Pollination relationships depend on the climate

Newsroom

A major international study has mapped the degree of mutual dependence between flowering plants and their pollinators. This research was led by Charles University in Prague (CUNI) and the Centre for Biology of the Czech Academy of Sciences (BC CAS), with the participation of a large group of researchers from the Institute for Global Change Research at Rey Juan Carlos University (IICG-URJC). The results of this study have been published in the journal Nature Ecology & Evolution and demonstrate that climate is the main factor explaining these patterns. This finding challenges the classical idea that pollination becomes more specialized as we move closer to the tropics.

Much of the plant world depends on animals that carry pollen from one flower to another. Pollination allows plants to reproduce, maintain their genetic diversity, and produce fruits and seeds that serve as food for countless animals. In turn, flowers provide nectar and pollen that sustain an astonishing variety of pollinators. Although bees are the most well-known, flies, beetles, butterflies, moths, wasps, and even birds and lizards also play this role. Even the human food supply depends on these associations, especially in the case of many crops such as fruits, vegetables, nuts, and oilseeds.

Many plants maintain specialized relationships with specific pollinators, while others are visited by a wide variety of generalist insects. Numerous ecologists have hypothesized that highly specialized plant-pollinator relationships are more frequent in tropical regions due to the greater number of plant and animal species interacting there. However, this assumption of a latitudinal gradient of specialization had been scarcely tested due to a lack of adequate data.

“Specialization can be understood as an evolutionary arrangement. A very close match between plant and pollinator can make feeding and pollination very efficient, but it also increases mutual dependence. If one of the partners disappears or becomes active at a different time, a specialist species has fewer alternatives,” explains the study’s lead author, Sailee Sakhalkar, who recently completed her PhD at CUNI.

To determine whether specialized associations are indeed more common in the tropics, researchers compiled 3.415 plant-pollinator interaction networks from 162 studies. The dataset included more than 110.000 interactions among 5.343 pollinator species and 6.126 plant species, spanning all major terrestrial biomes, from tropical rainforests and savannas to Mediterranean scrubland, temperate forests, grasslands, and subarctic tundras. The study brought together 142 researchers from 32 countries and six continents, reflecting years of fieldwork conducted worldwide.

“No single team could study pollination on this scale. By combining the work of research teams from around the world, we were finally able to observe both the global view and the enormous diversity that exists within it,” says Sakhalkar.

The need for collective work has also been highlighted by Marcos Méndez, researcher at IICG-URJC and professor at URJC, who points out that "the study and characterization of plant-pollinator networks require intense fieldwork in which teamwork is critical, even more so when studying networks in mountain environments."

In addition, José María Iriondo, also a researcher at IICG-URJC and professor in the Department of Biology at URJC, emphasizes that “two research groups from IICG-URJC have contributed data on plant-pollinator networks in Picos de Europa, Sierra Nevada and the Sierra de Guadarrama.”

The most surprising finding was that highly specialized ecological relationships were not more prevalent in the tropics. Although specialization often reached its highest levels near the northern boundary between tropical and subtropical regions, each group of plants and pollinators exhibited its own distinct patterns. Furthermore, the researchers discovered that temperature and rainfall better explained global patterns of specialization than latitude, and that their effects varied considerably among different pollinator groups.

Response of plants and pollinators to global change

These findings are important for understanding how plants and animals will respond to a changing climate, something that will likely also affect agricultural production, especially in crops that depend on specialized relationships with specific pollinators. “We tend to represent the geographic patterns of pollination as lines running from the poles to the equator, but plants and pollinators don’t experience latitude itself. What they experience is heat, cold, rain, and seasonal changes, each in its own way,” says Robert Tropek, head of the Insect Community Ecology Research Group, who co-led the study at CUNI and BC CAS.

Rising temperatures and altered rainfall patterns can modify species distribution, plant flowering times, and pollinator activity periods. As a result, they can redraw both the map and the timing of plant-pollinator encounters.