Through Arthropod Eyes Gaining Mechanistic Understanding of Calcareous Grassland Diversity
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Through arthropod eyes Gaining mechanistic understanding of calcareous grassland diversity Toos van Noordwijk Through arthropod eyes Gaining mechanistic understanding of calcareous grassland diversity Van Noordwijk, C.G.E. 2014. Through arthropod eyes. Gaining mechanistic understanding of calcareous grassland diversity. Ph.D. thesis, Radboud University Nijmegen, the Netherlands. Keywords: Biodiversity, chalk grassland, dispersal tactics, conservation management, ecosystem restoration, fragmentation, grazing, insect conservation, life‑history strategies, traits. ©2014, C.G.E. van Noordwijk ISBN: 978‑90‑77522‑06‑6 Printed by: Gildeprint ‑ Enschede Lay‑out: A.M. Antheunisse Cover photos: Aart Noordam (Bijenwolf, Philanthus triangulum) Toos van Noordwijk (Laamhei) The research presented in this thesis was financially spupported by and carried out at: 1) Bargerveen Foundation, Nijmegen, the Netherlands; 2) Department of Animal Ecology and Ecophysiology, Institute for Water and Wetland Research, Radboud University Nijmegen, the Netherlands; 3) Terrestrial Ecology Unit, Ghent University, Belgium. The research was in part commissioned by the Dutch Ministry of Economic Affairs, Agriculture and Innovation as part of the O+BN program (Development and Management of Nature Quality). Financial support from Radboud University for printing this thesis is gratefully acknowledged. Through arthropod eyes Gaining mechanistic understanding of calcareous grassland diversity Proefschrift ter verkrijging van de graad van doctor aan de Radboud Universiteit Nijmegen op gezag van de rector magnificus prof. mr. S.C.J.J. Kortmann volgens besluit van het college van decanen en ter verkrijging van de graad van doctor in de biologie aan de Universiteit Gent op gezag van de rector prof. dr. Anne De Paepe, in het openbaar te verdedigen op dinsdag 26 augustus 2014 om 10.30 uur precies door Catharina Gesina Elisabeth van Noordwijk geboren op 9 februari 1981 te Smithtown, USA Promotoren: Prof. dr. H. Siepel Prof. dr. D. Bonte (Universiteit Gent, België) Copromotoren: Prof. dr. M.P. Berg (Vrije Universiteit/Rijksuniversiteit Groningen) Dr. E.S. Remke (Stichting Bargerveen) Leden manuscriptcommissie: Prof. dr. A.J. Hendriks Prof. dr. M. Hoffmann (Universiteit Gent, België) Prof. dr. H. van Dyck (Katholieke Universiteit Leuven, België) Paranimfen: Marijn Nijssen Wilco Verberk Every kid has a bug period... I never grew out of mine. E.O. Wilson Contents 1 General introduction 9 2 Biotic homogenization and differentiation in response to grassland 23 management 3 Life‑history strategies as a tool to identify conservation constraints: A 49 case‑study on ants in chalk grasslands 4 Effects of large herbivores on grassland arthropod diversity 69 5 Impact of grazing management on hibernating caterpillars of the 103 butterflyMelitaea cinxia in calcareous grasslands 6 A multi‑generation perspective on functional connectivity for 127 arthropods in fragmented landscapes 7 Species‑area relationships are modulated by trophic rank, habitat affinity 147 and dispersal ability 8 Synthesis 171 References 191 Summary 219 Samenvatting 229 Dankwoord 239 CV and list of publications 245 Author addresses 250 Installing pitfall traps just before a thundery spring shower (Photo: Toos van Noordwijk) Chapter 1 General introduction C.G.E. (Toos) van Noordwijk chapter 1 10 Challenges in conservation ecology Over the past century, a multitude of anthropogenic stressors, including land-use change, eutrophication, fragmentation and climate change, have led to large-scale biodiversity declines (Millenium Ecosystem Assessment 2005). International conventions to halt biodiversity loss have led to the development of stringent policy to protect and manage (semi-)natural habitats. Prominent examples are the European Commission’s Habitats Directive and the subsequent formulation of the Natura 2000 network. A major challenge in conservation ecology is to devise practical strategies to turn these paper promises into reality. In semi-natural habitats like calcareous grasslands, which were formed over the centuries through low-intensity farming practices, the initial conservation response generally is to revert back to these traditional farming practices (Ostermann 1998). However, for a number of reasons this may not be the best option. Firstly, due to sharp increases in the costs of manual labour and drastic changes to farming practices, exactly copying traditional methods is seldom feasible for economical, practical and social reasons. Partially implementing traditional methods, e.g. reintroducing hay making, but executing it mechanically over large areas at once, may do more harm than good (e.g. Konvicka et al. 2008). Secondly, nutrient-cycles in semi-natural habitats, have changed dramatically with the arrival of artificial fertilizers (Bobbink et al. 1998; Bakker and Berendse 1999; Stevens et al. 2004). Traditional farming practices are likely to be insufficient to keep up with aerial nitrogen deposition, let alone with the nutrient enrichment that has built up in the soil during years of abandonment. Thirdly, in addition to factors operating within nature reserves, the landscape context has changed dramatically as well. Where semi-natural habitats once covered large parts of the agricultural landscape, they are now often reduced to small habitat fragments surrounded by intensively managed arable land, which is uninhabitable for the majority of plant and animal species (Benton et al. 2002; Kerr and Cihlar 2004; Green et al. 2005). This fragmentation and habitat isolation cause populations to be smaller and more isolated, putting them at greater risk of local extinction (MacArthur and Wilson 1967; Hanski 1999). Even if habitat quality has been restored successfully, habitat fragmentation and isolation still form a major constraint for biodiversity conservation (Tilman et al. 1994; Huxel and Hastings 1999; Ozinga et al. 2005). To adequately address all of these issues we thus need to design new conservation strategies that are effective in dealing with current environmental pressures and are practically, economically and socially feasible. This requires first and foremost, thorough understanding of the mechanisms shaping biodiversity in semi-natural habitats. Such mechanistic understanding of semi-natural ecosystems has grown over the years, but has to date focussed primarily on plants (WallisDeVries et al. 2002; Littlewood et al. 2012). Arthropods have received far less attention, despite being the most species-rich eukaryotic group on earth and performing many essential functions within ecosystems, including nutrient-cycling and pollination (Littlewood et al. 2012; Prather et al. 2013). Evidence is mounting that the response of arthropods to environmental stressors and conservation management differs crucially from plants (e.g. Morris 2000; Kruess and Tscharntke 2002a; WallisDeVries et al. 2002; Littlewood et al. 2012). Therefore, it is imperative to understand the specific mechanisms shaping arthropod communities. general introduction 11 Identifying main bottlenecks for conservation Community ecology has traditionally either focussed on the interactions between single pairs of species or taken a correlative approach to species-environment relationships (McGill et al. 2006) (Figure 1a). Species communities are often reduced to simple metrics like richness, abundance or dissimilarity and are correlated to one or multiple environmental factors. Alternatively, multivariate techniques are used to link the dominant pattern of variation in community composition to environmental gradients. Such approaches are valuable to accurately describe differences between localities in space or time and may be used to explore which factors, out of the multitude of measured ones, are associated with the observed differences in species occurrences. However, when it comes to finding the underlying mechanisms, they present two major problems. Firstly, correlation does not automatically imply a direct causal relationship (Weiner 1995; Michener 1997; Shipley 2004). Causal understanding is essential to predict which actions will be most effective a b Environment Environment Species Species species species sites sites Figure 1. Environmental factors like (from left to right) vegetation structure, management regime, habitat fragmentation and habitat area, affect arthropod communities. (a) Species-environment relationships are traditionally inferred from correlations (dashed black arrow) often between one or more environmental factor(s) and community metrics like species richness or (dis)similarity. (b) Trait- based methods aim to unravel the causal mechanism behind species-environment relationships (solid black arrows), by focusing on which species are affected and exploring how the environment affects their life cycles. chapter 1 12 for reaching conservation goals (Bradshaw 1996; Hobbs and Norton 1996). When environmental factors are correlated, which is often the case in conservation ecology (e.g. correlations between habitat area and the influence of edge-effects or between vegetation structure, microclimate and disturbance from management), it is impossible to establish the relative importance of each single factor with purely correlative studies. Secondly, when linking environmental factors to community metrics researchers generally include a limited set of standard parameters. Especially in complex restoration situations, the number of possible factors to measure is overwhelming. Many factors like microclimate, fragmentation