Floristic Dominance Research Articles

Evolution of Lower Brachyceran Flies (Diptera) and Their Adaptive Radiation with Angiosperms.

The Diptera (true flies) is one of the most species-abundant orders of Insecta, and it is also among the most important flower-visiting insects. Dipteran fossils are abundant in the Mesozoic, especially in the Late Jurassic and Early Cretaceous. Here, we review the fossil record and early evolution of some Mesozoic lower brachyceran flies together with new records in Burmese amber, including Tabanidae, Nemestrinidae, Bombyliidae, Eremochaetidae, and Zhangsolvidae. The fossil records reveal that some flower-visiting groups had diversified during the mid-Cretaceous, consistent with the rise of angiosperms to widespread floristic dominance. These brachyceran groups played an important role in the origin of co-evolutionary relationships with basal angiosperms. Moreover, the rise of angiosperms not only improved the diversity of flower-visiting flies, but also advanced the turnover and evolution of other specialized flies.

Beyond climate: convergence in fast evolving sclerophylls in Cape and Australian Rhamnaceae predates the mediterranean climate

Summary Morphological convergence in mediterranean‐type ecosystems (MTEs) has long been interpreted as adaptation to climatic similarities among the five MTEs of the world. Here, we challenge this model using the globally distributed Rhamnaceae. We collected functional trait data (specific leaf area, leaf area, spinescence, leaf phenology, growth form and leaf margin type) and biome data to test for trait convergence in MTEs, for models of trait evolution and ancestral state reconstruction and for the effect of traits on speciation and extinction rates, using a phylogenetic framework. We show that leaf functional traits evolve to three optima, which correspond to (i) the edaphically specialized Australian and Cape MTEs (AC), (ii) the mediterranean‐type climates, but edaphically normal Chile, California and Mediterranean Basin (CCM) and (iii) the non‐mediterranean habitats. We find that Rhamnaceae in CCM are predominantly characterized by non‐sclerophylly, the ancestral state in Rhamnaceae, and Rhamnaceae in AC by sclerophylly. These leaf character syndromes have evolved prior to mediterranean climates in MTEs, thereby failing to be adaptive to this selective regime. However, sclerophylly evolved contemporaneously with the transitions to AC and may therefore be an adaptation to nutrient‐poor soils. The evolution of sclerophylly has contributed to increased diversification rates of Pomaderreae in Australia and Phyliceae in the Cape, by reducing extinction rates and thereby facilitating evolutionary persistence. The historical relatively stable conditions in AC are consistent with this persistence hypothesis. Synthesis. In this study, we integrate the fields of macroevolution and ecology and show that low extinction rates may not only account for the ecological, but also for the floristic dominance of sclerophylly in the hyperdiverse Australian and Cape mediterranean‐type ecosystems.

Habitat requirements of Polygonetum natantis Soó 1927 and Potamogetonetum natantis Soó 1927 phytocenoses in north-eastern Poland

Comparison of habitats of <em>Polygonetum natantis</em> Soó 1927 and <em>Potamogetonetum natantis</em> Soó 1927 phytocenoses as regards physical and chemical properties of the water and substrate demonstrated that the habitat requirements of both these communities are different. <em>Polygonetum natantis</em> phytocenoses indicate a substrate poor in nutrient components and rich waters, whereas <em>Potamogetonetum natantis</em> patches, on the contrary, are evidence of fertile substrate and waters poor in biophilous components. The differences in habitat conditions demonstrated between the examined communities confirm the correctness of narrow classification of aquatic plant communities, based on floristic dominance.

Early Cretaceous angiosperms and beetle evolution

The Coleoptera (beetles) constitute almost one–fourth of all known life-forms on earth. They are also among the most important pollinators of flowering plants, especially basal angiosperms. Beetle fossils are abundant, almost spanning the entire Early Cretaceous, and thus provide important clues to explore the co-evolutionary processes between beetles and angiosperms. We review the fossil record of some Early Cretaceous polyphagan beetles including Tenebrionoidea, Scarabaeoidea, Curculionoidea, and Chrysomeloidea. Both the fossil record and molecular analyses reveal that these four groups had already diversified during or before the Early Cretaceous, clearly before the initial rise of angiosperms to widespread floristic dominance. These four beetle groups are important pollinators of basal angiosperms today, suggesting that their ecological association with angiosperms probably formed as early as in the Early Cretaceous. With the description of additional well-preserved fossils and improvements in phylogenetic analyses, our knowledge of Mesozoic beetle–angiosperm mutualisms will greatly increase during the near future.

Widespread plant species: natives versus aliens in our changing world

Estimates of the level of invasion for a region are traditionally based on relative numbers of native and alien species. However, alien species differ dramatically in the size of their invasive ranges. Here we present the first study to quantify the level of invasion for several regions of the world in terms of the most widely distributed plant species (natives vs. aliens). Aliens accounted for 51.3% of the 120 most widely distributed plant species in North America, 43.3% in New South Wales (Australia), 34.2% in Chile, 29.7% in Argentina, and 22.5% in the Republic of South Africa. However, Europe had only 1% of alien species among the most widespread species of the flora. Across regions, alien species relative to native species were either as well-distributed (10 comparisons) or more widely distributed (5 comparisons). These striking patterns highlight the profound contribution that widespread invasive alien plants make to floristic dominance patterns across different regions. Many of the most widespread species are alien plants, and, in particular, Europe and Asia appear as major contributors to the homogenization of the floras in the Americas. We recommend that spatial extent of invasion should be explicitly incorporated in assessments of invasibility, globalization, and risk assessments.

Chlorophyceae das represas Billings (Braço Taquacetuba) e Guarapiranga, SP, Brasil

A biodiversidade de Chlorophyceae foi estudada em duas das maiores represas da Regiao Metropolitana da cidade de Sao Paulo, Billings e Guarapiranga, que fornecem agua para o abastecimento de milhoes de pessoas. As coletas bimensais foram realizadas durante o periodo de janeiro a dezembro de 2004, em uma estacao localizada proximas a captacao de agua da Sabesp, em cada represa. As amostras foram filtradas com rede de plâncton de 20 µm de abertura de malha, preservadas em formol. Foram identificados, descritos e ilustrados 36 taxons de Chlorophyceae, distribuidos em duas ordens, dez familias e 24 generos. O genero Desmodesmus apresentou maior riqueza de especies (quatro), seguido de Ankistrodesmus e Scenedesmus (tres especies cada). Dez taxons constituiram primeiras citacoes para as represas estudadas. Oito taxons ocorreram exclusivamente na represa Guarapiranga e tres foram registrados exclusivamente na represa Billings, sendo que 70% das especies foi comum aos dois reservatorios. A elevada riqueza de especies de cloroficeas confirma o predominio floristico desta classe em corpos de agua tropicais e, geralmente, eutrofizados.

Temporal lags and overlap in the diversification of weevils and flowering plants.

The extraordinary diversity of herbivorous beetles is usually attributed to coevolution with angiosperms. However, the degree and nature of contemporaneity in beetle and angiosperm diversification remain unclear. Here we present a large-scale molecular phylogeny for weevils (herbivorous beetles in the superfamily Curculionoidea), one of the most diverse lineages of insects, based on approximately 8 kilobases of DNA sequence data from a worldwide sample including all families and subfamilies. Estimated divergence times derived from the combined molecular and fossil data indicate diversification into most families occurred on gymnosperms in the Jurassic, beginning approximately 166 Ma. Subsequent colonization of early crown-group angiosperms occurred during the Early Cretaceous, but this alone evidently did not lead to an immediate and major diversification event in weevils. Comparative trends in weevil diversification and angiosperm dominance reveal that massive diversification began in the mid-Cretaceous (ca. 112.0 to 93.5 Ma), when angiosperms first rose to widespread floristic dominance. These and other evidence suggest a deep and complex history of coevolution between weevils and angiosperms, including codiversification, resource tracking, and sequential evolution.

Temporal and spatial variation of habitat conditions in the zonation of littoral plant communities

In this study, zonal distribution of littoral plant communities conformed with the spatial gradient and temporal variation of habitat conditions. In the water of the successive zones, pH and the concentrations of Na and K increased towards open water, whereas oxidability, the concentrations of NO 3-N and PO 4-P sediment organic matter content decreased. Hydration was lowest in the vegetational zone nearest to the open water, whereas the sediment Ca content was highest in this zone. Temporal changes often proceeded at a different rate for a given component or factor in each zone. Water plant communities, distinguished on the basis of floristic dominance as distinct syntaxa, could be good indicators of littoral habitat conditions.

Angiosperm Diversification and Paleolatitudinal Gradients in Cretaceous Floristic Diversity

The latitudinally diachronous appearance of angiosperm pollen during the Cretaceous is well documented, but the subsequent diversification and accompanying significant changes in floristic dominance have not been assessed quantitatively for a wide range of paleolatitudes. Trend surfaces fitted to within-palynoflora diversity data from 1125 pollen and spore assemblages show that angiosperms first become floristically prominent in low paleolatitude areas( approximately 20 degrees N to 20 degrees S). Non-magnoliid dicotyledons show a similar but slightly delayed pattern of increase and are the principal component of angiosperm diversity from all areas sampled. Monocotyledons and magnoliid dicotyledons are significant primarily in low to middle paleolatitude palynofloras( approximately 50 degrees N to 20 degrees S) during the latest Cretaceous. As angiosperms become increasingly prevalent the importance of most non-angiosperm taxa either decreases or remains unchanged. The only apparent exception is a striking increase in gnetalean diversity concurrent with the initial angiosperm diversification at low paleolatitudes.

Habitat conditions of the phytocoenoses of myriophylletum alterniflori lemée 1937 em. Siss. 1943, myriophylletum verticillati soó 1927 and myriophylletum spicati soó 1927 in Poland

A comparative analysis of the habitats of 28 Myriophylletum alterniflori, 23 Myriophylletum verticillati and 29 Myriophylletum spicati phytocoenoses from 50 lakes within northern and south-eastern Poland was conducted. On the basis of phytosociological data, and the physical and chemical properties of water and substrate in the analysed phytocoenoses, it is demonstrated that the phytosociological distinction of the associations studied, based on floristic dominance, is confirmed in the distinction of their habitats, both with respect to water and substrate chemistry. Myriophylletum alterniflori phytocoenoses in Poland are restricted to soft, oligotrophic-mesotrophic waters, poor in calcium and magnesium, and to substrates also poor in these elements. Myriophylletum verticillati phytocoenoses occur in mesotrophic or slightly eutrophic waters, poor in NO 3N, PO 4P and K on hydrated, organic and organic-mineral substrates, mostly rich in calcium. The phytocoenoses of Myriophylletum spicati grow in waters with a wide trophic amplitude, although their optimum development occurs in typical eutrophic waters. They may be indicators of substrates poor in organic matter.

Quantitative analyses of the early angiosperm radiation

Although the pattern of the early angiosperm radiation has been substantially clarified by palaeobotanical and stratigraphic investigations over the last 30 years1–3, knowledge of associated vegetational and floristic change remains limited. Quantitative analyses of Cretaceous fossil floras indicate that by ∼90 million years before present (BP) angiosperms had achieved widespread floristic dominance, at least in the Northern Hemisphere. Although some non-angiosperm plant groups show no pronounced shifts in diversity in association with the angiosperm radiation, others show marked declines that contribute to profound alterations in the composition of terrestrial plant communities. Comparative trends in systematic diversity suggest competitive displacement of cycadophytes and pteridophytes by angiosperms, but current evidence is not sufficient to exclude the probability of a more complex basis for mid-Cretaceous floristic change.