Estimates Of Population Growth Rate Research Articles

Grazing preferences of three species of amoebae on cyanobacteria and green algae.

Twenty species/isolates of cyanobacteria and green algae were isolated from cyanobacterial bloom samples in lakes associated with the upper Qu'Appelle River drainage system in southern Saskatchewan, Canada. Three amoebae species (Cochliopodium sp., Vannella sp. and Vermamoeba vermiformis) were also isolated from one of these samples, and were subjected to grazing assays to determine which species of cyanobacteria or algae could potentially serve as a food source. Amoeba grazing rates were quantified based on the diameter of the plaque after 12 days on agar plate assays, and by estimation of the amoeba population growth rate from the rate of increase of plaque area. The common cyanobacterial bloom-formers Dolichospermum sp. and Aphanizomenon flos-aquae supported high growth rates for all three amoebae, while green algae, with the exception of one green alga/amoeba combination, did not support growth of the tested amoebae. Many of the cyanobacterial and algal isolates that did not support amoebae growth were ingested, suggesting that ingestion did not determine grazing success. Overall, while the cyanobacteria Dolichospermum sp. and Aphanizomenon flos-aquae were suitable food sources for the amoebae, the other cyanobacteria were grazed in an unpredictable manner, with some species/strains grazed by some amoebae and some species not grazed at all.

Uncertainty propagation in matrix population models: Gaps, importance and guidelines

Abstract Matrix population models (MPMs), which describe the demographic behaviour of a population based on age or stage through discrete time, are popular in ecology, evolutionary biology and conservation biology. MPMs provide a tool for guiding management decisions and can give insight into life history trade‐offs, patterns of senescence, transient dynamics and population trajectories. These models are parameterised with estimates of demographic rates (e.g. survival and reproduction) and can have multiple layers of underlying statistical analyses, all of which introduce uncertainty. For accurate and transparent results, this uncertainty should be propagated through to quantities derived from the MPMs, such as population growth rates (λ). However, full propagation is not always achieved, leading to omitted uncertainty and negative consequences for the reliability of inferences drawn. We summarised the contemporary standards regarding demographic rate uncertainty reporting and propagation, by reviewing papers using MPMs from 2010 to 2019. We then used reported uncertainties as the basis for a simulation study to explore the impact of uncertainty omission on inferences drawn from the analysis of MPMs. We simulated four scenarios of demographic rate propagation and evaluated their impact on population growth rate estimates. Although around 78% of MPM papers report some kind of uncertainty in their findings, only half of those report uncertainty in all aspects. Additionally, only 31% of papers fully propagate uncertainty through to derived quantities. Our simulations demonstrate that, even with moderate levels of uncertainty, incomplete propagation introduces bias. Omitting uncertainty may substantially alter conclusions, particularly for results showing small changes in population size. Biased conclusions were most common when uncertainty in the most influential demographic rates for population growth were omitted. We suggest comprehensive guidelines for reporting and propagating uncertainty in MPMs. Standardising methods and reporting will increase the reliability of MPMs and enhance the comparability of different models. These guidelines will improve the accuracy, transparency and reliability of population projections, increasing our confidence in results that can inform conservation efforts, ultimately contributing to biodiversity preservation.

Evaluating the importance of individual heterogeneity in reproduction to Weddell seal population dynamics using integral projection models.

Identifying and accounting for unobserved individual heterogeneity in vital rates in demographic models is important for estimating population-level vital rates and identifying diverse life-history strategies, but much less is known about how this individual heterogeneity influences population dynamics. We aimed to understand how the distribution of individual heterogeneity in reproductive and survival rates influenced population dynamics using vital rates from a Weddell seal population by altering the distribution of individual heterogeneity in reproduction, which also altered the distribution of individual survival rates through the incorporation of our estimate of the correlation between the two rates and assessing resulting changes in population growth. We constructed an integral projection model (IPM) structured by age and reproductive state using estimates of vital rates for a long-lived mammal that has recently been shown to exhibit large individual heterogeneity in reproduction. Using output from the IPM, we evaluated how population dynamics changed with different underlying distributions of unobserved individual heterogeneity in reproduction. Results indicate that the changes to the underlying distribution of individual heterogeneity in reproduction cause very small changes in the population growth rate and other population metrics. The largest difference in the estimated population growth rate resulting from changes to the underlying distribution of individual heterogeneity was less than 1%. Our work highlights the differing importance of individual heterogeneity at the population level compared to the individual level. Although individual heterogeneity in reproduction may result in large differences in the lifetime fitness of individuals, changing the proportion of above- or below-average breeders in the population results in much smaller differences in annual population growth rate. For a long-lived mammal with stable and high adult-survival that gives birth to a single offspring, individual heterogeneity in reproduction has a limited effect on population dynamics. We posit that the limited effect of individual heterogeneity on population dynamics may be due to canalization of life-history traits.

Leveraging projection models to evaluate long‐term dynamics of scrub mint translocations

AbstractTranslocated populations often show vigorous initial dynamics but eventually collapse. Modeling tools that incorporate basic ecological knowledge and allow for propagation of uncertainty can help identify potential risks. Here, we use Bayesian Integral Projection Models to estimate population growth rates (λs), associated elasticities, and extinction risks for the endangered Dicerandra christmanii. Our study compared natural populations in gaps (open areas) within the shrub matrix and roadsides, unoccupied gaps augmented with transplants, and introduced populations. These populations experienced different management, including prescribed fires, and had different initial conditions. Augmented gaps showed lower means but similar variation in λs as natural gaps. Yet, simulations indicate that augmentations can delay quasi‐extinction (40% of simulations) by 4 years at the population level. Introduced populations showed higher means and variation in λs as wild gaps. While vital rate estimates suggested initial translocation success, time to quasi‐extinction was projected to be 7 years shorter for introductions in gaps than for natural gap populations. These contradictory results are partially explained by the lack of established seed banks in introduced populations, which affected the response of early life stage transitions to a prescribed fire. This study highlights the need to account for site‐specific information in models of population dynamics, including initial conditions and management history, and especially cryptic life stages such as dormant seeds.

Abundance and demographic parameters of humpback whales from the Gulf of Maine, and stock definition relative to the Scotian Shelf

The Gulf of Maine is one of the principal summer feeding grounds for humpback whales (Megaptera novaeangliae) in the North Atlantic, and was one focus of effort in an ocean-basin-wide study known as the Years of the North Atlantic Humpback (YoNAH) project. Data from that project and from subsequent surveys were used to assess stock boundaries, abundance and demographic parameters for Gulf of Maine humpbacks. Surveys on the Scotian Shelf in the summers of 1998 and 1999 produced the first substantial dataset of identified individual humpbacks observed in this region, which lies between the well-studied areas of the Gulf of Maine and Newfoundland. The results gave a match rate of approximately 27% (14 of 52 individuals) between the Scotian Shelf and the Gulf of Maine, with evidence that many of the matched whales were transient in the Gulf of Maine; there were no matches to any other location in the North Atlantic. These data suggest that the range of most whales from the Gulf of Maine usually does not extend as far east as the Scotian Shelf or Newfoundland. Only one whale was observed on the Scotian Shelf in both the 1998 and 1999 surveys, and another seen in 1998 had also been sighted there in 1994. This low inter-annual match rate suggests that the abundance of humpback whales on the Scotian Shelf is larger than previously recognised. Three different but overlapping estimates of abundance for the Gulf of Maine population were calculated. Mark-recapture data from 1992/93 gave an estimate of abundance of 652 (CV = 0.29); however, this estimate is likely biased because of heterogeneity in sampling and in animal distribution. Photo-id data also provided a minimum population estimate of 497 humpbacks known to be alive in 1997; this estimate is also likely to be negatively biased because of heterogeneity. Finally, line-transect surveys conducted in 1999 yielded estimates of 816 (CV = 0.45) or 902 humpback whales (CV = 0.41, including a portion of the eastern Scotian Shelf stratum); these transect-based estimates are more consistent with the number of humpbacks (1,273, including dead animals) in the current photo-id catalogue for the Gulf of Maine. Overall, the size of the Gulf of Maine population is likely to be in the high hundreds, but no more precise estimate can be calculated at this time. The growth rate for the Gulf of Maine population was estimated using an interbirth interval method using data from 1992-2000. The estimate was either 1.00 (for a calf survival rate of 0.51) or 1.04 (for a calf survival rate of 0.875). Although confidence limits are not available (because maturation parameters could not be estimated), both estimates of population growth rate are outside the 95% confidence intervals of the previous estimate of 1.065 for the period 1979-1991 (Barlow and Clapham, 1997). It is unclear whether this apparent decline is an artefact resulting from a shift in distribution or is a real phenomenon; if the latter, it may be related to known high mortality among young-of-the-year whales in the waters of the US mid-Atlantic states. However, calf survival appears to have increased since 1996, presumably accompanied by an increase in population growth.

Population dynamics and harvest management of eastern mallards

AbstractManaging sustainable harvest of wildlife populations requires regular collection of demographic data and robust estimates of demographic parameters. Estimates can then be used to develop a harvest strategy to guide decision‐making. Mallards (Anas platyrhynchos) are an important species in the Atlantic Flyway for many users and they exhibited exponential growth in the eastern United States between the 1970s and 1990s. Since then, estimates of mallard abundance have declined 16%, prompting the Atlantic Flyway Council and United States Fish and Wildlife Service to implement more restrictive hunting regulations and develop a new harvest strategy predicated on an updated population model. Our primary objective was to develop an integrated population model (IPM) for use in an eastern mallard harvest management strategy. We developed an IPM using annual estimates of breeding abundance, 2‐season banding and recovery data, and hunter‐harvest data from 1998 to 2018. When developing the model, we used novel model selection methods to test various forms of a sub‐model for survival including estimating the degree of harvest additivity and any age‐specific trends. The top survival sub‐model included a negative annual trend on juvenile survival. The IPM posterior estimates for population abundance tracked closely with the observed estimates and estimates of mean annual population growth rate ranged from 0.88 to 1.08. Our population model provided increased precision in abundance estimates compared to survey methods for use in an updated harvest strategy. The IPM posterior estimates of survival rates were relatively stable for adult cohorts, and annual growth rate was positively correlated with the female age ratio, a measure of reproduction. Either or both of those demographic parameters, juvenile survival or reproduction, could be a target for management efforts to address the population decline. The resulting demographic parameters provided information on the equilibrium population size and can be used in an adaptive harvest strategy for mallards in eastern North America.

Habitat fragmentation reduces survival and drives source-sink dynamics for a large carnivore.

Rigorous understanding of how environmental conditions impact population dynamics is essential for species conservation, especially in mixed-use landscapes where source-sink dynamics may be at play. Conservation of large carnivore populations in fragmented, human-dominated landscapes is critical for their long-term persistence. However, living in human-dominated landscapes comes with myriad costs, including direct anthropogenic mortality and sublethal energetic costs. How these costs impact individual fitness and population dynamics are not fully understood, partly due to the difficulty in collecting long-term demographic data for these species. Here, we analyzed an 11-year dataset on puma (Puma concolor) space use, mortality, and reproduction in the Santa Cruz Mountains, California, USA, to quantify how living in a fragmented landscape impacts individual survival and population dynamics. Long-term exposure to housing density drove mortality risk for female pumas, resulting in an 18-percentage-point reduction in annual survival for females in exurban versus remote areas. While the overall population growth rate appeared stable, reduced female survival in more developed areas resulted in source-sink dynamics across the study area, with 42.1% of the Santa Cruz Mountains exhibiting estimated population growth rates <1. Since habitat selection is often used as a proxy for habitat quality, we also assessed whether puma habitat selection predicted source and sink areas. Patterns of daytime puma habitat selection predicted source areas, while time-of-day-independent habitat selection performed less well as a proxy. These results illuminate the individual- and population-level consequences of habitat fragmentation for large carnivores, illustrating that habitat fragmentation can produce source-sink dynamics that may not be apparent from other metrics of habitat quality. Locally, conserving high-quality source habitat within the Santa Cruz Mountains is necessary to support long-term puma population persistence. More broadly, source-sink dynamics may at play for other carnivore populations in similar fragmented systems, and linking landscape conditions to population dynamics is essential for effective conservation. Caution should be used in inferring habitat quality from habitat selection alone, but these results shed light on metrics of selection that may be better or worse proxies to identify source areas for large carnivores.

On the road to self-sustainability: reintroduced migratory European northern bald ibises Geronticus eremita still need management interventions for population viability

AbstractThe northern bald ibis Geronticus eremita disappeared from Europe in the Middle Ages. Since 2003 a migratory population has been reintroduced in Central Europe. We conducted demographic analyses of the survival and reproduction of 384 northern bald ibises over a period of 12 years (2008–2019). These data also formed the basis for a population viability analysis simulating the possible future development of the northern bald ibis population under different scenarios. We analysed life stage-specific survival rates, rearing protocols and colonies, and the influence of stochastic catastrophic events and reinforcement translocations on population growth. Life stage-specific survival probabilities were 0.64–0.78. Forty-five per cent of the mature females reproduced, with a mean fecundity of 2.15 fledglings per nest. The complementary population viability analysis indicated that the Waldrappteam population is close to self-sustainability, with an estimated population growth rate of 0.95 and a 24% extinction probability within 50 years. Of the 326 future scenarios tested, 94% reached the criteria of extinction probabilities &lt; 5% and population growth rates &gt; 1. Stochastic catastrophic events had only a limited effect. Despite comparatively high survival and fecundity rates the population viability analysis indicated that to achieve self-sustainability the Waldrappteam population needs further translocations to support population growth and the implementation of effective measures against major mortality threats: illegal hunting in Italy and electrocution on unsecured power poles. The findings of this study are to be implemented as part of a second European LIFE project.

A synthesis of Eurasian Curlew (Numenius arquata arquata) demography and population viability to inform its management

The European population of Eurasian Curlew Numenius arquata arquata, a near‐threatened wader subspecies, has undergone pronounced population declines over the past 30 years. To assess the demography and viability of its global population, we surveyed studies quantifying demographic rates (productivity and survival) and complemented this review with new estimates of survival probability at the flyway scale. Then, using a demographic model, we estimated population growth rates while accounting for the range of variation of demographic parameters, and compared these estimates (expected based on demographic rates) with those observed based on population censuses. Both observed and expected average growth rates were negative but the observed rates were higher than estimates from demographic models (λ = 0.98–0.99 compared with 0.85–0.95). This discrepancy implies that there is geographical variation in the demography of different populations that is not fully covered by current demographic data, namely unstudied regions with higher productivity. According to our calculations, at the flyway scale, productivity is currently c. 0.57 fledglings per pair per year, higher than the average reported productivity of 0.29, but lower than the 0.68 needed to achieve a stable global population size (λ = 1). Adult survival, estimated at 0.90, was the most sensitive parameter determining population growth rates, but the low productivity levels over the last few decades seems to be the most probable cause of population declines. The negative population growth rates require immediate conservation actions to preserve adult survival and increase the extremely low productivity in western and northern European populations to values above 0.68 fledglings per pair per year. We hope our synthesis on the demographic status of Curlew in Europe will encourage the collection of more demographic data and allow concrete management goals at the flyway scale to be established in order to recover the global population of this iconic species.

A Bayesian multi‐stage modelling framework to evaluate impacts of energy development on wildlife populations: an application to greater sage‐grouse (Centrocercus urophasianus)

Increased demand for domestic production of renewable energy has led to expansion of energy infrastructure across western North America. Much of the western U.S. comprises remote landscapes that are home to a variety of vegetation communities and wildlife species, including the imperiled sagebrush ecosystem and indicator species such as greater sage-grouse (Centrocercus urophasianus). Geothermal sources in particular have potential for continued development across the western U.S. but impacts to greater sage-grouse and other species are unknown. To address this information gap, we describe a novel two-pronged methodology that analyzes impacts of geothermal energy production on pattern and process of greater sage-grouse populations using (a) before-after control-impact (BACI) measures of population growth and lek absence rates and (b) concurrent-to-operation evaluations of demographic rates. Growth and absence rate analyses utilized 14 years of lek survey data collected prior (2005–2011) and concurrent (2012–2018) to geothermal operations at two sites in Nevada, USA. Demographic analyses utilized relocation data, restricted inference to concurrent years, and incorporated 17 additional control sites. Demographic results were applied to >100 potential geothermal sites distributed across the study region to generate spatially explicit predictions of unrealized population-level impacts.•State-space and generalized linear models yield estimates of population growth and lek absence rates, respectively, before and after the onset of geothermal energy production; distances ranging from 2–30 km are evaluated as alternative control-impact footprint hypotheses; this provides inference about the spatial extent as well as the magnitude of impacts associated with geothermal development.•Estimation of important population demographic rates are implemented to investigate the processes by which geothermal energy development might reduce population growth; independent estimates of confounding, environmental effects from 17 control sites are made spatially explicit within ‘impact’ models to establish baseline conditions otherwise masked by collinearity.•Population matrix models are built using estimates from demographic analyses to provide landscape mapping of impacts associated with potential geothermal sites.

Evaluation of seasonal site-level demography and management for northern bobwhite using integrated population models

Understanding the effects of landscape management on northern bobwhite (Colinus virginianus) population growth requires information on seasonal- and stage-specific demographic parameters linked across the full annual cycle. We evaluated site-level seasonal dynamics and population growth of bobwhites in southwest Missouri and compared differences between three extensively and two intensively managed sites from 2016 to 2019. Extensively managed sites were continuous tracts of native prairie. Intensively managed sites were composed of smaller native and non-native grassland units interspersed with strip crops, food plots, and woody field borders. We radio-marked adults and broods to estimate survival and productivity, conducted spring whistle counts to estimate abundance and developed a two-season, two-stage, two-sex integrated population model to estimate population dynamics. The number of young hatched per female-incubated nest was greater on the three extensively managed sites compared to the two intensively managed sites. Six-month period survival of adults during the breeding season was also greater on the three extensively managed sites compared to the two intensively managed sites. One hundred-day juvenile breeding season survival varied among sites and was highest on Talbot, compared to juvenile breeding season survival on the other four study sites. Six-month, non-breeding season period survival was lowest on the two smallest extensively managed sites, Stony Point Prairie and Shelton Conservation Area compared to non-breeding season survival on the other three study sites. Annual changes in bobwhite abundance were weakly correlated with female fecundity, though this positive relationship was stronger on extensively managed sites. Intensively managed sites exhibited low mean fecundity and breeding season adult survival relative to those that resulted in a stable population. Populations across sites declined from 2016 to 2019 and estimates of annual population growth rates overlapped across sites. Differences between observed changes in bobwhite abundance and estimates of observed demographic rates at some sites suggest unmeasured processes such as movement or bias associated with data and model assumptions influenced estimated vital rates. Overall, our integrated population model was an effective tool for understanding site-level seasonal dynamics and population growth of bobwhites. Based on comparisons of demography between extensively and intensively managed sites, we suggest increased native grassland cover managed with prescribed fire, low intensity grazing, and high mowing may increase bobwhite nesting success and breeding season adult survival, however, achieving stable or increasing rates of population growth may also require increased juvenile breeding season and non-breeding season survival.

Indigenous pig genetic resources: Preliminary documentation of current status and population trend of Tswana pigs in three districts of Botswana

This study aimed to assess the status, population and population trend of Tswana pigs in three districts of Botswana. A survey was conducted for three consecutive years from 2018 to 2020 in three districts to establish the status of indigenous Tswana pigs in the country in terms of their population. The three districts were Kgatleng, Kweneng and South-East. These districts were purposely chosen because they are the ones which have a considerable number of indigenous Tswana pigs. A structured questionnaire was administered to 71 farmers in 2018, 50 farmers in 2019 and 71 farmers in 2020. The population of indigenous Tswana pigs declined over the three years of study. South-East district had the highest number of indigenous pigs and Kweneng district had the least number during the three years of study. Sows and gilts were more than boars. The average herd size ranged from 3.5 to 20 over the three years. According to risk status classification by FAO, the status of indigenous Tswana breed in the southern districts of Botswana is ‘endangered’ and the estimated population growth rate is less than one. There is a strong positive and significant difference between the total number of pigs and the number of female pigs. The regression analysis indicated a positive impact of adult female pig numbers on the total number of Tswana pigs.

Range-Wide Population Projections for Northern Red-Bellied Cooters (Pseudemys rubriventris)

Northern Red-Bellied Cooters (Pseudemys rubriventris) have a disjunct distribution with a relictual population in southeastern Massachusetts and a larger range across the mid-Atlantic United States. The relictual population is currently listed with protections under the U.S. Endangered Species Act but the status of the population in the remainder of the species' range has not been assessed, and there is concern that it may be at risk of extinction without protection. The U.S. Fish and Wildlife Service requires scientific information of the species' status to inform conservation decisions. There is little empirical information available from P. rubriventris populations and, furthermore, the majority of what exists comes from the disjunct northern subpopulation. To fill data gaps in the species' life history and reduce geographic bias, we supplement available data from P. rubriventris with demographic rate estimates from other Pseudemys species to parameterize an age-structured population projection model. Our estimate of mean population growth rate was 0.987 (0.92–1.04), indicating that P. rubriventris populations may be in decline. However, there was considerable uncertainty in our results, with 35% of projections resulting in stable or increasing populations. Additional uncertainty about parameter values, geographic variation, and current threats limit the assessment. We discuss the merits and limitations of our population projection modeling (PPM) approach where other analytical methods are precluded by lack of available data.

Simple statistical models can be sufficient for testing hypotheses with population time-series data.

Time‐series data offer wide‐ranging opportunities to test hypotheses about the physical and biological factors that influence species abundances. Although sophisticated models have been developed and applied to analyze abundance time series, they require information about species detectability that is often unavailable. We propose that in many cases, simpler models are adequate for testing hypotheses. We consider three relatively simple regression models for time series, using simulated and empirical (fish and mammal) datasets. Model A is a conventional generalized linear model of abundance, model B adds a temporal autoregressive term, and model C uses an estimate of population growth rate as a response variable, with the option of including a term for density dependence. All models can be fit using Bayesian and non‐Bayesian methods. Simulation results demonstrated that model C tended to have greater support for long‐lived, lower‐fecundity organisms (K life‐history strategists), while model A, the simplest, tended to be supported for shorter‐lived, high‐fecundity organisms (r life‐history strategists). Analysis of real‐world fish and mammal datasets found that models A, B, and C each enjoyed support for at least some species, but sometimes yielded different insights. In particular, model C indicated effects of predictor variables that were not evident in analyses with models A and B. Bayesian and frequentist models yielded similar parameter estimates and performance. We conclude that relatively simple models are useful for testing hypotheses about the factors that influence abundance in time‐series data, and can be appropriate choices for datasets that lack the information needed to fit more complicated models. When feasible, we advise fitting datasets with multiple models because they can provide complementary information.

An initial assessment of the sustainability of waterbird harvest in the United Kingdom

Abstract There is a need to assess the sustainability of wild bird harvest in the United Kingdom (UK), and more widely, across Europe. Yet, data on populations and harvest sizes are limited. We used a demographic invariant method (DIM) to estimate potential excess growth (PEG) for populations of UK wintering waterbirds and calculated a sustainable harvest index (SHI) for each. We compared this with population trends and conservation classifications (e.g. Birds of Conservation Concern [BoCC]) to assess the sustainability of harvests and the utility of these classifications. Our approach found evidence for potential overharvest of mallard Anas platyrhynchos, Eurasian teal Anas crecca, gadwall Mareca strepera, Canada geese Branta canadensis, greylag geese Anser anser and woodcock Scolopax rusticola. Whether DIM methods predict overharvest is highly dependent on estimates of maximum population growth rates inferring PEG. We found estimates of maximum population growth to be variable across a range of different methods. We found no relationship between SHI and short‐term wintering trends or conservation classification under the UK's BoCC framework. There was however a positive relationship between SHI and long‐term wintering trends. Policy implications. Our results suggest that UK‐based harvest is unlikely to be a major determinant of population trends for the majority of UK overwintering waterbirds, but harvest rates for some species may exceed that required to maintain stationary population growth. The lack of a relationship between conservation classifications and SHI strongly suggests that such conservation classifications are not an appropriate tool for making decisions about harvest management. Instead, our assessment provides the basis for a framework to make evidence‐based decisions on sustainable harvest levels in the face of incomplete data. There is currently no clear policy instrument in the UK to support such a framework via controls on either harvest effort or mortality of waterfowl. We believe such an instrument is urgently needed to ensure the UK can adapt to changing pressures and ensure the sustainable use of our wildlife populations.

Temporal Population Trends and Habitat Associations for Mountain Whitefish in Central Idaho

AbstractMountain Whitefish Prosopium williamsoni have failed to garner the same level of attention as other members of the salmonid family in terms of scientific investigations, especially with regard to habitat associations and population status. Consequently, we used snorkel survey data from 1985 to 2019 to relate a suite of environmental factors to Mountain Whitefish occupancy and abundance and to estimate population growth rates in central Idaho. Mountain Whitefish population growth rates in the majority of subbasins in central Idaho appear to be stable or increasing over the past several decades, but more so in the Salmon River basin than in the Clearwater River basin. Mountain Whitefish occupancy and abundance were higher in stream reaches that were lower in elevation and gradient and larger in size, with an occupancy rate of &lt;0.10 in stream reaches that were &lt;6 m average wetted width but &gt;0.50 in stream reaches that were ≥9 m average wetted width. Road density was positively associated with the occupancy and abundance of Mountain Whitefish, contrasting previous studies that generally report negative associations between road density and salmonid population metrics. While this relationship may simply be correlative in nature, in the relatively sterile lotic environment of central Idaho, such anthropogenic disturbance may inadvertently result in nutrient enrichment, potentially benefitting the forage base of Mountain Whitefish. We also observed that conductivity positively influenced Mountain Whitefish abundance, likely stemming from its direct effect on stream productivity. Although the status of Mountain Whitefish in central Idaho appears generally stable, the paucity of studies reporting on the status of this species highlights the need for additional research devoted to a better understanding of trends in Mountain Whitefish abundance across their range.

Extrapolating Contaminant Effects from Individuals to Populations: A Case Study on Nanoparticle Toxicity to Daphnia Fed Environmentally Relevant Food Levels

Ecological risk assessment (ERA) is charged with assessing the likelihood a chemical will have adverse environmental or ecological effects. When assessing the risk of a potential contaminant to biological organisms, ecologists are most concerned with the sustainability of populations of organisms, rather than protecting every individual. However, ERA most commonly relies on data on the effect of a potential contaminant on individuals because these experiments are more feasible than costly population-level exposures. In this work, we address the challenge of extrapolating these individual-level results to predict population-level effects. Previous per-capita population growth rate estimates calculated from individual-level exposures of Daphnia pulicaria to silver nanoparticles (AgNPs) at different food rations predict a critical daily food requirement for daphnid populations exposed to 200μg/L AgNPs to avoid extinction. To test this, we exposed daphnid populations to the same AgNP concentration at three different food inputs, with the lowest ration close to the extinction threshold predicted from data on individuals. The two populations with the higher food inputs persisted, and the population with the lowest food input went extinct after 50days but did persist through two generations. We demonstrate that we can extrapolate between these levels of biological organization by parameterizing an individual-level biomass model with data on individuals' response to AgNPs and using these parameters to predict the outcome for control and AgNP-exposed populations. Key to successful extrapolation is careful modeling of temporal changes in resource density, driven by both the experimental protocols and feedback from the consumer. The implication for ecotoxicology is that estimates of extinction thresholds based on studies of individuals may be reliable predictors of population outcomes, but only with careful treatment of resource dynamics.

The effects of a decade of agri‐environment intervention in a lowland farm landscape on population trends of birds and butterflies

Abstract Declines in farmland biodiversity remain evident despite over three decades of research and implementation of agri‐environment schemes (AES). Although positive effects of AES are often demonstrated locally or in the short term, studies exploring longer term trends in biodiversity often show contradictory results. Evidence for the potential of AES to drive beneficial changes in populations remains sparse, especially for mobile taxa such as birds and butterflies. We analysed the abundance of 12 widespread bird and 9 butterfly species from a 10‐year study of AES intervention in a farmland landscape in southern England. We compared estimates of annual population growth rates from our study landscape with rates derived from large‐scale national monitoring schemes in equivalent landscapes without substantial AES. Species trends in our study landscape were frequently stable or increasing, in contrast to concurrent declining trends in equivalent landscapes without AES. These differences were significant for total abundance of granivorous species and for chaffinch Fringilla coelebs, blue tit Cyanistes caeruleus and great tit Parus major individually. For butterflies, differences in trends were significantly more positive for gatekeeper Pyronia tithonus and green‐veined white Pieris napi, while small white P. rapae showed a trend that was significantly more negative in our study landscape. Synthesis and applications. Our results demonstrate that, for some bird and butterfly species, the higher abundances associated with areas of AES uptake within a typical commercial farmland landscape can co‐occur with positive or stable population trends over long time scales and that these trends can show significant differences from those in equivalent landscapes without substantial AES interventions. Our results suggest that previously observed inconsistencies in AES benefits may in part reflect a lack of long‐term studies with accurate data on AES uptake and quality (i.e. successful implementation and management). Our results, thus, affirm the importance of delivering and monitoring high‐quality AES options if the design and implementation of the next generation of AES is to achieve significant benefits for biodiversity.

Evaluating the effect of expert elicitation techniques on population status assessment in the face of large uncertainty

Population projection models are important tools for conservation and management. They are often used for population status assessments, for threat analyses, and to predict the consequences of conservation actions. Although conservation decisions should be informed by science, critical decisions are often made with very little information to support decision-making. Conversely, postponing decisions until better information is available may reduce the benefit of a conservation decision. When empirical data are limited or lacking, expert elicitation can be used to supplement existing data and inform model parameter estimates. The use of rigorous techniques for expert elicitation that account for uncertainty can improve the quality of the expert elicited values and therefore the accuracy of the projection models. One recurring challenge for summarizing expert elicited values is how to aggregate them. Here, we illustrate a process for population status assessment using a combination of expert elicitation and data from the ecological literature. We discuss the importance of considering various aggregation techniques, and illustrate this process using matrix population models for the wood turtle (Glyptemys insculpta) to assist U.S. Fish and Wildlife Service decision-makers with their Species Status Assessment. We compare estimates of population growth using data from the ecological literature and four alternative aggregation techniques for the expert-elicited values. The estimate of population growth rate based on estimates from the literature (λmean = 0.952, 95% CI: 0.87–1.01) could not be used to unequivocally reject the hypotheses of a rapidly declining population nor the hypothesis of a stable, or even slightly growing population, whereas our results for the expert-elicited estimates supported the hypothesis that the wood turtle population will decline over time. Our results showed that the aggregation techniques used had an impact on model estimates, suggesting that the choice of techniques should be carefully considered. We discuss the benefits and limitations associated with each method and their relevance to the population status assessment. We note a difference in the temporal scope or inference between the literature-based estimates that provided insights about historical changes, whereas the expert-based estimates were forward looking. Therefore, conducting an expert-elicitation in addition to using parameter estimates from the literature improved our understanding of our species of interest.

Interpopulation differences in male reproductive effort drive the population dynamics of a host exposed to an emerging fungal pathogen.

Compensatory recruitment is a key demographic mechanism that has allowed the coexistence of populations of susceptible amphibians with Batrachochytrium dendrobatidis (Bd), a fungus causing one of the most devastating emerging infectious disease ever recorded among vertebrates. However, the underlying processes (e.g. density-dependent increase in survival at early life stages, change in reproductive traits) as well as the level of interpopulation variation in this response are poorly known. We explore potential mechanisms of compensatory recruitment in response to Bd infection by taking advantage of an amphibian system where male reproductive traits are easy to quantify in free-living populations. The Southern Darwin's frog Rhinoderma darwinii is a vocal sac-brooding species that exhibits a high susceptibility to lethal Bd infection. Using a 7-year capture-recapture study at four populations with contrasting Bd infection status (one high prevalence, one low prevalence and two Bd-free populations), we evaluated whether Bd-positive populations exhibited a higher adult recruitment and a higher male reproductive effort than Bd-negative populations. We also estimated population growth rates to explore whether recruitment compensated for the negative impacts of Bd on the survival of adults. In addition, we evaluated a potential demographic signal of compensatory recruitment (i.e. positive relationship between the proportion of juveniles and Bd prevalence) in response to Bd infection using raw count data from 13 R. darwinii populations. The high Bd prevalence population exhibited the highest male reproductive effort and the highest recruitment among the four monitored populations. This led to a growing population during the study period despite high mortality of adult hosts. In contrast, males from the population with low Bd prevalence had a low reproductive effort and this population, which had the lowest adult recruitment, was declining during the study period despite adults having a higher survival in comparison to the high Bd prevalence population. We also found a demographic signal of compensatory recruitment in response to Bd infection in our broader analysis of 13 R. darwinii populations. Our study underlines the importance of interpopulation variation in life-history strategies on the fate of host populations after infectious disease emergence. Our results also suggest that an increase in reproductive effort can be one of the processes underlying compensatory recruitment in populations of Bd-susceptible amphibians.