Predicted biodiversity loss from disappearing nature is greater when species dispersal is taken into account

If nature must disappear, sacrificing many small natural areas is more damaging to plant diversity than losing fewer larger ones. This is suggested by a new model study by Utrecht University ecologists Monique de Jager and Edwin Pos, published yesterday in the journal Ecosphere. The study shows that more realistic mathematical models, which account for differences in how plant species disperse, predict a greater loss of plant species following habitat loss than earlier models that ignored these differences.

“Actually, we do not need less nature, we need more nature,” says De Jager. “But if the loss of nature is unavoidable, is it better to fragment what remains or to keep it clustered? This question has long been debated and examined in numerous modeling studies. Some conclude that fragmentation is preferable, others that clustering is better, and some suggest that it makes no difference at all.”

The existing studies are difficult to compare because they focus on different spatial scales, ranging from local to global. “These models also did not account for the different ways plants disperse,” says De Jager. “Some species can spread their seeds over long distances, while others disperse more locally. If you leave these differences out of a model, you miss a large part of reality.”

Competition between dispersal strategies

That is why De Jager and Pos set out to investigate what happens when this variation in dispersal is taken into account. They also examined the effects of habitat loss on biodiversity at different spatial scales, from entire landscapes down to individual plant communities.

When differences in dispersal among plant species were included in the mathematical model, competition emerged between plants with different dispersal strategies. “In a contiguous landscape, plants that spread their seeds over long distances perform well. But once the landscape becomes fragmented, plants that spread their seeds more locally gain more opportunities.”

We do not need less nature, we need more nature.

De Jager explains: “Imagine a highly fragmented landscape. Many of the seeds of plants that disperse over long distances end up in areas between suitable habitats. Places where they cannot grow. Plants that disperse their seeds nearby stay within suitable habitat and lose fewer seeds. As a result, they are the ones that remain.”

To cluster or to fragment

This competition ultimately leads to a greater loss of plant species, regardless of whether the remaining habitat is fragmented or clustered. However, the model shows that when the original habitat becomes highly fragmented, fewer plant species persist in the long term. When the remaining areas are more clustered, overall species loss is lower.

When the remaining nature consists of small, widely separated patches, plants are no longer able to spread their seeds from one area to the next. As a result, within these small areas, species that are already common are likely to become dominant, while rarer species disappear. In contrast, when the remaining habitat forms larger, contiguous areas, seeds can continue to spread within these clusters, reducing the likelihood of local dominance or extinction. This helps preserve a greater diversity of plant species.

The next step I am working on is understanding how we can structure natural areas in ways that allow biodiversity to recover as effectively as possible.

The researchers found that it is useful to examine biodiversity loss at multiple spatial scales. “At the level of the entire landscape, the decline of a particular plant species may not seem severe,” says De Jager. “But when you zoom in, you can see that the species is disappearing locally.”

Natural gems

Although clustering remaining nature appears to be the better option when nature is lost, this does not mean that existing small, fragmented natural areas are not worth protecting. De Jager, together with Utrecht biodiversity professor Merel Soons and others, emphasized this in a background article published in NRC in 2024. “Scattered pieces of nature are still better than no nature at all,” De Jager says in the article.

The next step: nature restoration

According to De Jager, the modeling study shows that policies aimed at protecting or restoring biodiversity must take into account how far plants and animals can disperse. De Jager herself will now focus her work on questions related to nature restoration. “Of course, we already know that habitat loss is bad for biodiversity,” she says. “The next step I am working on is understanding how we can structure natural areas in ways that allow biodiversity to recover as effectively as possible.”