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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 margins in a deciduous lineage from the Greater Cape Floristic Region track climate in unexpected directions

   https://doi.org/10.1002/ajb2.1472  

   Frye, Henry A. ; Mocko, Kerri ; Moore, Timothy E. ; Schlichting, Carl D. ; Jones, Cynthia S. ( May 2020 , American Journal of Botany)

   The functional significance of leaf margins has long been debated. In this study, we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genusPelargonium.

   Leaves from 454 populations ofPelargonium(161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was calculated for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models.

   Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite those previously reported: species were more likely to be toothed with warmer temperatures, particularly for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction ofMATand the season of most rain; density declines with temperature as consistent with expectations, but only in winter‐rain dominated areas. Woody and nonwoody species withinPelargoniumhave similar associations between tooth presence/absence andMAT, contrary to the expectation that patterns within nonwoody species would be insignificant.

   We concludePelargoniumleaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.

    

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3. Climate explains population divergence in drought‐induced plasticity of functional traits and gene expression in a South African Protea

   https://doi.org/10.1111/mec.15705  

   Akman, Melis ; Carlson, Jane E. ; Latimer, Andrew M. ( November 2020 , Molecular Ecology)

   Long‐term environmental variation often drives local adaptation and leads to trait differentiation across populations. Additionally, when traits change in an environment‐dependent way through phenotypic plasticity, the genetic variation underlying plasticity will also be under selection. These processes could create a landscape of differentiation across populations in traits and their plasticity. Here, we performed a dry‐down experiment under controlled conditions to measure responses in seedlings of a shrub species from the Cape Floristic Region, the common sugarbush (Protea repens). We measured morphological and physiological traits, and sequenced whole transcriptomes of leaf tissues from eight populations that represent both the climatic and the geographical distribution of this species. We found that there is substantial variation in how populations respond to drought, but we also observed common patterns such as reduced leaf size and leaf thickness, and up‐regulation of stress‐related and down‐regulation of growth‐related gene groups. Both high environmental heterogeneity and milder source site climates were associated with higher plasticity in various traits and co‐expression gene networks. Associations between traits, trait plasticity, gene networks and the source site climate suggest that temperature may play a greater role in shaping these patterns when compared to precipitation, in line with recent changes in the region due to climate change. We also found that traits respond to climatic variation in an environment‐dependent manner: some associations between traits and climate were apparent only under certain growing conditions. Together, our results uncover common responses ofP. repenspopulations to drought, and climatic drivers of population differentiation in functional traits, gene expression and their plasticity.

    

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4. Climatic stability recorded in speleothems may contribute to higher biodiversity in the Cape Floristic Region

   https://doi.org/10.1111/jbi.14592  

   Braun, Kerstin ; Cowling, Richard M. ; Bar‐Matthews, Miryam ; Matthews, Alan ; Ayalon, Avner ; Zilberman, Tami ; Difford, Mark ; Edwards, R. Lawrence ; Li, Xianglei ; Marean, Curtis W. ( March 2023 , Journal of Biogeography)

   The geography and genesis of diversity remain an enduring topic in ecology and evolution. Mediterranean Climate Ecosystems (MCEs), with their high plant diversities in winter rainfall climates, pose a challenge to popular hypotheses evoking high water availability and temperature as necessary for the evolution of high diversity. We test the hypothesis of environmental stability as a driver for the evolution of regional‐scale floristic diversity using speleothem oxygen (δ¹⁸O) and carbon (δ¹³C) isotopic values as proxies for past climatic variability in the Cape Floristic Region (CFR) and other MCEs.

   south‐western Africa, California, Mediterranean Basin.

   Plantae.

   We present new speleothem δ¹⁸O and δ¹³C records from a cave near Robertson in the western CFR. Stable isotope samples included in the analyses cover the time intervals between 240 and 670 ka BP with hiatuses at 630–500 ka and 360–310 ka. The dispersion of these stable isotope records is used as a measure for climatic variability. We compare our new analyses to speleothem records that cover full glacial and interglacial conditions in other MCEs (California and the Mediterranean Basin) as well as in eastern regions of the CFR. All sites used in this comparison have lower vascular plant biodiversity than the western CFR.

   Analyses of the dispersion of the δ¹⁸O and δ¹³C datasets suggest that the highly diverse western CFR experienced climatic stability across several glacial–interglacial cycles, compared with the less diverse regions within and outside of the CFR.

   This result provides support for the hypothesis that lower extinction rates associated with Pleistocene biome stability may explain the higher diversity in the CFR relative to other MCEs.

    

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5. Generative spatial generalized dissimilarity mixed modelling ( spGDMM ): An enhanced approach to modelling beta diversity

   https://doi.org/10.1111/2041-210X.14259  

   White, Philip A. ; Frye, Henry A. ; Slingsby, Jasper A. ; Silander, Jr, John A. ; Gelfand, Alan E. ( December 2023 , Methods in Ecology and Evolution)

   Turnover, or change in the composition of species over space and time, is one of the primary ways to define beta diversity. Inferring what factors impact beta diversity is not only important for understanding biodiversity processes but also for conservation planning. At present, a popular approach to understanding the drivers of compositional turnover is through generalized dissimilarity modelling (GDM). We argue that the current GDM approach suffers several limitations and provide an alternative modelling approach that remedies these issues.

   We propose using generative spatial random effects models implemented in a Bayesian framework. We offer hierarchical specifications to yield full regression and spatial predictive inference, both with associated full uncertainties. The approach is illustrated by examining dissimilarity in three datasets: tree survey data from Panama's Barro Colorado Island (BCI), plant occurrence data from southwest Australia and plant abundance surveys from the Greater Cape Floristic Region (GCFR) of South Africa. We select a best model using out‐of‐sample predictive performance.

   We find that the form of the best model differs across the three datasets, but our models provide performance ranging from comparable to significant improvement over GDMs. Within the GCFR, the spatial random effects play a more important role in the modelling than all the environmental variables.

   We have proposed a model that provides several improvements to the current GDM framework. This includes advantages such as a flexible spatially varying mean function, spatial random effects that capture dependence unaccounted for by explanatory variables, and spatially heterogeneous variance structure. All these features are offered in a model that can adequately handle a large incidence oftotaldissimilarity through ‘one‐inflation’, as would be expected from highly biodiverse areas with steep turnover gradients.

    

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