Forest resilience to global warming is strongly modulated by local-scale topographic, microclimatic and biotic conditions

Resilience of endangered rear edge populations of cold-adapted forests in the Mediterranean basin is increasingly altered by extreme heatwave and drought pressures. It remains unknown, however, whether microclimatic variation in these isolated forests could ultimately result in large intra-population variability in the demographic responses, allowing the coexistence of contrasting declining and resilient trends across small topographic gradients. Multiple key drivers promoting spatial variability in the resilience of rear edge forests remain largely unassessed, including amplified and buffered thermal exposure induced by heatwaves along topographic gradients, and increased herbivory pressure on tree saplings in defaunated areas lacking efficient apex predators. Here we analysed whether indicators of forest resilience to global warming are strongly modulated by local-scale topographic, microclimatic and biotic conditions. We studied a protected rear edge forest of sessile oak Quercus petraea, applying a suite of 20 indicators of resilience of tree secondary growth, including multidecadal and short-term indices. We also analysed sapling recruitment success, recruit/adult ratios and sapling thermal exposure across topographic gradients. We found large within population variation in secondary growth resilience, in recruitment success and in thermal exposure of tree saplings to heatwaves, and this variability was spatially structured along small-scale topographical gradients. Multidecadal resilience indices and curves provide useful descriptors of forest vulnerability to climate warming, complementing assessments based in the analysis of short-term resilience indicators. Species-specific associations of trees with microclimatic variability are reported. Biotic factors are key in determining long-term resilience in climatically stressed rear edge forests, with strong limitation of sapling recruitment by increased roe deer and wild boar herbivory. Our results also support non-stationary effects of climate determining forest growth responses and resilience, showing increased negative effects of warming and drought over the last decades in declining stands. Synthesis. Our findings do not support scenarios predicting spatially homogeneous distributional shifts and limited resilience in rear edge populations, and are more supportive of scenarios including spatially heterogeneous responses, characterised with contrasting intra-population trends of forest resilience. We conclude that forest resilience responses to climate warming are strongly modulated by local-scale microclimatic, topographic and biotic factors. Accurate predictions of forest responses to changes in climate would therefore largely benefit from the integration of local-scale abiotic and biotic factors

Impacts of Global Change on Mediterranean Forests and Their Services

The increase in aridity, mainly by decreases in precipitation but also by higher temperatures, is likely the main threat to the diversity and survival of Mediterranean forests. Changes in land use, including the abandonment of extensive crop activities, mainly in mountains and remote areas, and the increases in human settlements and demand for more resources with the resulting fragmentation of the landscape, hinder the establishment of appropriate management tools to protect Mediterranean forests and their provision of services and biodiversity. Experiments and observations indicate that if changes in climate, land use and other components of global change, such as pollution and overexploitation of resources, continue, the resilience of many forests will likely be exceeded, altering their structure and function and changing, mostly decreasing, their capacity to continue to provide their current services. A consistent assessment of the impacts of the changes, however, remains elusive due to the difficulty of obtaining simultaneous and complete data for all scales of the impacts in the same forests, areas and regions. We review the impacts of climate change and other components of global change and their interactions on the terrestrial forests of Mediterranean regions, with special attention to their impacts on ecosystem services. Management tools for counteracting the negative effects of global change on Mediterranean ecosystem- services are finally discussed

Impacts of global change on Mediterranean forests and their services

The increase in aridity, mainly by decreases in precipitation but also by higher temperatures, is likely the main threat to the diversity and survival of Mediterranean forests. Changes in land use, including the abandonment of extensive crop activities, mainly in mountains and remote areas, and the increases in human settlements and demand for more resources with the resulting fragmentation of the landscape, hinder the establishment of appropriate management tools to protect Mediterranean forests and their provision of services and biodiversity. Experiments and observations indicate that if changes in climate, land use and other components of global change, such as pollution and overexploitation of resources, continue, the resilience of many forests will likely be exceeded, altering their structure and function and changing, mostly decreasing, their capacity to continue to provide their current services. A consistent assessment of the impacts of the changes, however,remains elusive due to the difficulty of obtaining simultaneous and complete data for all scales of the impacts in the same forests, areas and regions. We review the impacts of climate change and other components of global change and their interactions on the terrestrial forests of Mediterranean regions, with special attention to their impacts on ecosystem services. Management tools for counteracting the negative effects of global change on Mediterranean ecosystem- services are finally discussed

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all the world’s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world\u27s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Process-based insights into insect responses to climate change: linking microclimate, ecophysiology, and demography in a butterfly model system

Representant el 10% de la biomassa animal, els insectes juguen rols vitals en el funcionament dels ecosistemes terrestres i d'aigua dolça arreu del món. Tot i així, moltes poblacions d'insectes estan en declivi, fet que posa en perill les seves contribucions a la natura i a les societats humans. Aquests declivis s'atribueixen als canvis recents en els usos del sòl, la pèrdua d'hàbitats, la intensificació agrícola i, de manera cada cop més important, el canvi climàtic. Dècades de recerca sobre els impactes del canvi climàtic en els insectes han revelat que les seves respostes són polifacètiques i estan influenciades per un entramat complex de processos a diverses escales. Tot i així, els models predictius existents solen ometre els processos subjacents que modulen la seva exposició i sensibilitat climàtiques. A part, aquests models sovint agreguen les dades climàtiques a escales espaciotemporals massa grans per a reflectir acuradament l'experiència climàtica dels insectes, la qual està més estretament lligada a les condicions mesurades en els seus microhàbitats. L'objectiu d'aquesta tesi es construir models predictius més realistes que il·lustrin els impactes actuals i futurs del canvi climàtic sobre una espècie d'insecte molt coneguda -la blanqueta perfumada, Pieris napi- a la regió Mediterrània. Els capítols inicials caracteritzen l'exposició microclimàtica de la P. napi i la dinàmica de les seves plantes hoste en diverses poblacions. A més a més, hi examino la variació de trets de l'espècie determinants de la seva susceptibilitat climàtica. Els resultats indiquen que les poblacions de P. napi estan predominantment influenciades per les condicions estivals, les quals modulen l'exposició microclimàtica de les papallones i el seu accés a les plantes hoste. En els capítols subseqüents, utilitzo les dades recollides empíricament per a parametritzar dos models basats en processos. El primer model utilitza la tolerància tèrmica estimada experimentalment per a computar la mortalitat induïda per altes temperatures en resposta al microclima mesurat a camp. Les dades dels treballs empírics anteriors també s'utilitzen per a construir un model matricial de poblacions. Aquest segon model integra les taxes vitals de la P. napi al llarg del seu cicle vital considerant els efectes de l'exposició microclimàtica extrema i de l'escassetat de planta hoste induïda per la sequera. El model inicialment simula els règims actuals de temperatures extremes microclimàtiques, de sequera i la seva acció combinada (esdeveniments extrems compostos). Els resultats indiquen que els declivis presents en alguns poblacions de P. napi estan principalment conduïts pels efectes de la sequera sobre les plantes hoste. Després, el model prediu la dinàmica de les poblacions en futurs règims d'esdeveniments extrems a nivells creixents d'escalfament global. Aquests escenaris de futur anticipen un creixement en la freqüència d'esdeveniments actualment de baixa versemblança i d'alt impacte en relació a esdeveniments extrems més moderats i recurrents. A causa de la relació no lineal entre la temperatura i la mortalitat induïda per altes temperatures, les simulacions prediuen que en trajectòries de canvi climàtic no alineades amb els Acords de París, aquests esdeveniments de baixa probabilitat i alt impacte poden desencadenar declivis severs i extensos a les poblacions de Pieris napi. En conclusió, aquesta tesi subratlla el valor d'utilitzar models basats en processos que aprofiten les dades recollides a camp i experimentalment per a predir les respostes dels insectes al canvi climàtic. Els models predictius que hi he desenvolupat desgranen el conjunt de processos subjacents identificats en els estudis empírics i en quantifiquen la seva influència individual i combinada. A més a més, els models que he utilitzat destapen una amenaça a les poblacions d'insectes fins ara ignorada: l'escalada desproporcionada dels esdeveniments extrems de baixa versemblança i alt impacte amb el canvi climàtic.Representando el 10% de la biomasa animal, los insectos desempeñan roles vitales en el funcionamiento de los ecosistemas terrestres y de agua dulce alrededor del mundo. Aun así, muchas poblaciones de insectos están en declive, poniendo en peligro sus contribuciones a la naturaleza y a las sociedades humanas. Estos declives se atribuyen a los cambios recientes en los usos del suelo, la pérdida de hábitats, la intensificación agrícola y, de forma cada vez más importante, el cambio climático. Décadas de investigación sobre los impactos del cambio climático en los insectos han revelado que sus respuestas son polifacéticas y están influenciadas por un entramado complejo de procesos a distintas escalas. Aun así, los modelos predictivos existentes suelen omitir los procesos subyacentes que modulan su exposición y sensibilidad climáticas. A parte, estos modelos suelen agregar los datos climáticos a escalas espacio-temporales demasiado grandes para reflejar acuradamente la experiencia climática de los insectos, la cual está más estrechamente vinculada a las condiciones medidas en sus microhábitats. El objetivo de esta tesis es construir modelos predictivos más realistas que ilustren los impactos actuales y futuros del cambio climático sobre una especie de insecto muy conocida -la blanca verdinervada, Pieris napi- en la región Mediterránea. Los capítulos iniciales caracterizan la exposición microclimática de la P. napi y la dinámica de sus plantas huésped en distintas poblaciones. Además, examinan la variación en rasgos de la especie determinantes de su susceptibilidad climática. Los resultados indican que las poblaciones de P. napi están predominantemente influenciadas por las condiciones estivales, las cuales modulan la exposición microclimática de las mariposas y su acceso a las plantas huésped. En los capítulos subsiguientes, utilizo los datos recogidos empíricamente para parametrizar dos modelos basados en procesos. El primer modelo utiliza la tolerancia térmica estimada experimentalmente para computar la mortalidad inducida por altas temperaturas en respuesta al microclima medido en el campo. Los datos de los trabajos empíricos anteriores también se utilizan para construir un modelo matricial de poblaciones. Este segundo modelo integra las tasas vitales de la P. napi a lo largo de su ciclo vital considerando los efectos de la exposición microclimática extrema y de la escasez de planta huesped inducida por la sequía. El modelo inicialmente simula los regímenes actuales de temperaturas extremas, de sequía y su acción combinada. Los resultados indican que los declives presentes en algunas poblaciones de P. napi están principalmente conducidos por los efectos de la sequía en las plantas huésped. Después, el modelo predice la dinámica de las poblaciones en futuros regímenes de eventos extremos en niveles crecientes de calentamiento global. Estos escenarios de futuro anticipan un crecimiento en la frecuencia de eventos actualmente de baja verosimilitud y de alto impacto en relación a eventos extremos más moderados y recurrentes. A causa de la relación no lineal entre la temperatura y la mortalidad inducida por altas temperaturas, las simulaciones predicen que en trayectorias de cambio climático no alineadas con los Acuerdos de París, estos eventos de baja probabilidad y alto impacto pueden desencadenar declives severos y extensos en las poblaciones de Pieris napi. En conclusión, esta tesis subraya el valor de utilizar modelos basados en procesos que aprovechan los datos recogidos en el campo y experimentalmente para predecir las respuestas de los insectos al cambio climático. Los modelos predictivos que he desarrollado desgranan el conjunto de procesos subyacentes identificados en los estudios empíricos y cuantifican su influencia individual y combinada. Además, los modelos que he utilizado destapan una amenaza a las poblaciones de insectos hasta ahora ignorada: la escalada desproporcionada de los eventos extremos de baja verosimilitud y alto impacto con el cambio climático.Insects are in the warp and weft of the fabric of life on which we rely. Constituting 10% of animal biomass, insects play vital roles in ecological functions within terrestrial and freshwater ecosystems worldwide. However, many insect populations are experiencing declines, jeopardizing their significant contributions to both nature and human societies. These declines are primarily attributed to shifting land uses, habitat loss, agricultural intensification, and, as an increasingly influential factor, climate change. Decades of research on the impact of climate change on insects have revealed that their responses are multifaceted, influenced by a complex interplay of processes across various scales. However, existing predictive models often overlook the underlying climatic and ecological processes that shape insect exposure and sensitivity. These models frequently aggregate climatic data on broad spatiotemporal scales that do not accurately reflect insects' climatic experiences, which are more tightly linked to the conditions measured in their microhabitats and host plants. The objective of this thesis is to build more realistic predictive models that depict the current and future impacts of climate change on a well-known insect species -the green-veined white butterfly, Pieris napi- in the Mediterranean region. These models will be grounded in fundamental physiological and demographic processes. The initial chapters characterise P. napi's microclimatic exposure and the dynamics of their host plants across diverse populations. Additionally, I examine various traits of the butterfly species that determine their susceptibility to climate variations. Findings indicate that P. napi populations are predominantly influenced by summer conditions which shapes butterfly microclimatic exposure and the availability and quality of their host plants. In the subsequent chapters, I employ the empirically collected data to parameterise two process-based models. The first model employs the species' experimentally estimated thermal tolerance to compute heat-induced mortality in response to fluctuating microclimatic temperatures recorded in the field. Mortality rates caused by extreme thermal stresses are relatively low in declining lowland populations of P. napi, despite their limited access to microclimatic buffering. These outcomes underscore the pivotal role microclimatic mosaics and microhabitat choices play in mitigating the impacts of climate change on insects. The data from previous empirical work are then utilized to build a matrix population model. This second model integrates P. napi's vital rates across its life cycle, considering the effects of extreme microclimatic heat exposure and drought-induced scarcity of host plants on larval mortality and pupation. The model initially simulates present-day regimes of microclimatic heat extremes, drought, and their concurrent action (i.e. extreme hot-dry compound events). Results indicate that the existing declines in certain P. napi populations are primarily driven by drought-induced effects on host plants, corroborating prior field observations and highlighting the critical role indirect processes play in mediating insect responses to climate change. Subsequently, the model forecasts future regimes of extreme events under increasing global warming levels. These future scenarios anticipate a rise in the frequency of currently low-likelihood high-impact events relative to more moderate and recurrent extremes. Due to the nonlinear relationship between temperature and heat-induced mortality, simulations predict that under a global warming trajectory not aligned with the Paris Agreement, these low-probability, high-impact heat events will trigger more extensive and severe declines in P. napi populations. This effect could potentially surpass the impact of drought-induced plant scarcity. In conclusion, this thesis underscores the value of employing process-based models that leverage field and experimental data to predict insect responses to climate change. The predictive models developed herein unravel the core underlying processes identified in empirical studies and quantify their individual and combined influences. Furthermore, these process-based models unveil an overlooked threat to insect populations: the disproportional escalation of low-likelihood high-impact extreme heat events.Universitat Autònoma de Barcelona. Programa de Doctorat en Ecologia Terrestr

Process-based insights into insect responses to climate change : linking microclimate, ecophysiology, and demography in a butterfly model system

Representant el 10% de la biomassa animal, els insectes juguen rols vitals en el funcionament dels ecosistemes terrestres i d'aigua dolça arreu del món. Tot i així, moltes poblacions d'insectes estan en declivi, fet que posa en perill les seves contribucions a la natura i a les societats humans. Aquests declivis s'atribueixen als canvis recents en els usos del sòl, la pèrdua d'hàbitats, la intensificació agrícola i, de manera cada cop més important, el canvi climàtic. Dècades de recerca sobre els impactes del canvi climàtic en els insectes han revelat que les seves respostes són polifacètiques i estan influenciades per un entramat complex de processos a diverses escales. Tot i així, els models predictius existents solen ometre els processos subjacents que modulen la seva exposició i sensibilitat climàtiques. A part, aquests models sovint agreguen les dades climàtiques a escales espaciotemporals massa grans per a reflectir acuradament l'experiència climàtica dels insectes, la qual està més estretament lligada a les condicions mesurades en els seus microhàbitats. L'objectiu d'aquesta tesi es construir models predictius més realistes que il·lustrin els impactes actuals i futurs del canvi climàtic sobre una espècie d'insecte molt coneguda -la blanqueta perfumada, Pieris napi- a la regió Mediterrània. Els capítols inicials caracteritzen l'exposició microclimàtica de la P. napi i la dinàmica de les seves plantes hoste en diverses poblacions. A més a més, hi examino la variació de trets de l'espècie determinants de la seva susceptibilitat climàtica. Els resultats indiquen que les poblacions de P. napi estan predominantment influenciades per les condicions estivals, les quals modulen l'exposició microclimàtica de les papallones i el seu accés a les plantes hoste. En els capítols subseqüents, utilitzo les dades recollides empíricament per a parametritzar dos models basats en processos. El primer model utilitza la tolerància tèrmica estimada experimentalment per a computar la mortalitat induïda per altes temperatures en resposta al microclima mesurat a camp. Les dades dels treballs empírics anteriors també s'utilitzen per a construir un model matricial de poblacions. Aquest segon model integra les taxes vitals de la P. napi al llarg del seu cicle vital considerant els efectes de l'exposició microclimàtica extrema i de l'escassetat de planta hoste induïda per la sequera. El model inicialment simula els règims actuals de temperatures extremes microclimàtiques, de sequera i la seva acció combinada (esdeveniments extrems compostos). Els resultats indiquen que els declivis presents en alguns poblacions de P. napi estan principalment conduïts pels efectes de la sequera sobre les plantes hoste. Després, el model prediu la dinàmica de les poblacions en futurs règims d'esdeveniments extrems a nivells creixents d'escalfament global. Aquests escenaris de futur anticipen un creixement en la freqüència d'esdeveniments actualment de baixa versemblança i d'alt impacte en relació a esdeveniments extrems més moderats i recurrents. A causa de la relació no lineal entre la temperatura i la mortalitat induïda per altes temperatures, les simulacions prediuen que en trajectòries de canvi climàtic no alineades amb els Acords de París, aquests esdeveniments de baixa probabilitat i alt impacte poden desencadenar declivis severs i extensos a les poblacions de Pieris napi. En conclusió, aquesta tesi subratlla el valor d'utilitzar models basats en processos que aprofiten les dades recollides a camp i experimentalment per a predir les respostes dels insectes al canvi climàtic. Els models predictius que hi he desenvolupat desgranen el conjunt de processos subjacents identificats en els estudis empírics i en quantifiquen la seva influència individual i combinada. A més a més, els models que he utilitzat destapen una amenaça a les poblacions d'insectes fins ara ignorada: l'escalada desproporcionada dels esdeveniments extrems de baixa versemblança i alt impacte amb el canvi climàtic.Representando el 10% de la biomasa animal, los insectos desempeñan roles vitales en el funcionamiento de los ecosistemas terrestres y de agua dulce alrededor del mundo. Aun así, muchas poblaciones de insectos están en declive, poniendo en peligro sus contribuciones a la naturaleza y a las sociedades humanas. Estos declives se atribuyen a los cambios recientes en los usos del suelo, la pérdida de hábitats, la intensificación agrícola y, de forma cada vez más importante, el cambio climático. Décadas de investigación sobre los impactos del cambio climático en los insectos han revelado que sus respuestas son polifacéticas y están influenciadas por un entramado complejo de procesos a distintas escalas. Aun así, los modelos predictivos existentes suelen omitir los procesos subyacentes que modulan su exposición y sensibilidad climáticas. A parte, estos modelos suelen agregar los datos climáticos a escalas espacio-temporales demasiado grandes para reflejar acuradamente la experiencia climática de los insectos, la cual está más estrechamente vinculada a las condiciones medidas en sus microhábitats. El objetivo de esta tesis es construir modelos predictivos más realistas que ilustren los impactos actuales y futuros del cambio climático sobre una especie de insecto muy conocida -la blanca verdinervada, Pieris napi- en la región Mediterránea. Los capítulos iniciales caracterizan la exposición microclimática de la P. napi y la dinámica de sus plantas huésped en distintas poblaciones. Además, examinan la variación en rasgos de la especie determinantes de su susceptibilidad climática. Los resultados indican que las poblaciones de P. napi están predominantemente influenciadas por las condiciones estivales, las cuales modulan la exposición microclimática de las mariposas y su acceso a las plantas huésped. En los capítulos subsiguientes, utilizo los datos recogidos empíricamente para parametrizar dos modelos basados en procesos. El primer modelo utiliza la tolerancia térmica estimada experimentalmente para computar la mortalidad inducida por altas temperaturas en respuesta al microclima medido en el campo. Los datos de los trabajos empíricos anteriores también se utilizan para construir un modelo matricial de poblaciones. Este segundo modelo integra las tasas vitales de la P. napi a lo largo de su ciclo vital considerando los efectos de la exposición microclimática extrema y de la escasez de planta huesped inducida por la sequía. El modelo inicialmente simula los regímenes actuales de temperaturas extremas, de sequía y su acción combinada. Los resultados indican que los declives presentes en algunas poblaciones de P. napi están principalmente conducidos por los efectos de la sequía en las plantas huésped. Después, el modelo predice la dinámica de las poblaciones en futuros regímenes de eventos extremos en niveles crecientes de calentamiento global. Estos escenarios de futuro anticipan un crecimiento en la frecuencia de eventos actualmente de baja verosimilitud y de alto impacto en relación a eventos extremos más moderados y recurrentes. A causa de la relación no lineal entre la temperatura y la mortalidad inducida por altas temperaturas, las simulaciones predicen que en trayectorias de cambio climático no alineadas con los Acuerdos de París, estos eventos de baja probabilidad y alto impacto pueden desencadenar declives severos y extensos en las poblaciones de Pieris napi. En conclusión, esta tesis subraya el valor de utilizar modelos basados en procesos que aprovechan los datos recogidos en el campo y experimentalmente para predecir las respuestas de los insectos al cambio climático. Los modelos predictivos que he desarrollado desgranan el conjunto de procesos subyacentes identificados en los estudios empíricos y cuantifican su influencia individual y combinada. Además, los modelos que he utilizado destapan una amenaza a las poblaciones de insectos hasta ahora ignorada: la escalada desproporcionada de los eventos extremos de baja verosimilitud y alto impacto con el cambio climático.Insects are in the warp and weft of the fabric of life on which we rely. Constituting 10% of animal biomass, insects play vital roles in ecological functions within terrestrial and freshwater ecosystems worldwide. However, many insect populations are experiencing declines, jeopardizing their significant contributions to both nature and human societies. These declines are primarily attributed to shifting land uses, habitat loss, agricultural intensification, and, as an increasingly influential factor, climate change. Decades of research on the impact of climate change on insects have revealed that their responses are multifaceted, influenced by a complex interplay of processes across various scales. However, existing predictive models often overlook the underlying climatic and ecological processes that shape insect exposure and sensitivity. These models frequently aggregate climatic data on broad spatiotemporal scales that do not accurately reflect insects' climatic experiences, which are more tightly linked to the conditions measured in their microhabitats and host plants. The objective of this thesis is to build more realistic predictive models that depict the current and future impacts of climate change on a well-known insect species -the green-veined white butterfly, Pieris napi- in the Mediterranean region. These models will be grounded in fundamental physiological and demographic processes. The initial chapters characterise P. napi's microclimatic exposure and the dynamics of their host plants across diverse populations. Additionally, I examine various traits of the butterfly species that determine their susceptibility to climate variations. Findings indicate that P. napi populations are predominantly influenced by summer conditions which shapes butterfly microclimatic exposure and the availability and quality of their host plants. In the subsequent chapters, I employ the empirically collected data to parameterise two process-based models. The first model employs the species' experimentally estimated thermal tolerance to compute heat-induced mortality in response to fluctuating microclimatic temperatures recorded in the field. Mortality rates caused by extreme thermal stresses are relatively low in declining lowland populations of P. napi, despite their limited access to microclimatic buffering. These outcomes underscore the pivotal role microclimatic mosaics and microhabitat choices play in mitigating the impacts of climate change on insects. The data from previous empirical work are then utilized to build a matrix population model. This second model integrates P. napi's vital rates across its life cycle, considering the effects of extreme microclimatic heat exposure and drought-induced scarcity of host plants on larval mortality and pupation. The model initially simulates present-day regimes of microclimatic heat extremes, drought, and their concurrent action (i.e. extreme hot-dry compound events). Results indicate that the existing declines in certain P. napi populations are primarily driven by drought-induced effects on host plants, corroborating prior field observations and highlighting the critical role indirect processes play in mediating insect responses to climate change. Subsequently, the model forecasts future regimes of extreme events under increasing global warming levels. These future scenarios anticipate a rise in the frequency of currently low-likelihood high-impact events relative to more moderate and recurrent extremes. Due to the nonlinear relationship between temperature and heat-induced mortality, simulations predict that under a global warming trajectory not aligned with the Paris Agreement, these low-probability, high-impact heat events will trigger more extensive and severe declines in P. napi populations. This effect could potentially surpass the impact of drought-induced plant scarcity. In conclusion, this thesis underscores the value of employing process-based models that leverage field and experimental data to predict insect responses to climate change. The predictive models developed herein unravel the core underlying processes identified in empirical studies and quantify their individual and combined influences. Furthermore, these process-based models unveil an overlooked threat to insect populations: the disproportional escalation of low-likelihood high-impact extreme heat events

Data from: Phenotypic biomarkers of climatic impacts on declining insect populations: a key role for decadal drought, thermal buffering and amplification effects and host plant dynamics

1. Widespread population declines have been reported for diverse Mediterranean butterflies over the last three decades, and have been significantly associated to increased global change impacts. The specific landscape and climatic drivers of these declines remain uncertain for most declining species. 2. Here we analyse whether plastic phenotypic traits of a model butterfly species (Pieris napi) perform as reliable biomarkers of vulnerability to extreme temperature impacts in natural populations, showing contrasting trends in thermally exposed and thermally buffered populations. 3. We also examine whether improved descriptions of thermal exposure of insect populations can be achieved by combining multiple information sources (i.e. integrating measurements of habitat thermal buffering, habitat thermal amplification, host plant transpiration, and experimental assessments of thermal death time (TDT), thermal avoidance behaviour (TAB) and thermally induced trait plasticity). These integrative analyses are conducted in two demographically declining and two non-declining populations of P. napi. 4. The results show that plastic phenotypic traits (butterfly body mass and wing size) are reliable biomarkers of population vulnerability to extreme thermal conditions. Butterfly wing size is strongly reduced only in thermally exposed populations during summer drought periods. Lab rearing of these populations documented reduced wing size due to significant negative effects of increased temperatures affecting larval growth. We conclude that these thermal biomarkers are indicative of the population vulnerability to increasing global warming impacts, showing contrasting trends in thermally exposed and buffered populations. 5. Thermal effects in host plant microsites significantly differ between populations, with stressful thermal conditions only effectively ameliorated in mid-elevation populations. In lowland populations we observe a six-fold reduction in vegetation thermal buffering effects, and larval growth occurs in these populations at significantly higher temperatures. Lowland populations show reduced host plant quality (C/N ratio), reduced leaf transpiration rates and complete aboveground plant senescence during the peak of summer drought. Amplified host plant temperatures are observed in open microsites, reaching thermal thresholds that can affect larval survival. 6. Overall, our results suggest that butterfly population vulnerability to long-term drought periods is associated to multiple co-occurring and interrelated ecological factors, including limited vegetation thermal buffering effects at lowland sites, significant drought impacts on host plant transpiration and amplified leaf surface temperature, as well as reduced leaf quality linked to the seasonal advance of plant phenology. Our results also identify multi-annual summer droughts affecting larval growing periods as a key driver of the recently reported butterfly population declines in the Mediterranean biome