Responses of the clonal sedge, Carex bigelowii, to two seasons of simulated climate change

The effect of enhanced temperature was studied in open-top chambers on the arctic clonal sedge Carex bigelowii Torr. ex Schwein. at Latnjajaure Field Station, Swedish Lapland for two growing seasons. The flowering phenology of C. bigelowii accelerated during the first field season that the open-top chambers were erected. After the second season of perturbation the sexual reproductive investment was higher in the open-top chambers than in the controls and flowering phenology was still accelerated. Leaf phenology and the growth of vegetative tillers followed the same pattern in the open-top chambers as in the controls, but the leaves were longer in the open-top chambers from the end of June until the end of August. The results suggest that relatively late flowering clonal graminoids may be favoured by warmer climate, at least in the short term.     

Nitrogen uptake by rhizomes of the clonal sedge Carex bigelowii: a previously overlooked nutritional benefit of rhizomatous growth

Studies on the rhizomatous clonal sedge Carex bigelowii , at a fellfield site in subarctic Swedish Lapland examined the ecological potential of rhizomes as nitrogen uptake systems. Direct application of a solution of ¹⁵NH₄¹⁵NO₃ to the rhizomes of C. bigelowii significantly enriched the ¹⁵N content of the plant tissue. The pattern of enrichment indicated movement of labelled nitrogen into rhizomes and adjoining tissue (including roots and shoots), showing both uptake and translocation via the rhizome system. There was a gradient of decreasing ¹⁵N enrichment with increasing distance from the point of labelling, and estimation of the total mass of nitrogen taken up via labelled rhizomes showed low levels and rates of uptake. Quantification of the size of rhizome and root systems of C. bigelowii at the study site indicates that 80% of the living biomass may be below ground, and that the surface area of the rhizome system of C. bigelowii is approx. two-thirds that of the roots. The rhizome system of C. bigelowii can therefore act as a route for nitrogen uptake, with the potential to exploit almost as great a volume of soil as the root system. This mechanism of nitrogen uptake may play an important role in the Arctic, where many species have a clonal, rhizomatous growth form. In addition, plant growth in many arctic ecosystems is limited by low soil nutrient availability, a result of low temperatures (leading to slow soil decomposition rates) and patchy resource distribution. Nitrogen uptake via rhizomes may provide plants with the capacity to take advantage of transient nutrient supplies, and may partly compensate for the cost of developing and maintaining persistent rhizome networks in ecosystems where nutrient resources are in short supply.     

Analysis of population clonal diversity using microsatellite markers in the salt marsh sedge Carex scabrifolia in western Japan

Carex scabrifolia, a perennial herb that commonly grows on sandbars in lagoons and tidal estuaries, is threatened by habitat reduction in some areas of Japan. Clonal diversity and the extent of gene flow among ten populations located along the Seto Inland Sea and the Japan Sea in western Japan were examined using six microsatellite loci. From 299 samples, we detected 77 multilocus genotypes. The mean number of alleles per population was 2.8 and the mean clonal diversity was 0.23. Many populations consisted of small patches, and the mean number of genets per patch was 2.0. The average number of alleles per locus and clonal diversity were positively correlated with the number of patches within a watershed. Gene flow was detected between the Ichikawa River and the Ohta River populations along the Seto Inland Sea, and weak differentiation among populations located along the Seto Inland Sea was observed. Our results suggest that effective conservation of C. scabrifolia populations should include maintaining all patches within a watershed regardless of population size, thus promoting genotype preservation.     

Weather-dependent survival: implications of climate change for passerine population processes

Understanding demographic processes will be essential to construct robust models of population responses to climate change. We show that survival is related to the strength of the North Atlantic Oscillation in five out of ten British resident passerine species, and explore the importance of biologically more specific variables (duration of winter frosts and snow periods; occurrence of cold, wet days; spring temperature; and summer drought). The most important variables differed between species in relation to differences in foraging strategy. In almost all cases, first-year survival was influenced by weather more than was the survival of adult birds. Particularly vulnerable species, such as the Wren Troglodytes troglodytes , may exhibit a 25% reduction in juvenile survival rates due to adverse weather within the range experienced in the last 30 years; variation in survival by 10% or more is commonplace in most species. Thus, climate influences on food availability may provide the mechanism by which populations will alter under changed climatic conditions, though the presence of density dependence may reduce the impact of this on long-term population trajectories.     

Transmission intensity and drug resistance in malaria population dynamics: implications for climate change

Although the spread of drug resistance and the influence of climate change on malaria are most often considered separately, these factors have the potential to interact through altered levels of transmission intensity. The influence of transmission intensity on the evolution of drug resistance has been addressed in theoretical studies from a population genetics' perspective; less is known however on how epidemiological dynamics at the population level modulates this influence. We ask from a theoretical perspective, whether population dynamics can explain non-trivial, non-monotonic, patterns of treatment failure with transmission intensity, and, if so, under what conditions. We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s. Our theoretical analyses, with a transmission model that includes different levels of immunity, demonstrate that an increase in transmission beyond a threshold can lead to a decrease in drug resistance, as previously shown, but that a second threshold may occur and lead to the re-establishment of drug resistance. Estimates of the increase in transmission intensity from the 1970s to the 1990s for the Kenyan time series, obtained by fitting the two-stage version of the model with an explicit representation of vector dynamics, suggest that warmer temperatures are likely to have moved the system towards the first threshold, and in so doing, to have promoted the faster spread of drug resistance. Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region. Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.     

Conditions for seedling establishment and probable function of seed in the clonal sedge Carex rugulosa Kük. in riverside marshes

Carex rugulosa Kük. forms large meadows in moist zones along estuarine riversides. These meadows are usually maintained by rhizomatous ramet production (clonal growth), and the appearance of seedlings is uncommon. We studied the conditions required for seedling establishment. In areas in which clonal ramets were dense (906–1050/m²), and the relative light intensity at ground level was low (0.8–3.8%), seed germination was entirely suppressed. In contrast, many seedlings (288–513/m²) were observed in areas in which clonal ramets had been considerably reduced (13–269/m²) by continuous inundation in the previous year. In these areas, the relative light intensity had increased (20.5–79.3%). It was inferred that seeds resisted the prolonged inundation that killed the ramets, and that germination was induced under these open conditions. These results suggest that the main functions of sexual reproduction in C. rugulosa are recovery after severe damage to vegetation using seeds from the seed bank and the dispersal of seeds to areas without dense vegetation. Most seedlings died when the marshy meadow was temporarily inundated by heavy rain. However, transplanted seedlings survived better at artificially elevated sites that were not submerged. This shows that inundation during the seedling stage impedes seedling survival. Therefore, seeds can contribute to recovery after ramet decline or colonization to open area when (i) the rainfall is not heavy to cause seedling submergence or (ii) seeds are dispersed to higher area which is not inundated.     

Widespread parallel population adaptation to climate variation across a radiation: implications for adaptation to climate change

Global warming will impact species in a number of ways, and it is important to know the extent to which natural populations can adapt to anthropogenic climate change by natural selection. Parallel microevolution within separate species can demonstrate natural selection, but several studies of homoplasy have not yet revealed examples of widespread parallel evolution in a generic radiation. Taking into account primary phylogeographic divisions, we investigate numerous quantitative traits (size, shape, scalation, colour pattern and hue) in anole radiations from the mountainous Lesser Antillean islands. Adaptation to climatic differences can lead to very pronounced differences between spatially close populations with all studied traits showing some evidence of parallel evolution. Traits from shape, scalation, pattern and hue (particularly the latter) show widespread evolutionary parallels within these species in response to altitudinal climate variation greater than extreme anthropogenic climate change predicted for 2080. This gives strong evidence of the ability to adapt to climate variation by natural selection throughout this radiation. As anoles can evolve very rapidly, it suggests anthropogenic climate change is likely to be less of a conservation threat than other factors, such as habitat loss and invasive species, in this, Lesser Antillean, biodiversity hot spot.     

Vulnerability of mires under climate change: implications for nature conservation and climate change adaptation

Wetlands in general and mires in particular belong to the most important terrestrial carbon stocks globally. Mires (i.e. bogs, transition bogs and fens) are assumed to be especially vulnerable to climate change because they depend on specific, namely cool and humid, climatic conditions. In this paper, we use distribution data of the nine mire types to be found in Austria and habitat distribution models for four IPCC scenarios to evaluate climate change induced risks for mire ecosystems within the 21st century. We found that climatic factors substantially contribute to explain the current distribution of all nine Austrian mire ecosystem types. Summer temperature proved to be the most important predictor for the majority of mire ecosystems. Precipitation—mostly spring and summer precipitation sums—was influential for some mire ecosystem types which depend partly or entirely on ground water supply (e.g. fens). We found severe climate change induced risks for all mire ecosystems, with rain-fed bog ecosystems being most threatened. Differences between scenarios are moderate for the mid-21st century, but become more pronounced towards the end of the 21st century, with near total loss of climate space projected for some ecosystem types (bogs, quagmires) under severe climate change. Our results imply that even under minimum expected, i.e. inevitable climate change, climatic risks for mires in Austria will be considerable. Nevertheless, the pronounced differences in projected habitat loss between moderate and severe climate change scenarios indicate that limiting future warming will likely contribute to enhance long-term survival of mire ecosystems, and to reduce future greenhouse gas emissions from decomposing peat. Effectively stopping and reversing the deterioration of mire ecosystems caused by conventional threats can be regarded as a contribution to climate change mitigation. Because hydrologically intact mires are more resilient to climatic changes, this would also maintain the nature conservation value of mires, and help to reduce the severe climatic risks to which most Austrian mire ecosystems may be exposed in the 2nd half of the 21st century according to IPCC scenarios.     

Livestock and food security: vulnerability to population growth and climate change

Livestock production is an important contributor to sustainable food security for many nations, particularly in low‐income areas and marginal habitats that are unsuitable for crop production. Animal products account for approximately one‐third of global human protein consumption. Here, a range of indicators, derived from FAOSTAT and World Bank statistics, are used to model the relative vulnerability of nations at the global scale to predicted climate and population changes, which are likely to impact on their use of grazing livestock for food. Vulnerability analysis has been widely used in global change science to predict impacts on food security and famine. It is a tool that is useful to inform policy decision making and direct the targeting of interventions. The model developed shows that nations within sub‐Saharan Africa, particularly in the Sahel region, and some Asian nations are likely to be the most vulnerable. Livestock‐based food security is already compromised in many areas on these continents and suffers constraints from current climate in addition to the lack of economic and technical support allowing mitigation of predicted climate change impacts. Governance is shown to be a highly influential factor and, paradoxically, it is suggested that current self‐sufficiency may increase future potential vulnerability because trade networks are poorly developed. This may be relieved through freer trade of food products, which is also associated with improved governance. Policy decisions, support and interventions will need to be targeted at the most vulnerable nations, but given the strong influence of governance, to be effective, any implementation will require considerable care in the management of underlying structural reform.     

Impact of weather and climate variation on Hoopoe reproductive ecology and population growth

Preserving peripheral populations is a key conservation issue because of the adaptive potential to environmental change they provide for the species as a whole. Yet, peripheral populations are often small and isolated, i.e. more vulnerable to stochastic events and prone to extinction. We studied a peripheral population of Hoopoe (Upupa epops), a rare insectivorous farmland bird, in the Swiss Alps. We first investigated the effect of weather variation on food provisioning to chicks by Hoopoe parents. Second, while accounting for density-dependence, we tested the extent to which breeding success is governed by weather circumstances and assessed the possible consequences of climate variation on population growth. Provisioning rate and provisioned prey biomass were negatively affected by adverse weather (cool, rainy days), were higher in males and also increased with brood size. Much smaller proportions of molecrickets (Gryllotalpa gryllotalpa; the most profitable prey locally, constituting 93% of chicks’ food biomass) were provisioned on days with adverse weather, irrespective of brood size. Rainfall prior to hatching and during the first days of chick life had a negative impact on their survival, and there was a positive effect of temperature on chick survival just before fledging. Reproductive output was negatively affected by precipitation during the hatching period, but was enhanced by warm temperature just before hatching and in the last days before fledging. Our model showed that the variable reproductive output has a strong impact on the population growth: a succession of adverse, rainy springs would cause a rapid decline of the population. This case study confirms that conservation efforts may be obliterated if risks linked to increasing climate variability are not properly accounted for in the management of small peripheral populations.     

The role of vegetative spread and seed dispersal for optimal life histories of clonal plants: a simulation study

Sexual and vegetative reproduction of clonal plants phenotypically differ in dispersal distance, in the phenology of offspring production and establishment, and in the success of establishment. We applied a combination of analytical and of spatially explicit individual-based simulation modelling to calculate long-term fitness. We predicted optimal clonal plant life histories in a parameter space spanned by stolon number, stolon internode length, and relative allocation to sexual and vegetative reproduction. For a given allocation to sexual reproduction and number of stolons, fitness was optimised for rather short internode lengths under small disturbances, and for the longest possible internodes under larger disturbances. A trade-off between length and number of vegetative spacers drew parameters away from their unrestricted optima. Now, intermediate length and number of spacers led to maximum fitness under large disturbances. Simultaneous trade-offs between sexual and vegetative reproduction and between the length and number of spacers could also lead to fitness optima at intermediate parameter values, depending on the success of seedling establishment. We demonstrated that spatial habitat structure (1) selects for an efficient use of available space either by optimum internode length or by investment into seeds, which disperse farther than vegetative spacers, and (2) leads to an interaction between trade-offs. We conclude, that dispersal distance, i.e. a spatial life-history component, and trade-offs must be included in considerations on adaptive evolution of clonal life histories.     

Sexual lability during an individual's life: the case of the sedge Carex secalina

Various environmental and physiological factors that affect sex expression in plants have been identified. We made the presumption that in perennials, age may be a key factor that significantly diversifies sex expression over consecutive years of an individual's life. To test this hypothesis, we chose the sedge Carex secalina, a plant that reproduces only sexually and exhibits different sex expression patterns. These patterns had been previously observed in natural populations. In a four‐year experiment, the sex of spikes formed on reproductive tillers of 100 individuals originating from three populations was monitored. A significant association between individuals’ age and number of female/male spikes was found for each population. In addition, significant differences between the populations in the ratio of shoots with bisexual spikes to shoots with unisexual spikes were revealed. We also showed that the proportion of shoots with bisexual spikes in the individual populations changed significantly with the age of an individual and that in the successive years of the individual's life, the production level of female and male structures changed. Moreover, an age‐dependent decrease in both the number and length of female and male spikes was observed.     

Effects of simulated climate change on phenology and life history traits in Carex bigelowii

Climate change may have large effects on plants, especially in the Arctic. At two different sites, we studied the effects of enhanced temperature by using open-top chambers (OTCs) on the clonal sedge Carex bigelowii , a common plant in arctic and alpine tundra. At the subarctic-alpine site Latnjajaure, northern Sweden, overall flowering phenology was accelerated by open-top chambers (OTCs) during the five years of treatment. For this protogynous population, male flower phenology accelerated more than female flower phenology, which resulted in an increased gender phase overlap. Sexual reproductive effort at the ramet-level increased, both in male and female functions. Smut fungus incidence was not different among treatments, but a Dipteran seed predator attacked more ramets in the OTCs in one of five years. However, neither the fungus nor the seed predators affected plant growth or seed set measurably. Ramet-level growth increased in the OTCs at Latnjajaure, but decreased in the OTCs at the maritime subarctic site Thingvellir, Iceland after three years of treatment. At Latnjajaure, the initial ramet- level responses were still evident after five years, while responses at the ramet population level disappeared: there was no difference in flowering frequency of ramets in the fifth year of the warming treatment. This is interpreted as either meristem limitation or internal resource depletion. At Thingvellir flowering frequency was unaffected by warming treatment, while ramet production decreased. Ramet production was unaffected by the treatment at Latnjajaure. These site differences in responses could be the consequences of differences in climate or site specific conditions. The trade-off (negative correlation) between the number and size of vegetative offspring at Latnjajaure disappeared under enhanced temperatures (within the OTCs). This trade-off was not apparent under the warmer conditions at Thingvellir.     

Impact of clonal growth on effective population size in Hymenoxys herbacea (Asteraceae)

By influencing the proliferation of different genotypes, clonal growth can affect the maintenance of genetic variability and magnitude of genetic drift within plant populations. However, estimates of effective population size rarely incorporate the contribution of both asexual and sexual reproduction. We estimated effective size (Ne) for two populations of the clonal, self-incompatible plant, Hymenoxys herbacea, using a stage-structured demographic model for organisms with asexual and sexual recruitment and then examined the impact of reproductive strategy using an elasticity analysis. Plant rosettes monitored in two successive years had high survival rates in both populations (mean 0.94). The mean number of sexually derived recruits per initial ramet was 0.041 (SE 0.039), whereas the mean number of clonal recruits was 0.61 (SE 0.90). Effective size was 1642 and 5769 in the two populations and the Ne/N ratio averaged 0.34, comparable to values for other clonal species. Elasticity analysis indicated that increases in both clonal and sexual recruitment cause an increase in Ne while increasing the variance reduced Ne. However, Ne was more sensitive to changes in the mean and variance of asexual recruitment than sexual recruitment. These results highlight the importance of considering asexual modes of reproduction when examining the role of genetic stochasticity in populations.     

Impact of twenty-first century climate change on diadromous fish spread over Europe, North Africa and the Middle East

Climate change is expected to drive species ranges towards the poles and to have a strong influence on species distributions. In this study, we focused on diadromous species that are of economical and ecological importance in the whole of Europe. We investigated the potential distribution of all diadromous fish regularly encountered in Europe, North Africa and the Middle East (28 species) under conditions predicted for twenty‐first century climate change. To do so, we investigated the 1900 distribution of each species in 196 basins spread across all of Europe, North Africa and the Middle East. Four levels were used to semiquantitatively describe the abundance of species, that is missing, rare, common and abundant. We then selected five variables describing the prevailing climate in the basins, the physical nature of the basins and reflecting historical events known to have affected freshwater fish distribution. Logistic regressions with a four‐level ordinal response variable were used to develop species‐specific models. These predictive models related the observed distribution of these species in 1900 to the most explanatory combination of variables. Finally, we selected the A2 SRES scenario and the HadCM3 (Hadley Centre Coupled Model version 3) global climate model (GCM) to obtain climate variables (temperature and precipitation) at the end of this century. We used these 2100 variables in our models and obtained maps of climatically suitable and unsuitable basins, percentages of contraction or expansion for each species. Twenty‐two models were successfully built, that is there were five species for which no model could be established because their distribution range was too narrow and the Acipenser sturio model failed during calibration. All the models selected temperature or/and precipitation as explanatory variables. Responses to climate change were species‐specific but could be classified into three categories: little or no change in the distribution (five species), expansion of the distribution range (three species gaining suitable basins mainly northward) and contraction of the distribution (14 species losing suitable basins). Shifting ranges were in accordance with those found in other studies and underlined the high sensitivity of diadromous fish to modifications in their environment.     

The impact and implications of climate change for bats

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