Rhetorical Analysis of Competitive Release in Diets of Ocelot and Puma After Jaguar Decline 

            The following analysis shows the effects within the diets of cats such as the ocelot and puma after the decline of jaguars within Panama. The authors Ricardo S. Moreno and Rafael Samudio, Jr. of the Smithsonian Tropical Research and Ronaldo W. Kays of New York State Museum conducted a study of the diets of puma and ocelot through the process of fecal analyses at 2 sites in central Panama. This article was published in the Journal of Mammalogy in 2006. 

The issue presented is that diets would often overlap between Puma and Ocelot but due to competitive release post the decline of the jaguar, there are now drastic changes in diet for the ocelot. This prey shift is a direct result of the competitive release due to the Panama jaguar decline. 

Introduction

           As one can imagine, the decline of a predator can affect the ecosystem of an environment. Researchers Ricardo S. Moreno, Ronaldo W. Kays, and Rafael Samudio, Jr. go over the drastic changes that have occurred within tropical America after the decline of the jaguars using the IMRAD format. The introduction includes information establishing the John Swales’ model in Creating a Research Space (CARS). The researchers established their territory by giving the background information of older theories of competitive release such as predators expanding their diet due to the absence of a larger predator (Brown and Wilson 1956). Their investigation moves into step 2 by raising the question of how other big predators such as the puma or ocelot are affected by these changes, especially considering the past researched opinions when a big predator is removed. It’s a question that is of great importance as the removal of the jaguar could lead to not having a drastic change within the ecosystem or causing other big predators to also decline. “Regions that have lost only part of their large predator community face less dramatic, but still important, ecological changes in the re- maining species, which increase in density or change behavior after being ‘‘released’’ from competition or predation from the newly absent species (e.g., Berger et al. 2001; Courchamp et al. 1999; Crooks and Soule ́ 1999; Gehrt and Clark 2003; Henke and Bryant 1999). There is another alternative that although hasn’t been seen within big cats, but in insectivorous mammals, where the smaller species actually began to feed on larger prey (Dickman 1988). What’s alarming is the absence of a large predator, can amplify “the ecological effect of their extinction on the local ecosystem” (Moreno, Kays, and Samudio). The introduction also gives insight on the regular diets of the ocelots and puma. Both are adaptable hunters, however naturally puma aim for large animals while ocelots go for smaller animals. Move three steps into giving the segway to the methods section of the article, but also giving insight on the present research which consists of  “documenting the diet of 2 predators from 2 nearby sites in central Panama from which the top predator, the jaguar (Panthera onca), is very rare or locally extinct, and comparing that with the diet of other populations where jaguars are present” (Moreno, Kays, and Samudio).

Method

            The rhetorical devices used in the methods passage were ethos and logos, providing straight strategy and materials as well as citing sources for credibility. Sources were cited to give background on the habitat itself. The logos were also presented with the facts that were sited from these sources. Researchers collected feces from the study area, 2 sites within the Panama Canal Watershed. The Associacion Nacional por la Conservación de la Naturaleza 1995 is referenced as the first site was centered on Plantation road trail within the Soberania National Park, consisting of flat terrain. The second site references researcher Leigh is Barro Colorado Island (BCI) which is composed of mainly rolling hilltops, isolated from the mainland. The habitat is mainly moist tropical rainforest, split up into wet and dry seasons of the year (Leigh 1999; Tosi 1971). This is an example of ethos as past research is being shared to ensure the public knows that their method is valid. Logos is also exhibited as researchers explain how they were able to quantify the diets of ocelot and puma through scat analysis. While on BCI, researchers had searched for scat along trails at the research site and latrines several times a week through a 1999 rainy season and 2003 dry season.  They even added reasoning to why it was necessary to search frequently due to the moist habitat resulting in speedy decomposition of scat. In order to give the audience an understanding of how the scat was being evaluated, the researchers provided the criteria of identification based on size, odor, location and possible nearby footprints. They were even able to rationalize any lack of footprints off trails, scat collected larger than 2.8 cm in diameter was classified as puma, while all smaller scat were identified as ocelots. Tables were also utilized as a form of logos. This is highly important in supporting their hypothesis as sampling provided evidence of the puma and ocelots’ preys. The number of detections of an item was divided by the number of items detected. The percentage of occurrence was utilized by dividing the number of scats containing an item by the number of scats. Frequency of appearance was used to calculate the relative biomass of prey as a quantitative alternative to raw frequency data. Researchers also cited a use of ethos as they used the Pianka index to calculate the overlap in diet among species, sites, and seasons. 

Results

           The results section consisted of the evidence provided in the two tables and fours figures. In order for the audience to process all this data, the tables and figures are broken down so that everything interdependently is cohesive and makes sense. The data is shown as the following: Table 1 displayed the frequency of scat and items within the BCI  puma, BCI ocelot, and the mainland ocelot. Table 1 is the most lengthy with complex scientific names of species, but the later figures help ease this unfamiliarity for those who aren’t well knowledged on this area of expertise. Table 2 is much smaller compared to table 1 and briefly, but comprehensively breaks down the evidence to the average prey weight and the components of the forest used by the prey. Figure 1 is very straightforward and reveals the number of puma scats found on BCI. Figure 2 showed results of cluster analysis of  the dietary overlap between the ocelots and puma. Figure 3 presented the proportions of the total biomass that was eaten of the prey.  Lastly Figure 4 focuses solely on the weight of prey eaten by ocelots in three different sites, and even provides illustration as a component to make things more comprehensive. The data summed up to the analysis of 239 ocelot scats as well as 88 puma scats between 1999 and 2003. 190 ocelot scats collected on BCI  49 were collected on the mainland. All of the puma scat are collected on BCI. 90% of the ocelot scats were discovered at the latrines. Puma scat was found only on the trails, with obvious footprints nearby.  1 puma scat per month was discovered with the exception the wettest months between 1999 and 2003. The wetter months caused faster decomposition. Results concluded that the BCI ocelot diet was similar to both mainland ocelot and BCI puma. Pianka’s overlap = 0.721 compared to the lesser overlap results between BCI puma and mainland ocelot, = 0.530. The diet between puma and ocelot was most similar during the rainy season, during which all 3 populations’ diets consisted of agoutis. The prey eaten by ocelots on BCI and the mainland did not differ greatly in their use of forest layers or in body mass. With their diets being similar, it confirms that there were dietary changes as researchers had mentioned in the introduction that puma preys are larger than that of the ocelot.  

Discussion

            The start of the discussion section begins with a very important observation that connects it back to the decline of the jaguars. On the Barro Colorado Island, Panama, puma have been seen on the island regularly over 4 years, while no evidence of jaguars being present were found. Due to this information the two sites that were actually being viewed as a part of the study, jaguars can be ecologically extinct from there. The discussion over the results show that the diets of both animals is “governed by a combination of opportunistic predation of locally abundant prey species” (Moreno,Kays, and Samudio). Since their diets seem to be fully intact the ecological effect on others is unknown, but there has been a shift in diet. 

Conclusion

            Like every other paper for me, I did find it challenging especially since I’m new to this CARS model as well as the IMRAD format. It’s different from what I’m used to, which is argumentative essays. Despite my unfamiliarity, I did find it to be very guided since I’m formatting my paper to mirror that of the article, just in a rhetorical analysis perspective. I’m sure I found myself oversharing details, but I just deemed them as important. My strategy for this paper was reading the article and summarizing and outlining each section. This topic was dear to me as I have a love for big cats, but also being from Panama I’ve done much research on the jaguar decline therefore learning the effects of it on the rest of the ecosystem I was intrigued. 

References

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