Effects of habitat fragmentation on a tri-trophic system: Silene latifolia, Hadena bicruris and its parasitoids Elzinga, Jelmer Anne Effects of habitat fragmentation on a tri-trophic system: Silene latifolia, Hadena bicruris and its parasitoids / Elzinga J.A. Utrecht: Universiteit Utrecht, Faculteit Biologie, 2005 Thesis Utrecht University – with ref. – with a summary in Dutch Printed by Ponsen & Looijen BV, Wageningen ISBN 90-393-3904-X © 2005 J.A. Elzinga Front cover: female flowers of Silene latifolia with egg of Hadena bicruris, caterpillar of H. bicruris, and the parasitoids (from above): Microplitis tristis, Eurylabus tristis, Bracon variator and Ophion pteridis. Effects of habitat fragmentation on a tri-trophic system: Silene latifolia, Hadena bicruris and its parasitoids De effecten van habitatfragmentatie op een tritrofisch systeem: Silene latifolia, Hadena bicruris en haar parasitoïden (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de Rector Magnificus, Prof. Dr. W.H. Gispen, ingevolge het besluit van het College voor Promoties in het openbaar te verdedigen op maandag 24 januari 2005 des middags te 4.15 uur door Jelmer Anne Elzinga geboren op 17 juni 1976 te Leeuwarden Promotor: Prof. Dr. Jos M.M. van Damme Faculteit Biologie, Universiteit Utrecht Nederlands Instituut voor Ecologie (NIOO-KNAW) Cenrum voor Terrestrische Ecologie, Heteren Co-promotores: Dr. Arjen Biere Dr. Jeffrey A. Harvey Nederlands Instituut voor Ecologie (NIOO-KNAW) Centrum voor Terrestrische Ecologie, Heteren The research presented in this thesis was conducted at the Department of Plant Population Biology at the Centre for Terrestrial Ecology from the Netherlands Institute of Ecology (NIOO-KNAW) in Heteren, The Netherlands. Financial support was given through grant nr. 014-22-045 as part of the project “Biodiversity of metacommunity systems in fragmented (agricultural) landscapes. A study on the dynamics of plant- pollinator and multitrophic interactions” within the priority programme Biodiversity of the Netherlands Organisation for Scientific Research (NWO-ALW). This is NIOO thesis number 34. Foar myn âlden & Joanneke Beoordelingscommisie: Prof. Dr. Teja Tscharntke Fachgebiet Agrarökologie, Georg-August-Universität Göttingen Prof. Dr. Eddy van der Meijden Plantenecologie, Universiteit Leiden Prof. Dr. Louise E.M. Vet Nederlands Instituut voor Ecologie (NIOO-KNAW) Laboratorium voor Entomologie, Wageningen Universiteit Contents Chapter 1 General introduction 1 Chapter 2 The parasitoid complex associated with the specialist Hadena 19 bicruris (Lepidoptera: Noctuidae) on Silene latifolia (Caryophyllaceae) in the Netherlands along the river Waal Chapter 3 The effects of host weight at parasitism on fitness correlates 45 of the gregarious koinobiont parasitoid Microplitis tristis and consequences for food consumption by its host, Hadena bicruris Chapter 4 Dispersal patterns of three parasitoids and their specialist 65 herbivore host in a fragmented landscape Chapter 5 Effects of habitat fragmentation on herbivory and parasitism 91 rate of the plant Silene latifolia and its specialist herbivore Hadena bicruris Chapter 6 Age dependent clutch size in a koinobiont parasitoid 115 Chapter 7 Summarising discussion 135 References 145 Summary 165 Nederlandse samenvatting (Dutch summary) 169 Dankwoord (Acknowledgements) 179 Curriculum vitae 182 Publication list 183 Chapter 1 General introduction Habitat fragmentation The habitat of a species has been defined as “an area with the combination of resources and environmental conditions that promotes occupancy by individuals of a given species and allows those individuals to survive and reproduce” (Morrison et al. 1992). For an animal species a habitat can often be subdivided into several parts with specific resources present in each part. In herbivorous insects, for example, a large difference can exist between habitat suitable for immature (= larval) development and habitat in which an adult finds mates, feeds and disperses. In many cases the habitat for insect larvae is very narrow, due to specific dietary needs, while the habitat of the adults is much larger because they can use several types of resources from a variety of plants in different areas that are unsuitable for their progeny. For the sake of simplicity, the habitat of an insect species is often defined as the area where the suitable conditions for larval development are present (Anthes et al. 2003). In most cases the habitat of herbivorous insects can thus be defined as the places where their food plants grow. The habitat of specialist predators or parasitoids of the herbivore can be defined similarly although the actual presence of the herbivore is, of course, necessary. Most habitats exhibit varying degrees of heterogeneity so that the habitat is divided into distinct habitat patches (Hanski and Gilpin 1996, Hanski 1999). One can envisage such natural levels of fragmentation at virtually every scale from geographical scale e.g. mountains and islands, to landscape scale e.g. archipelago’s and forest patches, to local small scale heterogeneity e.g. vegetation gaps or single plants. Habitat fragmentation from a conservationists point of view is usually determined at the landscape level, i.e. 100 m to several kilometres (e.g. Krauss et al. 2003a). Many species are believed to live in metapopulation structures, where large populations are subdivided into local smaller populations which may regularly go extinct (Levins 1970, Ouborg 1993, Husband and Barrett 1996, Antonovics et al. 1997). Limited migration between habitat patches creates a balance between local extinction and recolonisation of patches, allowing the metapopulation as a whole to persist (Hanski and Gilpin 1996, Hanski 1999). 1 GENERAL INTRODUCTION However, nowadays humans are changing the landscape in a rigorous way and at an ever growing pace. Not only are habitats destroyed due to agricultural and urban development, road construction, deforestation, etc., leading to immediate local extinction of species, but the remaining habitat patches often become exceedingly fragmented (Saunders et al. 1991, Henle et al. 2004). Three consequences of fragmentation for the remaining habitat patches are distinguished (Fig. 1.1): (1) The size of patches becomes smaller, (2) the connectivity between patches decreases due to a reduction in the size of surrounding patches and/or increasing distances to them and (3) the edge:interior ratio increases. These changes can disturb the processes of recolonisation, migration and the population dynamics of component species. This may affect local population persistence negatively and in the long run it can make entire metapopulations of a species more prone to extinction. There is now a growing awareness, both amongst empiricists and conservationists, that habitat fragmentation can affect species persistence (Debinski and Holt 2000, Henle et al. 2004). In the Netherlands habitat fragmentation (or its opposite process “ontsnippering”) has become an important issue in biological conservation over the last two decades. In 1990, the government presented its plan to create the “Ecologische Hoofd Structuur” (EHS) (Ministerie van LNV 1990). By creating and preserving corridors and stepping stones of natural vegetation, existing core nature areas were connected to allow dispersal of species. Because the EHS mainly focused on dispersal of large mammals, in 2000 the government introduced “groenblauwe dooradering” (Ministerie van LNV 2000). This will create a network of small semi-natural landscape elements, such as ditches and hedges, that allows small species to disperse and persist in the agricultural landscape (Henkens and van Raffe 2002). Local effects of habitat fragmentation Natural and anthropogenic habitat fragmentation of a landscape can have several effects on the local population dynamics of a species in the remaining patches which ultimately may affect the entire metapopulation of that species. First, a decrease in patch size usually leads to a reduction in the local population size of a species. If less individuals are present, the population will be more prone to stochastic effects (Shaffer 1981, Lande 1993). In particular, smaller populations are more susceptible to environmental (Menges 1998), demographic (Kery et al. 2003) and genetic stochasticity (Ellstrand and Elam 1993) that may increase the chance of extinction of the 2 CHAPTER 1 A B C D Figure 1.1 Schematic presentation of different levels of habitat fragmentation. (A) A decrease in habitat area. (B) Fragmentation into remnant habitat patches. (C) A decrease in size of the remnant patches and increasing distance between habitat remnants. (D) Only small isolated habitat remnants remain. Note, that from A to D the total habitat area decreases and the edge:interior ratio increases. local population. Also, populations might need a certain minimum viable size to allow successful mating and persistence (the so-called Allee effect (Courchamp et al. 1999)). Dispersing individuals might be less able to locate small patches, thus decreasing recolonisation chances (Thomas and Jones 1993, Krauss et al. 2003b). Many empirical studies indeed show that in small habitat patches species have a larger chance of local extinction and/or a smaller chance of (re)colonisation (Antonovics 1993, Eber and Brandl 1996, Förare and Solbreck 1997, Krauss et al. 2003b, Matthies et al. 2004). 3 GENERAL INTRODUCTION Second, as the connectivity