Accounting for trait variability and coordination in predictions of drought-induced range shifts in woody plants

Functional traits offer a promising avenue to improve predictions of species range shifts under climate change, which will entail warmer and often drier conditions. Although the conceptual foundation linking traits with plant performance and range shifts appears solid, the predictive ability of individual traits remains generally low. In this review, we address this apparent paradox, emphasizing examples of woody plants and traits associated with drought responses at the species' rear edge. Low predictive ability reflects the fact not only that range dynamics tend to be complex and multifactorial, as well as uncertainty in the identification of relevant traits and limited data availability, but also that trait effects are scale- and context-dependent. The latter results from the complex interactions among traits (e.g. compensatory effects) and between them and the environment (e.g. exposure), which ultimately determine persistence and colonization capacity. To confront this complexity, a more balanced coverage of the main functional dimensions involved (stress tolerance, resource use, regeneration and dispersal) is needed, and modelling approaches must be developed that explicitly account for: trait coordination in a hierarchical context; trait variability in space and time and its relationship with exposure; and the effect of biotic interactions in an ecological community context.

Concepts in Alpine Plant Ecology

The alpine life zone is perhaps the only biome that occurs globally where mountains are high enough. At latitudinally varying elevation, the alpine belt hosts small stature plants that vary greatly in morphology, anatomy and physiology. In this contribution, I summarize a number of principles that govern life in what is often considered a cold and hostile environment. The 12 conceptual frameworks depicted include the key role of aerodynamic decoupling from free atmospheric climatic conditions, the problematic concepts of limitation and stress in an evolutionary context, and the role of developmental flexibility and functional diversity. With its topography driven habitat diversity, alpine plant diversity is buffered against environmental change, and the multitude of microclimatic gradients offers 'experiments by nature', the power of which awaits multidisciplinary exploration.

Postglacial species arrival and diversity buildup of northern ecosystems took millennia

What drives ecosystem buildup, diversity, and stability? We assess species arrival and ecosystem changes across 16 millennia by combining regional-scale plant sedimentary ancient DNA from Fennoscandia with near-complete DNA and trait databases. We show that postglacial arrival time varies within and between plant growth forms. Further, arrival times were mainly predicted by adaptation to temperature, disturbance, and light. Major break points in ecological trait diversity were seen between 13.9 and 10.8 calibrated thousand years before the present (cal ka BP), as well as break point in functional diversity at 12.0 cal ka BP, shifting from a state of ecosystem buildup to a state where most habitat types and biotic ecosystem components were in place. Trait and functional diversity stabilized around 8 cal ka BP, after which both remained stable, although changes in climate took place and species inflow continued. Our ecosystem reconstruction indicates a millennial-scale time phase of formation to reach stable and resilient levels of diversity and functioning.

Pollen-based reconstruction reveals the impact of the onset of agriculture on plant functional trait composition

The onset of agriculture improved the capacity of ecosystems to produce food, but inadvertently altered other vital ecosystem functions. Plant traits play a central role in determining ecosystem properties, therefore we investigated how the onset of agriculture in Europe changed plant trait composition using 78 pollen records. Using a novel Bayesian approach for reconstructing plant trait composition from pollen records, we provide a robust method that can account for trait variability within pollen types. We estimate an overall four-fold decrease in plant size through agriculture and associated decreases in leaf and seed size. We show an increase in niche space towards the resource-acquisitive end of the leaf economic spectrum. Decreases in leaf phosphorus might have been caused by nutrient depletion through grazing and burning. Our results show that agriculture, from its start, has likely been gradually impacting biogeochemical cycles through altered vegetation composition.

Climate and Species Traits Drive Changes in Holocene Forest Composition Along an Elevation Gradient in Pacific Canada

Projected changes in climate are expected to shift the ranges of many tree species poleward and to higher elevations. Here, we examine past changes in forest composition in Pacific Canada using a paleoecological approach and investigate the role of past changes in climate and differences in species traits in changing forest compositions. We present a new pollen record from a mid-elevation fen on central Vancouver Island, British Columbia that shows (1) Pinus contorta-dominated communities starting 14,000 cal yr BP, (2) an abrupt transition to Pseudotsuga menziesii and Tsuga heterophylla forests by 10,600 cal yr BP, and (3) a gradual transition to Tsuga heterophylla-dominated forests in the mid-Holocene. We combine this mid-elevation record with nearby pollen records along a 1,400-m elevation gradient to assess sorting of dominant woody plant taxa and their life history and stress tolerance traits over the last 14,000 years. Multivariate time series confirm elevational sorting of woody plant taxa through time with the modern elevational zonation of tree taxa established by 6,000 cal yr BP. Some taxa have consistently occupied low and middle elevations (P. menziesii, Alnus rubra) or high elevations (Tsuga mertensiana), whereas other taxa (P. contorta, T. heterophylla) have occurred at a wider range of elevations. Three-table statistical techniques reveal significant relationships among forest composition, independent paleoclimate records, and species traits. Tree species with similar traits tend to be most abundant at similar times and those that are functionally dissimilar are separated in time. For example, species with “fast” life history strategies (e.g., P. contorta, Alnus viridis) are most abundant in late-glacial plant communities, while those with “slow” life history strategies (e.g., T. heterophylla, T. mertensiana) are most abundant in mid-late Holocene forests. This research highlights that woody plant taxa and their functional traits are sorted on long timescales in association with environmental change. Turnover in forest composition is driven primarily by changes in climate, which acts as a filter on species traits to direct changes in forest dynamics.

Searching for Function: Reconstructing Adaptive Niche Changes Using Geochemical and Morphological Data in Planktonic Foraminifera

Dead species remain dead. The diversity record of life is littered with examples of declines and radiations, yet no species has ever re-evolved following its true extinction. In contrast, functional traits can transcend diversity declines, often develop iteratively and are taxon-free allowing application across taxa, environments and time. Planktonic foraminifera have an unrivaled, near continuous fossil record for the past 200 million years making them a perfect test organism to understand trait changes through time, but the functional role of morphology in determining habitat occupation has been questioned. Here, we use single specimen stable isotopes to reconstruct the water depth habitat of individual planktonic foraminifera in the genus Subbotina alongside morphological measurements of the tests to understand trait changes through the Middle Eocene Climatic Optimum [MECO: ∼40 Myr ago (mega annum, Ma)]. The MECO is a geologically transient global warming interval that marks the beginning of widespread biotic reorganizations in marine organisms spanning a size spectrum from diatoms to whales. In contrast to other planktonic foraminiferal genera, the subbotinids flourished through this interval despite multiple climatic perturbations superimposed on a changing background climate. Through coupled trait and geochemical analysis, we show that Subbotina survival through this climatically dynamic interval was aided by trait plasticity and a wider ecological niche than previously thought for a subthermocline dwelling genus supporting a generalist life strategy. We also show how individually resolved oxygen isotopes can track shifts in depth occupancy through climatic upheaval. During and following the MECO, temperature changes were substantial in the thermocline and subthermocline in comparison to the muted responses of the surface ocean. In our post-MECO samples, we observe restoration of planktonic foraminifera depth stratification. Despite these changing temperatures and occupied depths, we do not detect a contemporaneous morphological response implying that readily available traits such as test size and shape do not have a clear functional role in this generalist genus. Modern imaging measurement technologies offer a promising route to gather more informative morphological traits for functional analysis, rather than the traditional candidates that are most easily measured.

Chironomidae Morphological Types and Functional Feeding Groups as a Habitat Complexity Vestige

Chironomid (Diptera: Chironomidae) larvae play an important role in a wide range of aquatic ecosystems. The study focuses on Chironomidae trophic guilds and morphological types as indicator traits in reconstructions of habitat changes in shallow water bodies. Mentum and ventromental plates are important mouthparts whose shape depends on food type and feeding behavior. Chironomidae larvae strongly vary in the mode of life and feeding habits, representing almost every feeding group. Here we classified the mentum types into 16 groups and tested if they indicated similar past habitat changes as the Chironomidae functional feeding groups (FFGs), and tribes/subfamilies. Paleoecological data of biotic and abiotic proxies were derived from short sequences from a Late Glacial oxbow and a nearby medieval moat located in Central Poland. The study revealed that the habitat substratum structure, vegetation and physicochemical conditions are associated both with the feeding types and morphological traits. This provides a valuable tool for future reconstructions of habitat changes.