Butterfly abundance is determined by food availability and is mediated by species traits

Establishing the distribution of Carpophilus truncatus in Australia using an integrative approach for an emerging global pest

The nitidulid beetle Carpophilus truncatus is rapidly becoming a major pest of nut crops around the world. This insect first infested Australian almonds in 2013 and has since escalated to be the preeminent insect pest for the industry. Data pertaining to C. truncatus distribution are scant, but without awareness of its origin, distribution, and ecological factors that influence distribution, efforts to understand and manage the insect as a pest are stymied. Here, we employ an integrative approach to gain a multifaceted understanding of the distribution of C. truncatus in Australia. Methods employed were (1) reviewing historical records in insect collections to establish the presence of C. truncatus prior to commercial almond horticulture, (2) field trapping of insects to establish presence in regions of interest, (3) laboratory trials to determine the thermal limits of the organism, and (4) correlative species distribution modelling to describe its current distribution. We find that C. truncatus is more widespread across Australia than was previously known, with historical records preceding commercial almond production in Australia by a century. The methods developed in this study can be applied elsewhere in the world where C. truncatus is an emerging pest, or to novel pest species as they arise with increasing frequency in a globalised and warming world.

Dispersal mediates trophic interactions and habitat connectivity to alter metacommunity composition

Dispersal contributes vitally to metacommunity structure. However, interactions between dispersal and other key processes have rarely been explored, particularly in the context of multitrophic metacommunities. We investigated such a metacommunity in naturally fragmented habitats populated by butterfly species (whose dispersal capacities were previously assessed), flowering plants, and butterfly predators. Using data on butterfly species abundance, floral abundance, and predation (on experimentally placed clay butterfly models), we asked how dispersal ability mediates interactions with predators, mutualists, and the landscape matrix. In contrast to expectations, high densities of strong dispersers were found in more isolated sites and sites with low floral resource density, while intermediate dispersers maintained similar densities across isolation and floral gradients, and higher densities of poor dispersers were found in more connected sites and sites with higher floral density. These findings raise questions about how strong dispersers experience the landscape matrix and the quality of isolated and low-resource sites. Strong dispersers were able to escape habitat patches with high predation, while intermediate dispersers maintained similar densities along a predation gradient, and poor dispersers occurred at high densities in these patches, exposing them to interactions with predators. This work demonstrates that species that vary in dispersal capacities interact differently with predators and mutualist partners in a landscape context, shaping metacommunity composition.

A 12-Year Experimental Design to Test the Recovery of Butterfly Biodiversity in an Urban Ecosystem: Lessons from the Parc Urbain des Papillons

Urbanization is one of the main threats to biodiversity. However, some urban green spaces could act as refuges for urban fauna if the composition of the flora were less horticultural and if a less intensive management strategy is adopted. Among the taxa, butterflies are experiencing a strong decline from European to regional scales. An ecological engineering project based on a plantation of host and nectariferous plants backed up by a well thought out management strategy was carried out in Marseille at the Parc Urbain des Papillons (the Butterflies Urban Park). We assessed its effectiveness by comparing the butterfly communities in this park before and after the engineering work, and we compared it to a neighboring wasteland with natural habitats. After 12 years of the project, the results show a significant change in the species composition. The species richness greatly increased from 25 to 42 species. Some specialist species we targeted appeared, and their numbers increased from one to five. However, three Mediterranean species are still absent compared to the wasteland with natural habitats. As the plant palette used and the management strategy implemented enabled us to significantly increase the number of species, we now plan to work on the structure of the vegetation.

Environmental factors affecting honey bees (Apis cerana) and cabbage white butterflies (Pieris rapae) at urban farmlands

Rapid urbanization results in a significantly increased urban population, but also the loss of agricultural lands, thus raising a concern for food security. Urban agriculture has received increasing attention as a way of improving food access in urban areas and local farmers' livelihoods. Although vegetable-dominant small urban farmlands are relatively common in China, little is known about environmental factors associated with insects that could affect ecosystem services at these urban farmlands, which in turn influences agricultural productivity. Using Asian honey bee (Apis cerana) and cabbage white butterfly (Pieris rapae) as examples, I investigated how environmental features within and surrounding urban farmlands affected insect pollinator (bee) and pest (butterfly) abundance in a megacity of China during winters. I considered environmental features at three spatial scales: fine (5 m-radius area), local (50 m-radius area), and landscape (500 m-raidus and 1 km-radius areas). While the abundance of P. rapae increased with local crop diversity, it was strongly negatively associated with landscape-scale crop and weed covers. A. cerana responded positively to flower cover at the fine scale. Their abundance also increased with local-scale weed cover but decreased with increasing landscape-scale weed cover. The abundance of A. cerana tended to decrease with increasing patch density of farmlands within a landscape, i.e., farmland fragmentation. These results suggest that cultivating too diverse crops at urban farmlands can increase crop damage; however, the damage may be alleviated at farmlands embedded in a landscape with more crop cover. Retaining a small amount of un-harvested flowering crops and weedy vegetation within a farmland, especially less fragmented farmland can benefit A. cerana when natural resources are scarce.

Effects of human activities on Sericinus montela and its host plant Aristolochia contorta

Sericinus montela, a globally threatened butterfly species, feeds exclusively on Aristolochia contorta (Northern pipevine). Field surveys and glasshouse experiments were conducted to obtain a better understanding of the relationship between the two species. Interviews with the persons concerned with A. contorta were conducted to collect information about the site management measures. We found that management practices to control invasive species and manage the riverine areas might reduce the coverage of A. contorta and the number of eggs and larvae of S. montela. Our results indicated that the degraded quality of A. contorta may result in a decrease in S. montela populations by diminishing their food source and spawning sites. This study implies that ecological management in the riverine area should be set up to protect rare species and biodiversity.

Forest Quality and Available Hostplant Abundance Limit the Canopy Butterfly of Teinopalpus aureus

Hostplant limitation is a key focus of the spatial interaction between a phytophagous butterfly and a hostplant. The possible drivers related to the hostplants are species richness, abundance, or availability, but no consensus has been reached. In this study, we investigated the butterfly-hostplant interaction using the case of the forest canopy butterfly T. aureus in Asia, whose narrow distribution is assumed to be limited by its exclusive hostplant, Magnoliaceae, in tropic and subtropic regions. We recorded the Magnoliaceae species, as well as plant and butterfly individuals in transect, and we collected tree traits and topography variables. The results confirm that this butterfly is limited by the hostplants of their larval stage. The hostplants occurred exclusively in the middle-mountain region, with preference only for primeval forests. The hostplant resource was superior in the middle-mountain region, particularly concentrating in primeval forests. The hostplant's abundance, together with altitude and habitat types, was critical to this butterfly's occurrence, while those hostplant trees with an exposed crown, which are demanded by this butterfly in its oviposition, were the best drivers of positive butterfly-hostplant interactions. Therefore, the hostplant's limitation was mainly determined by the availability of the hostplant. This case study supports the hypothesis that the limitation on this butterfly's occurrence was driven by the hostplant's availability, and it suggests that protecting high-quality forests is a valuable activity and essential in the conservation of canopy butterflies.

Occurrence of an endangered grassland butterfly is mainly driven by habitat heterogeneity, food availability, and microclimate

The Marsh Fritillary (Euphydryas aurinia) was once widespread in large parts of Central Europe. However, in the course of the last century, populations of the butterfly largely collapsed. Here, we surveyed patch and microhabitat occupancy and its drivers in one of the last vital populations in calcareous grasslands. Our study revealed that environmental conditions at the landscape and habitat level determined the occurrence of E. aurinia in a montane agricultural landscape with low land-use intensity. Patch occupancy increased with the cover of Devil's-bit Scabious (Succisa pratensis) grasslands in the surroundings of the patches, habitat heterogeneity and host-plant cover. Microhabitat occupancy was driven by a warm microclimate and high availability of host plants. In the well-connected landscape of nutrient-poor grasslands, patch occupancy of E. aurinia was driven by parameters defining a high habitat quality. Habitat heterogeneity very likely buffers E. aurinia populations against environmental stochasticity and, hence, enhances long-term viability. For the gregariously feeding caterpillars of E. aurinia, host-plant biomass is essential. Due to their more luxuriant growth, S. pratensis plants were clearly preferred, although the Glossy Scabious (Scabiosa lucida) was also widespread. Additionally, the growth of large Succisa plants was favored by soil humidity and grassland abandonment. To cope with the adverse macro- and mesoclimatic conditions of the study area, females of the butterfly selected host plants growing in extraordinarily warm microhabitats for oviposition. To secure long-term viability of E. aurinia populations, we recommend creating mosaics of traditionally managed grasslands and early stages of abandonment within the patches.

Annual Population Dynamics and Their Influencing Factors for an Endangered Submerged Macrophyte (Ottelia cordata)

Due to wetland loss, Ottelia cordata (O. cordata, Wallich) Dandy has been categorized as an endangered species on the List of Key Protected Wild Plants in China. Quantifying the relative importance of demographic (i.e., growth, survival, and reproduction) and habitat preference traits on the population dynamics (abundance) of O. cordata could guide how to develop the best recovery strategies of O. cordata, yet currently, there are no studies that investigate this. By monitoring monthly changes in O. cordata abundance and demographic traits (plant height, leaf area, flower sex ratio, and seed number) that were highly correlated with growth rate, photosynthetic rate, and water depth, we identified several relationships. Linear mixed-effect models and variance partition quantified the specific effects of four demographic traits and water depth on O. cordata abundance in three habitat types (paddyfield, stream, and spring). The linear mixed-effect models indicate that among the four demographic traits, height could be significantly positively correlated to abundance in all three habitat types. In contrast, other three traits (leaf area, sex ratio, and seed numbers) were non-significantly associated with abundance across each habitat. Height was determined by water depth, so water depth rather than photosynthetic rate and reproduction rate may promote the development and recovery of O. cordata populations. Variance partition results showed that water depth mediated the positive influence of growth rate on the abundance of O. cordata in the living habitats (paddyfield and spring). In contrast, water depth but not growth rate determined the abundance of O. cordata in the living habitat (stream). However, water depth had a significantly negative impact on the abundance of O. cordata in stream habitats, likely because all of the streams were shallow. Altogether, in the short term for avoiding the potential harm or even extinction of O. cordata, keeping appropriate water depth or transplanting O. cordata to spring should be an effective strategy because the water is not only deep enough but also clear in spring habitats. Additionally, water turbidity was shown to affect the density of O. cordata growth, wherein O. cordata was sparsely distributed when turbidity was high. Therefore, in the long run, to make the population gradually recovery, it will be necessary to restore the degraded wetland. This could be accomplished by reducing water pollution and removing sludge to reduce turbidity and increase hydrological connectivity.

Large scale propagation and in vitro weaning for the restoration of Viola palustris to support assisted colonisation of a threatened butterfly

The distribution and abundance of Boloria selene (small pearl-bordered fritillary butterfly, SPBF) declined over recent decades in many parts of the UK. Availability of food plants, especially marsh violet (Viola palustris), for the caterpillars of the SPBF has been identified as one of the major causes of this decline. To achieve augmentation of existing colonies and develop new populations of SPBF large numbers of marsh violet propagules were required specifically to feed the larvae. The main objectives of the study were to produce thousands of good quality marsh violet propagules to restore selected habitats in the Heart of Durham, Northern England, using in vitro methods. Preliminary trials showed that in vitro multiplication of seedlings from wild collected seeds through conventional agar-based cultures was lengthy, expensive and turned out to be a non-viable route to achieve the objectives. This study explored the potential of bioreactor-based cloning and cost-effective one step rooting and weaning. Robust propagules, ready for transplantation following rapid propagation and one step rooting and weaning in vitro, were raised in a plug system for transplantation and establishment under field conditions. This was achieved by using simple and cost-effective methods to support the large-scale restoration exercise using 14,000 propagules. Application of high throughput micropropagation and low cost one step weaning systems for time-bound conservation and restoration projects are discussed in detail. This research highlights the important role of in vitro methods to support integrated biodiversity conservation of a native larval host plant and threatened butterfly.

Butterfly declines in protected areas of Illinois: Assessing the influence of two decades of climate and landscape change

Despite increasing concern regarding broad-scale declines in insects, there are few published long-term, systematic butterfly surveys in North America, and fewer still that have incorporated the influence of changing climate and landscape variables. In this study, we analyzed 20 years of citizen science data at seven consistently monitored protected areas in Illinois, U.S.A. We used mixed models and PERMANOVA to evaluate trends in butterfly abundance, richness, and composition while also evaluating the effects of temperature and land use. Overall butterfly richness, but not abundance, increased in warmer years. Surprisingly, richness also was positively related to percent impervious surface (at the 2 km radius scale), highlighting the conservation value of protected areas in urban landscapes (or alternately, the potential negative aspects of agriculture). Precipitation had a significant and variable influence through time on overall butterfly abundance and abundance of resident species, larval host plant specialists, and univoltine species. Importantly, models incorporating the influence of changing temperature, precipitation, and impervious surface indicated a significant overall decline in both butterfly abundance and species richness, with an estimated abundance decrease of 3.8%/year and richness decrease of 1.6%/year (52.5% and 27.1% cumulatively from 1999 to 2018). Abundance and richness declines were also noted across all investigated functional groups except non-resident (migratory) species. Butterfly community composition changed through time, but we did not find evidence of systematic biotic homogenization, perhaps because declines were occurring in nearly all functional groups. Finally, at the site-level, declines in either richness or abundance occurred at five of seven locations, with only the two largest locations (>300 Ha) not exhibiting declines. Our results mirror those of other long-term butterfly studies predominantly in Europe and North America that have found associations of butterflies with climate variables and general declines in butterfly richness and abundance.

Influences of landscape structure on butterfly diversity in urban private gardens using a citizen science approach

Although urbanization is increasing worldwide, private gardens may help mitigate the impact of urbanization on butterfly diversity. We investigated how local and landscape factors correspond with the observed butterfly species diversity and species composition in Viennese private gardens. The goal is to determine the importance of private gardens for butterfly conservation. Butterfly species were observed by skilled volunteers by applying a citizen science approach. We related butterfly species numbers in private gardens with local parameters and landscape composition in a radius of 1 km around each garden. Data were analyzed using a regression approach based on generalized linear models. The butterfly species richness in private gardens was positively correlated with butterfly species richness in the surrounding landscapes. Butterfly species richness in private gardens increased with higher proportions of area relevant for butterflies in the surrounding landscape and with increasing numbers of host and nectar plant species in the private gardens. A higher proportion of wooded areas in the surrounding landscape was related with a smaller proportion of the landscape butterfly species pool being observed in the private gardens. Overall, our results could be useful in land use planning, and for future studies of how to integrate citizen science and make urban gardens more beneficial for butterfly conservation.

Engaging the community in pollinator research: the effect of wing pattern and weather on butterfly behavior

Community science, which engages students and the public in data collection and scientific inquiry, is often integrated into conservation and long-term monitoring efforts. However, it has the potential to also introduce the public to, and be useful for, sensory ecology and other fields of study. Here we describe a community science project that exposes participants to animal behavior and sensory ecology using the rich butterfly community of Northwest Arkansas, USA. Butterflies use visual signals to communicate and to attract mates. Brighter colors can produce stronger signals for mate attraction but can also unintentionally attract negative attention from predators. Environmental conditions such as weather can affect visual signaling as well, by influencing the wavelengths of light available and subsequent signal detection. However, we do not know whether the signals butterflies present correlate broadly with how they behave. In this study, we collaborated with hundreds of students and community members at the University of Arkansas (UARK) and the Botanical Gardens of the Ozarks (BGO) for over 3.5 years to examine relationships among wing pattern, weather, time of day, behavior, and flower choice. We found that both weather and wing color influenced general butterfly behavior. Butterflies were seen feeding more on cloudy days than on sunny or partly cloudy days. Brown butterflies fed or sat more often, while white butterflies flew more often relative to other butterfly colors. We also found that there was an interaction between the effects of weather and wing color on butterfly behavior. Furthermore, butterfly color predicted the choice of flower colors that butterflies visited, though this effect was influenced by observer group (UARK student or BGO participant). These results suggest that flower choice may be associated with butterfly wing pattern, and that different environmental conditions may influence butterfly behavior in wing-pattern-specific ways. They also illustrate one way that public involvement in behavioral studies can facilitate the identification of coarse-scale, community-wide behavioral patterns, and lay the groundwork for future studies of sensory niches.

Urban green spaces in Dhaka, Bangladesh, harbour nearly half the country’s butterfly diversity

Cities currently harbour more than half of the world’s human population and continued urban expansion replaces natural landscapes and increases habitat fragmentation. The impacts of urbanisation on biodiversity have been extensively studied in some parts of the world, but there is limited information from South Asia, despite the rapid expansion of cities in the region. Here, we present the results of monthly surveys of butterflies in three urban parks in Dhaka city, Bangladesh, over a 3-year period (January 2014 to December 2016). We recorded 45% (137 of the 305 species) of the country’s butterfly richness, and 40% of the species detected are listed as nationally threatened. However, butterfly species richness declined rapidly in the three study areas over the 3-year period, and the decline appeared to be more severe among threatened species. We developed linear mixed effect models to assess the relationship between climatic variables and butterfly species richness. Overall, species richness was positively associated with maximum temperature and negatively with mean relative humidity and saturation deficit. Our results demonstrate the importance of urban green spaces for nationally threatened butterflies. With rapidly declining urban green spaces in Dhaka and other South Asian cities, we are likely to lose refuges for threatened fauna. There is an urgent need to understand urban biodiversity dynamics in the region, and for proactive management of urban green spaces to protect butterflies in South Asia.

Differences in Response of Butterfly Diversity and Species Composition in Urban Parks to Land Cover and Local Habitat Variables

Background and Objectives: As urbanisation is a significant global trend, there is a profound need for biodiversity protection in urban ecosystems. Moreover, the potential of urban green space to support urban biodiversity should be appreciated. Butterflies are environmental indicators that are sensitive to urbanisation. Therefore, it is important to identify butterfly distribution patterns and the factors influencing butterfly diversity and species composition in urban parks within cities. Research Highlights: To our knowledge, ours is the first study evaluating the effects of both land cover and local habitat features on butterfly species composition in urban parks of Beijing, China. Materials and Methods: In this study, we surveyed butterfly richness and abundance in 28 urban parks in Beijing, China. The parks differed in age and location in the urban area. Meanwhile, we investigated the green space in the surroundings of the parks at multi-spatial scales at the landscape level. We also investigated local park characteristics including the age of the park (Age), perimeter/area ratio of the park (SQPRA), area of the park (ha) (Area), green space cover within the park (Greenp), nectar plant species richness (Necpl), abundance of flowering nectar plants (Necabu) and overall plant species richness (Pl). Generalised linear models (GLMs) and redundancy discriminant analysis (RDA) were applied to relate butterfly diversity and butterfly species composition to environmental variables, respectively. Results: We recorded 3617 individuals belonging to 26 species from July to September in 2019. Parks on the city fringe had significantly higher butterfly diversity. Butterfly species richness was mostly related to total plant richness. The abundance of flowering nectar plants was closely linked to butterfly abundance. Land cover had little impact on butterfly diversity and community structure in urban parks. Conclusions: Once a park has sufficient plants and nectar resources, it becomes a useful haven for urban butterflies, regardless of the surrounding land cover. Well-planned urban parks focused on local habitat quality support butterfly conservation.

Butterfly richness and abundance along a gradient of imperviousness and the importance of matrix quality

Heterogeneity in quantity and quality of resources provided in the urban matrix may mitigate adverse effects of urbanization intensity on the structure of biotic communities. To assess this we quantified the spatial variation in butterfly richness and abundance along an impervious surface gradient using three measures of urban matrix quality: floral resource availability and origin (native vs. exotic plants), tree cover, and the occurrence of remnant habitat patches. Butterfly richness and abundance were surveyed in 100 cells (500 × 500 m), selected using a random-stratified sampling design, across a continuous gradient of imperviousness in Melbourne, Australia. Sampling occurred twice during the butterfly flight season. Occurrence data were analyzed using generalized linear models at local and mesoscales. Despite high sampling completeness, we did not detect 75% of species from the regional species pool in the urban area, suggesting that urbanization has caused a large proportion of the region's butterflies to become absent or extremely rare within Melbourne's metro-area. Those species that do remain are largely very generalist in their choice of larval host plants. Butterfly species richness and abundance declined with increasing impervious surface cover and, contrary to evidence for other taxa, there was no evidence that richness peaked at intermediate levels of urbanization. Declines in abundance appeared to be more noticeable when impervious surface cover exceeded 25%, while richness declined linearly with increasing impervious surface cover. We find evidence that the quality of the urban matrix (floral resources and remnant vegetation) influenced butterfly richness and abundance although the effects were small. Total butterfly abundance responded negatively to exotic floral abundance early in the sampling season and positively to total floral abundance later in the sampling season. Butterfly species richness increased with tree cover. Negative impacts of increased urbanization intensity on butterfly species richness and abundance may be mitigated to some extent by improving the quality of the urban matrix by enhancing tree cover and the provision of floral resources, with some evidence that native plants are more effective.

Host-plant availability drives the spatiotemporal dynamics of interacting metapopulations across a fragmented landscape

The dynamics of ecological communities depend partly on species interactions within and among trophic levels. Experimental work has demonstrated the impact of species interactions on the species involved, but it remains unclear whether these effects can also be detected in long‐term time series across heterogeneous landscapes. We analyzed a 19‐yr time series of patch occupancy by the Glanville fritillary butterfly Melitaea cinxia, its specialist parasitoid wasp Cotesia melitaearum, and the specialist fungal pathogen Podosphaera plantaginis infecting Plantago lanceolata, a host plant of the Glanville fritillary. These species share a network of more than 4,000 habitat patches in the Åland islands, providing a metacommunity data set of unique spatial and temporal resolution. To assess the influence of interactions among the butterfly, parasitoid, and mildew on metacommunity dynamics, we modeled local colonization and extinction rates of each species while including or excluding the presence of potentially interacting species in the previous year as predictors. The metapopulation dynamics of all focal species varied both along a gradient in host plant abundance, and spatially as indicated by strong effects of local connectivity. Colonization and to a lesser extent extinction rates depended also on the presence of interacting species within patches. However, the directions of most effects differed from expectations based on previous experimental and modeling work, and the inferred influence of species interactions on observed metacommunity dynamics was limited. These results suggest that although local interactions among the butterfly, parasitoid, and mildew occur, their roles in metacommunity spatiotemporal dynamics are relatively weak. Instead, all species respond to variation in plant abundance, which may in turn fluctuate in response to variation in climate, land use, or other environmental factors.

Mobility costs and energy uptake mediate the effects of morphological traits on species' distribution and abundance

Individuals of large or dark-colored ectothermic species often have a higher reproduction and activity than small or light-colored ones. However, investments into body size or darker colors should negatively affect the fitness of individuals as they increase their growth and maintenance costs. Thus, it is unlikely that morphological traits directly affect species' distribution and abundance. Yet, this simplification is frequently made in trait-based ecological analyses. Here, we integrated the energy allocation strategies of species into an ecophysiological framework to explore the mechanisms that link species' morphological traits and population dynamics. We hypothesized that the effects of morphological traits on species' distribution and abundance are not direct but mediated by components of the energy budget and that species can allocate more energy towards dispersal and reproduction if they compensate their energetic costs by reducing mobility costs or increasing energy uptake. To classify species' energy allocation strategies, we used easily measured proxies for the mobility costs and energy uptake of butterflies that can be also applied to other taxa. We demonstrated that contrasting effects of morphological traits on distribution and abundance of butterfly species offset each other when species' energy allocation strategies are not taken into account. Larger and darker butterfly species had wider distributions and were more abundant if they compensated the investment into body size and color darkness (i.e., melanin) by reducing their mobility costs or increasing energy uptake. Adults of darker species were more mobile and foraged less compared to lighter colored ones, if an investment into melanin was indirectly compensated via a size-dependent reduction of mobility costs or increase of energy uptake. Our results indicate that differences in the energy allocations strategies of species account for a considerable part of the variation in species' distribution and abundance that is left unexplained by morphological traits alone and ignoring these differences can lead to false mechanistic conclusions. Therefore, our findings highlight the potential of integrating proxies for species' energy allocation strategies into trait-based models not only for understanding the physiological mechanisms underlying variation in species' distribution and abundance, but also for improving predictions of the population dynamics of species.

Developmental trap or demographic bonanza? Opposing consequences of earlier phenology in a changing climate for a multivoltine butterfly

A rapidly changing climate has the potential to interfere with the timing of environmental cues that ectothermic organisms rely on to initiate and regulate life history events. Short-lived ectotherms that exhibit plasticity in their life history could increase the number of generations per year under warming climate. If many individuals successfully complete an additional generation, the population experiences an additional opportunity to grow, and a warming climate could lead to a demographic bonanza. However, these plastic responses could become maladaptive in temperate regions, where a warmer climate could trigger a developmental pathway that cannot be completed within the growing season, referred to as a developmental trap. Here we incorporated detailed demography into commonly used photothermal models to evaluate these demographic consequences of phenological shifts due to a warming climate on the formerly widespread, multivoltine butterfly (Pieris oleracea). Using species-specific temperature- and photoperiod-sensitive vital rates, we estimated the number of generations per year and population growth rate over the set of climate conditions experienced during the past 38 years. We predicted that populations in the southern portion of its range have added a fourth generation in recent years, resulting in higher annual population growth rates (demographic bonanzas). We predicted that populations in the Northeast United States have experienced developmental traps, where increases in the thermal window initially caused mortality of the final generation and reduced growth rates. These populations may recover if more growing degree days are added to the year. Our framework for incorporating detailed demography into commonly used photothermal models demonstrates the importance of using both demography and phenology to predict consequences of phenological shifts.

Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA

Severe insect declines make headlines, but they are rarely based on systematic monitoring outside of Europe. We estimate the rate of change in total butterfly abundance and the population trends for 81 species using 21 years of systematic monitoring in Ohio, USA. Total abundance is declining at 2% per year, resulting in a cumulative 33% reduction in butterfly abundance. Three times as many species have negative population trends compared to positive trends. The rate of total decline and the proportion of species in decline mirror those documented in three comparable long-term European monitoring programs. Multiple environmental changes such as climate change, habitat degradation, and agricultural practices may contribute to these declines in Ohio and shift the makeup of the butterfly community by benefiting some species over others. Our analysis of life-history traits associated with population trends shows an impact of climate change, as species with northern distributions and fewer annual generations declined more rapidly. However, even common and invasive species associated with human-dominated landscapes are declining, suggesting widespread environmental causes for these trends. Declines in common species, although they may not be close to extinction, will have an outsized impact on the ecosystem services provided by insects. These results from the most extensive, systematic insect monitoring program in North America demonstrate an ongoing defaunation in butterflies that on an annual scale might be imperceptible, but cumulatively has reduced butterfly numbers by a third over 20 years.

Larval Food Limitation in a Speyeria Butterfly (Nymphalidae): How Many Butterflies Can Be Supported?

For herbivorous insects the importance of larval food plants is obvious, yet the role of host abundance and density in conservation are relatively understudied. Populations of Speyeria butterflies across North America have declined and Speyeria adiaste is an imperiled species endemic to the southern California Coast Ranges. In this paper, we study the link between the food plant Viola purpurea quercetorum and abundance of its herbivore Speyeria adiaste clemencei to better understand the butterfly’s decline and aid in restoration of this and other Speyeria species. To assess the degree to which the larval food plant limits adult abundance of S. a. clemencei in 2013, we compared adult population counts to population size predicted from a Monte Carlo simulation using data for number of V. pur. quercetorum plants, number of leaves per plant, and leaf area per plant, with lab estimates of leaf area consumed to reach pupal stage on the non-native host V. papilionacea. Results indicated an average estimate of 765 pupae (median = 478), with 77% of the distribution being <1000 pupae. However, this was heavily dependent on plant distribution, and accounting for the number of transect segments with sufficient host to support a pupa predicted 371 pupae. The adult population empirical estimate was 227 individuals (95% CI is 146 to 392), which lies near the first quartile of the simulated distribution. These results indicate that the amount of host available to larvae was more closely linked to adult abundance than the amount of host present, especially when considering assumptions of the analyses. The data also indicate that robust populations require host density well in excess of what is eaten by larvae, in combination with appropriate spacing, to mitigate factors such as competition, starvation from leaving host patches, or unrelated to food plant, such as mortality from drought, predators, parasites, or disease.

Anthropogenic fragmentation of landscapes: mechanisms for eroding the specificity of plant-herbivore interactions

Reduced ecological specialization is an emerging, general pattern of ecological networks in fragmented landscapes. In plant-herbivore interactions, reductions in dietary specialization of herbivore communities are consistently associated with fragmented landscapes, but the causes remain poorly understood. We propose several hypothetical bottom-up and top-down mechanisms that may reduce the specificity of plant-herbivore interactions. These include empirically plausible applications and extensions of theory based on reduced habitat patch size and isolation (considered jointly), and habitat edge effects. Bottom-up effects in small, isolated habitat patches may limit availability of suitable hostplants, a constraint that increases with dietary specialization. Poor hostplant quality due to inbreeding in such fragments may especially disadvantage dietary specialist herbivores even when their hostplants are present. Size and isolation of habitat patches may change patterns of predation of herbivores, but whether such putative changes are associated with herbivore dietary specialization should depend on the mobility, size, and diet breadth of predators. Bottom-up edge effects may favor dietary generalist herbivores, yet top-down edge effects may favor dietary specialists owing to reduced predation. An increasingly supported edge effect is trophic ricochets generated by large grazers/browsers, which remove key hostplant species of specialist herbivores. We present empirical evidence that greater deer browsing in small forest fragments disproportionately reduces specialist abundances in lepidopteran assemblages in northeastern USA. Despite indirect evidence for these mechanisms, they have received scant direct testing with experimental approaches at a landscape scale. Identifying their relative contributions to reduced specificity of plant-herbivore interactions in fragmented landscapes is an important research goal.

Landscape simplification weakens the association between terrestrial producer and consumer diversity in Europe

Land-use change is one of the primary drivers of species loss, yet little is known about its effect on other components of biodiversity that may be at risk. Here, we ask whether, and to what extent, landscape simplification, measured as the percentage of arable land in the landscape, disrupts the functional and phylogenetic association between primary producers and consumers. Across seven European regions, we inferred the potential associations (functional and phylogenetic) between host plants and butterflies in 561 seminatural grasslands. Local plant diversity showed a strong bottom-up effect on butterfly diversity in the most complex landscapes, but this effect disappeared in simple landscapes. The functional associations between plant and butterflies are, therefore, the results of processes that act not only locally but are also dependent on the surrounding landscape context. Similarly, landscape simplification reduced the phylogenetic congruence among host plants and butterflies indicating that closely related butterflies become more generalist in the resources used. These processes occurred without any detectable change in species richness of plants or butterflies along the gradient of arable land. The structural properties of ecosystems are experiencing substantial erosion, with potentially pervasive effects on ecosystem functions and future evolutionary trajectories. Loss of interacting species might trigger cascading extinction events and reduce the stability of trophic interactions, as well as influence the longer term resilience of ecosystem functions. This underscores a growing realization that species richness is a crude and insensitive metric and that both functional and phylogenetic associations, measured across multiple trophic levels, are likely to provide additional and deeper insights into the resilience of ecosystems and the functions they provide.