جستجوی مقالات مرتبط با کلیدواژه « shannon diversity index » در نشریات گروه « علوم پایه »

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.

Measurement of diversity indices and the local vegetation study are often suitable tools for studying the status of forests and rangelands and evaluating them. The purpose of this study is to evaluate the trend of vegetation changes in the dust center of Khuzestan province. In this study, the effect of rainfall fluctuations and irrigation of seedlings cultivated in the region on the percentage of cover and the type of native species during four consecutive years and in two seasons in the Hanitiah region was investigated. For this purpose, 5 transects with a length of 100 meters with 50-meter intervals were constructed in a systematic random manner in the study area. A total of 30 fixed plots were installed along transects. In two growing seasons, spring and autumn, from 2017 to 2020, the type and percentage of coverage of native species were recorded. Indices of dominance, uniformity, and species diversity of Simpson and Shannon were measured using PAST software. The results of one-way analysis of variance (ANOVA) showed that there is a significant difference between the mean of dominance, Shannon and Simpson indices, percentage of cover, and the number of species in the spring of different harvest years. But in comparing Shannon and Simpson indices and summer coverage, there is no significant difference between July 2019 and 2018. The species in the plots were all short-lived and the measured variability was time-dependent. From the above observations and results from the Hanitiah region, it can be concluded that despite the return of many short-lived species following the irrigation of cultivated seedlings and recent rains, the area is still very sensitive and fragile. Therefore, for complete revival, it still needs complete management, planning, and exclusion.

Agricultural biodiversity is considered as one of the key factors determining the sustainability of agroecosystems. Preservation of biodiversity and its effective management have an important role in achieving economical, social and environmental measures of agroecosystem sustainability, hence it is essential that through precise evaluation of diversity trend in agricultural landscapes, while its preservation, effective steps also accomplish to proper management of diversity with considering the regional characteristics. Hence, current study was carried out with the aim of evaluation and analysis the changes in crop biodiversity of Isfahan province during 2003-2012 using ecological indices of diversity, including Margalef richness index, Evenness index and Shannon diversity index. Evaluation of variation trends of study indices showed that during 2003-2012 period, crop area, evenness index, Shannon index and beta diversity of Isfahan crops have significantly decreased. The downward trend of Isfahan province’s crop plants Shannon index indicated that during this period, the crop species biodiversity of Isfahan province has decreased. As, the Shannon index value of Isfahan crop species was decreased from about 2.30 in initial years of 2003-2012 period up to 2.15 in its terminal years. Results showed that significant decrease in evenness of crop area distribution and also significant reduction of crop area due to continues droughts and land use changes are among the main reasons for decline in crop diversity of Isfahan province during study period. According to cluster analysis, the townships of Isfahan province were also classified into six groups regarding their ten years average of Shannon diversity index.

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.