The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 285

annual crops with asynchronous vegetation growth and timing of harvest could
provide a temporal continuity of resources for this generalist predatory species.
The persistence of carabid populations in a cultivated mosaic within a year might
not necessarily require permanent habitats, but complementary cropped habitats
that are spatially and temporally connected.
14.3.2 Effect of Crop Rotation and Management Succession
Over Years
The pluri-annual effects of the spatio-temporal heterogeneity of the cropping
systems mosaic on biodiversity are still mainly unknown. However, crop rotation
and management succession over years will determine the temporal availability of
suitable cultivated resources patches for species. Moreover, the ability of species
to spatially and temporally complement or supplement their resources between
cropped habitats during their life cycle will partly drive their survival from one
year to another, and therefore over the long term (Rusch et al. 2011 ; Thorbek and
Topping 2005 ).
14.3.2.1 The Influence of Crop Rotations on Solitary Bees
To persist in a landscape, wild bees require nectar and pollen as food for brood and
adults as well as suitable nesting sites (Westrich 1996 ). Intensive agriculture
negatively affects the quality of bee habitat in several ways: (1) increasing crop
field area results in the loss of suitable habitats including grasslands that are known
to be highly beneficial habitats for bees (Klemm 1996 ; Steffan-Dewenter et al.
2002 ); (2) fertilizers, herbicides and intensive grazing reduce floral resources (De
Snoo and Van der Poll 1999 ); (3) harvesting and tillage impede the nesting of most
ground-nesting species (Shuler et al. 2005 ; Morandin et al. 2007 ); (4) some pes-
ticides induce direct mortality or sublethal effects (Desneux et al. 2007 ). However,
the crop mosaic can offer a great amount of easily available food resources when
mass flowering crops such as oilseed rape or sunflower are cultivated (Westphal
et al. 2003 ).
In order to better understand how landscape patterns influence solitary bee 1
communities, we took into account both spatial and temporal heterogeneities of the
crop mosaic in addition to the commonly studied semi-natural elements (wooded
elements and long-term grasslands) (Le Féon et al. 2011 ). Thus we considered the
proportion of semi-natural elements, of oilseed rape and non-flowering crops at the
1 Wild bees comprise of social species (Bombus sp.) and solitary bees (even if different forms of
primitive or advanced social behavior exist in some species). Our study only focuses on solitary
bees, which represent more than 80 % of wild bee species in Europe.