Source-sink Population Dynamics Research Articles

Population connectivity of the swordtip squid Uroteuthis edulis between southern Japan and northern Taiwan using statolith trace elemental analysis

Uroteuthis edulis (Hoyle, 1885) is an Indo-Pacific squid species widely distributing in the western Pacific, and commercially important especially in Japan and Taiwan. It has been suggested that some individuals are possibly transported from the spawning ground in north Taiwan to the coasts of Japan, however, the strength of population connectivity between those areas and its influence on U. edulis population dynamics were unveiled. To understand the U. edulis population connectivity in this area, the correlations between statolith trace elements and abiotic/biotic factors were examined first, and then squid experienced environments were postulated throughout their entire life cycle. Sr/Ca ratio showed a strongly negative correlation with ambient water temperature but no correlation with individual growth rate, suggesting that Sr/Ca ratio can be used to reflect squid experienced temperatures. Most squid caught in the Sea of Japan hatched in the areas having similar water temperature with where Taiwanese squid hatched, that would be off the north Taiwan or even warmer area. Statolith trace elements successfully distinguished the catch locations but not the hatching grounds, implying that hatching grounds of Japan and Taiwan squid were largely overlapped. Thus, we suggest that there is strong population connectivity of U. edulis population between southern Japan and northern Taiwan. As there was no clear evidence for existence of local population hatched in the Sea of Japan in this study, U. edulis population might display a source-sink population dynamics, that is, population in Taiwanese waters and/or further south as the source, and the one in the Sea of Japan as a sink population. As U. edulis should be considered as a metapopulation, collaboration among countries in the northwestern Pacific is required for sustainable fishery management of this species.

Freshwater Reservoir, Ecological Traps and Source-Sink Dynamics

Odonata are biodiversity indicators that adequately represent many aquatic and semi-aquatic animal species. We recorded over two field seasons a rich lentic community of Odonata (18 species) in a large artificial freshwater reservoir (ca. 55 ha) built 40 years ago. The release of water from the dam in summer for crop irrigation leads to the desiccation of large parts of the reservoir, which prevents the reproduction of half of the species of this Odonata community. We identify two adaptations that allow eight species to cope with desiccation, i.e., a precocious breeding period allowing the emergence of adults before the retreat of water, or a delayed adult emergence due to egg diapause from oviposition to the end of winter. The reservoir acts thus as an ecological trap for individuals of 10 species that developed elsewhere and were attracted to the site without successfully breeding there. As consequence of the local population extinction at each generation, the presence of individuals of these 10 species at the reservoir depends on source-sink population dynamics in the landscape. In the context of global warming that encourages the creation of artificial freshwater reservoirs, the multiplication of such sinks could threaten the persistence in the landscape of species maladapted to desiccation.

Large-scale population disappearances and cycling in the white-lipped peccary, a tropical forest mammal.

Many vertebrate species undergo population fluctuations that may be random or regularly cyclic in nature. Vertebrate population cycles in northern latitudes are driven by both endogenous and exogenous factors. Suggested causes of mysterious disappearances documented for populations of the Neotropical, herd-forming, white-lipped peccary (Tayassu pecari, henceforth "WLP") include large-scale movements, overhunting, extreme floods, or disease outbreaks. By analyzing 43 disappearance events across the Neotropics and 88 years of commercial and subsistence harvest data for the Amazon, we show that WLP disappearances are widespread and occur regularly and at large spatiotemporal scales throughout the species' range. We present evidence that the disappearances represent 7-12-year troughs in 20-30-year WLP population cycles occurring synchronously at regional and perhaps continent-wide spatial scales as large as 10,000-5 million km2. This may represent the first documented case of natural population cyclicity in a Neotropical mammal. Because WLP populations often increase dramatically prior to a disappearance, we posit that their population cycles result from over-compensatory, density-dependent mortality. Our data also suggest that the increase phase of a WLP cycle is partly dependent on recolonization from proximal, unfragmented and undisturbed forests. This highlights the importance of very large, continuous natural areas that enable source-sink population dynamics and ensure re-colonization and local population persistence in time and space.

Potential linkages between juvenile nurseries and exploited populations of Mulloway (Argyrosomus japonicus), explored using otolith chemistry

Many exploited coastal species rely on estuarine nurseries, however, the importance of different estuaries and their contribution to exploited populations can vary. Identification of connectivity between source nurseries and exploited populations is important for effective habitat and fishery management. We present a case study which employs otolith chemistry to investigate source-sink population dynamics across broad spatial scales for an exploited migratory sciaenid, Mulloway (Argyrosomus japonicus). Specifically, we compared the otolith chemical fingerprints of juveniles in putative estuarine nurseries across south-eastern Australia with the sub-yearling chemical fingerprints of post-recruited fish in the exploited component of the stock. Multinomial Logistic Regression (MLR) suggested that two of the eight estuarine nurseries sampled were particularly important sources of Mulloway recruits, and there was strong evidence of stock mixing which exceeded that expected from historic tag-recapture studies. However, there was some uncertainty in the patterns resolved. Variation in otolith signatures between the known-source juveniles and post-recruit fish may be explained by inter-annual variability in these systems, caused by extensive flooding on the central and northern-NSW coast during the study period. These events contributed considerable extrinsic variation to the chemical composition, influencing the lack of overlap between otolith chemistry of putative nurseries and sub-yearling otolith chemistry of exploited fish. The approach presented highlights the importance of considering inter-annual variability when examining source-sink relationships in long-lived species, but the use of otolith fingerprints shows promise for evaluating these questions for both Mulloway and other exploited fish species.

Mobility and infectiousness in the spatial spread of an emerging fungal pathogen.

Emerging infectious diseases can have devastating effects on host communities, causing population collapse and species extinctions. The timing of novel pathogen arrival into naïve species communities can have consequential effects that shape the trajectory of epidemics through populations. Pathogen introductions are often presumed to occur when hosts are highly mobile. However, spread patterns can be influenced by a multitude of other factors including host body condition and infectiousness.White‐nose syndrome (WNS) is a seasonal emerging infectious disease of bats, which is caused by the fungal pathogen Pseudogymnoascus destructans. Within‐site transmission of P. destructans primarily occurs over winter; however, the influence of bat mobility and infectiousness on the seasonal timing of pathogen spread to new populations is unknown. We combined data on host population dynamics and pathogen transmission from 22 bat communities to investigate the timing of pathogen arrival and the consequences of varying pathogen arrival times on disease impacts.We found that midwinter arrival of the fungus predominated spread patterns, suggesting that bats were most likely to spread P. destructans when they are highly infectious, but have reduced mobility. In communities where P. destructans was detected in early winter, one species suffered higher fungal burdens and experienced more severe declines than at sites where the pathogen was detected later in the winter, suggesting that the timing of pathogen introduction had consequential effects for some bat communities. We also found evidence of source–sink population dynamics over winter, suggesting some movement among sites occurs during hibernation, even though bats at northern latitudes were thought to be fairly immobile during this period. Winter emergence behaviour symptomatic of white‐nose syndrome may further exacerbate these winter bat movements to uninfected areas.Our results suggest that low infectiousness during host migration may have reduced the rate of expansion of this deadly pathogen, and that elevated infectiousness during winter plays a key role in seasonal transmission. Furthermore, our results highlight the importance of both accurate estimation of the timing of pathogen spread and the consequences of varying arrival times to prevent and mitigate the effects of infectious diseases.

Estimation of vital population rates to assess the relative health of mussel assemblages in the Upper Mississippi River

Abstract Native freshwater mussels are a guild of benthic, filter feeding invertebrates that perform important ecological functions in rivers. Because of their long lifespans (30–50 years or longer), mussels are slow to respond to human‐induced alterations. Thus, development of sensitive indicators of mussel population responses to river conditions and management would be beneficial. Compared to marine species, estimation of vital rates (e.g. survival, growth) in freshwater mussels has received little attention. We placed passively integrated transponder tags on 578 mussels of four species (Amblema plicata, Cyclonaias pustulosa, Obliquaria reflexa, and Pleurobema sintoxia) in a well‐studied mussel assemblage in a side channel of the upper Mississippi River. Growth and survival of tagged mussels were assessed annually for 4 years across core (high density) and peripheral (low density) areas of the assemblage. Overall survival was highly variable, ranging from c. 15 to 90%, and was related to life history, habitat quality, and hydrologic events. Survival, which varied significantly among species and over time, was consistently higher in the dense and species‐rich core of the mussel assemblage, relative to the periphery because substrates were consistently more stable in the core of the mussel bed relative to the periphery. Substrate movement during low flows was an order of magnitude lower in the core relative to the periphery, and survival was inversely related to stability of river substrates. Patterns in habitat‐specific survival indicate source–sink population dynamics such that mussels in the core habitat provide recruitment to the periphery, but mussels in the periphery are subject to unsustainably low survival; additional studies to track the source of recruitment in the periphery are needed to test this hypothesis. Growth rate did not vary significantly between core and peripheral areas but did vary by species. Growth rate (proportional change per year) declined with age, and was similar at mean age for A. plicata (0.016 per year), P. sintoxia (0.015 per year), and C. pustulosa (0.013 per year), but much lower for O. reflexa (0.008 per year). Effective management decisions for mussels requires a better understanding of how vital rates govern populations and how they vary across a suite of physical and biological factors. Information on how population vital rates vary among species and over time gives managers another tool to understand how mussels may respond to management actions such as habitat restoration projects. Given the importance of substrate stability inferred from this study, management actions that maintain or increase substrate stability are likely to result in high quality mussel assemblages and may restore a valuable component of ecosystem function in this region.

Territoriality drives preemptive habitat selection in recovering wolves: Implications for carnivore conservation

According to the ideal-free distribution (IFD), individuals within a population are free to select habitats that maximize their chances of success. Assuming knowledge of habitat quality, the IFD predicts that average fitness will be approximately equal among individuals and between habitats, while density varies, implying that habitat selection will be density dependent. Populations are often assumed to follow an IFD, although this assumption is rarely tested with empirical data, and may be incorrect when territoriality indicates habitat selection tactics that deviate from the IFD (e.g. ideal-despotic distribution or ideal-preemptive distribution). When territoriality influences habitat selection, species' density will not directly reflect components of fitness such as reproductive success or survival. In such cases, assuming an IFD can lead to false conclusions about habitat quality. We tested theoretical models of density-dependent habitat selection on a species known to exhibit territorial behaviour in order to determine whether commonly applied habitat models are appropriate under these circumstances. We combined long-term radiotelemetry and census data from grey wolves Canis lupus in the Upper Peninsula of Michigan, USA to relate spatiotemporal variability in wolf density to underlying classifications of habitat within a hierarchical state-space modelling framework. We then iteratively applied isodar analysis to evaluate which distribution of habitat selection best described this recolonizing wolf population. The wolf population in our study expanded by >1,000% during our study (~50 to >600 individuals), and density-dependent habitat selection was most consistent with the ideal-preemptive distribution, as opposed to the ideal-free or ideal-despotic alternatives. Population density of terrestrial carnivores may not be positively correlated with the fitness value of their habitats, and density-dependent habitat selection patterns may help to explain complex predator-prey dynamics and cascading indirect effects. Source-sink population dynamics appear likely when species exhibit rapid growth and occupy interspersed habitats of contrasting quality. These conditions are likely and have implications for large carnivores in many systems, such as areas in North America and Europe where large predator species are currently recolonizing their former ranges.

Habitat quality, configuration and context effects on roe deer fecundity across a forested landscape mosaic.

Effective landscape-scale management of source-sink deer populations will be strengthened by understanding whether local variation in habitat quality drives heterogeneity in productivity. We related female roe deer Capreolus capreolus fecundity and body mass to habitat composition and landscape context, separately for adults and yearlings, using multi-model inference (MMI) applied to a large sample of individuals (yearlings: fecundity = 202, body mass = 395; adults: fecundity = 908, body mass = 1669) culled during 2002-2015 from an extensive (195 km2) heterogeneous forest landscape. Adults were heavier (inter-quartile, IQ, effect size = +0.5kg) when culled in buffers comprising more arable lands while contrary to our prediction no effects on body mass of grassland, young forest or access to vegetation on calcareous soil were found. Heavier adults were more fertile (IQ effect size, +12% probability of having two embryos instead of one or zero). Counter-intuitively, adults with greater access to arable lands were less fecund (IQ effect of arable: -7% probability of having two embryos, instead of one or zero), and even accounting for greater body mass of adults with access to arable, their modelled fecundity was similar to or lower than that of adults in the forest interior. In contrast, effects of grassland, young forest and calcareous soil did not receive support. Yearling body mass had an effect on fecundity twice that found in adults (+23% probability of having one additional embryo), but yearling body mass and fecundity were not affected by any candidate habitat or landscape variables. Effect of arable lands on body mass and fecundity were small, with little variance explained (Coefficient of Variation of predicted fecundity across forest sub-regions = 0.03 for adults). More variance in fecundity was attributed to other differences between forest management sub-regions (modelled as random effects), suggesting other factors might be important. When analysing source-sink population dynamics to support management, an average value of fecundity can be appropriate across a heterogeneous forest landscape.

Isolation by Distance, Source-Sink Population Dynamics and Dispersal Facilitation by Trade Routes: Impact on Population Genetic Structure of a Stored Grain Pest.

Population genetic structure of agricultural pests can be impacted not only by geographic distance and the broader ecological and physical barriers but also by patterns related to where crops are produced and how they are moved after harvest. Stored-product pests, for instance, specialize in exploiting grains such as wheat and rice from on-farm storage through transportation to final processing at often geographically distant locations; therefore human-aided movement may impact their dispersal. Although stored product insects are associated with stored grain, they can also exploit resources in the surrounding environments so different ecological regions where the grain is grown and stored may also influence population structure. Here we used 1,156 SNP markers to investigate how geographic distance, ecological and agricultural variables can impact the genetic structure and gene flow of the stored food pest beetle Rhyzopertha dominica. We found a substantial degree of admixture between weakly structured populations in the US. Ecological regions were more important in explaining R. dominica population structure than crop type, suggesting insect movement between wheat and rice grain distribution channels. We have also found a significant correlation between the genetic and geographical distance (i.e., isolation by distance). However, our modeling approach combining the ecological and management variables has highlighted the importance of the volume of grain received by a location in the dispersal dynamics of the pest. The first-generation migrant analysis offered additional supported to movement over great distances that are likely associated with grain movement. Our data suggest that a multitude of factors play small but significant parts in the movement dynamics of the pest. The beetles can take advantage of the source-sink dynamic of grain movement in the US, but also engage in a high rate of movement at the local scale. Understanding population structure for R. dominica will provide insights into the potential for local processes of adaptation and broader patterns of movement that will impact management programs and the potential for spread of resistance genes.

Ocean currents predict fine-scale genetic structure and source-sink dynamics in a marine invertebrate coastal fishery

AbstractEstimates of connectivity are vital for understanding population dynamics and for the design of spatial management areas. However, this is still a major challenge in the marine environment because the relative contributions of factors influencing connectivity amongst subpopulations are difficult to assess. This study combined population genetics with hydrodynamic modelling (Regional Ocean Modeling System, ROMS) to assess spatial and temporal exchange of individuals among subpopulations of the New Zealand scallop, Pecten novaezelandiae, within the Coromandel fishery area open to commercial fishing. Significant genetic differentiation was revealed among subpopulations with variable levels of recruitment. Connectivity, as assessed by ROMS, was a significant explanatory variable of genetic differentiation when accounting for the spatial dependency between locations. Although additional research is needed before source-sink population dynamics can be confidently used in management, these results imply that higher yields could be available from this fishery at lower risk of over-exploitation if the fishing of each subpopulation could be tailored to its contribution to recruitment, perhaps using subpopulation catch limits. This study highlights inter-annual patterns of connectivity, the importance of combining different methods for a better prediction of population dynamics, and how such an approach may contribute to management of living marine resources.

Demographic history of the Magellanic Penguin (Spheniscus magellanicus) on the Pacific and Atlantic coasts of South America

Spatial subdivision, local extinction and recolonization influence the genetic variation of natural populations. Different levels of population structure can be identified in nature, from panmictic populations, in which high gene flow homogenizes diversity across localities, to metapopulations, where combinations of moderate to high levels of population differentiation and source-sink population dynamics are expected. Gene flow, dispersal and recolonization can be affected by changes in ecological conditions such as climate and resource distribution. Evaluating demographic history is crucial for understanding current population dynamics. We assessed a mitchondrial DNA (mtDNA) control region and microsatellite data for 210 Magellanic Penguins (Spheniscus magellanicus) from 13 breeding colonies on the coastlines of Chile and Argentina, covering a great portion of the species’ distribution. We found high levels of genetic diversity and detected two genetic-geographic regions, Pacific and Atlantic, probably due to interruption of the connection between the oceans during the Last Glacial Maximum (LGM), when several parts of the Magellanic Channel were connected to the continent. The Atlantic ocean colonies showed a slight differentiation between the northern and southern colonies, and the Falkand/Malvinas one seems to be a mix of northern, southern and Pacific colonies. Magellanic Penguins showed intense gene flown among colonies, and exhibited low levels of genetic differentiation in each region. Furthermore, our findings indicate that the Magellanic Penguin experienced a population expansion around 17,500 years ago, which is in agreement with the timing of a decreased sea level and the exposure of the continental shelf along the coast of Argentina and the Falkland/Malvinas Islands at the end of the LGM. Thus, our results suggest that climate changes that affect the sea level in South America can play important roles in the migration of Magellanic Penguins.

Spatially varying density dependence drives a shifting mosaic of survival in a recovering apex predator (Canis lupus).

Understanding landscape patterns in mortality risk is crucial for promoting recovery of threatened and endangered species. Humans affect mortality risk in large carnivores such as wolves (Canis lupus), but spatiotemporally varying density dependence can significantly influence the landscape of survival. This potentially occurs when density varies spatially and risk is unevenly distributed. We quantified spatiotemporal sources of variation in survival rates of gray wolves (C. lupus) during a 21‐year period of population recovery in the Upper Peninsula of Michigan, USA. We focused on mapping risk across time using Cox Proportional Hazards (CPH) models with time‐dependent covariates, thus exploring a shifting mosaic of survival. Extended CPH models and time‐dependent covariates revealed influences of seasonality, density dependence and experience, as well as individual‐level factors and landscape predictors of risk. We used results to predict the shifting landscape of risk at the beginning, middle, and end of the wolf recovery time series. Survival rates varied spatially and declined over time. Long‐term change was density‐dependent, with landscape predictors such as agricultural land cover and edge densities contributing negatively to survival. Survival also varied seasonally and depended on individual experience, sex, and resident versus transient status. The shifting landscape of survival suggested that increasing density contributed to greater potential for human conflict and wolf mortality risk. Long‐term spatial variation in key population vital rates is largely unquantified in many threatened, endangered, and recovering species. Variation in risk may indicate potential for source‐sink population dynamics, especially where individuals preemptively occupy suitable territories, which forces new individuals into riskier habitat types as density increases. We encourage managers to explore relationships between adult survival and localized changes in population density. Density‐dependent risk maps can identify increasing conflict areas or potential habitat sinks which may persist due to high recruitment in adjacent habitats.

Source-sink population dynamics driven by a brood parasite: A case study of an endangered songbird, the black-capped vireo

A thorough understanding of the effects of spatially and temporally variable demographic drivers of population processes is necessary to accurately evaluate potential source-sink dynamics, estimate long-term population viability, and devise effective management practices. The black-capped vireo (Vireo atricapilla) is an endangered songbird that suffers from high rates of parasitism by the brown-headed cowbird (Molothrus ater). The largest breeding population of vireos is located on the Fort Hood Military Installation in central Texas. This large reserve is well studied but its role in vireo metapopulation dynamics is largely unknown. Furthermore, the evolving cowbird control regime across Fort Hood and nearby isolated populations could impact the local source-sink dynamics. From 2011 through 2014, we monitored breeding vireos at eleven sites across central Texas that varied in cowbird control level. From observations of fecundity and survival, we calculated stochastic and deterministic population growth rates and assessed populations as sources or sinks. We also calculated quasi-extinction probabilities and the sensitivity and elasticity of population growth to demographic parameters. Sites with at least some cowbird control had greater nest success than sites with no cowbird control. We identified four source populations, three of which were on the large Fort Hood reserve and had comprehensive cowbird control across all study years. Although not all sites with cowbird control were sources on average, population dynamics were variable between years and the implementation of cowbird management was generally associated with the growth of local populations. Importantly, source and sink populations were not static, revealing a complex and temporally dynamic system driven largely by variations in adult survival and evolving cowbird control regimes.

A Reassessment of the Distribution of Virginia’s Warbler in the Black Hills of South Dakota

virginia’s Warbler (Oreothlypis virginiae) reaches the northeastern limit of its breeding range in the southern Black Hills of South Dakota, where it is considered a species of conservation concern. this population occurs in pine–juniper–shrub habitat in several canyons in extreme western Custer County. additional such habitat occurs in the southern Black Hills south and east of the documented breeding populations, but these areas have received few systematic surveys, and whether virginia’s Warbler occupies them was uncertain. therefore, to define the species’ distribution in the South Dakota Black Hills more precisely, we surveyed with the aid of broadcast song and reviewed other reports. virginia’s Warblers occurred in appropriate habitats all along the southwestern front (approximately 30 km total) of the Black Hills in Custer County but did not occur in similar habitat along the southeastern front, approximately 25 km distant. the species’ relative abundance in previously and newly identified pine–juniper–shrub habitats was similar. virginia’s Warbler occurrence was positively associated with shrub cover (primarily mountain-mahogany, Cercocarpus montanus), pine overstory, and slopes of >15°. its association with the Spotted towhee (Pipilo maculatus) was negative, with the yellow-rumped Warbler (Setophaga coronata) tended toward positive, and with the Dusky flycatcher (Empidonax oberholseri) was variable (negative along the southwestern front but weakly positive across all sites). these data extend the documented breeding range of virginia’s Warbler in South Dakota by more than 20 km to the southeast. to clarify conservation priorities for this species at the northeastern limit of its range, future studies should delineate local and landscape-level characteristics of this population’s habitat more precisely and address its source–sink population dynamics. virginia’s Warbler (Oreothlypis virginiae) nests widely in mountainous regions of southwestern north america from southeastern idaho and southwestern Wyoming into southern arizona, new Mexico, and western texas (olson and Martin 1999). the species’ northeasternmost population is isolated in the southwestern Black Hills of South Dakota, separated by over 200 km from the next nearest breeding population in south-central Wyoming (Swanson et al. 2000). Breeding habitat occurs on mountain slopes and consists of dense, shrubby vegetation with taller plants interspersed or nearby (olson and Martin 1999). in various portions of the breeding range the shrubby vegetation may include chokecherry (Prunus virginiana), snowberry (Symphoricarpos spp.), currant (Ribes spp.), serviceberry (Amelanchier spp.), manzanita (Arctostaphylos spp.), scrub oak (Quercus gambelii), or mountain-mahogany (Cercocarpus montanus) (olson and Martin 1999). the taller vegetation may consist of pinyon pine (Pinus spp.), juniper (Juniperus spp.), ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), taller scrub oak, or aspen (Populus tremuloides) (olson and Martin 1999). virginia’s Warbler was first definitively recorded in South Dakota in 1997,

Effect of pyric herbivory on source–sink dynamics in grassland birds

Summary Grasslands world‐wide provide a host of ecosystem services. In particular, these grasslands serve as biodiversity repositories for a myriad of imperilled animal species. One such group is grassland birds, which have experienced significant declines, predominantly caused by extensive loss and degradation of native grasslands. Rangeland management that promotes increasing and sustaining livestock production through reducing the inherent, disturbance‐driven variability that historically occurred in grasslands is considered a major contributing factor to these declines. An alternative approach to this homogeneous management paradigm attempts to restore a shifting mosaic of disturbance patches across the landscape through the spatial and temporal interactions of fire and grazing (i.e. pyric herbivory). Application of pyric herbivory through patch‐burn grazing increases overall habitat heterogeneity, likely a critically important factor in maintaining and enhancing grassland bird populations. We compared reproductive rates and estimates of fecundity of three grassland birds nesting in grasslands maintained by traditional and patch‐burn grazing management paradigms in the Southern Great Plains of North America. Additionally, we used a sensitivity analysis approach to assess population stability (i.e. λ = 1) and source–sink population dynamics under the two management practices. Nest survival for dickcissels Spiza americana and grasshopper sparrows Ammodramus savannarum was higher in patch‐burned grasslands than in traditionally managed grasslands, while nest survival for eastern meadowlarks Sturnella magna was higher in traditionally managed grasslands than in patch‐burned grasslands. Dickcissels and grasshopper sparrows responded positively to patch burning with source habitats occurring over a wider range of survival rates under patch burning than traditional management, while no clear pattern emerged in source–sink dynamics of eastern meadowlarks. Synthesis and applications. Management strategies such as patch‐burn grazing offer opportunities to restore landscape heterogeneity to benefit bird communities while maintaining livestock production goals. Applying patch‐burn grazing to rangelands can increase productivity of grassland birds and could be effective for reversing the decline of grassland birds by providing source habitats more consistently than traditional rangeland management. Our results emphasize the utility of using sensitivity analyses to determine source–sink population dynamics when evaluating management practices. However, land managers should consider that source–sink models have shortcomings and designation of a habitat as a sink does not necessarily mean the habitat has low conservation value.

Deer abundance estimation at landscape-scales in heterogeneous forests

Reliable estimates of deer abundance support effective management of source-sink population dynamics in complex landscapes and improve understanding of the relation between deer density and biodiversity impacts. Performance of distance sampling using thermal imaging of Reeves’ muntjac Muntiacus reevesi and roe deer Capreolus capreolus was examined across 123km2 of conifer forest in Eastern England, sampling 1567km in total. For muntjac distance sampling was compared to estimates from drive counts in 2007. For each of three subsequent winters (2008–2010), we compared the magnitude and precision of forest-wide abundance estimated from analytical designs that: (i) ignored potential habitat-specific detectability, either with uneven or balanced sampling effort; (ii) controlled for sampling effort and/or density among seven forest blocks (mean=18.8km2±11.1 SD); (iii) accounted for potential movement prior detection; (iv) accounted for varying detectability among habitat classes (as a covariate), while controlling for differing densities among blocks. Detectability was further examined in models that stratified to estimate habitat-specific Effective Strip Width (ESW).Estimated muntjac densities from distance sampling were of similar magnitude to estimates from drive counts. Over 2008–2010, we observed 1926 muntjac and 921 roe groups; allowing robust abundance estimation and habitat-specific analysis. ESWs in open habitat were 31% and 27% greater than in mature and 45% and 46% greater than in dense habitat, for roe and muntjac respectively. Although differences in densities among model designs were not large, ignoring block or habitat effects gave higher estimates, while models that accounted for habitat-specific detectability gave lower (−8%) and more precise (38% reduction in CV) estimates (n=3, muntjac: 5.3–7.5% CV; roe deer: 8.8–12.6% CV). The similarity of density estimates between ungrouped and grouped data and analysis of behaviour of detected deer support the conclusion that distance estimates were not biased by avoidance.We conclude that distance sampling using thermal imaging is a robust and powerful method for estimating deer density. In heterogeneous forest density estimates will be improved by accounting for varying detectability among growth stages or habitats.

Scientific Opinion addressing the state of the science on risk assessment of plant protection products for non‐target arthropods

Following a request from the European Food Safety Authority, the Panel on Plant Protection Products and their Residues developed an opinion on the science to support the development of a risk assessment scheme of plant protection products for non-target arthropods. The current risk assessment scheme is reviewed, taking into consideration recent workshops and progress in science. Proposals are made for specific protection goals which aim to protect important ecosystem services such as food web support, pest control and biodiversity. In order to address recovery and source–sink population dynamics, conducting a landscape-level risk assessment is suggested. A new risk assessment scheme is suggested which integrates modelling approaches. The main exposure routes for non-target arthropods are identified and proposals are made on how to integrate them in the risk assessment. The appropriateness of the currently used vegetation distribution factor was investigated. It is proposed that new tests be included in order to address exposure via oral uptake of residues and uncertainties related to differences in species sensitivity.

Lack of genetic structure in Kentish PloverCharadrius alexandrinusfrom the Iberian coast. What’s wrong with the endangered north-western population?

SummaryCoastal wader species are sensitive to anthropogenic activity and habitat change along the coastal edge, which has been responsible for the decline in the populations of these birds. Correct management requires knowledge of the pattern and scale of genetic variation within and among populations as well as the relationships between population dynamics and genetic structure. We investigated these factors in the Kentish PloverCharadrius alexandrinusfrom the Iberian coast to determine the degree of vulnerability of the endangered north-western population. We analysed the genetic structure and gene flow using a 631-bp fragment of the mitochondrial (mtDNA) control region and eight microsatellite markers in 113 unrelated individuals from 31 Iberian beaches. The results do not support the recent decline hypothesis because there was no evidence of a bottleneck, but they do support a population expansion along the Atlantic coast. We found no genetic structure or isolation-by-distance, in agreement with results recently observed on a continental scale. However, explanations for high continental gene flow, such as temporary breeding habitats and high breeding dispersal, do not seem to apply to the Galician population. Galician Kentish Plovers breed solely on beaches, a suitable and more predictable habitat during the breeding period than ephemeral inland wetlands, and female movements during the breeding period are uncommon, mainly due to the extremely low hatching success. This study suggests a demographic connectivity between Portuguese and Galician populations that is referred to as source-sink population dynamics, in which individuals dispersing from Portugal support the Galician coastal population. This dispersal pattern highlights the importance of supranational management plans to protect endangered species.

Population trends of northern fur seals (Callorhinus ursinus) from a metapopulation perspective

A metapopulation model was created to explore source-sink population dynamics in northern fur seals (Callorhinus ursinus), for which the largest source population is declining, but smaller, newly established populations are either stable or growing. A declining source population could therefore slow down the growth of newly established populations. We also investigated changes in mortality and birth rates that could stabilize the declining population trend on the Pribilof Islands. The six main breeding populations—in the Pribilof Islands, Commander Islands, Kuril Islands, Robben Island, San Miguel Island, and Bogoslof Island—were modeled as individual age-structured populations, that were linked together using a migration model. The migration model component allowed movement of subadults among the six populations, with rules based on distances between populations, average travel speeds, habitat preferences, and El Nino events. The metapopulation model revealed the importance of immigration to newly established populations during the first 8years of population growth. After the initial growth period, additional immigration had no noticeable effect on population growth in sink populations. The population trend on the Pribilof Islands was difficult to stabilize, and immigration from smaller populations could not slow the population decline. Consequently, conservation of the Pribilof Islands population likely requires a long recovery period following reductions in population-specific mortality rates for adult females, juveniles and pups.

HABITAT USE OF AN ENDEMIC MOLLUSC ASSEMBLAGE IN A HYDROLOGICALLY ALTERED REACH OF THE SNAKE RIVER, IDAHO, USA

Major waterways have been dramatically altered by dams some of which have operated with consistent and significant flow alterations annually since the early 1900s. Re-operation strategies are increasingly being considered for such dams in regions where biodiversity hotspots of sensitive taxa remain. Understanding the impacts of current dam operations on sensitive species is vital to designing re-operations that effectively promote species conservation. Our objectives were to examine the effects of consistent and dramatic flow alterations from a major dam on the distribution of a highly diverse endemic mollusc assemblage in the middle Snake River, Idaho, USA. Quarter metre plots were surveyed along transects with a Venturi suction dredge and classified as permanently or seasonally wetted habitat by depth. Species were classified by degree of endemism. Chi-square analysis was used to compare species presence between habitat types and analysis of variance was used to assess the significance of habitat type as a predictor of mollusc abundance, species richness and Shannon's H. Multivariate analyses were used to investigate mollusc assemblage composition and correlations with environmental parameters. The majority of mollusc species, including species of conservation concern, were found more frequently and in greater abundance in permanently wetted habitat. In addition, the mollusc assemblage in permanently wetted habitat was more diverse. Species presence and abundance patterns were consistent with source sink population dynamics with permanently wetted habitat serving as a source for seasonally wetted habitat. Results indicate that most mollusc species do not use seasonally wetted habitat even four months after it becomes available despite viable environmental conditions, highly mobile species and colonization sources. Our findings suggest that dam re-operations which reduce the magnitude and duration of seasonal low flows may improve habitat availability for sensitive benthic assemblages. Copyright © 2013 John Wiley & Sons, Ltd.