As ecologists, we strive to find meaning in how different species interact with each other and with the greater landscape, and the role that humans play in facilitating landscape level change. Yet, very rarely do we question why we as humans fundamentally care about biodiversity loss and ecological change, and why we prioritize the interests of certain species over others. This thesis describes my journey through an interdisciplinary investigation of my research in (1) invasion ecology and (2) environmental ethics by addressing the following questions: (1) What soil conditioning effects, if any, does knotweed in its invasive range have on the performance of native, introduced, and agricultural species, what are the implications of these effects for restoration, and how are these effects manifested in genetically based variation of knotweed along a biogeographic cline? (2) Why do people feel they have moral obligations to conserve other species at all, and why do we feel moral concern for some species more than others? Responses to question (2) provide an eco-evolutionary explanation for why conservation ethics (moral beliefs, attitudes, and social norms regarding other species) and behaviors (cooperative behaviors toward those species) are widespread and why they manifest differently in different contexts. In responding to question (2), we propose an evolutionary perspective that informs why we care about question (1)—why we manage invasive species and invest in restoration of species that are locally beneficial. In Chapter 1, I describe the context for this thesis. Knotweeds are one of the most invasive species worldwide, yet we lack a comprehensive understanding of the primary mechanisms through which knotweed confers its ecological dominance. As a result, we struggle to identify the most appropriate management strategies to suppress invader abundance and impacts. Facilitating recolonization by native species into invaded ecosystems (i.e., restoration) is contingent upon the effectiveness of management strategies to reduce competitive ability of the invader and overcome any negative soil legacy effects. However, to better address such challenges, we need to understand the role that evolution of morality plays in shaping moral behaviors toward other species and their management. Chapter 2 is an investigation of biotic plant-soil feedback, using knotweed in its introduced range as the study system to assess potential soil legacy effects on seedling emergence and performance of competing plant species. Chapter 2 also investigates whether emergent patterns in knotweed soil conditioning effects can be attributed to genetically based variation across knotweed populations and along a latitudinal cline in population collection location. In order to identify useful emergent patterns when studying mechanisms of invasion, it is critical to assess how invasions mediate biotic interactions across abiotic gradients. Chapters 3 and 4 present results of empirical studies investigating whether the theory of evolution of natural selection, using perceived fitness interdependence (PFI) as a proximate indicator of shared fate, can explain why conservation ethics exist and why they vary around the world and over time. Chapter 3 reports two novel scales: the PFI scale measures perceived shared fate with specific organisms, and the conservation ethics scale assesses moral obligations to those organisms. Chapter 4 applies those scales to test eco-evolutionary predictions that PFI predicts strength of moral concern (conservation ethics) for and pro-social behavior (conservation behavior) towards members of other species. A comprehensive evolutionary framework for how and why conservation ethics and behaviors vary promotes diverse moral justifications for biodiversity and resolves persistent moral contentions about how conservation efforts should be allocated. Therefore, to better address invasive species management and conservation challenges, we need to better understand the evolutionary underpinnings of and justifications for human morality towards non-humans. How we justify conservation ethics will influence our impacts on different species and the ecosystems they inhabit.