Environmental drivers of annual population fluctuations in a trans-Saharan insect migrant
Hu, Gao (Nanjing Agricultural University. Department of Entomology)
Stefanescu, Constantí (Centre de Recerca Ecològica i d'Aplicacions Forestals)
Oliver, Tom (University of Reading. School of Biological Sciences)
Roy, David B. (Uk Centre for Ecology and Hydrology)
Brereton, Tom (Butterfly Conservation)
Van Swaay, Chris (Dutch Butterfly Conservation)
Reynolds, Don R. (University of Greenwich. Natural Resources Institute)
Chapman, Jason W. (Nanjing Agricultural University. Department of Entomology)

Data:	2021
Resum:	The painted lady butterfly is an annual migrant to northern regions, but the size of the immigration varies by more than 100-fold in successive years. Unlike the monarch, the painted lady breeds year round, and it has long been suspected that plant-growing conditions in winter-breeding locations drive this high annual variability. However, the regions where caterpillars develop over winter remained unclear. Here, we show for the European summer population that winter plant greenness in the savanna of sub-Saharan Africa is the key driver of the size of the spring immigration. Our results show that painted ladies regularly cross the Sahara Desert and elucidate the climatic drivers of the annual population dynamics. Many latitudinal insect migrants including agricultural pests, disease vectors, and beneficial species show huge fluctuations in the year-to-year abundance of spring immigrants reaching temperate zones. It is widely believed that this variation is driven by climatic conditions in the winter-breeding regions, but evidence is lacking. We identified the environmental drivers of the annual population dynamics of a cosmopolitan migrant butterfly (the painted lady Vanessa cardui) using a combination of long-term monitoring and climate and atmospheric data within the western part of its Afro-Palearctic migratory range. Our population models show that a combination of high winter NDVI (normalized difference vegetation index) in the Savanna/Sahel of sub-Saharan Africa, high spring NDVI in the Maghreb of North Africa, and frequent favorably directed tailwinds during migration periods are the three most important drivers of the size of the immigration to western Europe, while our atmospheric trajectory simulations demonstrate regular opportunities for wind-borne trans-Saharan movements. The effects of sub-Saharan vegetative productivity and wind conditions confirm that painted lady populations on either side of the Sahara are linked by regular mass migrations, making this the longest annual insect migration circuit so far known. Our results provide a quantification of the environmental drivers of large annual population fluctuations of an insect migrant and hold much promise for predicting invasions of migrant insect pests, disease vectors, and beneficial species.
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Insect migration ; Population dynamics ; Painted lady butterfly ; Lepidoptera
Publicat a:	Proceedings of the National Academy of Sciences of the United States of America, Vol. 118, Issue 26 (June 2021) , art. e2102762118, ISSN 1091-6490

DOI: 10.1073/pnas.2102762118
PMID: 34155114

11 p, 2.1 MB

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