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Parameters describing the structure of the Garraf polli- nation network based on field surveys (F), pollen analysis (P), and field surveys + pollen analyses (FP)
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Pollination network studies are based on pollinator surveys conducted on focal plants. This plant-centred approach provides insufficient information on flower visitation habits of rare pollinator species, which are the majority in pollinator communities. As a result, pollination networks contain very high proportions of pollinator species linked to...
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... found no pollen of one of the surveyed plant species (Iris lutescens Lam.) on any of the captured specimens. Thus, the P matrix was smaller (18 plant species, 107 pollinator species) than the F and FP matrices (Table 1). Some pollinator specimens carried pollen of species not found in our study area (not included in the analyses). ...
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... was 15.14 in F, 18.43 in P, and 21.61 in FP (Table 1, Fig. 1). The increased connectance in FP was not solely due to increased sampling effort. ...
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... plant connectivity increased from c. 19 in F and P to 26.4 in FP, and average pollinator connectivity from c. 3 to 4.1. The percentage of extreme specialist (one- link) pollinator species decreased from 45.9% in F, to 29.9% in P and 27.9% in FP (Table 1, Fig. 1). This dramatic decrease in specialization did not result in changes in the shape of the connectivity distribution. ...
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... degree centralization was low in the three matrices and, contrary to our expectations, increased with the addition of pollen data (Table 1, Fig. 1), strengthening differences among species in connectivity. Similarly, nest- edness did not decrease with the addition of pollen data. ...
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... nest- edness did not decrease with the addition of pollen data. All three matrices were significantly nested and, in fact, NODF and N* tended to increase with the addition of pollen data (Table 1). Thus, despite the overall increase in connectivity, interactions between specialists remained scarce. ...
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... species in module 4 experienced the highest % between-module link gain (Table 2; ANOVA, F 3,137 = 5.488, P = 0.001). Table 2 Within-and between-module link gain with the addition of pollen data in species belonging to the various modules of the Garraf pollination network Module 1 Module 2 Module 3 Module 4 Species 45 27 51 18 Within-module links gained 53 12 20 10 Between-module links gained 29 13 4 9 % Within-module link gain* 40.5 ± 4.9 40.9 ± 8.9 9.5 ± 1.8 19.3 ± 5.5 % between-module link gain ...
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Citations
... However, pollen deposition analyses are extremely time-consuming and consequently prohibitive for landscape-scale studies. Alternatively, pollen loads analyses of flower visitors also provide valuable information regarding an animal's capacity as a pollinator and are suitable for large-scale studies given their relative simplicity [21,22]. Pollen-transport networks have been studied at singular sites and local scales [23][24][25][26] and pollen metanetworks across land-use types [27], but, to our knowledge, there is no study analysing pollen-transport networks and metanetworks over gradients of habitat size, isolation and landscape diversity. ...
... The specialization of pollination networks can be higher than that of visitation networks [23,29] given that the pollen richness on the bodies of flower visitors is usually a subset of the flowers they visit [30]. However, pollen analyses can also reveal interactions established with rare and unfrequently visited plant species that could lead to higher pollen-transport network connectance [22,31] and lower network specialization [32,33]. The specialization of mutualistic networks is affected by habitat loss and isolation through species turnover [34] and through a shift towards a higher prevalence of opportunistic interactions among generalists [35]. ...
... To ensure that pollen diversity was captured, the slides were scanned systematically in consecutive horizontal lines starting from the left upper corner of each slide and up to the count of 200 pollen grains. Following Bosch et al. [22], we considered the presence of at least 10 pollen grains in our samples as proof of true visitation to the corresponding flowering species (i.e. threshold for pollen-bee interactions). ...
Understanding the organization of mutualistic networks at multiple spatial scales is key to ensure biological conservation and functionality in human-modified ecosystems. Yet, how changing habitat and landscape features affect pollen-bee interaction networks is still poorly understood. Here, we analysed how bee-flower visitation and bee-pollen-transport interactions respond to habitat fragmentation at the local network and regional metanetwork scales, combining data from 29 fragments of calcareous grasslands, an endangered biodiversity hotspot in central Europe. We found that only 37% of the total unique pairwise species interactions occurred in both pollen-transport and flower visitation networks, whereas 28% and 35% were exclusive to pollen-transport and flower visitation networks, respectively. At local level, network specialization was higher in pollen-transport networks, and was negatively related to the diversity of land cover types in both network types. At metanetwork level, pollen transport data revealed that the proportion of single-fragment interactions increased with landscape diversity. Our results show that the specialization of calcareous grasslands' plant-pollinator networks decreases with landscape diversity, but network specialization is underestimated when only based on flower visitation information. Pollen transport data, more than flower visitation, and multi-scale analyses of metanetworks are fundamental for understanding plant-pollinator interactions in human-dominated landscapes.
... Therefore, FV networks may not fully reflect the plant-pollinator interactions and interspecific pollination processes. An alternative approach is to construct plant-pollinator networks by identifying the species and amounts of pollen load (PL) on pollinators (Barker & Arceo-Gómez, 2021;Bosch et al., 2009;de Manincor et al., 2020;Tourbez et al., 2023;Zhao et al., 2019). This approach further explored the effectiveness of visitors as pollen vectors (Zhao et al., 2019), particularly in distinguishing between nectar foraging and pollen collecting, although both are considered effective interactions in FV networks. ...
... Moreover, identifying pollen on insect bodies can increase the likelihood of detecting rare plant-pollinator links that are difficult to observe in the field (Alarcón, 2010;Jędrzejewska-Szmek & Zych, 2013). Previous studies have shown that PL networks observed more diverse links than FV networks, suggesting that pollen load could more accurately capture the plant-pollinator interactions in natural communities (Barker & Arceo-Gómez, 2021;Bosch et al., 2009;Tourbez et al., 2023). In addition, the PL on the pollinator body can represent interactions between animals and plants over a relatively long period, reducing the constraints of observation time in flower visit network. ...
... The unique links of each network generally had lower link strength, indicating that the PL could detect more links. These results are similar to previous studies(Barker & Arceo-Gómez, 2021;Bosch et al., 2009;Tourbez et al., 2023), which found that networks based on pollen load increased the connectivity and the average degree of plants and pollinators, and reduced the specialization of the networks. We also found that the positions of plant and pollinator species in the FV and PL networks were sig-nificantly correlated, indicating that both network types are effective in identifying important plant-pollinator interactions from different perspectives. ...
The mutualistic network of plant–pollinator also involves interspecific pollination caused by pollinator sharing. Plant–pollinator networks are commonly based on flower visit observations, which may not adequately represent the actual pollen transfer between co‐flowering plant species. Here, we compared the network structure of plant–pollinator interactions based on flower visits (FV) and pollen loads (PL) on the bodies of pollinators and tested how the degree of pollinator sharing in the two networks affected heterospecific pollen transfer (HPT) between plant species in a subalpine meadow. The FV and PL networks were largely overlapped. PL network included more links than FV network. The positions of plant and pollinator species in the FV and PL networks were positively correlated, indicating that both networks could detect major plant–pollinator interactions. The degree of pollinator sharing, based on either the FV or the PL network, positively influenced the amount of heterospecific pollen transferred between plant species pairs. However, the degree of pollinator sharing had a low overall explanatory power for HPT, and the explanatory powers of the FV and PL networks were similar. Overall, our study highlights the importance of FV and PL for understanding the drivers and outcomes of plant–pollinator interactions, as well as their relevance to HPT.
... Global change and declines in biodiversity are likely to disrupt mutualistic interactions, including pollination services (Silberbauer et al. 2004;Bosch et al. 2009;Jones 2014;Wood et al. 2019;Wagner et al. 2021;Balmaki et al. 2022a). An analysis of butterflies in the Great Basin and the Sierra Nevada Mountain range in the Western USA suggests that pollen-butterfly species interactions are vulnerable to disruptions, and that pre-drought butterfly-pollen networks have higher richness, nestedness, and connectance than post-drought collections (Balmaki et al. 2022a, b). ...
Shifts in flowering time among plant communities as a result of climate change, including extreme weather events, are a growing concern. These plant phenological changes may affect the quantity and quality of food sources for specialized insect pollinators. Plant–pollinator interactions are threatened by habitat alterations and biodiversity loss, and changes in these interactions may lead to declines in flower visitors and pollination services. Most prior research has focused on short-term plant–pollinator interactions, which do not accurately capture changes in pollination services. Here, we characterized long-term plant–pollinator interactions and identified potential risks to specialized butterfly species due to habitat loss, fragmented landscapes, and changes in plant assemblages. We used 21 years of historical data from museum specimens to track the potential effects of direct and indirect changes in precipitation, temperature, monsoons, and wildfires on plant–pollinator mutualism in the Great Basin and Sierra Nevada. We found decreased pollen richness associated with butterflies within sites, as well as an increase in pollen grain abundance of drought-tolerant plants, particularly in the past 10 years. Moreover, increased global temperatures and the intensity and frequency of precipitation and wildfires were negatively correlated with pollen diversity. Our findings have important implications for understanding plant–pollinator interactions and the pollination services affected by global warming.
... The use of various sampling techniques is paramount in optimizing the effectiveness of interaction sampling (Figure 1.3), largely because different methods complement each other in the range of species detected (Bosch et al. 2009). This Ph.D. thesis project serves as a good example, as we employ up to six different methods (direct and indirect) for sampling plant-animal interactions. ...
Plant-animal interactions are crucial for maintaining ecosystem functionality and
biodiversity. Ecological research has shown that these interactions can be modified in
different contexts, affecting natural dynamics. Currently, significant changes in the
landscape, such as rural abandonment or the protection of natural areas, are creating
a new ecological context for the formation and regeneration of new forested areas.
Although the role of mutualistic and antagonistic interactions between plants and
animals in ecosystems is acknowledge, we lack a comprehensive understanding of their role during the processes of colonization and expansion. Understanding the structure of interactions and the role of the species involved along natural expansion gradients is key to comprehending the natural dynamics underlying expansion processes, as well as the mechanisms that may or may not facilitate the formation of new forests and biodiverse natural ecosystems.
The aim of this PhD thesis is to document the structure and consequences of
plant-animal interactions that are related to plant reproductive success along a natural
expansion gradient. To achieve this, we analyze the interactions, both antagonistic
and mutualistic, of predispersal seed predation and seed dispersal at the individual
plant level and the resulting patterns such as seed rain and its maternal composition
along the natural expansion gradient experienced by the Juniperus phoenicea subsp.
turbinata population in the Doñana National Park since its protection five decades
ago.
We found that the interaction networks that shape individual plants, both with
antagonistic (predispersal seed predators) and mutualistic (seed dispersers) species,
were concordantly reconfigured along the population expansion gradient. The
structuring at the individual level was influenced by the animals’ preferences for certain phenotypic traits of the plants, as well as the neighborhood and maturity context in which they were found. Interactions with most animal species, including mutualists and antagonists, are well established in mature stands; however, at the colonization front, only certain species dominate the interaction networks. Both seed loss before dispersal and seed dispersal were accentuated in the expansion front stand due to the interaction with dominant species (Chloris chloris and Turdus philomelos). These results suggest a compensatory effect between opposite interactions that facilitates the contribution of propagules along the gradient, particularly at the colonization front, thereby driving population expansion. Furthermore, by characterizing the seed rain and its maternal genetic composition, we found that the frugivore assembly generates a seed rain that is equally dense and genetically diverse (in terms of source trees included) along the entire expansion gradient. This result highlights the potential of animal-mediated seed dispersal to mitigate the expected negative effects during rapid population expansion processes (founder effects) and promote colonization dynamics that guarantee the diversity of new forests.
Both the combination of multiple sampling methods for ecological interactions
together with field experiments and laboratory work for genetic analyses allowed
an integrative study of dispersal dynamics. Taken together, our results suggest that
ecological interactions between plants and animals are structured at individual level,
and at local scale, and are consistently reshaped along natural expansion gradients.
Collectively, the chapters presented in this thesis represent a major step forward in our
understanding of the ecology and implications of plant-animal interactions during the
expansion of natural populations.
... The perception of relatively specialised communities is largely based upon observations of insects visiting flowers rather than on observations of pollination per se (Bosch et al. 2009, Ballantyne et al. 2015. Flower-visitor sampling typically reveals only a single interaction per individual insect, although in rare cases individuals can be tracked over multiple visits in a small area (Heinrich 1979, Couvillon et al. 2015). ...
... Flower-visitor sampling typically reveals only a single interaction per individual insect, although in rare cases individuals can be tracked over multiple visits in a small area (Heinrich 1979, Couvillon et al. 2015). An alternative approach which reliably records many interactions per individual is to use the composition of pollen loads carried by insects to infer their recent visits to plants (Bosch et al. 2009, Alarcón 2010, Popic et al. 2013, Bell et al. 2017). Networks of plants and pollinators constructed based on pollen-load data tend to suggest that insects are more generalist than is indicated by visitation data (Bosch et al. 2009, Ritchie et al. 2016, with few insects visiting only one plant species (Lucas et al. 2018). ...
... An alternative approach which reliably records many interactions per individual is to use the composition of pollen loads carried by insects to infer their recent visits to plants (Bosch et al. 2009, Alarcón 2010, Popic et al. 2013, Bell et al. 2017). Networks of plants and pollinators constructed based on pollen-load data tend to suggest that insects are more generalist than is indicated by visitation data (Bosch et al. 2009, Ritchie et al. 2016, with few insects visiting only one plant species (Lucas et al. 2018). Nonetheless, a few studies suggest no change in specialisation until pollen deposition is taken into account (Alarcón 2010, Ballantyne et al. 2015, Zhao et al. 2019. ...
Most animal pollination results from plant–insect interactions, but how we perceive these interactions may differ with the sampling method adopted. The two most common methods are observations of visits by pollinators to plants and observations of pollen loads carried by insects. Each method could favour the detection of different species and interactions, and pollen load observations typically reveal more interactions per individual insect than visit observations. Moreover, while observations concern plant and insect individuals, networks are frequently analysed at the level of species. Although networks constructed using visitation and pollen‐load data have occasionally been compared in relatively specialised, bee‐dominated systems, it is not known how sampling methodology will affect our perception of how species (and individuals within species) interact in a more generalist system. Here we use a Diptera‐dominated high‐Arctic plant–insect community to explore how sampling approach shapes several measures of species' interactions (focusing on specialisation), and what we can learn about how the interactions of individuals relate to those of species. We found that species degrees, interaction strengths, and species motif roles were significantly correlated across the two method‐specific versions of the network. However, absolute differences in degrees and motif roles were greater than could be explained by the greater number of interactions per individual provided by the pollen‐load data. Thus, despite the correlations between species roles in networks built using visitation and pollen‐load data, we infer that these two perspectives yield fundamentally different summaries of the ways species fit into their communities. Further, individuals' roles generally predicted the species' overall role, but high variability among individuals means that species' roles cannot be used to predict those of particular individuals. These findings emphasize the importance of adopting a dual perspective on bipartite networks, as based on the different information inherent in insect visits and pollen loads.
... Certainly, comparisons of visit-and pollen-based networks indicate that pollen-transport networks are smaller and more specialized compared with their respective visitation networks 13,69-71 (but see Jędrzejewska-Szmek and Zych 72 and Walton et al. 13 ). However, in terms of network metrics such as nestedness, modularity, and connectance (evaluated in this study), the results of these comparisons lack clear patterns [72][73][74][75][76] . This diversity of results aligns better with "noise" than with a consistent bias due to differences in sampling methods. ...
... This diversity of results aligns better with "noise" than with a consistent bias due to differences in sampling methods. On the other hand, the few existing studies combining pollen and flower visitor networks 12,73,75 have shown higher connectivity and nestedness compared to visitor-only networks 73,75 . If the addition of nocturnal interactions would simply introduce a bias in network parameters, we would expect the combined network parameters to be biased in the same direction shown by the comparative studies of visit vs. pollen networks. ...
Although the ecological network approach has substantially contributed to the study of plant-pollinator interactions, current understanding of their functional structure is biased towards diurnal pollinators. Nocturnal pollinators have been systematically ignored despite the publication of several studies that have tried to alleviate this diurnal bias. Here, we explored whether adding this neglected group of pollinators had a relevant effect on the overall architecture of three high mountain plant-pollinator networks. Including nocturnal moth pollinators modified network properties by decreasing total connectivity, connectance, nestedness and robustness to plant extinction; and increasing web asymmetry and modularity. Nocturnal moths were not preferentially connected to the most linked plants of the networks, and they were grouped into a specific “night” module in only one of the three networks. Our results indicate that ignoring the nocturnal component of plant-pollinator networks may cause changes in network properties different from those expected from random undersampling of diurnal pollinators. Consequently, the neglect of nocturnal interactions may provide a distorted view of the structure of plant-pollinator networks with relevant implications for conservation assessments.
... Since most visitors at night were active from sunset to midnight, and the number of Lepidoptera was highest at midnight (Knop et al., 2018), the traps were strategically placed on the path closest to the meadows and operated from 2000 to 2400 h. Six light traps were used, each with an interval of 5-10 days (Table A.2). Captured insects were retained in individual tubes and stored in a freezer until pollen analysis (Bosch et al., 2009;Devoto et al., 2011) and identification. ...
... . It is therefore desirable to use a combination of traditional morphology-based and newer molecularbased methods in order to characterise network structural properties (Bosch et al., 2009;Pornon et al., 2017). ...
Pollen grains attached to insects are a valuable source of ecological information which can be used to reconstruct visitation networks. Morphological pollen identification relies on light microscopy with pollen usually stained and mounted in fuchsin jelly, which is also used to remove pollen from the bodies of insects. Pollen embedded in fuchsin jelly could potentially be used for DNA barcoding and metabarcoding (large‐scale taxonomic identification of complex mixed samples) and thus provide additional information for pollination networks. In this study, we determine whether fuchsin‐embedded pollen can be used for downstream molecular applications. We evaluate the quality of plant barcode (ITS) sequences amplified from DNA extracted from both fresh (untreated) pollen, and pollen which had been embedded in fuchsin jelly. We show that the addition of fuchsin to DNA extraction does not impact DNA barcode sequence quality during short‐term storage. DNA extractions from both untreated and fuchsin‐treated pollen produced reliable barcode sequences of high quality. Our findings suggest that pollen which has been collected, stained, and embedded in fuchsin jelly for preliminary microscopy work can be used within several days for downstream genetic analysis, though the quality of DNA from pollen stored in fuchsin jelly for extended periods is yet to be established.
... Currently, rapid changes in the structure of plant communities combined with their temporal trends, mainly related to global changes, occurred at diverse spatial scales such as in France (Martin et al. 2019) which can redefine insect pollinator assemblages by their intimate interactions (Bosch et al. 2009). Floral resources, including pollen and nectar, play a vital role in the life cycle of pollinators. ...
This research thesis investigated into the critical issue of declining insect populations, particularly pollinators, in the crucial context of ecosystem functioning, agriculture, and human health. Focusing on bees, hoverflies, and apoid wasps, we explore the impact of landscape degradation, caused by agricultural intensification and urbanization, on pollinator communities in temperate agricultural and urban landscapes. Four case studies are presented, offering valuable insights and
recommendations for conservation and restoration efforts. The first study examined ecological diversification on two farms in early ecological transition, uncovering valuable data on wild bees and hoverflies. Results highlighted specific diversity with 101 bee species and 31 hoverfly species, indicating the potential for ecological diversification and agroecological practices to support rare and endangered pollinators. Building on this study, we investigated the impact of flower strips in
intercropping systems with winter wheat. Multifloral strips attracted a diverse range of hoverflies, presenting a promising ecological and economic solution for farmers. In urban landscapes, we analyzed pollen availability and foraging behavior of honeybee colonies along an urban-rural gradient in Tokyo. Landscape factors significantly influenced floral species visited by honeybees, offering valuable insights for urban planning. Lastly, we explored the nesting potential of
pavements for ground-nesting Hymenoptera in Brussels. We identify 22 species of wild bees and apoid wasps nesting in specific urban surfaces, providing essential recommendations for encouraging these pollinators. These studies underscored the significance of food and nesting resources for pollinator communities and advocated for conservation efforts in disturbed environments. Our findings contribute to the growing body of knowledge on agricultural and urban
ecology, paving the way for future scientific endeavors in this crucial field.
... Connectance decreases with higher species richness, suggesting that regions with high pollinator diversity, such as tropical areas, are likely to exhibit lower connectance (Vizentin-Bugoni et al. 2018). The low connectance in plant-pollinator networks contributes to the limited community-level generalization (Bosch et al. 2009). Nestedness, on the other hand, can either increase or decrease with changes in connection. ...
Background
The topology of the plant–pollinator network can be explained by the species’ abundance and their random interactions. Plant–pollinator networks can be studied in the context of a landscape, because each patch can accommodate a certain local network. Local populations of pollinators in the landscape can be connected through migration and then constitute a metanetwork that is known as a combination of spatial and ecological networks. In this regard, habitat fragmentation can affect the topology of plant–pollinator metanetworks through changes in the species abundance and limiting their interactions. However, it is not clear what pattern (fragmented or aggregated) of the landscape structure can accommodate networks with a higher degree of specialization.
Methods
we created simulated landscapes with different forest proportions scenarios (from 5% to 50% of the total landscape) and degrees of fragmentation. Then, for each landscape, we limited the proportion of pollinators to the forest patch. We assumed that plants and pollinators are randomly distributed around the landscape and interact randomly. We used landscape metrics to measure different aspects of landscape structure and bipartite metrics for calculating the degree of specialization in plant–pollinator networks.
Results
The statistical relationship between bipartite and landscape metrics showed that the relationship between the topology of plant–pollinator networks and the landscape structure is affected by the forest amount in the landscape and the degree of forest fragmentation. We also found that according to the nestedness and H2 (a measure of specialization) metrics, fragmented landscapes contain more general plant–pollinator networks.
Conclusions
Our findings suggest that fragmented landscapes, characterized by scattered forest patches, can promote higher levels of interaction between limited pollinators and diverse flowers, leading to more general plant–pollinator networks.
