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Appendix A. Details of feeder construction.

Details of feeder construction

Appendix B. Estimating nestling body condition.

Estimating nestling body condition

Distribution of three measures of monarch butterfly larval density.

<p>Histograms of the sum of egg and larval density (all instars), egg density, and large larvae (3^rd, 4^th, and 5^th instars) density from field surveys data compiled from the literature <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Cockrell1" target="_blank">[11]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Lynch1" target="_blank">[25]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Riley1" target="_blank">[26]</a>. The predicted strength of density dependence is influenced by the different life-stages considered when estimating larval density and whether the density-dependent survival function is applied to the larval density at each site or to the mean population density (vertical dashed line). Using the mean population density to calculate the strength of density dependence excludes the extreme density values that occur regularly in the data set and results in conservative estimates of the strength of density dependence.</p

Density-dependent survival in monarch butterflies.

<p>The density-dependent effect of intraspecific competition presented as the mean (± SE) survival probability of monarch butterflies from egg to eclosion as a function on egg density per plant. There were six replicates per density treatment. The line represents the logit-link transformed survival function from a general linear model of survival using a quasibinomial error structure. The equation of the line is: _.</p

Effect of density on monarch butterfly length and mass.

<p>The mean (± SE) length (left) and mass (right) of pupae (top) and adult (bottom) monarch butterflies that were raised at different densities. Adult length is the length of the forewing. Both males (filled) and females (unfilled) are included in the plots of adults but sex only has a significant effect on eclosed mass (see text). No adult females were weighed or measured at the lowest density.</p

Predicted proportion reduction in population size in monarch butterflies caused by intraspecific density-dependent larval competition.

<p>Mean (standard error) percent population reduction caused by intraspecific density-dependent larval competition in monarch butterflies using two different methods of calculating the predicted proportion reduction population size. The three measures of density incorporate different life-stages. Densities of eggs and larvae include all larval instars whereas large larvae include only 3^rd, 4^th and 5^th instars. Data come from published field surveys of milkweed and monarch larvae <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Cockrell1" target="_blank">[11]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Lynch1" target="_blank">[25]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045080#pone.0045080-Riley1" target="_blank">[26]</a> and are for the early phase of the breeding season in the South (see text).</p

Supplementary Methods from Fear creates an Allee effect: experimental evidence from seasonal populations

Detailed method

Confidence in assignment tests of monarchs captured throughout the Great Lakes region where each monarch was re-sampled 100 times and assignments were determined based on the highest P_b^* value. Stable isotope value from each monarch were resampled 100 times.

*<p>stable isotope values from each monarch were re-sampled 100 times.</p><p>Confidence in assignments represent the proportion of 100 re-samples for each monarch that were estimated to have originated from the same region based on subsequent assignments. The percentage of monarchs that are assigned to a breeding region with a given confidence (>0.5–>0.9) is shown for each state/province.</p

Summary of predictions (first two rows) to distinguish whether monarchs arriving in northern portion of the breeding range adopt a single sweep (SS) or successive brood (SB) strategy.

<p>Notes:</p>1<p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031891#pone-0031891-g001" target="_blank">Figure 1</a> for information on stable-hydrogen isotope values between regions and Methods for information on assignment tests.</p>2<p>Individuals with wing wear scores between 1–3 were considered to have been born in the sampling year while individuals with wing wear scores of 4 or 5 were considered to have been born the previous year (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031891#s2" target="_blank">Methods</a> for details). The only exception to this is for individuals that were assigned to the GC region. In this case, all individuals must have been born the sampling year regardless of wing wear because it is unlikely that GC monarchs overwinter in Mexico because milkweed does not grow in the Gulf Coast during late summer when the migratory generation is produced (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031891#s4" target="_blank">Discussion</a> for details).</p>3<p>Monarchs born in the GL region in the year they were sampled could be either the offspring from monarchs migrating north from over wintering sites in Mexico (SS) or from monarchs that were born the GC or CE regions the same year (SB).</p