Predicting spatial and temporal habitat use of rodents in a highly intensive agricultural area
Introduction
Landscape modification in terms of e.g. habitat loss, degradation, isolation, and simplified crop rotations are major threats to species richness in human-modified landscapes (Fischer and Lindenmayer, 2007). Landscapes, especially agricultural areas, are fragmented by replacing semi-natural habitats, such as forest fragments and hedges, with agricultural fields (Benton et al., 2003, Firbank et al., 2008). This reduces native vegetation and habitat connectivity and increases edge effects through an increasing patch-matrix contrast (Fischer and Lindenmayer, 2007). Furthermore, an intensification of crop management, such as high input farming related to high levels of pesticide and fertiliser applications, has also negative impacts on farmland biodiversity (Geiger et al., 2010, Stoate et al., 2001). The effects of these processes have been studied on many kinds of organisms (Robinson and Sutherland, 2002, Stoate et al., 2001), but further research is needed on a landscape scale, studying biodiversity in modified landscapes as well as in remnants of (semi-) natural habitat patches (Fischer and Lindenmayer, 2007). Trade-offs have to be found between biodiversity conservation in combination with related ecosystem functions and a sustainable food production in order to meet increased global food demand (Barraquand and Martinet, 2011, Tscharntke et al., 2012).
Small rodents (<60 g) populate various habitats and are common throughout agricultural landscapes (Heroldová et al., 2007). However, it is predicted that global warming may reduce small mammal species richness in the future (Blois et al., 2010). There are only a few long term studies on small rodent occurrence in relation to agricultural intensification. In addition to regular population fluctuations, Butet and Leroux (2001) found declining vole populations in grasslands and crop fields over a 25-year period with increasing area of crop production. The importance of small rodents can be determined by their various ecological functions, which can have positive or negative impacts on agricultural areas. Positive effects are rodents’ contribution to soil aeration (Laundre and Reynolds, 1993) and their function as consumers of weeds and insects (Gliwicz and Taylor, 2002). As they may also maintain ectomycorrhizal fungi (Schickmann et al., 2012), their presence may increase plant community productivity and diversity, and they are important links in food webs. They represent the main food resources (prey) for mammalian and avian predators (Arlettaz et al., 2010, Aschwanden et al., 2005, Salek et al., 2010) enhancing the persistence and survival of species of higher trophic levels (Butet and Leroux, 2001). Rodents detrimentally effect human interests by their negative impacts on agricultural crops throughout the world (Brown et al., 2007, Heroldová and Tkadlec, 2011), their ability to disperse weed seeds in agricultural fields (Kiviniemi and Telenius, 1998) and their function as reservoir hosts for various diseases (Vorou et al., 2007).
Until now, most of the studies on the impacts of agricultural intensification on small rodent occurrence mainly focused on abundances and species richness in either agricultural used fields (Fischer et al., 2011, Heroldová et al., 2004) or in semi-natural habitats interspersed in the agricultural matrix (Michel et al., 2006, Renwick and Lambin, 2011), but not in modified landscapes and habitat patches simultaneously (but see Aschwanden et al., 2007, Panzacchi et al., 2010). Landscape scale effects on small mammals shown by Silva et al. (2005) indicate that species richness decreases with increasing amount of cultivated areas, whereas Michel et al. (2006) and Millán de la Peña et al. (2003) found only limited effects. On a local scale in temperate Europe, small rodent abundance and species richness are higher in forests, field margins or in ecological compensation areas, such as wild-flower strips, compared to agricultural fields, meadows and grassland (Arlettaz et al., 2010, Aschwanden et al., 2007). Local habitat preferences also depend on species-specific habitat specialization (Panzacchi et al., 2010). Open-land species such as Microtus arvalis PALLAS (common vole) mainly occur in agricultural fields. Forest species such as Myodes glareolus SCHREBER (bank vole) frequently occur in forests and woody habitats like hedges, whereas forest-field species such as Apodemus sylvaticus L. (long-tailed field mouse) are habitat generalists and can occur in almost all habitats within the agricultural landscape (Heroldová et al., 2007, Millán de la Peña et al., 2003). Furthermore, local micro-habitat conditions, such as increasing vegetation height and density, provide refuges from predators and increase small mammal abundance and species richness (Jacob, 2008, Silva and Prince, 2008; but see Aschwanden et al., 2007). To find trade-offs between small rodent conservation, promoting biodiversity as whole and sustainable food production decreasing rodent abundances, it is necessary to study landscape and local scale effects, as well as temporal variations simultaneously in more detail.
We conducted landscape wide rodent sampling, where we studied small rodent abundance, species richness and community composition in the most frequent habitats (agricultural fields, semi-natural and natural habitats, such as extensive agricultural production or uncultivated habitats) of a highly intensive agricultural area selected along a gradient of landscape complexity, measured as % of arable land in a radius of 500 m around trapping transects. Furthermore, we considered local micro-habitat conditions such as vegetation cover and temporal variations within a growing season comparing rodent occurrence before and after the crop harvest. We hypothesize that:
- 1.
Increasing landscape complexity increases rodent abundance and species richness and influences community composition by providing a wide variety of different habitats for species specialized to open habitats as well as forest specialists.
- 2.
Natural and semi-natural habitats support highest rodent abundance and species richness, where management intensity is lowest and structural heterogeneity is highest.
- 3.
High vegetation cover, especially after the crop harvest, increases small rodent abundance and species richness.
Section snippets
Study area
The study area was located in the Uckermark region in North-East Germany (state of Brandenburg) in the catchment area of the River Quillow (centred at 53°21′N, 13°39′E; Fig. A1). The landscape is characterized by highly intensive agriculture with 62% of the study region being arable land planted mainly with cereals, maize and oilseed rape. Furthermore, 13% of the study region is covered by forests, 11% by cultivated grassland, 4% by urban fabric and 10% by other landscape units, such as
Results
In total 455 small rodents of seven species were trapped in 3840 trap-nights. Four mice species: A. agrarius, A. flavicollis MELCHIOR (yellow-necked field mouse), A. sylvaticus, Micromys minutus PALLAS (Eurasian harvest mouse), and three vole species: Microtus agrestis L. (field vole), M. arvalis, M. glareolus were recorded and used for analysis. Overall, 4.70 ± 0.65 individuals and 1.30 ± 0.13 species were recorded per study site (n = 96). Before the crop harvest we found 2.72 ± 1.03 (n = 60) and after
Discussion
Small rodents were surveyed before and after the crop harvest in 60 study sites from six different habitats selected along a gradient of landscape complexity. This approach allowed us to disentangle the effects of landscape complexity, local (micro-) habitat conditions and temporal variation within a growing season on rodent occurrence. Previous studies analysed either landscape or local (micro-) habitat effects separately (Arlettaz et al., 2010, Aschwanden et al., 2007, Michel et al., 2006,
Conclusions
Rodent occurrence in agricultural landscape should be reasonably examined with respect to two traditionally opposed management strategies: first from a nature conservation point of view because rodents are important links in food webs (Aschwanden et al., 2005, Salek et al., 2010) and second from an economic point of view, because rodents are often considered as harmful pests in agricultural areas throughout the world (Brown et al., 2007, Heroldová and Tkadlec, 2011).
From the conservation point
Acknowledgements
We thank the AgroScapeLabs project (www.scapelabs.org) providing a platform for the present research. G. Verch head of the ZALF research station Dedelow provided valuable information on the study area. We also thank C. Hönicke for help with the field work, P. Vorpahl for statistical support, the Biodiversity Exploratories for providing traps, E. Walker for language correction, and the land owners for allowing us to work on their land. All procedures were obtained for the research in accordance
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