Preservation of Patrick’s marsh wren
Cisothorus palustris dawsonii, commonly known as Patrick’s marsh wren is a species of bird local to southeastern Central Valley in California. It is considered an isolated population of the species Cisothorus palustris, also known as Marsh wren. This particular type of bird is an inhabitant of grasslands and wetlands such as marshes and creeks. Patrick’s marsh wren are limited in the distance they travel for new breeding grounds and are usually restricted to approximately 100 km away from their place of origin. The marsh wren migrate during the winter to Baja California, but return to Central Valley in order to breed and raise their offspring in the spring.
Green Valley Ranch, a large beef producer, has the intent of removing one of the natural habitats of the marsh wren, Phillip Flat, in order to integrate a dike along the river, which will allow the surrounding ranches to be unharmed, by seasonal flooding. The dike, if built, will directly interfere with one of the four marsh wren habitats and therefore will affect the species living in the area, for the worse. As an environmentalist, it is in my best interest to guarantee safety for this species and by not allowing the Green Valley Ranch to take control of the area that includes one of the few remaining habitats of Patrick’s marsh wren. I will explain why I am against the building of the dike that will destroy Phillip Flat. There is no reason for a species, which already has a few natural habitats, to lose a habitat that has such a large impact on their survival rate. In order to advocate for this position, I will provide evidence to support the claim that building a dike will essentially do more harm than good for Patrick’s wren marsh.
In order to explicate my argument further, a series of simulations, using RAMAS, were conducted in which various scenarios were depicted in order to understand the effects of building a dike that runs through Phillip Flat. There were a total of five potential models that display the effects on Patrick’s marsh wren. The first simulation is known as Unaltered Type, which is the constant/control in the model where the Phillip Flat habitat is unchanged and the total initial abundance is 400 individuals. The second simulation is known as the Unaltered degraded habitat in which Phillip Flat is slowly degrading. The carrying capacity of Philip Flat in this model is decreasing by 1. The initial abundance remains 400. The third simulation is also known as Unaltered degrading habitat and is similar to the second one; however, the carrying capacity is decreasing by 2. Everything else is unchanged in respect to simulation one. In simulation four, also known as Altered habitat, with no remediation, I see a model where Phillip Flat is completely destroyed and because of this, the collective initial abundance amongst the four habitats is no longer 400, rather 305. The last simulation is used to represent the introduction of a dike. In this scenario, half of the Phillip Flat population is translocated to another Marsh wens habitat, Delinger Meadow, and then Phillip Flat is destroyed in order to accommodate the dike. The total population size is 352 individuals.
In Table 1, I see a clear distinction in probabilities of the species falling below 200 individuals within the five models. In the first simulation, there is a probability of approximately 84%. This suggests that there is an 84% chance that the population falls below 200 individuals. Because this is the control simulation, I used this one to compare and contrast the other simulations in order to better understand the dynamics of the habitat. Simulation two has a lower probability: 83%. This means that the unaltered degrading habitat, where the carrying capacity is decreasing by one individual every year, has a rate of falling below 200 individuals less than the control. Similarly, the third simulation has a risk of 81%, which is less than both previous simulations. The rate of falling below 200 individuals is the highest in the fourth simulation where there is an altered habitat, but no remediation to compensate. The risk is approximately 93% and this clearly displays that eliminating Phillip Flat completely is hazardous to the survival of the species. Last but not least, in simulation five, there is an 87% risk of falling below 200 individuals, which displays that there is a negative cause and effect relationship between destroying the Philip Flat habitat and shifting the birds, and the survivability of the birds.
In table 2, we see the population sizes where the risk of extinction is 100%. The highest population size occurs in the second simulation: 526 individuals. Similarly, the third simulation holds the second highest population size of 479 individuals. The lowest is seen by the complete demolition of Phillip Flat, or simulation 3, at 339 individuals. For the control simulation, we have a population size of 452. Lastly, for the fifth simulation, the population size is 363 individuals.
In order to further understand the various factors affecting the population, a sensitivity analysis was conducted. Within this analysis, two different simulations were run. In the first simulation the initial abundance of a different habitat of Patrick’s wren marsh, Three-Mile Marsh, was changed from 125 to 180 and then the risk of falling below 200 individuals was measured. In the second simulation, the change in the abundance of Three-Mile Marsh was maintained and in addition, Phillip Flat was demolished. In table 3, there is a difference in the risks of falling below 200 individuals. In simulation A, the risk is approximately 80% and the risk in simulation B is 91%.
Based on the data given above, we see clear evidence that supports the preservation of Phillip Flat without the integration of a dike system. According to table 1, we see that maintaining the Philip Flat in simulation one produces a lower risk of decline as opposed to simulations 4 and 5, which both include destroying Phillip Flat. Green Valley Ranch should not continue with their efforts to create a dike that runs through Phillip Flat because as we can see in our sensitivity analysis, Phillip Flat is an integral part of Patrick’s marsh wren as well as maintaining the rest of the habitats. In table 3, as previously noted, the two simulations have a large difference in risk of extinction. Due to the nature of the marsh wren, dispersal mainly occurs near breeding grounds and therefore most birds travel within a smaller range of kilometers. Even if we were to increase the initial abundance of Three-Miles Marsh, the rate of extinction would still be significantly large if Phillip Flat were destroyed because it is the center of the other habitats, therefore creating a larger distance between the other habitats in its absence. The rate of survival would, in turn, decrease significantly because resource availability and breeding would be affected.
As discussed in this paper, it is imperative that Phillip Flat be maintained in order to sustain the marsh wren population. By allowing a dike to be integrated within the river, Green Valley Ranch is catalyzing the deterioration of the species. In order to further stabilize the marsh wren population, the old dike that is located near the Delinger Meadow should be removed to allow the species to prevail and prosper. In order to further the research that occurs regarding Patrick marsh wren preservation, it is necessary to run multiple sensitivity analysis experiments to understand the direct and indirect causes of population decline and/or population increase. This will aid our efforts to preserve the species.