Abstract
Conservation biological control in agroecosystems requires a landscape
management perspective, because most arthropod species experience
their habitat at spatial scales beyond the plot level, and there
is spillover of natural enemies across the crop noncrop interface.
The species pool in the surrounding landscape and the distance of
crop from natural habitat are important for the conservation of enemy
diversity and, in particular, the conservation of poorly-dispersing
and specialized enemies. Hence, structurally complex landscapes with
hi,gh habitat connectivity may enhance the probability of pest regulation.
In contrast, generalist and highly vagile enemies may even A p rofit
from the high primary productivity of crops at a landscape scale
and their abundance may partly compensate for losses in enemy diversity.
Conservation biological control also needs a multitrophic perspective.
For example, entomopathogenic fungi, plant pathogens and endophytes
as well as below- and above-ground microorganisms are known to influence
pest-enemy interactions in ways that vary across spatiotemporal scales.
Enemy distribution in agricultural landscapes is determined by beta
diversity among patches. The diversity needed for conservation biological
control may occur where patch heterogeneity at larger spatial scales
is high. However, enemy communities in managed systems are more similar
across space and time than those in natural systems, emphasizing
the importance of natural habitat for a spillover of diverse enemies.
According to the insurance hypothesis, species richness can buffer
against spatiotemporal disturbances, thereby insuring functioning
in changing environments. Seemingly redundant enemy species may become
important under global change. Complex landscapes characterized by
highly connected crop-noncrop mosaics may be best for long-term conservation
biological control and sustainable crop production, but experimental
evidence for detailed recommendations to design the composition and
configuration of agricultural landscapes that maintain a diversity
of generalist and specialist natural enemies is still needed. (c)
2007 Elsevier Inc. All rights reserved.
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