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Tages- und jahreszeitliche Dynamik ökologischer Interaktionsnetzwerke und ihre funktionelle Bedeutung

Fachliche Zuordnung Ökologie und Biodiversität der Tiere und Ökosysteme, Organismische Interaktionen
Ökologie und Biodiversität der Pflanzen und Ökosysteme
Förderung Förderung von 2016 bis 2021
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 322833943
 
Erstellungsjahr 2021

Zusammenfassung der Projektergebnisse

This project has focused on how interactions between plants and pollinators change over time, within a single day as well as over longer time spans. We used a multitude of approaches to address this topic. We found that the most pronounced changes happen over the regular progress of seasons within a year, but that changes are also important on smaller (different times of a day) and larger (variation among years) timescales. When studying networks of interactions among multiple species of plants and animals, the timescale is important to consider: networks exhibit different structures, depending on whether they are based on a single day of observations, a month, or even multiple years. For example, species in long-time networks appear more generalized. There are, at least, three reasons: more observation time means more of the existing interactions are detected, longer time means species encounter different partners at different times, and over time, species tend to interact with different species out of those available. An important part of this project was to develop and evaluate new (open source) software tools to analyze ecological network datasets in order to better understand how they change with time. These tools include a method to predict new interactions based on species traits and abundances, as well as a method to understand how much of the difference between two networks is due to species behaving differently in different situations. Surprisingly, despite good performance with simulated data, adding traits and phylogenetics provided little additional information over just using abundance for the test dataset of plant-hummingbird interactions. As for the other tool, we were surprised to find how strongly a published method for quantifying the similarity between networks underestimated the influence of differences in species composition. Across all studies of this project, we repeatedly found that a key determinant of how the networks change over time is the availability of interaction partners in time. Species are not always present, but only have restricted flowering or flight periods. Also, sometimes a species is abundant and at other times it is scarcely available. These changes in availability are often the most important driver of temporal network dynamics. For example, we performed a field experiment in which we made flowers of a certain group (Cichorieae), which normally closes its flowers around noon, available in the afternoon, to find that if these flowers are available at unusual times they are nevertheless visited at normal rates by both specialist and generalist pollinators. Although this plant group is very common in Central Europe and can cause very strong changes of plant-pollinator networks within a day, we found it to be largely irrelevant for a meadow dataset that we collected in this study. When comparing the importance of changes within a day to changes within year, we surprisingly found that although species differed in timing on both timescales, only seasonal timing appeared to be important for the structure of plant-pollinator networks as measured by typical statistical indicators. Despite a superficial description of the plant group Cichorieae as having flowers open in the morning, we found large variation in opening and closing times among species in this group. Accordingly, wild bees switched from visiting one species of the group in one hour to another species the next hour. As Cichorieae flowers are important for many wild bees, having multiple species of this group flower together may be beneficial for both bees and plants. This project was basic science and an important aim was to improve the study of species interaction networks by including a temporal perspective. As such, immediate applications outside the realm of science are not expected. That being said, given the enormous attention that pollinators currently receive, the research of this project could certainly be used to improve concepts for sustainable agriculture and insect conservation. The continuity of floral resources through time, both within the day and within the year, could be considered when trying to support pollinators by land management, e.g. when designing seed mixtures for wild flower strips. Likewise, for reliable crop pollination a high diversity of wild pollinators that occur at different times would be best.

Projektbezogene Publikationen (Auswahl)

 
 

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