Agriculture, Ecosystems and Environment 144 (2011) 302–307 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment jo u r n al hom ep age: www.elsevier.com/locate/agee Differential survival rates in a declining and an invasive farmland gastropod species Sophie Ryser a , Nicole Rindlisbacher a , Martin U. Grüebler b , Eva Knop a,∗ a Institute of Ecology and Evolution, Baltzerstr. 6, CH-3012 Bern, Switzerland b Swiss Ornithological Institute, Seerose 1, CH-6204 Sempach, Switzerland a r t i c l e i n f o Article history: Received 6 May 2011 Received in revised form 10 August 2011 Accepted 11 August 2011 Keywords: Agricultural intensification Arion lusitanicus Arion rufus Molluscs Mark–recapture analysis Adult survival a b s t r a c t Individual marking by using transponders represents a promising tool to further investigate causes of population trends of farmland invertebrates and the dynamics of farmland biodiversity. Once common in agricultural fields the slug Arion rufus is now restricted to forests, whereas the closely related and similar Arion lusitanicus recently built up high populations. Here, it was tested whether (1) transponder tagging combined with artificial shelters for recapturing is a suitable approach for quantifying adult survival of farmland gastropods under real field conditions, (2) whether captive bred and wild A. lusitanicus differ in survival, and (3) whether in agricultural fields the declining slug A. rufus shows reduced survival rates compared to the invasive slug A. lusitanicus. One hundred and thirty transponder-tagged slugs were released and individual-based mark–recapture models were performed. Individual marking by using transponders proved to be a successful method for quantifying survival rates of the slugs. The favoured model showed no differences in survival or encounter rates between captive bred and wild A. lusitanicus. A. rufus showed significantly reduced survival rates compared to A. lusitanicus coinciding with their population trends in farmland areas. This might be due to differential susceptibility to habitat degradation, differential predation rates or promotion of the invasive competitor species. A further decrease of A. rufus in agricultural landscapes is expected. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Agricultural intensification during the second half of the 20th century has caused a dramatic loss of biodiversity in most Euro- pean countries (Donald et al., 2001; Stoate et al., 2001, 2009; Benton et al., 2002; Robinson and Sutherland, 2002; Postma-Blaauw et al., 2010). On a large scale, agricultural intensification resulted in a more homogenous landscape with only a few fragmented semi- natural habitats (Tscharntke et al., 2005). On a local scale, increased pesticide and fertilizer application has reduced farmland species diversity (e.g. Kleijn et al., 2009). Thus, today the occurrence of farmland wildlife is restricted to small habitat fragments with reduced populations that face an increased risk of local extinction (Caughley, 1994). Studies investigating the effects of agricultural intensification on farmland wildlife often focus on species diversity patterns, and do not consider demographic parameters of target species (e.g. Knop et al., 2006; MacLeod and Moller, 2006; Holzschuh et al., 2007; Attwood et al., 2008; Firbank et al., 2008; Kleijn et al., 2009; Jose- Maria et al., 2010; Le Feon et al., 2010), though this would be crucial ∗ Corresponding author. Tel.: +41 31 631 45 39; fax: +41 31 631 48 88. E-mail address: eva.knop@iee.unibe.ch (E. Knop). to understand the underlying mechanism of species decline and, in turn, to predict the long-term impacts of land-use changes on biodiversity (Mills, 2007). The existing evidence that demographic rates of farmland species are impaired by agricultural intensifica- tion is widely restricted to studies on vertebrates (e.g. Rands, 1985; Peach et al., 1999; Morris et al., 2005; Hart et al., 2006; Grüebler et al., 2008) while it is neglected in studies on invertebrates (but see Goulson et al., 2010). The estimation of demographic parameters is often only possi- ble by marking and recapturing a sample of focal individuals over a period of their life. Individual marking techniques such as ringing, color banding and radio-tagging have been used for a long time in ornithology and mammalogy while it has only recently started to be used for invertebrates (Grimm, 1996, 2001b; Diekotter et al., 2007; Henry and Jarne, 2007; Rouquette and Thompson, 2007; Young and Isely, 2008). Among the demographic parameters adult sur- vival is one of the most important factors affecting population size, and therefore changes in adult survival can be a key determinant underlying the decline of many farmland species (Peach et al., 1999; Saether and Bakke, 2000; Newton, 2004). Many gastropod species are sensitive to agricultural intensi- fication, even when the intensification occurred years ago and restoration measures have been undertaken (Boschi and Baur, 2008). This is particularly true for endangered and declining 0167-8809/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2011.08.005