Stable species and interactions in plant-pollinator networks deviate from core position in fragmented habitats

Species and their interactions are more dynamic over time and space in
fragmented habitats than in continuous habitats. In fragmented habitats,
the low nestedness of mutualistic networks may be related to the position
change of stable (high persistence over time/space) species and
interactions in the networks. Previous studies have shown
that stable species and interactions tend to be in the core
position of mutualistic networks. However, in fragmented habitats, it
remains unknown whether stable species or interactions still tend to be in
the core position. To address this gap, here we evaluated the
correlation between the position of proximity to the network core and the
temporal/spatial stability of species and interactions, using the
observation of 42 plant-pollinator networks conducted in a fragmented
island landscape over 3 years. We showed that temporally/spatially stable
species and interactions deviated from the network core to varying
degrees. Temporally stable plants were most likely to deviate from the
network core, followed by pollinators and interactions, while only
spatially stable pollinators tend to deviate from the network core. When
unstable species (present in few time/space points, typically specialists)
and interactions occupy the network core, they cannot interact with most
species in the network as generalists do, resulting in the decrease of
network nestedness. Therefore, from the perspective of position and
stability, stable species and interactions deviate from the network core
in fragmented habitats, which is an important reason for the decrease of
nestedness in mutualistic networks. Our study suggests that
protecting plants that occupy the core in large plant-pollinator networks
is essential for maintaining the network persistence in fragmented
habitats.