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Climate change remains one of the most urgent challenges for biodiversity conservation. Recent studies have highlighted that climate extremes (CLEXs) can lead to widespread and negative effects across all taxa and ecological levels, but most of these studies are based on short-term periods and small spatial scales and lack a multi-species approach. Here, using generalised additive models (GAMs) and the UK Breeding Bird Survey (BBS), we described response curves for the abundance of 100 resident bird species over large spatial and temporal scales and identified the species showing a greater sensitivity to CLEXs. We used five climatic indices computed at 1-km spatial resolution as proxies of CLEXs during the winter or breeding season and considered both 1- and 2-year lagged effects. The results demonstrated widespread and significant effects of CLEXs on bird abundances at both time lags and in both seasons. Winter frost days (FD0), summer days (SU25) during the breeding season and simple precipitation intensity index (SDII) during the breeding season mainly showed negative effects. Daily temperature range (DTR) in both winter and breeding season and dry days (DD) during the breeding season led to diversified responses across the species, with a prevalence of positive effects. A large proportion of species showed a high sensitivity to CLEXs, highlighting that these species may deserve attention in future studies aimed at biodiversity conservation. We demonstrated that CLEXs can represent a significant driver affecting population abundances over large spatial and temporal scales, emphasising the need for understanding mechanistic processes at the basis of the observed effects.

Population responses to environmental changes can often vary geographically and between environments, potentially as a consequence of differing niche dynamics. The Eurasian Skylark Alauda arvensis is an open-habitat passerine bird that is declining throughout Europe, mainly due to agricultural intensification. We compared population trends (1992-2021) of the species across three sub-regions of northern Italy characterized by different environmental conditions and human pressures: the Alpine sub-region (less anthropized mountains), the Plain (strongly anthropized and intensively cultivated) and the Oltrepo (extensively cultivated hills), with changes in the realized Grinnellian niches over three decades. In each sub-region, niche comparisons did not show divergence over the study. However, we found an overall reduction in niche occupancy over time. In the Alpine sub-region, a reduction in niche occupancy in hayfields and pastures was not associated with population decline; indeed, we found an increasing population (+164%), probably because high availability of natural grasslands counteracted niche contraction. Conversely, in the Plain and Oltrepo sub-regions, the observed population declines (-99% and -36%, respectively) are associated with a general reduction of niche occupancy in arable lands that represented the core of the niche in these ranges. In the Plain, the lack of alternative suitable habitats might have limited any opportunity for the species to colonize new environments. Conversely, in the Oltrepo, the less severe population decline is combined with increased niche occupancy in hayfields and pastures at higher elevations. The joint application of population trend analysis and niche modelling as well as the decomposition of population changes across different environmental contexts can contribute to a better understanding of ecological processes affecting population dynamics, supporting policy-makers to implement targeted conservation strategies.

Functional diversity has proven to be more responsive than traditional taxonomic diversity to alterations for a wide set of communities, especially in aquatic ecosystems. Habitat alterations are among the most relevant causes of biodiversity loss in freshwater ecosystems, nevertheless their effect on functional diversity has been scarcely investigated so far. In this study, functional diversity of fish communities in the River Po basin, north Italy, were related to habitat quality at different spatial scales. Land use and riparian vegetation were identified as the most influent factors on freshwater fish functional diversity. On the other hand, habitat descriptors at smaller scale did not influence functional diversity of fish. The evidenced responses were driven by the contribution of exotic species, which maximized ecological niche occupancy, either by exploiting increased habitat heterogeneity or by interaction with native species. Moreover, traits filtering, disadvantaging large predators such as salmonids, was also observed in the studied communities, but likely this effect was related to other factors than habitat alterations. Overall, this study confirms that land use changes can be considered as valid proxies for anthropogenic alterations. Moreover, possible effects at ecosystem level, also related to the spread of exotic species, could be hypothesized, giving that traits mostly influencing the observed patterns of diversity in communities were related to trophic niche, a factor that has been associated with crucial processes like nutrient cycling or energy transfer.

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ESs), including water quality improvement and supply, food provisioning, and biodiversity support, despite significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This situation is likely exacerbated by the lack of a full-scale understanding of the importance of ponds. In this review, we provide a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlight the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFAs), delivered through them to the terrestrial environment; however, the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, that influence pond diversity and integrity are discussed. We provide our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, are the most promising to mitigate the loss of natural ponds and restore and conserve natural small waterbodies as refuges and diversity hotspots in increasingly urbanized landscapes.

Un’approfondita conoscenza circa le risposte delle popolazioni selvatiche ai cambiamenti ambientali e climatici rappresenta un obiettivo primario per migliorare le politiche ambientali e promuovere la conservazione della biodiversità. La capacità di una popolazione nel rispondere ai cambiamenti che avvengono negli ecosistemi è uno dei principali fattori che può determinare la sua traiettoria nel tempo e nello spazio. La presente tesi illustra, sia da un punto di vista metodologico che applicativo, quattro studi che analizzano alcuni tipi di risposte a lungo termine delle popolazioni di uccelli, fornendo nuovi e significativi risultati in una prospettiva ecologica di ampio respiro. Il primo lavoro si è focalizzato su aspetti metodologici che riguardano la modellizzazione dei trend di popolazione al fine di fornire un utile contributo per migliorare i processi di stima. Proponendo un approccio a step multipli, il lavoro ha investigato gli effetti dell’environmental bias, causato da variazioni avvenute nello sforzo o nel disegno di campionamento nello spazio e nel tempo, e di due proprietà statistiche dei dati di conteggio, cioè overdispersion e zero inflation, sul processo di stima. I risultati hanno evidenziato che l’environmental bias è il fattore principale nel determinare differenze tra i trend stimati dai diversi modelli. In aggiunta, l’overdispersion e la zero inflation sono in grado di influenzare, anche in modo significativo, le stime, perciò devono essere tenuti in considerazione nell’approccio statistico. Nel secondo lavoro, tale proposta modellistica è stata impiegata per stimare i trend di popolazione a lungo termine per gli uccelli nidificanti in nord Italia. Inoltre, attraverso un trait-based approach, è stato investigato se specie con analoghe caratteristiche life-history ed ecologiche (traits) condividessero simili dinamiche di popolazione. I risultati hanno identificato le specie che richiedono maggiore attenzione di conservazione e per le, An extensive knowledge about population responses to ongoing environmental and climatic changes is a primary goal to enhance environmental policies and promote biodiversity conservation. The capacity of a population in responding to rapid changes occurring within ecosystems is one of the most important aspects that can determine its trajectory over space and time. This thesis describes four studies that analyse some long-term responses of bird populations from both a methodological and applicative point of view, providing novel and valuable findings not only for bird studies but also in a broad ecological perspective. The first research focused on some methodological issues in population trend modelling. Changes in population size over time (i.e. population trends) are one of the clearest responses of populations to environmental changes and represent a key tool for wildlife conservation. Thus, improving the capacity of estimating trends is pivotal. The study investigated the effects of the environmental bias, which may affect many existing surveys because of a variation in the sampling effort or design over space and time, and of two statistical properties of count data, namely overdispersion and zero inflation, on the estimation process of population trends. A multi-step modelling approach was proposed, and findings highlighted that the environmental bias was the most important factor that causes differences in trend estimates across models. Additionally, overdispersion and zero inflation can influence, also significantly, the estimates, and modelling frameworks should consider their evaluation in the statistical approach. In the second work, this modelling framework was applied to assess the long-term population trends for common breeding birds at regional scale (northern Italy). Additionally, through a trait-based approach, the study investigated whether species with similar life-history and ecological traits shared similar population dynamics. Findings allowed

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ESs), including water quality improvement and supply, food provisioning, and biodiversity support, despite significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This situation is likely exacerbated by the lack of a full-scale understanding of the importance of ponds. In this review, we provide a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlight the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFAs), delivered through them to the terrestrial environment; however, the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, that influence pond diversity and integrity are discussed. We provide our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, are the most promising to mitigate the loss of natural ponds and restore and conserve natural small waterbodies as refuges and diversity hotspots in increasingly urbanized landscapes.

Context: Nestedness is a common pattern of species assemblages in fragmented landscapes. The spatial pattern and ecological drivers of nested communities have been widely explored, but few studies investigated their long-term variability. Objectives: To investigate the variability of nestedness and species-specific fragment occupancy of forest birds in a fragmented landscape affected by environmental changes over 16 years. Methods: Data were obtained from the Monitoring Program of Breeding Birds in Lombardy (northern Italy). For two study periods (1997–2001, 2013–2017), we tested for overall nestedness and for sites and species nestedness independently using the NODF metric. We tested for nestedness drivers (variable selection on multiple linear regression models) and evaluated the effect of species ecological traits on fragment occupancy changes (variable selection on multiple linear regression model). Results: The community showed a significant nestedness driven by both selective extinction and selective colonization in both study periods. Sites nestedness was significant in the second study period only. Over 16 years the effect of distance from source areas was completely lost and only local isolation conditions drove selective colonization in the second study period. Between the two study periods, we discovered a general occupancy decrease of interior species and a significant occupancy increase of generalist species characterized by large size and large minimum area requirement. Conclusions: Nestedness drivers of the investigated community significantly varied over time probably because of both environmental and demographic changes. Long-term studies are crucial to explore spatial pattern changes and to address management strategies for species conservation in fragmented landscapes.

The assessment of population trends is a key point in wildlife conservation. Survey data collected over long period may not be comparable due to the presence of environmental biases (i.e. inadequate representation of the variability of environmental covariates in the study area). Moreover, count data may be affected by both overdispersion (i.e. the variance is larger than the mean) and excess of zero counts (potentially leading to zero inflation). The aim of this study was to define a modelling procedure to assess long-term population trends that addressed these three issues and to shed light on the effects of environmental bias, overdispersion, and zero inflation on trend estimates. To test our procedure, we used six bird species whose data were collected in northern Italy from 1992 to 2019. We designed a multi-step approach. First, using generalised additive models (GAMs), we implemented a full factorial design of models (eight models per species) taking or not into account the environmental bias (including or not including environmental covariates, respectively), overdispersion (using a negative binomial distribution or a Poisson distribution, respectively), and zero inflation (using or not using zero-inflated models, respectively). Models were ranked according to the Akaike Information Criterion. Second, annual population indices (median and 95% confidence interval of the number of breeding pairs per point count) were predicted through a parametric bootstrap procedure. Third, long-term population trends were assessed and tested for significance fitting weighted least square linear regression models to the predicted annual indices. To evaluate the effect of environmental bias, overdispersion, and zero inflation on trend estimates, an average discrepancy index was calculated for each model group. The results showed that environmental bias was the most important driver in determining different trend estimates, although overlooking overdispersion and zero inflation

Freshwater fish communities are impacted by multiple pressures, determining loss of functional diversity and redundancy. Our aim was to disentangle the roles and relevancies of different pressures in shaping fish communities in small streams of the Po plain (North Italy). Long term trend (1998–2018) of functional diversity of 31 fish communities was assessed and modeled in respect to three potential pressures: temperature increase, intensity of exotic fish invasion, and habitat quality degradation. Ecological traits mostly influenced by the pressures were also identified. Reduction of functional richness mostly due to local extinction or contraction of cold adapted predators, such as salmonids, was linked to increasing temperatures. Warming probably also led to a shift of generalist and dominant species, which became more abundant in streams hosting mixed communities of salmonids and cyprinids, and determined the increase of functional dispersion and uniqueness. Reduction of functional redundancy and increasing functional dispersion were both also related to the introduction of new ecological traits brought by expanding exotic species. Low functional overlap was found among native and exotic species, indicating that the invasion process was mainly controlled by competitive interactions and/or resource opportunism. Functional response to habitat quality was not clearly evident. In conclusion, the impact of temperature increase and exotic species on fish functional diversity was effective, idiosyncratic and mediated by the scale of analysis and by the intensity of pressures.