نتایج جستجو برای: speciation

تعداد نتایج: 14852  

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2016
Kerry L Shaw Rosemary G Gillespie

Remote island archipelagos offer superb opportunities to study the evolution of community assembly because of their relatively young and simple communities where speciation contributes to the origin and evolution of community structure. There is great potential for common phylogeographic patterns among remote archipelagos that originate through hotspot volcanism, particularly when the islands f...

Journal: :Trends in genetics : TIG 2004
Olga Zhaxybayeva J Peter Gogarten

In this article, we explore the large-scale structure of the tree of life by using a simple model with a constant number of species and rates of speciation that equal the rates of extinction. In addition, we discuss the consequences of horizontal gene transfer for the concept of a most recent common ancestor of all living organisms (cenancestor). A simple null hypothesis based on coalescence th...

Journal: :iranian journal of science and technology (sciences) 2014
g. forghani

the mobility and bioavailability of trace elements in the agricultural soils are extremely important in assessing the risk of toxicity to the growing plants. a five step sequential extraction procedure (sep) has been employed to study the speciation of as, sb, cr, cu, cd, pb, zn, ni, fe and mn in 18 soil samples neighboring an industrial complex in isfahan, central iran. enrichment factor (ef) ...

Journal: :international journal of environmental research 2009
j. k. ygard e. gjengedal

landfill leachates and leachate sediments were investigated in order to survey the discharge of uranium (u) from municipal solid waste (msw) landfills and municipal solid waste incinerator (mswi) bottom ash landfills. concentrations of u in the leachates were as high as or higher than concentrations of cd, a metal more often discussed when considering the environmental effects of landfill leach...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2013
Luke C Strotz Andrew P Allen

Assessing the extent to which population subdivision during cladogenesis is necessary for long-term phenotypic evolution is of fundamental importance in a broad range of biological disciplines. Differentiating cladogenesis from anagenesis, defined as evolution within a species, has generally been hampered by dating precision, insufficient fossil data, and difficulties in establishing a direct l...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2009
Pincelli M Hull Richard D Norris

In contrast with speciation in terrestrial organisms, marine plankton frequently display gradual morphological change without lineage division (e.g., phyletic gradualism or gradual evolution), which has raised the possibility that a different mode of evolution dominates within pelagic environments. Here, we reexamine a classic case of putative gradual evolution within the Globorotalia plesiotum...

Journal: :Ecology letters 2009
Adam C Algar Jeremy T Kerr David J Currie

The latitudinal diversity gradient has been hypothesized to reflect past evolutionary dynamics driven by climatic niche conservation during cladogenesis, i.e. the tropical conservatism hypothesis. Here we show that the species diversity of treefrogs (Hylidae) across the western hemisphere is actually independent of evolutionary niche dynamics. We evaluated three key predictions of the tropical ...

Journal: :Evolution; international journal of organic evolution 2006
Jason T Weir

Late Pliocene and Pleistocene climatic instability has been invoked to explain the buildup of Neotropical biodiversity, although other theories date Neotropical diversification to earlier periods. If these climatic fluctuations drove Neotropical diversification, then a large proportion of species should date to this period and faunas should exhibit accelerated rates of speciation. However, the ...

Journal: :PLoS Biology 2008
Albert B Phillimore Trevor D Price

A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stro...

Journal: :Systematic biology 1998
J Stone J Repka

Three properties of bifurcating branching diagrams that are used for representing a specific number of taxa are (1) the number of possible arrangements, (2) the number of possible topologies, and (3) the probabilities of formation according to particular models of cladogenesis. Of these, the probabilities have received the least attention in the literature. Indeed, many biologists would be asto...

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