Refugia and connectivity sustain amphibian metapopulations afflicted by disease

Metapopulation persistence in fragmented landscapes depends on habitat patches that can support resilient local populations and sufficient connectivity between patches. Yet epidemiological theory for metapopulations has largely overlooked the capacity of particular patches to act as refuges from disease, and has suggested that connectivity can undermine persistence. Here, we show that relatively warm and saline wetlands are environmental refuges from chytridiomycosis for an endangered Australian frog, and act jointly with connectivity to sustain frog metapopulations. We coupled models of microclimate and infection probability to map chytrid prevalence, and demonstrate a strong negative relationship between chytrid prevalence and the persistence of frog populations. Simulations confirm that frog metapopulations are likely to go extinct when they lack environmental refuges from disease and lose connectivity between patches. This study demonstrates that environmental heterogeneity can mediate host–pathogen interactions in fragmented landscapes, and provides evidence that connectivity principally supports host metapopulations afflicted by facultative pathogens.     

Plant composition and diversity in a semi-natural Mediterranean island landscape: the importance of environmental factors

Abstract

Islands crucially contribute to the Mediterranean Basin’s high floristic diversity, which, however, is at risk facing climate and land-use changes. Besides the identification of highly diverse areas, the knowledge about factors favouring diversity is of great importance. We analysed plant species diversity and composition related to environmental factors over varied vegetation units on a former Italian prison island in the northwest of Sardinia. Due to a long history of land use with grazing and later abandonment the nowadays protected island features a semi-natural landscape and can serve as an example for strongly anthropogenic altered insular ecosystems. Floristic composition, soil properties, microclimate and ungulate abundance were assessed. Relationships of vegetation composition and diversity with abiotic variables were examined by Canonical Correspondence Analysis, which indicated the importance of air temperature, soil moisture, slope gradient and C/N ratio for floristic differentiation. Most important abiotic factors for plant species richness were relative air humidity and soil moisture, while floristic diversity was mainly determined by air temperature and pH. Furthermore, observation data pointed to an adverse influence of ungulate abundance for plant species diversity. Regarding nature conservation, grazing intensity thus must be critically taken into account, especially for sensitive vegetation units like the coastal garrigue.     

Buildings promote higher incubation temperatures and reduce nest attentiveness in a Neotropical thrush

Incubation is an energetically costly parental task of breeding birds. Incubating parents respond to environmental variation and nest‐site features to adjust the balance between the time spent incubating (i.e. nest attentiveness) and foraging to supply their own needs. Non‐natural nesting substrates such as human buildings impose new environmental contexts that may affect time allocation of incubating birds but this topic remains little studied. Here, we tested whether nesting substrate type (buildings vs. trees) affects the temperature inside the incubation chamber (hereafter ‘nest temperature’) in the Pale‐breasted Thrush Turdus leucomelas, either during ‘day’ (with incubation recesses) or ‘night’ periods (representing uninterrupted female presence at the nest). We also tested whether nesting substrate type affects the incubation time budget using air temperature and the day of the incubation cycle as covariates. Nest temperature, when controlled for microhabitat temperature, was higher at night and in nests in buildings but did not differ between daytime and night for nests in buildings, indicating that buildings partially compensate for incubation recesses by females with regard to nest temperature stability. Females from nests placed in buildings exhibited lower nest attentiveness (the overall percentage of time spent incubating) and had longer bouts off the nest. Higher air temperatures were significantly correlated with shorter bouts on the nest and longer bouts off the nest, but without affecting nest attentiveness. We suggest that the longer bouts off the nest taken by females of nests in buildings is a consequence of higher nest temperatures promoted by man‐made structures around these nests. Use of buildings as nesting substrate may therefore increase parental fitness due to a relaxed incubation budget, and potentially drive the evolution of incubation behaviour in certain urban bird populations.     

A taxonomic and phylogenetic perspective on plant community assembly along an elevational gradient in subtropical forests

亚热带森林植物群落沿海拔梯度的分类与系统发育研究 生物多样性沿海拔梯度的分布格局已受到广泛关注。然而,生物多样性格局沿海拔梯度的变异及其潜在机制尚不清楚。整合生物多样性的多维度信息为理解群落构建机制提供了新思路。本研究在我国东部亚热带森林沿海拔270–1470 m的梯度上设置了17个木本植物固定样地,分析了沿海拔梯度植物群落 构建的生态和进化驱动力。基于样地内物种出现(0–1数据)和多度信息,计算群落内被子植物的物种和系统发育alpha和beta多样性、系统发育结构等,并量化多样性指标与微气候和地形之间的关系。研究发现,不论多度加权与否,物种alpha多样性均沿海拔升高而增加,物种和系统发育的相似性随海拔距离的增加而呈衰减趋势。然而,多度加权与否会形成不同的系统发育alpha多样性格局。对于系统发育结构而言,沿海拔增加并无明显趋势。地形和微气候是多样性格局和系统发育结构的主要驱动力。与未考虑物种多度的多样性指标相比,多度加权的指标与坡度和胸高断面积相关性更高。这些结果表明,由局域物种多度介导的确定性过程对沿海拔梯度的植物群落构建具有一定影响。     

Body mass and hibernation microclimate may predict bat susceptibility to white‐nose syndrome

In multihost disease systems, differences in mortality between species may reflect variation in host physiology, morphology, and behavior. In systems where the pathogen can persist in the environment, microclimate conditions, and the adaptation of the host to these conditions, may also impact mortality. White‐nose syndrome (WNS) is an emerging disease of hibernating bats caused by an environmentally persistent fungus, Pseudogymnoascus destructans. We assessed the effects of body mass, torpid metabolic rate, evaporative water loss, and hibernaculum temperature and water vapor deficit on predicted overwinter survival of bats infected by P. destructans. We used a hibernation energetics model in an individual‐based model framework to predict the probability of survival of nine bat species at eight sampling sites across North America. The model predicts time until fat exhaustion as a function of species‐specific host characteristics, hibernaculum microclimate, and fungal growth. We fit a linear model to determine relationships with each variable and predicted survival and semipartial correlation coefficients to determine the major drivers in variation in bat survival. We found host body mass and hibernaculum water vapor deficit explained over half of the variation in survival with WNS across species. As previous work on the interplay between host and pathogen physiology and the environment has focused on species with narrow microclimate preferences, our view on this relationship is limited. Our results highlight some key predictors of interspecific survival among western bat species and provide a framework to assess impacts of WNS as the fungus continues to spread into western North America.     

Elevated CO2 effects on canopy and soil water flux parameters measured using a large chamber in crops grown with free-air CO2 enrichment

An arable crop rotation (winter barley-sugar beet-winter wheat) was exposed to elevated atmospheric CO(2) concentrations ([CO(2) ]) using a FACE facility (Free-Air CO(2) Enrichment) during two rotation periods. The atmospheric [CO(2) ] of the treatment plots was elevated to 550 ppm during daylight hours (T>5°C). Canopy transpiration (E(C) ) and conductance (G(C) ) were measured at selected intervals (>10% of total growing season) using a dynamic CO(2) /H(2) O chamber measuring system. Plant available soil water content (gravimetry and TDR probes) and canopy microclimate conditions were recorded in parallel. Averaged across both growing seasons, elevated [CO(2) ] reduced E(C) by 9%, 18% and 12%, and G(C) by 9%, 17% and 12% in barley, sugar beet and wheat, respectively. Both global radiation (Rg) and vapour pressure deficit (VPD) were the main driving forces of E(C) , whereas G(C) was mostly related to Rg. The responses of E(C) and especially G(C) to [CO(2) ] enrichment were insensitive to weather conditions and leaf area index. However, differences in LAI between plots counteracted the [CO(2) ] impact on E(C) and thus, at least in part, explained the variability of seasonal [CO(2) ] responses between crops and years. As a consequence of lower transpirational canopy water loss, [CO(2) ] enrichment increased plant available soil water content in the course of the season by ca. 15 mm. This was true for all crops and years. Lower transpirational cooling due to a [CO(2) ]-induced reduction of E(C) increased canopy surface and air temperature by up to 2 °C and 0.5 °C, respectively. This is the first study to address effects of FACE on both water fluxes at canopy scale and water status of a European crop rotation.     

A cost‐effective method of assessing thermal habitat quality for endotherms

The conservation of many endothermic species depends critically on the availability of suitable retreat sites, yet we know little about the variation in thermal quality of such microhabitats. Studies of thermal habitat suitability for birds and mammals must account for the effect of endothermic heat production on their microclimates. For example, endotherms may significantly raise the air temperature in their retreat sites and this effect must be considered when assessing retreat site quality. We devised an inexpensive means by which to construct pseudo‐endothermic ‘environmental temperature’ models with the use of disposable heat pads. We applied this technique to investigate thermal aspects of nest box design, illustrating the potential positive and negative effects of nest box insulation depending on the environmental context. We suggest that, from a thermal perspective, the avoidance of heat stress is an important and underappreciated issue in the retreat site selection of endotherms.     

13. Lake Saloio (Nazaré, western Portugal)

The possible impact of altitude and the related microclimatic conditions on the total production of fruiting branches, inflorescences, flowers and pollen grains of olive trees Olea europaea was analysed. A total of 90 Picual cultivar trees, the most extensive olive cultivar in the Iberian Peninsula, were studied for a three-year period (2007–2009). The study shows that production of flowers and pollen grains in a cultivar of the olive tree varies according to the microclimate. Our study also indicates that the olive trees frequently can have up to half a million flowers per tree. Moreover, the total flower production differs between years and study areas. In the Picual cultivar, the average production of pollen grains per anther is usually more than 60?000 grains. The total production of pollen per tree is around 72?000 million on average. The most favourable microclimatic conditions for reproduction in olive trees are found in years and olive growing areas with low temperature and high precipitation records during the months prior to flowering of the olive trees. We hypothesise that olive trees tend to increase their pollen production rate as altitude increases, which can be interpreted as a reproductive strategy to ensure fertilisation.     

Predicting future climate at high spatial and temporal resolution

Most studies on the biological effects of future climatic changes rely on seasonally aggregated, coarse‐resolution data. Such data mask spatial and temporal variability in microclimate driven by terrain, wind and vegetation, and ultimately bear little resemblance to the conditions that organisms experience in the wild. Here, I present the methods for providing fine‐grained, hourly and daily estimates of current and future temperature and soil moisture over decadal timescales. Observed climate data and spatially coherent probabilistic projections of daily future weather were disaggregated to hourly and used to drive empirically calibrated physical models of thermal and hydrological microclimates. Mesoclimatic effects (cold‐air drainage, coastal exposure and elevation) were determined from the coarse‐resolution climate surfaces using thin‐plate spline models with coastal exposure and elevation as predictors. Differences between micro and mesoclimate temperatures were determined from terrain, vegetation and ground properties using energy balance equations. Soil moisture was computed in a thin upper layer and an underlying deeper layer, and the exchange of water between these layers was calculated using the van Genuchten equation. Code for processing the data and running the models is provided as a series of R packages. The methods were applied to the Lizard Peninsula, United Kingdom, to provide hourly estimates of temperature (100 m grid resolution over entire area, 1 m for a selected area) for the periods 1983–2017 and 2041–2049. Results indicated that there is a fine‐resolution variability in climatic changes, driven primarily by interactions between landscape features and decadal trends in weather conditions. High‐temporal resolution extremes in conditions under future climate change were predicted to be considerably less novel than the extremes estimated using seasonally aggregated variables. The study highlights the need to more accurately estimate the future climatic conditions experienced by organisms and equips biologists with the means to do so.     

Hiding from the climate: Characterizing microrefugia for boreal forest understory species

Climate warming is likely to shift the range margins of species poleward, but fine‐scale temperature differences near the ground (microclimates) may modify these range shifts. For example, cold‐adapted species may survive in microrefugia when the climate gets warmer. However, it is still largely unknown to what extent cold microclimates govern the local persistence of populations at their warm range margin. We located 99 microrefugia, defined as sites with edge populations of 12 widespread boreal forest understory species (vascular plants, mosses, liverworts and lichens) in an area of ca. 24,000 km² along the species' southern range margin in central Sweden. Within each population, a logger measured temperature eight times per day during one full year. Using univariate and multivariate analyses, we examined the differences of the populations' microclimates with the mean and range of microclimates in the landscape, and identified the typical climate, vegetation and topographic features of these habitats. Comparison sites were drawn from another logger data set (n = 110), and from high‐resolution microclimate maps. The microrefugia were mainly places characterized by lower summer and autumn maximum temperatures, late snow melt dates and high climate stability. Microrefugia also had higher forest basal area and lower solar radiation in spring and autumn than the landscape average. Although there were common trends across northern species in how microrefugia differed from the landscape average, there were also interspecific differences and some species contributed more than others to the overall results. Our findings provide biologically meaningful criteria to locate and spatially predict potential climate microrefugia in the boreal forest. This opens up the opportunity to protect valuable sites, and adapt forest management, for example, by keeping old‐growth forests at topographically shaded sites. These measures may help to mitigate the loss of genetic and species diversity caused by rear‐edge contractions in a warmer climate.