Ben-Gurion University of the Negev Jacob Blaustein Institutes for Desert Research Albert Katz International School for Desert Studies
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Ben-Gurion University of the Negev Jacob Blaustein Institutes for Desert Research Albert Katz International School for Desert Studies Effects of disturbance on beetle and spider assemblages in a Mediterranean woodland Thesis submitted in partial fulfilment of the requirements for the degree of “Master of Science” By Noa Angel Under the supervision of Prof. Yael Lubin Marco and Louise Department of Desert Ecology Dr. Elli Groner Marco and Louise Department of Desert Ecology Author’s Signature …………..….……………………… Date ……………. Approved by the Supervisor……………….……………. Date ……………. Approved by the Supervisor……………….……………. Date ……………. Approved by the Director of the School...…….………….. Date ……………. i Effects of disturbances on beetle and spider assemblages in a Mediterranean woodland By: Noa Angel Thesis is submitted in partial fulfillment of the degree of Master of Science (M.Sc.) Ben-Gurion University of the Negev, Jacob Blaustein Institutes for Desert Research, Albert Katz International School for Desert Studies, 2009 Abstract In Mt. Meron Nature Reserve landscape is becoming homogeneous following tree encroachment. Understory vegetation encompasses lower herbaceous plant species richness than adjacent open patches which are scarcely shaded or modulated by the canopy. This study aimed to examine the canopy effects on higher trophic groups. The research tested whether beetle and spider species diversity was higher in the open patches, following herbaceous species richness, or if it is positively affected by the filtering of the trees, and therefore higher in areas with higher tree cover. I tested two main hypotheses in which the spider and beetle richness in the woody patches are expected to increase with a decrease in canopy area. The Landscape Modulator-filtering hypothesis postulated that trees modulate their environment thus allowing the existence of woody-affiliated species. With the decrease in tree cover, beetle and spider species richness in the woody patch was predicted to decrease. The taxonomic diversity hypothesis postulates a direct relationship between plant species richness and arthropod species richness thus predicting an increase in beetle and spider species richness as a function of herbaceous species richness. Open patches-affiliated species were predicted to have a positive relation with both herbaceous plant richness and increased open area. ii . I examined these hypotheses through the use of two disturbance forms of management affecting the woody patch. Tree removal was used to decrease the tree cover, or increase the open area and cattle grazing was introduced in order to test its disturbance effects through grazing and browsing on regenerating trees. The results of this study partially supported the landscape modulator-filtering hypothesis. Ground-dwelling predator and detritivore species diversity decreased in their diversity with decreased tree cover. The taxonomic diversity hypothesis was also only partially supported. Herbivore species richness increased only in open patches as a function of herbaceous richness. Disturbance effects were attributed mostly to tree removal which had a large effect on beetle and spider diversity patterns and composition while grazing had little to no effect. The interaction between grazing and removal decreased diversity of ground- dwelling spiders and beetles in the woody patches. Removal with no grazing generally increased vegetation-dwelling beetle and spider richness and abundance. Removal changed the assemblage composition of ground-dwelling spiders and beetles and removed woody patches were more similar in their composition to open patches than to woody unremoved patches. Vegetation-dwelling beetles exhibited different communities in the two patch types with and without removal. My study shows that beetle and spider diversity and composition is influenced more through the effect of the tree as a dominant landscape modulator than the change in herbaceous plant richness. Removal can be used as an effective land-use management tool in order to manipulate the landscape patch mosaic. iii Acknowledgements I would like to thank my supervisors Prof. Yael Lubin and Dr. Elli Groner who helped me throughout the research and gave me the chance to have this learning experience. Dr. Vladimir Chikatunuv and Habteab Habtom who helped identify the beetles from Mt. Meron. Iris Musli and Dr. Gershom Levy (RIP) who identifies the spiders, and Harel Agra who allowed me to use the plant data he collected. Dr.Eugene Unger and Amir Arnon for collecting abiotic and biomass measurements. I appreciate the visits to Prof. Moshe Shachack, Sol Brand and Dr. Bert Boeken to discuss topics related or unrelated to my research. Prof. Thorsten Assmann, Jorg Buse and Anika Pimm taught me a great deal about the world of beetles through their endless knowledge and enthusiasm. I want to thank the MARAG family whose past and future studies, as well as conferences helped me in many ways. I would like to thank Dr. Amos Bouskila and Dr. Efrat Gavish-Regev for the help in discovering the world of CANOCO. I express my gratitude to all my lab members, past and present that without their comments and encouragement it would have been much more difficult. Habteab Habtom, Ram Tamir, Oren Shelef, Reut Berger-Tal, Itai Opatovsky, Iaara Sandomirsky, Ranit Kirshenbaum, Achikam Averbuch, Itai Renan, Moran and Michal Segoli, Daphi Gutliv, Mor Solomon, Meirav Perry, Lucy Muithui. I want to also express my gratitude to Tal Levanony for all her help during the sampling sessions in Meron and for being there every time I needed her. Lastly, a special thanks goes to Zvika Steiner and my family for their endless support and for believing in me. iv Table of Contents Absract………………………………………………………………………..…i Acknowledgements …………………………………………………………....iii List of Figures……………………………………………………………….….vi List of Tables and abbreviations………………………………………………..ix 1. Introduction…………………………………………………………………………1 1.1 Problems in conserving diversity……………………………………...1 1.2 Landscape diversity and modulation…………………………………..3 1.3 Disturbance and management………………………………………….7 1.4 Beetles and spiders as indicators of landscape change………………..11 1.5 Community assemblages………………………………………………13 1.6 Research aims………………………………………………………….15 1.7 Research hypotheses.............................................................................. 16 1.7.1 Working hypotheses..................................................................... 16 1.7.2 Disturbance and manipulations on spider and beetle richness...... 19 2. Methods............................................................................................................... 20 2.1 Study area……………..………………………………………………..20 2.2 Experimental design…………………………………………………...20 2.3 Sampling methods……………………………………………………...21 2.4 Specimen identification………………………………………………...23 2.5 Plant diversity and tree cover…………………………………………..24 2.6 Data analysis……………………………………………………………24 3. Results………………………………………………………………………….28 3.1 Species richness correlations…..……………………………………….28 3.2 Effects of disturbance on beetles............................................................ 30 3.2.1 Ground-dwelling beetle diversity………………………………30 3.2.2 Trophic structure partitioning…………………………………..31 v 3.2.3 Ground-dwelling beetle composition…………………………..32 3.2.4 Vegetation-dwelling beetle diversity ......................................... 34 3.2.5 Vegetation-dwelling beetle composition.................................... 35 3.3 Effects of disturbance on spiders…………………………………….…36 3.3.1 Ground-dwelling spider diversity………………………………36 3.3.2 Ground-dwelling spider guild structure………………………...37 3.3.3 Ground-dwelling spider composition…………………………..39 3.3.4 Vegetation-dwelling spider diversity…………………………...40 3.3.5 Figures and tables………………………………………………41 4. Discussion……………………………………………………………………...69 4.1 Tree cover and herbaceous plant richness……………………………..69 4.2 Disturbance effects on beetle and spider diversity…………………….70 4.3 Disturbance effects on spider and beetle composition…………………71 4.4 Synthesis and applications……………………………………………..72 4.5 Conservation and management implications…………………………..76 4.6 References……………………………………………………………...79 4.7 Appendices……………………………………………………………..94 vi List of Figures Figure 1.1 – The Taxonomic Diversity Hypothesis……………………………………17 Figure 1.2 – The Landscape Modulator Filtering Hypothesis…………………………18 Figure 3.1 – Rank abundance distribution of beetle and spider families ……………...41 Figure 3.2 – Proportion of beetle trophic levels and spider feeding guilds in the different sampling methods………………………………………………42 Figure 3.3 – Multiple regression of ground-dwelling beetle species richness…………43 Figure 3.4 – Multiple regression of vegetation-dwelling beetle species richness……..43 Figure 3.5 – Multiple regression of ground-dwelling spider richness…………………43 Figure 3.6 – Effect of patch on beetle richness and abundance in the undisturbed treatment…………………………………………………………………44 Figure 3.7 – Effect of treatment on plot-scale beetle richness…………………………45 Figure 3.8 – Effect of treatment on plot-scale beetle abundance………………………45 Figure 3.9 – Effect of patch type and treatment on ground-dwelling beetle abundance………………………………………………………………..46 Figure 3.10 – Effect of patch type and treatment on ground-dwelling beetle richness…………………………………………………………………..46 Figure 3.11 – Rarefaction curves of ground-dwelling beetle species richness………..47 Figure 3.12 - Rarefaction curves of patch-scale ground-dwelling beetle species richness…………………………………………………………………..48 Figure