Biology subjects

Halsch, C. A.

Publications and source records attributed to Halsch, C. A..

3 recordsLinked to original sources

bioRxiv2020

Insects and recent climate change

Insects have diversified through 400 million years of Earths changeable climate, yet recent and ongoing shifts in patterns of temperature and precipitation pose novel challenges as they combine with decades of other anthropogenic stressors including the conversion and degradation of land. Here we consider how insects are responding to recent climate change, while summarizing the literature on long-term monitoring of insect populations in the context of climatic fluctuations. Results to date suggest that climate change impacts on insects have the potential to be considerable, even when compared to changes in land use. The importance of climate is illustrated with a case study from the butterflies of Northern California, where we find that population declines have been severe in high-elevation areas removed from the most immediate effects of habitat loss. These results shed light on the complexity of montane-adapted insects responding to changing abiotic conditions and raise questions about the utility of temperate mountains as refugia during the Anthropocene. We consider methodological issues that would improve syntheses of results across long-term insect datasets and highlight directions for future empirical work. Significance statementAnthropogenic climate change poses multiple threats to society and biodiversity, and challenges our understanding of the resilience of the natural world. We discuss recent ideas and evidence on this issue and conclude that the impacts of climate change on insects in particular have the potential to be more severe than might have been expected a decade ago. Finally, we suggest practical measures that include the protection of diverse portfolios of species, not just those inhabiting what are currently the most pristine areas.

ecology↗

bioRxiv2020

Pesticide contamination of milkweeds across the agricultural, urban, and open spaces of low elevation Northern California

Monarch butterflies (Danaus plexippus) are in decline in the western United States and are encountering a range of anthropogenic stressors. Pesticides are among the factors that likely contribute to this decline, though the concentrations of these chemicals in non-crop plants is not well documented, especially in complex landscapes with a diversity of crop types and land uses. In this study, we collected 227 milkweed (Asclepias spp.) leaf samples from 19 sites representing different land use types across the Central Valley of California. We also sampled plants purchased from two stores that sell to home gardeners. We found 64 pesticides (25 insecticides, 27 fungicides, and 11 herbicides, as well as 1 adjuvant) out of a possible 262 in our screen. Pesticides were detected in every sample, even at sites with little or no pesticide use based on information from landowners. On average, approximately 9 compounds were detected per plant across all sites, with a range of 1 to 25 compounds in any one sample. For the vast majority of pesticides detected, we do not know the biological effects on monarch caterpillars that consume these plants, however we did detect a few compounds for which effects on monarchs have been experimentally investigated. Chlorantraniliprole in particular was identified in 91% of our samples and found to exceed a tested LD50 for monarchs in 58 out of 227 samples. Our primary conclusion is the ubiquity of pesticide presence in milkweeds in an early-summer window of time that monarch larvae are likely to be present in the area. Thus, these results are consistent with the hypothesis that pesticide exposure could be a contributing factor to monarch declines in the western United States. This both highlights the need for a greater understanding of the lethal and sublethal effects of these compounds (individually, additively, and synergistically) and suggests the urgent need for strategies that reduce pesticide use and movement on the landscape. Contribution to the FieldInsects are facing multifaceted stressors in the Anthropocene and are in decline in many parts of the world. The widespread use of pesticides is believed to be an important part of the problem. In particular, the monarch butterfly is in sharp decline in the western United States. Here we show that milkweeds in the Central Valley of California, a large urban and agricultural landscape that is part of the monarch breeding and migration route, are contaminated with a diverse array of pesticides. We found a few in high concentrations and many in trace amounts. We do not know how these compounds act together and with other large-scale stressors to cause declines, but it is clear that monarchs and other non-target insects are encountering these pesticides. These results provide critical insight into the growing literature on the impact of pesticides on butterflies specifically and non-target insects more broadly. We hope these field realistic concentrations will aid in the design of further experiments in the field and the lab.

ecology↗

bioRxiv2019

A winner in the Anthropocene: changing host plant distribution explains geographic range expansion in the gulf fritillary butterfly

O_LIThe changing climate is altering the geographic distributions of species around the world with consequences for population dynamics, resulting in winners and losers in the Anthropocene.\nC_LIO_LIAgraulis vanillae, the gulf fritillary butterfly, has expanded its range in the past one hundred years in the western United States. We combine time series analysis with species distribution modeling to investigate factors limiting the distribution of A. vanillae and to predict future shifts under warming scenarios.\nC_LIO_LIIn the western US, where we have time series and geographic data, urban development has a positive influence (the host plant is an ornamental in gardens), being associated with year of colonization. Colonization was also associated to a lesser extent with winter maximum temperatures, while a negative impact of minimum temperatures and precipitation was apparent on population growth rates.\nC_LIO_LIAcross the country, the butterfly is primarily limited by host availability and positively affected by human presence. Perhaps counter-intuitively for a largely tropical ectotherm, current effects of a warming climate (in the years post-colonization) are either negative (on population growth rate) or indirect, likely mediated through availability of areas that can support the host.\nC_LIO_LIUnder future climate scenarios, conditions are predicted to become more suitable for Passiflora in many urban areas, which would likely result in further expansion of A. vanillae during the dispersive season. These results illustrate the value of combining time series with spatial modeling to understand and predict shifting geographic ranges in the Anthropocene.\nC_LI

ecology↗