Article

Ecological Niches in Sequential Generations of Eastern North American Monarch Butterflies (Lepidoptera: Danaidae): The Ecology of Migration and Likely Climate Change Implications

Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN 55108, USA.
Environmental Entomology (Impact Factor: 1.3). 01/2008; 36(6):1365-73. DOI: 10.1603/0046-225X(2007)36[1365:ENISGO]2.0.CO;2
Source: PubMed

ABSTRACT

Eastern North American monarch butterflies (Danaus plexippus L.) show a series of range shifts during their breeding season. Using ecological niche modeling, we studied the environmental context of these shifts by identifying the ecological conditions that monarchs use in successive summer months. Monarchs use a consistent ecological regimen through the summer, but these conditions contrast strikingly with those used during the winter. Hence, monarchs exhibit niche-following among sequential breeding generations but niche-switching between the breeding and overwintering stages of their annual cycle. We projected their breeding ecological niche onto monthly future climate scenarios, which indicated northward shifts, particularly at the northern extreme of their summer movements, over the next 50 yrs; if both monarchs and their milkweed host plants cannot track these changing climates, monarchs could lose distributional area during critical breeding months.

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    • "This allows us to account for monarch development time and the fact that MLMP volunteers monitor weekly. While generations sometimes overlap between these time periods, our visualizations of region-wide data suggested that this overlap is usually not relevant within in any given region, as the vast majority of the population moves in a predictable way from one region to another during the year (Batalden et al. 2007). An alternative would have been to measure survival over the entire year, but we wanted to capture differences from one generation to the next. "
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    ABSTRACT: The eastern North American monarch population is declining, as evidenced by the area occupied by overwintering adults. Recently, decreasing availability of breeding habitat has been most strongly implicated in this decline. An alternative, nonexclusive explanation for the recent population decline is decreasing survival. We used 18 yr of data from the Monarch Larva Monitoring Project, a citizen science program, to determine immature monarch mortality rates over time as well as factors associated with increased mortality. Our data included field measures of mortality from egg to the final larval instar, and mortality due to parasitoids and other causes, assessed by rearing field-collected monarchs. Average egg to fifth-instar survival ranged from ∼7 to 10% across all regions. Survival from fifth instar to adult ranged from ∼60 to 90%, although this overestimates survival because monarchs are not exposed to many mortality factors when reared indoors. Both survival rates showed a great deal of temporal and spatial variation. Survival tended to be higher in sites that were planted and had more milkweed plants. There was a negative effect of per plant egg density on survival, suggesting density dependence. Survival rates appear to be declining from 1997 to 2014, and we discuss possible reasons for this pattern. Finally, we estimate that across all years in the north-central United States, where we have the most data, a minimum number of ∼29 milkweed plants are required to produce an adult monarch that will be part of the fall migratory generation.
    Preview · Article · Aug 2015 · Annals of the Entomological Society of America
    • "Since the surveys conducted by Silvie (1993) in restricted cereal and cotton-cropping areas, no large-scale quantitative surveys have been undertaken in the country. The abundance and distribution of stem-borer pests and their main natural enemies are expected to vary considerably with the current climate variability (Parmesan et al., 1999; Batalden et al., 2007; Trnka et al., 2007). The objectives of this study were to (i) assess the relative importance of the different stem borer species and their associated natural enemies on maize, and (ii) evaluate cereal producers' perception on the effect of the current climate variability, on the maize stem and ear borers and on their mitigation strategies to alleviate the impact of climate change on their cropping system. "
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    ABSTRACT: Objective: The objectives of this study were to (i) assess the importance of the different stemborer species and their associated natural enemies on maize, and (ii) evaluate cereal producers’ perception on the effect of the current climate variability, on the maize stem and ear borers and their mitigation strategies to alleviate the impact of climate change on their cropping system. Methodology and results: Surveys were conducted in 2012 during the long cropping season lasting from March to July and the short one from September to October in southern Togo, to determine geographic distribution, relative importance of lepidopterous stemborers and their parasitism by natural enemies on maize. A questionnaire was introduced to evaluate cereal farmers’ perception of climate change and its effects on maize stem and ear borers. Of the total borer species recovered, the most abundant was Sesamia calamistis Hampson (Lepidoptera: Noctuidae) (76.02%), followed by Busseola fusca Füller (Lepidoptera: Noctuidae) (21.71%) and then Eldana saccharina Walker (Lepidoptera: Pyralidae) (2.27%). The borers’ abundance was affected by the agroecological zones and cropping seasons. Eldana saccharina was found in Zio and Yoto in coastal zone whereas B. fusca was recorded only in Yoto. Sesamia calamistis was the only species found in all the surveyed agroecological zones (III, IV and V). Fields were infested by all borer species at 34.4% and 83.3% in the long and short cropping seasons respectively. The percentage of infested plants ranged from 0 to 72% in the first cropping season, and 33 to 95% in the second cropping season. The borer densities varied from 0 to 3 larvae per plant in the long cropping season and 1 to 8 larvae per plant in the short cropping season. The egg parasitoid Telenomus busseolae Gahan (Hymenoptera: Scelionidae) was identified as the most important with a high natural parasitism rate of 82% on S. calamistis. The main larval parasitoid recorded was Sturmiopsis parasitica Curan (Diptera: Tachnidae) with mean parasitism ranged of between 0 and 8%. Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) infection rate vary from 0 to 5%.of borers’ larvae. Data on farmer’s perception showed that all producers recognized stem and ear borers and their damages. However, they perceive climate change effects differently by high temperatures, rains irregularity, floods, strong winds and to a lesser extent the proliferation of new pests such as termites (Isoptera), Zonocerus variegatus (L) (Orthoptera: Pyrgomorphidae) and Cicadulina spp. (Hemiptera: Cicadellidae). Adaptation strategies practiced by farmers are the choice of early maturing crop varieties, the spacing of sowing period and the crop diversification. Conclusion and application of funding: From these results, we conclude that S. calamistis, E. saccharina, and B. fusca and their associated natural enemies are present in all agroecological zones of southern Togo. These findings could serve as baseline data for further studies.
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    • "These crude projections are in line with niche modeling that shows the optimal climate window tracking north based on a 50 year climate projection (Batalden et al., 2007). No modeling approach has yet captured the full complexity of how climate interacts with all the potential factors that influence monarch population growth, including the condition and number of incoming migrants from Mexico, milkweed growth and congruence with monarch arrivals, natural enemies, and appropriate climatic environments for activity and growth throughout each phase of their migratory cycle. "
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    ABSTRACT: Understanding the impacts of climate on migratory species is complicated by the fact that these species travel through several climates that may be changing in diverse ways throughout their complete migratory cycle. Most studies are not designed to tease out the direct and indirect effects of climate at various stages along the migration route. We assess the impacts of spring and summer climate conditions on breeding monarch butterflies, a species that completes its annual migration cycle over several generations. No single, broad-scale climate metric can explain summer breeding phenology or the substantial year-to-year fluctuations observed in population abundances. As such, we built a Poisson regression model to help explain annual arrival times and abundances in the Midwestern United States. We incorporated the climate conditions experienced both during a spring migration/breeding phase in Texas as well as during subsequent arrival and breeding during the main recruitment period in Ohio. Using data from a state-wide butterfly monitoring network in Ohio, our results suggest that climate acts in conflicting ways during the spring and summer seasons. High spring precipitation in Texas is associated with the largest annual population growth in Ohio and the earliest arrival to the summer breeding ground, as are intermediate spring temperatures in Texas. On the other hand, the timing of monarch arrivals to the summer breeding grounds is not affected by climate conditions within Ohio. Once in Ohio for summer breeding, precipitation has minimal impacts on overall abundances, whereas warmer summer temperatures are generally associated with the highest expected abundances, yet this effect is mitigated by the average seasonal temperature of each location in that the warmest sites receive no benefit of above average summer temperatures. Our results highlight the complex relationship between climate and performance for a migrating species and suggest that attempts to understand how monarchs will be affected by future climate conditions will be challenging.
    Full-text · Article · Oct 2012 · Global Change Biology
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