The Invertebrate Diversity of Marram Dunes and How This Is Influenced by Spatial Configuration of Marram Grass and Marram Grass Properties
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Biology Department Research Group Terrestrial Ecology _________________________________________________________________________________ THE INVERTEBRATE DIVERSITY OF MARRAM DUNES AND HOW THIS IS INFLUENCED BY SPATIAL CONFIGURATION OF MARRAM GRASS AND MARRAM GRASS PROPERTIES Laurian Van Maldeghem Studentnumber: 01308986 Supervisor(s): Prof. Dr. Dries Bonte Prof. Dr. Martijn Vandegehuchte Scientific tutor: Ruben Van De Walle Master’s dissertation submitted to obtain the degree of Master of Science in Biology Academic year: 2018 - 2019 © Faculty of Sciences – research group Terrestrial Ecology All rights reserved. This thesis contains confidential information and confidential research results that are property to the UGent. The contents of this master thesis may under no circumstances be made public, nor complete or partial, without the explicit and preceding permission of the UGent representative, i.e. the supervisor. The thesis may under no circumstances be copied or duplicated in any form, unless permission granted in written form. Any violation of the confidential nature of this thesis may impose irreparable damage to the UGent. In case of a dispute that may arise within the context of this declaration, the Judicial Court of Gent only is competent to be notified. 2 TABLE OF CONTENTS I. Introduction p.4 ▪ Biodiversity and its prominent role p.4 ▪ Keystone species p.4 ▪ Foundation species p.5 ▪ Factors driving arthropod assemblages p.5 ▪ The role of spatial factors p.6 ▪ Marram foredunes p.7 II. Objectives p.9 III. Material and methods p.10 ▪ Study area p.10 ▪ Data collection p.10 ▪ Species identification p.11 ▪ Marram grass properties at the sampling sites p.11 ▪ Spatial configuration of marram grass around the sampling sites p.12 ▪ Data analysis p.14 IV. Results p.16 ▪ Data exploration p.16 ▪ Diversity p.18 ▪ Link between diversity and spatial configuration of marram grass p.21 ▪ Link between diversity and marram properties at local scale p.23 ▪ Community composition p.25 V. Discussion p.26 ▪ Observations from data exploration p.26 ▪ Occurrence of specific diversity p.26 ▪ Difference in diversity between locations within Belgium and France p.27 ▪ The effect of the spatial configuration of marram grass on diversity p.28 ▪ The effect of local factors on diversity p.29 ▪ Indications from species composition p.30 VI. Conclusion p.31 VII. Summaries p.32 VIII. Acknowledgments p.35 IX. Reference list p.36 X. Appendices p.39 ▪ Appendix 1 – classification list of identified species p.39 ▪ Appendix 2 – Output of ANOVA-analyses and post-hoc analyses p.51 ▪ Appendix 3 – Output of models on complete diversity p.54 ▪ Appendix 4 – Output of models in specific diversity p.61 ▪ Appendix 5 – Output of PERMANOVA analyses p.68 ▪ Appendix 6 – Maps of the Westhoek area p.70 ▪ Appendix 7 – R-code p.72 3 I. INTRODUCTION BIODIVERSITY AND ITS PROMINENT ROLE: Life on earth is currently experiencing a major decline in diversity. Around 25% of species is threatened and 1 million species are on the verge of extinction according to the latest Ipbes report on biodiversity (IPBES 2019). This decline is well documented for familiar taxonomic groups, such as mammals (IUCN 2011), birds (BirdLife 2012), amphibians (Stuart et al. 2007) or pollinators (Potts et al. 2010). Although global trends on insect populations remain unknown due to lack of sufficient data, documented rapid declines of certain insect populations indicate that many insect groups are likely experiencing similar declines (Thomas et al. 2004). With the estimations of species extinction rates being unprecedented in human history the current biodiversity crisis has been referred to as the sixth mass extinction (Barnosky et al. 2011). Unlike some of the previous mass extinctions, it is now without doubt human caused. The primary drivers of species extinctions are land use change, overexploitation of organisms, climate change, pollution and invasion of alien species. These primary drivers are themselves driven by an series of underlying causes such as global population growth, trade, technological innovation and societal behaviours (e.g. production and consumption patterns). And although these have without doubt contributed significantly to human well-being and quality of life, nature has also been used in an unsustainable way and at the increasing expense of its ability to provide ecosystem services in the future (Millennium Ecosystem Assessment 2005). Research has shown that biodiversity plays a crucial role in providing these ecosystem services. Higher biodiversity in terrestrial ecosystems leads to increased ecosystem functioning and resilience through mechanisms of complementarity, positive interactions and increased selection of highly performing species (Loreau et al. 2001). Research in aquatic ecosystems shows similar trends. A robust positive link is observed between diversity, productivity and stability and is caused by similar mechanisms to the ones operating in terrestrial ecosystems (Worm et al. 2006). However, the diversity of species that regulate ecosystem processes and as such safeguard its functioning is highly dependent on the ecosystem under consideration. In various ecosystems is functioning often regulated by only one or a few select species. These species have a dominant effect on the ecosystem and are referred to as dominant species or other types depending on their specific features. KEYSTONE SPECIES: One type of these species are keystone species. This term was first proposed by Paine in his paper that investigated the interaction strengths of food webs in rocky intertidal zones (Paine 1966) and it has been used numerous time since then. There are many definitions of keystone species in scientific literature, from keystone predators to keystone preys and keystone modifiers (Mills et al. 1993). These definitions all share 2 characteristics, namely that they are species with a large effect on the ecosystem compared to their relative abundance and that they are species whose presence is essential in maintaining the organization and diversity of the ecological community. Due to this last characteristic, it has been proposed that conservation of keystone species should be prioritized in efforts to protect against the ongoing biodiversity crisis. 4 FOUNDATION SPECIES: Another type species are foundation species. These are defined as species that occupy low trophic levels, are locally abundant and regionally common. They regulate many biogeochemical stocks and fluxes in the ecosystem by altering physical and chemical conditions and they create habitats for other species. As such they “fundamentally shape the structure of ecological assemblages and modulate ecosystem processes”, as stated by Ellison et al. (2017). As a consequence, the impact of a foundation species on the ecosystem it shapes, is controlled by a few but strong interactions between the foundation species and the environment. This leads to systems where even a small perturbation can lead to catastrophic shifts between alternative stable states which are characterized by differences in structure, functioning and the associated community (Ellison et al. 2005). Since foundation species are often locally abundant and regionally common they have traditionally received less attention in light of conservation. Some authors have argued that their conservation should be prioritized over rare and endangered species because their conservation would retain more biodiversity in the long run (Gaston and Fuller 2007, 2008). However, despite their often abundant occurrence, foundation species have proven difficult to be identified when they co-occur with other abundant species without long-term experimental data (Ellison et al. 2019, Ellison et al. 2017). DIVERSITY OF COMMUNITIES AND THEIR DRIVING FACTORS: Community composition and its resulting diversity has long been considered to be mainly the result of deterministic processes, such as for example habitat specialization resulting from adaptive evolution through natural selection. According to the niche theory (Vandermeer 1972) or the habitat heterogeneity hypothesis (Báldi 2008) is the diversity and composition of a community determined by the availability of different habitats or niches. These result from different abiotic and biotic factors and are occupied by species specifically adapted to these conditions (niche partitioning). The positive relationship between habitat heterogeneity and species diversity has been well documented on both local and regional scales (Tews et al. 2004). For arthropod communities it has been shown that factors at the local scale, such as vegetation richness and structure, positively influence the community and its diversity (Morris 2000; Schaffers et al. 2008). And at the landscape scale, factors such as spatial arrangement of niches, which is influenced by different spatial factors, has also been shown to positively influence arthropod community and diversity (Jeanneret et al. 2003). Theories that predict the composition of communities and its diversity to be influenced by stochastic processes have also received support. Hubbell’s unified neutral theory (Hubbell 2001) assumes that species of trophically similar levels are neutral and do not differ in competitive abilities. It states that the biodiversity of a community arises at random since the establishment of species in the community is the result of random walks. The classic island biogeography theory (MacArthur and Wilson 1967) states that the diversity of an island or patch is simply