جستجوی مقالات مرتبط با کلیدواژه « Shannon diversity index » در نشریات گروه « محیط زیست »

Urbanization is considered the most important extinction driver of various fauna and flora species in the present century due to the degradation of habitat quality and its fragmentation. Therefore, investigation of changes in the land use land cover mosaic can provide useful information about the alteration of ecological processes, especially changes in bird diversity in urban landscapes. Bird survey was carried out from April to May 1400 between 8 and 11 am with three repetitions at 55 points located on 11 transects (5 points per transect). Transects and points were selected by examining land use and land cover changes on the rural-urban gradient. Then, 10 variables related to the area, mean distance and density of green cover, road network and habitat were computed in 4 circular buffers with radii of 750, 1500, 2250 and 3000 at each point of bird observation to assess their relationship with the Shannon diversity index using the multiple linear regression model. 2085 birds belonging to 46 bird species were observed. The domestic sparrow was found as the most abundant bird species with 1381 individuals. Among the independent parameters, percentage of green cover in buffer 1500 m, percentage of road cover in buffer 750 m, area of the nearest green cover, distance to the nearest green cover and mean distance to the nearest green cover in buffer 2250 m as variables were entered in the regression model (r2 = 0.64) as predictors of diversity Shannon. The findings of this study showed that the area of small green spaces, their long distance from each other and the high density of the road network are the most important factors in reducing the presence and diversity of bird species in the urban environment. Although areas close to the urban physical border showed higher bird diversity, their sharp decline toward the city center could be offset by accurate locating of urban green parks and reduction of traffic effects in nearby areas.

Soil macrofauna is one of the important components of soil biodiversity. This research was conducted to study the effect of climate and land use on soil macrofauna biodiversity in Northern Khorasan in 2009. The impact of climate was considered with selection two regions including Shirvan, with semi-arid climate and Jajarm, with arid-climate. In each region, two land uses including rangeland and agricultural land were considered. In sample units, the macrofauna were collected with pitfall traps, sorted and counted in terms of family. The analysis of data were perfumed using of t-test, ANOVA and PCA. The results showed that land use had significant impact on diversity in both regions. So, the taxonomic richness and Shannon diversity index were lower in rangelands compared to agricultural lands. This was attributed to low plant diversity and pressure of livestock grazing in rangelands. Also different composition of macrofauna was formed in two land uses. Impact of climate on diversity and composition of macrofauna was too much, so the favorable climate in the Shirvan compared to Jajarm region led to its improvement of soil macrofauna biodiversity.