Scientists reveal yet another reason fig trees are titans of biodiversity

insectivores

Biologist David Mackay got a surprise when he began studying the birds visiting fig trees in his native Australia: While he expected to see plenty of species coming to eat the figs, he didn’t expect the insect eaters to outnumber them two-to-one.

Mackay already knew that figs feed more bird species than any other fruit. His research, published in June, would show that fig trees are disproportionately important for insect-eaters too. It adds to growing evidence that fig trees are titans of biodiversity with important roles to play in conservation.

What makes fig trees so crucial is their ancient relationship with tiny wasps. The trees depend on the wasps to pollinate their flowers, while the wasps can only breed and lay eggs inside their partner’s figs. Thanks to this partnership, figs are available year-round and have been called ‘keystone’ resources for fruit eaters. Mackay’s study is the first to show that fig-wasps emerging from figs before they ripen are also valuable year-round resources for a diverse variety of insect-eating birds.

Altogether, Mackay recorded 55 bird species visiting Ficus rubiginosa fig trees to feed on insects. They included ten species — such as the superb fairy-wren and the shining bronze-cuckoo —whose recent declines in numbers have concerned conservationists. Mackay and his colleagues say fig trees are “very likely” to be similarly important to insect-eating birds throughout tropical, subtropical, and temperate regions globally.

To support this view, Mackay points out that in just his study and two others in localised areas of India and Costa Rica, researchers have already identified more than a hundred insect-eating birds visiting fig trees. “The presence of avian insectivores in figs in these three continents strongly suggests their occurrence in figs is ubiquitous,” he says.

“I can hazard a wild guess that there are at least several hundred species of insectivorous birds that forage in fig trees worldwide,” Mackay told me. “This has important implications for the conservation of insectivores, many of which have suffered and continue to suffer declines in response to habitat loss and fragmentation.”

As Mackay points out, the number of fig-wasps emerging from figs on a single Ficus rubiginosa tree in just a few weeks could approach ten million. He adds that insect-eating bats would also relish fig-wasps, many of which fly at night. His study adds to a growing body of evidence that fig trees are centrepieces of vast food webs that include tens of thousands of species.

“I suspect fig trees could play an important role in conservation of declining insectivores as well as contributing to the conservation of other species in the wider communities they inhabit, including frugivores and the other plants that depend on them for seed dispersal,” Mackay said.

Increasingly, researchers and conservationists are turning to fig trees to boost rainforest regeneration by attracting seed-dispersers. Mackay said that using fig trees could also slow or even reverse declines of insect-eating birds: “If we don’t do these restoration projects with figs then we stand a chance of losing these birds altogether.”

This post was first published by Mongabay.com on 6 July 2018 and is reproduced here under a Creative Commons licence.

Read more about the ecological and cultural importance of fig trees in my book, published in the UK as Ladders to Heaven and in North America as Gods, Wasps and Stranglers.

Reference

Mackay, K.D., Gross, C.L. & Rossetto, M. 2018. Small populations of fig trees offer a keystone food resource and conservation benefits for declining insectivorous birds. Global Ecology and Conservation. Published online on 20 June 2018. https://doi.org/10.1016/j.gecco.2018.e00403

Photo credits

Left to right —  Superb fairy wren (Malurus cyaneus): Patrick_K59 / Wikimedia Commons; Eastern yellow robin (Eopsaltria australis): Graham Winterflood / Wikimedia Commons; Eastern spinebill (Acanthorhynchus tenuirostris): DavidFrancis34 / Wikimedia Commons

Religion + fig trees = a boost for biodiversity

Hanuman-temple-and-fig-tree-Ficus-religiosa-in-Bangalore-Anoop-Negi

A sacred fig tree at a Hindu temple in Bengaluru (Bangalore) – credit Anoop Negi

When Tarsh Thekaekara and Shruti Agarwal spotted a lone fig tree in sea of tea bushes in southern India, they knew it had to be special. The researchers were documenting sacred groves in tea plantations to see if they helped conserve wild species. They learned that the fig tree was all that remained of a grove consecrated by local Paniya people who, for generations, had convinced tea estate managers not to fell the tree.

As in many other countries, fig trees have been sacred species in India for thousands of years. Wherever they grow, figs are also key resources for wildlife. Thanks to their curious biology, they feed more bird and mammal species globally than any other fruit and so sustain the seed dispersers of thousands of other plant species. In India, and in many other countries, fig trees could play key roles in protecting biodiversity and regenerating lost forests — but policies to protect these trees are rare.

Writing in the Indian Express, Thekaekara and Agarwal tell how they returned to the lone fig tree and set up camera traps to find out what wildlife visited. They soon recorded monkeys, many bird species, civets and a species of flying squirrel. “As the figs ripened and fell to the ground, the place really came alive,” they write. “Porcupine, wild boar, barking deer, sambhar deer, bear and, even, an elephant! A leopard also walked by, probably feeling like she was missing the party, and to try to dine on a couple of fig-eaters!”

Thekaekara and Agarwal highlight the important ecological role the tree plays in a landscape dominated by tea bushes. “The irony is that even with this knowledge, there is no official protection for the tree,” they write, “and it could legally be cut if the correct permissions are sought.” They note that, across their study area, many sacred groves had been reduced to just a solitary tree — most commonly a fig tree.

In India’s urban areas too, the loss of wildlife-friendly trees is elevating the importance of surviving fig trees. In a new study, Harini Nagendra and colleagues documented 5504 trees at religious sites— 62 temples, churches and Hindu, Christian and Muslim cemeteries — in Bengaluru (Bangalore).

Compared with trees in the city’s parks and streets, the trees at religious sites were far more likely to be native species, which offer more to local biodiversity. As in the tea plantation, fig trees (Ficus species) are disproportionately important in urban areas as they feed so many birds and mammals, and at least one fig species was present at 71% of the religious sites the researchers surveyed.

“Fig trees play a critical role in supporting Bangalore’s threatened biodiversity,” says Nagendra. “Bangalore’s tree cover is extremely fragmented, and Ficus trees act as keystone species, improving canopy-to-canopy connectivity and supporting a wide range of species, including birds, butterflies, bees, bats, macaques, and even the endangered slender loris.”

The researchers found 286 individuals of just one fig species — the banyan, Ficus benghalensis — at the religious sites, where it was the fourth most common tree species. But in the city’s streets and parks, all species of fig trees were relatively rare. None ranked in the top ten species the researchers counted there. Nagendra and colleagues says the large numbers of Ficus trees in sacred sites “demonstrate a strong potential” for urban conservation.

“Unfortunately, there is no policy to promote the planting or fig trees, or to conserve them,” Nagendra told me. “Many Ficus trees in Bangalore are heritage trees, decades and even centuries old. Yet many are now under threat, their branches pruned, the bases concreted, or are cut down for road expansion projects.”

In fields and cities in India and all across the tropics, fig trees play key roles in sustaining wildlife. The ecological importance of these trees results from their 80-million-year old relationship with their pollinator wasps, and it helps explain why fig trees have become embedded in religions in many countries.

Over millennia, diverse cultures have protected fig trees but few societies today value them in the same way. Yet, with the right policies in place, these trees could help us to address 21st century challenges — from conserving biodiversity to restoring forest cover.

Tarsh Thekaekara is a biodiversity conservation researcher with The Shola Trust. Shruti Agarwal worked with The Shola Trust before joining the Centre for Science and Environment in Delhi. Harini Nagendra is a professor of sustainability at Azim Premji University, Bengaluru.

Related posts

The majesty and mystery of India’s sacred banyan trees

Why one fig tree in the middle of nowhere has a 24-hour armed guard

Fresh evidence of the power of fig trees to sustain wildlife and restore lost forests

Photo credit

A fig tree (Ficus religiosa) alongside a Hindu temple dedicated to the monkey god Hanuman in Bengaluru (Bangalore) — Anoop Negi (reproduced with permission). See Anoop Negi’s website for more images.

References

Jaganmohan, M. et al. 2018. Biodiversity in sacred urban spaces of Bengaluru, India. Urban Forestry & Urban Greening 32: 64-70. [Read online]

Thekaekara, T. & Agarwal, S. 2018. The Ficus in the Tea: The fight for the lonely atti maram (fig tree). The Indian Express. 22 April 2018. [Read online]

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