Plant-Pollinator Networks

 

My primary research is the analysis of plant-pollinator systems and the interplay between their structure and dynamics (including stability) under different kinds of anthropogenic perturbations. In this area, I follow a theoretical approach which relies on statistical analysis of the structures of empirical plant-pollinator networks. This approach uses the architecture of interactions (who pollinates whom) to parameterize mathematical models which describe the population dynamics of each species of the network.

Structure and stability of the networks

 

Networks of mutualistic interactions between plants and pollinating animals are one of the most important forces for generating and maintaining terrestrial biodiversity. These networks, however, are threatened by global pollinator declines and local extinctions of plant species and biotic invasions, making it critically important to understand the mechanisms that drive network stability. We aim to understand and predict the ecological and evolutionary mechanisms behind the structure and dynamics of plant-pollinator networks

Our TedEd lesson on the structure and dynamics of Plant-pollinator networks
Adaptive foraging (AF)

 

The widely observed preference of consumers for more-available resources, adaptive foraging (AF), has been documented to stabilize the dynamics of complex food webs (Valdovinos et al. 2010). In Valdovinos et al. (2013), we found that the incorporation of AF into the dynamics of the pollination networks increased the persistence and diversity of its constituent species, and reduced secondary extinctions of both plants and animals. These findings were best explained by the following underlying processes: 1) AF increased the amount of floral resources extracted by specialist pollinators, and 2) AF raised the visitation rates received by specialist plants.

Valdovinos et al. (2013) Population dynamics model

 

Our model includes the trophic dimension of mutualistic interactions by explicitly modeling the dynamics of the resources including floral rewards. In this way we could incorporate the next biologically important process within the analysis of mutualistic networks: 1) the production and animal consumption rates of plant rewards, 2) the competition and/or facilitation among plants via shared pollen/seed animal vectors, 3) the competition among animals for plant rewards, and 4) the animals’ allocation of foraging efforts. These processes were neglected by the traditional models of mutualistic networks, which simply represent mutualistic relationships as phenomenological positive effects among species. Our research shows that these four processes affect the interplay of network structure and dynamics which some studies have documented over the last years, such as the effects of nestedness, connectance and richness on the species persistence of those networks.

Here, we assess how adaptive foraging (AF) interacts with network architecture to determine the stability of plant–pollinator networks. We find that AF reverses negative effects of nestedness and positive effects of connectance on the stability of the networks by partitioning the niches among species within guilds. This behavior enables generalist pollinators to preferentially forage on the most specialised of their plant partners which increases the pollination services to specialist plants and cedes the resources of generalist plants to specialist pollinators. We corroborate these behavioural preferences with intensive field observations of bee foraging. Our results show that incorporating key organismal behaviors with well-known biological mechanisms such as consumer-resource interactions into the analysis of ecological networks may greatly improve our understanding of complex ecosystems.
Niche partitioning due to adaptive foraging reverses effects of nestedness and connectance on pollination network stability
Valdovinos et al. 2016, Ecology Letters

 

Much research debates whether properties of ecological networks such as nestedness and connectance stabilise biological communities while ignoring key behavioural aspects of organisms within these networks.

Species traits and network structure predict the success and impacts of pollinator invasions
Valdovinos et al. 2018, Nature Communications

Species invasions constitute a major and poorly understood threat to plant-pollinator systems.  General theory predicting which factors drive species invasion success and subsequent effects on native ecosystems is particularly lacking. We address this problem using a consumer-resource model of adaptive behavior and population dynamics to evaluate the invasion success of alien pollinators into plant-pollinator networks and their impact on native species. 

We introduce pollinator species with different foraging traits into network models with different levels of species richness, connectance and nestedness.  Among 31 factors tested including network and alien properties, we find that aliens with high foraging efficiency are the most successful invaders. Networks exhibiting high alien-native diet overlap, fraction of alien-visited plant species, most-generalist plant connectivity and number of specialist pollinator species are the most impacted by invaders. Our results mimic several disparate observations conducted in the field and potentially elucidate the mechanisms responsible for their variability.
NSF-RAPID: Re-wiring of montane pollination networks under severe drought stress
Brosi & Valdovinos

 

A severe drought is expected in the western Rockies in 2018, after the second lowest snowpack on record the preceding winter. The drought is expected to dramatically alter which species are present in the ecosystems of the Rockies, as well as their relative abundances.

The drought thus presents an unusual opportunity to study how pollination networks (the connections between interacting pollinator and plant species) are affected by disturbances. This is particularly key given that extreme environmental events are expected to become increasingly common and that pollination is critically important for the maintenance of wild plant populations and the productivity and security of many agricultural crops. Specifically, this project is focused on 1) how species in ecosystems can “re-wire” or form new connections to other species after disturbances; 2) how new connections can be predicted even following major disturbance; and 3) the implications of new linkage patterns for understanding system-level responses to disturbance. This work will contribute to better understanding of how networks more generally (including other ecological networks, but also other network types including economic, engineered, and social networks) respond to disturbances, particularly in terms of the formation of new connections.
This project will use existing plant-pollinator network field data from non-drought years (2016 and 2017) to build and test mechanism-focused models of network structure, based on plant and pollinator abundances, competition between pollinators for flowers, and data on plant and pollinator physical traits (such as body size). Model predictions will be compared with field data from the severe drought year (2018) in which it is anticipated that there will be a strong reduction in which species are present (for example, many long-lived plant species may not bloom when drought-stressed) as well as substantial changes in relative abundances of flowers and pollinators. In particular, the project will also assess how well this new network model performs relative to existing alternative models (none of which currently perform well in predicting interactions). The researchers will then use models to assess generally how substantial capacity for re-wiring will affect system-level responses to perturbations.
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Dept. Ecology & Evolutionary Biology (EEB)

Ann Arbor, Michigan

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fsvaldov@umich.edu