Insects have diversified through more than 450 million y of Earth’s changeable climate, yet rapidly shifting patterns of temperature and precipitation now 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 with 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. We also consider methodological issues that would improve syntheses of results across long-term insect datasets and highlight directions for future empirical work.

Uncertainty remains regarding the role of anthropogenic climate change in declining insect populations, partly because our understanding of biotic response to climate is often complicated by habitat loss and degradation among other compounding stressors. We addressed this challenge by integrating expert and community scientist datasets that include decades of monitoring across more than 70 locations spanning the western United States. We found a 1.6% annual reduction in the number of individual butterflies observed over the past four decades, associated in particular with warming during fall months. The pervasive declines that we report advance our understanding of climate change impacts and suggest that a new approach is needed for butterfly conservation in the region, focused on suites of species with shared habitat or host associations.

24Insects have diversified through 400 million years of Earth's changeable climate, yet recent and 25 ongoing shifts in patterns of temperature and precipitation pose novel challenges as they 26 combine with decades of other anthropogenic stressors including the conversion and degradation 27 of land. Here we consider how insects are responding to recent climate change, while 28 summarizing the literature on long-term monitoring of insect populations in the context of 29 climatic fluctuations. Results to date suggest that climate change impacts on insects have the 30 potential to be considerable, even when compared to changes in land use. The importance of 31 climate is illustrated with a case study from the butterflies of Northern California, where we find 32 that population declines have been severe in high-elevation areas removed from the most 33 immediate effects of habitat loss. These results shed light on the complexity of montane-adapted 34 insects responding to changing abiotic conditions and raise questions about the utility of 35 temperate mountains as refugia during the Anthropocene. We consider methodological issues 36 that would improve syntheses of results across long-term insect datasets and highlight directions 37 for future empirical work. 38 39 Key words 40 Anthropocene, climate change, population decline, extinction, extreme weather 41 42 43 51 52 53 54 From invasive species to habitat loss, pesticides and pollution, the stressors of the Anthropocene 55 are many and multi-faceted, but none are as geographically pervasive or as likely to interact with 56 all other factors as climate change (1, 2). For these reasons, understanding the effects of 57 anthropogenic climate change on natural systems could be considered the defining challenge for 58 the ecological sciences in the 21 st century (3). It is of particular interest to ask how insects will 59 respond to recent and ongoing climate change, because they are the most diverse lineage of 60 multicellular organisms on the planet, and of fundamental importance to the functioning of 61 terrestrial ecosystems. The issue also has new urgency in light of recent and ongoing reports of 62 insect declines from around the globe (4). Insects and climate change have been discussed 63 elsewhere (5-8), and our goal here is not to cover all aspects of the problem. Instead, we focus 64 on recent discoveries and questions inspired by long-term records of insect populations, 65

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22Insects are facing multifaceted stressors in the Anthropocene and are in decline in many parts of 23 the world. The widespread use of pesticides is believed to be an important part of the problem. In 24 particular, the monarch butterfly is in sharp decline in the western United States. Here we show 25 that milkweeds in the Central Valley of California, a large urban and agricultural landscape that 26 is part of the monarch breeding and migration route, are contaminated with a diverse array of 27 pesticides. We found a few in high concentrations and many in trace amounts. We do not know 28 how these compounds act together and with other large-scale stressors to cause declines, but it is 29 clear that monarchs and other non-target insects are encountering these pesticides. These results 30 provide critical insight into the growing literature on the impact of pesticides on butterflies 31 specifically and non-target insects more broadly. We hope these field realistic concentrations 32 will aid in the design of further experiments in the field and the lab. 33 34 Abstract 35 Monarch butterflies (Danaus plexippus) are in decline in the western United States and are 36 encountering a range of anthropogenic stressors. Pesticides are among the factors that likely 37 contribute to this decline, though the concentrations of these chemicals in non-crop plants is not 38 well documented, especially in complex landscapes with a diversity of crop types and land uses.39In this study, we collected 227 milkweed (Asclepias spp.) leaf samples from 19 sites representing 40 different land use types across the Central Valley of California. We also sampled plants 41 purchased from two stores that sell to home gardeners. We found 64 pesticides (25 insecticides, 42 27 fungicides, and 11 herbicides, as well as 1 adjuvant) out of a possible 262 in our screen. 43Pesticides were detected in every sample, even at sites with little or no pesticide use based on 44 information from landowners. On average, approximately 9 compounds were detected per plant 45 across all sites, with a range of 1 to 25 compounds in any one sample. For the vast majority of 46 pesticides detected, we do not know the biological effects on monarch caterpillars that consume 47 these plants, however we did detect a few compounds for which effects on monarchs have been 48 experimentally investigated. Chlorantraniliprole in particular was identified in 91% of our 49 samples and found to exceed a tested LD50 for monarchs in 58 out of 227 samples. Our primary 50 conclusion is the ubiquity of pesticide presence in milkweeds in an early-summer window of 51 time that monarch larvae are likely to be present in the area. Thus, these results are consistent 52 with the hypothesis that pesticide exposure could be a contributing factor to monarch declines in 53 the western United States. This both highlights the need for a greater understanding of the lethal 54 and sublethal effects of these compounds (individually, additively, and synergistically) and 55 suggests the urgent need for s...

Practitioners are challenged with choosing among many potentially effective methods for sowing seed in ecological restoration projects to achieve sufficient native plant establishment. We tested the effectiveness of seed sowing techniques on moderate and steep slopes in a Mediterranean climate by measuring native seedling density immediately following germination, as well as plant density, recruitment success, and soil movement through the second growing season. We calculated cost effectiveness of different methods as the native plant density per dollar spent sowing seed. While all sowing techniques resulted in significant native establishment compared with unseeded controls, hydro seeding on moderate slopes was the most cost effective (native seedlings established per dollar spent). Although all steep‐sloped seeding techniques resulted in high densities of native species, all methods also resulted in significant soil loss. Shrubs preferred hand seeding followed by jute netting on steep slopes, while forbs reached greatest densities with hydro seeding on moderate slopes. Seedlings of species with heavy seeds were present in greater densities than species with lighter seeds in imprint sowing treatments. The “best” seed sowing technique varied depending on slope and metric of success (native density, species richness, shrub density, or forb density). Different combinations of slope, technique, and success metric resulted in significantly different project costs, which implies opportunities for savings given careful decision‐making relative to mitigation needs on heterogeneous landscapes. Evaluations of techniques for restoring slopes are limited, yet critical for expanding the area capable of being restored and the application of limited conservation funding.

1. The changing climate is altering species distributions with consequences for population dynamics, resulting in winners and losers in the Anthropocene.2. Agraulis vanillae, the gulf fritillary butterfly, has expanded its range in the past 100 years in the western U.S.A. Time series analysis is combined with species distribution modelling to investigate factors limiting the distribution of A. vanillae and to predict future shifts under warming scenarios.3. Time series analyses from the western U.S.A. show that urban development has a positive association with year of colonisation (the host plant Passiflora is an ornamental in gardens). Colonisation was also associated positively and to a lesser extent with winter maximum temperatures, whereas a negative impact of minimum temperatures and precipitation was apparent on population growth rates after establishment.4. Species distribution models vary by region. In the eastern U.S.A., the butterfly is primarily limited by minimum temperatures in the winter and host availability later in the season. Eastern U.S. projected expansion broadly follows the expectation of poleward distributional shifts, especially for the butterfly's maximum annual extent. Western U.S. distributions are limited by the host plant, which in turn is dependent on urban centres. Projected western U.S. expansion is not limited to a single direction and is driven by urban centres becoming more suitable for the host plant.5. These results demonstrate the value of combining time series with spatial modelling, at the same time as incorporating biotic interactions, aiming to understand and predict shifting geographical ranges in the Anthropocene.

Restoring biodiversity to degraded sites in the wildland–urban interface is challenging due to many factors, including competition with non‐native species and increased herbivore pressure. In a unique collaboration between land managers, environmental educators, students, and academic ecologists, we tested the effectiveness of multiple restoration techniques in an adaptive management framework, modifying methods each year based on results in the previous years. We evaluated the impact of non‐native species and rabbit herbivores on soil moisture and native plant growth. We added native seedlings to our site either immediately adjacent to existing native shrubs (potential nurse plants) or in the open. One native species, Artemisia californica, was significantly negatively influenced by the presence of an existing shrub and grew more in the open in both a wet and a dry year. Another native species, Eriogonum fasciculatum, experienced high mortality by rabbit herbivores when it was not protected by fencing. Fencing also increased abundance of non‐native plants, so a combination of fencing and non‐native removal without a nurse plant was optimal for restoration. Soil moisture was greater in the open than under existing native shrubs, indicating that existing shrubs decreased soil water available to seedlings. Data collected by trained students was indistinguishable from that collected by professional ecologists. Our use of community‐engaged science demonstrates how scientific adaptive management experiments can include a diversity of participants and allow for immediate dissemination and implementation of results.