We present the results of two exploratory parsimony analyses of DNA sequences from 475 and 499 species of seed plants, respectively, representing all major taxonomic groups. The data are exclusively from the chloroplast gene rbcL, which codes for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO or RuBPCase). We used two different state-transformation assumptions resulting in two sets of cladograms: (i) equal-weighting for the 499-taxon analysis; and (ii) a procedure that differentially weights transversions over transitions within characters and codon positions among characters for the 475-taxon analysis. The degree of congruence between these results and other molecular, as well as morphological, cladistic studies indicates that rbcL sequence variation contains historical evidence appropriate for phylogenetic analysis at this taxonomic level of sampling. Because the topologies presented are necessarily approximate and cannot be evaluated adequately for internal support, these results should be assessed from the perspective of their predictive value and used to direct future studies, both molecular and morphological. In both analyses, the three genera of Gnetales are placed together as the sister group of the flowering plants, and the anomalous aquatic Ceratophyllum (Ceratophyllaceae) is sister to all other flowering plants. Several major lineages identified correspond well with at least some recent taxonomic schemes for angiosperms, particularly those of Dahlgren and Thorne. The basalmost clades within the angiosperms are orders of the apparently polyphyletic subclass Magnoliidae sensu Cronquist. The most conspicuous feature of the topology is that the major division is not monocot versus dicot, but rather one correlated with general pollen type: uniaperturate versus triaperturate. The Dilleniidae and Hamamelidae are the only subclasses that are grossly polyphyletic; an examination of the latter is presented as an example of the use of these broad analyses to focus more restricted studies. A broadly circumscribed Rosidae is paraphyletic to Asteridae and Dilleniidae. Subclass Caryophyllidae is monophyletic and derived from within Rosidae in the 475-taxon analysis but is sister to a group composed of broadly delineated Asteridae and Rosidae in the 499-taxon study.
The carnivorous habit in flowering plants represents a grade of structural organization. Different morphological features associated with the attraction, trapping, and digestion of prey characterize a diversity of specialized forms, including the familiar pitcher and flypaper traps. Phylogenetic analysis of nucleotide sequence data from the plastic rbcL gene indicates that both carnivory and stereotyped trap forms have arisen independently in different lineages of angiosperms. Furthermore, these results demonstrate that flypaper traps share close common ancestry with all other trap forms. Recognition of these patterns of diversification may provide ideal, naturally occurring systems for studies of developmental processes underlying macromorphological evolution in angiosperms.
We investigated patterns of mammal assemblage structure on the Atherton Tableland in the Wet Tropics biogeographic region of northeastern Australia. We used live trapping and quantitative estimates of stratified vegetation density to examine the relationships between the structure of the mammal assemblage and habitat structure over three nested spatial scales across a natural vegetation gradient from rain forest to dry, open forest. The narrow transition zone enabled us to examine the relationships between mammal assemblage structure and habitat structure while minimizing the confounding effects of distance, climate, and biogeographic history. The structure of the mammal assemblages was closely related to vegetation structure across and within habitats, and over all spatial scales examined. Vegetation complexity and heterogeneity both influenced assemblage structure, but the relationships varied with spatial scale. Species richness was highest in the open forest and decreased across the gradient into the rain forest. Point diversity was only weakly explained by vegetation structure, whereas Ͼ80% of the variation in species richness at the local scale could be explained by vegetation structure. Local-scale species richness of ground-dwelling mammals was mostly a product of the spatial variability in assemblage structure ( diversity), which was associated with the spatial variability in vegetation structure. Local-scale habitat heterogeneity thus promoted local-scale species richness via the close ecological interaction between mammals and habitat structure. The multiscale approach used here, and the nesting of spatial variability in within-habitat vegetation structure, enabled us to demonstrate the scale-dependent effects of spatial habitat heterogeneity and complexity on the structure and diversity of the small-mammal assemblage.
Biodiversity bill update I n its second year before Congress, the biological diversity bill has gained additional cosponsors in both the House and Senate and continues to wind its way through the legislative process. At press time, HR 1268, introduced by James H.
Species with narrow environmental niches typically have small geographic ranges. Small range size is, in turn, often associated with low local abundance. Together, these factors should mean that ecological specialists have very small total populations, putting them at high risk of extinction. But some specialized and geographically restricted species are ancient, and some ecological communities have high proportions of rare and specialized endemics. We studied niche characteristics and patterns of distribution and abundance of terrestrial vertebrates in the rainforests of the Australian Wet Tropics (AWT) to identify mechanisms by which rare species might resist extinction. We show that species with narrow environmental niches and small geographic ranges tend to have high and uniform local abundances. The compensation of geographic rarity by local abundance is exact, such that total population size in the rainforest vertebrates of the AWT is independent of environmental specialization. This effect would tend to help equalize extinction risk for specialists and generalists. Phylogenetic analysis suggests that environmental specialists have been gradually accumulating in this fauna, indicating that small range size/environmental specialization can be a successful trait as long as it is compensated for by demographic commonness. These results provide an explanation of how range-restricted specialists can persist for long periods, so that they now form a major component of high-diversity assemblages such as the AWT.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.