Prediction of species composition of plant communities in a rural landscape based on species traits

The species composition of a community is a subset of the regional species pool, and predicting the species composition of a community from ecological traits of organisms is an important objective in ecology. If such a prediction can be made feasible, we could assess the risk of invasion of locally new species (alien species and genetically modified species) into natural communities. We developed and tested statistical models to predict a community’s species composition from ecological traits of the species pool. Various types of communities (forest, meadow, and weed communities) exist in a small area of traditional rural landscape in Japan, and have been maintained by human activities. These communities and the tracheophytes species pool in the 1-km² research area were considered. We used logistic regression and decision-tree analysis to construct predictive models of community species composition based on plant traits, using the presence or absence of species in a community as the dependent variable and ecological traits as independent variables. Plant traits were grouped by cluster analysis, and the average in each trait group was used for model building to avoid multiple collinearity. Statistical prediction models were significant in all communities. About 60–75% of species composition could be predicted from the measured plant traits in forest communities, but 33–56% in the meadow and weed communities. Our results showed the possibility of predicting the species composition of plant communities from the ecological traits of the plant species together with the information on local species pool.     

Correlation of drought traits and the predictability of osmotic potential at full leaf turgor in vegetation from New Zealand

Scientists do not know precisely how severe will be the impact of climate change on species. Evidence suggests that for some species, their future distributions might be jeopardized by local extinctions and drought‐induced tree mortality. Thus, we require models capable of estimating drought tolerance across many species. We can approach this goal by assessing functional traits. The trait osmotic potential at full turgor, π_O, is potentially a good drought indicator; however, few studies address its importance as a drought‐tolerance predictor and it is difficult to measure in the field with accuracy. In this work, we aim to answer the questions: which drought traits correlate with π_O?; do morpho‐anatomical traits correlate with π_O?; and which trees and shrubs are more (or less) vulnerable to drought? To achieve this aim, we assessed physiological and morpho‐anatomical traits for 14 native species from New Zealand forests. We included leaf‐ and wood‐related traits, π_O, water potential and stomatal conductance. We examined how these traits correlate with π_O and sought to generate models to predict π_O as a function of other traits. We tested 33 different models and evaluated them using Akaike's information criterion. Unfortunately, none of the morpho‐anatomical traits correlated well with π_O. Instead, water potential correlated most strongly with π_O. None of the models using only morpho‐anatomical traits produced plausible results. The model with the best predictive performance incorporated the effects of both morpho‐anatomical and physiological traits: water potential and wood saturated water content. Of the species analysed, and based on their π_O response, Lophozonia menziesii was considered the most vulnerable to drought stress, whereas Plagianthus regius was the least vulnerable. Our findings imply that it is potentially valuable to keep exploring the use of π_O as a drought indicator and that the effort required to measure some physiological traits, such as water potential, may be essential to consider plant drought responses and to predict π_O.     

Non‐equilibrium in plant distribution models – only an issue for introduced or dispersal limited species?

Species distribution models rely on the assumption that species' distributions are at equilibrium with environmental conditions within a region – i.e. they occur in all suitable habitats. If this assumption holds, species occurrence should be predictable from measures of the environment. Introduced species may be poor candidates for distribution models due to their presumed lack of equilibrium within the landscapes they occupy, although predicting their potential distributions is often of critical importance to natural resource managers. We determined if the accuracy of species distribution models differed between 17 native and 17 introduced riparian plant species in the western United States. We also assessed if model accuracy was associated with both environmental and biological factors that can influence dispersal. We used Random Forests to model species distributions and linear regression to determine if model accuracy was associated with dispersal‐related traits. Model accuracy for introduced species was higher than that for native species. Dispersal‐related traits did not affect model accuracy or improvement, though two other traits, family affiliation and rarity on the landscape, did have an effect. Distance‐based measures of dispersal potential improved model fit equally for both native and introduced species and for species with a variety of dispersal traits, suggesting that the importance of regional propagule pressure is relatively constant across species with different dispersal opportunities. Several lines of future questioning are suggested by our results, including why introduced species may in some cases produce more accurate distribution models than native species and how species dispersal traits relate to distribution model accuracy at different spatial scales.     

Life History Traits and Niche Instability Impact Accuracy and Temporal Transferability for Historically Calibrated Distribution Models of North American Birds

A primary assumption of environmental niche models (ENMs) is that models are both accurate and transferable across geography or time; however, recent work has shown that models may be accurate but not highly transferable. While some of this is due to modeling technique, individual species ecologies may also underlie this phenomenon. Life history traits certainly influence the accuracy of predictive ENMs, but their impact on model transferability is less understood. This study investigated how life history traits influence the predictive accuracy and transferability of ENMs using historically calibrated models for birds. In this study I used historical occurrence and climate data (1950-1990s) to build models for a sample of birds, and then projected them forward to the ‘future’ (1960-1990s). The models were then validated against models generated from occurrence data at that ‘future’ time. Internal and external validation metrics, as well as metrics assessing transferability, and Generalized Linear Models were used to identify life history traits that were significant predictors of accuracy and transferability. This study found that the predictive ability of ENMs differs with regard to life history characteristics such as range, migration, and habitat, and that the rarity versus commonness of a species affects the predicted stability and overlap and hence the transferability of projected models. Projected ENMs with both high accuracy and transferability scores, still sometimes suffered from over- or under- predicted species ranges. Life history traits certainly influenced the accuracy of predictive ENMs for birds, but while aspects of geographic range impact model transferability, the mechanisms underlying this are less understood.     

Revisiting the Holy Grail: using plant functional traits to understand ecological processes

One of ecology's grand challenges is developing general rules to explain and predict highly complex systems. Understanding and predicting ecological processes from species' traits has been considered a ‘Holy Grail’ in ecology. Plant functional traits are increasingly being used to develop mechanistic models that can predict how ecological communities will respond to abiotic and biotic perturbations and how species will affect ecosystem function and services in a rapidly changing world; however, significant challenges remain. In this review, we highlight recent work and outstanding questions in three areas: (i) selecting relevant traits; (ii) describing intraspecific trait variation and incorporating this variation into models; and (iii) scaling trait data to community‐ and ecosystem‐level processes. Over the past decade, there have been significant advances in the characterization of plant strategies based on traits and trait relationships, and the integration of traits into multivariate indices and models of community and ecosystem function. However, the utility of trait‐based approaches in ecology will benefit from efforts that demonstrate how these traits and indices influence organismal, community, and ecosystem processes across vegetation types, which may be achieved through meta‐analysis and enhancement of trait databases. Additionally, intraspecific trait variation and species interactions need to be incorporated into predictive models using tools such as Bayesian hierarchical modelling. Finally, existing models linking traits to community and ecosystem processes need to be empirically tested for their applicability to be realized.     

Matching consumer feeding behaviours and resource traits: a fourth‐corner problem in food‐web theory

For decades, food web theory has proposed phenomenological models for the underlying structure of ecological networks. Generally, these models rely on latent niche variables that match the feeding behaviour of consumers with their resource traits. In this paper, we used a comprehensive database to evaluate different hypotheses on the best dependency structure of trait‐matching patterns between consumers and resource traits. We found that consumer feeding behaviours had complex interactions with resource traits; however, few dimensions (i.e. latent variables) could reproduce the trait‐matching patterns. We discuss our findings in the light of three food web models designed to reproduce the multidimensionality of food web data; additionally, we discuss how using species traits clarify food webs beyond species pairwise interactions and enable studies to infer ecological generality at larger scales, despite potential taxonomic differences, variations in ecological conditions and differences in species abundance between communities.     

Transition from wind pollination to insect pollination in sedges: experimental evidence and functional traits

Transitions from wind pollination to insect pollination were pivotal to the radiation of land plants, yet only a handful are known and the trait shifts required are poorly understood. We tested the hypothesis that a transition to insect pollination took place in the ancestrally wind-pollinated sedges (Cyperaceae) and that floral traits modified during this transition have functional significance. We paired putatively insect-pollinated Cyperus obtusiflorus and Cyperus sphaerocephalus with related, co-flowering, co-occurring wind-pollinated species, and compared pairs in terms of pollination mode and functional roles of floral traits. Experimentally excluding insects reduced seed set by 56-89% in putatively insect-pollinated species but not in intermingled wind-pollinated species. The pollen of putatively insect-pollinated species was less motile in a wind tunnel than that of wind-pollinated species. Bees, beetles and flies preferred inflorescences, and color-matched white or yellow models, of putatively insect-pollinated species over inflorescences, or color-matched brown models, of wind-pollinated species. Floral scents of putatively insect-pollinated species were chemically consistent with those of other insect-pollinated plants, and attracted pollinators; wind-pollinated species were unscented. These results show that a transition from wind pollination to insect pollination occurred in sedges and shed new light on the function of traits involved in this important transition.     

Plant traits and wood fates across the globe: rotted,burned, or consumed?

Wood represents the defining feature of forest systems, and often the carbon in woody debris has a long residence time. Globally, coarse dead wood contains 36–72 Pg C, and understanding what controls the fate of this C is important for predicting C cycle responses to global change. The fate of a piece of wood may include one or more of the following: microbial decomposition, combustion, consumption by insects, and physical degradation. The probability of each fate is a function of both the abiotic environment and the wood traits of the species. The wood produced by different species varies substantially in chemical, micro- and macro-morphological traits; many of these characteristics of living species have 'afterlife' effects on the fate and turnover rate of dead wood. The colonization of dead wood by microbes and their activity depends on a large suite of wood chemical and anatomical traits, as well as whole-plant traits such as stem-diameter distributions. Fire consumption is driven by a slightly narrower range of traits with little dependence on wood anatomy. Wood turnover due to insects mainly depends on wood density and secondary chemistry. Physical degradation is a relatively minor loss pathway for most systems, which depends on wood chemistry and environmental conditions. We conclude that information about the traits of woody plants could be extremely useful for modeling and predicting rates of wood turnover across ecosystems. We demonstrate how this trait-based approach is currently limited by oversimplified treatment of dead wood pools in several leading global C models and by a lack of quantitative empirical data linking woody plant traits with the probability and rate of each turnover pathway. Explicitly including plant traits and woody debris pools in global vegetation climate models would improve predictions of wood turnover and its feedback to climate.     

Leaf trait integration mediates species richness variation in a species-rich neotropical forest domain

Environmental gradients are known to drive changes in mean trait values, but changes in the trait integration strength across local communities are less well understood, particularly with regard to possible links with species richness variation. Here, we tested if climate, soil, and topography gradients drive species richness indirectly via constraints on trait integration in the Atlantic Forest of South America. We evaluated seven traits (from leaf, wood, seed, and plant size) of 1456 species occurring across 84 local communities. Generalized least square models and a path model were applied to test direct and indirect relationships. Correlations were higher between leaf traits (average r?=?0.28) and lower when other traits were included (average r?=?0.16). In line with this result, species richness was related to a multivariate index of interspecific trait integration (ITI) computed for leaf traits, but not to the ITI for all the seven traits. Abiotic gradients influenced species richness both directly and indirectly through the leaf trait integration. A total of 33% and 26% of the variation in species richness and ITI, respectively, were explained by the models, with climatic conditions showing higher contribution than topographic and edaphic factors. These results support a significant but reduced environmental selection role behind the trait-based community assembly and may suggest that other processes are involved in the constrain of trait integration at larger spatial scales. In addition, different directional trends in trait–trait relationships across local communities suggest that global trait relationships may not necessarily hold at local contexts.

     

Intra-specific variability and the competition–colonisation trade-off: coexistence, abundance and stability patterns

Intra-specific variability often produces an overlap between species distributions of individual performances which can influence competition relations and community dynamics. We analysed a two-species competition–colonisation model of vegetation with intra-specific variability in juvenile growth. On each patch colonised by both species, the winner was the juvenile with higher individual growth. Intra-specific variability disproportionately favoured the more fecund species because the tail of its distribution represented more individuals. In some cases, this process could even lead to a reversal of competition hierarchy and exclusion of the species with higher mean juvenile performance. In the space of species 2 mean growth and fecundity traits, the combinations of traits allowing coexistence with species 1 appeared close to an ideal trade-off curve. Along this curve, species 2 and species 1 coexisted at similar abundance. The balance of relative abundances diminished with the distance of species 2 from this curve. For a given level of relative species performances, coexistence stability increased continuously as species differentiation increased. In contrast to classical models that exhibit abrupt changes of equilibrium community properties when species traits vary, our model displayed continuous changes of these properties in relation to the balance of life traits within and among species. Intra-specific variability allows flexible patterns of community dynamics and could explain discrepancies between observations and classical theories.     

Survival rates indicate that correlations between community‐weighted mean traits and environments can be unreliable estimates of the adaptive value of traits

Correlations between community‐weighted mean (CWM) traits and environmental gradients are often assumed to quantify the adaptive value of traits. We tested this assumption by comparing these correlations with models of survival probability using 46 perennial species from long‐term permanent plots in pine forests of Arizona. Survival was modelled as a function of trait × environment interactions, plant size, climatic variation and neighbourhood competition. The effect of traits on survival depended on the environmental conditions, but the two statistical approaches were inconsistent. For example, CWM‐specific leaf area (SLA) and soil fertility were uncorrelated. However, survival was highest for species with low SLA in infertile soil, a result which agreed with expectations derived from the physiological trade‐off underpinning leaf economic theory. CWM trait–environment relationships were unreliable estimates of how traits affected survival, and should only be used in predictive models when there is empirical support for an evolutionary trade‐off that affects vital rates.     

Low availability of functional seed trait data from the tropics could negatively affect global macroecological studies,predictive models and plant conservation

BackgroundPlant seeds have many traits that influence ecological functions, ex situ conservation, restoration success and their sustainable use. Several seed traits are known to vary significantly between tropical and temperate regions. Here we present three additional traits for which existing data indicate differences between geographical zones. We discuss evidence for geographical bias in availability of data for these traits, as well as the negative consequences of this bias.ScopeWe reviewed the literature on seed desiccation sensitivity studies that compare predictive models to experimental data and show how a lack of data on populations and species from tropical regions could reduce the predictive power of global models. In addition, we compiled existing data on relative embryo size and post-dispersal embryo growth and found that relative embryo size was significantly larger, and embryo growth limited, in tropical species. The available data showed strong biases towards non-tropical species and certain families, indicating that these biases need to be corrected to perform truly global analyses. Furthermore, we argue that the low number of seed germination studies on tropical high-mountain species makes it difficult to compare across geographical regions and predict the effects of climate change in these highly specialized tropical ecosystems. In particular, we show that seed traits of geographically restricted páramo species have been studied less than those of more widely distributed species, with most publications unavailable in English or in the peer-reviewed literature.ConclusionsThe low availability of functional seed trait data from populations and species in the tropics can have negative consequences for macroecological studies, predictive models and their application to plant conservation. We propose that global analyses of seed traits with evidence for geographical variation prioritize generation of new data from tropical regions as well as multi-lingual searches of both the grey- and peer-reviewed literature in order to fill geographical and taxonomic gaps.     

Species traits are associated with the quality of bioclimatic models

Aim To analyse the effects of nine species trait variables on the accuracy of bioclimatic envelope models built for 98 butterfly species. Location Finland, northern Europe. Methods Data from a national butterfly atlas monitoring scheme (NAFI) collected from 1991–2003 with a resolution of 10 × 10 km were used in the analyses. Generalized additive models (GAMs) were constructed for 98 butterfly species to predict their occurrence as a function of climatic variables. Modelling accuracy was measured as the cross‐validation area under the curve (AUC) of the receiver–operating characteristic plot. Observed variation in modelling accuracy was related to species traits using multiple GAMs. The effects of phylogenetic relatedness among butterflies were accounted for by using generalized estimation equations. Results The values of the cross‐validation AUC for the 98 species varied between 0.56 and 1.00 with a mean of 0.79. Five species trait variables were included in the GAM that explained 71.4% of the observed variation in modelling accuracy. Four variables remained significant after accounting for phylogenetic relatedness. Species with high mobility and a long flight period were modelled less accurately than species with low mobility and a short flight period. Large species (>50 mm in wing span) were modelled more accurately than small ones. Species inhabiting mires had especially poor models, whereas the models for species inhabiting rocky outcrops, field verges and open fells were more accurate compared with other habitats. Main conclusions These results draw attention to the importance of species traits variables for species–climate impact models. Most importantly, species traits may have a strong impact on the performance of bioclimatic envelope models, and certain trait groups can be inherently difficult to model reliably. These uncertainties should be taken into account by downweighting or excluding species with such traits in studies applying bioclimatic modelling and making assessments of the impacts of climate change.     

The range implications of lizard traits in changing environments

Aim Most predictions of species ranges are based on correlating current species localities to environmental conditions. These correlative models do not explicitly include a species' biology. In contrast, some mechanistic models link traits to energetics and population dynamics to predict species distributions. These models enable one to ask whether considering a species' biology is important for predicting its range. I implement mechanistic models to investigate how a species' morphology, physiology and life history influence its range. Location North America. Methods I compare the mechanistic model predictions with those of correlative models for eight species of North American lizards in both current environments and following a uniform 3 °C temperature warming. I then examine the implications of superimposing habitat and elevation requirements on constraints associated with environmental tolerances. Results In the mechanistic model, species with a narrower thermal range for activity are both predicted and observed to have more restricted distributions. Incorporating constraints on habitat and elevation further restricts species distributions beyond areas that are thermally suitable. While correlative models generally outperform mechanistic models at predicting current distributions, the performance of mechanistic models improves when incorporating additional factors. In response to a 3 °C temperature warming, the northward range shifts predicted by the mechanistic model vary between species according to trait differences and are of a greater extent than those predicted by correlative models. Main conclusions These findings highlight the importance of species traits for understanding the dynamics of species ranges in changing environments. The analysis demonstrates that mechanistic models may provide an important complement to correlative models for predicting range dynamics, which may underpredict climate‐induced range shifts.     

Reproductive uncertainty and the relative competitiveness of simultaneous hermaphroditism versus dioecy

Hermaphroditism is typically associated with a sedentary existence, whereas dioecy is associated with mobility. This pattern is reflected within flowering plants, as dioecious species commonly possess traits that promote high dispersal. We investigated these associations with three population dynamics models (an individual-based simulation and two mathematical models, one deterministic and the other stochastic) that allowed us to examine competition for space between a hermaphroditic and dioecious species from different perspectives. The competing species are identical in every way but their sexual system. Separation of the sexes increases the variances of pollen import and seed dispersal for the dioecious species. These variances propagate through subsequent reproductive processes and ultimately reduce mean recruitment as a result of nonlinear averaging (Jensen's inequality). A dioecious species could overcome this disadvantage simply by producing more gametes than hermaphrodites; however, in line with the association with mobility, selection on dioecious species should also favor traits that reduce reproductive uncertainty, such as extensive dispersal.     

A trait‐based trade‐off between growth and mortality: evidence from 15 tropical tree species using size‐specific relative growth rates

A life‐history trade‐off between low mortality in the dark and rapid growth in the light is one of the most widely accepted mechanisms underlying plant ecological strategies in tropical forests. Differences in plant functional traits are thought to underlie these distinct ecological strategies; however, very few studies have shown relationships between functional traits and demographic rates within a functional group. We present 8 years of growth and mortality data from saplings of 15 species of Dipterocarpaceae planted into logged‐over forest in Malaysian Borneo, and the relationships between these demographic rates and four key functional traits: wood density, specific leaf area (SLA), seed mass, and leaf C:N ratio. Species‐specific differences in growth rates were separated from seedling size effects by fitting nonlinear mixed‐effects models, to repeated measurements taken on individuals at multiple time points. Mortality data were analyzed using binary logistic regressions in a mixed‐effects models framework. Growth increased and mortality decreased with increasing light availability. Species differed in both their growth and mortality rates, yet there was little evidence for a statistical interaction between species and light for either response. There was a positive relationship between growth rate and the predicted probability of mortality regardless of light environment, suggesting that this relationship may be driven by a general trade‐off between traits that maximize growth and traits that minimize mortality, rather than through differential species responses to light. Our results indicate that wood density is an important trait that indicates both the ability of species to grow and resistance to mortality, but no other trait was correlated with either growth or mortality. Therefore, the growth mortality trade‐off among species of dipterocarp appears to be general in being independent of species crossovers in performance in different light environments.     

Local versus regional intraspecific variability in regeneration traits

Intraspecific trait variability has a fundamental contribution to the overall trait variability. However, little is known concerning the relative role of local (e.g. disturbances and species interaction) and regional (biogeographical) processes in generating this intraspecific trait variability. While biogeographical processes enhance plant trait variability between distant populations, in fire-prone ecosystems, recurrent fires may have a preponderant role in generating variability at a local scale. We hypothesize that plants respond to the local spatio-temporal heterogeneity generated by fire by having a relatively large local variability in regeneration traits in such a way that overrides the variability at a broader biogeographical scale. We test this hypothesis by assessing the intraspecific variability in fire-related regeneration traits of two species (Cistus salviifolius and Lavandula stoechas) growing in fire-prone ecosystems of the Mediterranean Basin. For each species, we selected six populations in two distant regions, three in the east (Anatolian Peninsula) and three in the west (Iberian Peninsula). For each species and population, we analysed the following regeneration traits: seed size, seed dormancy and stimulated germination by fire-related cues (heat and smoke). To evaluate the distribution of the variability in these traits, we decomposed the variability of trait values at each level, between regions (regional) and between population within region (local), using linear mixed-effect models. Despite the biogeographical and climatic differences between regions, for the two species, intraspecific variability in regeneration traits was higher at a local (within regions) than at a regional scale (between regions). Our results suggest that, in Mediterranean ecosystems, fire is an important source of intraspecific variability in regeneration traits. This supports the prominent role of fire as an ecological and evolutionary process, producing trait variability and shaping biodiversity in fire-prone ecosystems.     

Tree hydraulic traits are coordinated and strongly linked to climate‐of‐origin across a rainfall gradient

Plant hydraulic traits capture the impacts of drought stress on plant function, yet vegetation models lack sufficient information regarding trait coordination and variation with climate‐of‐origin across species. Here, we investigated key hydraulic and carbon economy traits of 12 woody species in Australia from a broad climatic gradient, with the aim of identifying the coordination among these traits and the role of climate in shaping cross‐species trait variation. The influence of environmental variation was minimized by a common garden approach, allowing us to factor out the influence of environment on phenotypic variation across species. We found that hydraulic traits (leaf turgor loss point, stomatal sensitivity to drought [P_gs], xylem vulnerability to cavitation [P_x], and branch capacitance [C_branch]) were highly coordinated across species and strongly related to rainfall and aridity in the species native distributional range. In addition, trade‐offs between drought tolerance and plant growth rate were observed across species. Collectively, these results provide critical insight into the coordination among hydraulic traits in modulating drought adaptation and will significantly advance our ability to predict drought vulnerability in these dominant trees species.