Global change is threatening both plant and pollinator species, leading to a rapid loss of ecological interactions. Surprisingly, our knowledge of plant reproductive ecology and plant-pollinator interactions remains largely disconnected and there is a need to better understand how plant reproductive strategies affect, and are affected by, the structure of plant-pollinator interactions. This thesis tries to progress knowledge by investigating (i) plant reproductive trade-offs; (ii) how these tradeoffs determine plant-pollinator interactions; (iii) the effects of pollinator sharing for plant reproduction; and (iv) methods to assess the state of vegetation communities, as this can influence the condition of pollinator communities.

First, I compiled information on 17 reproductive traits for more than 1506 flowering plants from 64 plant-pollinator networks distributed across the globe to explore plant reproductive trade-offs and how they influence interactions with floral visitors. Second, using 60 of these plant-pollinator networks, I examined the structural properties of network motifs (subsets of interactions) that describe both direct and indirect interactions among plants and pollinators. I then assessed over- and under-representation of the different plant and floral visitor functional groups on the distinct motif positions and position combinations. Third, I explored one of the consequences of indirect interactions, heterospecific pollen deposition on floral stigmas, by creating an experimental co-flowering community with heterogeneous traits and contrasting phylogenetic relatedness. This allowed me to investigate the impact, mechanisms and competitive structure of heterospecific pollen arrival. Finally, because plant and pollinator species interactions depend on the state of natural systems, I investigated the performance of three remotely sensed metrics (two cover metrics and one novel indicator of ecological condition) to assess the state of vegetation across environmental gradients.

Of the flowering plants recorded, two main reproductive trade-offs were evident (‘flower number - flower size’ and ‘pollinator dependence’) that explained over half of the reproductive trait variation. These plant reproductive trade-offs determined their interactions with floral visitors worldwide. The analysis of network motifs revealed that the structure of motifs in real plant-pollinator networks is non-random. Further, the different floral visitor functional groups associated with distinct motif positions describe contrasting ecological roles. Interestingly, the combination of functional groups within motifs cannot be retrieved by their observed probabilities indicating the presence of underlying ecological processes that constrain motif composition. In the experimental plant communities, heterospecific pollen deposition showed a prevailing negative effect on seed production. These impacts were mainly driven by pollen recipient traits and specific pollen recipient - pollen donor combinations of traits. In addition, the structure of pollen competition was hierarchical with clear ‘winner’ and ‘loser’ species. Lastly, the different remote sensing metrics tested to assess vegetation cover and condition indicated good performance on tree-dominated communities but they were not reliable for specific ecosystem types from arid regions.

Greater understanding of plant reproductive ecology is clearly essential to progress knowledge on the global spectrum of plant trait variation, but also to understand the structure of plant-pollinator interactions (e.g., pollination syndromes). Further, pollinator-mediated interactions among plants (e.g., competitive or facilitative processes) and the consequences for plant fitness need to be considered to disentangle the main ecological drivers of species coexistence. Finally, there is an urgent need to develop precise indices that can capture the state of vegetation for species conservation and enable better understanding of the different ecological processes that mediate plant-pollinator interactions.

1. Pollinator sharing can have negative consequences for plant fitness via competition for visits as well as with the arrival of heterospecific pollen. Plant traits and relatedness of donor and recipient species have been suggested to drive the observed variation in plant fitness effects of both processes, but how they shape the structure of interspecific pollen competition networks has been overlooked at the community level.
2. To understand the importance of reproductive traits and relatedness to the impact of heterospecific pollen, we conducted a controlled glasshouse experiment with an artificial co-flowering community. We performed 2,200 hand pollination crosses by experimentally transferring conspecific pollen alone or with 50% and 100% foreign pollen among 10 species belonging to three different plant families.
3. Relative to conspecific pollen alone, there was a significant reduction in seed set with 50% heterospecific pollen for 67% of the crosses. This effect is driven largely by recipient traits and the interaction between recipient and donor traits under specific circumstances of trait matching. In general, species with shorter styles, smaller stigmas and lower pollen:ovule ratios were more impacted by heterospecific pollen. These traits and their differences among species led to a hierarchical (or transitive) structure of pollen competition with clear winners and losers. However, phylogenetic distance among recipient and donor species did not explain the effects.
4. Synthesis. Our study shows that specific traits and trait combinations between donor and recipient species are important in determining seed production outcomes with heterospecific pollen receipt. Moreover, the differences in traits between species lead to a competitive structure with clear 'winners' or 'losers' species. The results of this study highlight the importance of specific traits in understanding the position of the competitive hierarchy of the species and the mechanisms underlying heterospecific pollen impacts upon plant reproductive success.

1. Globally, plants display enormous variation in life-history strategies and trait combinations. However, evidence suggests that evolutionary and physiological constraints limit the number of plant ecological strategies. Although there have been recent advances in understanding correlations among plant traits, reproductive traits are rarely considered, despite their key role in shaping plant life-history strategies and interactions with pollinators.
2. Here, using a global dataset of 18 reproductive traits for 1506 species, we investigate the reproductive spectrum of flowering plants to identify how it shapes interactions with pollinators.
3. We show that over 50% of all trait variation is explained by the first two reproductive axes, which represent the negative correlation between flower number and flower size, and the negative correlation between autonomous selfing and floral display size. In addition, these reproductive axes were associated with the identity and number of visits of the distinct pollinator guilds. However, reproductive axes explain a relatively small amount of variance in pollinator interactions highlighting the need to incorporate other factors along with reproductive traits to fully explain large-scale patterns of plant-pollinator interactions.
4. Our study identifies the major reproductive trait correlations in flowering plants and their role in shaping plant-pollinator interactions at a macro-ecological scale. These findings emphasise the importance of considering reproductive traits in the global spectrum of plant form and function, and the need to explore beyond floral morphological traits to broaden our understanding of plant-pollinator interactions.