Archive for July, 2009

My research program addresses how climate change and human alterations of water resources impact animal migration. Large-scale animal migrations that possess recurring migratory paths are some of the most spectacular biological events, but human land uses and lack of statutory protections for migratory species and their corridors have led to the loss of many large-scale animal migrations. In North America, the annual monarch butterfly (Danaus plexippus L.) migration covers the greatest spatial extent (up to 4800 km) of any other current insect migration, traveling from southern Canada to central Mexico’s Transverse Neovolcanic Range. Unfortunately, however, the monarch migration has become an endangered biological phenomenon due to habitat destruction within overwintering sites in Mexico and coastal California, land conversion within the monarch’s habitats, alterations of its migratory corridors, and potentially climate change. The current lack of information on the monarch’s use of specific migratory corridors perpetuates the lack of appropriate conservation planning and management of ecosystems for the monarch’s endangered migration.

To address this issue, my research has three primary goals. First, my research program will establish a large-scale operation in the western deserts to develop an understanding of monarch migration in the western US, especially regarding specific migration corridors. This will be accomplished both from tagging/occurrence data and genetic data. The monarch migration in the western US has been largely unexplored, particularly in the western deserts of the US which constitute over 1.38 x 10⁶ km². The ‘classic’ model for the migration of monarch butterflies in the western US, west of the Rocky Mountains, holds that most monarchs migrate from inland areas to coastal California during autumn to overwinter in large aggregations, remigrating inland during spring and summer. This classic model is undergoing revisions due to recent observations. An alternative model of monarch migration in the West suggests that there may be exchanges of monarchs between the western US and Mexico. Indeed, this model has been suspected for years and a few recent observations support this contention. But, it remains largely unknown as to how many individuals undergo that migration and what specific migratory corridors are utilized.

My research will use tagging and occurrence data to examine use of migratory corridors by (1) establishing counting and tagging stations across the western deserts of the US during migration season, (2) developing an online monarch location data form, and (3) populating a database via the online form via qualified biologists. Current tagging operations involve the simple application of a sticker with identification data. With appropriate funding, radio telemetry equipment also will be utilized. Recent advances in radio telemetry technology have allowed for extremely light-weight equipment that can be affixed to a monarch butterfly’s body and signals can be gathered as far as 10-15 km from the radio telemetry receiver/antenna unit. Tracking monarchs via radio telemetry in the western deserts is likely to be quite successful given the basin and range landscape and lack of obstructions that would otherwise block radio signals. The monarch butterfly in the western United States is thought to use rivers, in part, as migratory corridors to reach their overwintering sites. However, monarch occurrence data on specific river systems is lacking or non-existent, raising the question of what role particular river systems play in terms of guiding monarch migration in the West.

My research program also aims to team with molecular ecologists that can run genetic analyses on monarchs to examine relatedness between monarchs in western deserts, coastal California overwintering sites, and Mexican overwintering sites. Surprisingly, ecologists have avoided using genetic analyses to determine how closely related these monarchs are and whether the eastern population and western population of monarchs constitute genetically different populations. Combining genetic and landscape data could be used to test hypotheses on whether particular landscapes attributes constitute effective barriers to migration or to overwintering sites. Thus, my research will assess these types of questions for their individual benefit of understanding migration barriers and as a basis for understanding potential impacts from climate change and water resource alterations.

Second, my research aims to assess the natal origins of monarchs because appropriate conservation measures necessitate an understanding of where most monarchs at particular overwintering sites have originated. Stable isotope analyses, in conjunction with the counting and tagging program, offers a powerful method for understanding the butterfly’s natal origins and possible migration trajectories. Methods already have been developed for using stable isotopes of carbon and hydrogen to assess the natal origins of monarchs in the eastern US. But given that monarchs in the US are considered to be of two largely distinct population units, eastern population and western population, research is needed to understand where the natal origins are located for western monarchs that occur at various overwintering sites in the western US and Mexico. I also plan to assess stable isotopes of other elements, such as N, S, or Sr, for their possible use in gathering finer resolution data of migration patterns.

Third, data from counts, tags, online data inputs, genetics, and stable isotope analyses will be used in conjunction with theory to develop ecological models that project climate change and water use impacts on the monarch’s migration. Climate change and increased demand for potable water has caused changes in the distribution of water, vegetation, and animals. Given that climate change has altered the phenology of plants, researchers have suspected that animal migrations that are tied to plants also may be altered. However, research has not examined the potential compounding effects from changes in water distribution caused from climate change and increased demand for freshwater on animal migrations. These issues converge in several regions across the globe. One prime example is in the western United States where climate change has caused warmer and drier conditions and human land uses have caused altered distributions and increased demand of water resources. In this changing landscape, the migration of the monarch butterfly is hypothesized be water-dependent, using hydrological features such as rivers to help guide their migration and using hostplants that occur along riparian areas of streams and rivers. My research will use the monarch butterfly as a model organism to assess the effects of climate change and water resource changes on migration.