Timing matters: Climate change, phenology, demography, and management of the invasive weed Carduus nutans
Open Access
- Author:
- Keller, Joseph
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 19, 2019
- Committee Members:
- Katriona Shea, Dissertation Advisor/Co-Advisor
Katriona Shea, Committee Chair/Co-Chair
Margot Wilkinson Kaye, Committee Member
Michael Saunders, Committee Member
James Rosenberger, Outside Member - Keywords:
- Carduus nutans
climate change
weed management
integral projection model
phenology
biological control - Abstract:
- Invasive plants pose a substantial threat to many ecosystems, including the agroecosystems we rely on for food production. Climate change may affect invasive plants’ performance, potentially exacerbating food security challenges. Furthermore, climate change may also alter the effectiveness of management practices used to control invasive species. In this dissertation, I consider the potential for rising temperatures to affect the performance of the invasive weed musk thistle (Carduus nutans), and I investigate warming’s potential impact on physical and biological control for this weed. In Chapter 1, I outline the damage that invasive plants can cause and describe potential climate change impacts on these pests and their management. In Chapter 2, I show that the timing of seed release, which is expected to shift earlier in the year under warming, has dramatic effects on the musk thistle life cycle. Early seed release increases the rate at which individuals reproduce as annuals, rather than as biennials or perennials. This change, together with increased growth and survival observed under experimental warming in the field, is projected to increase musk thistle population growth rates. In Chapter 3, I report the results of a field experiment that tested the effectiveness of mowing to control musk thistle under warming in the field. Results from this experiment show that warmed plants are more likely to survive mowing, grow taller, flower earlier, and produce more flower heads than plants grown at ambient conditions. In Chapter 4, I investigate whether the effects of warming on musk thistle and the biological control weevil Rhinocyllus conicus are linear or nonlinear. I show that R. conicus attack and musk thistle phenology and height follow linear trends across experimentally manipulated temperatures, while flower head production has an unexpected non-linear trend, with plants grown at intermediate temperatures producing the fewest flower heads. In Chapter 5, I detail an observational study that tracked the interaction between musk thistle and R. conicus across an urban-rural temperature gradient. In this study, I show that musk thistle and R. conicus have differing responses to temperature, changing the seasonal pattern of weevil oviposition on musk thistle flower heads and also reducing overall amounts of attack at warmer sites. Finally, Chapter 6 synthesizes results and suggests possible future directions. Taken together, these findings suggest that managing musk thistle will become a more difficult challenge in the future. This dissertation indicates that climate change may alter both weed performance and the effectiveness of physical and biological weed control efforts, and demonstrates that management plans for invasive weeds may require adjustments to account for both these sources of change.