Tracking multi-generational colonization of the breeding grounds by monarch butterflies in eastern North America.
Insect migration may involve movements over multiple breeding generations at continental scales, resulting in formidable challenges to their conservation and management. Using distribution models generated from citizen scientist occurrence data and stable-carbon and -hydrogen isotope measurements, we tracked multi-generational colonization of the breeding grounds of monarch butterflies (Danaus plexippus) in eastern North America. We found that monarch breeding occurrence was best modelled with geographical and climatic variables resulting in an annual breeding distribution of greater than 12 million km(2) that encompassed 99% occurrence probability. Combining occurrence models with stable isotope measurements to estimate natal origin, we show that butterflies which overwintered in Mexico came from a wide breeding distribution, including southern portions of the range. There was a clear northward progression of monarchs over successive generations from May until August when reproductive butterflies began to change direction and moved south. Fifth-generation individuals breeding in Texas in the late summer/autumn tended to originate from northern breeding areas rather than regions further south. Although the Midwest was the most productive area during the breeding season, monarchs that re-colonized the Midwest were produced largely in Texas, suggesting that conserving breeding habitat in the Midwest alone is insufficient to ensure long-term persistence of the monarch butterfly population in eastern North America.
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. dflockha@uoguelph.ca
D T Tyler
DT
Flockhart
Leonard I
LI
Wassenaar
Tara G
TG
Martin
Keith A
KA
Hobson
Michael B
MB
Wunder
D Ryan
DR
Norris
D025041:Animal Migration; D000818:Animals; D002080:Butterflies / Q000502:physiology*; D003247:Conservation of Natural Resources; D005843:Geography; D009656:North America; D011157:Population Dynamics; D012098:Reproduction; D012621:Seasons
Danaus plexippus; carbon-13; deuterium; insect migration; migratory connectivity; stable isotopes