نتایج جستجو برای: natural ecosystems

تعداد نتایج: 518661  

2005
A. C. Dam

This paper describes a research on the biological validity of virtual ecosystems. Artificial Life systems are designed in the pursuit of creating an instance of life in a computational environment. The reproduction mechanisms of these systems are compared with nature’s reproduction mechanisms as described by Ernst Mayr. This research determines if the ecosystems give a correct representation of...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه تربیت معلم تهران - دانشکده علوم 1370

determination of uranium in natural water and complex solutions using ion exchange chromatography: a combined procedure using ion exchange chromatography and uv-vis spectrophotometry techniques has been developed to measure uranum in natural water and complex solutions. after conditicing , one hundred milli liters of sample solutions have been passed through an ion exchange column,pachked with ...

2015
Michael Staab Michael Ohl Chao-Dong Zhu Alexandra-Maria Klein

Global biodiversity is rapidly declining, leading inevitably to a loss of ecosystem functionality when species and their associated life-history traits vanish. Unfortunately, even in the 21(st) century, a large proportion of Earth's species are yet unknown and also for most described species science lacks a deeper understanding of the functional role of species and thus of ecosystems. In this A...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 1997
J H Brown T J Valone C G Curtin

Natural ecosystems contain many individuals and species interacting with each other and with their abiotic environment. Such systems can be expected to exhibit complex dynamics in which small perturbations can be amplified to cause large changes. Here, we document the reorganization of an arid ecosystem that has occurred since the late 1970s. The density of woody shrubs increased 3-fold. Severa...

Journal: :Ecology letters 2007
James B Grace T Michael Anderson Melinda D Smith Eric Seabloom Sandy J Andelman Gayna Meche Evan Weiher Larry K Allain Heli Jutila Mahesh Sankaran Johannes Knops Mark Ritchie Michael R Willig

Theoretical analyses and experimental studies of synthesized assemblages indicate that under particular circumstances species diversity can enhance community productivity through niche complementarity. It remains unclear whether this process has important effects in mature natural ecosystems where competitive feedbacks and complex environmental influences affect diversity-productivity relations...

2010
Patrick Gonzalez Ronald P. Neilson James M. Lenihan Raymond J. Drapek

Aim Climate change threatens to shift vegetation, disrupting ecosystems and damaging human well-being. Field observations in boreal, temperate and tropical ecosystems have detected biome changes in the 20th century, yet a lack of spatial data on vulnerability hinders organizations that manage natural resources from identifying priority areas for adaptation measures. We explore potential methods...

Journal: :EMBO reports 2004
Zdena Palková

Our present in-depth knowledge of the physiology and regulatory mechanisms of microorganisms has arisen from our ability to remove them from their natural, complex ecosystems into pure liquid cultures. These cultures are grown under optimized laboratory conditions and allow us to study microorganisms as individuals. However, microorganisms naturally grow in conditions that are far from optimal,...

Journal: :بوم شناسی کشاورزی 0
علیرضا کوچکی مهدی نصیری محلاتی افسانه امین غفوری منصوره محلوجی راد فرنوش فلاح پور

introduction due to its multifunctional nature agriculture play important roles in ecological processes such as carbon sequestration, flood control, groundwater recharge, nutrient cycling, and purifying water, soil and air in addition to providing food, feed and fiber. these cover almost all ecological services provided by natural ecosystems, including provisioning services, regulating services...

2005
John A. Stanturf

Forested ecosystems are dynamic, subject to natural developmental processes as well as natural and anthropogenic stresses and disturbances. Degradation is a related term. for lowered productive capacity from changes to forest structure of function (FAO. 2001). Degradation is not synonymous with disturbance, however; disturbance becomes degradation when natural resilience mechanisms are overwhel...

Journal: :international journal of environmental research 0

urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystemfunctions, therefore these areas not only support a unique biodiversity but also have a social value for maintainingpublic health andwellbeing. for this reason, urbanization is considered to be one the biggest threats to ecosystems,leading to native biodiversity simplification and, thus, to a detrime...

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