Monarch butterfly populations are thriving in North America — University of #Georgia – Coyote Gulch

Summer numbers have held steady for 25 years despite dire warnings

For years, scientists have warned that monarch butterflies are dying off en masse due to dwindling winter colonies. But new research from the University of Georgia shows that the monarch summer population has remained relatively stable over the past 25 years.

Published in Global Change Biology, the study suggests that population growth during the summer compensates for butterfly losses due to migration, winter weather and changing environmental factors.

“There’s this perception that monarch populations are in big trouble, but we’ve found that’s not the case at all,” said Andy Davis, the study’s corresponding author and assistant researcher at the school. of UGA Odum Ecology. “It goes against what everyone thinks, but we found that they are doing quite well. In fact, monarchs are actually one of the most common butterflies in North America.

The study authors caution against complacency, as rising global temperatures may lead to new, growing threats not just to monarchs, but to all insects.

Callippe Silverspot butterfly (Speyeria callippe callippe). By SACRAMENTO FISH AND WILDLIFE OFFICE; US Fish and Wildlife Service – This image is from the United States Fish and Wildlife Service National Digital Library on this pageThis tag does not indicate the copyright status of the attached work. A normal copyright tag is still required. See Commons:Licensing.See Category:Images from the United States Fish and Wildlife Service., Public Domain, https://commons.wikimedia.org/w/index.php?curid=15237505

“There are once-widespread butterfly species that are now in trouble,” said William Snyder, co-author of the paper and a professor in UGA’s College of Agricultural and Environmental Sciences. “So much attention is being given to monarchs instead, and they seem to be in pretty good shape overall. It feels like a missed opportunity. We don’t want to give the impression that insect conservation is not important because it is. It’s just that maybe this particular insect doesn’t have as many problems as we thought.

This study represents the largest and most comprehensive assessment of the breeding population of monarch butterflies to date.

Summer reproduction compensates for winter losses of monarchs

Researchers compiled more than 135,000 sightings of monarch butterflies from the North American Butterfly Association between 1993 and 2018 to examine population patterns and possible drivers of population change, such as rainfall and widespread herbicide use. agricultural.

The North American Butterfly Association uses citizen scientists to document and count butterfly species across North America for a two-day period each summer. Each group of observers has a set circle to patrol that spans about 15 miles in diameter, and observers count all the butterflies they see, including monarchs.

Looking closely at monarch sightings, the team found an overall annual increase in relative monarch abundance of 1.36% per year, suggesting that the breeding monarch population in North America is not declining on average. . Although overwintering populations in Mexico have seen documented declines in recent years, the results suggest that the butterflies’ summer breeding in North America is compensating for these losses.

That marathon run in Mexico or California each fall, Davis said, could get tougher for the butterflies as they face traffic, bad weather and more obstacles along the way south. So fewer butterflies reach the finish line.

“But when they come back up north in the spring, they can really make up for those losses,” Davis said. “A single female can lay 500 eggs, so they are able to bounce back a lot, given the right resources. This means that the winter colony declines are almost like a red herring. They are not really representative of the whole population of the species, and they are rather misleading. Even the recent increase in winter colony size in Mexico is not as significant as some would like to think.

Roadside milkweed. Photo: Katie McVey/USFWS

Changing Monarch Migration Patterns

One of the concerns of conservationists is the alleged national decline of milkweed, the only food source for monarch caterpillars. But Davis believes this study suggests breeding monarchs already have all the habitat they need in North America. If they hadn’t, Davis said, the researchers would have seen it in that data.

“Everyone thinks monarch habitat is being lost left and right, and for some insect species that might be true, but not for monarchs,” Davis said. If you think about it, monarch habitat is people habitat. Monarchs are really good at using the landscapes we have created for ourselves. Backyard gardens, pastures, roadsides, ditches, abandoned fields – these are all monarch habitats.

In parts of the United States, monarchs are present year-round or nearly so, leading some researchers to believe that the insects may in part be drifting away from the annual migration to Mexico. San Francisco, for example, hosts monarch butterflies year-round because people plant non-native tropical milkweed. And Florida experiences fewer freezes each year, making its climate an alternative for monarch butterflies that would normally cross the border.

“There’s this idea of ​​an insect apocalypse — all insects are going to be lost,” Snyder said. ” But it is not that simple. Some insects are likely to be injured; some insects will take advantage of it. You really have to take this big pig picture on a more continental scale over a relatively long period of time to get a true picture of what’s going on.

The study was supported by grants from the USDA National Institute of Food and Agriculture.

The article was co-authored by Timothy Meehan, National Audubon Society; Matthew Moran, of Hendrix College; and Jeffrey Glassberg, of Rice University and the North American Butterfly Association. Michael Crossley, who worked on the study as a postdoctoral researcher in the Department of Entomology and is now at the University of Delaware, is the paper’s first author.


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