Causes Of Population Change Research Articles

Quantifying hurricane impacts on United States Virgin Islands reef fishes using a catchability invariant approach to compare uncalibrated survey indices

The United States Virgin Island's (USVI) coral reefs support many economically and ecologically important fish species. Located in the Caribbean Sea, they are subject to frequent severe weather disturbances, including two category 5 hurricanes, Irma and Maria, in 2017. The overarching goal of this study was to identify reef fish community impacts following these extreme events using discontinuous survey indices. Long-term (2001–2021), in situ, fishery-independent survey data using two methods were standardized to the extent possible in two regions of the USVI, St. Thomas/St. John (STT/STJ) and St. Croix (STX). Comparable data were assessed, 73 species collected on hard- bottom habitat, to identify the number of these species with significant changes in density and/or mean length between 2-yr survey intervals over the historic baseline (2001–2015), disturbance (2017–2019), and postdisturbance (2019–2021) periods. The results varied by region: STT/STJ had no disturbance impact and STX had a significant disturbance impact. In STX, 20 species had significant changes in density in the disturbance period compared to an average of 9.7 (SD 3.8) species for the baseline period. The proportion of species with significant density increases and decreases were similar suggesting that overall disturbance impacts are nuanced. Mean length observations were less informative, likely due to survey method and sample size changes. However, in combination with density they provided useful insights into the possible causes of population change. The successful use of discontinuous survey indices to obtain meaningful biological insights has broader applications to ecosystem and fishery datasets with similar limitations.

Causal mechanisms for negative impacts of energy development inform management triggers for sagebrush birds

AbstractEstimated population trends can identify declining species to focus biological conservation, but monitoring may fail to illuminate causes of population change and strategies for reversing declines. Monitoring programs can relate trends with environmental attributes to test causal hypotheses, but typical analytical approaches do not explicitly support causal inference, diluting available data for informing conservation. The U.S. Bureau of Land Management (BLM) extended Integrated Monitoring in Bird Conservation Regions with a quasi‐experimental sampling design over a 10‐year period (2010–2019) to evaluate the impacts of oil and gas development on sagebrush birds within the Atlantic Rim Natural Gas Field Development Project in southern Wyoming. We analyzed resulting data using a multiscale community occupancy model to estimate trends in species occupancy and richness relevant to management triggers. Additionally, we employed path analysis to evaluate mechanisms underlying observed trends to inform potential management responses. Fine‐scale occupancy for sage thrasher (Oreoscoptes montanus) declined within the high‐development stratum at a rate sufficient to meet an a priori management trigger established by the BLM. Two additional sagebrush‐associated species, Brewer's (Spizella breweri) and sagebrush sparrow (Artemisiospiza nevadensis), exhibited negative development relationships with trend, as did overall species richness, and richness of grassland, sagebrush, and generalist guilds. We identified well pad density and invasive plants associated with energy development as causal factors contributing to these negative development impacts. We demonstrate an analytical approach for both estimating occupancy trends and identifying underlying causes to inform conservation action. Reducing the development footprint, including well pad density and associated invasive plants, could help reduce or limit impacts on birds within this landscape.

Relative effects of sample size, detection probability, and study duration on estimation in integrated population models.

Understanding mechanistic causes of population change is critical for managing and conserving species. Integrated population models (IPMs) allow for quantifying population changes while directly relating environmental drivers to vital rates, but power of IPMs to detect trends and environmental effects on vital rates remains understudied. We simulated data for an IPM fewer than 41 scenarios to determine the power to detect trends and environmental effects on vital rates based on study duration, sample size, detection probability, and effect size. Our results indicated that temporal duration of a study and effect size, rather than sample size of each individual data set or detection probability, had the greatest influence on the power to identify trends in adult survival and fecundity. When using only 10 years of data, we were unable to identify a 50% increase in adult survival but were able to identify this increase with 22 years of data. When using only capture-recapture data in a traditional Cormack-Jolly-Seber analysis, we lacked sufficient power to identify trends in survival, and power of the Cormack-Jolly-Seber model was always less than the IPM. The IPM had greater power to identify trends and environmental effects on fecundity (e.g., we detected a 58% change in fecundity using 12 years of data). Models with effects of environmental variables on vital rates had less power than trends, likely to be due to increased annual variation in the vital rate when modeling responses to environmental effects that varied by year. Lack of power in the Cormack-Jolly-Seber analysis could be due to the relatively small variability in adult survival compared with fecundity, given the life history of our simulated species. As interannual variation in environmental conditions will probably increase with climate change, this type of analysis can help to inform the study duration needed, which may be a shifting target given future climate uncertainty and the complex nature of environmental correlations with demography.

The demographic causes of population change vary across four decades in a long-lived shorebird.

Understanding which factors cause populations to decline begins with identifying which parts of the life cycle, and which vital rates, have changed over time. However, in a world where humans are altering the environment both rapidly and in different ways, the demographic causes of decline likely vary over time. Identifying temporal variation in demographic causes of decline is crucial to assure that conservation actions target current and not past threats. However, this has rarely been studied as it requires long time series. Here we investigate how the demography of a long‐lived shorebird (the Eurasian Oystercatcher Haematopus ostralegus) has changed in the past four decades, resulting in a shift from stable dynamics to strong declines (−9% per year), and recently back to a modest decline. Since individuals of this species are likely to respond differently to environmental change, we captured individual heterogeneity through three state variables: age, breeding status, and lay date (using integral projection models). Timing of egg‐laying explained significant levels of variation in reproduction, with a parabolic relationship of maximal productivity near the average lay date. Reproduction explained most variation in population growth rates, largely due to poor nest success and hatchling survival. However, the demographic causes of decline have also been in flux over the last three decades: hatchling survival was low in the 2000s but improved in the 2010s, while adult survival declined in the 2000s and remains low today. Overall, the joint action of several key demographic variables explain the decline of the oystercatcher, and improvements in a single vital rate cannot halt the decline. Conservations actions will thus need to address threats occurring at different stages of the oystercatcher's life cycle. The dynamic nature of the threat landscape is further supported by the finding that the average individual no longer has the highest performance in the population, and emphasizes how individual heterogeneity in vital rates can play an important role in modulating population growth rates. Our results indicate that understanding population decline in the current era requires disentangling demographic mechanisms, individual variability, and their changes over time.

Moth species richness and diversity decline in a 30-year time series in Norway, irrespective of species\u2019 latitudinal range extent and habitat

IntroductionInsects are reported to be in decline around the globe, but long-term datasets are rare. The causes of these trends are elusive, with changes in land use and climate among the top candidates. Yet if species traits can predict rates of population change, this can help identify underlying mechanisms. If climate change is important, for example, high-latitude species may decline as temperate species expand. Land use changes, however, may impact species that rely on certain habitats.Aims and methodsWe present 30 years of moth captures (comprising 97,032 individuals of 808 species) from a site in southeast Norway to test for population trends that are correlated with species traits. We use time series analyses and joint species distribution models combined with local climate and habitat data.Results and discussionSpecies richness declined by 8.2% per decade and total abundance appeared to decline as well (−9.4%, p = 0.14) but inter-annual variability was high. One-fifth of species declined, although 6% increased. Winter and summer weather were correlated with annual rates of abundance change for many species. Opposite to general expectation, many species responded negatively to higher summer and winter temperatures. Surprisingly, species’ northern range limits and the habitat in which their food plants grew were not strong predictors of their time trends or their responses to climatic variation. Complex and indirect effects of both land use and climate change may play a role in these declines.Implications for insect conservationOur results provide additional evidence for long-term declines in insect abundance. The multifaceted causes of population changes may limit the ability of species traits to reveal which species are most at risk.

Sandpipers go with the flow: Correlations between estuarine conditions and shorebird abundance at an important stopover on the Pacific Flyway.

Estuaries of major rivers provide important stopover habitat for migratory birds throughout the world. These estuaries experience large amounts of freshwater inputs from spring runoff. Understanding how freshwater inputs affect food supply for migrating birds, and how birds respond to these changes will be essential for effective conservation of critical estuarine habitats. We estimated trends over time in counts of Western Sandpiper (Calidris mauri) and Pacific Dunlin (Calidris alpina pacifica) during northward migration on the Fraser River estuary, British Columbia, Canada, where shorebirds feed extensively on intertidal biofilm and invertebrates. We also examined whether counts were correlated with a suite of environmental variables related to local conditions (precipitation, temperature, wind speed and direction, solar radiation, tidal amplitude, and discharge rates from the Fraser River) during a total of 540 surveys from 1991 to 2019. Counts of Western Sandpiper declined ~54% (−2.0% per annum) over the entire study period, and 23% from 2009 to 2019 (−0.9% per annum). Counts of Pacific Dunlin did not show a statistically significant change over the study period. Counts of shorebirds were lower when discharge from the Fraser River was high, which we propose results from a complex interaction between the abrupt changes in salinity and the estuarine food web related to the quantity or quality of intertidal biofilm. Counts were also higher when tidal amplitude was lower (neap tides), potentially related to longer exposure times of the mudflats than during spring tides. Effects of wind are likely related to birds delaying departure from the stopover site during unfavorable wind conditions. The negative trend in migrating Western Sandpipers is consistent with declines in nonbreeding areas as observed in Christmas Bird Counts. Understanding causes of population change in migratory shorebirds highlights the need for research on mechanistic pathways in which freshwater inputs affect food resources at estuarine stopovers.

Local‐scale climatic refugia offer sanctuary for a habitat‐forming species during a marine heatwave

Abstract Gradual climate change and discrete extreme climatic events have driven shifts in the structure of populations and the distribution of species in many marine ecosystems. The most profound impacts of recent warming trends have been generally observed at species' warm edges and on large conspicuous species. However, given that different species and populations exhibit different responses to warming, and that responses are highly variable at regional scales, there is a need to broaden the evidence to include less conspicuous species and to focus on both local‐ and regional‐scale processes. We examined the population dynamics of canopy‐forming seaweed populations situated at the core range of their distribution during a regional marine heatwave (MHW) event that occurred in the Mediterranean Sea in 2015, to determine between‐site variability in relation to the intensity of the MHW. We combined field observations with a thermo‐tolerance experiment to elucidate mechanisms underlying observed responses. Despite our study populations are located in the species core range, the MHW was concomitant with a high mortality and structural shifts in only one of the two surveyed populations, most likely due to differences in habitat characteristics between sites (e.g. degree of shelter and seawater transfer). The experiment showed high mortalities at temperatures of 28°C, having the most severe implications for early life stages and fertility, which is consistent with warming being the cause of population changes in the field. Crucially, the regional‐scale quantification of the MHW (as described by satellite‐derived SSTs) did not capture local‐scale variation in MHW conditions at the study sites, which likely explained variation in population‐level responses to warming. Synthesis. Enclosed and semi‐enclosed seas, such as the Mediterranean Sea, often highly impacted by human perturbations, are also global hotspots for ocean warming and are highly susceptible to future MHWs. Our findings highlight that local‐scale variability in the magnitude of extreme climatic events can lead to local extinctions of already fragmented populations of habitat‐forming seaweeds, even towards the species' core range. However, our results highlight the potential for local‐scale climatic refugia, which could be identified and managed to safeguard the persistence of canopy‐forming seaweeds.

Cholera Toxin Production in Vibrio cholerae O1 El Tor Biotype Strains in Single-Phase Culture.

Vibrio cholerae O1 serogroup strains have been classified into classical and El Tor biotypes. Cholera, a life-threatening diarrheal disease, can be caused by either biotype through the cholera toxin (CT) that they produce. To increase our knowledge of the pathogenicity of bacteria, we must understand the toxigenicity of bacteria. CT production by classical biotype strains in simple single-phase cell cultures has been established; however, special culture media and growth conditions that are not appropriate for mass production of CT are required to facilitate CT production in El Tor biotype strains. In this report, we produced CT in El Tor biotype strains using simple media and single-phase culture conditions. A single point mutation in ToxT, a transcriptional activator of toxin co-regulated pilus (TCP) and CT, enabled the El Tor biotype strains to produce CT in similar quantities as classical biotype strains in single-phase laboratory culture conditions. CT production capacity varied between El Tor biotype strains. Wave 2 and 3 atypical El Tor strains tended to produce more CT than prototype Wave 1 strains. Wave 2 and 3 strains lack neutral fermentation; however, the capacity for neutral fermentation was not associated with significant differences in CT production by El Tor biotype strains. The Wave 3 strain that caused the 2010 cholera outbreak in Haiti produced CT only when neutral fermentation was abolished. The disparity in CT production between the seventh cholera pandemic strains highlight the differences in virulence between strains and the cause of population changes in V. cholerae.

A life cycle simulation model for exploring causes of population change in Alewife (Alosa pseudoharengus)

Over the last two decades, major changes in abundance and population characteristics of Alewife (Alosa pseudoharengus), an anadromous herring species, have been observed along the US Atlantic coast. Loss of spawning habitat, bycatch mortality in the directed pelagic fisheries, increased predation mortality by rebounding predators such as Striped Bass, changes in water flow and temperature affecting recruitment success, changes in ocean thermal habitat and direct and indirect effects of changes in zooplankton community have been expounded by different researchers as putative hypotheses for population changes in Alewife. Unfortunately, long-term, concurrently-measured time series of regional factors and direct measures of biological processes needed to elucidate underlying causes are severely lacking for Alewife. Therefore, we developed, calibrated and validated a mechanistic, spatially-explicit, full life-cycle simulation model that can be used to explore population responses of Alewife to various exogeneous drivers. Daily processes such as spawning, recruitment, mortality, exploitation, predation and movements are generated by using empirically-derived deterministic and stochastic relationships and time-series of environmental data linked to specific life stages. We demonstrate the use of the model as an investigative tool by simulating three hypotheses and comparing model results to observed trends in Alewife populations from southern New England.

Rapid condition monitoring of an endangered marine vertebrate using precise, non-invasive morphometrics

Understanding causes of population change is critical for conservation. Quantifying these causes can be difficult, especially for hard to sample animals like marine vertebrates (e.g. pinnipeds). One solution is to investigate spatiotemporal differences in a species' body condition by measuring body size and mass. Collecting traditional morphological measurements is risky and labour intensive, making less invasive and more efficient techniques desirable. Using Australian sea lions (Neophoca cinerea) of known size and mass as a case study, we tested the suitability of using drone-derived photogrammetry to estimate morphological measurements and assess body condition. Drone-derived measurements were precise and without bias. Animal mass was highly correlated with the 2-dimensional and 3-dimensional measurements of simplified area and volume, explaining >77% and >84% (all P < .01) of the variation in mass, depending on the age-sex class. The juvenile class exhibited the strongest associations (both 2D and 3D R2 > 0.99). Using each measurement as a proxy for mass, we calculated body condition indices for each class by standardising the variables by animal length. Photogrammetric indices ranked individuals comparably to those generated from ground-collected data (rs = 0.77–1, depending on age-sex class). Our technique provides a workflow for the non-invasive collection of morphometric data to quantify animal condition, which is transferrable to other pinniped species with species-specific calibration. It will also facilitate the efficient collection of morphometric data of vertebrates from remotely sensed imagery.

Foraging behaviour and habitat use by Indian Yellow-nosed Albatrosses (Thalassarche carteri) breeding at Prince Edward Island

ABSTRACTDemographic parameters of wild animals are often closely associated with their foraging distribution and behaviour, and understanding these attributes can assist in identifying causes of population changes. The Indian Yellow-nosed Albatross (Thalassarche carteri) is endangered but little information is available on its at-sea distribution and behaviour. It breeds only in French (Iles Amsterdam, St Paul, Kerguelen and Crozet) and South African (Prince Edward Island, PEI) territories in the south-west Indian Ocean, with PEI supporting about 20% of the global population. This study aimed to investigate the at-sea distributions of adult Indian Yellow-nosed Albatrosses provisioning chicks at PEI and to compare them with distributions of Yellow-nosed Albatrosses breeding at other localities. Using satellite transmitters, we identified two areas that were particularly favoured for foraging. Parents whose partners were brooding small chicks frequently moved north-east of PEI to shallow, productive waters where cold, nutrient-rich water upwells and results in enhanced levels of chlorophyll-a. By contrast, parents with older chicks that could be left unattended often foraged along the Agulhas Bank where eddies and shear forces promote vertical mixing. The at-sea distribution of birds breeding at PEI was located between those reported for Indian Yellow-nosed Albatrosses breeding at Ile Amsterdam and Atlantic Yellow-nosed Albatrosses (T. chlororhynchos) breeding at Gough Island, so that birds from these localities may face different threats at sea. Our study is the first to highlight key feeding areas for Indian Yellow-nosed Albatrosses from PEI and to demonstrate partitioning of foraging grounds by Yellow-nosed Albatrosses from different localities.

Temporal variation in survival and recovery rates of lesser scaup: A response

ABSTRACTWe recently analyzed long‐term (1951–2011) continental band‐recovery data from lesser scaup (Aythya affinis) and demonstrated that harvest rates declined through time, but annual survival rates exhibited no such trends; moreover, annual harvest and survival rates were uncorrelated for all age‐sex classes. We therefore concluded that declining fecundity was most likely responsible for recent population declines, rather than changes in harvest or survival. Lindberg et al. () critiqued our conclusions, arguing that we did little more than fail to reject a null hypothesis of compensatory mortality, postulated ecologically unrealistic changes in fecundity, and failed to give sufficient consideration to additive harvest mortality. Herein, we re‐summarize our original evidence indicating that harvest has been compensatory, or at most weakly additive, and demonstrate that our analysis had sufficient power to detect strongly additive mortality if it occurred. We further demonstrate that our conclusions were not confounded by population size, band loss, or individual heterogeneity, as suggested by Lindberg et al. (), and we provide additional support for our conjecture that low fecundity played a major role in declining scaup populations during 1983–2006. We therefore reiterate our original management recommendations: given low harvest rates and lack of demonstrable effect on scaup survival, harvest regulations could return to more liberal frameworks, and waterfowl biologists should work together to continue banding lesser scaup and use these data to explore alternative hypotheses to identify the true ecological causes of population change, given that it is unlikely to be excessive harvest. © 2017 The Wildlife Society.

Four Pillars of Statisticalism

Over the past fifteen years there has been a considerable amount of debate concerning what theoretical population dynamic models tell us about the nature of natural selection and drift. On the causal interpretation, these models describe the causes of population change. On the statistical interpretation, the models of population dynamics models specify statistical parameters that explain, predict, and quantify changes in population structure, without identifying the causes of those changes. Selection and drift are part of a statistical description of population change; they are not discrete, apportionable causes. Our objective here is to provide a definitive statement of the statistical position, so as to allay some confusions in the current literature. We outline four commitments that are central to statisticalism. They are: 1. Natural Selection is a higher order effect; 2. Trait fitness is primitive; 3. Modern Synthesis (MS)-models are substrate neutral; 4. MS-selection and drift are model-relative.

Recoveries and cascading declines of native mammals associated with control of an introduced predator

Invasive animal species are a major factor in the extinction and endangerment of native species worldwide. Longterm monitoring reveals some mammal recoveries have not been sustained in the presence of a broad-scale threat abatement program aimed at reducing the impact of the introduced Vulpes vulpes (red fox)-a top-order predator and key threat to many native species in Australia. Over 51,000 records of 19 terrestrial mammal species reported from a range of survey methods (pitfall traps, Elliott box traps, wire cage traps, spotlighting, sand plots, and nest boxes) across the Upper Warren region of southwestern Australia were used to investigate population changes over 41 years (1974-2014). Since the mid-1990s, populations of at least 7 native mammal species or genera have successively declined at similarly rapid rates and magnitudes (80-100%): Sminthopsis spp., Rattus fuscipes, Phascogale tapoatafa, Isoodon obesulus, Pseudocheirus occidentalis, Bettongia penicillata, and Notamacropus irma. R. fuscipes has not been recorded in the region since 2005 and may have become locally extinct. The other species that have declined remain at risk of becoming locally extinct. Three species have increased since 2000: Trichosurus vulpecula, Dasyurus geoffroii, and Notamacropus eugenii. The Upper Warren region in which this community disassembly has occurred is one of the principal sites for the conservation of many threatened mammal species and is within Australia's global biodiversity hotspot. We discuss the critical importance of long-term monitoring and the need to identify the causes of population change to inform how conservation and management activities can best be focussed. Predation by the introduced Felis catus (cat) is hypothesized as the most likely common or primary cause behind many of the recent declines in the Upper Warren. The integrated reduction of both cats and foxes, conducted within an experimental framework, is the most direct and definitive action to test this and deliver the greatest practical conservation outcomes.

Unexpected decline in a population of speckled tortoises

ABSTRACTLong‐lived, iteroparous species exhibit various mechanisms to overcome temporary unfavorable conditions and promote adult survival and population persistence. Consequently, populations may appear relatively stable while subtle and slow‐progressing threats cause their decline. The speckled tortoise (Homopus signatus) is a long‐lived, iteroparous species in South Africa that is thought to be secure in areas that meet the species’ known requirements. To verify its stability, I monitored a dense speckled tortoise population, integrating 2 mark‐recapture studies (2000–2004 and 2012–2015) in long‐term joint live and dead encounters and POPAN population models. From 2000 to 2015, the study site remained fenced, ungrazed, and was not modified in any way, yet the size‐class frequency distribution, sex ratio, and abundance of speckled tortoises drastically changed. Population numbers decreased 66%, mainly because of the disappearance of juveniles and males. Modeling results identified a reduction in the number of entrants into the population (via births and immigration) as the likely cause of population changes, whereas apparent survival remained high. Observations, in part anecdotal, of increasing numbers of pied crows (Corvus albus) on the study site suggest that increased predation on speckled tortoise hatchlings contributed to the population decline. Examination of rainfall data for 1990–2015 did not reveal evidence of aridification in the study area, a documented cause of reduced reproduction in speckled tortoises. The results of this study caution against the assumption that areas in the range of the speckled tortoise that meet its known requirements can maintain healthy populations. © 2017 The Wildlife Society

Rise and fall of Ross Sea emperor penguin colony populations: 2000 to 2012

AbstractThere are seven emperor penguin (Aptenodytes forsteri) colonies distributed throughout the traditional boundaries of the Ross Sea from Cape Roget to Cape Colbeck. This coastline is c. 10% of the entire coast of Antarctica. From 2000 to 2012, there has been a nearly continuous record of population size of most, and sometimes all, of these colonies. Data were obtained by analysing aerial photographs. We found large annual variations in populations of individual colonies, and conclude that a trend from a single emperor penguin colony may not be a good environmental sentinel. There are at least four possibilities for census count fluctuations: i) this species is not bound to a nesting site like other penguins, and birds move within the colony and possibly to other colonies, ii) harsh environmental conditions cause a die-off of chicks in the colony or of adults elsewhere, iii) the adults skip a year of breeding if pre-breeding foraging is inadequate and iv) if sea ice conditions are unsatisfactory at autumn arrival of the adults, they skip breeding or go elsewhere. Such variability indicates that birds at all Ross Sea colonies should be counted annually if there is to be any possibility of understanding the causes of population changes.

Are changes in breeding habitat responsible for recent population changes of long-distance migrant birds?

ABSTRACTCapsule: The direction and magnitude of changes in structure of UK woodlands since the 1980s, are inconsistent with them playing a causative role in the declines of four migrant bird species in upland oak woods.Aims: To investigate whether changes in woodland structure were a possible cause of population changes of four Afro-Palearctic migrants (Wood Warbler Phylloscopus sibilatrix, Tree Pipit Anthus trivialis, Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus) in the upland oakwoods of western and northern Britain.Methods: Bird population estimates and measures of woodland structure were recorded in two time periods 1982–85 and 2003–04 across six regions of the UK. We modelled the effect of habitat change and initial habitat state on population changes between the two time periods. The predicted effects of habitat change on populations were then compared with observed population changes across the different regions.Results: All four species underwent population declines; there were also significant increases in ground cover and understorey cover. The number of birds in 2003–04 was influenced by habitat structure at this time in addition to showing regional differences. Change in bird numbers varied between regions and was affected by both the initial habitat state and change in habitat structure, with regional variation in the effect of habitat change. There was however no relationship between the predicted effect of change in habitat structure on population size and observed regional population changes.Conclusions: Changes in woodland structure are unlikely to be the main driver of population change in these four migrant bird species, and large-scale factors affecting demographics in other parts of their breeding range or in their wintering areas are likely reasons for local population declines.

Management of modern agricultural landscapes increases nest predation rates in Black‐tailed Godwits Limosa limosa

Effective conservation of endangered species requires a solid understanding of the demographic causes of population change. Bird populations breeding on agricultural grasslands have declined because their preferred habitat of herb‐rich meadows has been replaced by grassland monocultures. The timing of agricultural activities in these monocultural grasslands is critical, as they often coincide with the nesting phase of breeding birds. Here, we aim to identify the effect of habitat management and targeted nest protection on nest survival of Black‐tailed Godwits Limosa limosa in the Netherlands, a population that has shown a 70% reduction in breeding population size since the 1970s. To protect nests in monocultures from destruction, farmers are paid to either delay mowing or leave a patch of unmown grass around the nest, a patch which in practice varied in size. In herb‐rich meadows, which are typically managed for bird conservation purposes, mowing occurs after hatching. Nest survival declined as the season advanced, more steeply on monocultures than on meadows. Targeted nest protection was only partially successful, as nest predation was considerably higher on mown grassland monocultures with small unmown patches around the nest than in mown monocultures with large unmown patches and in unmown fields. Increased predator densities over the years have been suggested as an important cause of the trend towards lower nest survival, but here we show that nest survival was higher on herb‐rich meadows than on monocultures, and similar to the 1980s. It thus seems that increased predator densities are an increased threat during the egg stage only if habitat quality is low. High‐quality habitat in the form of herb‐rich meadows therefore provides a degree of protection against predators.

Evidence for contrasting causes of population change in two closely related, sympatric breeding species the Whinchat Saxicola rubetra and Stonechat Saxicola torquata in Britain

Capsule The recent population decline of Whinchats has accelerated, including core breeding areas of Britain. Contrasting patterns of change with Stonechat suggest a large-scale environmental driver is affecting the entire Whinchat population.Aims To explore broad geographical and landscape related differences in long-term patterns of population change in the Whinchat and Stonechat across Britain to identify candidate mechanisms of change.Methods The study uses 40 years of large-scale, long-term data from a series of three atlas studies to compare trends in range and abundance in Whinchats and Stonechats relative to landscape and weather variables.Results For Whinchats there has been a long-term and accelerating decline in abundance, that includes stronghold areas of Britain. The Stonechat population has undergone a net gain in abundance with regional and altitudinal variations. These two very different patterns of change suggest the relative ubiquity of decline in Whinchats has a common source affecting the whole population.Conclusions The scale and magnitude of decline in Whinchats should stimulate a revision of the species conservation status in Britain, with renewed focus on studying the species' ecology across its breeding and winter range in order to determine the likely large-scale drivers of its decline.

Climate change and the population collapse during the “Great Famine” in pre‐industrial Europe

Population dynamics, economy, and human demography started with Malthus, the idea that population growth is limited by resources and “positive checks” occur when population growth overshoots the available resources. In fact, historical evidence indicates that long-term climate changes have destabilized civilizations and caused population collapses via food shortages, diseases, and wars. One of the worst population collapses of human societies occurred during the early fourteenth century in northern Europe; the “Great Famine” was the consequence of the dramatic effects of climate deterioration on human population growth. Thus, part of my motivation was to demonstrate that simple theoretical-based models can be helpful in understanding the causes of population change in preindustrial societies. Here, the results suggest that a logistic model with temperature as a “lateral” perturbation effect is the key element for explaining the population collapse exhibited by the European population during the “Great Famine”.