Shifting Rainfall Patterns Will Affect Whether An Imperiled Butterfly Survives Climate Change

When we think of climate change, we often imagine how a warmer world will impact species, but a new study highlights the importance of changes in precipitation. The finding suggests that paying attention to the environmental triggers within each species’ lifecycle will help us better understand how they will be affected by climate change.

The research focused on the Miami blue butterfly (Cyclargus thomasi bethunebakeri), a federally-listed endangered species that exists solely in a pocket of habitat in southern Florida. Their federal status directs more resources towards their conservation, and understanding the Miami blue’s lifecycle in relation to our changing climate is critical for predicting how they will fare in the future.

Like many tropical insect species, the lifecycle of Miami blue butterflies includes a state called “diapause,” when larvae suspend their development during dry conditions. The onset of the wet season triggers diapausing larvae to restart their development into adult butterflies. The duration of the dry period, and therefore the duration of diapause, can have a significant effect on population numbers. If larvae have a short diapause, then they are more likely to reach adulthood and reproduce than if there is a long dry season with an extended period of diapause.

“We found that shifting rainfall patterns can determine whether the Miami blue butterfly populations grow or shrink, even without any other environmental variables changing,” says Erica Henry, a postdoc in applied ecology at NC State and author of the study. “This is not only concerning for this rare butterfly, but for all insects in precipitation-driven systems. Both the tropics and rainfall patterns have been largely overlooked in the conversation about climate change and animal lifecycles.”

Several species have precipitation-based environmental triggers within their lifecycles. And unlike temperature, which largely trends up under climate change, shifts in precipitation will be more varied and nuanced across the globe: some areas will dry out, some will become inundated, and some will see no change. And in some places, like southern Florida, it’s uncertain how rainfall patterns will shift with climate change. To account for this, the researchers simulated future conditions using 20 different climate models to test how Miami blue populations would respond. In most of those tests, butterfly populations declined when rainfall was delayed and the diapause duration increased, even when all other environmental conditions did not change.

“The tropics, and more specifically that fuzzy area we call the sub-tropics, covers an extremely diverse set of ecosystems that are sensitive to shifts in precipitation,” says Adam Terando, a U.S. Geological Survey Research Ecologist and adjunct professor in the Department of Applied Ecology at NC State who co-authored the study. “The problem is, compared to temperature, there’s also a lot more uncertainty about how precipitation will change as the planet warms. We wanted to bring attention to these rainy-season ecosystems and demonstrate how linking climate science with ecology can give us new insights into what to expect in the future.”

This research is one of the first efforts to examine a tropical insect under climate change using the lens of precipitation rather than temperature. Tropical insect species in areas that are expected to dry under climate change will likely see similar impacts on their lifecycles, possible declines. In fact, changes in precipitation patterns may explain currently declining populations.

“Climate change is happening everywhere,” says Henry. “We can get a better handle on what actions may minimize the negative impacts to biodiversity by thinking more broadly about what that change really means in different parts of the globe.”

The article, “Shifting precipitation regimes alter the phenology and population dynamics of low latitude ectotherms,” was published in the journal Climate Change Ecology on 3 February 2022. The paper is also authored by William Morris from Duke University, Jaret Daniels from the University of Florida, and Nick Haddad from Michigan State University. The research was funded by a Southeast Climate Adaptation Science Center Global Change Fellowship for Erica Henry and the Disney Conservation Fund and Florida Keys National Wildlife Refuges.

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Note to editors: The study abstract follows.

“Shifting precipitation regimes alter the phenology and population dynamics of low latitude ectotherms”

Authors: Erica Henry and Adam Terando, North Carolina State University; William Morris, Duke University; Jaret Daniels, The University of Florida; and Nick Haddad, Michigan State University.

Published: February 2, 2022, Climate Change Ecology

DOI: 10.1016/j.ecochg.2022.100051

Abstract: Predicting how species respond to changes in climate is critical to conserving biodiversity. Modeling efforts to date have largely centered on predicting the effects of warming temperatures on temperate species phenology. In and near the tropics, the effects of a warming planet on species phenology are more likely to be driven by changes in the seasonal precipitation cycle rather than temperature. To demonstrate the importance of considering precipitation-driven phenology in ecological studies, we present a case study wherein we construct a mechanistic population model for a rare subtropical butterfly (Miami blue butterfly, Cyclargus thomasi bethunebakeri) and use a suite of global climate models to project butterfly populations into the future. Across all iterations of the model, the trajectory of Miami blue populations is uncertain. We identify both biological uncertainty (unknown diapause survival rate) and climate uncertainty (ambiguity in the sign of precipitation change across climate models), and their interaction as key factors that determine persistence vs. extinction. Despite uncertainty, the most optimistic iteration of the model predicts that Miami blue butterfly populations will decline under the higher emissions scenario (RCP 8.5). The lack of climate model agreement across the projection ensemble suggests that investigations into the effect of climate change on precipitation-driven phenology require a higher level of rigor in the uncertainty analysis compared to analogous studies of temperature. For tropical species, a mechanistic approach that incorporates both biological and climate uncertainty is the best path forward to understand the effect shifting precipitation regimes have on phenology and population dynamics.

This post was originally published in NC State News.