The decline in mammals and birds has made it more difficult for many plants to adapt to climate change. These are plants that depend on animals for the dispersal of their seeds. That ecologists conclude in an article which was published on Thursday in Science.
Climate zones are shifting due to global warming. For example, the Netherlands is expected to have the climate of Bordeaux in southern France in thirty years’ time. Plants that are bound to a certain climate zone have to move along. They do this by spreading their seeds. How quickly climate zones are shifting varies per place. “It could be a few meters a year, but it could also be up to a kilometer a year,” or much more, says Jens-Christian Svenning, a professor of ecology at Aarhus University and one of the authors of the publication.
Half of all plant species have their seeds dispersed by animals. The decline of many animal species over the past thousands of years, and their eventual extinction, has affected the ability of many plants to proliferate. In the now published article, the researchers have tried to quantify that effect worldwide. “In a very clever way,” responds Patrick Jansen, associate professor of ecology at Wageningen University, and not involved in the study.
The researchers first combined a number of databases with data on the interaction between seed dispersing animal species and the plants from which they disperse the seed. On that basis, they built (via machine learning) a computer model that predicts which interactions occur between a seed dispersing animal species and its associated plant, and what this means for seed dispersal.
They then calculated how much the capacity of plants to disperse their seed has been affected by the decline and extinction of species of mammals and birds over the past 50,000 years. They conclude that that capacity (an index for the amount of seed that is spread and germinates, and the distance over which seed is spread) has already decreased by 60 percent worldwide. If species of mammals and birds that are now vulnerable continue to decline and become extinct, that capacity will increase by another 15 percentage points.
The researchers write that climate zones are shifting rapidly in Europe and eastern North America, for example. The capacity of plants to keep up with this is actually low, because many large mammals in particular have disappeared in the past.
According to Jansen, the study draws attention to “a deeply underestimated problem.” The researchers did not even include other barriers, such as the fragmentation of nature. “Plant seed can end up a few kilometers away via a bird, but if the seed ends up on a street or a field, it is of no use to the plant.” In addition, nature reserves are often fenced. Larger, seed-dispersing mammals, such as deer, cannot spread seed outside that area.