Traits help explain species' performance away from their climate niche centre

Aim

Climate change impacts on biota are variable across sites, among species and throughout individual species' ranges. Niche theory predicts that population performance should decline as site climate becomes increasingly different from the species' climate niche centre, though studies find significant variation from these predictions. Here, we propose that predictions about climate responses can be improved by incorporating species' trait information.

Location

Europe.

Methods

We used observations of plant species abundance change over time to assess variation in climate difference sensitivity (CDS), defined as how species performance (colonization, extinction and abundance change) relates to the difference of site climate from the mean temperature and precipitation of each species' range. We then investigated if leaf economics, plant size and seed mass traits were associated with the species' CDS.

Results

Species that performed better (e.g. increased in abundance) towards sites progressively cooler than their niche centre were shorter and had more resource-acquisitive leaves (i.e. lower leaf dry matter content or LDMC) relative to species with zero or the opposite pattern of temperature difference sensitivity. This result supports the hypothesis that if sites cooler than niche centres are more stressful for a species, then shorter stature is advantageous compared with taller species. The LDMC result suggests the environment selects for more resource-acquisitive leaf strategies towards relatively cooler climates with shorter growing seasons, counter to expectations that conservative strategies would be favoured in such environments. We found few consistent relationships between precipitation difference sensitivities and traits.

Main Conclusions

The results supported key a priori foundations on how trait-based plant strategies dictate species responses to climate variation away from their niche centre. Furthermore, plant height emerged as the most consistent trait that varied with species CDS, suggesting height will be key for theory development around species response to climate change.     

Competition and facilitation structure plant communities under nurse tree canopies in extremely stressful environments

Nurse plant facilitation in stressful environments can produce an environment with relatively low stress under its canopy. These nurse plants may produce the conditions promoting intense competition between coexisting species under the canopy, and canopies may establish stress gradients, where stress increases toward the edge of the canopy. Competition and facilitation on these stress gradients may control species distributions in the communities under canopies. We tested the following predictions: (1) interactions between understory species shift from competition to facilitation in habitats experiencing increasing stress from the center to the edge of canopy of a nurse plant, and (2) species distributions in understory communities are controlled by competitive interactions at the center of canopy, and facilitation at the edge of the canopy. We tested these predictions using a neighbor removal experiment under nurse trees growing in arid environments. Established individuals of each of four of the most common herbaceous species in the understory were used in the experiment. Two species were more frequent in the center of the canopy, and two species were more frequent at the edge of the canopy. Established individuals of each species were subjected to neighbor removal or control treatments in both canopy center and edge habitats. We found a shift from competitive to facilitative interactions from the center to the edge of the canopy. The shift in the effect of neighbors on the target species can help to explain species distributions in these canopies. Canopy‐dominant species only perform well in the presence of neighbors in the edge microhabitat. Competition from canopy‐dominant species can also limit the performance of edge‐dominant species in the canopy microhabitat. The shift from competition to facilitation under nurse plant canopies can structure the understory communities in extremely stressful environments.     

Extinction risk of Chinese angiosperms varies between woody and herbaceous species

Aim

Understanding how species' traits and environmental contexts relate to extinction risk is a critical priority for ecology and conservation biology. This study aims to identify and explore factors related to extinction risk between herbaceous and woody angiosperms to facilitate more effective conservation and management strategies and understand the interactions between environmental threats and species' traits.

Location

China.

Taxon

Angiosperms.

Methods

We obtained a large dataset including five traits, six extrinsic variables, and 796,118 occurrence records for 14,888 Chinese angiosperms. We assessed the phylogenetic signal and used phylogenetic generalized least squares regressions to explore relationships between extinction risk, plant traits, and extrinsic variables in woody and herbaceous angiosperms. We also used phylogenetic path analysis to evaluate causal relationships among traits, climate variables, and extinction risk of different growth forms.

Results

The phylogenetic signal of extinction risk differed among woody and herbaceous species. Angiosperm extinction risk was mainly affected by growth form, altitude, mean annual temperature, normalized difference vegetation index, and precipitation change from 1901 to 2020. Woody species' extinction risk was strongly affected by height and precipitation, whereas extinction risk for herbaceous species was mainly affected by mean annual temperature rather than plant traits.

Main conclusions

Woody species were more likely to have higher extinction risks than herbaceous species under climate change and extinction threat levels varied with both plant traits and extrinsic variables. The relationships we uncovered may help identify and protect threatened plant species and the ecosystems that rely on them.     

Plant recolonization of reclamation areas from patches of salvaged forest floor material

Question

Understorey development is a great challenge in the restoration of many forest sites, particularly when sources of vegetation propagules are scarce. Can placement of propagule‐rich soil patches within reclaimed landscapes otherwise covered with propagule‐poor material promote the dispersal of vegetation from the patches into the surrounding areas?

Location

Large reclamation site in the Canadian (Alberta) boreal forest.

Method

Patches of propagule‐rich forest floor material were placed within a matrix of propagule‐poor peat material. Vegetation assessments (cover estimates, seed rain) were done surrounding these patches in the third and fourth growing seasons.

Results

There was significant egress of species from the patches into the peat after four growing seasons, and overall species associated with the patches had higher cover in the peat than species that were associated with the peat itself. While wind‐dispersed herbaceous species from the patches were found at the leading edge of the egressing community, most species used vegetative propagation, resulting in short egress distances. Several patch‐associated species were found in seed rain collected on the peat areas but were not observed in this material, suggesting seedbed limitations.

Conclusion

Despite the relatively short distance of egress, this experiment suggests that placement of propagule‐rich soil material within reclaimed landscapes will promote egress into adjacent propagule‐poor soil material.     

Facilitation allows plant coexistence in Cuban serpentine soils

Serpentine soils represent stressful habitats where plants have to cope with heavy metals, moisture limitation and low nutrient availability. We propose that facilitation is an important mechanism structuring plant communities under such stressful conditions. Facilitation has been shown to generate the spatial association of species, forming discrete vegetation patches of phylogenetically distant species. We measured these spatial and phylogenetic signatures left by facilitation in a serpentine plant community of central Cuba. Our results show that seedlings preferentially grow under plants of different species, and that adults are significantly aggregated into vegetation patches. In these patches, adults tend to co‐occur with distant relatives, ultimately forming phylogenetically diverse neighbourhoods. We discuss possible mechanisms explaining how species adapted to serpentine areas may be acting as nurses, reducing the stressful conditions for the establishment of other species.     

Species distributions models may predict accurately future distributions but poorly how distributions change: A critical perspective on model validation

Aim

Species distribution models (SDMs) are widely used to make predictions on how species distributions may change as a response to climatic change. To assess the reliability of those predictions, they need to be critically validated with respect to what they are used for. While ecologists are typically interested in how and where distributions will change, we argue that SDMs have seldom been evaluated in terms of their capacity to predict such change. Instead, typical retrospective validation methods estimate model's ability to predict to only one static time in future. Here, we apply two validation methods, one that predicts and evaluates a static pattern, while the other measures change and compare their estimates of predictive performance.

Location

Fennoscandia.

Methods

We applied a joint SDM to model the distributions of 120 bird species in four model validation settings. We trained models with a dataset from 1975 to 1999 and predicted species' future occurrence and abundance in two ways: for one static time period (2013–2016, ‘static validation’) and for a change between two time periods (difference between 1996–1999 and 2013–2016, ‘change validation’). We then measured predictive performance using correlation between predicted and observed values. We also related predictive performance to species traits.

Results

Even though static validation method evaluated predictive performance as good, change method indicated very poor performance. Predictive performance was not strongly related to any trait.

Main Conclusions

Static validation method might overestimate predictive performance by not revealing the model's inability to predict change events. If species' distributions remain mostly stable, then even an unfit model can predict the near future well due to temporal autocorrelation. We urge caution when working with forecasts of changes in spatial patterns of species occupancy or abundance, even for SDMs that are based on time series datasets unless they are critically validated for forecasting such change.     

The influence of floral symmetry,dependence on pollinators and pollination generalization on flower size variation

Background and Aims

The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared with actinomorphic flowers. However, the degree of ecological generalization and of dependence on pollinators varies greatly among species of both flower symmetry types and this may also affect flower size variation.

Methods

Data on 43 species from two contrasting communities (one alpine and one lowland community) were used to test the relationships and interactions between flower size phenotypic variation, floral symmetry, ecological pollination generalization and species'' dependence on pollinators.

Key Results

Contrary to what was expected, higher flower size variation was found in zygomorphic than in actinomorphic species in the lowland community, and no difference in flower size variation was found between symmetry types in the alpine community. The relationship between floral symmetry and flower size variation depended on ecological generalization and species'' dependence on pollinators, although the influence of ecological generalization was only detected in the alpine community. Zygomorphic species that were highly dependent on pollinators and that were ecologically specialized were less variable in flower size than ecologically generalist and selfing zygomorphic species, supporting the pollinator-mediated stabilizing selection hypothesis. However, these relationships were not found in actinomorphic species, probably because they are not dependent on any particular pollinator for efficient pollination and therefore their flower size always shows moderate levels of variation.

Conclusions

The study suggests that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species'' dependence on pollinators.     

Causal inference and large-scale expert validation shed light on the drivers of SDM accuracy and variance

Aim

To develop a causal understanding of the drivers of Species distribution model (SDM) performance.

Location

United Kingdom (UK).

Methods

We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.

Results

According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.

Main conclusions

Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile.     

Shift from facilitative to neutral interactions by the cushion plant Silene acaulis along a primary succession gradient

Background

The stress‐gradient hypothesis predicts a shift from facilitative to competitive plant interactions with decreasing abiotic stress. This has been supported by studies along elevation and temperature gradients, but also challenged by the hypothesis of a facilitation collapse at extremely harsh sites. Although facilitation is known to be important in primary succession, few studies have examined these hypotheses along primary succession gradients.

Aim

To examine whether there is a relationship between the presence of the circumpolar cushion plant Silene acaulis and other species, and if so, whether there is a shift between positive and negative interactions along a primary succession gradient in a glacier foreland.

Location

Finse, southern Norway.

Methods

We examined the performance of the common alpine forb Bistorta vivipara, species richness of vascular plants, bryophytes and lichens, and the number of seedlings and fertile vascular plants in S. acaulis cushions, and control plots without S. acaulis, along a succession gradient with increasing distance from a glacier front, and thus decreasing abiotic stress. To examine if S. acaulis cushions modify the abiotic environment, we recorded soil temperature, moisture, organic content and pH in cushions and control plots.

Results

Bistorta vivipara performed better, as shown by bigger leaves in S. acaulis cushions compared to control plots in the harshest part of the gradient close to the glacier. There were few differences in B. vivipara performance between cushion and control plots in the more benign environment further away from the glacier. This suggests a shift from facilitative to mainly neutral interactions by S. acaulis on the performance of B. vivipara with decreasing abiotic stress. A trend, although not significant, of higher vascular species richness and fertility inside S. acaulis cushions along the whole gradient, suggests that S. acaulis also facilitates community‐level species richness. The causal mechanism of this facilitation is likely that the cushions buffer extreme temperatures.

Conclusions

Our results support the stress‐gradient hypothesis for the relationship between the cushion plant S. acaulis and the performance of a single species along a primary succession gradient in a glacier foreland. S. acaulis also tended to increase vascular plant species richness and fertility regardless of stress level along the gradient, suggesting facilitation at the community level. We found no collapse of facilitation at the most stressful end of the gradient in this alpine glacier foreland.     

Stress exposure in specific growth periods associates with children's weight,height, and body mass index

Objectives

We investigate associations between children exposure to stressful events, considering: (1) the period in which the event took place, (2) the type of event, and (3) the cumulative effect of the events on children's weight, height and body mass index (BMI).

Methods

A total of 8429 Portuguese children (3349 exposed to at least one stressful event during their lifetime; 50.2% males; mean age = 7.21 ± 1.85 years) were included in the analysis. The occurrence of stressful (i.e., adverse) events was reported in a parental questionnaire; children's weight and height were objectively measured.

Results

When the stress event took place in the first 2 years of life, compared with during pregnancy or after the 2 years, children were shorter; but the association was weak and only significant for boys. After adjustment for child's birthweight, gestational age, breastfeeding duration, number of siblings, and father's education, the experience of 3+ stressful events (vs. 1 or 2) was associated with higher weight and height in boys. No interaction effect was found between stress and BMI.

Discussion

We found some evidence of associations between exposure to stressful events and physical growth of boys. We highlight the complex relationship between exposure to stressful experiences and children's physical growth, particularly the different effects of specific characteristics of the stress event and the sex differences.

     

Shrub facilitation drives tree establishment in a semiarid fog‐dependent ecosystem

Questions

The exceptional occurrence of tall rain forest patches on foggy coastal mountaintops, surrounded by extensive xerophytic shrublands, suggests an important role of plant–plant interactions in the origin and persistence of these patches in semi‐arid Chile. We asked whether facilitation by shrubs can explain the growth and survival of rain forest tree species, and whether shrub effects depend on the identity of the shrub species itself, the drought tolerance of the tree species and the position of shrubs in regard to wind direction.

Location

Open area–shrubland–forest matrix, Fray Jorge Forest National Park, Chile.

Methods

We recorded survival after 12 years of a ~3600 tree saplings plantation (originally ~30‐cm tall individuals) of Aextoxicon punctatum, Myrceugenia correifolia and Drimys winteri placed outside forests, beneath the shrub Baccharis vernalis, and in open (shrub‐free) areas. We assessed the effects of neighbouring shrubs and soil humidity on survival and growth along a gradient related to the direction of fog movement.

Results

B. vernalis had a clear facilitative effect on tree establishment and survival since, after ~12 years, saplings only survived beneath the shrub canopy. Long‐term survival strongly depended on tree species identity, drought tolerance and position along the soil moisture gradient, with higher survival of A. punctatum (>35%) and M. correifolia (>14%) at sites on wind‐ and fog‐exposed shrubland areas. Sites occupied by the shrub Aristeguietia salvia were unsuitable for trees, presumably due to drier conditions than under B. vernalis.

Conclusions

Interactions between shrubs and fog‐dependent tree species in dry areas revealed a strong, long‐lasting facilitation effect on planted tree's survival and growth. Shrubs acted as benefactors, providing sites suitable for tree growth. Sapling mortality in the shrubland interior was caused by lower soil moisture, the consequence of lower fog loads in the air and thus insufficient facilitation. While B. vernalis was a key ecosystem engineer (nurse) and intercepted fog water that dripped to trees planted underneath, drier sites with A. salvia were unsuitable for trees. Consequently, nurse effects related to water input are strongly site and species specific, with facilitation by shrubs providing a plausible explanation for the initiation of forest patches in this semi‐arid landscape.     

Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied?

Background

Species Distribution Models (SDMs) aim on the characterization of a species'' ecological niche and project it into geographic space. The result is a map of the species'' potential distribution, which is, for instance, helpful to predict the capability of alien invasive species. With regard to alien invasive species, recently several authors observed a mismatch between potential distributions of native and invasive ranges derived from SDMs and, as an explanation, ecological niche shift during biological invasion has been suggested. We studied the physiologically well known Slider turtle from North America which today is widely distributed over the globe and address the issue of ecological niche shift versus choice of ecological predictors used for model building, i.e., by deriving SDMs using multiple sets of climatic predictor.

Principal Findings

In one SDM, predictors were used aiming to mirror the physiological limits of the Slider turtle. It was compared to numerous other models based on various sets of ecological predictors or predictors aiming at comprehensiveness. The SDM focusing on the study species'' physiological limits depicts the target species'' worldwide potential distribution better than any of the other approaches.

Conclusion

These results suggest that a natural history-driven understanding is crucial in developing statistical models of ecological niches (as SDMs) while “comprehensive” or “standard” sets of ecological predictors may be of limited use.     

Environmental control of plant species abundance in a microtidal Mediterranean saltmarsh

Question: To what extent are environmental factors the main determinants of species abundance in Mediterranean coastal marshlands? Location: The Llobregat delta, Barcelona, Spain. Methods: Vegetation relevés were performed and a set of water table and soil variables were periodically monitored in 43 sampling points randomly distributed in four marsh areas (sites) along a coastal–inland gradient. A canonical correspondence analysis (CCA) was performed to identify the primary water and soil correlates of species cover, after considering the effect of site and point spatial location. The realized niches of dominant species were modeled through GLMs performed on the first two axes of CCA. Niche overlapping among these species was compared with their coexistence, assessed through pairwise correlations of relative species cover in each sampling point. Results: Water and soil variables explained more of the variation in species' abundance than site and spatial position. Mean water table level, maximum water conductivity and sodium adsorption ratio (SAR), summarized in the two first CCA axes, explained 23.8% of the variability in species' cover. Arthrocnemum fruticosum, Phragmites australis subsp. australis, Juncus acutus, Spartina versicolor and Juncus maritimus dominated the vegetation stands. Niches obtained from GLM response curves showed moderate overlapping among all these species except for A. fruticosum. However, pairwise correlations were mainly negative or non‐significant, indicating low coincidence, and even segregation, between species' cover. Conclusions: The abundance of dominant plants in Mediterranean marshes is only partly explained by the environmental gradients summarized in niche models. The role of other factors such as facilitation or competition between species and random recruitment should be explored.     

Sampling strategy matters to accurately estimate response curves' parameters in species distribution models

Aim

Assessing how different sampling strategies affect the accuracy and precision of species response curves estimated by parametric species distribution models.

Major Taxa Studied

Virtual plant species.

Location

Abruzzo (Italy).

Time Period

Timeless (simulated data).

Methods

We simulated the occurrence of two virtual species with different ecology (generalist vs specialist) and distribution extent. We sampled their occurrence following different sampling strategies: random, stratified, systematic, topographic, uniform within the environmental space (hereafter, uniform) and close to roads. For each sampling design and species, we ran 500 simulations at increasing sampling efforts (total: 42,000 replicates). For each replicate, we fitted a binomial generalised linear model, extracted model coefficients for precipitation and temperature, and compared them with true coefficients from the known species' equation. We evaluated the quality of the estimated response curves by computing bias, variance and root mean squared error (RMSE). Additionally, we (i) assessed the impact of missing covariates on the performance of the sampling approaches and (ii) evaluated the effect of incompletely sampling the environmental space on the uniform approach.

Results

For the generalist species, we found the lowest RMSE when uniformly sampling the environmental space, while sampling occurrence data close to roads provided the worst performance. For the specialist species, all sampling designs showed comparable outcomes. Excluding important predictors similarly affected all sampling strategies. Sampling limited portions of the environmental space reduced the performance of the uniform approach, regardless of the portion surveyed.

Main Conclusions

Our results suggest that a proper estimate of the species response curve can be obtained when the choice of the sampling strategy is guided by the species' ecology. Overall, uniformly sampling the environmental space seems more efficient for species with wide environmental tolerances. The advantage of seeking the most appropriate sampling strategy vanishes when modelling species with narrow realised niches.     

Context dependency in interference competition among birds in an endangered woodland ecosystem

Aim

Much research has quantified species responses to human-modified ecosystems. However, there is limited work on how human-modified ecosystems may reshape competitive interactions between species. Using a 19-year study across 3 million ha, we aimed to answer the question: Are levels of interference competition between bird species context dependent and influenced by habitat structure and productivity? We focussed on the hyper-aggressive behaviour of the Noisy Miner (Manorina melanocephala), which is recognized as a key threatening process for other woodland bird species in Australia. Whether environmental conditions such as amount of forest cover and net primary productivity (NPP) mediate the Noisy Miners' impact remains untested at large spatiotemporal scales.

Location

Temperate woodlands of south-eastern Australia.

Methods

We gathered data on bird site occupancy from repeated surveys of field sites and assembled satellite data on tree cover and NPP. We constructed Bayesian multi-species occupancy/detection models of bird species in woodland patches and tested the fixed and interactive effects of Noisy Miner presence, the amount of tree cover, NPP, and time. We quantified the responses of 31 species, many with known interactions with the Noisy Miner documented previously at fine spatial scales.

Results

We identified negative associations between the Noisy Miner and 18 bird species, including, unexpectedly, both small and large bodied taxa. Site occupancy in some species was influenced by interactions between Noisy Miner presence and increasing amounts of tree cover or productivity. For some species, interference competition by the Noisy Miner is context-dependent and mitigated by increasing tree cover and/or increasing NPP.

Main Conclusions

Our analyses revealed that woodland bird conservation in our study region will be promoted by protecting refugia characterized by areas of high NPP and high tree cover. Preventing vegetation clearing that reduces tree cover could reduce interference competition by the Noisy Miner on parts of the remaining woodland bird community, including species of conservation concern.     

Threatened fish species in the Northeast Atlantic are functionally rare

Aim

The criteria used to define the International Union for Conservation of Nature (IUCN) Red List categories are essentially based on demographic parameters at the species level, but they do not integrate species' traits or their roles in ecosystems. Consequently, current IUCN-based protection measures may not be sufficient to conserve ecosystem functioning and services. Some species may have a singular combination of traits associated with unique functions. Such functionally distinct species are increasingly recognized as a key facet of biodiversity since they are, by definition, functionally irreplaceable. The aim of this study is to investigate whether threatened species are also functionally rare and to identify which traits determine extinction risk.

Location

European continental shelf seas.

Time period

1984–2020.

Major taxa studied

Marine fish.

Methods

Using newly compiled trait information of 425 marine fish species in European waters, and more than 30 years of scientific bottom trawl surveys, we estimated the functional distinctiveness, restrictedness and scarcity of each species and cross-referenced it with their IUCN conservation status.

Results

In European continental shelf seas, 38% of the species threatened with extinction (9 out of 24 species) were identified as the most functionally distinct. By mapping extinction risk in the multidimensional species trait space, we showed that species with the greatest risk of extinction are long-lived and of high trophic level. We also identified that the most functionally distinct species are sparsely distributed (4% of the total area on average) and have scarce abundances (<1% of the relative mean abundance of common species).

Main Conclusions

Because a substantial proportion of threatened species are functionally distinct and thus may play unique roles in ecosystem functioning, we stress that species traits—especially functional rarity—should become an indispensable step in the development of conservation management plans.     

Immigration rates in fragmented landscapes--empirical evidence for the importance of habitat amount for species persistence

Background

The total amount of native vegetation is an important property of fragmented landscapes and is known to exert a strong influence on population and metapopulation dynamics. As the relationship between habitat loss and local patch and gap characteristics is strongly non-linear, theoretical models predict that immigration rates should decrease dramatically at low levels of remaining native vegetation cover, leading to patch-area effects and the existence of species extinction thresholds across fragmented landscapes with different proportions of remaining native vegetation. Although empirical patterns of species distribution and richness give support to these models, direct measurements of immigration rates across fragmented landscapes are still lacking.

Methodology/Principal Findings

Using the Brazilian Atlantic forest marsupial Gray Slender Mouse Opossum (Marmosops incanus) as a model species and estimating demographic parameters of populations in patches situated in three landscapes differing in the total amount of remaining forest, we tested the hypotheses that patch-area effects on population density are apparent only at intermediate levels of forest cover, and that immigration rates into forest patches are defined primarily by landscape context surrounding patches. As expected, we observed a positive patch-area effect on M. incanus density only within the landscape with intermediate forest cover. Density was independent of patch size in the most forested landscape and the species was absent from the most deforested landscape. Specifically, the mean estimated numbers of immigrants into small patches were lower in the landscape with intermediate forest cover compared to the most forested landscape.

Conclusions/Significance

Our results reveal the crucial importance of the total amount of remaining native vegetation for species persistence in fragmented landscapes, and specifically as to the role of variable immigration rates in providing the underlying mechanism that drives both patch-area effects and species extinction thresholds.     

Human land use is comparable to climate as a driver of global plant occurrence and abundance across life forms

Aim

Historically, climate has been a dominant driver of global vegetation patterns. Recently, ecological understanding has been updated to acknowledge the influence of human land use (the dominant driver of biodiversity change) in shaping global vegetation patterns. We test whether Raunkiær's life form, a plant classification system designed to reflect climatic drivers, affects how plants respond to both land use and climate.

Location

Forty-one countries across six continents.

Time period

1990 to 2013.

Major taxa studied

Terrestrial plants.

Methods

Combining data from the biodiversity and land use database PREDICTS, and plant trait databases TRY and BIEN, we use generalized linear mixed models with weighted effects coding to test whether Raunkiær's life form affects plant response to land use and climate in over 4800 species at over 300 sites globally.

Results

We provide evidence that human land use is comparable to climate in influencing life form occurrence and that land use produces divergent outcomes across life forms.

Main conclusions

Combined with climatic suitability, land use acts as a filter contracting the realized niche of trees and expanding the realized niche of disturbance-tolerant species. Our results highlight the fundamental role of human activity in shaping species' distribution.     

Vegetation patch dynamics in rangelands: How feedbacks between large herbivores,vegetation and soil fauna alter patches over space and through time

Aim

Large herbivore grazing is a popular conservation management tool to promote vegetation structural diversity of rangelands. However, vegetation patch dynamics, that is, how patches of grazing-defended tall vegetation and grazer-preferred short lawns shift over space and time, is poorly understood. Here, we describe a new conceptual framework for patch dynamics within rangelands, combining theories of classical cyclical succession, self-organization and multitrophic feedbacks between grazers, vegetation and bioturbating soil fauna.

Location

We use the cattle-grazed salt marsh of the island Schiermonnikoog, The Netherlands, as a model system. The grazed salt marsh is characterized by distinct tall vegetation patches dominated by the grazing-defended rush Juncus maritimus and grazing-intolerant grass Elytrigia atherica, surrounded by a matrix of grazing lawn (dominated by Festuca rubra).

The Framework

Based on previous observational and experimental studies, we propose a cyclical patch dynamic where plant species composition and structure transitions through four phases: patch initiation (a) occurs when the grazing-defended rush J. maritimus establishes in the grazed lawn. Patch establishment (b) follows when the grazing-intolerant grass E. atherica establishes in the patch due to associational defence by J. maritimus and produces a large amount of litter that attracts the key bioturbating amphipod Orchestia gammarellus. Patch expansion (c) occurs when O. gammarellus activities improve soil properties of the patch, which favours E. atherica growth, leading to E. atherica competitively displacing J. maritimus in the centre of the patch. Patch degeneration (d) follows when cattle enter the enlarged patch to consume E. atherica in the centre, trample the soil, displace O. gammarellus and decrease vegetation cover, opening space for grazing-lawn species to invade. The cycle restarts when remnants of the rush J. maritimus in the degenerated patches (or individuals recently established from seed dispersal) initiate new patches in the grazing lawn.

Synthesis

Our proposed patch-dynamic model provides a means to describe the mechanisms driving vegetation patch dynamics and serves as a foundation for further experimental and observational exploration, not only for this specific system, but more generally for grazed systems worldwide that show patches of typical grazing-defended and grazer-preferred vegetation.