The Structure and Dynamics of Agricultural Landscapes as Drivers of Biodiversity - Landscape Ecology for Sustainable Environment and Culture - page 284

These localized changes in butterfly abundances in mown and unmown grasslands
can probably be explained by a redistribution of butterflies from disturbed

grasslands into remnant suitable herbaceous patches.
To compensate for these local and abrupt changes in resource availability on a
given patch, the presence of alternative suitable and accessible resource patches
will be crucial for species to realize their life cycle (Kennedy and Storer 2000 ;
Men et al. 2004 ; Carrière et al. 2006 ; Bressan et al. 2010 ). Some asynchrony
between farming practices and crop cover states might allow to compensate for the
ephemeral suitability of crops, by ensuring a temporal continuity of resources for
species. A study of a generalist predatory carabid species with limited mobility
(Pterostichus melanarius Illiger) in annual crops illustrates these processes
(Vasseur 2012 ). Carabid movements were surveyed at the edges between different
types of annuals crops (winter cereals, spring maize and pea) with contrasted cover
states during the activity-period of carabids. Bidirectional interception traps,
adapted from Hawthorne et al. ( 1998 ), were used to sample carabid movements
between six adjacent crops. The interception traps were open continuously and
collected weekly from early May to early September. As an example, Fig. 14.3
displays the orientation of carabid movements at field edges between a pea crop
and two adjacent maize fields. It shows that, in the early summer, carabid beetles
move more frequently from maize fields (with bare soil at this period) to pea fields
(with dense vegetation cover). In late July, an inversion of the orientation of
carabid movements at edges is observed, i.e. more movements from pea to maize
fields, in relationship with pea harvest and vegetation growth in maize. Thus, P.
melanarius seems to move throughout its activity-period from crops with unsuit-
able, sparse vegetation to crops with dense cover. This suggests that adjacent

20 2.5

15

Pea
harvest

1.5

10

5

0.5

0

-0.5

-5

-10

May June July Aug. Sep.

-1.5

-15

-20 -2.5

Carabid movements Maize height Pea height

Fig. 14.3 Direction of carabid movements at edges between pea and adjacent maize fields from
May to September