Discussion
We found that interactions involving generalist plants and pollinators
are more persistent in time and space. More specifically, interactions
near the network core were more persistent across the five years, more
persistent within seasons, and more persistent across plots. Moreover,
the same interactions that were persistent within seasons also tended to
be persistent across years and among plots, and that interactions
persistent across years are persistent across plots. Generalist species
tended to be more widespread in time and space. These patterns suggest
that tolerance to environmental variation across space and time is
associated with interaction generalization through the increased
spatiotemporal overlap of interacting partners.
Our study conceptually and
empirically links the persistence of interactions in time and space. The
patterns of temporal and spatial persistence are consistent with
previous studies that have found this relationship in either space or
time (Aizen et al. 2012; Chacoff et al. 2018). Our study
links these disparate patterns in temporal and spatial persistence of
interactions with the tolerances of environmental conditions as a
proposed mechanism linking them. At the species level, the connection
between distributions and generalization also relates disparate concepts
of niche breadth that emphasize species environmental constraints
(Grinnellian niche) and their role in the community via interactions
(Eltoninan niche) (Chase & Leibold 2003; Devictor et al. 2010;
Gravel et al. 2019). We define generalization focusing on the
number of partners of each species across a range of spatial and
environmental conditions. We recognize that species’ roles themselves
are dynamic and context-dependent (Devictor et al. 2010;
CaraDonna & Waser 2020; Miele et al. 2020) and that
generalization can be quantified in different ways to describe different
aspects of species (Blüthgen et al. 2006).
As the specificity of environmental conditions and spatiotemporal
distributions can be interrelated with abundance (Rabinowitz 1981; Brown
1984) it is important to consider the role of abundance in the patterns
observed. Species that are widespread in time and space are likely to
have larger population sizes. Large population sizes could make species
of plants and pollinators less susceptible to local extinctions and thus
allow greater spatiotemporal persistence allowing for greater
generalization. Because spatiotemporal overlap of interacting partners
and abundance are primary factors in driving interaction patterns it
supports the view that interactions are strongly driven by opportunism
(Waser et al. 1996; Memmott 1999). Higher abundances could also
increase the detectability of species and their interactions (McCarthyet al. 2013; Chacoff et al. 2018). While the observation
methods of this study aimed to minimize biases stemming from
detectability by observing all flowers in plots during the survey
period, disentangling sampling effects from biological processes in
network studies remains an important challenge and priority (Vázquezet al. 2009; CaraDonna et al. in press).
Despite these promising results, much work remains to be done. With the
increasing availability of interaction network datasets, there is an
opportunity to synthesize patterns of spatiotemporal interaction
persistence across studies with different environmental contexts and
temporal and spatial scales. To this end, whenever possible future
studies should record interaction data that are temporally and spatially
explicit. Also, associated data on environmental conditions in the
context of the interactions and the physiology of organisms (e.g.,
thermal tolerances) would allow further assessing the role of
environmental variation on interaction persistence.
Generalist species are the
linchpins of networks, as their presence promotes network robustness to
environmental perturbations (Bascompte & Stouffer 2009). Despite their
pivotal roles, common and generalist species are taken for granted and
lack conservation protections that are conventionally aimed at rare
species (Lindenmayer et al. 2011). However, we know that
abundant, generalized species may be susceptible to decline and
extinction in the face of environmental change (Wagner 2020), e.g.,Bombus dahlbomii in Patagonia, see (Morales et al. 2013).
The possibility of such declines puts the stability of ecological
communities in jeopardy. Therefore, conservation priorities should not
overlook the pivotal roles that generalists play in supporting
biodiversity across time and space.