Date of Award:

12-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Zachariah Gompert

Committee

Zachariah Gompert

Committee

Norah Saarman

Committee

Yoshimitsu Chikamoto

Abstract

Climate change is transforming the natural world, altering the timing of key events in the lives of plants and animals, such as when flowers bloom or when butterflies take flight. These timing changes, known as phenology shifts, can disrupt ecosystems and species interactions, creating ripple effects through food webs and biodiversity. While scientists have studied these shifts for decades, much of the focus has been on simple metrics, like the first or last day a butterfly is seen flying each year. However, these measures do not tell the whole story of how climate change is impacting the entire flight season or even why different species respond in different ways.

In this study, we used decades of butterfly observations from five mountain sites in California to explore how climate affects butterfly flight seasons. By examining 135 butterfly species across sites ranging from low to high elevations, we looked at how temperature and precipitation influence their flight periods.

We found that climate has complex effects on butterflies. Warmer daytime spring temperatures made butterflies fly earlier across all elevations, while snowy winters delayed their activity in areas with a substantial amount of snowfall. Even small changes in nighttime spring temperatures significantly shifted the timing of their flight seasons.

Interestingly, not all species responded to climate in the same way. We saw large differences in how climate affected butterflies. Differences in their natural history traits, like how many generations a species has per year (voltinism), what types of plants their caterpillars feed on (diet breadth), and the life stage at which they survive the winter (overwintering stage) do not fully explain these variations in the effect of climate.

Our research highlights the need to study the full flight season of butterflies, not just isolated moments, to better understand how they are being impacted by climate change. These insights can help conservationists make smarter decisions about protecting butterflies and the ecosystems they support, ensuring we’re better prepared to address the challenges of a warming world.

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