Corr. coef. = 0.521 + 62.250 93.696 87.500 87.273 97.500 93.750 98.333 97.500 100 100 41 P < 0.001 (27) (23) (4) (11) (16) (20) (12) (6) (2) (9) (1) Discussion Invertebrate richness and abundances Our results show that the richness of species groups increased with increasing age of the field margins and that this trend was consistent during
the first 11 years. This represents an important finding, indicating the conservation value of long-lasting semi-natural elements in agricultural areas. To our knowledge, this is the first time that such a pattern has been described for field margins for a broad range of invertebrates and over a considerable period of time. It is not surprising that there is see more a slow but steady increase in richness, because the small margins have to be colonised by small invertebrates moving through a hostile environment (Steffan-Dewenter and Tscharntke 1999; Öckinger and Smith 2007; Kohler et al. 2008), and similar patterns of increasing diversity have been described for other selleck habitats (Mook 1971;
Judd and Mason 1995; Desender et al. 2006; Cameron and Bayne 2009). Increasing functional diversity in species communities will lead to a greater variety of ecosystem processes (Naeem et al. 1994; Tilman et al. 1996; Heemsbergen et al. 2004) and with time, therefore, margins left on their own may develop towards more natural ecosystems. Predators form an important aspect of our study, as some of these invertebrates are beneficial to farmers because of their potential as pest control (Carter and Rypstra 1995; Obrycki and Kring 1998; Collins et al. 2002). Predator abundance decreased with progressing age of the margins (in contrast to Denys and Tscharntke 2002, but in line with Woodcock et al. 2008),
due probably to the vegetation developing from a recently sown, open situation to higher standing biomass and a denser sward, although in our analyses this development selleck products was only expressed by a significant effect of age (Noordijk et al. 2010). Ground-dwelling predatory invertebrates often depend on open, sun-lit places where they can easily move to find prey (Harvey et al. 2008). Those species potentially invading the arable fields have a particular preference for the open vegetation in the margins, as this is quite similar to conditions in the fields themselves (Samu and Szinetar 2002). Consequently, young margins appear to provide the best conditions for providing pest-control services. On the other hand, it has been shown that high vegetation cover in winter provides most opportunities for predators to hide during this period (e.g., Dennis et al. 1994; Collins et al. 2003). We found herbivore abundance to be favoured by the width of the margin, but most significantly by the age of field margin and vegetation cover in summer (see also Meek et al. 2002; Harvey et al. 2008). This latter relationship can be explained by more plant biomass being available to provide food for more individuals (e.g., McFarlin et al.