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Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plants growing along wide elevation gradients in mountains experience considerable variations in environmental factors that vary across elevations. The most pronounced elevational changes are in climate conditions with characteristic decrease in air temperature with an increase in elevation. Studying intraspecific elevational variations in plant morphological traits and biomass allocation gives opportunity to understand how plants adapted to steep environmental gradients that change with elevation and how they may respond to climate changes related to global warming. In this study, phenotypic variation of an alpine plant Soldanella carpatica Vierh. (Primulaceae) was investigated on 40 sites distributed continuously across a 1,480-m elevation gradient in the Tatra Mountains, Central Europe. Mixed-effects models, by which plant traits were fitted to elevation, revealed that on most part of the gradient total leaf mass, leaf size and scape height decreased gradually with an increase in elevation, whereas dry mass investment in roots and flowers as well as individual flower mass did not vary with elevation. Unexpectedly, in the uppermost part of the elevation gradient overall plant size, including both below-and aboveground plant parts, decreased rapidly causing abrupt plant miniaturization. Despite the plant miniaturization at the highest elevations, biomass partitioning traits changed gradually across the entire species elevation range, namely, the leaf mass fraction decreased continuously, whereas the flower mass fraction and the root:shoot ratio increased steadily from the lowest to the highest elevations. Observed variations in S. carpatica phenotypes are seen as structural adjustments to environmental changes across elevations that increase chances of plant survival and reproduction at different elevations. Moreover, results of the present study agreed with the observations that populations of species from the 'Soldanella' intrageneric group adapted to alpine and subnival zones still maintain typical 'Soldanella'-like appearance, despite considerable reduction in overall plant size. [ABSTRACT FROM AUTHOR]

Crown development is closely related to the biomass and growth rate of the tree and its width (CW) is an important covariable in growth and yield models and in forest management. To date, various CW models have been proposed. However, limited studies have explicitly focused on additive and inherent correlation of crown components and total CW as well as the influence of competition on crown radius from the corresponding direction. In this study, two model systems were used, i.e., aggregation method system (AMS) and disaggregation method system (DMS), to develop crown width additive model systems. For calculating spatially explicit competition index (CI), four neighbor tree selection methods were evaluated. CI was decomposed into four cardinal directions and added into the model systems. Results show that the power model form was more proper for our data to fit CW growth. For each crown radius and total CW, height to the diameter at breast height (HDR) and basal area of trees larger than the subject tree (BAL) significantly contributed to the increase of prediction accuracy. The 3-m fixed radius was optimal among the four neighborhoods selection ways. After adding decomposed competition Hegyi index into model systems AMS and DMS, the prediction accuracy improved. Of the model systems evaluated, AMS based on decomposed CI provided the best performance as well as the inherent correlation and additivity properties. Our study highlighted the importance of decomposed CI in tree CW modelling for additive model systems. This study focused on methodology and could be applied to other species or stands. [ABSTRACT FROM AUTHOR]

Plant architecture strongly influences plant growth habits, as it determines the arrangement, function and fate of meristems. How architecture could be involved in the monocarpic life history, i.e. dying after flowering, remains poorly investigated. Monocarpy is evident in some species since they are annual or because their single stem flowers apically. However, monocarpy in long-lived branched trees is rare and remains poorly understood. We aim to highlight the architectural features involved in the monocarpic strategy of Cerberiopsis candelabra , a rainforest tree endemic to New Caledonia. We conducted a comparative analysis of the genus, which comprises three species with different growth habits. Twenty plants of each species were studied at different ontogenic stages. We compared their developmental sequence and analysed their processes of growth, branching, flowering and reiteration. We identified a combination of traits that distinguish the species, and we found a syndrome of two architectural features that support the monocarpic strategy in C. candelabra : the synchronous flowering of all terminal meristems and the absence of delayed branching. Flowering in C. candelabra preferentially occurs when the complete architectural sequence is developed, but the plant never shows signs of senescence, suggesting that environmental stresses, such as wind disturbance, could be the main trigger for flowering. The architecture of C. candelabra is suggested to be the most derived in the genus. [ABSTRACT FROM AUTHOR]

Cultivated sunflower (Helianthus annuus L.) pollen helps attract wild and managed bees needed to produce hybrid seed. Pollen quantity and grain size (≈quality) are affected by the environment, but are also heritable traits of interest for breeding. Florets from public inbred B-lines (maintainer) and R-lines (restorer) were used to evaluate pollen quantity and quality, test for trait correlations and determine if line development has changed pollen traits. Pollen quantity (≈25,000–67,000 grains per floret) and diameter (≈30–37 μm) were similar to previous reports and values of each parameter were correlated across years. Pollen quantity per floret was positively correlated with floret size (area; mm2) but floret sizes and pollen quantity were unrelated to pollen grain size. Groups of lines released relatively early (1968–1986) or late (1988–2006) did not differ in pollen quantity or size, and male (R-line) parents did not produce larger grains. The strong, positive correlation between floret size and pollen quantity reveals a possible trade-off because wild bees generally prefer sunflowers with shallower florets. The apparent lack of change in pollen quantity or pollen grain size over time (and lack of increased pollen size in R-lines relative to B-lines) suggests that the quantity and quality of pollen may not be limiting factors in the success of inbred lines or resulting hybrids. Though sunflower lines with larger florets contain more pollen, additional variation in pollen visible on sunflower heads may relate to the timing or completeness of pollen extrusion from anther tubes. [ABSTRACT FROM AUTHOR]

Understanding how communities respond to environmental change is frustrated by the fact that both species interactions and movement affect biodiversity in unseen ways. To evaluate the contributions of species interactions on community growth, dynamic models that can capture nonlinear responses to the environment and the redistribution of species across a spatial range are required. We develop a time-series framework that models the effects of environment–species interactions as well as species–species interactions on population growth within a community. Novel aspects of our model include allowing for species redistribution across a spatial region, and addressing the issue of zero inflation. We adopt a hierarchical Bayesian approach, enabling probabilistic uncertainty quantification in the model parameters. To evaluate the impacts of interactions and movement on population growth, we apply our model using data from eBird, a global citizen science database. To do so, we also present a novel method of aggregating the spatially biased eBird data collected at point-level. Using an illustrative region in North Carolina, we model communities of six bird species. The results provide evidence of nonlinear responses to interactions with the environment and other species and demonstrate a pattern of strong intraspecific competition coupled with many weak interspecific species interactions. Supplementary materials accompanying this paper appear online. [ABSTRACT FROM AUTHOR]

Rosa rugosa Thunb. (Japanese Rose) is one of the most invasive species in Europe. It spreads spontaneously in coastal areas of western, central and northern Europe, posing a threat to dune habitats, including those indicated in the EU Habitats Directive as particularly valuable. R. rugosa has already been reported to displace native plants and alter soil properties. However, little is known about how these effects are mediated by the habitat context or the invader condition (health, ontogenetic stage). This study addressed that gap by examining vegetation and soil in 22 R. rugosa-invaded sites, half of which were in yellow dunes and the other half in grey dunes, i.e. two habitats representing the earlier and later stages of dune succession. The study was conducted on the Hel Peninsula (Poland’s Baltic coast). R. rugosa had a significant impact on dune vegetation, but the impact was strongly dependent on the habitat type. In the yellow dune sites, R. rugosa outcompeted most resident plant species, which translated into a strong decline in their total cover and richness. The invasion was almost not accompanied by changes in soil properties, suggesting that it affected the resident vegetation directly (through space takeover and shading). In the grey dunes, R. rugosa caused a shift in species composition, from that characteristic of open communities to that typical of forests. In this habitat, a significant increase in the soil organic layer thickness under R. rugosa was also observed, which means that both direct and indirect effects of the invasion on the vegetation should be assumed. Finally, a negative relationship was found between the total chlorophyll content in R. rugosa leaves and the parameters of resident plant communities, showing that the invasion effects can vary not only across habitats, but also with the condition of the invader. The results may have practical implications for managing R. rugosa invasions in coastal sand dune systems. Since R. rugosa accelerates grey dune succession, protecting this habitat may be more urgent and, at the same time, more complicated than protecting dunes at the earlier stages of development. [ABSTRACT FROM AUTHOR]

Copyright of Arboriculture & Urban Forestry is the property of International Society of Arboriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In structured populations, persistence under environmental change may be particularly threatened when abiotic factors simultaneously negatively affect survival and reproduction of several life cycle stages, as opposed to a single stage. Such effects can then be exacerbated when species interactions generate reciprocal feedbacks between the demographic rates of the different species. Despite the importance of such demographic feedbacks, forecasts that account for them are limited as individual-based data on interacting species are perceived to be essential for such mechanistic forecasting—but are rarely available. Here, we first review the current shortcomings in assessing demographic feedbacks in population and community dynamics. We then present an overview of advances in statistical tools that provide an opportunity to leverage population-level data on abundances of multiple species to infer stage-specific demography. Lastly, we showcase a state-of-the-art Bayesian method to infer and project stage-specific survival and reproduction for several interacting species in a Mediterranean shrub community. This case study shows that climate change threatens populations most strongly by changing the interaction effects of conspecific and heterospecific neighbours on both juvenile and adult survival. Thus, the repurposing of multi-species abundance data for mechanistic forecasting can substantially improve our understanding of emerging threats on biodiversity. [ABSTRACT FROM AUTHOR]

Quantitative genetics aims at untangling the genetic and environmental effects on phenotypic variation. Trait heritability, which summarizes the relative importance of genetic effects, is estimated at the intraspecific level, but theory predicts that heritability could influence long-term evolution of quantitative traits. The phylogenetic signal concept bears resemblance to heritability and it has often been called species-level heritability. Under certain conditions, such as trait neutrality or contribution to phylogenesis, within-species heritability and between-species phylogenetic signal should be correlated. Here, we investigate the potential relationship between these two concepts by examining the evolution of multiple morphological traits for which heritability has been estimated in Drosophila melanogaster. Specifically, we analysed 42 morphological traits in both sexes on a phylogeny inferred from 22 nuclear genes for nine species of the melanogaster subgroup. We used Pagel's λ as a measurement of phylogenetic signal because it is the least influenced by the number of analysed taxa. Pigmentation traits showed the strongest concordance with the phylogeny, but no correlation was found between phylogenetic signal and heritability estimates mined from the literature. We obtained data for multiple climatic variables inferred from the geographical distribution of each species. Phylogenetic regression of quantitative traits on climatic variables showed a significantly positive correlation with heritability. Convergent selection, the response to which depends on the trait heritability, may have led to the null association between phylogenetic signal and heritability for morphological traits in Drosophila. We discuss the possible causes of discrepancy between both statistics and caution against their confusion in evolutionary biology. [ABSTRACT FROM AUTHOR]

Natural hybridization is a crucial evolutionary process and a long‐standing topic of study in evolutionary biology. Hybrid zones, where two congeneric species interact, can provide insight into the process of natural hybridization, especially with respect to how taxon diversity is maintained. In this study, we used double digest restriction‐site associated DNA sequencing technology (ddRAD‐seq) to examine genetic structure and estimate introgression in four hybrid zones of Ligularia tongolensis and Ligularia cymbulifera. Our analysis demonstrated that parental species were highly differentiated, whereas pairwise FST between parents and their hybrids was low, indicating that sympatric sites can form hybrid zones. As most F1 hybrid individuals were observed within these zones, our finding also implied the presence of substantial barriers to interbreeding. Furthermore, some individuals that possessed the typical morphology of the parental species belonged to the F1 generation. Genomic clines analysis revealed that a large fraction of single nucleotide polymorphisms (SNPs) deviated from a model of neutral introgression in the four hybrid zones, and most SNPs exhibited selection favoring the L. cymbulifera genotype. Bidirectional but asymmetric introgression was revealed as evident in the four hybrid zones. Habitat differences between the four hybrid zones may affect isolation barriers between both species. Taken together, these findings suggest that where incomplete reproductive barriers allow natural hybridization, the introgression between species generates rich genetic recombination that contributes to the fast adaptation and diversification of the widespread Ligularia in the Hengduan Mountains Region (HMR). [ABSTRACT FROM AUTHOR]

Ecosystems are influenced by multiple drivers, which shape ecosystem state and biodiversity. In some ecosystems, interactions and feedbacks among drivers can produce traps that confine an ecosystem to a particular state or condition and influence processes like succession. A range of traps has been recognized, with one of these – "a landscape trap" first proposed a decade ago for the tall, wet Mountain Ash and Alpine Ash forests of Victoria, south-eastern Australia. Under such a trap, young flammable forest is at high risk of reburning at high severity, thereby precluding stand maturation, and potentially leading to ecosystem collapse. These young forests are more common because recurrent wildfire and widespread clearcutting have transformed historical patterns of forest cover from widespread old-growth with small patches of regrowth embedded within it, to the reverse. Indeed, approximately 99% of the montane ash ecosystem is now relatively young forest. Based on new empirical insights, we argue that at least three key inter-related pre-conditions underpin the development of a landscape trap in montane ash forests. A landscape trap has been sprung in these forests because the pre-conditions for its development have been met. We show how inter-relationships among these pre-conditions, leading to frequent high-severity fire, interacts with life history attributes (e.g., time to viable seed production) to make montane ash forests (e.g., which have been highly disturbed through logging and frequent fire) vulnerable to ecosystem collapse. We conclude with the ecological and resource management implications of this landscape trap and discuss how the problems created might be rectified. [ABSTRACT FROM AUTHOR]

From hillslope to small catchment scales (< 50 km2), soil carbon management and mitigation policies rely on estimates and projections of soil organic carbon (SOC) stocks. Here we apply a process-based modeling approach that parameterizes the MIcrobial-MIneral Carbon Stabilization (MIMICS) model with SOC measurements and remotely sensed environmental data from the Reynolds Creek Experimental Watershed in SW Idaho, USA. Calibrating model parameters reduced error between simulated and observed SOC stocks by 25%, relative to the initial parameter estimates and better captured local gradients in climate and productivity. The calibrated parameter ensemble was used to produce spatially continuous, high-resolution (10 m2) estimates of stocks and associated uncertainties of litter, microbial biomass, particulate, and protected SOC pools across the complex landscape. Subsequent projections of SOC response to idealized environmental disturbances illustrate the spatial complexity of potential SOC vulnerabilities across the watershed. Parametric uncertainty generated physicochemically protected soil C stocks that varied by a mean factor of 4.4 × across individual locations in the watershed and a − 14.9 to + 20.4% range in potential SOC stock response to idealized disturbances, illustrating the need for additional measurements of soil carbon fractions and their turnover time to improve confidence in the MIMICS simulations of SOC dynamics. [ABSTRACT FROM AUTHOR]

Single species distribution models (SSDMs) are typically used to understand and predict the distribution and abundance of marine fish by fitting distribution models for each species independently to a combination of abiotic environmental variables. However, species abundances and distributions are influenced by abiotic environmental preferences as well as biotic dependencies such as interspecific competition and predation. When species interact, a joint species distribution model (JSDM) will allow for valid inference of environmental effects. We built a joint species distribution model of marine fish and invertebrates of the Northeast US Continental Shelf, providing evidence on species relationships with the environment as well as the likelihood of species to covary. Predictive performance is similar to SSDMs but the Bayesian joint modeling approach provides two main advantages over single species modeling: (1) the JSDM directly estimates the significance of environmental effects; and (2) predicted species richness accounts for species dependencies. An additional value of JSDMs is that the conditional prediction of species distributions can use not only the environmental associations of species, but also the presence and abundance of other species when forecasting future climatic associations. [ABSTRACT FROM AUTHOR]

Summary: Botanical gardens make unique contributions to climate change research, conservation, and public engagement. They host unique resources, including diverse collections of plant species growing in natural conditions, historical records, and expert staff, and attract large numbers of visitors and volunteers. Networks of botanical gardens spanning biomes and continents can expand the value of these resources. Over the past decade, research at botanical gardens has advanced our understanding of climate change impacts on plant phenology, physiology, anatomy, and conservation. For example, researchers have utilized botanical garden networks to assess anatomical and functional traits associated with phenological responses to climate change. New methods have enhanced the pace and impact of this research, including phylogenetic and comparative methods, and online databases of herbarium specimens and photographs that allow studies to expand geographically, temporally, and taxonomically in scope. Botanical gardens have grown their community and citizen science programs, informing the public about climate change and monitoring plants more intensively than is possible with garden staff alone. Despite these advances, botanical gardens are still underutilized in climate change research. To address this, we review recent progress and describe promising future directions for research and public engagement at botanical gardens. [ABSTRACT FROM AUTHOR]

Background: Hybridization and introgression are vital sources of novel genetic variation driving diversification during reticulated evolution. Quercus is an important model clade, having extraordinary diverse and abundant members in the Northern hemisphere, that are used to studying the introgression of species boundaries and adaptive processes. China is the second-largest distribution center of Quercus, but there are limited studies on introgressive hybridization. Results: Here, we screened 17 co-dominant nuclear microsatellite markers to investigate the hybridization and introgression of four oaks (Quercus acutissima, Quercus variabilis, Quercus fabri, and Quercus serrata) in 10 populations. We identified 361 alleles in the four-oak species across 17 loci, and all loci were characterized by high genetic variability (HE = 0.844–0.944) and moderate differentiation (FST = 0.037–0.156) levels. A population differentiation analysis revealed the following: allopatric homologous (FST = 0.064) < sympatric heterogeneous (FST = 0.071) < allopatric heterogeneous (FST = 0.084). A Bayesian admixture analysis determined four types of hybrids (Q. acutissima × Q. variabilis, Q. fabri × Q. serrata, Q. acutissima × Q. fabri, and Q. acutissima × Q. variabilis × Q. fabri) and their asymmetric introgression. Our results revealed that interspecific hybridization is commonly observed within the section Quercus, with members having tendency to hybridize. Conclusions: Our study determined the basic hybridization and introgression states among the studied four oak species and extended our understanding of the evolutionary role of hybridization. The results provide useful theoretical data for formulating conservation strategies. [ABSTRACT FROM AUTHOR]

Proactive interference occurs when consolidated memory traces inhibit new learning. This kind of interference decreases the efficiency of new learning and also causes memory errors. Exercise has been shown to facilitate some types of cognitive function; however, whether exercise reduces proactive interference to enhance learning efficiency is not well understood. Thus, this review discusses the effects of exercise on proactive memory interference and explores potential mechanisms, such as neurogenesis and neurochemical changes, mediating any effect. [ABSTRACT FROM AUTHOR]

Summary: The tree of life is highly reticulate, with the history of population divergence emerging from populations of gene phylogenies that reflect histories of introgression, lineage sorting and divergence. In this study, we investigate global patterns of oak diversity and test the hypothesis that there are regions of the oak genome that are broadly informative about phylogeny.We utilize fossil data and restriction‐site associated DNA sequencing (RAD‐seq) for 632 individuals representing nearly 250 Quercus species to infer a time‐calibrated phylogeny of the world's oaks. We use a reversible‐jump Markov chain Monte Carlo method to reconstruct shifts in lineage diversification rates, accounting for among‐clade sampling biases. We then map the > 20 000 RAD‐seq loci back to an annotated oak genome and investigate genomic distribution of introgression and phylogenetic support across the phylogeny.Oak lineages have diversified among geographic regions, followed by ecological divergence within regions, in the Americas and Eurasia. Roughly 60% of oak diversity traces back to four clades that experienced increases in net diversification, probably in response to climatic transitions or ecological opportunity.The strong support for the phylogeny contrasts with high genomic heterogeneity in phylogenetic signal and introgression. Oaks are phylogenomic mosaics, and their diversity may in fact depend on the gene flow that shapes the oak genome. See also the Editorial on this article by Plomion & Martin, 226: 943–946. [ABSTRACT FROM AUTHOR]

Summary: One of Anthropocene's most daunting challenges for conservation biology is habitat extinction, caused by rapid global change. Tree diversity has persisted through previous episodes of rapid change, even global extinctions. Given the pace of current change, our management of extant diversity needs to facilitate and even enhance the natural ability of trees to adapt and diversify. Numerous processes contribute to this evolutionary flexibility, including introgression, a widespread yet under‐studied process. Reproductive networks, in which species remain distinct despite interspecific gene flow, are called syngameons, a concept largely inspired from work focusing on Quercus. Delineating and analyzing such species groups, empirically and theoretically, will provide insights into the nonadditive effects on evolution of numerous partially interfertile species exchanging genetic material episodically under changing environmental conditions. To conserve tree diversity, crossing experiments designed with an empirical and theoretical understanding of the constituent syngameon should be set up to assist diversification and adaptation in the Anthropocene. Our increasingly detailed knowledge of the oak genome and of oak interspecific and intraspecific phenotypic variation will improve our ability to sustain the diversity of this tree through an unpredictable and unprecedented future. See also the Editorial on this article by Plomion & Martin, 226: 943–946. [ABSTRACT FROM AUTHOR]

Key message: UAV-based photogrammetry can provide detailed, accurate, and consistent structural models of open-grown trees across different species and growth forms. Environmental and ambient light conditions impact the results. Our empirical knowledge of the complicated and highly dynamic three-dimensional structure of trees is limited. Drone-based photogrammetry offers a powerful and effective tool for capturing, analyzing, and monitoring adult trees, particularly individuals growing outside of the closed canopy forest (subsequently termed "open-grown") in both natural and built environments. Here, we test the accuracy and consistency of high-resolution models of individual open-grown trees of three structurally distinct species. To validate model accuracy, we compared model estimates with direct measurements of branch diameter and internode length. We also examined the consistency of models of the same individual given different ambient light conditions by comparing corresponding measurements from two models of each tree. We use readily available equipment and software, so our protocol can be rapidly adopted by professional and citizen scientists alike. We found that the models captured diameter and interior internode length well (r2 = 0.87 and 0.98, respectively). Difference between measurements from different models of the same tree was less than 3 cm for diameters and interior internode lengths of most size classes. Thin distal branches were not captured well: measurements of terminal internodes in most size classes were underestimated by 50–60 cm. Models from overcast days were more accurate than models from sunny days (p = 0.0056), and a high-contrast background helps capture thin branches. Our approach constructs accurate and consistent three-dimensional models of individual open-grown trees that can provide the foundation for a wide range of physiological, behavioral, and growth studies. [ABSTRACT FROM AUTHOR]

ContentsSummary669I.Model clades for the study and integration of ecology and evolution670II.Oaks: an important model clade671III.Insights from the history of the American oaks for understanding community assembly and ecosystem dominance673IV.Bridging the gap between micro‐ and macroevolutionary processes relevant to ecology679V.How do we reconcile evidence for adaptive evolution with niche conservatism and long‐term stasis?682VI.High plasticity and within‐population genetic variation contribute to population persistence683VII.Emerging technologies for tracking functional change685VIII.Conclusions685Acknowledgements686References686 Summary: Ecologists and evolutionary biologists are concerned with explaining the diversity and composition of the natural world and are aware of the inextricable linkages between ecological and evolutionary processes that maintain the Earth's life support systems. Yet examination of these linkages remains challenging due to the contrasting nature of focal systems and research approaches. Model clades provide a critical means to integrate ecology and evolution, as illustrated by the oaks (genus Quercus), an important model clade, given their ecological dominance, remarkable diversity, and growing phylogenetic, genomic, and ecological data resources. Studies of the clade reveal that their history of sympatric parallel adaptive radiation continues to influence community assembly today, highlighting questions on the nature and extent of coexistence mechanisms. Flexible phenology and hydraulic traits, despite evolutionary stasis, may have enabled adaptation to a wide range of environments within and across species, contributing to their high abundance and diversity. The oaks offer fundamental insights at the intersection of ecology and evolution on the role of diversification in community assembly processes, on the importance of flexibility in key functional traits in adapting to new environments, on factors contributing to persistence of long‐lived organisms, and on evolutionary legacies that influence ecosystem function. [ABSTRACT FROM AUTHOR]

Summary: Here we study hybridization, introgression and lineage diversification in the widely distributed canyon live oak (Quercus chrysolepis) and the relict island oak (Q. tomentella), two Californian golden cup oaks with an intriguing biogeographical history. We employed restriction‐site‐associated DNA sequencing and integrated phylogenomic and population genomic analyses to study hybridization and reconstruct the evolutionary past of these taxa. Our analyses revealed the presence of two cryptic lineages within Q. chrysolepis. One of these lineages shares its most recent common ancestor with Q. tomentella, supporting the paraphyly of Q. chrysolepis. The split of these lineages was estimated to take place during the late Pliocene or the early Pleistocene, a time corresponding well with the common presence of Q. tomentella in the fossil records of continental California. Analyses also revealed historical hybridization among lineages, high introgression from Q. tomentella into Q. chrysolepis in their current area of sympatry, and widespread admixture between the two lineages of Q. chrysolepis in contact zones. Our results support that the two lineages of Q. chrysolepis behave as a single functional species phenotypically and ecologically well differentiated from Q. tomentella, a situation that can be only accommodated considering hybridization and speciation as a continuum with diffuse limits. [ABSTRACT FROM AUTHOR]