نتایج جستجو برای: extinction of rare species

تعداد نتایج: 21217683  

Journal: :PLoS ONE 2008
Zoe T. Richards Madeleine J. H. van Oppen Carden C. Wallace Bette L. Willis David J. Miller

BACKGROUND Coral reefs worldwide face a variety of threats and many coral species are increasingly endangered. It is often assumed that rare coral species face higher risks of extinction because they have very small effective population sizes, a predicted consequence of which is decreased genetic diversity and adaptive potential. METHODOLOGY/PRINCIPAL FINDINGS Here we show that some Indo-Paci...

Journal: :Ecology 2012
Glenda Yenni Peter B Adler S K Morgan Ernest

Theory has recognized a combination of niche and neutral processes each contributing, with varying importance, to species coexistence. However, long-term persistence of rare species has been difficult to produce in trait-based models of coexistence that incorporate stochastic dynamics, raising questions about how rare species persist despite such variability. Following recent evidence that rare...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه گیلان 1390

during 2010-2011 a faunistic survey was carried out for collection and identification of edaphic mesostigmatic mites (acari: mesostigmata) in jiroft and suburb. mites were extracted from soil samples by berlese funnel. the mites were cleared in nesbit fluid and were mounted in hoyer medium on microscopic slides. in this study 43 spices from 26 genera and 16 families were collected and identifie...

پایان نامه :وزارت علوم، تحقیقات و فناوری - پژوهشگاه دانشهای بنیادی (مرکز تحقیقات فیزیک نظری و 1387

we show that when both sources ( lepton flavor violation sources and cp-violating phases) are present, the electric dipole moment of the electron, $d_e$, receives a contribution from the phase of the trilinear $a$-term of staus, $phi_{a_ au}$. for $phi_{a_ au}=pi/2$, the value of $d_e$, depending on the ratios of the lfv mass elements, can range between zero and three orders of magnitude a...

Journal: :Ecology letters 2009
Susanne A Fritz Olaf R P Bininda-Emonds Andy Purvis

Whereas previous studies have investigated correlates of extinction risk either at global or regional scales, our study explicitly models regional effects of anthropogenic threats and biological traits across the globe. Using phylogenetic comparative methods with a newly-updated supertree of 5020 extant mammals, we investigate the impact of species traits on extinction risk within each WWF ecor...

Journal: :Proceedings. Biological sciences 2012
Paul G Harnik Carl Simpson Jonathan L Payne

Rarity is widely used to predict the vulnerability of species to extinction. Species can be rare in markedly different ways, but the relative impacts of these different forms of rarity on extinction risk are poorly known and cannot be determined through observations of species that are not yet extinct. The fossil record provides a valuable archive with which we can directly determine which aspe...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه فردوسی مشهد - دانشکده کشاورزی 1388

چکیده به منظور بررسی اثر تنوع گیاهی و نوع منبع تغذیه ای بر تنوع و تراکم علفهای هرز و حشرات، کارایی مصرف نهاده ها ( نور، آب، عناصر غذایی) و عملکرد و خصوصیات کیفی چند گونه زراعی، آزمایشی به صورت کرتهای خردشده بر پایه طرح بلوکهای کامل تصادفی با سه تکرار در دو سال زراعی 1385-1384 و 1386-1385 در مزرعه تحقیقاتی دانشکده کشاورزی دانشگاه فردوسی مشهد به اجرا درآمد. تیمارهای مورد بررسی دو منبع کود دامی و...

2007
C. J. E. Metcalf K. Hampson D. N. Koons

Sudden catastrophic events like fires, hurricanes, tsunamis, landslides and deforestation increase population densities in habitat fragments, as fleeing animals encroach into these refuges. Such sudden overcrowding will trigger transient fluctuations in population size in the refuges, which may expose refuge populations to an increased risk of extinction. Until recently, detailed information ab...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2008
Stephen P Hubbell Fangliang He Richard Condit Luís Borda-de-Agua James Kellner Hans Ter Steege

New roads, agricultural projects, logging, and mining are claiming an ever greater area of once-pristine Amazonian forest. The Millennium Ecosystems Assessment (MA) forecasts the extinction of a large fraction of Amazonian tree species based on projected loss of forest cover over the next several decades. How accurate are these estimates of extinction rates? We use neutral theory to estimate th...

2015
Yuval R. Zelnik Sorin Solomon Gur Yaari

Ecosystems greatly vary in their species composition and interactions, yet they all show remarkable resilience to external influences. Recent experiments have highlighted the significant effects of spatial structure and connectivity on the extinction and survival of species. It has also been emphasized lately that in order to study extinction dynamics reliably, it is essential to incorporate st...

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