Relative Population Size Research Articles

Purifying Selection Influences the Comparison of Heterozygosities between Populations.

Heterozygosity is a fundamental measure routinely used to compare between populations to infer the level of genetic variation and their relative effective population sizes. However, such comparison is highly influenced by the magnitude of selection pressure on the genomic regions used. Using over 2 million Single Nucleotide Variants (SNVs) from chimpanzee and mouse populations, this study shows that the heterozygosities estimated using neutrally evolving sites of large populations were two times higher than those of small populations. However, this difference was only ~1.6 times for the heterozygosities estimated using nonsynonymous sites. This suggests an excess in the nonsynonymous heterozygosities due to the segregation of deleterious variants in small populations. This excess in the nonsynonymous heterozygosities of the small populations was estimated to be 23-31%. Further analysis revealed that the magnitude of the excess is modulated by effective population size (Ne) and selection intensity (s). Using chimpanzee populations, this investigation found that the excess in nonsynonymous diversity in the small population was little (6%) when the difference between the Ne values of large and small populations was small (2.4 times). Conversely, this was high (23%) when the difference in Ne was large (5.9 times). Analysis using mouse populations showed that the excess in the nonsynonymous diversity of highly constrained genes of the small population was much higher (38%) than that observed for the genes under relaxed selective constraints (21%). Similar results were observed when the expression levels of genes were used as a proxy for selection intensity. These results emphasize the use of neutral regions, less constrained genes, or lowly expressed genes when comparing the heterozygosities between populations.

On Population and the International Order

AbstractThis essay expores demographic effects on the international order over the postwar decades and potentially through the next half‐century. Such effects derive from the relative sizes of populations and labor forces among states, contrasts in age distributions (resulting from the regionally staggered timing of fertility decline), and high levels of international migration, fueled by economic disparities and civil conflict. In coming decades, differential population growth and aging—in some states, entrenchment of population decline—will shift the global distribution of labor away from East Asia and Europe and toward South and West Asia and especially Africa. Short‐range migration may be pressed by environmental change; longer‐range migration toward rich countries, much of it illicit and already an intractable public policy issue in many of them, will face increased societal resistance and stronger efforts to police entry. The future international order will see a states system with the Global North further demographically marginalized; India as an emerging economic‐demographic superpower, joining a fast‐aging China and plausibly a less internationally engaged United States; and a demographically dominant Africa with as yet a wholly unclear place in the global political economy. Although not part of standard demographic projections, there are extreme global warming scenarios and other disaster eventualities that could be radically transformative of this order.

Estimating the impact of sarcoptic mange epidemic on the population size of wild raccoon dogs (Nyctereutes procyonoides) from wildlife rescue data

The impact of infectious diseases on host populations is often not quantified because it is difficult to observe the host population and infectious disease dynamics. To address this problem, we developed a state-space model to simultaneously estimate host population and disease dynamics using wildlife rescue data. Using this model, we aimed to quantify the impact of sarcoptic mange on a Japanese raccoon dog population by estimating the change in their relative population size. We classified the status of rescued raccoon dogs into four categories: i) rescued due to infection with mange, ii) rescued due to traffic accidents without mange, iii) rescued due to traffic accidents with mange, and iv) rescued due to causes other than traffic accidents or mange. We modelled the observation process for each category and fitted the model to the reported number of raccoon dogs rescued between 1990 and 2010 at three wildlife rescue facilities in Kanagawa Prefecture, Japan. The mortality rate induced by mange was estimated to be 1.09 (95% credible interval (CI): 0.47–1.72) per year. The estimated prevalence of sarcoptic mange ranged between 4–80% in the study period. When a substantial prevalence of mange was observed (1995 to 2002), the host population size decreased by 91.2% (95% credible intervals: 86.3–94.7). We show that the impact of infectious disease outbreak on the wildlife population can be estimated from the time-series data of wildlife rescue events due to multiple causes. Our estimates suggest that sarcoptic mange triggered a substantial decrease in the Japanese wild raccoon dog populations.

Population monitoring and conservation implications of intra- and interspecific nest occupation rates in swallows.

With the exception of a few groups of birds, such as large raptors and colonial seabirds, direct counts of nests cannot be conducted over very large areas for most of the abundant and widely distributed species, and thus indirect methods are used to estimate their relative abundances and population sizes. However, many species of the Family Hirundinidae (swallows and martins) build their mud nests in discrete, predictable and accessible sites, which are reused across years. Therefore, the direct count of active nests could constitute a reliable method for estimating breeding population sizes and their changes at large spatial and temporal scales. We illustrate the feasibility of this monitoring approach through a single year survey of >2700 nests of three coexisting Old-World species, the barn swallow (Hirundo rustica), the red-rumped swallow (Cecropis daurica), and the crag martin (Ptyonoprogne rupestris), distributed across Portugal and Spain. Our results revealed changes in the use of nesting substrates and increases in interspecific nest usurpation rates over recent decades. While 56% of the nests of C. daurica were located in rocks five decades ago, almost 100% are nowadays located in anthropogenic substrates such as bridges, road culverts, and abandoned buildings, which could have favored the range expansion of this species. Nest occupation rates were surprisingly low (12% in C. daurica, 21% in H. rustica, and 37% in P. rupestris), and the proportion of abandoned nesting sites was very high (65% in C. daurica, 50% in H. rustica, and 27% in P. rupestris). Abandonment rates reflect the population decline reported for H. rustica. Notably, the usurpation of nests of C. daurica by house sparrows Passer domesticus, which is the main cause of breeding failure, has increased from 2.4% in 1976-1979 to 34.7% of the nests nowadays. The long-term monitoring of nests may constitute a reliable and affordable method, with the help of citizen science, for assessing changes in breeding population sizes and conservation threats of these and other mud-nest building hirundines worldwide.

Do counts of radiocarbon-dated archaeological sites reflect human population density? A preliminary empirical validation examining spatial variation across late Holocene California

AbstractResearchers increasingly rely on aggregations of radiocarbon dates from archaeological sites as proxies for past human populations. This approach has been critiqued on several grounds, including the assumptions that material is deposited, preserved, and sampled in proportion to past population size. However, various attempts to quantitatively assess the approach suggest there may be some validity in assuming date counts reflect relative population size. To add to this conversation, here we conduct a preliminary analysis coupling estimates of ethnographic population density with late Holocene radiocarbon dates across all counties in California. Results show that counts of late Holocene radiocarbon-dated archaeological sites increase significantly as a function of ethnographic population density. This trend is robust across varying sampling windows over the last 5000 BP. Though the majority of variation in dated-site counts remains unexplained by population density. Outliers reveal how departures from the central trend may be influenced by regional differences in research traditions, development-driven contract work, organic preservation, and landscape taphonomy. Overall, this exercise provides some support for the “dates-as-data” approach and offers insights into the conditions where the underlying assumptions may or may not hold.

Voting Local? Electoral Rules and Geographical Representation in Europe

ABSTRACT In comparison with the expanding body of literature on representation, the number of studies examining geographical aspects of it remains relatively limited. This relates primarily to comparative analyses, but also to the array of methodological tools used to measure localness. Our study seeks to address this gap by introducing a novel measurement based on Gallagher’s index of disproportionality. Drawing on contemporary data from 27 European countries, we envisioned an operationalisation of geographical representation which prevents the expected lack of representation of small municipalities to affect the index values, instead focusing on relative population sizes in correlation with the relative number of elected MPs. We introduce the data, and then proceed to establish which country-level determinants influence the Index of territorial disproportionality. The findings indicate that district magnitude and number, parliament size, and the difference between established and new democracies have a high impact on the proportionality of local representation. On the other hand, the opening of lists for more voters’ influence within the PR list system, implemented mainly through preferential voting, appears to have no impact, indicating that parties tend to nominate (and voters tend to elect) local candidates even when institutional incentives of the electoral system are low.

Accelerated farmland bird population declines in European countries after their recent EU accession

Agricultural intensification is a major driver of global biodiversity loss. In Europe, intensification progressed over the 20th century and was accelerated by instruments of the EU's Common Agricultural Policy. Central and Eastern European (CEE) countries standing outside the EU until the beginning of the 21st century employed less intensive farming and are considered one of the continent's farmland biodiversity strongholds. Their recent EU accession might be either viewed as a threat to farmland biodiversity due to the availability of funds to increase agricultural production or as an opportunity to implement conservation measures aimed to preserve biodiversity. Here we assessed these possibilities using long-term monitoring data on farmland bird populations in seven CEE countries. We tested whether mean relative abundance and population trends changed after countries' EU accession, and whether such changes also occurred in agricultural management and conservation measures. Both agricultural intensity and spending for agri-environmental and climatic schemes increased when the CEE countries joined the EU. At the same time, farmland bird populations started to decline and their relative abundance was lower after than before EU accession. In addition, increases in fertilizer application were negatively associated with annual changes in relative farmland bird population sizes, indicating a negative impact of intensive agriculture. Taken together, these results indicate that despite the great power of the EU's environmental legislation to improve the population status of species at risk, this does not apply to farmland birds. In their case, the adverse impacts of agricultural intensification most likely overrode the possible benefits of conservation measures. To secure this region as one of the continent's farmland biodiversity strongholds, policy and management actions are urgently needed.

Ecological scales of effect vary across space and time

The spatial scale at which an environmental variable is summarized can have considerable impacts on ecological inference of species distribution and abundance. While several analytical approaches have emerged to determine biologically relevant spatial scales – the spatial scale that most strongly influences the ecological patterns observed – identifying key ecological drivers of scale of effect is still underway. Additionally, several predicted ecological drivers of scale of effect can vary across space and time, but little research on spatiotemporal patterns has occurred. Here, I assessed spatial and temporal variation in scales of effect across 32 North American bird species using 18 years of empirical data from the North American breeding bird survey. Scale estimation was then coupled with trait‐based analyses and hypotheses testing of underlying processes of spatial and temporal variation in scales of effect. All 32 species tested exhibited varied scales of effect across years (average annual scales of effect ranging from 0.2 to 4.97 km) and Bird Conservation Regions (BCR), with spatial variability being the most pronounced. Trait‐based analyses revealed a contrary relationship between hand‐wing index, body size, and scale of effect, though the strength of this relationship was contingent on migratory status. Temporal variation in scales of effect was best explained by changes in human development over time, indicating that avian space use can be explained by an increasing human footprint. Additionally, relative population size, consistent with theoretical predictions stemming from density‐dependent population dynamics, explained notable variation in spatial and temporal scales of effect. These findings contribute to the growing landscape ecology literature by providing empirical evidence for hypothesized drivers of scales of effect. By delineating species‐specific scales of effect and elucidating their ecological drivers, this study enhances our understanding of spatial and temporal scales in ecological processes, aiding conservation efforts in a rapidly changing world.

Ecology and abundance of a relict population of the bush cricket Saga pedo in the Northern Apennines, Italy.

The expansion of forest cover and intensification of agriculture represent the main threats to the bush cricket Saga pedo, currently listed as Vulnerable globally by the IUCN and included in Annex IV of the European Union Habitats Directive. Gathering information on its ecology and population size is challenging due to its low abundance and localized distribution. Additionally, the elusive and cryptic behavior of this species reduces the likelihood of its detection, potentially resulting in population underestimations. Thus, in this study, we aimed to (1) estimate S. pedo population size in relation to environmental variables and prey availability and (2) predict abundance of S. pedo in our study area for future monitoring in nearby territories. We found that the population of S. pedo in our study area consists of 197 (±115) individuals with a detection probability of 21.01% (±11.09). Detection probability of S. pedo further decreases on windy days. Moreover, we found that the investigated population of S. pedo occupies suboptimal areas, as highlighted not only by the predicted abundances but also by the association between S. pedo and other subfamilies of orthoptera that are ecologically very distant from our target species and mostly linked to mesophilic biotopes. Most of the individuals we observed are concentrated in small clearings completely within wooded matrices and therefore isolated from each other. Based on our results, it is possible that forest expansion toward open meadows represents the main threat to this population, transforming the clearings and xeric meadows (to which S. pedo is linked) into small and fragmented patches that are suboptimal and insufficient to host viable populations.

Analysis of population size of Pterygoplichthys multiradiatus and its intake of microplastics in streams with different land uses

Most freshwater habitats have been substantially affected by anthropogenic factors such as fish introductions, plastic pollution, and river regulation. Urban rivers are highly vulnerable to impacts associated with land use changes resulting from increasing urbanization, including altering habitat and establishing aquatic biological communities in these areas. In turn, the introduction of exotic species into sensitive and threatened ecosystems such as tropical urban streams and their rapid establishment, such as Pterygoplichthys multiradiatus, was used as an ecological model to determine the relative population size of the species. Also, the species was used to evaluate the presence of microplastics (MPs) in the gastrointestinal tract (GIT) of fish in rivers with different land use history. Our results showed significant differences in pleco abundance between areas with high and low urban (LU) development in the watersheds. The study demonstrated that abiotic environmental factors directly influence the relative abundance of plecos at the range and watershed scales. In a total of 42 fish examined, only 85.7% showed MPs retained in the GIT, with fibers and fragments being the most common. A total of 22 pieces of microplastic were identified with Nile Red staining by slide analysis. A significant difference was found between the abundance of microplastic ingested per total fish length between streams with high and LU development reaches. Therefore, in relatively small amounts, microplastic ingestion appears to be common in P. multiradiatus species, regardless of the habitat in which they are found and the diet present.

Incorporating intraspecific variation into species responses reveals both their resilience and vulnerability to future climate change

Incorporating intraspecific variation into species responses can improve our understanding of the effects of climate change. However, most studies overlook such variation or model intraspecific groups independently, leading to widely varying estimates at the species level. In this study, we used a generalized additive framework to model the climate responses of 25 bird species in the tropical Andes, allowing for the estimation of nonlinear responses between subspecies. We measured the effects of environmental covariates (climate, topography, and primary productivity) on relative abundances and projected population trends for near‐future (2050) scenarios. Compared with models that ignored subspecies, the subspecies‐level models performed better in terms of accuracy, discrimination, and goodness‐of‐fit, while projecting fewer species to decline in relative abundance. Thus, species could be more resilient than estimated using species‐level models that ignore intraspecific variation. Nevertheless, our modeling approach also revealed that intraspecific groups may be vulnerable to future threats. We found that subspecies can have low relative abundances and small population sizes. Additionally, based on a preliminary IUCN Red List assessment, one in four subspecies could be threatened due to a small geographical range or a declining population trend. Most of these subspecies at risk inhabit centers of endemism in the northern Andes, such as the Santa Marta Mountains and the Serranía de Perijá. We suggest that protecting subspecies and other intraspecific groups (e.g. populations) could be a critical conservation strategy to buffer against the impacts of climate change, especially in biologically diverse regions.

In Pursuit of Cultural Equity: DEI Grantmaking Practices of U.S. Local Arts Agencies in Community Context

As grantmaking intermediary organizations, local arts agencies (LAAs) play an important but under-researched role in realizing cultural equity—the incorporation of underrepresented groups and counternarratives into democratic discourse—in thousands of local communities throughout the United States. In deploying their diversity, equity, and inclusion grantmaking practices, LAAs vary in the degree to which they proactively encourage the artistic expression of underrepresented groups, such as immigrants and racial-ethnic minorities. Little research has been directed at the relationship between the relative population size of underrepresented groups in an LAA service area and an LAA’s likelihood of having a formal “race-ethnic targeting” policy, the proactive channeling of arts economic resources toward underrepresented community groups. Framing our analysis in sociological race relations theories, we examine patterns of association between an LAA’s likelihood of having a formal race-ethnic targeting policy and the percentage foreign-born of the residential population in an LAA service area based on 462 LAAs of the 2018 Local Arts Agency Profile collected by Americans for the Arts, a national dataset of LAAs that we augmented with U.S. Census demographic data on LAA service-area populations. We conclude by deriving from the curvilinear pattern of findings a “representation thesis” on the community social contexts in which proactive LAAs tend to target race-ethnic minorities for distributing arts economic resources.

Top-down and bottom-up effects and relationships with local environmental factors in the water frog–helminth systems in Latvia

Semi-aquatic European water frogs (Pelophylax spp.) harbour rich helminth infra-communities, whose effects on host population size in nature are poorly known. To study top-down and bottom-up effects, we conducted calling male water frog counts and parasitological investigations of helminths in waterbodies from different regions of Latvia, supplemented by descriptions of waterbody features and surrounding land use data. We performed a series of generalized linear model and zero-inflated negative binomial regressions to determine the best predictors for frog relative population size and helminth infra-communities. The highest-ranked (by Akaike information criterion correction, AICc) model explaining the water frog population size contained only waterbody variables, followed by the model containing only land use within 500 m, while the model containing helminth predictors had the lowest rank. Regarding helminth infection responses, the relative importance of the water frog population size varied from being non-significant (abundances of larval plagiorchiids and nematodes) to having a similar weight to waterbody features (abundances of larval diplostomids). In abundances of adult plagiorchiids and nematodes the best predictor was the host specimen size. Environmental factors had both direct effects from the habitat features (e.g., waterbody characteristics on frogs and diplostomids) and indirect effects through parasite-host interactions (impacts of anthropogenic habitats on frogs and helminths). Our study suggests the presence of synergy between top-down and bottom-up effects in the water frog–helminth system that creates a mutual dependence of frog and helminth population sizes and helps to balance helminth infections at a level that does not cause over-exploitation of the host resource.

A 91% decline in a common anuran in an otherwise stable amphibian community inferred from 17 years of rapid road surveys

AbstractAmphibians are disproportionately represented among the many vertebrate taxa that are declining globally. Few long‐term studies of amphibians exist, especially in temperate climates, hindering our understanding of long‐term trends in amphibian communities, which may delay or prevent management action. Here, we develop and deploy an inexpensive monitoring method with potentially broad scientific and community uptake, ‘rapid road surveys’. We test whether this protocol is useful in understanding relative abundance in an amphibian community over a 17‐year period. From 2003 to 2019, we performed thousands of rapid (5–15 min) amphibian surveys and recorded the number of on‐road amphibians along a single, 267 m stretch of secondary roads in rural Canada. Assuming that on‐road occurrence reflects relative amphibian population sizes, we show that amphibians have declined by approximately 73% from 2003 to 2019. The decline was driven by a remarkable 91% decrease in the abundance of northern leopard frogs (Lithobates pipiens), the species comprising the most observation records, while all other species did not show a temporal trend. We cannot attribute a definitive mechanism to the L. pipiens decline. However, by ruling out a number of putative causes, we hypothesize that it may be related to land‐use change or infectious disease. Our results show that a simple, temporally replicated road survey protocol, deployed in a spatially restricted area, can be a valuable tool for conservation scientists to understand trends in abundance across an entire community. We discuss how these rapid road surveys are likely a viable option for future community science initiatives.

Debt issuance incentives and creative accounting: Evidence from municipal mergers in Japan

Creative accounting has been a considerable problem in the field of governance and has caused serious economic issues. However, how governments determine the scale of creative accounting is unknown in the existing literature.We study whether a difference in the usage and the scale of creative accounting is determined by the intensity of the incentive to issue excessive debt. To study this, we focus on municipal mergers, a well-known setting wherein smaller merging municipalities have a stronger incentive to enjoy freeriding and issue debt since the debt burden will be shared and mainly owed by larger merging municipalities. This setting enables us to use the relative population size as a continuous treatment representing the strength of debt issuance incentives, whereas existing papers focused on binary treatments. Utilizing the data of Japanese municipal mergers, we find that governments with small relative populations, which have a strong debt issuance incentive, employed creative accounting more intensively than others. Moreover, we investigate how governments used the money obscured through creative accounting for the first time and find that it was not used to overcome financial difficulties nor increase politicians’ pecuniary gains but to increase resident welfare.

Allele frequencies and selection coefficients in locally adapted populations

Understanding the role of natural selection in driving evolutionary change requires accurate estimates of the strength of selection acting at the genetic level in the wild. This is challenging to achieve but may be easier in the case of populations in migration-selection balance. When two populations are at equilibrium under migration-selection balance, there exist loci whose alleles are selected different ways in the two populations. Such loci can be identified from genome sequencing by their high values of FST. This raises the question of what is the strength of selection on locally-adaptive alleles. To answer this question we analyse a 1-locus 2-allele model of a population distributed between two niches. We show by simulation of selected cases that the outputs from finite-population models are essentially the same as those from deterministic infinite-population models. We then derive theory for the infinite-population model showing the dependence of selection coefficients on equilibrium allele frequencies, migration rates, dominance and relative population sizes in the two niches. An Excel spreadsheet is provided for the calculation of selection coefficients and their approximate standard errors from observed values of population parameters. We illustrate our results with a worked example, with graphs showing the dependence of selection coefficients on equilibrium allele frequencies, and graphs showing how FST depends on the selection coefficients acting on the alleles at a locus. Given the extent of recent progress in ecological genomics, we hope our methods may help those studying migration-selection balance to quantify the advantages conferred by adaptive genes.

Optimal spatial evaluation of a pro rata vaccine distribution rule for COVID-19

The COVID-19 Vaccines Global Access (COVAX) is a World Health Organization (WHO) initiative that aims for an equitable access of COVID-19 vaccines. Despite potential heterogeneous infection levels across a country, countries receiving allotments of vaccines may follow WHO’s allocation guidelines and distribute vaccines based on a jurisdictions’ relative population size. Utilizing economic—epidemiological modeling, we benchmark the performance of this pro rata allocation rule by comparing it to an optimal one that minimizes the economic damages and expenditures over time, including a penalty representing the social costs of deviating from the pro rata strategy. The pro rata rule performs better when the duration of naturally- and vaccine-acquired immunity is short, when there is population mixing, when the supply of vaccine is high, and when there is minimal heterogeneity in demographics. Despite behavioral and epidemiological uncertainty diminishing the performance of the optimal allocation, it generally outperforms the pro rata vaccine distribution rule.

An evolutionarily conserved coronin-dependent pathway defines cell population size.

Maintenance of cell population size is fundamental to the proper functioning of multicellular organisms. Here, we describe a cell-intrinsic cell density-sensing pathway that enabled T cells to reach and maintain an appropriate population size. This pathway operated "kin-to-kin" or between identical or similar T cell populations occupying a niche within a tissue or organ, such as the lymph nodes, spleen, and blood. We showed that this pathway depended on the cell density-dependent abundance of the evolutionarily conserved protein coronin 1, which coordinated prosurvival signaling with the inhibition of cell death until the cell population reached threshold densities. At or above threshold densities, coronin 1 expression peaked and remained stable, thereby resulting in the initiation of apoptosis through kin-to-kin intercellular signaling to return the cell population to the appropriate cell density. This cell population size-controlling pathway was conserved from amoeba to humans, thus providing evidence for the existence of a coronin-regulated, evolutionarily conserved mechanism by which cells are informed of and coordinate their relative population size.

RGAI: An R package for fitting the generalized abundance index to seasonal count data.

The generalized abundance index (GAI) provides a useful tool for estimating relative population sizes and trends of seasonal invertebrates from species' count data and offers potential for inferring which external factors may influence phenology and demography through parametric descriptions of seasonal variation. We provide an R package that extends previous software with the ability to include covariates when fitting parametric GAI models, where seasonal variation is described by either a mixture of Normal distributions or a stopover model which provides estimates of life span. The package also generalizes the models to allow any number of broods/generations in the target population within a defined season. The option to perform bootstrapping, either parametrically or nonparametrically, is also provided. The new package allows models to be far more flexible when describing seasonal variation, which may be dependent on site‐specific environmental factors or consist of many broods/generations which may overlap, as demonstrated by two case studies. Our open‐source software, available at https://github.com/calliste‐fagard‐jenkin/rGAI, makes these extensions widely and freely available, allowing the complexity of GAI models used by ecologists and applied statisticians to increase accordingly.

Breeding ground temperature rises, more than habitat change, are associated with spatially variable population trends in two species of migratory bird

Habitat loss and climate change are key drivers of global biodiversity declines but their relative importance has rarely been examined. We attempted to attribute spatially divergent population trends of two Afro‐Palaearctic migrant warbler species, Willow Warbler Phylloscopus trochilus and Common Chiffchaff Phylloscopus collybita, to changes in breeding grounds climate or habitat. We used bird counts from over 4000 sites across the UK between 1994 and 2017, monitored as part of the BTO/JNCC/RSPB Breeding Bird Survey. We modelled Willow Warbler and Common Chiffchaff population size and growth in relation to habitat, climate and weather. We then used the abundance model coefficients and observed environmental changes to determine the extent to which spatially varying population trends in England and Scotland were consistent with attribution to climate and habitat changes. Both species' population size and growth correlated with habitat, climate and weather on their breeding grounds. Changes in habitat, in particular woodland expansion, could be linked to small population increases for both species in England and Scotland. Both species' populations correlated more strongly with climate than weather, and both had an optimum breeding season temperature: 11°C for Willow Warbler and around 13.5°C for Common Chiffchaff (with marginally different predictions from population size and growth models). Breeding ground temperature increases, therefore, had the potential to have caused some of the observed Willow Warbler declines in England (where the mean breeding season temperature was 12.7°C) and increases in Scotland (mean breeding season temperature was 10.2°C), and some of the differential rates of increase for Common Chiffchaff. However, much of the variation in species' population abundance and trends were not well predicted by our models and could be due to other factors, such as species interactions, habitat and climate change in their wintering grounds and on migration. This study provides evidence that the effect of climate change on a species may vary spatially and may switch from being beneficial to being detrimental if a temperature threshold is exceeded.