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1. Impact of rainfall seasonality on intraspecific trait variation in a shrub from a Mediterranean climate

   https://doi.org/10.1111/1365-2435.13533  

   Moore, Timothy E. ; Jones, Cynthia S. ; Chong, Caroline ; Schlichting, Carl D. ; Seymour, ed., Colleen ( February 2020 , Functional Ecology)

   Selection pressures along climate gradients give rise to predictable variation in plant functional traits of individual species suggestive of local adaptation. Species whose ranges include winter rainfall, Mediterranean climates, or other strongly seasonal climates, may be exposed to divergent selection pressures at different ends of seasonality gradients.

   Here, we evaluate how rainfall seasonality in conjunction with other key climatic variables impacts patterns of trait variation inPelargonium scabrum, a woody shrub from the Greater Cape Floristic Region of South Africa. This biodiversity hotspot encompasses a Mediterranean climate (wet winters and hot, dry summers) and displays steep gradients in temperature and water availability.

   We used Bayesian regression models to evaluate leaf trait–trait and trait–climate relationships among 26 populations. Models included rainfall seasonality and its interaction with other climate variables (mean annual temperature, mean annual precipitation and potential evapotranspiration) as predictors to test for the impact of climate variation on three leaf traits: size, dissection and leaf mass per area (LMA). We evaluated model explanatory power by calculating BayesianR²values, and predictive power via leave‐one‐out cross‐validation.

   Trait–trait associations were modulated by rainfall seasonality, including a reversal in the relationship between leaf size and dissection depending on the proportion of rain received in winter. Trait–climate models were improved by including rainfall seasonality as a predictor for both explanatory and predictive power. For leaf dissection and LMA, we detected significant interactions between rainfall seasonality and other environmental variables, leading to reversals in the relationships between these traits and the three environmental variables depending on the proportion of winter rainfall.

   Differences in the timing of rainfall, coupled with strong differences in the covariation of climate variables, impose divergent selection pressures onP. scabrumpopulations resulting in divergence of trait values, trait integration and responses to climate gradients. These patterns are consistent with local adaptation ofP. scabrumpopulations mediated by the interactions between temperature and the amount and timing of rainfall. Species arrayed along broad climate gradients represent an excellent opportunity for investigating patterns of trait variation and abundances and distributions of species in relation to future changes in climate.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Leaf spectroscopy reveals divergent inter‐ and intra‐species foliar trait covariation and trait–environment relationships across NEON domains

   https://doi.org/10.1111/nph.18204  

   Wang, Zhihui ; Townsend, Philip A. ; Kruger, Eric L. ( May 2022 , New Phytologist)

   Concurrent measurement of multiple foliar traits to assess the full range of trade‐offs among and within taxa and across broad environmental gradients is limited. Leaf spectroscopy can quantify a wide range of foliar functional traits, enabling assessment of interrelationships among traits and with the environment.

   We analyzed leaf trait measurements from 32 sites along the wide eco‐climatic gradient encompassed by the US National Ecological Observatory Network (NEON). We explored the relationships among 14 foliar traits of 1103 individuals across and within species, and with environmental factors.

   Across all species pooled, the relationships between leaf economic traits (leaf mass per area, nitrogen) and traits indicative of defense and stress tolerance (phenolics, nonstructural carbohydrates) were weak, but became strong within certain species. Elevation, mean annual temperature and precipitation weakly predicted trait variation across species, although some traits exhibited species‐specific significant relationships with environmental factors.

   Foliar functional traits vary idiosyncratically and species express diverse combinations of leaf traits to achieve fitness. Leaf spectroscopy offers an effective approach to quantify intra‐species trait variation and covariation, and potentially could be used to improve the characterization of vegetation in Earth system models.

    

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3. Shifts in taxonomic and functional composition of trees along rainfall and phosphorus gradients in central Panama

   https://doi.org/10.1111/1365-2745.13442  

   Umaña, María Natalia ; Condit, Richard ; Pérez, Rolando ; Turner, Benjamin L. ; Wright, Stuart Joseph ; Comita, Liza S. ; Gibson, ed., David ( July 2020 , Journal of Ecology)

   Environmental gradients act as potent filters on species distributions driving compositional shifts across communities. Compositional shifts may reflect differences in physiological tolerances to a limiting resource that result in broad distributions for tolerant species and restricted distributions for intolerant species (i.e. a nested pattern). Alternatively, trade‐offs in resource use or conflicting species' responses to multiple resources can result in complete turnover of species along gradients.

   We combined trait (leaf area, leaf mass per area, wood density and maximum height) and distribution data for 550 tree species to examine taxonomic and functional composition at 72 sites across strong gradients of soil phosphorus (P) and rainfall in central Panama.

   We determined whether functional and taxonomic composition was nested or turned over completely and whether community mean traits and species composition were more strongly driven by P or moisture.

   Turnover characterized the functional composition of tree communities. Leaf traits responded to both gradients, with species having larger and thinner leaves in drier and more fertile sites than in wetter and less fertile sites. These leaf trait–moisture relationships contradict predictions based on drought responses and suggest a greater role for differences in light availability than in moisture. Shifts in wood density and maximum height were weaker than for leaf traits with taller species dominating wet sites and low wood density species dominating P‐rich sites.

   Turnover characterized the taxonomic composition of tree communities. Geographic distances explained a larger fraction of variation for taxonomic composition than for functional composition, and community mean traits were more strongly driven by P than moisture.

   Synthesis. Our results offer weak support for the tolerance hypothesis for tree communities in central Panama. Instead, we observe functional and taxonomic turnover reflecting trade‐offs and conflicting species' responses to multiple abiotic factors including moisture, soil phosphorus and potentially other correlated variables (e.g. light).

    

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4. Aridity drives coordinated trait shifts but not decreased trait variance across the geographic range of eight Australian trees

   https://doi.org/10.1111/nph.16795  

   Anderegg, Leander D. L. ; Loy, Xingwen ; Markham, Ian P. ; Elmer, Christina M. ; Hovenden, Mark J. ; HilleRisLambers, Janneke ; Mayfield, Margaret M. ( August 2020 , New Phytologist)

   Large intraspecific functional trait variation strongly impacts many aspects of communities and ecosystems, and is the medium upon which evolution works. Yet intraspecific trait variation is inconsistent and hard to predict across traits, species and locations.

   We measured within‐species variation in leaf mass per area (LMA), leaf dry matter content (LDMC), branch wood density (WD), and allocation to stem area vs leaf area in branches (branch Huber value (HV)) across the aridity range of seven Australian eucalypts and a co‐occurringAcaciaspecies to explore how traits and their variances change with aridity.

   Within species, we found consistent increases in LMA, LDMC and WD and HV with increasing aridity, resulting in consistent trait coordination across leaves and branches. However, this coordination only emerged across sites with large climate differences. Unlike trait means, patterns of trait variance with aridity were mixed across populations and species. Only LDMC showed constrained trait variation in more xeric species and drier populations that could indicate limits to plasticity or heritable trait variation.

   Our results highlight that climate can drive consistent within‐species trait patterns, but that patterns might often be obscured by the complex nature of morphological traits, sampling incomplete species ranges or sampling confounded stress gradients.

    

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5. Trade‐offs between seed size and biotic interactions contribute to coexistence of co‐occurring species that vary in fecundity

   https://doi.org/10.1111/1365-2745.13491  

   Maron, John L. ; Hahn, Philip G. ; Hajek, Karyn L. ; Pearson, Dean E. ; Mariotte, ed., Pierre ( September 2020 , Journal of Ecology)

   Despite theoretical advances, the ecological factors and functional traits that enable species varying in seed size and fecundity to coexist remain unclear. Given inherent fecundity advantages, why don't small‐seeded species dominate communities?

   In perennial grasslands, we evaluated whether small‐seeded species are less tolerant of competition from the community dominant bunchgrass than large‐seeded species, but also less vulnerable to seed predation by mice. We also explored whether trade‐offs involving competitive tolerance include two other functional traits, height and leaf mass per area (LMA). We added seeds of 17 forb species to plots where bunchgrass competition and rodent seed predation were manipulated across sites varying in bunchgrass productivity and thus competitive intensity. Seeds were added at densities mimicking interspecific variation in fecundity among target species.

   Standardizing for differences in fecundity (i.e. seed input, which enabled us to evaluate inherent interspecific differences in susceptibility to biotic interactions), bunchgrass competition more greatly reduced recruitment and establishment of small‐ versus large‐seeded species, whereas rodent seed predation more greatly reduced the recruitment of large‐ versus small‐seeded species. Plant height and LMA were unrelated to the competition effect size.

   Small‐seeded species abundance decreased across sites increasing in bunchgrass productivity, whereas this was not the case for large‐seeded species. For adult plants but not seedlings, community‐weighted functional trait means (CWM) for seed size, height and LMA increased in plots with versus without bunchgrass competition and the CWM for seed size and height also increased at sites with greater bunchgrass productivity (for adults only). In contrast, rodent seed predation had no significant effects on CWM seed size.

   At the end of the experiment, adult abundance positively correlated with plant fecundity in plots lacking bunchgrass, indicating the inherent advantages accrued to high fecundity small‐seeded species. However, with bunchgrass competition, abundances were equalized across species due to reduced competitive tolerance of high fecundity small‐seeded species.

   Synthesis. Our results suggest that coexistence among subordinate forb species varying in seed size and fecundity is in‐part due to a trade‐off involving competitive tolerance and fecundity, mediated by seed size and associated functional traits.

    

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