Life Is Uncertain: Inherent Variability Exhibited by Organisms, and at Higher Levels of Biological Organization

Organisms act stochastically. A not uncommon view in the ecological literature is that this is mainly due to the observer having insufficient information or a stochastic environment-and not partly because organisms themselves respond with inherent unpredictability. In this study, I compile the evidence that contradicts that view. Organisms generate uncertainty internally, which results in irreducible stochastic responses. I consider why: for instance, stochastic responses are associated with greater adaptability to changing environments and resource availability. Over longer timescales, biologically generated uncertainty influences behavior, evolution, and macroecological processes. Indeed, it could be stated that organisms are systems defined by the internal generation, magnification, and record-keeping of uncertainty as inputs to responses. Important practical implications arise if organisms can indeed be defined by an association with specific classes of inherent uncertainty: not least that isolating those signatures then provides a potential means for detecting life, for considering the forms that life could theoretically take, and for exploring the wider limits to how life might become distributed. These are all fundamental goals in astrobiology.

Sufficient conditions for rapid range expansion of a boreal conifer

Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra¹, thereby reducing albedo^2–4, altering carbon cycling⁴ and further changing climate^1–4, yet the patterns and processes of this biome shift remain unclear⁵. Climate warming, required for previous boreal advances^6–17, is not sufficient by itself for modern range expansion of conifers forming forest–tundra ecotones^{5,12–15,17–20}. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented⁵ advancing at rates following the last glacial maximum (LGM)^6–8. Here we describe a population of white spruce (Picea glauca) advancing at post-LGM rates⁷ across an Arctic basin distant from established treelines and provide evidence of mechanisms sustaining the advance. The population doubles each decade, with exponential radial growth in the main stems of individual trees correlating positively with July air temperature. Lateral branches in adults and terminal leaders in large juveniles grow almost twice as fast as those at established treelines. We conclude that surpassing temperature thresholds^1,6–17, together with winter winds facilitating long-distance dispersal, deeper snowpack and increased soil nutrient availability promoting recruitment and growth, provides sufficient conditions for boreal forest advance. These observations enable forecast modelling with important insights into the environmental conditions converting tundra into forest.

A boreal conifer is advancing northwards into Arctic tundra, with this treeline advance facilitated by climate warming together with winter winds, deeper snow and increased soil nutrient availability.

The Synergy of Patterns vs. Processes at Community Level: A Key Linkage for Subtropical Native Forests along the Urban Riparian Zone

Riparian zones possesses unique ecological position with biota differing from aquatic body and terrestrial lands, and plant–animal coevolution through a propagule-dispersal process may be the main factor for the framework of riparian vegetation was proposed. In the current study, the riparian forests and avifauna along with three subtropical mountainous riparian belts of Chongqing, China, were investigated, and multivariate analysis technique was adopted to examine the associations among the plants’ and birds’ species. The results show that: (1) the forest species’ composition and vertical layers are dominated by native catkins of Moraceae species, which have the reproductive traits with small and numerous propagules facilitating by frugivorous bird species, revealing an evolutionary trend different from the one in the terrestrial plant climax communities in the subtropical evergreen broad-leaved forests. The traits may provide a biological base for the plant–bird coevolution; (2) there are significant associations of plant–bird species clusters, i.e., four plant–bird coevolution groups (PBs) were divided out according to the plant species’ dominance and growth form relating to the fruit-dispersing birds’ abundance; (3) the correlation intensity within a PB ranks as PB I > II > IV > III, indicating the PB I is the leading type of coevolution mainly shaped by the dominant plant species of Moraceae; (4) the PB correlation may be a key node between patterns vs. process of a riparian ecosystem responsible for the riparian native vegetation, or even the ecosystem health. Our results contribute understanding the plant–animal coevolution interpreting the forests’ structures in riparian environments. The results may also be used by urban planner and managers to simulate the patterns for restoring a more stable riparian biota, a better functioning ecosystem in subtropical zone.

North American tree migration paced by climate in the West, lagging in the East

Suitable habitats for forest trees may be shifting fast with recent climate change. Studies tracking the shift in suitable habitat for forests have been inconclusive, in part because responses in tree fecundity and seedling establishment can diverge. Analysis of both components at a continental scale reveals a poleward migration of northern species that is in progress now. Recruitment and fecundity both contribute to poleward spread in the West, while fecundity limits spread in the East, despite a fecundity hotspot in the Southeast. Fecundity limitation on population spread can confront conservation and management efforts with persistent disequilibrium between forest diversity and rapid climate change.

Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.

An integrodifference model for vegetation patterns in semi-arid environments with seasonality

Vegetation patterns are a characteristic feature of semi-deserts occurring on all continents except Antarctica. In some semi-arid regions, the climate is characterised by seasonality, which yields a synchronisation of seed dispersal with the dry season or the beginning of the wet season. We reformulate the Klausmeier model, a reaction–advection–diffusion system that describes the plant–water dynamics in semi-arid environments, as an integrodifference model to account for the temporal separation of plant growth processes during the wet season and seed dispersal processes during the dry season. The model further accounts for nonlocal processes involved in the dispersal of seeds. Our analysis focusses on the onset of spatial patterns. The Klausmeier partial differential equations (PDE) model is linked to the integrodifference model in an appropriate limit, which yields a control parameter for the temporal separation of seed dispersal events. We find that the conditions for pattern onset in the integrodifference model are equivalent to those for the continuous PDE model and hence independent of the time between seed dispersal events. We thus conclude that in the context of seed dispersal, a PDE model provides a sufficiently accurate description, even if the environment is seasonal. This emphasises the validity of results that have previously been obtained for the PDE model. Further, we numerically investigate the effects of changes to seed dispersal behaviour on the onset of patterns. We find that long-range seed dispersal inhibits the formation of spatial patterns and that the seed dispersal kernel’s decay at infinity is a significant regulator of patterning.

Climate Change Strengthens Selection for Mast Seeding in European Beech

Climate change is altering patterns of seed production worldwide [1-4], but the potential for evolutionary responses to these changes is poorly understood. Masting (synchronous, annually variable seed production by plant populations) is selectively beneficial through economies of scale that decrease the cost of reproduction per surviving offspring [5-7]. Masting is particularly widespread in temperate trees [8, 9] impacting food webs, macronutrient cycling, carbon storage, and human disease risk [10-12], so understanding its response to climate change is important. Here, we analyze inter-individual variability in plant reproductive patterns and two economies of scale-predator satiation and pollination efficiency-and document how natural selection acting upon them favors masting. Four decades of observations for European beech (Fagus sylvatica) show that predator satiation and pollination efficiency select for individuals with higher inter-annual variability of reproduction and higher reproductive synchrony between individuals. This result confirms the long-standing theory that masting, a population-level phenomenon, is generated by selection on individuals. Furthermore, recent climate-driven increases in mean seed production have increased selection pressure from seed predators but not from pollination efficiency. Natural selection is thus acting to restore the fitness benefits of masting, which have previously decreased under a warming climate [13]. However, selection will likely take far longer (centuries) than climate warming (decades), so in the short-term, tree reproduction will be reduced because masting has become less effective at satiating seed predators. Over the long-term, evolutionary responses to climate change could potentially increase inter-annual variability of seed production of masting species.

Plant community diversity will decline more than increase under climatic warming

Regions and localities may lose many species to extinction under rapid climate change and may gain other species that colonize from nearby warmer environments. Here, it is argued that warming-induced species losses will generally exceed gains and there will be more net declines than net increases in plant community richness. Declines in richness are especially likely in water-limited climates where intensifying aridity will increasingly exceed plant tolerances, but also in colder temperature-limited climates where steep climatic gradients are lacking, and therefore, large pools of appropriate species are not immediately adjacent. The selectivity of warming-induced losses may lead to declines in functional and phylogenetic diversity as well as in species richness, especially in water-limited climates. Our current understanding of climate-caused diversity trends may be overly influenced by numerous studies coming from north-temperate alpine mountaintops, where conditions are unusually favourable for increases-possibly temporary-in local species richness. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Extinction debts and colonization credits of non-forest plants in the European Alps

Mountain plant species shift their elevational ranges in response to climate change. However, to what degree these shifts lag behind current climate change, and to what extent delayed extinctions and colonizations contribute to these shifts, are under debate. Here, we calculate extinction debt and colonization credit of 135 species from the European Alps by comparing species distribution models with 1576 re-surveyed plots. We find extinction debt in 60% and colonization credit in 38% of the species, and at least one of the two in 93%. This suggests that the realized niche of very few of the 135 species fully tracks climate change. As expected, extinction debts occur below and colonization credits occur above the optimum elevation of species. Colonization credits are more frequent in warmth-demanding species from lower elevations with lower dispersal capability, and extinction debts are more frequent in cold-adapted species from the highest elevations. Local extinctions hence appear to be already pending for those species which have the least opportunity to escape climate warming.

Cracking the Code of Biodiversity Responses to Past Climate Change

How individual species and entire ecosystems will respond to future climate change are among the most pressing questions facing ecologists. Past biodiversity dynamics recorded in the paleoecological archives show a broad array of responses, yet significant knowledge gaps remain. In particular, the relative roles of evolutionary adaptation, phenotypic plasticity, and dispersal in promoting survival during times of climate change have yet to be clarified. Investigating the paleo-archives offers great opportunities to understand biodiversity responses to future climate change. In this review we discuss the mechanisms by which biodiversity responds to environmental change, and identify gaps of knowledge on the role of range shifts and tolerance. We also outline approaches at the intersection of paleoecology, genomics, experiments, and predictive models that will elucidate the processes by which species have survived past climatic changes and enhance predictions of future changes in biological diversity.

Range dynamics of mountain plants decrease with elevation

Many studies report that mountain plant species are shifting upward in elevation. However, the majority of these reports focus on shifts of upper limits. Here, we expand the focus and simultaneously analyze changes of both range limits, optima, and abundances of 183 mountain plant species. We therefore resurveyed 1,576 vegetation plots first recorded before 1970 in the European Alps. We found that both range limits and optima shifted upward in elevation, but the most pronounced trend was a mean increase in species abundance. Despite huge species-specific variation, range dynamics showed a consistent trend along the elevational gradient: Both range limits and optima shifted upslope faster the lower they were situated historically, and species' abundance increased more for species from lower elevations. Traits affecting the species' dispersal and persistence capacity were not related to their range dynamics. Using indicator values to stratify species by their thermal and nutrient demands revealed that elevational ranges of thermophilic species tended to expand, while those of cold-adapted species tended to contract. Abundance increases were strongest for nutriphilous species. These results suggest that recent climate warming interacted with airborne nitrogen deposition in driving the observed dynamics. So far, the majority of species appear as "winners" of recent changes, yet "losers" are overrepresented among high-elevation, cold-adapted species with low nutrient demands. In the decades to come, high-alpine species may hence face the double pressure of climatic changes and novel, superior competitors that move up faster than they themselves can escape to even higher elevations.

Vulnerability of eastern US tree species to climate change

Climate change is expected to alter the distribution of tree species because of critical environmental tolerances related to growth, mortality, reproduction, disturbances, and biotic interactions. How this is realized in 21st century remains uncertain, in large part due to limitations on plant migration and the impacts of landscape fragmentation. Understanding these changes is of particular concern for forest management, which requires information at an appropriately fine spatial resolution. Here we provide a framework and application for tree species vulnerability to climate change in the eastern United States that accounts for influential drivers of future distributions. We used species distribution models to project changes in habitat suitability at 800 m for 40 tree species that vary in physiology, range, and environmental niche. We then developed layers of adaptive capacity based on migration potential, forest fragmentation, and propagule pressure. These were combined into metrics of vulnerability, including an overall index and spatially explicit categories designed to inform management. Despite overall favorable changes in suitability, the majority of species and the landscape were considered vulnerable to climate change. Vulnerability was significantly exacerbated by projections of pests and pathogens for some species. Northern and high-elevation species tended to be the most vulnerable. There were, however, some notable areas of particular resilience, including most of West Virginia. Our approach combines some of the most important considerations for species vulnerability in a straightforward framework, and can be used as a tool for managers to prioritize species, areas, and actions.

Study design and parameter estimability for spatial and temporal ecological models

The statistical tools available to ecologists are becoming increasingly sophisticated, allowing more complex, mechanistic models to be fit to ecological data. Such models have the potential to provide new insights into the processes underlying ecological patterns, but the inferences made are limited by the information in the data. Statistical nonestimability of model parameters due to insufficient information in the data is a problem too‐often ignored by ecologists employing complex models. Here, we show how a new statistical computing method called data cloning can be used to inform study design by assessing the estimability of parameters under different spatial and temporal scales of sampling. A case study of parasite transmission from farmed to wild salmon highlights that assessing the estimability of ecologically relevant parameters should be a key step when designing studies in which fitting complex mechanistic models is the end goal.

Late Quaternary climate stability and the origins and future of global grass endemism

BACKGROUND AND AIMS

Earth's climate is dynamic, with strong glacial-interglacial cycles through the Late Quaternary. These climate changes have had major consequences for the distributions of species through time, and may have produced historical legacies in modern ecological patterns. Unstable regions are expected to contain few endemic species, many species with strong dispersal abilities, and to be susceptible to the establishment of exotic species from relatively stable regions. We test these hypotheses with a global dataset of grass species distributions.

METHODS

We described global patterns of endemism, variation in the potential for rapid population spread, and exotic establishment in grasses. We then examined relationships of these response variables to a suite of predictor variables describing the mean, seasonality and spatial pattern of current climate and the temperature change velocity from the Last Glacial Maximum to the present.

KEY RESULTS

Grass endemism is strongly concentrated in regions with historically stable climates. It also depends on the spatial pattern of current climate, with many endemic species in areas with regionally unusual climates. There was no association between the proportion of annual species (representing potential population spread rates) and climate change velocity. Rather, the proportion of annual species depended very strongly on current temperature. Among relatively stable regions (<10 m year^-1), increasing velocity decreased the proportion of species that were exotic, but this pattern reversed for higher-velocity regions (>10 m year^-1). Exotic species were most likely to originate from relatively stable regions with climates similar to those found in their exotic range.

CONCLUSIONS

Long-term climate stability has important influences on global endemism patterns, largely confirming previous work from other groups. Less well recognized is its role in generating patterns of exotic species establishment. This result provides an important historical context for the conjecture that climate change in the near future may promote species invasions.

Establishing a baseline on the distribution and pattern of occurrence of Salvadora persica L. with meteorological data and assessing its adaptation in the adjacent warmed-up zones

The natural occurrence of Salvadora persica L., stretching from the coastal area of the Arabian sea to northward along the Indus floodplains, was surveyed to document the pattern of its occurrence with the available meteorological record showing increasing trends of frost northwards. Information was compiled from various sources to generate the past and present temperature data in order to establish relationship between the changing temperature factors and the extent of the area available due to climate change over the years for introducing species beyond its range of natural distribution. In addition, the species was experimentally introduced in the warmed-up zones to monitor its performance and to evaluate its adaptability. The reconnaissance survey showed that the natural populations of thorn forest communities with S. persica, as associate, are now surviving only as degraded remnants. Its common occurrence is documented in zones where the mean winter temperatures are above the threshold level of frost, whereas it is rarely found in zones where it drops below this level for a single month, which seems to be its range edge. S. persica does not occur in zones where low temperature could persist for 2 months. Recent temperature data suggests that the month of December has warmed up above the threshold level; therefore, it was expected that correspondingly the range edge of the frost-sensitive species has potentially shifted further northwards. The response of the species introduced at the experimental sites beyond its natural occurrence suggests high survival and growth, demonstrating its adaptability to the new sites beyond its limit of distribution.

The impacts of increasing drought on forest dynamics, structure, and biodiversity in the United States

We synthesize insights from current understanding of drought impacts at stand-to-biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand-level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. In the eastern US, the effects of increasing drought are becoming better understood at the level of individual trees, but this knowledge cannot yet be confidently translated to predictions of changing structure and diversity of forest stands. While eastern forests have not experienced the types of changes seen in western forests in recent decades, they too are vulnerable to drought and could experience significant changes with increased severity, frequency, or duration in drought. Throughout the continental United States, the combination of projected large climate-induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought-tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.

How Far Can the Palm Weevil, Rhynchophorus vulneratus (Coleoptera: Curculionidae), Fly?

The palm weevil, Rhynchophorus vulneratus, is native to Southeast Asia and was recovered from an infested Canary Islands date palm in Laguna Beach, California, USA, in 2010. The detection of this potentially destructive palm pest initiated a detection, containment, and eradication program that was reliant, in part, on the deployment of bucket traps loaded with aggregation pheromone and baited with fermenting fruit. A key question that pertained to the deployment of traps was “how far can R. vulneratus fly?” This question could not be answered and in response to this knowledge deficit, computerized flight mill studies were conducted with field-captured R. vulneratus in an outdoor screen house in Sumatra, Indonesia. Of the 63 weevils tethered to flight mills, ∼27% failed to fly >1 km in 24 h and were excluded from analyses. In total, 46 weevils (35 females and 11 males) flew >1 km on flight mills and of these adults, the average total distance flown in 24 h was significantly greater for females (∼32 km) when compared with males (∼15 km). A small proportion of females (∼16%) flew 50-80 km, and one female flew 100.1 km in 24 h. Flying weevils exhibited an average weight loss of ∼13–17% and non-flying control weevils (n=27) lost 10–13% body weight in 24 h. The distribution of flight distances for female and male weevils combined was leptokurtic, which suggests that faster than expected spread by R. vulneratus may be possible in invaded areas.

Species traits and climate velocity explain geographic range shifts in an ocean-warming hotspot

Species' ranges are shifting globally in response to climate warming, with substantial variability among taxa, even within regions. Relationships between range dynamics and intrinsic species traits may be particularly apparent in the ocean, where temperature more directly shapes species' distributions. Here, we test for a role of species traits and climate velocity in driving range extensions in the ocean-warming hotspot of southeast Australia. Climate velocity explained some variation in range shifts, however, including species traits more than doubled the variation explained. Swimming ability, omnivory and latitudinal range size all had positive relationships with range extension rate, supporting hypotheses that increased dispersal capacity and ecological generalism promote extensions. We find independent support for the hypothesis that species with narrow latitudinal ranges are limited by factors other than climate. Our findings suggest that small-ranging species are in double jeopardy, with limited ability to escape warming and greater intrinsic vulnerability to stochastic disturbances.

Environmental factors contribute to the formation and maintenance of the contact zone observed in deciduous broad-leaved tree species in Japan

Contact zones are defined as areas where populations from different refugia meet during a postglacial expansion and distinct DNA lineages are mixedly distributed. In Japan, contact zones of various plants and animals were reported from the Kinki-Chugoku region. These contact zones appear to be maintained without any drastic topographic barriers such as those observed in the Alps and Pyrenees Mountains. In this study, the mechanisms underlying the formation and/or maintenance of these contact zones were investigated using six deciduous broad-leaved tree species (Carpinus laxiflora, C. tschonoskii, C. japonica, Magnolia obovata, Padus grayana, and Euonymus oxyphyllus). First, the precise location of the contact zones was examined by intensive genetic analysis of the six species. Second, the relationships between the geographic location of the contact zone and various environmental factors, including climate and topography, were investigated by generalized additive models to reveal the mechanisms of the formation and maintenance of the contact zones. As a result, four of the six examined plant species clearly showed a geographically common contact zone in Hyogo Prefecture and its adjacent areas. The results of the generalized additive models indicate that the pattern of low habitat suitability estimated by ecological niche modeling was the most important factor for determining the location of the common contact zone. These results suggest that areas with low habitat suitability in Hyogo Prefecture restrict the migration and gene flow of the four species in this region, and thus, they maintain the pattern of the contact zones. This study suggests that there are major effects of habitat suitability on the formation and maintenance of the contact zones.

Integrating physiological threshold experiments with climate modeling to project mangrove species' range expansion

Predictions of climate-related shifts in species ranges have largely been based on correlative models. Due to limitations of these models, there is a need for more integration of experimental approaches when studying impacts of climate change on species distributions. Here, we used controlled experiments to identify physiological thresholds that control poleward range limits of three species of mangroves found in North America. We found that all three species exhibited a threshold response to extreme cold, but freeze tolerance thresholds varied among species. From these experiments, we developed a climate metric, freeze degree days (FDD), which incorporates both the intensity and the frequency of freezes. When included in distribution models, FDD accurately predicted mangrove presence/absence. Using 28 years of satellite imagery, we linked FDD to observed changes in mangrove abundance in Florida, further exemplifying the importance of extreme cold. We then used downscaled climate projections of FDD to project that these range limits will move northward by 2.2-3.2 km yr(-1) over the next 50 years.

Marine population connectivity: reconciling large-scale dispersal and high self-retention

Predicting connectivity patterns in systems with fluid transport requires descriptions of the spatial distribution of propagules. In contrast to research on terrestrial seed dispersal, where much attention has focused on localized physical factors affecting dispersal, studies of oceanic propagule dispersal have often emphasized the role of large-scale factors. We link these two perspectives by exploring how propagule dispersal in the ocean is influenced by the "coastal boundary layer" (CBL), a region of reduced velocities near the shoreline that might substantially modify local-scale dispersal. We used a simple simulation model to demonstrate that accounting for the CBL markedly alters transport distances, the widths of dispersal distributions, and the fraction of larvae retained near their sites of origin (self-retention). Median dispersal distances were up to 59% shorter in simulations with a CBL than in those without. Self-retention of larvae increased by up to 3 orders of magnitude in the presence of CBLs, but only minor changes arose in the long-distance tails of the distributions, resulting in asymmetric, non-Gaussian kernels analogous to those quantified for terrestrial seed dispersal. Because successfully settling larvae are commonly those that remain close to shore and interact with the CBL, ignoring this pervasive oceanographic feature will substantially alter predictions of population self-persistence, estimates of connectivity, and outcomes of metapopulation analyses.

Acceleration of evolutionary spread by long-range dispersal

The spreading of evolutionary novelties across populations is the central element of adaptation. Unless populations are well mixed (like bacteria in a shaken test tube), the spreading dynamics depend not only on fitness differences but also on the dispersal behavior of the species. Spreading at a constant speed is generally predicted when dispersal is sufficiently short ranged, specifically when the dispersal kernel falls off exponentially or faster. However, the case of long-range dispersal is unresolved: Although it is clear that even rare long-range jumps can lead to a drastic speedup--as air-traffic-mediated epidemics show--it has been difficult to quantify the ensuing stochastic dynamical process. However, such knowledge is indispensable for a predictive understanding of many spreading processes in natural populations. We present a simple iterative scaling approximation supported by simulations and rigorous bounds that accurately predicts evolutionary spread, which is determined by a trade-off between frequency and potential effectiveness of long-distance jumps. In contrast to the exponential laws predicted by deterministic "mean-field" approximations, we show that the asymptotic spatial growth is according to either a power law or a stretched exponential, depending on the tails of the dispersal kernel. More importantly, we provide a full time-dependent description of the convergence to the asymptotic behavior, which can be anomalously slow and is relevant even for long times. Our results also apply to spreading dynamics on networks with a spectrum of long-range links under certain conditions on the probabilities of long-distance travel: These are relevant for the spread of epidemics.

Topo-climatic microrefugia explain the persistence of a rare endemic plant in the Alps during the last 21 millennia

Ongoing rapid climate change is predicted to cause local extinction of plant species in mountain regions. However, some plant species could have persisted during Quaternary climate oscillations without shifting their range, despite the limited evidence from fossils. Here, we tested two candidate mechanisms of persistence by comparing the macrorefugia and microrefugia (MR) hypotheses. We used the rare and endemic Saxifraga florulenta as a model taxon and combined ensembles of species distribution models (SDMs) with a high-resolution paleoclimatic and topographic dataset to reconstruct its potential current and past distribution since the last glacial maximum. To test the macrorefugia hypothesis, we verified whether the species could have persisted in or shifted to geographic areas defined by its realized niche. We then identified potential MR based on climatic and topographic properties of the landscape and applied refined scenarios of MR dynamics and functions over time. Last, we quantified the number of known occurrences that could be explained by either the macrorefugia or MR model. A consensus of two or three SDM techniques predicted absence between 14-10, 3-4 and 1 ka bp, which did not support the macrorefugia model. In contrast, we showed that S. florulenta could have contracted into MR during periods of absence predicted by the SDMs and later re-colonized suitable areas according to the macrorefugia model. Assuming a limited and realistic seed dispersal distance for our species, we explained a large number of the current occurrences (61-96%). Additionally, we showed that MR could have facilitated range expansions or shifts of S. florulenta. Finally, we found that the most recent and the most stable MR were the ones closest to current occurrences. Hence, we propose a novel paradigm to explain plant persistence by highlighting the importance of supporting functions of MR when forecasting the fate of plant species under climate change.

On improving the communication between models and data

The potential for model-data synthesis is growing in importance as we enter an era of 'big data', greater connectivity and faster computation. Realizing this potential requires that the research community broaden its perspective about how and why they interact with models. Models can be viewed as scaffolds that allow data at different scales to inform each other through our understanding of underlying processes. Perceptions of relevance, accessibility and informatics are presented as the primary barriers to broader adoption of models by the community, while an inability to fully utilize the breadth of expertise and data from the community is a primary barrier to model improvement. Overall, we promote a community-based paradigm to model-data synthesis and highlight some of the tools and techniques that facilitate this approach. Scientific workflows address critical informatics issues in transparency, repeatability and automation, while intuitive, flexible web-based interfaces make running and visualizing models more accessible. Bayesian statistics provides powerful tools for assimilating a diversity of data types and for the analysis of uncertainty. Uncertainty analyses enable new measurements to target those processes most limiting our predictive ability. Moving forward, tools for information management and data assimilation need to be improved and made more accessible.

Rapid shifts in dispersal behavior on an expanding range edge

Dispersal biology at an invasion front differs from that of populations within the range core, because novel evolutionary and ecological processes come into play in the nonequilibrium conditions at expanding range edges. In a world where species' range limits are changing rapidly, we need to understand how individuals disperse at an invasion front. We analyzed an extensive dataset from radio-tracking invasive cane toads (Rhinella marina) over the first 8 y since they arrived at a site in tropical Australia. Movement patterns of toads in the invasion vanguard differed from those of individuals in the same area postcolonization. Our model discriminated encamped versus dispersive phases within each toad's movements and demonstrated that pioneer toads spent longer periods in dispersive mode and displayed longer, more directed movements while they were in dispersive mode. These analyses predict that overall displacement per year is more than twice as far for toads at the invasion front compared with those tracked a few years later at the same site. Studies on established populations (or even those a few years postestablishment) thus may massively underestimate dispersal rates at the leading edge of an expanding population. This, in turn, will cause us to underpredict the rates at which invasive organisms move into new territory and at which native taxa can expand into newly available habitat under climate change.

How will biotic interactions influence climate change-induced range shifts?

Biotic interactions present a challenge in determining whether species distributions will track climate change. Interactions with competitors, consumers, mutualists, and facilitators can strongly influence local species distributions, but few studies assess how and whether these interactions will impede or accelerate climate change-induced range shifts. In this paper, we explore how ecologists might move forward on this question. We first outline the conditions under which biotic interactions can result in range shifts that proceed faster or slower than climate velocity and result in ecological surprises. Next, we use our own work to demonstrate that experimental studies documenting the strength of biotic interactions across large environmental gradients are a critical first step for understanding whether they will influence climate change-induced range shifts. Further progress could be made by integrating results from these studies into modeling frameworks to predict how or generalize when biotic interactions mediate how changing climates influence range shifts. Finally, we argue that many more case studies like those described here are needed to explore the importance of biotic interactions during climate change-induced range shifts.

Disequilibrium vegetation dynamics under future climate change

PREMISE OF THE STUDY

Near-future climate changes are likely to elicit major vegetation changes. Disequilibrium dynamics, which occur when vegetation comes out of equilibrium with climate, are potentially a key facet of these. Understanding these dynamics is crucial for making accurate predictions, informing conservation planning, and understanding likely changes in ecosystem function on time scales relevant to society. However, many predictive studies have instead focused on equilibrium end-points with little consideration of the transient trajectories.

METHODS

We review what we should expect in terms of disequilibrium vegetation dynamics over the next 50-200 yr, covering a broad range of research fields including paleoecology, macroecology, landscape ecology, vegetation science, plant ecology, invasion biology, global change biology, and ecosystem ecology.

KEY RESULTS

The expected climate changes are likely to induce marked vegetation disequilibrium with climate at both leading and trailing edges, with leading-edge disequilibrium dynamics due to lags in migration at continental to landscape scales, in local population build-up and succession, in local evolutionary responses, and in ecosystem development, and trailing-edge disequilibrium dynamics involving delayed local extinctions and slow losses of ecosystem structural components. Interactions with habitat loss and invasive pests and pathogens are likely to further contribute to disequilibrium dynamics. Predictive modeling and climate-change experiments are increasingly representing disequilibrium dynamics, but with scope for improvement.

CONCLUSIONS

The likely pervasiveness and complexity of vegetation disequilibrium is a major challenge for forecasting ecological dynamics and, combined with the high ecological importance of vegetation, also constitutes a major challenge for future nature conservation.

Winter climate change and coastal wetland foundation species: salt marshes vs. mangrove forests in the southeastern United States

We live in an era of unprecedented ecological change in which ecologists and natural resource managers are increasingly challenged to anticipate and prepare for the ecological effects of future global change. In this study, we investigated the potential effect of winter climate change upon salt marsh and mangrove forest foundation species in the southeastern United States. Our research addresses the following three questions: (1) What is the relationship between winter climate and the presence and abundance of mangrove forests relative to salt marshes; (2) How vulnerable are salt marshes to winter climate change-induced mangrove forest range expansion; and (3) What is the potential future distribution and relative abundance of mangrove forests under alternative winter climate change scenarios? We developed simple winter climate-based models to predict mangrove forest distribution and relative abundance using observed winter temperature data (1970-2000) and mangrove forest and salt marsh habitat data. Our results identify winter climate thresholds for salt marsh-mangrove forest interactions and highlight coastal areas in the southeastern United States (e.g., Texas, Louisiana, and parts of Florida) where relatively small changes in the intensity and frequency of extreme winter events could cause relatively dramatic landscape-scale ecosystem structural and functional change in the form of poleward mangrove forest migration and salt marsh displacement. The ecological implications of these marsh-to-mangrove forest conversions are poorly understood, but would likely include changes for associated fish and wildlife populations and for the supply of some ecosystem goods and services.

Rapid northward spread of a zooxanthellate coral enhanced by artificial structures and sea warming in the western Mediterranean

The hermatypic coral Oculina patagonica can drive a compositional shift in shallow water benthic marine communities in the northwestern Mediterranean. Here, we analyze a long-term, large-scale observational dataset to characterize the dynamics of the species' recent northward range shift along the coast of Catalonia and examine the main factors that could have influenced this spread. The variation in the distributional range of Oculina patagonica was examined by monitoring 223 locations including natural and artificial habitats along >400 km of coastline over the last 19 years (1992–2010). Abundance of the species increased from being present in one location in 1992 to occur on 19% of the locations in 2010, and exhibited an acceleration of its spreading over time driven by the join action of neighborhood and long-distance dispersal. However, the pattern of spread diverged between artificial and natural habitats. A short lag phase and a high slope on the exponential phase characterized the temporal pattern of spread on artificial habitats in contrast to that observed on natural ones. Northward expansion has occurred at the fastest rate (22 km year⁻¹) reported for a coral species thus far, which is sufficiently fast to cope with certain climate warming predictions. The pattern of spread suggests that this process is mediated by the interplay of (i) the availability of open space provided by artificial habitats, (ii) the seawater temperature increase with the subsequent extension of the growth period, and (iii) the particular biological features of O. patagonica (current high growth rates, early reproduction, and survival to low temperature and in polluted areas). These results are indicative of an ongoing fundamental modification of temperate shallow water assemblages, which is consistent with the predictions indicating that the Mediterranean Sea is one of the most sensitive regions to global change.

Multiscale analysis of compartment models with dispersal

The characterization of the population dynamics of animal populations and dispersal provides the underlying setting of this article. Novel results emerge from our exploration of the role of disease in this context. We focus on the study of the impact of dispersal on the dynamics of populations that account for (a) induced Allee effects; (b) disease dynamics; and (c) spatial heterogeneity, using deterministic and stochastic models. Specifically, the models incorporate disease-driven effects on the individuals' competitive ability to acquire resources as well as on their ability to move or reproduce. The results bring to the forefront the role of initial conditions and patch quality as well as 'topological' structure or connectivity landscape structure (the physical space where individuals move, reproduce, get sick, die, or compete for resources). The emphasis is placed on the dynamics of populations when disease is an important selective force. This article surveys the appropriate literature while including original research.

Fish dispersal in fragmented landscapes: a modeling framework for quantifying the permeability of structural barriers

Dispersal is a key determinant of the spatial distribution and abundance of populations, but human-made fragmentation can create barriers that hinder dispersal and reduce population viability. This study presents a modeling framework based on dispersal kernels (modified Laplace distributions) that describe stream fish dispersal in the presence of obstacles to passage. We used mark-recapture trials to quantify summer dispersal of brook trout (Salvelinus fontinalis) in four streams crossed by a highway. The analysis identified population heterogeneity in dispersal behavior, as revealed by the presence of a dominant sedentary component (48-72% of all individuals) characterized by short mean dispersal distance (<10 m), and a secondary mobile component characterized by longer mean dispersal distance (56-1086 m). We did not detect evidence of barrier effects on dispersal through highway crossings. Simulation of various plausible scenarios indicated that detectability of barrier effects was strongly dependent on features of sampling design, such as spatial configuration of the sampling area, barrier extent, and sample size. The proposed modeling framework extends conventional dispersal kernels by incorporating structural barriers. A major strength of the approach is that ecological process (dispersal model) and sampling design (observation model) are incorporated simultaneously into the analysis. This feature can facilitate the use of prior knowledge to improve sampling efficiency of mark-recapture trials in movement studies. Model-based estimation of barrier permeability and its associated uncertainty provides a rigorous approach for quantifying the effect of barriers on stream fish dispersal and assessing population dynamics of stream fish in fragmented landscapes.

Disentangling effects of uncertainties on population projections: climate change impact on an epixylic bryophyte

Assessment of future ecosystem risks should account for the relevant uncertainty sources. This means accounting for the joint effects of climate variables and using modelling techniques that allow proper treatment of uncertainties. We investigate the influence of three of the IPCC's scenarios of greenhouse gas emissions (special report on emission scenarios (SRES)) on projections of the future abundance of a bryophyte model species. We also compare the relative importance of uncertainty sources on the population projections. The whole chain global climate model (GCM)-regional climate model-population dynamics model is addressed. The uncertainty depends on both natural- and model-related sources, in particular on GCM uncertainty. Ignoring the uncertainties gives an unwarranted impression of confidence in the results. The most likely population development of the bryophyte Buxbaumia viridis towards the end of this century is negative: even with a low-emission scenario, there is more than a 65 per cent risk for the population to be halved. The conclusion of a population decline is valid for all SRES scenarios investigated. Uncertainties are no longer an obstacle, but a mandatory aspect to include in the viability analysis of populations.

Modeling range dynamics in heterogeneous landscapes: invasion of the hemlock woolly adelgid in eastern North America

Range expansion by native and exotic species will continue to be a major component of global change. Anticipating the potential effects of changes in species distributions requires models capable of forecasting population spread across realistic, heterogeneous landscapes and subject to spatiotemporal variability in habitat suitability. Several decades of theory and model development, as well as increased computing power and availability of fine-resolution GIS data, now make such models possible. Still unanswered, however, is the question of how well this new generation of dynamic models will anticipate range expansion. Here we develop a spatially explicit stochastic model that combines dynamic dispersal and population processes with fine-resolution maps characterizing spatiotemporal heterogeneity in climate and habitat to model range expansion of the hemlock woolly adelgid (HWA; Adelges tsugae). We parameterize this model using multiyear data sets describing population and dispersal dynamics of HWA and apply it to eastern North America over a 57-year period (1951-2008). To evaluate the model, the observed pattern of spread of HWA during this same period was compared to model predictions. Our model predicts considerable heterogeneity in the risk of HWA invasion across space and through time, and it suggests that spatiotemporal variation in winter temperature, rather than hemlock abundance, exerts a primary control on the spread of HWA. Although the simulations generally matched the observed current extent of the invasion of HWA and patterns of anisotropic spread, it did not correctly predict when HWA was observed to arrive in different geographic regions. We attribute differences between the modeled and observed dynamics to an inability to capture the timing and direction of long-distance dispersal events that substantially affected the ensuing pattern of spread.

Long-distance gene flow and adaptation of forest trees to rapid climate change

Forest trees are the dominant species in many parts of the world and predicting how they might respond to climate change is a vital global concern. Trees are capable of long-distance gene flow, which can promote adaptive evolution in novel environments by increasing genetic variation for fitness. It is unclear, however, if this can compensate for maladaptive effects of gene flow and for the long-generation times of trees. We critically review data on the extent of long-distance gene flow and summarise theory that allows us to predict evolutionary responses of trees to climate change. Estimates of long-distance gene flow based both on direct observations and on genetic methods provide evidence that genes can move over spatial scales larger than habitat shifts predicted under climate change within one generation. Both theoretical and empirical data suggest that the positive effects of gene flow on adaptation may dominate in many instances. The balance of positive to negative consequences of gene flow may, however, differ for leading edge, core and rear sections of forest distributions. We propose future experimental and theoretical research that would better integrate dispersal biology with evolutionary quantitative genetics and improve predictions of tree responses to climate change.