“From dawn’s first light to twilight’s embrace, every hour tells a new story about plants and pollinators.”

Imagine nature as a stage for a dance, where life unfolds in graceful and harmonious movements. In this spectacle, ecological interactions are the dancers, dancing to the rhythm of sunlight, temperature changes, and the nuances of the environment. They are like the invisible choreography that maintains life on Earth in perfect balance, a dance that never stops and never repeats in the same way. 

However, this ecological dance is not just a spectacle to admire; it is the essential foundation that sustains all forms of life on our planet. Every step, every movement, every interaction between species is a fundamental piece of the biodiversity puzzle and the stability of ecosystems. Therefore, understanding this ever-changing choreography is essential for the conservation and understanding of how life functions on Earth. 

Particularly, when we look at the interactions between plants and pollinators, we can see how synchronised this ‘dance’ is. In plant-pollinator interactions, plant species synchronise precisely the opening of flowers with the greatest insect activity to increase their chances of interacting. This process is better known as ‘phenological overlap’ and is one of the main drivers of plant-pollinator interactions.  However, most studies evaluating the spatio-temporal dynamics of interactions come from studies carried out on larger temporal scales, such as months, climatic seasons or years. Still, there is still much to explore regarding the details of these interactions, especially when understanding what happens in a single day. 

With this in mind, Yuta Nagano conducted a study to understand how plants and pollinators respond to changes in biotic and abiotic contexts throughout the day. Specifically, the author aimed to comprehend how plants and pollinators responded to changes in light, temperature, and other environmental factors. Additionally, he analysed the patterns of flower opening and closing and how pollinators adjust their behaviour according to these rhythms.  

To do this, the author conducted field observations in semi-natural meadows within an agricultural landscape in Japan for six days. These observations were conducted at regular two-hour intervals, starting at 8:00 in the morning and continuing until 4:00 in the afternoon. 

One of the key findings of this study is that the diversity of pollinators and the number of interactions varied as the hours passed. In the morning, the richness of insects and interactions was low, but as the temperature increased throughout the day, insects became more active, resulting in an increase in both insect richness and the number of interactions. During the afternoon, as the day progressed and temperatures fell, insect activity decreased, leading to a decline in both insect richness and the number of interactions. 

Interestingly, the author discovered that different groups of insects responded differently to these changes throughout the day. Bees, flies, and butterflies, for example, followed a bell-shaped response pattern, where the diversity and the number of interactions increased, peaked, and then decreased again during the day. However, moths exhibited a ‘U-shaped’ response, with a decrease in insect diversity and the number of interactions in the morning, reaching a minimum and then increasing again in the afternoon.

Figure 1: Diagram illustrating variations in species richness and interactions throughout the day. A) Bell-shaped response pattern, where species richness and number of interactions peak at midday. B) ‘U’-shaped response, where species richness and number of interactions is lower at midday. I corresponds to the time period between 8:00 and 10:00, II to the time period between 10:00 and 14:00, and III to the time period between 14:00 and 16:00. Image: Victor H.D. Silva

The most surprising aspect of this discovery is how the timing of these interactions is closely related to the moment when different plant species offer their floral resources, such as nectar and pollen. Most plants opened their flowers and offered their resources during specific parts of the day, also displaying a bell-shaped response pattern. However, Adenophora triphylla var. japonica exhibited a unique ‘U’-shaped response, as this species reserves its nectar for the night when its pollinators, in this case, some species of moths, are most active. This resource availability and dependency on moths may favour a greater diversity of insects during the night and, in turn, promote a greater diversity of insects and interactions at dawn and dusk but not throughout the day. This complex relationship between insects and plants highlights how nature works in concert and how timing is an important factor in the ecology of both plants and insects. 

Figure 2: Plant species with different response patterns. A) Picris hieracioides subsp. japonica, wich has a bell-shaped response pattern (Photo by Qwert1234, Wikicommons). B) Adenophora triphylla var. japonica, wich has ‘U’-shaped response (Photo by Qwert1234, Wikicommons). 

Another intriguing discovery made by the author was that throughout the day, the importance of the key factors affecting variations in interactions between insects and plants varied significantly. In the morning, it was observed that the interaction rewiring played a more prominent role. In other words, during the morning, insects changed the plants with they interacted more frequently.  

This likely occurs due to changes in the activity peaks of species. Most pollinators tend to be more active during the early morning hours. At the same time, in the morning, most plants open their petals, release scents, and produce nectar to attract pollinators. This increased species activity increases the likelihood of two species interacting and expands the range of interaction options. This increase in interactions, in turn, favours changes in the patterns of interactions between insects and plants. 

However, during the afternoon, species turnover – the change of species in interaction, either by gaining or losing different species– emerged as the most crucial factor for the dynamics of interactions. Surprisingly, at noon, these two components balanced out and became equally fundamental to interaction dynamics. 

On the other hand, during the afternoon, the peak activity of insects decreases, and some plants may start to close their flowers or reduce their nectar production to conserve water and energy, resulting in a decrease in the number of species and interactions. At this time, these species are replaced by species that are more active during the late afternoon and evening, increasing the importance of species turnover for interactions. 

Overall, the author’s conclusions emphasize how dynamic plant-pollinator interactions are. Furthermore, the results suggest that the drivers behind changes in interactions between plants and pollinators can vary at different time scales, challenging our understanding of ecological interactions. These findings provide valuable insights into the delicate balance of nature, with potential implications for biodiversity conservation and ecosystem sustainability. 

READ THE ARTICLE: Nagano, Y. (2023). Changes in pollinators’ flower visits and activities potentially drive a diurnal turnover of plant‐pollinator interactions. Ecological Entomology. https://doi.org/10.1111/een.13262 

Portuguese translation by Victor H.D. Silva.

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