The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study

Background and Aims Large clades of angiosperms are often characterized by diverse interactions with pollinators, but how these pollination systems are structured phylogenetically and biogeographically is still uncertain for most families. Apocynaceae is a clade of >5300 species with a worldwide distribution. A database representing >10 % of species in the family was used to explore the diversity of pollinators and evolutionary shifts in pollination systems across major clades and regions. Methods The database was compiled from published and unpublished reports. Plants were categorized into broad pollination systems and then subdivided to include bimodal systems. These were mapped against the five major divisions of the family, and against the smaller clades. Finally, pollination systems were mapped onto a phylogenetic reconstruction that included those species for which sequence data are available, and transition rates between pollination systems were calculated. Key Results Most Apocynaceae are insect pollinated with few records of bird pollination. Almost three-quarters of species are pollinated by a single higher taxon (e.g. flies or moths); 7 % have bimodal pollination systems, whilst the remaining approx. 20 % are insect generalists. The less phenotypically specialized flowers of the Rauvolfioids are pollinated by a more restricted set of pollinators than are more complex flowers within the Apocynoids + Periplocoideae + Secamonoideae + Asclepiadoideae (APSA) clade. Certain combinations of bimodal pollination systems are more common than others. Some pollination systems are missing from particular regions, whilst others are over-represented. Conclusions Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades

A synthesis of animal-mediated seed dispersal of palms reveals distinct biogeographic differences in species interactions

Aim:  To synthesize published knowledge on palm–frugivore seed dispersal observations and to test whether broad‐scale differences in geographic coverage, diversity, composition and functional structure of plant–animal interactions emerge between biogeographical regions. Location:  Neotropics and Afrotropics. Methods:  We constructed a meta‐network for both regions by aggregating observations of pairwise palm–frugivore interactions from the primary literature. We assessed sampling completeness with accumulation curves and estimated knowledge gaps for individual palm species and geographic units within biogeographical regions. We compared the taxonomic composition as well as structural indices of regional interaction networks and tested whether functional trait matching (i.e., the relationship between palm fruit size and frugivore body size) differs between regions. Results:  A total of 750 unique pairwise interaction records were retrieved from the primary literature covering 340 frugivores and 126 palms. Sampling completeness of frugivore interactions within biogeographical regions and for individual palm species was low (often <50%), geographic coverage limited, and relative knowledge gaps were largest in areas with high palm species richness. Interaction diversity and network modularity was larger in the Neotropics than the Afrotropics. A positive fruit size–body mass relationship (i.e., functional trait matching) was statistically significant in the Afrotropics, but not in the Neotropics. Main conclusions:  Available data on palm–frugivore interactions suggest major biogeographical differences in ecological networks among regions, even when taking differences in palm species richness into account. The Neotropics showed a larger interaction diversity and more modular network structure than the Afrotropics. Broad‐scale morphological trait matching among plants and frugivores was only observed in the Afrotropics. The lack of a Neotropical trait matching relationship might be driven by the late Quaternary extinctions of mammalian megafauna in this region. Although our work has increased the digital availability of palm–frugivore interaction observations, massive knowledge gaps of interaction diversity remain in the tropics

Spatial structure of an individual-based plant-pollinator network

The influence of space on the structure (e.g. modularity) of complex ecological networks remains largely unknown. Here, we sampled an individual-based plant-pollinator network by following the movements and flower visits of marked bumblebee individuals within a population of thistle plants for which the identities and spatial locations of stems were mapped in a 50 × 50 m study plot. The plant-pollinator network was dominated by parasitic male bumblebees and had a significantly modular structure, with four identified modules being clearly separated in space. This indicated that individual flower visitors opted for the fine-scale division of resources, even within a local site. However, spatial mapping of network modules and movements of bumblebee individuals also showed an overlap in the dense center of the plant patch. Model selection based on Akaike information criterion with traits as predictor variables revealed that thistle stems with high numbers of flower heads and many close neighbours were particularly important for connecting individuals within the modules. In contrast, tall plants and those near the patch center were crucial for connecting the different modules to each other. This demonstrated that individual-based plant-pollinator networks are influenced by both the spatial structure of plant populations and individual-specific plant traits. Additionally, bumblebee individuals with long observation times were important for both the connectivity between and within modules. The latter suggests that bumblebee individuals will still show locally restricted movements within sub-patches of plant populations even if they are observed over a prolonged time period. Our individual-based and animal-centered approach of sampling ecological networks opens up new avenues for incorporating foraging behaviour and intra-specific trait variation into analyses of plant-animal interactions across space

Geographical variation in mutualistic networks:similarity, turnover and partner fidelity

Although species and their interactions in unison represent biodiversity and all the ecological and evolutionary processes associated with life, biotic interactions have, contrary to species, rarely been integrated into the concepts of spatial beta-diversity. Here, we examine beta-diversity of ecological networks by using pollination networks sampled across the Canary Islands. We show that adjacent and distant communities are more and less similar, respectively, in their composition of plants, pollinators and interactions than expected from random distributions. We further show that replacement of species is the major driver of interaction turnover and that this contribution increases with distance. Finally, we quantify that species-specific partner compositions (here called partner fidelity) deviate from random partner use, but vary as a result of ecological and geographical variables. In particular, breakdown of partner fidelity was facilitated by increasing geographical distance, changing abundances and changing linkage levels, but was not related to the geographical distribution of the species. This highlights the importance of space when comparing communities of interacting species and may stimulate a rethinking of the spatial interpretation of interaction networks. Moreover, geographical interaction dynamics and its causes are important in our efforts to anticipate effects of large-scale changes, such as anthropogenic disturbances

Disclosing the double mutualist role of birds on Galápagos.

[eng] Life on oceanic islands deviate in many ways from that on the mainland. Their biodiversity is relatively poor and some groups are well-represented, others not, especially not insects. A scarcity of insects forces birds to explore alternative food, such as nectar and fruit. In this way, island birds may pollinate and disperse seed to an extent unseen on any mainland; they may even first consume floral resources of a plant species and then later harvest the fruit of the same species. Through this biotic reuse, they may act as double mutualists. The latter have never been studied at the level of the network, because they are traditionally considered rare. We sampled pollination and seed-dispersal interactions on Galápagos and constructed a plant-bird mutualism network of 108 plant (12% being double mutualists) and 21 bird species (48% being double mutualists), and their 479 interactions, being either single (95%) or double mutualisms (5%). Double mutualists constitute the core in the pollination-dispersal network, coupling the two link types together. They may also initiate positive feedbacks (more pollination leading to more dispersal), which theoretically are known to be unstable. Thus, double mutualisms may be a necessary, but risky prerequisite to the survival of island biodiversity

Native and alien flower visitors differ in partner fidelity and network integration

<div><div>These data files support the following publication</div><div><br></div><div>Trøjelsgaard, K., Heleno, R., & Traveset, A. <b>Native and alien flower visitors differ in partner fidelity and network integration</b>. Ecology Letters, <i>accepted. </i>doi: 10.1111/ele.13287</div><div><i><br></i></div><div>For more details see the Read Me file or the original publication.</div></div><div><br></div><div><b><u>Abstract</u></b></div><div>Globalisation persistently fuels the establishment of non-native species outside their natural ranges. While alien plants have been intensively studied little is known about alien flower visitors, and especially, how they integrate into natural communities. Here we focus on mutualistic networks from five Galápagos islands to quantify whether alien and native flower visitors differ consistently in their pairwise interactions. We find that i) alien flower visitors have more interaction partners and larger species strengths (i.e. plants are more connected to alien insects), ii) native insects tend to have higher partner fidelity as they deviate more from random partner utilization, and iii) the difference between native and alien flower visitors in network integration intensifies with island degradation. Thus, native and alien flower visitors are not interchangeable, and alien establishment might have yet unforeseen consequences for the pairwise dynamics between plants and flower visitors on the Galápagos – especially on the heavily disturbed islands. <br></div