In the parts of the world that have distinct seasons, the development of plants and animals is often controlled by temperature, humidity or light. These environmental signals cause the animals or plants to know when to start different developmental stages like blossoming, hibernating or breeding. The life cycles of the animal and plants can be influenced differently by environmental signals, which may affect the interaction between different species. For example, imagine a plant that is dependent on a particular insect for pollination. If the plant reacts more strongly to warmer temperatures than the insect does, a warmer climate could cause the plant to bloom before the insect can fly and pollinate it, causing the plant to reproduce less successfully.

Photo: Katarina Fast Ehrlén.

The study shows that since the 1980s, when major climate change began, many species began developing earlier in the year. It also shows that the change in timing between different species that interact has increased during this period. This means that species that act together either develop closer in time in the year or at times further apart. For example, the larvae of an insect that needs certain leaves for food could hatch either earlier or later compared to when the leaves appear.

However, there are no clear indications that the plants and animals are consistently developing in less synchrony than before. The study shows that there is a higher rate of change since more significant climate change began about 35 years ago. However, this cannot be definitively linked to climate change. The next challenge is to improve the ability to predict what changes will occur in the species’ seasonal development and what consequences this will have for different species.

- In order to get a better picture of how changes in the environment such as a warmer climate affect the timing between species, we need to understand what environmental factors influence the species’ seasonal development and how this differs between species, says Johan Ehrlén, professor at the Department of Ecology and Plant Sciences, Stockholm University, and one of the authors of the study.

Kjell Bolmgren, researcher at the Swedish University of Agricultural Sciences and at Stockholm University, is another author of the study. He also coordinates citizen science in the “Nature Calendar” project.

- I find it particularly exciting that the public can contribute with observations of flowers, insects, birds and other animals. Researchers can predict future effects of climate change through experiments, but we need to test these predictions by noting what really happens in nature. And here, the public can help by reporting observations from their own region.

The study is based on 27 different studies from four continents on changes in the seasonal appearance of interacting species from 1951 to 2013, both on land and in the ocean.
 
The study "Global shifts in the phenological sync of species interactions over recent decades" is published in the American Academy of Sciences journal PNAS.