POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION
2.2.1.2 Changes in land cover spatial
configuration
2.2.1.2.1 Effect of changes in land cover
configuration on pollinators
Besides leading to habitat loss and degradation, changes
in land use can fragment and alter the area and the spatial
configuration of land cover and habitats. Thus, changes
in land use can lead to habitat fragmentation (i.e., the
sub-division of continuous habitat), affecting the size of
habitat patches within an area, as well as their connectivity
(Hadley and Betts, 2012; Hooke and Martín-Duque, 2012;
Kearns et al., 1998). In these scenarios, although habitats
are still available to pollinators, the fact that their relative
spatial configuration has changed can lead to reductions
in pollinator fitness (breeding success; Battin, 2004) and
population sizes and thus can increase the chances
of extinction.
Recent studies have shown that variation in landscape
configuration can affect pollinator richness, species
diversity and evenness in indirect and complex manners. A
continental analysis of wild bees and butterflies in Europe
(Marini et al., 2014) showed that species evenness and
FIGURE 2.2.2
Conceptual visualization of the effects
of gradients of habitat fragmentation
and natural and semi-natural land
cover loss on pollinators and
pollination. Landscape fragmentation
(green rectangles) and increased loss
of natural and semi-natural land cover
(landscape cartoons) reduce patch
sizes (smaller green rectangles with
increased fragmentation) and interpatch
connectivity (more isolated green
sections in cartoons with increased
land cover change and fragmentation),
negatively affecting pollinator richness
and abundance, and pollination. Grey
lateral triangles show gradients of
landscape modification (right) and
pollination, pollinator richness and
abundance (left). Modified from Steffan-
Dewenter and Westphal (2008).
diversity were negatively correlated, and that while patch
area related negatively to pollinator evenness, connectivity
showed the opposite relationship. These results agree with
what was observed by Winfree et al. (2011) for abundance
and diversity of an array of pollinators. In that study, there
were, however, differences among pollinator groups. On
the one hand, bees were the most negatively affected by
habitat fragmentation and loss (referred to as “land use” by
the authors), followed by butterflies and hoverflies. On the
other hand, larger vertebrate pollinators (i.e., birds, bats)
were more positively affected by habitat fragmentation
and loss (Table 2.2.1). This difference could be due to the
greater dispersal ability of large vertebrates or to a bias in
the analyzed datasets (Winfree et al., 2011). A more recent
meta-analysis of bee species richness and abundance
found little effect of landscape configuration (Kennedy
et al., 2013), although it identified that loss of conne
ctivity negatively affects social bee abundance. Overall,
fragmented habitats may be able to maintain a greater
level of pollinator diversity (related to this, see the concept
of agricultural matrix, treated in section 2.2.2 and Chapter
6). However, although it is well established that landscape
connectivity and especially the surrounding habitat
availability correlate with components of biodiversity (e.g.,
Prugh et al., 2008), few studies have explicitly examined
Pollination services
Pollination richness and abundance
Habitat fragmentation, reduction of
patch size and isolation