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  • Thumbnail for A Trophic Cascade and the Potential Consequences of Trophic Downgrading: The Cougar-Elk-Aspen System
    A Trophic Cascade and the Potential Consequences of Trophic Downgrading: The Cougar-Elk-Aspen System by Camp, Bryson Sawyer

    A trophic cascade can be defined as a specific food web or trophic structure where a predator preys on a herbivorous consumer which forages on a local vegetative resource; therefore, in this type of trophic structure top-down processes allow carnivorous apex predators to have indirect effects on local vegetative resources through their effects on the density or behavior/traits of the herbivores (M. Kummel, personal communication, April 8, 2019 and Ford et. al. 2015). In the case of predation on herbivorous consumers, both density and trait mediation can indirectly effect the density and growth pattern of vegetation that correlate directly to the alteration of prey populations via density and trait mediation (Ford et. al. 2015). Cougars have been identified as one of the seven apex predators that have been specifically associated with trophic cascades based on other empirical studies (Ripple et. al. 2014). Trophic downgrading follows the same pattern as alterations to trophic cascade structures: Trophic downgrading can have numerous direct and indirect ramifications on the local ecology. Trophic downgrading has similar consequences and is defined as, “the consequences of removing large apex consumers from nature (Estes et. al. 2011, 301).” Due to the unique characteristics that define the 6th mass extinction, one species has been the cause of most of the extinctions and the period has been characterized by the extinction of various large bodied animals, addressing trophic downgrading has become a prominent issue in the management of a wide array of ecological contexts globally (Estes et. al. 2011). In addition, apex predators, like cougars, facilitate ecosystem services such as carbon storage to buffer climate change, biodiversity enhancement, the reestablishment of native plant diversity, riparian restoration, and even the regulation of diseases (Estes et. al. 2011 and Ripple et. al. 2014). Thorough analyses of cougar habitat selection are rare, and have yet to be conducted in relation to the movement of elk and the growth of aspen saplings in the Pikes Peak region of Colorado U.S.A. until now. Through this study, it was observed and statistically shown that the number of aspen saplings tends to increase in areas that correspond with preferential habitat usage of cougars; whereas, the number of aspen saplings decreases in areas that correspond with a high prominence of observed elk herbivory. Therefore, in the Cougar-Elk-Aspen system within the Pikes Peak region cougars, carnivorous apex predators, are having indirect effects on local plants through top-down processes: This is a trophic cascade scenario.