Challenges for Monitoring the Extent and Land Use/Cover Changes in Monarch Butterflies’ Migratory Habitat across the United States and Mexico

Abstract

This paper presents a synopsis of the challenges and limitations presented by existing and emerging land use/land cover (LULC) digital data sets when used to analyze the extent, habitat quality, and LULC changes of the monarch (Danaus plexippus) migratory habitat across the United States of America (US) and Mexico. First, the characteristics, state of the knowledge, and issues related to this habitat are presented. Then, the characteristics of the existing and emerging LULC digital data sets with global or cross-border coverage are listed, followed by the data sets that cover only the US or Mexico. Later, we discuss the challenges for determining the extent, habitat quality, and LULC changes in the monarchs’ migratory habitat when using these LULC data sets in conjunction with the current state of the knowledge of the monarchs’ ecology, behavior, and foraging/roosting plants used during their migration. We point to approaches to address some of these challenges, which can be categorized into: (a) LULC data set characteristics and availability; (b) availability of ancillary land management information; (c) ability to construct accurate forage suitability indices for their migration habitat; and (d) level of knowledge of the ecological and behavioral patterns of the monarchs during their journey.

Changes in landscape and climate in Mexico and Texas reveal small effects on migratory habitat of monarch butterflies (Danaus plexippus)

“…For example, degraded shrubland sites had different temporal patterns of NDVI than intact sites 63 . Given these issues the LULC, nectar, and milkweed resources analyses were designed to identify large changes in habitat and map them at coarse spatial resolutions 64 . Given the categorical nature of the LULC analyses, these efforts focused on changes in habitat quantity, and we used the climate variables and NDVI, to assess possible changes in habitat quality.…”

“…Our methodological choices were based, in part, on data availability. For example, milkweed and nectar densities are not well-sampled across our study extent, and land cover data vary between the US and Mexico 64 . We used land cover datasets from Mexico and Texas to estimate land cover change, then used Monte-Carlo methods to link changes in land cover to changes in monarch habitat (spring and fall nectar and milkweed resources) using empirical data and surveys of experts.…”

“…We previously reviewed land cover datasets that could be used in comparisons across Mexico and Texas 64 . For this study, we wanted land cover data with high levels of spatial resolution to track change in habitat that also covered the time series of overwintering abundance in Mexico (1994-present).…”

Distribution, phenology, and land cover preference risk assessments of four South-Central US milkweeds (Asclepias spp.) important for monarch butterflies

“…Milkweeds are also preferred nectar plants of adult monarchs (USDA NRCS 2015a,b; and can be important for fueling the spring and fall migrations (Brower et al 2006;Hobson et al 2020). Because of the importance of South-Central US milkweed habitat for maintaining monarch functional connectivity along the migratory corridors, spatially explicit risk assessments for milkweed habitat are needed to inform regional monarch conservation planning efforts (Moreno-Sanchez et al 2019). Species spatial risk assessments are a category of spatial environmental or ecological risk assessment (e.g., Suter 2007;van Westen and Greiving 2017) applied in the context of a spatially explicit species habitat model, that can facilitate conservation planning (Duggan et al 2015;Hashim et al 2017).…”