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An-Najah National University (2008)

Ecological Investigations on Terresterial Arthropod Biodiversity Under Different Grassland Ecosystems in El-Fara’ Area (Palestine)

Wasef Mohammed Deeb Ali

Titre : Ecological Investigations on Terresterial Arthropod Biodiversity Under Different Grassland Ecosystems in El-Fara’ Area (Palestine)

Auteur : Wasef Mohammed Deeb Ali

Université de soutenance : An-Najah National University

Grade : Master of Environmental Sciences 2008

Résumé
Despite the importance of arthropods in grassland ecosystems, few studies have examined how grassland arthropods have been impacted by disturbances in the Wadi Afara in the West Bank Objectives : This work was aimed at studying the effects of animal grazing on arthropod diversity, including species composition, species richness and species diversity, in a semi-arid Mediterranean grassland ecosystem at Alfara’ area in the Palestinian West Bank. Methodology : The field work was conducted at the Tallouza village, located in the north-eastern part of the West-Bank. The experiment was established in 2006 in an area of about 2000 donums of a mainly grassland ecosystem usually used for grazing sheep and goats herds, under different land use management systems : recently fenced grassland, undisturbed natural grassland, and recently reclaimed agricultural land. Within this area, three sites (2000m² each) with similar topographic and edaphic features were selected to study the effect of land use management practices on arthropods diversity including species composition, species richness and species diversity : one site was previously a part of a grassland suffering from grazing by mainly sheep and goats herds. In October 2005 the land was fenced and protected from any agricultural practices or grazing ; a second site was under grazing for the last 25 years, and the third site was undisturbed natural grassland where no human activities, agricultural practices or grazing had taken place for the last 5 years. Terrestrial arthropod communities were sampled seasonally at the three sites using pitfall traps, over the period of Apr 2006 to Apr 2007. One year of collections at comparison sites were used to quantify the seasonal variation of arthropod species and these parameters were correlated with climatic and edaphic conditions. Results and discussion : Arthropods communities were found to be sensitive to livestock grazing. Overall population levels of arthropods were highest in the undisturbed natural grassland, followed by grazed grasslands, and the fenced grassland. Certain insect orders (Coleoptera and Hymenoptera) were generally, negatively impacted by livestock grazing. However, members of the family (Carabidea, ground beetles) (order Coleoptera) especially Carabus impressus, were richer in grazed sites. On the other hand families of Hymenoptera like (Sphegidae, Cephidea and Apiddae) were not detected in the grazed grassland. On the other hand the unidentified species (Form 5) of the family (Formicidae) found only in the grazed grassland. A significant seasonal variation pattern was detected for total arthropod populations (P<0.05) at the different study sites, with the highest population levels detected in summer and early autumn, and lowest population levels detected in winter. The fluctuation patterns were comparable in the three sites. Comparable fluctuation patterns were also found for Hymenoptera and Coleoptera. Higher arthropod population levels in summer months coincided with higher air temperatures and lower soil moisture content, whereas, lower arthropod population levels in winter, coincided with lower temperatures and higher soil moisture content. Conclusion : Grazing has a considerable impact on the biodiversity of grassland arthropods in Alfara’ area. Some of the insect components, especially Carbus impresses, of the family Carabidae (order Coleoptera) are well adapted to grazing disturbance, and therefore can be used as bio indicators of habitat disturbance such as grazing.

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