Different factors limit early‐ and late‐season windows of opportunity for monarch development
Authors: Yang Louie H. , Swan Karen , Bastin Eric , Aguilar Jessica , Cenzer Meredith , Codd Andrew , Gonzalez Natalie , Hayes Tracie , Higgins August , Lor Xang , Macharaga Chido , McMunn Marshall , Oto Kenya , Winarto Nicholas , Wong Darren , Yang Tabatha , Afridi Numan , Aguilar Sarah , Allison Amelia , Ambrose‐Winters Arden , Amescua Edwin , Apse Mattias , Avoce Nancy , Bastin Kirstin , Bolander Emily , Burroughs Jessica , Cabrera Cristian , Candy Madeline , Cavett Ariana , Cavett Melina , Chang Lemuel , Claret Miles , Coleman Delaney , Concha Jacob , Danzer Paxson , DaRosa Joe , Dufresne Audrey , Duisenberg Claire , Earl Allyson , Eckey Emily , English Maddie , Espejo Alexander , Faith Erika , Fang Amy , Gamez Alejandro , Garcini Jackelin , Garcini Julie , Gilbert‐Igelsrud Giancarlo , Goedde‐Matthews Kelly , Grahn Sarah , Guerra Paloma , Guerra Vanessa , Hagedorn Madison , Hall Katie , Hall Griffin , Hammond Jake , Hargadon Cody , Henley Victoria , Hinesley Sarah , Jacobs Celeste , Johnson Camille , Johnson Tattiana , Johnson Zachary , Juchau Emma , Kaplan Celeste , Katznelson Andrew , Keeley Ronja , Kubik Tatum , Lam Theodore , Lansing Chalinee , Lara Andrea , Le Vivian , Lee Breana , Lee Kyra , Lemmo Maddy , Lucio Scott , Luo Angela , Malakzay Salman , Mangney Luke , Martin Joseph , Matern Wade , McConnell Byron , McHale Maya , McIsaac Giulia , McLennan Carolanne , Milbrodt Stephanie , Mohammed Mohammed , Mooney‐McCarthy Morgan , Morgan Laura , Mullin Clare , Needles Sarah , Nunes Kayla , O'Keeffe Fiona , O'Keeffe Olivia , Osgood Geoffrey , Padilla Jessica , Padilla Sabina , Palacio Isabella , Panelli Verio , Paulson Kendal , Pearson Jace , Perez Tate , Phrakonekham Brenda , Pitsillides Iason , Preisler Alex , Preisler Nicholas , Ramirez Hailey , Ransom Sylvan , Renaud Camille , Rocha Tracy , Saris Haley , Schemrich Ryan , Schoenig Lyla , Sears Sophia , Sharma Anand , Siu Jessica , Spangler Maddie , Standefer Shaili , Strickland Kelly , Stritzel Makaila , Talbert Emily , Taylor Sage , Thomsen Emma , Toups Katrina , Tran Kyle , Tran Hong , Tuqiri Maraia , Valdes Sara , VanVorhis George , Vue Sandy , Wallace Shauna , Whipple Johnna , Yang Paja , Ye Meg , Yo David , Zeng Yichao 
Published: July 2022

Seasonal windows of opportunity are intervals within a year that provide improved prospects for growth, survival, or reproduction. However, few studies have sufficient temporal resolution to examine how multiple factors combine to constrain the seasonal timing and extent of developmental opportunities. Here, we document seasonal changes in milkweed (Asclepias fascicularis)–monarch (Danaus plexippus) interactions with high resolution throughout the last three breeding seasons prior to a precipitous single‐year decline in the western monarch population. Our results show early‐ and late‐season windows of opportunity for monarch recruitment that were constrained by different combinations of factors. Early‐season windows of opportunity were characterized by high egg densities and low survival on a select subset of host plants, consistent with the hypothesis that early‐spring migrant female monarchs select earlier‐emerging plants to balance a seasonal trade‐off between increasing host plant quantity and decreasing host plant quality. Late‐season windows of opportunity were coincident with the initiation of host plant senescence, and caterpillar success was negatively correlated with heatwave exposure, consistent with the hypothesis that late‐season windows were constrained by plant defense traits and thermal stress. Throughout this study, climatic and microclimatic variations played a foundational role in the timing and success of monarch developmental windows by affecting bottom‐up, top‐down, and abiotic limitations. More exposed microclimates were associated with higher developmental success during cooler conditions, and more shaded microclimates were associated with higher developmental success during warmer conditions, suggesting that habitat heterogeneity could buffer the effects of climatic variation. Together, these findings show an important dimension of seasonal change in milkweed–monarch interactions and illustrate how different biotic and abiotic factors can limit the developmental success of monarchs across the breeding season. These results also suggest the potential for seasonal sequences of favorable or unfavorable conditions across the breeding range to strongly affect monarch population dynamics.