3 years ago



northern Indiana,

northern Indiana, Illinois, Iowa, Michigan, or the upper Midwest compared to the 1996 breeding season. Flockhart et al. (2013) went beyond study of the overwintering generation to determine the natal origins of successive monarch generations produced in the east throughout the 2011 breeding season. The natal origins showed a broad spatial distribution that encompassed the entire breeding range in eastern North America, though the preponderance of individuals originated from northern Texas to western Ohio, in a region extending from the southern Great Plains through the Midwestern Corn Belt (Figure 16). Over this particular breeding season, fewer butterflies originated in the upper Midwest, northeastern and eastern states, and southern Canada, than in the Texas-to-Ohio zone. There were few indications of natal origins from Mississippi, Alabama, Georgia and Florida despite the fact that areas located north of these locations were sampled extensively. Figure 16. Probability distribution for natal origins of monarchs collected in eastern North America during the 2011 breeding season, based on isotope analysis of butterflies. Red dots represent monarch capture locations. The color gradient on the map (light green to dark blue) represents the natal origins of the 839 butterflies analyzed, with increasing numbers of butterflies born in areas with progressively darker coloration, as indicated by the scaled bar to the right of the map. Figure 3 from Flockhart et al. (2013), original caption omitted. Monarch ESA Petition 42

When butterflies were collected for the Flockhart et al. (2013) study, the overwintering monarch population size was drastically reduced from the 1996-1997 level. During the winter of 2010– 2011, the estimated population size was 200 million individuals (Figure 12, above), compared to the estimated billion butterflies at the time of the earlier study. In 2010 almost all soybean and most corn fields were Roundup Ready and few milkweeds remained in those fields to provide habitat for breeding monarchs (as discussed in detail in the Threats—Habitat Loss section of this petition). Overwintering butterfly numbers have continued to decline, as discussed above, coinciding with the greatly reduced availability of common milkweed in agricultural fields as a result of the large increase in use of the herbicide glyphosate made possible by widespread planting of genetically-engineered, herbicide-resistant (Roundup Ready) crops (Pleasants and Oberhauser 2012). To predict monarch risk of extinction, Flockhart et al. (2014) “developed a spatially-structured, stochastic and density-dependent periodic projection matrix model that integrates patterns of migratory connectivity and demographic vital rates across the annual cycle” (p. 2). Their “yearround population model predicted population declines of an additional 14 percent,” from already drastically reduced population size, and a quasi-extinction probability (meaning less than 1000 surviving individuals) of greater than five percent within the next 100 years (p. 2). This “nontrivial” extinction risk (see: demonstrates that monarchs are threatened in the foreseeable future. The model is a conservative, yet realistic, minimum estimate of quasi-extinction of eastern monarch butterflies, and provides strong published evidence that breeding season habitat loss is driving monarch population decline. Yet the model also underestimates the extinction risk facing monarchs for several reasons. The model does not incorporate further expected losses of milkweed in Conservation Reserve Program lands which are being rapidly converted to crop production, primarily Roundup Ready corn and soybeans, due to Program cutbacks and continuing strong demand for biofuels (See Threats…Habitat Loss and Degradation, Loss of Monarch Habitat Due to Agricultural Intensification to Produce Biofuels). It does not consider the imminent release of new genetically-engineered herbicide-resistant crops, which will reduce nectar resources for monarch adults via herbicide drift and continue to eliminate milkweed from cropland once commercialized (See Threats- Habitat Loss and Degradation, New Herbicide-Resistant Crops Promise Further Habitat Degradation). Nor does it take into consideration the release of new pesticides that are in development that will be harmful to monarchs (See Threats…Other Factors). The model also underestimates the risk that climate change poses to monarch butterflies. The model is based on the assumption that there will be a reduced probability of catastrophic mortality events on the wintering grounds in Mexico, but other authors have predicted increased probability of winter mortality due to climate change (Brower et al. 2011, p. 28, Barve et al. 2012, p. 820, Brower et al. 2012a, p. 98). In fact, other models have predicted that the entire Mexican overwintering grounds could become unsuitable to support monarchs in the foreseeable future (Oberhauser and Peterson 2003, p. 14067, Saenz-Romero et al. 2012, p. 98). The model also underestimates climate risk because it uses temperatures from weather stations that are on average 274 m (~900 ft) below the elevation at which butterflies cluster (Flockhart et al. 2014, Monarch ESA Petition 43

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