Long-term Population Persistence Research Articles

Origin, Persistence, and Vulnerability to Climate Changes of Podocarpus Populations in Central African Mountains

Background and objectives—Podocarpus latifolius (synonym of P. milanjianus) is a key tree representative of Afromontane forests where it is highly threatened by climate and land-use changes. While large populations occur in East Africa, only a few isolated and usually small populations remain in western Central Africa (Cameroon to Angola). Studying the evolutionary history of such relictual populations can thus be relevant to understand their resilience under changing environments. Materials and Methods—we developed nine polymorphic nuclear microsatellites (nSSRs) to estimate genetic variability, (historical) gene flow, and demographic changes among natural populations from Central to East Africa. Results—despite the extended distribution range of P. latifolius, a strong isolation-by-distance pattern emerges at the intra-population scale, indicating low seed and pollen dispersal capacities. Central African populations display a lower genetic diversity (He = 0.34 to 0.61) and are more differentiated from each other (FST = 0.28) than are East African populations (He = 0.65 to 0.71; FST = 0.10), suggesting high genetic drift in the Central African populations. Spatial genetic structure reveals past connections between East and West Africa but also a gene flow barrier across the equator in western Central Africa. Demographic modelling anchors the history of current lineages in the Pleistocene and supports a strong demographic decline in most western populations during the last glacial period. By contrast, no signature of demographic change was detected in East African populations. Conclusions—in Cameroon, our results exclude a recent (re)colonization from one source population of all mountain ranges, but rather indicate long-term persistence of populations in each mountain with fluctuating sizes. A higher impact of genetic drift and further loss of diversity can be expected by survival through climatically unfavorable periods in such small refugial populations. Tracking the Quaternary legacy of podocarp populations is thus essential for their conservation since there is a temporal gap between environment crises and an ecological/genetic answer at the population level.

Winter Survival and Resource Use of Translocated Northern Bobwhite in the Mid-Atlantic United States

Northern bobwhite (Colinus virginianus; hereafter, bobwhite) in the Mid-Atlantic United States have been experiencing precipitous population declines due to a combination of habitat deterioration, urban and suburban sprawl, change in forest management regimes, and farming practices. In recent years, restocking of bobwhite through translocation efforts has gained interest to rebuild local populations. However, empirical studies are warranted to understand the limitations of translocation as it relates to its potential use for long-term population recovery and persistence in this region. Further, few studies nation-wide have evaluated resource use and survival during the non-breeding season on translocated sites. As such, we translocated 360 bobwhites from source populations from southern latitudes during March–April 2015–2017 into 2 different landscape types similar to the source population vegetative communities (agricultural cropland dominated in Maryland, USA versus pine forest dominated in New Jersey, USA) and tested the effects of habitat fragmentation on survival and habitat use during the subsequent non-breeding season. We found habitat fragmentation negatively affecting survival and resource use among translocated bobwhite on fragmented cropland-dominated sites as compared to larger unfragmented forested sites. Survival was lower on cropland sites compared to forested sites such that bobwhite in cropland-dominated landscapes were >125 times less likely to survive the winter than those on forested sites. In our examination of resource use, bobwhite in structurally complex forested sites used cut pine, early-successional woody, early-successional herbaceous, and thinned pine more than what was available on the landscape. On the cropland sites bobwhite used food plots, early-successional woody, and mixed woods more than what was available on the landscape and only food plots at the home range scale. While larger unfragmented forested bobwhite habitat ultimately provided a more successful translocation landscape, birds still had large home ranges and relatively low survival. Therefore, proper pine management may be necessary to optimize habitat availability during the non-breeding season. Our findings provide rare information on demographic resiliency and resource use for translocated bobwhite during the non-breeding season. Further, this research provides valuable information to improve future translocation efforts in the Mid-Atlantic.

A Simulation Model of Sustained-Yield Harvest for Northern Bobwhite in South Texas

Recommended sustainable harvest rates for northern bobwhite (Colinus virginianus) vary greatly and range from 25% to 70% of the prehunt population. Because northern bobwhite populations have declined across their geographic range, determining sustainable harvest levels is critical for effective management. Our objectives were to use simulation modeling to identify sustainable rates of bobwhite harvest, probability of population persistence, and minimum viable population estimates. We also conducted a sensitivity analysis to evaluate the impacts of harvest on northern bobwhite populations in Texas, USA. We constructed a simulation model using Program STELLA 9.0 for a hypothetical northern bobwhite population on 800 ha in the South Texas Plains USA and modeled population dynamics to 100 years over a range of harvest rates (0–40%). A 20% harvest rate produced the greatest average yields (mean ± standard error = 231 ± 10 bobwhites harvested/year). Given a quasi-extinction criterion of ≤40 bobwhites (≤0.05 bobwhite/ha), a 30% harvest rate resulted in a high probability of quasi-extinction (PE = 0.75) within 47.8 ± 2.3 years. A 40% harvest rate was not sustainable (PE = 1.0), with quasi-extinction occurring within 15.5 ± 2.6 years. Harvesting northern bobwhite populations in the South Texas Plains at rates of 20−25% of the prehunt population should maximize long-term harvest while minimizing the probability of population extinction. Spring densities of 0.60−0.80 bobwhite/ha may represent minimum viable spring densities for northern bobwhite populations in the South Texas Plains as these are the densities associated with sustainable 20-25% harvest rates. Harvest rates >30% are likely to be excessive with respect to long-term population persistence for northern bobwhite populations in the South Texas Plains.

Optimising conservation translocations of threatened

Context Conservation translocations are increasingly being used in the management of rare plants, yet have low success in maintaining populations through recruitment. Aims We investigated whether the survival of translocated plants, recruitment and, therefore, cost effectiveness, can be improved by selecting optimal microsites for both adults and seedlings. Methods Caladenia colorata plants propagated symbiotically with Serendipita australiana (n = 735) were introduced to four sites where the pollinator was present and vegetation matched wild populations. Plant demography was monitored over 6 years. The relationship between microsite variables and measures of orchid survival, re-emergence, flowering and recruitment were analysed with generalised linear mixed-effects models. We then estimated potential improvement in emergence and recruitment, if microsite selection was optimised. Key results A total of 77% of plants survived translocation, and populations grew by 84% through recruitment (n = 615). Survival was positively associated with cover of leaf litter, graminoids and cryptogams. Recruitment was positively correlated with soil moisture. The majority of recruitment was within 5 cm of adult C. colorata plants. The potential improvement by selecting favourable microsites increased adult survival by up to 8% and recruitment by 10–40%. Conclusions Incorporating both the germination niche and adult plant niche within plant translocations more broadly could significantly improve long-term population persistence and the utilisation of conservation funding. Implications Our results are directly applicable to 58 endangered Caladenia species in the subgenus Calonema, owing to their shared mycorrhizal association with S. australiana. Furthermore, our results are applicable to all plant translocations as understanding germination niche and microhabitat requirements is likely to improve success overall.

Oviposition behaviour and emergence through time of the small blue butterfly (Cupido minimus) in a nature reserve in Bedfordshire, UK

Climate change affects butterflies in many ways, influencing the timing of emergence and reproduction, habitat preferences, and behaviour. The small blue (Cupido minimus Fuessley, 1775) is highly specialised in its host plant requirements, feeding on the seeds of a single species, kidney vetch (Anthyllis vulneraria), on which the larvae occur singly to avoid cannibalism. The butterfly is likely to be vulnerable to temperature-related changes in oviposition, adult emergence, and host plant flowering times, and is, therefore, a good model species for investigating climate change-related impacts. Using 26 years of data from the national UK Butterfly Monitoring Scheme (1993–2019) from one nature reserve, and 4 years of targeted egg searches (2006, 2007, 2008, 2020) from three reserves in Bedfordshire, UK, we investigated the effects of local temperature on small blue emergence date and total abundance, whether flowerhead or local environmental characteristics predicted small blue oviposition behaviour, and whether this changed between years. Small blue adults emerged on earlier dates over time, and earlier in years with higher maximum February temperatures. Total adult abundance was not predicted by monthly temperatures or total abundance in the previous year. Oviposition behaviour was broadly consistent across years, with egg presence more likely and egg abundance higher on kidney vetch flowerheads that were taller than the surrounding vegetation, and surrounded by taller vegetation and fewer mature flowerheads. The effect of solar radiation differed between years, with a negative effect on the probability of egg presence in 2007 and 2008, but a positive effect in 2020. Egg abundance per flowerhead was highly variable between years, with 2006 having four times more eggs per flowerhead than other years. This was likely driven by high adult abundance in 2006, which could have increased competition for flowerheads.Implications for insect conservationOur results indicate that management for greater availability of taller kidney vetch amongst taller vegetation would encourage small blue oviposition on a greater number of flowerheads, providing a possible means of reducing competition and increasing larval survival, and that this would be effective despite variation in adult abundance between years. The high level of competition we observed in the year with the highest adult abundance indicates that higher numbers of host plants should be encouraged to reduce competition and larval cannibalism in peak years, increasing the likelihood of long-term population persistence and growth.

Hatching Success Rather Than Temperature-Dependent Sex Determination as the Main Driver of Olive Ridley (Lepidochelys olivacea) Nesting Activity in the Pacific Coast of Central America.

Simple SummaryIn marine turtles, sex is determined during a precise period during incubation: males are produced at lower temperatures and females at higher temperatures, a phenomenon called temperature-dependent sex determination. Most predictions about the long-term persistence of sea turtle populations in the face of climate change have focused on the effect of incubation temperature on sex ratios. In Central America, the alternations in dark sand beaches (hotter sand) and light sand beaches (cooler sand) are observed. Due to the higher production of females at high temperatures and the natal homing phenomenon in marine turtles, the largest proportion of nests on dark sand beaches was expected. However, the inverse was observed. We hypothesize that high beach temperatures, being seen in darker sand, increased female-biased primary sex ratios but reduced the output of female hatchlings due to embryo thermal lethality at high temperature. Our study reveals that when we think about sea turtle population dynamics, we should consider a variety of factors and not only sex ratio.In marine turtles, sex is determined during a precise period during incubation: males are produced at lower temperatures and females at higher temperatures, a phenomenon called temperature-dependent sex determination. Nest temperature depends on many factors, including solar radiation. Albedo is the measure of the proportion of reflected solar radiation, and in terms of sand color, black sand absorbs the most energy, while white sand reflects more solar radiation. Based on this observation, darker sand beaches with higher temperatures should produce more females. As marine turtles show a high degree of philopatry, including natal homing, dark beaches should also produce more female hatchlings that return to nest when mature. When sand color is heterogeneous in a region, we hypothesize that darker beaches would have the most nests. Nevertheless, the high incubation temperature on beaches with a low albedo may result in low hatching success. Using Google Earth images and the SWOT database of nesting olive ridleys (Lepidochelys olivacea) in the Pacific coast of Mexico and Central America, we modeled sand color and nesting activity to test the hypothesis that darker beaches host larger concentrations of females because of feminization on darker beaches and female philopatry. We found the opposite result: the lower hatching success at beaches with a lower albedo could be the main driver of nesting activity heterogeneity for olive ridleys in Central America.

Impact of climate change on the success of population support management and plant reintroduction at steep, exposed limestone outcrops in the German Swabian Jura

Species-rich rocky outcrops and cliff vegetation in central Europe distributed outside alpine regions are typically associated with historical landscapes of interrelated natural and cultural features such as the Swabian Alb in Germany. Consequently, in these regions, biodiversity is highly threatened by various factors, such as land use change and increased land use intensity. In central Europe, the flagship species closely associated with these vegetation types is Cheddar Pink (Dianthus gratianopolitanus), whose total European population is declining. Herein, we exemplified a successful reintroduction experiment at two different sites at the species’ distribution center in Germany on the Swabian Alb. In total 549 individuals were reintroduced in 2017 and 2018 and monitored in the field until 2020. Using a subset of clonally replicated plants it was shown under controlled conditions in greenhouses during 2016–2019 that climate change and, in particular, increased temperature sum in late winter and during spring had a great effect on the phenology and population fitness of D. gratianopolitanus ex situ. It was demonstrated that these effects were independent of genetic variation and cultivation effects. Global climate change and increased temperature sums not only caused significant earlier flowering, but also significantly reduced number of flowers and seed set, thereby drastically affecting population viability in a negative way. We concluded that ecological micro-niches of the studied species are spatially shifting and that the germination and seedling phases will become increasingly crucial for its long-term population persistence. Our study has potential implications for future cliff management and successful long-term habitat protection strategies.

Alternative developmental and transcriptomic responses to host plant water limitation in a butterfly metapopulation.

Predicting how climate change affects biotic interactions poses a challenge. Plant-insect herbivore interactions are particularly sensitive to climate change, as climate-induced changes in plant quality cascade into the performance of insect herbivores. Whereas the immediate survival of herbivore individuals depends on plastic responses to climate change-induced nutritional stress, long-term population persistence via evolutionary adaptation requires genetic variation for these responses. To assess the prospects for population persistence under climate change, it is therefore crucial to characterize response mechanisms to climate change-induced stressors, and quantify their variability in natural populations. Here, we test developmental and transcriptomic responses to water limitation-induced host plant quality change in a Glanville fritillary butterfly (Melitaea cinxia) metapopulation. We combine nuclear magnetic resonance spectroscopy on the plant metabolome, larval developmental assays and an RNA sequencing analysis of the larval transcriptome. We observed that responses to feeding on water-limited plants, in which amino acids and aromatic compounds are enriched, showed marked variation within the metapopulation, with individuals of some families performing better on control and others on water-limited plants. The transcriptomic responses were concordant with the developmental responses: families exhibiting opposite developmental responses also produced opposite transcriptomic responses (e.g. in growth-associated transcripts). The divergent responses in both larval development and transcriptome are associated with differences between families in amino acid catabolism and storage protein production. The results reveal intrapopulation variability in plasticity, suggesting that the Finnish M. cinxia metapopulation harbours potential for buffering against drought-induced changes in host plant quality.

Long-term persistence of experimental populations beyond a species' natural range.

Ecological experiments usually infer long-term processes from short-term data, and the analysis of geographic range limits is a good example. Species' geographic ranges may be limited by low fitness due to niche constraints, a hypothesis most directly tested by comparing the fitness of populations transplanted within and beyond the range. Such studies often fail to find beyond-range fitness declines strong enough to conclude that geographic range limits are solely imposed by niche limits. However, almost all studies only follow transplants for a single generation, which will underestimate the importance of niche limitation because critical but infrequent range-limiting events may be missed and methodological issues may artificially boost the fitness of beyond-range transplants. Here, we present the first multi-generation beyond-range transplant experiment that involves adequate replication and proper experimental controls. In 2005, experimental populations of the coastal dune plant Camissoniopsis cheiranthifolia were planted at four sites within and one site beyond the northern limit. Fitness of initial transplants was high beyond the limit, suggesting that the range was limited by dispersal and not niche constraints. To better address the niche-limitation hypothesis, we quantified density and fitness of descendant C. cheiranthifolia populations 12-14 yr (˜10 generations) after transplant. Average annual fruit production and density of reproductive individuals were as high beyond the range as at four comparable experimental populations and eight natural populations within the range, and the beyond-range population had more than tripled in size since it was planted. This provides unprecedented support for the conclusion that northern range limit of C. cheiranthifolia results from something other than niche limitation, likely involving constraints on local dispersal.

Long-term demographics of a coral-reef fish: growth, survival and abundance at several spatial scales

In marine organisms, pelagic larval dispersal often results in genetic panmixis among widely separated populations; however, local conditions may produce populations of marine organisms that differ in key life history traits. Here, we assess spatial differences in growth, body condition, survivorship and movement over a decade for lemon damselfish Pomacentrus moluccensis. Newly recruited fish were tagged on the southern (One Tree Island, 23°S), and northern Great Barrier Reef (Lizard Island, 15°S), 1200 km apart, and monitored for over a decade to provide direct data on growth and survivorship. New recruit physiological condition (lipid content) had a weak positive influence on early survival, but not on long-term persistence or growth, and the larval supply signal was lost after 2 years, suggesting post-settlement processes were key in long-term population persistence. Fish exhibited extreme site fidelity, with older/larger fish moving most (all less than 7 m). At Lizard Island, under 5% of individuals remained after 3 years, none after 4 years, while at One Tree Island 5% of individuals survived over 5 years, with 1% remaining after a decade, suggesting Lizard Island populations may require more frequent replenishment to persist. Among-site (within location) variation in mortality was high, and not related to density, suggesting local conditions such as wave exposure and predators were important. Surprisingly, mean growth at the two locations, which differ by around 2 °C on average in sea temperature, was practically identical, levelling off after 3 years, but with high variation among nearby sites within each location, which would affect size-based fecundity and time of first reproduction at these smaller spatial scales. Neither early post-settlement growth nor mortality were density-dependent, and early growth was not related to overall longevity. These small reef fishes are highly sedentary and some demographic parameters, but not others, differ at a range of scales, with post-settlement populations likely driven largely by mortality patterns at the larger spatial scale. Latitudinal and smaller-spatial scale differences in performance (growth, survival) of this species, leading to offsets in expected time to maturity an fecundity, are contrasted by evidence of stability of adult populations over two decades at One Tree Island, which suggests that resilience to environmental change/climate change and other externalities differ considerably across this species’ distribution.

Species' traits drive amphibian tolerance to anthropogenic habitat modification.

Anthropogenic habitat modification is accelerating, threatening the world's biodiversity. Understanding species' responses to anthropogenic modification is vital for halting species' declines. However, this information is lacking for globally threatened amphibians, informed primarily by small community-level studies. We integrated >126,000 verified citizen science observations of frogs, with a global continuous measure of anthropogenic habitat modification for a continental scale analysis of the effects of habitat modification on frogs. We derived a modification tolerance index-accounting for anthropogenic stressors such as human habitation, agriculture, transport and energy production-for 87 species (36% of all Australian frog species). We used this index to quantify and rank each species' tolerance of anthropogenic habitat modification, then compiled traits of all the frog species and assessed how well these equipped species to tolerate modified habitats. Most of Australia's frog species examined were adversely affected by habitat modification. Habitat specialists and species with large geographic range sizes were the least tolerant of habitat modification. Call dominant frequency, body size, clutch type and calling position (i.e. from vegetation) were also related to tolerance of habitat modification. There is an urgent need for improved consideration of anthropogenic impacts and improved conservation measures to ensure the long-term persistence of frog populations, particularly focused on specialists and species identified as intolerant of modified habitats.

Cats, cars, and crossings: The consequences of road networks for the conservation of an endangered felid

Encroaching urban development is a leading cause of habitat loss, replacing natural areas with anthropogenic infrastructure and road networks. Roadways can influence the spatial ecology and survival of mammalian carnivores, particularly felids, thereby threatening long-term persistence and conservation of sensitive populations. Ocelots (Leopardus pardalis) are a federally endangered felid in the United States with breeding populations restricted to the Lower Rio Grande Valley of South Texas, an area of extensive anthropogenic expansion. We evaluated the influence of road networks on ocelot survival using a long-term telemetry dataset (1982–2001, n = 59) and draw comparisons with a spatially referenced historical dataset of ocelot-vehicle collisions in the same area (1982–2020, n = 54). Vehicle collisions accounted for 40% of radio-collared ocelot fatalities. Annual survival rates were 0.90 (95% CI = 0.84–0.95) for resident ocelots and 0.66 (95% CI = 0.45–0.97) for transient ocelots. We evaluated biological and road-related factors that may influence ocelot survival using Cox proportional hazards regression. The top model included density of unpaved, low-volume, and high-volume roads within home ranges and resident-transient status. Mortality risk increased 16% with every 0.07 km/km2 increase of high-volume roads within annual home range, decreased 45% with every 1.12 km/km2 increase of unpaved roads, and decreased 276% for residents compared to transients. Further, probability of mortality specifically from vehicle collision increased with greater density of low-volume roads within ocelot home ranges. Within the historical dataset of ocelot-vehicle collisions, 46% occurred on low-volume roads while 39% occurred on high-volume roads. Our results highlight the necessity for mitigation strategies on low-volume roads which cause the most ocelot-vehicle collisions. In addition, continued attention towards high-volume roads is necessary to ocelot conservation. Understanding how road attributes affect the survival of species sensitive to urbanization and habitat fragmentation can aid in their conservation.

Population projections from holey matrices: Using prior information to estimate rare transition events

Population projection matrices are a common means for predicting short- and long-term population persistence for rare, threatened and endangered species. Data from such species can suffer from small sample sizes and consequently miss rare demographic events resulting in incomplete or biologically unrealistic life cycle trajectories. Matrices with missing values (zeros; e.g., no observation of seeds transitioning to seedlings) are often patched using prior information from the literature, other populations, time periods, other species, best guess estimates, or are sometimes even ignored. To alleviate this problem, we propose using a multinomial-Dirichlet model for parameterizing transitions and a Gamma for reproduction to patch missing values in these holey matrices. This formally integrates prior information within a Bayesian framework and explicitly includes the weight of the prior information on the posterior distributions. We show using two real data sets that the weight assigned to the prior information mainly influences the dispersion of the posteriors, the inclusion of priors results in irreducible and ergodic matrices, and more biologically realistic inferences can be made on the transition probabilities. Because the priors are explicitly stated, the results are reproducible and can be re-evaluated if alternative priors are available in the future.

Diverse large lepidopteran pollinators promote the naturalisation of Crinum asiaticum in invaded and disturbed habitats, despite apparent floral specialisation

Crinum asiaticum is phenotypically specialised with white, scented, very long-tubed flowers, suggesting that only long-proboscid hawkmoths may be effective pollinators. However, this species has frequently escaped cultivation in many tropical and subtropical regions. We therefore investigated the reproductive biology of C. asiaticum to understand how it is able to naturalise, despite phenotypic specialisation. We examined the ability for autonomous selfing and reliance on sexual versus vegetative reproduction in C. asiaticum var. sinicum, using a group individuals growing and propagating naturally in a suburban botanical garden. We also analysed the floral syndrome, recorded floral visitors, determined the pollination effectiveness of floral visitors, and reviewed records of floral visitors at different observation sites. Sexual reproduction provides a much greater potential for dispersal than vegetative reproduction in C. asiaticum var. sinicum. This plant does not perform autonomous selfing and shows poor self-compatibility. The floral syndrome strongly points to long-proboscid hawkmoth pollination, whereas both hawkmoths and swallowtail butterflies with varied tongue lengths were observed as floral visitors because the nectar can accumulate to high levels and therefore fills the majority or all of the perianth tube. Both butterflies and hawkmoths effectively deposited pollen on stigmas. Thus, natural propagation should be attributed to sufficient cross pollination by local lepidopterans. Our findings suggest that autonomous selfing and vegetative reproduction may not be necessary for naturalisation and long-term persistence of plant populations in highly disturbed habitats or new ranges, even if the plants exhibit an extremely specialised floral syndrome.

Imprints of selection in peripheral and ecologically marginal central-eastern European Scots pine populations.

Knowledge of the molecular mechanisms underlying the stress response in plants is essential to understand evolutionary processes that result in long-term persistence of populations. Populations inhabiting marginal ecological conditions at the distribution range periphery may have preserved imprints of natural selection that have shaped functional genetic variation of the species. Our aim was to evaluate the extent of selection processes in the extremely fragmented, peripheral and isolated populations of Scots pine in central-eastern Europe. Autochthonous populations of the Carpathian Mts. and the Pannonian Basin were sampled and drought stress-related candidate genes were re-sequenced. Neutrality tests and outlier detection approaches were applied to infer the effect and direction of selection. Populations retained high genetic diversity by preserving a high number of alleles and haplotypes, many of them being population specific. Neutrality tests and outlier detection highlighted nucleotide positions that are under divergent selection and may be involved in local adaptation. The detected genetic pattern confirms that natural selection has played an important role in shaping modern-day genetic variation in marginal Scots pine populations, allowing for the long-term persistence of populations. Selection detected at functional regions possibly acts to maintain diversity and counteract the effect of genetic erosion.

Evolvability and evolutionary rescue.

The survival prospects of threatened species or populations can sometimes be improved by adaptive change. Such evolutionary rescue is particularly relevant when the threat comes from changing environments, or when long-term population persistence requires range expansion into new habitats. Conservation biologists are therefore often interested in whether or not populations or lineages show a disposition for adaptive evolution, that is, if they are evolvable. Here, we discuss four alternative perspectives that target different causes of evolvability and outline some of the key challenges those perspectives are designed to address. Standing genetic variation provides one familiar estimate of evolvability. Yet, the mere presence of genetic variation is often insufficient to predict if a population will adapt, or how it will adapt. The reason is that adaptive change not only depends on genetic variation, but also on the extent to which this genetic variation can be realized as adaptive phenotypic variation. This requires attention to developmental systems and how plasticity influences evolutionary potential. Finally, we discuss how a better understanding of the different factors that contribute to evolvability can be exploited in conservation practice.

Population structure and body size of the Sahara blue-eyed pond turtle Mauremys leprosa saharica, from an isolated pond in the Lower Draa Basin, southern Morocco.

The marginal populations of the Sahara blue-eyed pond turtle, Mauremys leprosa saharica (Testudines: Geoemydidae) in the pre-Saharan area in the Lower Draa Valley, are faced to extreme environmental conditions of arid climate and anthropogenic activities including overuse of water and land salinization. In this study, we investigated a small isolated population of the blue-eyed pond turtle at Sidi El Mehdaoui Oasis, Lower Draa Valley, to determine its population structure and morphometric characteristics. Water salinity was about 24% of seawater and dissolved oxygen concentration was less than 3mgl-1 (sub-hypoxia). The average body size of adults (carapace length) was much lower in comparison to other Moroccan populations. Among adult individuals, the mean carapace lengths were 103 ± 21mm and 104.4 ± 35mm for males and females, respectively. The corresponding mean body mass were 173 ± 92.4g and 135 ± 52g. There were no significant differences between sexes for size or weight. The studied population is small, with a predominance of adults (75%). A significant sexualsize dimorphism was found. In fact, the Sexual Dimorphism Index for size had the lowest level ever described for the species possibly because of the low productivity of this marginal isolated habitat. The increased drought and salinization are major threats to the long-term persistence of the vulnerable populations of the Saharan blue-eyed pond turtle and their habitats. Therefore, conservation measures of these populations through the protection of their habitats are very urgent.

Captive-bred populations of a partially migratory salmonid fish are unlikely to maintain migratory polymorphism in natural habitats.

Variation in life history is fundamental to the long-term persistence of populations and species. Partial migration, in which both migratory and resident individuals are maintained in a population, is commonly found across animal taxa. However, human-induced habitat fragmentation continues to cause a rapid decline in the migratory phenotype in many natural populations. Using field and hatchery experiments, we demonstrated that despite both migrants and residents being maintained in captive environments, few individuals of the red-spotted masu salmon, Oncorhynchus masou ishikawae, became migrants in natural streams when released prior to the migration decision. Released fish rarely reached the threshold body size necessary to become migrants in natural streams, presumably owing to lower growth rates in natural than in captive environments. The decision to migrate is often considered a threshold trait in salmonids and other animal taxa. Our findings highlight the need for management programmes that acknowledge the effects of the environment on the determination of the migratory phenotypes of partially migratory species when releasing captive-bred individuals prior to their migratory decisions.

A new methodology to assess landscape reserves in Lithuania

The first state reserve in Lithuania was established in 1960; however, no detailed assessments of changes in the state of the protected values therein have been performed ever since. Landscape reserves are the most complex ones and they pursue the twofold goal – to conserve the values and to use them sustainably. In order to be resilient themselves, thus contributing to broader objectives of social-ecological resilience, the reserves should be able to adapt to ever-changing social and ecological conditions in a way that supports the long-term persistence of population, communities, and ecosystems of conservation concern. Therefore, it is necessary to update information on the status of values protected in the reserves. The article addresses this need by offering a concise and user-friendly methodology for assessing the status of landscape reserves. The methodology focuses on three main components: (1) general features of the landscape structure, (2) the effectiveness of protection of values and (3) the pressures and threats they experience. Two state landscape reserves were selected for testing the applicability of the methodology: one in Vilnius city, the other 50 km to the west, in the countryside. Application of the common methodology will allow to assess the condition of landscape reserves in the country. Further development of the methodology could include evaluation of external pressures (e.g. urbanization) as well as addition of remote sensing techniques.

Birds advancing lay dates with warming springs face greater risk of chick mortality

In response to a warming planet with earlier springs, migratory animals are adjusting the timing of essential life stages. Although these adjustments may be essential for keeping pace with resource phenology, they may prove insufficient, as evidenced by population declines in many species. However, even when species can match the tempo of climate change, other consequences may emerge when exposed to novel conditions earlier in the year. Here, using three long-term datasets on bird reproduction, daily insect availability, and weather, we investigated the complex mechanisms affecting reproductive success in an aerial insectivore, the tree swallow (Tachycineta bicolor). By examining breeding records over nearly half a century, we discovered that tree swallows have continuously advanced their egg laying by ∼3 d per decade. However, earlier-hatching offspring are now exposed to inclement weather events twice as often as they were in the 1970s. Our long-term daily insect biomass dataset shows no long-term trends over 25 y but precipitous drops in flying insect numbers on days with low ambient temperatures. Insect availability has a considerable impact on chick survival: Even a single inclement weather event can reduce offspring survival by >50%. Our results highlight the multifaceted threats that climate change poses on migrating species. The decoupling between cold snap occurrence and generally warming spring temperatures can affect reproductive success and threaten long-term persistence of populations. Understanding the exact mechanisms that endanger aerial insectivores is especially timely because this guild is experiencing the steepest and most widespread declines across North America and Europe.