جستجوی مقالات مرتبط با کلیدواژه « preference index » در نشریات گروه « کشاورزی »

One of the important factors in determining the grazing capacity of rangelands is determining the preferred value of rangeland plants according to the type of livestock using the rangeland and its changes during the grazing season. In this study, the preference value of rangeland species in Zaminsang rangeland in Hormozgan province in the months of grazing season (January to May) and different years (2007-2010) was investigated. To determine the preference value, the method of utilization percentage of plant species and determination of preference index were used. The results were analyzed in a split plot statistical design in time in a randomized complete block design in SAS software and the statistical mean of the studied trait was compared with LSD test. The results showed that the most preferred livestock is primarily Aeluropus lagopoides and Atriplex leucoclada and Alhagi graecorum. The lowest percentage of exploitation was from Halocnemum strobilaceum and Desmostachya bipinnata. Based on the preference value index classification, Aeluropus lagopoides and Atriplex leucoclada species are relatively palatable species (relative preference), Alhagi graecorum and Halocnemum strobilaceum species are moderately palatable species (moderate preference) and Desmostachya bipinnata was one of the almost non-palatable (relative avoidance) species.

In this research, the preference value of rangeland species in Sahand rangelands of East Azarbayjan province was studied for four years (2007-2010). The preference index method was used for this purpose. After determining the amount of production and consumption of each species selected in the grazing season (June, July, August, and September) and calculating the share of each species in the forage production of the region and livestock feed, and calculating the preference index, the data analyzed in split-plot design based on the completely randomized design in SAS software. The results showed that the effect of the year in three species, the effect of the month in four species, and the interaction of year and four species at (p≤0.01) were significant on the preference index. The preference index is a very important factor in determining the preference value of plant species for livestock. The species of Festuca rubra, Tanacetum chiliophyllum, with an average preference index of 1.4 to 1.6 during four-year, has a relative preference and is a relatively benign species and was placed in the palatable class I. Tanacetum chiliophyllum, with the highest average preference index, was ranked first among all herbaceous species. The species of Bromus tomentellus, Festuca ovina, Alopecorus textilis with an average preference index of 0.7 to 1.2 were of moderate preference and were classified as moderate in palatability and classified in the palatability class II.  Astragalus aureus, with an average preference index of about 0.3, had a relative preference, and this species was almost non-chewed and ranked in the palatable class III. Overall, the results of this study showed that the preference value of Festuca rubra and Tanacetum chiliophyllum was more than the other species, and the sheep preferred the forbs, followed by grasses and shrubs for sheep grazing.

The green lacewing Chrysoperla carnea is one of the natural enemies, which attacks various pests on crops and orchards. Feeding preference of natural enemies is one of the most important criteria used in evaluation of their efficiency. In this research, feeding preferences and switching of the second and third instar larvae of C. carnea were studied on the citrus aphid, Aphis spiraecola and the melon aphid, Aphis gossypii. The experiments were carried out on orange leaves in a growth chamber at 27±2°C, 65±5% RH and a photoperiod of 16L: 8D h. The results showed that when A. spiraecola or A. gossypii were separately offered to the second and third instar larvae of predator, the predation rate was higher on A. gossypii compared to A. spiraecola. Providing different combinations of A. gossypii: A. spiraecola significantly affected the consumption of C. carnea larvae in switching experiment. In different combinations, the consumption of the second and third instar larvae of the predator varied from 7.90 to 21.10 and from 15.70 to 31.00 on A. spiraecola, and from 14.60 to 29.60 and from 24.50 to 38.20 on A. gossypii, respectively. The values of Manly’s preference index in equal ratios of A. gossypii: A. spiraecola were calculated 0.632:0.368 and 0.647:0.353 for second and third larval instars, respectively, showing the preference of the larvae to A. gossypii. The results of the present study showed that the types

Host selection by parasitoids has vital effects on their fitness. Trissolcus vassilievi (Hym., Platygastridae) is a species with high biological potential in sunn pest control. Those parasitoids that develop in higher quality hosts are more vital and fecund than those develop in lower quality hosts. In this study, host preference and switching behavior of two populations of T. vassilievi (Tabriz and Varamin) was investigated on the same populations of the host at ratios of 5:1, 4:2, 3:3, 2:4 and 1:5 clutches. Host measurements revealed that host eggs was significantly heavier in the Varamin bugs than the Tabriz ones. The Varamin wasps were also larger than the Tabriz wasps and the progeny of the crosses was closer to the maternal populations. Data analysis was done by Murdoch (1969) and Cock (1978) methods. Referring to the values of c1 (preference index for Tabriz sunn pest) and c2 (preference index for Varamin sunn pest), Varamin population of T. vassilievi presented negative tendency to Tabriz host and positive tendency although non-significant to Varamin host. Linear regression analysis also showed significant trend of the parameter "c" over the host ratio in both parasitoids which confirms presence of switching behavior. In general, we can say that difference between host populations is less considerable than what can affect host-preference by the wasp.

This study was performed in the Qorveh rangeland of Kurdistan for five years (2006 2010) to determine the preference value of range species and grazing behavior. The preference value of range species was measured with two methods (time study and preference index). According to the obtained results, significant differences were found for the years and plant species in terms of grazing time percentage, at 1% level of probability. Mean comparison of grazing time percentage showed that Bromus tomentellus with an average of 12.31% together with annuals was classified in one class, and Galium verum, Thymus daenensis, Pterocephalus canus, Poa bulbosa and other species were classified in another class. The lowest grazing time percentage (0.33%) was recorded for Prangos ferulacea. Our results clearly showed that Stipa bromoiedes and Festuca ovina were much less grazed by livestock.

The study on the livestock dietary and preference value of different species are essential for rangeland management. Therefore، this study was carried out to evaluate the preference indices of 14 plant species in Kahnuj، during two different phenological stages (vegetative growth and after-seed-dispersal). The close observation method was used to measure the preference index for three age classes of Rainian goat (one، three and five years). The results showed that main and interaction effects of goat age، plant phenological stage and the kind of plant species on preference values were significant. Older goat consumed a higher time to graze in the study area. Stipa capensis had the highest preference index and Rhazya stricta had the lowest. The preference index of most plant species was significantly variable between two phenological stages. In addition، in each phenological stage، the preference value of plant species was significantly different. In the vegetative growth stage that annual plant species were abundant، goats mostly focused on these plant species for grazing. However، in the after-seed-dispersal stage in which the annual cover decreased، goats (particularly older ones) focused on shrubs for browsing. As a result، Rainian goat is a grazer in the normal situation and he can be a browser in the hard condition. It was suggested that the cover of Taverniera cuneifolia to be increased in the study area in order to compensate the deficiency of forage in long term. Artificial foraging is useful to reserve the performance of goats (particularly younger ones) in short term.

In range management practices it is impotant to understnd growing and production of key speceis as well as changes in their preference values according to seasons and habitat characteristics. The aim of this study is comparison of preference values of Festuca ovina species at different times and different regions of semi-steppic rangeland of Iran in 2006 to 2009. Random sampling with one square meter frames was emplyed to study vegetation during different growing monthes. Preference index method was used to determine the preference value of F. ovina. To calculate preference index, the ratio of the species in the diet and in the species composition were used. To compare preference value in different places and times randomized complete design with combined analysis in year and place was conducted. The results showed that among the studied sites and between the months are significant difference at α=0/05. Changes in preference values of F. ovina indicated that value of preference of this species increased until August and then decreased in September.