2017-Predator Prey Activity Budgets
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Determining the Significance of Relative Abundance in Overlap of Predator-Prey Activity Budgets for Mammalian Species in the Cloud Forests of Costa Rica Ellen Asselin Mentor: Michael Mooring Committee: Ryan Botts, Heidi Woelbern ABSTRACT. – A rudimentary knowledge of the relationships between organisms in an ecosystem is important for the monitoring and conservation of an ecosystem. Predator-prey relationships can provide insight into the fluctuation of specific populations, and inequalities in predator-prey populations can explain unnatural behaviors such as predation upon livestock by a predator that no longer has access to a sufficient abundance of its preferred prey species (Burgas et al., 2014). These relationships have frequently been determined via direct observation and dietary analysis from fecal sampling. Morphological and DNA analysis of fecal samples, while potentially challenging to identify to the species level, can provide valuable information about the dietary habits of predators by indicating which prey species’ DNA is found in predator’s feces. In the tropical montane forests of Costa Rica’s Talamanca mountain range, however, these methods are unrealistic options to gain an understanding of the basic network of predator- prey relationships. The Cordillera de Talamanca is a characteristic mountain region that separates the Atlantic coast from the Pacific coast from central Costa Rica to northern Panama- its rugged terrain has impeded direct survey efforts of medium to large mammals. The mammals in this range are seldom witnessed due to their elusive nature, and high rainfall and tropical temperatures lead to rapid detritus turnover, making fecal sample collection difficult (Tobler et al., 2006). The cloud forests of the Talamanca Cordillera are home to numerous subsistence ranchers, whose livestock’s wellbeing is contingent upon adequate prey populations for such large carnivorous felines such as the jaguar Panthera onca and puma Puma concolor, keystone predators who are capable of livestock predation (Burgas et al., 2014). As natural prey species populations dwindle because of hunting or poaching, jaguars and pumas are more likely to turn to predation on livestock, and this incites the ranchers to hunt and kill large felines: this struggle is termed the human-felid conflict. Dramatic decreases in the populations of these felids could lead to empty forests, where the cloud forest appears to be ecologically sound, but lacks all large mammals, because a shift in the population of these apex predators could initiate a top-down trophic cascade, and alter the abundance or behavior of their prey, altering the predation patterns for successively lower trophic levels (Redford, 1992). However, there are other species that also play a major role in the makeup of the environment. The cloud forests also serve as a last retreat for lowland mammals- such as the endangered Tapirus bairdii- driven to higher ground due to the agricultural development and fragmentation of their lowland habitats (Gonzalez-Maya et al., 2012). The feeding habits and movements of these tapirs- and their fellow ungulates the collared peccaries (Tayassu tajuca)-can play a major role in modifying the structure and composition of vegetation in their environment (Beck 2006, Fragoso 1997). The disappearance or extreme reduction of populations of these ungulates would have a disproportionately dramatic effect on the ecosystem compared to the reduction in populations of other species, because of their capacity for ‘ecosystem engineering’ (Fragoso 1997, Keuroghlian and Eaton 2009). Knowledge of the likely predators of tapirs and other ungulates is critical for conservation purposes. The use of camera trapping has increased over the past two decades as a low-cost method of noninvasive quantitative sampling to monitor terrestrial mammal inventories (Tobler et al., 2008). Data analyses of photo captures can also provide researchers with a wealth of data, including temporal activity budgets for species. Studies have indicated that predators and their main prey have a significant degree of temporal overlap in activity budgets, suggesting that predators are likely to modify their activity times to reduce foraging energy expenditure (Sunquist & Sunquist, 1989). Temporal segregation according to prey species activity has also been noted in large sympatric felines, suggesting that their behavior is directed more significantly by prey activity than attempts at reducing competition between predator species (Karanth & Sunquist, 2000). However, modification of predator activity is not the only force at work- prey species may modify their own activity in order to avoid predation. This complicated balance between prey species’ foraging and their predator avoidance may be studied through mathematical modeling (Skalski & Gilliam, 2002). The focus of our studies was to determine if relative abundance of prey species significantly affected predator-prey overlap in order to begin developing a noninvasive method of predicting predator-prey relationships via camera trapping. Predators must optimize their activity according to a wide range of variables, which could include human presence, inter-predator competition, and prey availability (Fig. 1). We wanted to determine if the latter affected predator activity patterns. In order to do so, we compared predator-prey overlap to the fluctuation in relative abundance of prey species across different survey sites. Simply, does prey abundance dictate activity of the predator? If so, we predict a positive correlation between relative prey abundance and predator-prey overlap coefficient. Figure 1. A few of the many possible variables affecting predator activity include human presence, inter- predator competition, the predator’s natural circadian rhythm, and prey abundance. The latter is highlighted in red in the figure and will be tested for significance in this study. The aim of this study was to determine the significance of relative abundance of prey as a factor in determining overlap in predator-prey relationships between the medium to large mammalian species of the Cloud Forest in the Talamanca Cordillera of Costa Rica. This would help gain a better idea of the role of elusive species in the existing ecosystem, aim to reduce human-felid conflict, and to increase our knowledge base of the behavioral networks of mammals in this poorly studied ecosystem. STUDY AREAS.— This study used data collected from three national parks, and two reserves located in the Talamanca Cordillera. The first survey, the Chirripo survey, is located in the central Talamanca Cordillera within the bounds of Chirripo National Park. This park consists of both cloud forest and scarce páramo biomes, and contains Cerro Chirripo, which, at 3,820 meters, is the highest peak in Central America and is a renowned ecotourism area. The Tapantí survey was conducted in the northern Talamanca Cordillera in Tapantí National Park. The park encompasses 58,323 hectares and boasts the highest annual rainfall in Costa Rica at 6,550mm (Bernard et al., 2009). The Savegre survey was conducted in the Savegre Valley and parts of the nearby Los Quetzales National Park. Los Quetzales is Costa Rica’s newest national park, previously part of Los Santos Forest Reserve, which contained possibly the last large and unfragmented expanse of neotropical montane forest in Central America (Kappelle et al., 1992). Savegre Valley is an ecotourism hot spot flanking Los Quetzales National Park, and contains a trail system for hiking and birdwatching. El Copal Biological Reserve and La Marta Wildlife Refuge, the sites of the fourth and fifth surveys, are 160 and 1500 hectare wildlife preserves, respectively. They are situated in the northern Talamanca Cordillera and serve as buffer zones to Tapantí National Park (Poorboy, 2015). MATERIALS AND METHODS. — Camera Traps Motion-sensing Bushnell Trophy Cameras equipped with infrared flash for nocturnal captures were used for this study. The cameras were housed in steel cases and strapped to trees along trails with Python cable locks. A scent station was placed in the field of view of the camera as an attractant. This scent station was comprised of meter-high PVC pipe topped with a sponge inside a tube soaked in Calvin Klein Obsession for Men, which contains synthetic civetone, the main odorous constituent of civet pheromones that has been shown to elicit attractive responses in captive felines (Thomas et al., 2005). The cameras were set up to capture three successive photos when triggered by movement, and would continue to capture sets of photos until movement ceased. A resolution of 8-12 megapixels was used, as this resolution was sufficient to determine the species of the mammal that triggered the capture. The camera traps were positioned at 1-2 km intervals along trails easily accessed for monitoring purposes. The number of camera stations in Savegre was greater in the summer than in other months, while all cameras were maintained and monitored in collaboration with the research team and park guards. Throughout all other seasons, the number and locations of camera stations was constant for each survey. Table 1 indicates the number of seasons during which each survey site was monitored, as well as the initial and final season from which data was compiled for this study. Total camera days were calculated by multiplying the number of camera traps by the number of monitoring days across all monitoring seasons. Table 1. Start and end seasons, total monitoring seasons, and total camera days for all five survey sites used in this study. Total Camera Survey Initial Season Final Season Seasons Days Savegre Summer 2010 Fall 2015 17 17432 Chirripo Fall 2011 Spring 2016 15 11842 El Copal Fall 2013 Summer 2015 4 1035 La Marta Fall 2013 Summer 2015 7 2621 Tapantí Fall 2012 Summer 2015 11 13694 The camera traps in Savegre Valley were monitored every 2 weeks by an undergraduate research team during the summer. The rest of the camera traps were monitored every few months throughout the year by collaborators, often national park guards. Each monitoring event consisted of removing and replacing the memory card, and replacing lithium AA batteries and desiccants as needed.