Monarch butterflies are believed to be vulnerable to the effects of climate change.
Ecological niche models predict current over-wintering sites in Mexico will be unsuitable
for monarchs in 40 to 50 years. Climate is likely to be equally or more important during
the summer. Here, I seek to predict the consequences of climate change for monarchs
during the summer breeding season and fall migration and determine their ability to cope
with these changes.
Using ecological niche modeling, I predicted a marked northward range shift
throughout the summer breeding season, necessitating movement before each summer
generation and a longer, faster migration. It is unclear whether monarchs can track
geographic changes to their ecological niche, and if not, they stand to loose up to half
their available breeding habitat.
If monarchs can withstand temperatures hotter than their current ecological niche,
their range shifts may not be as drastic. I assessed the lethal and sub-lethal impacts of
exposure to temperatures above their predicted ecological niche. Daytime temperatures of
38 and 40oC caused a slight increase in mortality, as well as difficulty pupating, smaller adult size and a longer development time. Daytime temperatures of 42oC caused
substantially more mortality and no larvae survived exposure to 44oC. These results
suggest that the ecological niche models are accurate and monarchs could lose a
substantial amount of available breeding habitat.
To assess the monarch butterfly’s potential to cope with a changing climate and
adjust its migration, I aimed to identify any level of plasticity currently present in the migration. An introduced species of milkweed, Asclepias curassavica, present in Texas,
may be changing the monarchs’ breeding habits during its fall migration. Data from the
Monarch Larva Monitoring Project and field studies I conducted indicate that female
monarchs prefer the introduced milkweed to native milkweed particularly during the fall
migration. If monarchs are already changing their migration in response to this
environmental change, there may be the variability in monarch migratory and
reproductive behavior that could allow this species to adjust to future climate change.
University of Minnesota Ph.D. dissertation. August 2011. Major: Ecology, Evolution and Behavior. Advisor: Dr. Karen S. Oberhauser. 1 computer file (PDF); viii. 108 pages.
Batalden, Rebecca Victoria.
Potential impacts of climate change on monarch butterflies, Danaus plexippus.
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