Ants 'sow the seeds' of the Cape

Fynbos shrubland in South Africa's Western Cape The fire-prone fynbos shrubland in South Africa's Western Cape is a biodiversity hotspot

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Ants helped create a biodiversity hotspot in the Cape region of South Africa, scientists believe.

Researchers have highlighted two recent studies that suggest seeds spread by ants may be an important driver of plant diversity in the Cape.

The two studies used genetic data from areas with and without seed-dispersing ants to assess their contribution to diversity.

The scientists said the evidence showed a "great role for tiny players".

Professor Jonathan Majer and Professor Ladislav Mucina from Curtin University in Australia wrote their report in response to a scholarly article calling for the causes of diversification in the Cape region to be identified.

Need for seed

Waxwing holding berry

"It's one of the world's global biodiversity hotspots," Prof Majer, an expert in insect conservation, told BBC Nature.

The area is climatically similar to the south west of Western Australia. Both are exposed to the same wind currents, rainfall patterns and similar latitude.

But the biodiversity of each region has puzzled scientists.

Prof Majer is the co-author of two previous studies on how certain ant species disperse seeds, a process known as myrmecochory.

Some plants exploit this by producing seeds with an elaiosome, a fleshy appendage that attracts ants.

"Ants pick up the seed often by grabbing the elaiosome, take it back to their nest and feed on it," said Prof Majer.

"They often discard the remaining seed, which is not killed, either in the nest or in the soil around the nest...and this dispersal is known as myrmecochory."

That takes seeds away from the parent plants, ensuring they don't compete, and shields them from predators and scrubland fire.

"Sometimes the ant nest is richer in nutrients because of faecal material and waste so it may end up in a nutrient enriched area, which is better for the process of germination."

An Australian Iridomyrmex ant is attracted to a Guinea flower seed An Australian Iridomyrmex ant is attracted to a Guinea flower seed's elaiosome

This process is an adaptation to nutrient-poor soil.

Because it is particularly widespread in south west Australia and the cape of South Africa, it may also be a key driver of biodiversity in each region, Prof Majer said.

"Ants spread seeds over short dispersal distances [causing] low gene flow. Because the genes don't flow you're likely to get higher speciation."

"Secondly because the seed has been buried, put into a microsite in the ground, it has a higher population fitness and a lower extinction rate."

Prof Majer has tested the idea that diversification is fastest when large numbers of specialist seed-dispersing ants are around, by comparing the diversity of closely related species or "clades" across the world.

"Basically we found there were twice as many species in the ant-dispersed clade as there were in the non-ant dispersed clades," he said.

The results of the study suggest that myrmecochory may have driven a doubling of plant diversification.

In another study, Prof Majer worked with colleagues to survey the evolution of seed dispersal by ants around the world.

"You can go back through the fossil record and ants increased in abundance about 50-60 million years ago."

"That is when mymecochory started to pop up in great quantities. It seems to have been mirroring the evolution of ant abundance," he said.

That study found that a particularly large proportion of myrmecochorous lineages were Australian or South African, backing the idea that ants may be driving the mysterious biodiversity hotspots in the South African Cape region.

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