نتایج جستجو برای: mean of richness margalef
تعداد نتایج: 21177290 فیلتر نتایج به سال:
We sampled benthic algae monthly for 15 months in 12 New Zealand gravel-bed streams to investigate amongstream differences in algal taxonomic richness and how this might relate to among-stream differences in flood disturbance and nutrient resource regimes. The mean number of benthic algal taxa per month ranged from 9.4 to 21.3 among streams. There were moderate month-to-month fluctuations in ri...
forest reserves are one of the most important approaches in ecosystem management in iran. in order to determine the effects of reserve management on plants diversity (woody plants and ground flora) in three zones (core zone, buffer zone, and transmission zone of chamhesar pear forest reserve), we mapped land form units. then 18 main sampling units (20×50=1000 m2) distributed randomly were chose...
Abstract The positive ecological interaction between gap formation and natural regeneration has been examined but little research carried out on the effects of gaps in forests under different intensities disturbance. This study evaluates composition, diversity, density abundance tree species undisturbed, intermittently disturbed, disturbed forest sites. Bia Tano Forest Reserve Ghana was area th...
Canals of Sundarbans in India are highly vulnerable to anthropogenic pressures which directly or indirectly impact the biological components such ecosystems. Being at base trophic pyramid, phytoplankton is exposed environmental stressors and will be reflected upper strata aquatic food chain. Hence, communities along with their interrelationship parameters were assessed Bhetkimari canal, a semi-...
—North American monilophyte (fern) and lycophyte richness patterns are examined at three taxonomic levels (species, genus, and family). We determine: (1) if fern richness patterns are associated with water and energy variables that are predicted by the productivity-diversity hypothesis and (2) whether the pattern or strength of the relationship varies with taxonomic level. We present species ri...
Bird species richness is mediated by local, regional, and historical factors, for example, competition, environmental heterogeneity, contemporary, and historical climate. Here, we related bird species richness with phylogenetic relatedness of bird assemblages, plant species richness, topography, contemporary climate, and glacial-interglacial climate change to investigate the relative importance...
N and P often limit primary and secondary production in ecosystems, but they also can cause eutrophication and negatively influence sensitive species above a certain level or threshold point. Aquatic biodiversity can have negative threshold relationships with water-quality variables at large scales, but the specific mechanism(s) driving these threshold relationships are not well established. We...
Understanding what drives the geographic variation of species richness across the globe is a fundamental goal of ecology and biogeography. Environmental variables have been considered as drivers of global diversity patterns but there is no consensus among ecologists on what environmental variables are primary drivers of the geographic variation of species richness. Here, I examine the relations...
Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?
Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance b...
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