Explained: Why survival of plants depends on saving mammals, birds

While the importance of plants and trees in the survival of human race is known, the role played by animals in helping these trees adapt to climate change is not well documented.

A new study, however, suggests that plants have a 60% less chance of survival in the years to come because of rapid fall in the number of birds and mammals.

Plant diversity and animal survival

For eons, birds and mammals have played an important role in seed dispersal (a type of pollination) for plants, which is return provide food to the animals. The mutually beneficial relationship has been in existence, and mostly intact, since eternity.

Now that climate change is resulting in drastic changes in landforms due to altered rainfall patterns, plants feel a stronger need to ‘migrate’ to be able to survive extreme droughts and rainfall. Generally, mammals and birds are capable of dispersing seeds to faraway places, mainly through their droppings or excreta. The seeds of fruits they consume pass through their digestive systems, come out undigested with dung and germinate when conditions are appropriate.

Evan Fricke, the lead author of the report, “Living Planet Report 2020”, and an ecologist at Rice University, US, told Down To Earth: “While adult plants that are rooted down can’t migrate, their seeds can. It is pertinent to note that more than 50% of all plant species on earth depend on animals for spreading their seeds far and wide.”

The report adds that the number of mammals, birds, fish, plants and insects has gone down by about 70 per cent between 1970 and 2016. With less animals, and lesser biodiversity in animals, fewer seeds will move to newer lands. Thus, researchers fear plants may lose their ability to migrate to newer and more suitable conditions.

Use of artificial intelligence

The researchers used artificial intelligence and computer modelling to understand the seed dispersal habits of all species because we clearly do not have adequate data to know the ability of different animals to either destroy or propagate seeds. The scientists then employed computer models to compare seed dispersal in the real world against a simulated world with no extinctions and range shrinkage of birds and mammals. The researchers found that that the seed dispersal capacity of species has come down significantly with 60 per cent fewer seeds travelling far enough to keep pace with climate change.

Also read: To stop species annihilation, protect forests, adopt regenerative agriculture

The effects were more severe in temperate regions across Americas, Europe and Australia, scientists said, adding that this could be because, in the past, animals and birds, that dispersed seeds to far away lands, may have disappeared over the years.

Tropical regions still have a higher ability to propagate seeds because most of the large seed dispersers still exist in these regions, said Fricke. “If endangered species go extinct, tropical regions in South America, Africa and Southeast Asia too would be most affected,” Fricke added.

Impact on India

India has a rich biodiversity in plants and animals. It is home to over 45,000 species of plants and 91,000 species of animals. Over the last 50 years, the country has lost 12 per cent of its wild mammals, 19 per cent amphibians and 3 per cent birds, Sejal Worah, programme director of World Wide Fund for Nature, India, said while launching the Living Planet Report 2020.

Worah pointed out that decline in number of elephants and bats (good seed dispersers) in north India is affecting plant diversity. Land fragmentation and habitat degradation are major challenges to effective seed dispersal.

Since India has small forests, it is quite evident that birds drop off seeds on rooftops. “Livestock grazing in forest areas too affects seed dispersal. Invasion is another major issue,” Worah said.