Managing for Disturbance: Trade-Offs Associated With Population Resilience and Ecosystem Size

Populations can recover from and withstand disturbance through characteristics such as reproduction and maintaining large abundances. While these traits are beneficial to native species conservation, they can simultaneously challenge effective invasive species management. Effective invasive species control requires sufficient efforts to overcome a population's ability to recover from disturbance, such as harvest. My dissertation aimed to address how the size of an invasive population and its ability to recover from disturbance impact a suite of invasive species control methods, including those that (1) target mainly larger and older individuals (i.e., mechanical removal), (2) target all sizes of individuals (i.e., targeted poison bait), and (3) aim to limit future generations' reproductive ability through genetic methods (i.e., Trojan Y Chromosome stocking). Each of these strategies have minimum effort levels, below which little to no biomass reduction occurs. This means that if management fails to exert effort at or above this intensity, there may be a substantial investment resulting in no meaningful population impact. Additionally, I examine the potential for different combinations of these methods to control a population of invasive common carp (Cyprinus carpio) in Utah Lake, UT, assessing the trade-offs between control effectiveness and cost. I highlight that there are minimum efforts required, regardless of control method employed, to achieve meaningful progress towards invasive species control targets. Further, I demonstrate how methods can be combined to produce desired population impacts and illustrate how combining mechanical removal and Trojan Y Chromosome stocking could be an effective strategy for my case study of the Utah Lake common carp control program. However, all of the combined methods explored herein that achieve control targets would require substantial budgetary increases for Utah Lake. Overall, my research advances our understanding of the relationship between necessary levels of invasive species control efforts and the size and reproductive ability of the target population. An agency's ability to adequately apply effort to control an invasive species can ultimately be limited by resource availability. While substantial increases in investment may be necessary, combining multiple control methods could reduce the long-term investment required to achieve management targets. Regardless of methods applied, failure to reach or surpass the necessary effort level can result in prolonged investment of resources with minimal impact on the targeted population.