The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 282

14.3 The Role of the Cropping System Mosaic
We have shown that semi-natural elements contribute to produce landscape
structures of ecological importance. But, because many species use crops
(including grasslands) during their life cycle, the heterogeneity of the cropping
systems mosaic is potentially important from an ecological point of view (Ken-
nedy and Storer 2000 ; Benton 2003 ). At a given time, this mosaic can be viewed as
a spatially heterogeneous mosaic of cropped habitats with varying resources for
species (food resources, host plants, shelter), and of disturbances with direct effects
on species survival (e.g. insecticide spraying). The cropping system mosaic also
generates a spatiotemporal heterogeneity at different time scales (Burel and
Baudry 2005 ). Crop phenology and farming practices lead to fast asynchronous
variations of resources from field to field within a year; over several years, crop
rotation and management succession result in spatio-temporal variations of
resources availability, localization and accessibility, i.e. landscape connectivity for
species. In this shifting mosaic, habitat patches are ephemeral regarding the life
span of many species. Species survival will therefore depend on their ability to find
and colonize new suitable resource patches to supplement or complement habitats
and complete their life cycle (Dunning et al. 1992 ; Wissinger 1997 ) as well as
availability of ephemeral, but suitable habitats over years.
In the following sections, we illustrate how the cropping systems mosaic can
influence the movement of organisms, their population dynamics and species
diversity at the community level, at infra- and/or- pluriannual time scales. We
utilize results from empirical and modeling studies conducted on the LTER ''Zone
Atelier Armorique'' for several insect taxa: two species with contrasted habitat
requirements and dispersal abilities, i.e. a grassland butterfly and a carabid beetle
of cropped habitats, and the community of wild bees. We will emphasize the
temporal dimension by stating the effects of the changing crop mosaic within a
year studying insect movements between crops, and looking at the spatial and
temporal distribution of organisms during one rotation cycle.
14.3.1 Effects of Crop Phenology and Farming Practices
at the Infra-Annual Time Scale
Species movements between habitat patches depend not only on functional land-
scape connectivity (Kindlmann and Burel 2008 ), but also on the dynamics of
resource quality in patches (Schooley and Branch 2011 ). For insects using annual
crops or grasslands, whether they are phytophageous, nectariferous or predatory,
crop cover states control the availability of biotic and abiotic resources (e.g. Alston
et al. 1991 ). These cover states vary throughout the season from crop sowing and
growth to harvest. These changes induce quick and frequent changes in insect
movements and distributions in the cultivated mosaic (Kennedy and Storer 2000 ).