Wetlands are of international conservation importance for the biological diversity they support, including wet grasslands, which were historically managed for low- intensity agricultural production using extensive grazing or hay-cutting (Joyce & Wade, 1998). Flood alleviation, drainage, and agricultural intensification have reduced wetland extent and quality, while abandonment of management threatens wetland biodiversity (Strijker, 2005) through reed (Phragmites australis) and scrub encroachment (Leibak & Lutsar, 1996; Joyce & Wade, 1998; Luhamaa et al., 2001; Burnside et al., 2007). Therefore initiatives to reinstate appropriate management to wetlands in Europe and North America have been developed. Wetlands comprise more than 30% of Estonia (Paal, 1998) but coastal wetlands have declined from an estimated 28 750 ha in the 1950s to 8000 ha in 2000 (Luhamaa et al., 2001; Kuresoo & Magi, 2004), many being abandoned due to political and economic changes (Unwin, 1997).
Wetlands are important habitats for small mammals (Bowland & Perrin, 1993; Kristofik, 2001) but research into factors affecting their distribution and relative abundance within wetland landscapes is relatively scanty. Small mammals play a fundamental role in ecosystem functioning as they constitute the prey base for many predators (Schmidt et al., 2002) and may potentially influence vegetation composition via selective foraging (Brown & Heske, 1990). Generally, habitats with increased structural heterogeneity positively influence small mammal abundance and richness (Ecke et al., 2002). Mammal diversity tends to be lower in open habitats, where cover providing food and resources (Silva et al., 2005) is reduced, leading to lower fecundity (Grant et al., 1982) as well as increased predation risk (Kotler, 1997; Andreassen & Ims, 1998). Changes in landscape use and management can lead to a reduction in suitable habitats for small mammals (Raoul et al., 2001; Van Apeldoorn et al., 1992), which is compounded by habitat fragmentation causing isolation of populations (Kozakiewicz, 1993; Fitzgibbon, 1997), and consequentially gene flow (Witt & Huntly, 2001). Animal movement and dispersal are affected by vegetation structure, habitat type, landscape composition, and connectivity (Szacki et al., 1993; Fitzgibbon, 1997; Mazerolle & Villard, 1999). Hence landscape mosaic and characteristics, as well as habitat type availability, are potentially influential in determining species presence and persistence (Kupfer et al., 2006).
In this study we investigated the impact of habitat type and landscape composition on small mammal relative abundance and diversity in coastal wetlands in western Estonia. This region has some of the most biologically rich wetlands in Europe supporting internationally important numbers of birds and rare plants (Paal, 1998; Puurmann & Ratas, 1998; Luhamaa et al., 2001; Rannap et al., 2004), although comparatively little is known about their small mammal communities and the extent to which they utilize different habitats within the wetland landscape. The analysis of scale is important within landscape ecological studies as scale relates to the spatial and temporal dimensions of a landscape or habitat system (Farina, 1998). Forman (1997) defines the landscape as a mosaic where the mix of land use or ecosystems occurs over kilometre-wide areas, and habitats are local in scale, relatively homogeneous and distinct by their boundary. We surveyed small mammals in six different wetland sites with representative management intensities, habitat types, and landscape composition. Our objectives were to (a) assess species abundance, composition, and structure of small mammal assemblages in representative wetland habitats; (b) assess landscape characteristics of the wetland sites in relation to small mammal assemblages; (c) determine which habitat features locally influence mammal abundance at the species level. …