aquatic larval stage. It then goes into a semi-terrestrial juvenile stage and finally into the adult stage, which has the widest variety for its diet and has the most difficulty surviving.
The Rana catesbeiana is different from the Rana pipiens in the fact that it will eat anything that it can put into its mouth. In 1913 stomach content studies suggest that the bullfrog preys on any animal it can overpower and stuff down its throat. They have been found with animals such as rodents, small turtles, snakes, frogs (bullfrogs included), birds, and even a bat. All of these types of food suggest that the Rana catesbeiana will eat anything that it sees. The Rana catesbeiana has also been known to eat insects and macroinvertebrates, so it competes with the Rana pipiens for food. It is unique in the fact that it is the only Rana that includes a large percentage of aquatic animals such as fish, tadpoles, planorbid snails, and dytiscid beetles. The Rana catesbeiana is native to Eastern Northern America and it was first introduced by the Division of Wildlife. The Rana catesbeianas lifecycle is very similar to the Rana Pipiens lifecycle because it also starts as an egg and turns into an aquatic larvae. After that it goes into a semi-terrestrial juvenile stage and finally turns into an adult. As with many amphibians there is a low percentage that survives from being an egg to an adult.
When the biology class of 2015 went to Durango Nature Studies they used multiple tools to check for populations in the area of both Rana pipiens and Rana catesbeiana. One of the methods they used was using pitfall traps. There were four pitfall traps set up in total, two near the pond and two near the river. As they checked the pitfall traps they also conducted visual encounter surveys every day. To do this they walked around the pond and up the river to see how many frogs they saw. On the third day while they were conducting a visual encounter survey they also tagged the frogs that they saw with pink elastomer in the right hind leg. They did this so that the next day when they went out they would be able to tell if they recaptured frogs or if they were new frogs that were captured and released. After they finished the visual encounter survey they started taking water chemistry tests. They tested the Nitrates, Phosphates, Dissolved Oxygen, and the pH level. The Dissolved Oxygen test was deemed incorrect so they aren’t going to use this test for the final tests. As for the pH level test, Nitrates, and Phosphates they had to collect water samples and test them once they got back to the school. These tests were conducted in both the pond and in the river so that they can estimate the pollution in the river and pond. There were also people collecting macroinvertebrates in the river and in the pond. These were collected as another way to see the pollution in the area. This helped see the pollution because some macroinvertebrates, like stoneflies, have a much lower pollution tolerance than something like the mayfly.
While at Durango Nature Studies the class of Animas High School conducted many tests, some of which were pH levels, Nitrate Levels, Dissolved Oxygen, Phosphate Levels, and Coliform. The Nitrate Levels in both the pond and in the river were above average, but substantially below the dangerous levels. On the other hand there are the Phosphate levels, which are substantially higher than usual. There was coliform in both the pond and in the river. The dissolved oxygen was at normal levels for the river, but it was low for the pond. The pH levels were high, meaning that it the water is acidic. In the pond the number of macroinvertebrates has decreased dramatically since last year, leading the thought that the water quality is decreasing rapidly. This could possibly be because of the water quality decreasing between this year and last year, or possibly because it is getting more acidic. As for the river the case is the complete opposite. The macroinvertebrate population has increased by almost 25%. This could be because of the headwaters of the river becoming healthier and in turn making the lower area of the river healthier.
An algal bloom is when water has a low dissolved oxygen level, meaning that the pond is at risk for an algal bloom. What an algal bloom does is it takes things from the water that organisms need to survive, such as oxygen. It starts when there is a low oxygen level and it then takes even more oxygen from the water and this causes fish and other organisms that live in the water to die due to a lack of oxygen. Other data, such as nitrate levels, mean that there are mammal feces in the water. In the Florida River upstream there are cows and that’s where the feces come from for the river. For the pond feces could possibly be coming from animals like deer, bears, or other small rodents. Amphibian populations need certain conditions to survive, some of which are clean water and an abundance of food. It is easy for the Rana catesbeiana populations to get out of control because they can eat any type of food that they can fit in their mouth, making it an invasive species that is hard to control. Amphibian populations in general are a very delicate thing because they require very specific things to live. They need to have clean water and a healthy environment with plenty of food. Water quality is a determining factor in whether there is a healthy ecosystem because everything uses it. Many things go into determining the quality of water, some of which are animals in the area, the species living in the water, and the environment around the water. Some things like the sunlight level and even the organisms within the dirt affect the quality of the water. Although it may not be a large impact on the environment it is still an impact and it can severely affect the environment if one of these things were to change suddenly without warning. Some of the ways that an algal bloom could be prevented within the pond would be to possibly introduce herbivorous fish to keep the algae levels in check. Avoiding dumping non-essential items into the pond, such as fertilizers which has high levels of nitrogen in it, will also keep the algae from growing. One last way to prevent an algal bloom would be to use natural algae preventatives that can be found at stores. The methods used by Animas High School were the best methods to estimate the population of Rana Pipiens around the pond, and therefor need no improvement. As for the pond being managed for the Rana Pipiens, there could be a better use of aquatic plants that will take nitrates and phosphates out of the water
Bibliography
Northern Leopard Frog. Rep. EPA, n.d. Web. 10 Oct. 2012. http://www.epa.gov/region1/ge/thesite/restofriver/reports/final_era/B%20-%20Focus%20Species%20Profiles/EcoRiskProfile_leopard_frog.pdf
"Bullfrog." Wikipedia. Wikimedia Foundation, 10 Nov. 2012. Web. 10 Oct. 2012. http://en.wikipedia.org/wiki/Bullfrog