Species Management Plan:
Species Management Plan for Rana pipiens and Rana catesbeiana on the Durango Nature Studies Nature Center Property
Lacey Meek and Helen Thomson
Durango, CO
2011
Field Condition Form: Helen Thomson
Durango Nature Studies (DNS) would like to manage their 140 acre property in order to eliminate the invasive bullfrog (Rana catesbeina) population and promote the northern leopard frog (Rana pipiens) population (Figure 1). Bullfrogs are considered one of the world’s most invasive species, and if left unmanaged have potential to out compete native amphibian species such as the northern leopard frog (Spitzen, 2010). Bullfrogs were first spotted on the DNS property three years ago. The goal is to completely eliminate the bullfrogs in order to maintain native biodiversity.
Throughout the year, DNS is host to many programs including: summer programs, school programs, field camps, river days, various workshops, hikes, celebrations and trainings for both kids and adults. Research and interactions with the land is a primary focus for many of these programs and activities, therefore maintenance of quality native ecosystems is a high priority for DNS.
The sophomore class from Animas High School recently went out on the DNS property to conduct field research including water quality tests, wildlife inventory, and amphibian visual encounter surveys. This field research was done in order to assess habitat quality and estimate frog populations on the property.
Durango Nature Studies has set aside $2,000 for promoting the northern leopard frog population and decreasing the bullfrog population. Work on this can be carried out anywhere on the property where these frogs are found as long as it does not interfere with other research on the property.
Plan Development: Helen Thomson
The northern leopard frog is native to North America. Northern leopard frogs need a wide range of habitats and a landscape pattern of habitats that are close together. The breeding habitat for the leopard frog is a semi-permanent pond that is free of predaceous fish, has warm water and a moderate amount of vegetation. As tadpoles the leopard frogs can live in a shallow body of water that has no predaceous fish and no overhead canopy. As the tadpoles mature they migrate to a larger body of water to feed (Smith and Keinath, 2004). Their diet is mainly made up of insects including: beetles, moths and butterflies larvae, grasshoppers, crickets, bees, and ants. They also have been known to eat spiders, snails, frogs and plant matter (Northern, 2011). In the summer they feed in grassy areas but come fall they migrate to a place to overwinter, which is usually a stream or lake where they can hibernate under water where there is enough dissolved oxygen present in the water (Smith and Keinath, 2004).
Bullfrogs need a permanent body of water to live in. It needs to be highly vegetated, deep, warm, and have nutrient rich water. Although bullfrogs can be found in many bodies of water including lakes, rivers and streams, they prefer ponds (Rana, 2009). The diet of a bullfrog consists of: crayfish, insects, worms, fish eggs, frogs, sometimes even their own young, and aquatic plants (Bruening, 2002).
The bullfrog is native to eastern North America but it has since spread throughout the United States especially in the West, as well as British Columbia, South America, Europe and Asia (Figure 2) (Introduced, 2008). Unlike many native amphibians, the bullfrogs are not affected by the presence of alien fish species and in western North America they have no natural predators, which is one reason they are so invasive (Roach, 2004). Another reason that bullfrogs are invasive is because they are able to thrive in many places including man made or modified bodies of water (Bruening, 2002). They are also very mobile and have a large reproductive capacity (Witmer and Snow, 2010). Depending on the size and maturity of a female, she lays approximately 20,000 eggs (Roach, 2004) compared to 2,000 - 6,000 of the northern leopard frog (Northern, 2011), which results in rapid population growth of bullfrogs. The bullfrogs can also travel up to 9.5 km in a few weeks to colonize a new place (Roach, 2004).
The DNS property (Nature Canter) is located between Farmington, New Mexico and Durango, Colorado. Durango Nature Studies manages 140 acres of land, which they acquired in 1998 but is under conservation easement, a voluntary agreement that allows a landowner to limit the type and amount of development that is done on the property. This land is home to many different habitats including riparian, meadows, oak woodlands, pinyon-juniper forests and desert arroyos. The Florida River runs through their property, and a small pond is located in the NW quadrant of the property that is home to much of the frog population (Durango, 2010).
Animas High School recently conducted field research including water quality tests, wildlife inventory, and amphibian visual encounter surveys to assess habitat quality and estimate frog populations of the ecosystem on the DNS property. They were able to make conclusions based upon the data they collected about the quality and health of the water and ecosystem. They first tested the pond and river for pH levels and found that both the river and the pond had a pH of 8.5 which is considered alkaline (Figure 3), meaning the water is not acidic, this pH is adequate for amphibian species (Care, 2010). Waters were tested for nitrate and results of the data were that the pond had approximately 1ppm and the river had approximately 2ppm. This is a low nitrate level that also suggests that the water is unpolluted and suitable for amphibians (Nitrate, 2010). When tested for dissolved oxygen in the water they found that the river had 8.5 mg/L and the pond had 6.5 mg/L. These numbers are moderate to high and express that the water in both the pond and river is able to support most pond animals (Dissolved, 2011). Levels of phosphate were also tested for in the water and the data concluded 2 ppm for the pond and 1 ppm for the river. These numbers were high and may be the cause of all the plant growth, especially in the pond. Excess phosphorus causes extensive algae growth which can result in an algal blooms and these can cause unstable levels of dissolved oxygen. Coliform was also tested for and tested positive for both the pond and the river. Along with testing the water, samples were taken from both the pond and river to look at the macroinvertebrates present (Figure 4). Mayflies, macroinvertebrates with a low pollution tolerance, were found present in both the river and the pond suggesting that the pond and river have a low level of pollution. Stoneflies though were not found and they have the lowest pollution tolerance. Lastly they calculated the biodiversity index using the Shannon-Wiener equation. They calculated this using the information they gathered about how many different types and how big the populations were of macro invertebrates found in the pond and river. For the pond a biodiversity index of 0.98 was recorded and for the river 1.02 was recorded. Both of these numbers conclude that the biodiversity of both ecosystems are low and could eventually degrade. So to a large extent the water seems to be healthy enough to support a good leopard frog population but the ecosystem could use more biodiversity.
Plan Implementation: Lacey Meek
To manage and promote the leopard frog (Rana pipiens) population, Animas High School will apply for a license from the state to conduct mark recapture studies. Once the license has been obtained, these mark-recapture studies will be carried out to determine the current population. Traps will continue to be set for three days after it is found that all captured frogs are already marked. This will allow a chance for un-marked frogs to be captured so that more accurate data can be provided. During the first year, there will be observations in teams of threes to visually assess the leopard frog population and its size. These teams will be comprised of Animas High School students. Annually, there will be another mark-recapture session using live traps in the first mark-recapture session and in all mark-recapture sessions following. There will be a comparison of the new data to the old. This will be done in the least invasive manner possible so as not to disrupt the data by familiarizing the leopard frogs with humans (Lettink, 2003). With these actions, the population of the leopard frogs can be managed and evaluations can be made. This process has been used for similar purposes, and the numbers of volunteers working on the project should limit human interaction without heavily interfering with the frogs (Lettink, 2003).
This plan will be carried out by Animas High School Biology students and DNS volunteers. Four live traps baited with live insects will be set at intervals around the pond. This number will allow for there to be decent coverage of the banks of the pond without being overly strenuous to the budget provided. The intervals will be set at four points around the pond and directly across from each other. The traps will consist of PVC piping, 6 inches in diameter and two feet high, with a small entry hole provided. The pipes can be bought from Home Depot for $26.00 (Figure 5). The pipes would be embedded vertically in the dirt. In the morning, volunteer teams will go to check the traps and mark all leopard frogs inside. Depending on success, the traps will either be re-baited or hand captures will ensue. All those with field experience in mark-recapture studies, having used this process at least twice before will be asked to inject the dye into the frogs’ legs. The license, if obtained through Animas High School should be at no cost to her due to the school’s association with the state. This process will be repeated until all frogs captured in the traps are marked, or until the frogs captured by hand are consistently marked. Volunteers will check the traps once every morning. Lunch should be provided as extra incentive for the workers. This will be done around the DNS pond, in the shallow water near the grasses where leopard frogs are more likely to reside. (Smith and Keinath, 2007) For maximum efficiency, this plan must be carried out at the end of winter, when most of the snow has melted and the frogs are still sluggish from hibernation but have not yet left for breeding grounds. (Smith and Keinath, 2007)
To manage the bullfrog population, DNS volunteers will spend three days attempting to capture bullfrogs through six pitfall traps established around the pond’s shore. Six will allow for more coverage of the pond, therefore raising the chances that bullfrogs will be captured. This is also monetarily practical seeing as a set of three buckets may be purchased from Home Depot for $7.02, cheaper than buying separate buckets. These will be made from 5 gallon buckets and a tarp which has been cut to cover the top. Both of these can be purchased from Home Depot for a total falling around $21.00. Once at least two bullfrogs have been captured, or after there are none spotted in an observation following the captures, the frogs will be given to Animas High School and Mountain Middle School for use as class pets and possible dissection. The bullfrogs must be separated, no two together, to avoid breeding. They must not be released back into the wild. If Animas or Mountain Middle have a need to dispose of the frogs, they will be euthanized humanely and used for dissections in Biology classes. Annually, there will be a two hour observation of the pond every day for the course of a week. If problem has not been effectively managed, the process will be repeated. If a spike in the bullfrog population is observed, then more drastic measures, such as shooting, will be taken against the bullfrogs. This will ensure more specific targeting of bullfrogs alone. Accompanying this, with shootings, bullfrogs may be in any part of the pond, rather than having to fall into a specific trap.
This plan will be implemented by DNS volunteers in teams of eight to encircle the pond at even spacing. Eight will allow for there to be apt coverage of the shore without overcrowding. Each team will have a two hour shift and there will be three shifts per day, covering several of the daylight hours with 24 people hours put in a day. The volunteers will start outside of the weeds and brush, walking in towards the shore and, if necessary, into the water. The volunteers will be advised to bring shoes they don’t mind getting wet. This process should not take longer than three days due to the fact that these shifts added together will be equal to72 people hours, or three full days in people hours. From the observations conducted by Animas High School, it has been determined that at least two bullfrogs must be caught, but since there is the possibility of more than just two bullfrogs, observations will be conducted after the two are caught to watch for any more frogs. If there are more frogs, another day will be given and this process will repeat. These captures should be done quickly and effectively, when the first of winter has just set in and the snow melts quickly. In this time frame there should still be warm days so that the volunteers don’t freeze. If the weather is deemed too harsh or cold for the captures then the volunteers will wait until the snow has mostly thawed to capture the bullfrogs. Once the frogs are captured, they will be given to Animas High School and Mountain Middle School, where they can either serve time as class pets or euthanized and used for dissections in Biology classes. If either school has a need to dispose of the frogs, they will be either humanely euthanized or sent home with willing students. The bullfrogs must never share a tank and must never be released back into the wild to avoid any possibility of breeding. If frogs have managed to breed, due to someone’s lack of attention to these directions, the female will be immediately euthanized.
Plan Evaluation: Helen Thomson
This plan is designed to affect the DNS property as little as possible. The only disturbance would be around the pond. The set traps may make the pond less accessible for people and limit some of the activities that use the pond, especially school and summer programs. The traps may also attract and catch non-target species or wildlife such as insects, small rodents, and other small amphibians. To minimize the mortality of these other species, traps will be checked regularly and non-target species will be released back into their environment. Although the visual encounter surveys will be done carefully, all of the irregular activity could disturb the pond and species living there, putting more stress on the ecosystem than normal. Measures will be taken to minimize these disturbances, for example the observers will space themselves in a way that they are not overcrowding a certain area, only one person will be in the pond at a time, they will keep their voices low and if they are to handle a frog they must wash their hands in the river to remove excess oils and treat the frogs with care.
To monitor the northern leopard frog population and determine whether the proposed plan is working there will be mark-recapture studies performed. These will be done every year for four years in the month of April. Pitfall traps will be set out to determine the northern leopard frog population and fluorescent elastomer will be used to mark the frogs. The population will then be estimated annually using the mark-recapture data. These traps will also be checked for bullfrogs just in case, and if found will be caught and given to Mountain Middle School or Animas High School, but observations will also be done to assess if the bullfrog plan has been successful.
The bullfrog management can be deemed successful if after four years no bullfrogs are sighted in the observations performed. The reason for waiting four years to deem the management successful is because bullfrog tadpoles take 3-5 years of growth to develop into a mature frog (Bruening, 2002). The leopard frog management can then be deemed successful when every year the new data on population size is compared to the old and we are able to see a population trend that concludes their population size has stayed the same or increased.
Figure 1
Figure 2
Tests
|
Pond
|
River
|
pH
|
8.5
|
8.5
|
Phosphates
|
2ppm
|
1ppm
|
Nitrates
|
1ppm
|
2ppm
|
Dissolved Oxygen
|
6.5 mg/L
|
8.5 mg/L
|
Coliform
|
Positive
|
Positive
|
Figure 3
Species
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Damselflies
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Mayflies
|
Midges
|
Caddisflies
|
Dragonflies
|
Blackflies
|
Coleoptera
|
Stoneflies
|
Total
|
Pond
|
53
|
41
|
5
|
2
|
1
|
0
|
0
|
0
|
102
|
River
|
0
|
125
|
15
|
120
|
0
|
5
|
5
|
0
|
270
|
Figure 4
Project Reflection:
The purpose of this project was to teach us about invasive species and their effects on ecosystems. Our main focus was on bullfrogs (Rana catesbeiana) and the impacts of their invasiveness towards Northern leopard frogs (Rana pipiens). We went out to Durango Nature Studies (DNS) property and conducted field work: visual encounter surveys, wildlife inventory, macroinvertebrate testing, and water tests to assess the quality of the habitat. In the results of the macroinvertebrate testing, we found from a high population of mayflies that the water must be mostly unpolluted. This is due to the mayflies’ low pollution tolerance. However, there were no stoneflies in the river, and since the stoneflies have a pollution tolerance that is even lower than the mayflies’, this suggests that the water isn’t incredibly clean either. From the water testing we found unusually high amounts of phosphorus, which can lead to dangerous algal blooms in pond. We also found that coliform was present in the water, which can indicate the presence of harmful viruses in the water. These are both things that DNS should look into for the health of the habitat. Finally, we also looked at the biodiversity index. For the pond, the results were: 0.98, and the river results were: 1.02. Anything below a one is considered unstable and degrading, while anything above a three is considered healthy. These results are both on the very low end of that scale, meaning that the habitats are possibly degrading and actions should be taken to boost habitat quality. From this data we created charts and tables, and created species management plans to take action against the bullfrogs, which are aggressive generalist predators (they eat anything that fits in their mouths, including leopard frogs).
After our projects, we read an article, “Time to Stop Worrying about Invasive Species?” which speaks about how the management of each invasive species should be taken on a case-by-case basis, because some invasive species are not detrimental to the habitats they invade. For example: although cane toads incredibly harmful to the areas they invade, other species are not so problematic and often boost the biodiversity of a habitat. This article suggests that organisms should be assessed on their impacts to the local environment rather than simply whether or not they’re native. This is supported in the article by mentioning the mountain pine beetles, which are very harmful even in the areas that they are native to. I do feel that this is the way that non-native species should be judged, but I it would have been nice to have more time to look at this article at the beginning of the project rather than introduce it to us when the project was finished, meaning that our weeks of work could be completely moot depending on the bullfrogs’ impacts upon the Durango Nature Center.
Bullfrogs are native to the Eastern half of the United States, including the Eastern half of Colorado. They have now spread to the Western half of Colorado, to many other areas on the map, and within 40 European countries outside of the US. I don’t know the impacts that their invasiveness has had upon these countries, but all the same, it is clear that an eye must be kept on these frogs. Small quantities of frogs would not likely be an issue, but due to the bullfrogs’ ability to lay up to 20,000 eggs in one season, they will multiply rapidly. The problem with invasive species, here and all over the globe, is their abilities to outcompete the native ones and the predation of the native species by some invasive organisms. This is how they spread and must compete, because otherwise they would not be able to spread with as much proficiency as they do. Although some invasive species may not pose threats to the ecosystems they invade, many do. Likewise, though it is good to monitor these species before taking actions, sometimes that wait time makes it even harder to remove the species that are harmful. This is why it is better to manage them as quickly as possible. This is why I feel that the last eight weeks that we have spent on these management plans is worthwhile. Bullfrogs are already so dense in many other areas that we should thin them out whenever possible.
I have learned many things throughout the course of this project. I’ve learned technical writing, which is a very tricky thing for me due to the fact that I am usually writing stories and therefore enjoy the use of descriptive writing rather than the flatness of a technical paper. I’ve also learned in more depth about ecology, the impacts of invasive species, and how to correctly write citations. This project helped me hone my presentation skills and my abilities to identify a species by a key or guide when I need to. Overall, it taught me how to write a management plan which may be necessary if I ever go into a field of work requiring Biology. This project has helped me to look at other species closer and to understand the finer points of an ecosystem, what I need to survive even though I might not think of it. The writing and presentation of these management plans was difficult at times, but I feel that I will be able to carry many new abilities away from it. I will be able to remember what I’ve learned, and this is what project based learning is about.
My Biology blog, if you're interested... http://2011biology.blogspot.com/
My Biology blog, if you're interested... http://2011biology.blogspot.com/
