Thesis (Ph. D.)--University of Florida, 2002. / Title from PDF title page (viewed on July 3, 2005). Includes vita. Includes bibliographical references (p. 113-118).

Monarch butterflies (Danaus plexippus) are well known to depend almost exclusively on milkweed (genus Asclepias) host plants for oviposition sites, as their larvae need to ingest compounds critical for adult butterfly chemical defense against predators. Many phytophagous insects make fast and accurate decisions on the quality of host plants, and whether or not to accept them as oviposition sites. We were interested in the cues that attract monarchs (males and females) to milkweed, while in flight, before contact stimulation can occur. We developed a novel flight apparatus to test monarch attraction behaviour, under a number of different experimental protocols, to both milkweed and control stimuli in order to identify the cues necessary or sufficient for monarch attraction to milkweed. Monarchs were found to be attracted to milkweed stimuli when the visual image alone of milkweed was available or when olfactory cues alone were available. Attraction behaviour was maximized when both cues were available. It was also discovered that attraction to milkweed was significantly diminished when ultraviolet reflection from milkweed leaves was prevented from being detected by monarchs in flight. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2007-08-09 12:22:17.691

The presence of inhabitants in protected areas, a common occurrence in developing countries, represents a major challenge for conservation. This MA thesis questions the state's strategy in the case of the Monarch Butterfly Biosphere Reserve, in Mexico, a strategy which is officially based on the implementation of sustainable development through the participation of local communities. Working with the assumption that sustainable development is a political concept that implies a competition between different actors in order to define what has to be sustained, for whom, by whom, why, and how, I first analyze the factors that, until now, have impeded local inhabitants' participation. I argue that the subordination of civil society by the state during the last century is a historical burden that has debilitated civil society's capacity for effective participation. Second, I discuss the state's vision of sustainable development and the weight given to the two conflicting visions held, on the one hand, by local inhabitants and, on the other, by the environmentalists and biologists. I conclude that the state's appeal for the participation of local communities is not in recognition of the fact that local inhabitants have the right to greater input in the definition of sustainable development in the region, but needs to be understood as a strategy to achieve rule compliance. Unfortunately, then, while the Monarch Butterfly Biosphere Reserve may be managed according to a vision of sustainable development, this is not a vision that has emerged from a dialogue between the state and civil society. Local support is thus unlikely since transforming local communities into allies would rather require achieving a compromise based upon genuine dialogue.

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Given the rapid population decline and recent petition for listing of the monarch butterfly (Danaus plexippus L.) under the Endangered Species Act, an accurate estimate of the Eastern, migratory population size is needed. Because of difficulty in counting individual monarchs, the number of hectares occupied by monarchs in the overwintering area is commonly used as a proxy for population size, which is then multiplied by the density of individuals per hectare to estimate population size. There is, however, considerable variation in published estimates of overwintering density, ranging from 6.9-60.9 million ha(-1). We develop a probability distribution for overwinter density of monarch butterflies from six published density estimates. The mean density among the mixture of the six published estimates was similar to 27.9 million butterflies ha(-1) (95% CI [2.4-80.7] million ha(-1)); the mixture distribution is approximately log-normal, and as such is better represented by the median (21.1 million butterflies ha(-1)). Based upon assumptions regarding the number of milkweed needed to support monarchs, the amount of milkweed (Asciepias spp.) lost (0.86 billion stems) in the northern US plus the amount of milkweed remaining (1.34 billion stems), we estimate >1.8 billion stems is needed to return monarchs to an average population size of 6 ha. Considerable uncertainty exists in this required amount of milkweed because of the considerable uncertainty occurring in overwinter density estimates. Nevertheless, the estimate is on the same order as other published estimates, The studies included in our synthesis differ substantially by year, location, method, and measures of precision. A better understanding of the factors influencing overwintering density across space and time would be valuable for increasing the precision of conservation recommendations.

Species are experiencing shifts in their phenology (i.e., seasonal timing of recurring biological events) due to climate change, leading to disruptions in the relative timing of interacting species. These shifts can be detrimental to the fitness of the consumer (e.g., herbivore) in the interaction. In its larval form, the monarch butterfly (Danaus plexippus) is a specialist herbivore that feeds on milkweed plants (Asclepias spp.). Given that plants generally experience seasonal declines in quality, it is hypothesized that if climate change disrupts the timing of the larval stage relative to the availability of younger milkweed plants, monarch performance will be negatively affected. In this thesis, I explore the potential for negative consequences for the eastern monarch population due to potential shifts in the timing of their interaction with milkweed—due to phenological shifts in either species. I used field surveys around Ottawa, ON to determine monarch oviposition preference on common milkweed (Asclepias syriaca) plants and the seasonal availability of their preferred plants. To determine the potential consequences for monarch fitness where females oviposit on non-preferred plants, I conducted a field experiment to assess the effect of milkweed size on monarch larval performance. Based on field surveys, females preferentially oviposited on smaller milkweed plants in earlier developmental stages with low levels of discolouration. Plants in early developmental stages were consistently available in large proportion over the summer season. These results suggest that even if the relative timing of the monarch-milkweed interaction in the eastern population is shifted due to climate change, there will likely be suitable milkweed plants available for oviposition throughout the breeding season, which could act as a buffer to disruptions in the relative timing of the interaction. I found that bigger plants exuded more latex and had thicker leaves than smaller plants. However, larval performance was unaffected by these plant quality differences. While it is unclear how the relative timing of the monarch-milkweed interaction will change in the future, my results suggest that shifts in the relative timing of their interaction within the breeding season are unlikely to have negative consequences for larval performance in eastern Ontario. Future studies should determine how the relative timing of the interaction will change in the region and explore how climate change will affect the quality of milkweed plants.

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Managing Monarch butterfly overwintering groves: making room among the eucalyptus Proper management and conservation of the coastal California overwintering sites used by western Monarch butterflies (Danaus plexippus L.) is critical for continued use of these sites by monarchs. Many management efforts are currently concentrating on eucalyptus-only sites because of the prevailing notion that monarchs prefer eucalyptus over native tree species. Yet, whether a preference exists or not has never been tested. Herein, we test the “eucalyptus preference” hypothesis with data from five overwintering sites comprised of blue gum eucalyptus (Eucalyptus globulus) and at least one other native tree species from fall 2009 to spring 2012. We found that when monarchs clustered disproportionately on a tree species relative to its availability, they clustered significantly more than expected on native trees and significantly less than expected on eucalyptus. Also, in years when the overwintering population was highest, monarchs clustered disproportionately on native conifers, and they often switched from clustering on eucalyptus in the early winter to native conifers in the middle or late winter. Our results suggest that overwintering groves should be managed to include a mixture of tree species. We cannot recommend simply planting more eucalyptus. At overwintering sites in central coastal California, native conifers such as Monterey cypress (Hesperocyparis macrocarpa) and pitch canker-resistant Monterey pine (Pinus radiata) should be planted as replacements for blue gum eucalyptus in areas where trees are likely to fall, and around the perimeter of groves. Testing the Monarch butterfly eucalyptus preference hypothesis at California overwintering sites Western Monarch butterflies (Danaus plexippus L.) overwinter in groves of native and non-native trees along the California coast. Eucalyptus is abundant in coastal counties, and overwintering monarchs utilize this type of tree more than any other. This has led to the belief that monarchs prefer eucalyptus. Yet whether a preference exists has never been tested. We tested the “eucalyptus preference” hypothesis at five California overwintering sites with canopies comprised of eucalyptus and at least one native conifer species. We found that at no time over the course of three years did monarchs cluster on trees in proportion to their availability in the canopy. Overall, they did not cluster on one tree species significantly more frequently than another, indicating that monarchs do not prefer eucalyptus—or any tree species—all of the time. However, more often than not monarchs clustered significantly more than expected on native trees, particularly at midseason when the weather was most inclement. They also clustered disproportionately on native conifers when the overwintering population size was highest. At most sites monarchs exhibited tree switching, shifting from eucalyptus to native conifers in the middle or late winter. Based on these results, we reject the “eucalyptus preference” hypothesis. In its place, we propose the “conditional preference hypothesis”, wherein monarchs are predicted to prefer cluster trees according to microclimate conditions and prefer alternate trees within a site as climatic conditions change. Rejection of the eucalyptus preference hypothesis suggests that sites comprised exclusively of eucalyptus may not offer monarchs a suitable range of microhabitats, and further suggests we should rethink “eucalyptus-centric” management. Monarch butterflies overwintering in coastal California: low site fidelity and high intersite movement Western monarch butterflies (Danaus plexippus L.) overwinter in large aggregations at hundreds of sites along the California coast. Management plans and census methods are both founded on the assumption that individual monarchs arrive at an overwintering site in the fall and stay at that site for the winter. Though populations potentially coalesce en masse from autumnal sites onto climax overwintering sites, very little individual movement between sites is inferred. Monarch movement is therefore thought to be primarily into sites (as opposed to out of or among them). We refer to this assumption and inference as the accrual hypothesis. In light of previous studies that provide evidence for movement among sites, we propose that overwintering monarchs may belong to a superpopulation. The existence of a superpopulation comprised of individuals moving in and out of sites would force us to rethink our ideas of landscape-level resource use by monarchs, our site-centric (rather than landscape-level) management strategies, and our abundance estimation techniques, which employ closed population models. We tested the closed population model, the accrual hypothesis, and the superpopulation model at three California overwintering sites using a mark-resight study design. We found that a large proportion of the monarchs at a site moved among (into and out of) monitored sites, both while the population size increased in October and November, and while the population appeared to exhibit an equilibrium winter maximum. The pattern of abundance of both tagged and untagged monarchs at monitored sites leads us to reject the closed population model and the accrual hypothesis. We found that monarchs at all three study sites are part of a larger superpopulation, though the sites do not contribute to the superpopulation equally. We determined that mark-resight is a viable alternative to existing population estimation techniques, though mark-resight methods would need to be explored further before being applied routinely. Our results suggest we need to move away from site-based management and manage instead for landscape-level overwintering (superpopulation) dynamics.