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

If we cook these tiny wasps, we put the heat on hundreds of other species

Poll2

From the wings of tiny creatures hang the fates of hundreds of bird and mammal species, and perhaps even entire rainforests. They are fig wasps and they play a disproportionate role in the grand drama of life on Earth. They shape our own story too because of this. But new research warns that these insects could be “extremely vulnerable” to global warming.

This matters because each of the 750+ species of fig tree (Ficus species) relies utterly on particular species of fig wasp to pollinate its flowers. Without the fig wasps there would be no fig seeds to create the next generation of trees, and there would be no ripe figs for animals to eat.

In the case of any other group of trees this would not be such a big deal, but figs are special. Their pollinator wasps only live for about a day and each wasp species can only lay its eggs inside the flowers of its specific fig partner. So, to keep their pollinator species alive, each fig species needs to produce flowers and figs year-round. This means a year-round supply of food for birds and mammals, and helps to explain why figs feed more creatures than any other trees do (see A job for conservation’s keystone cops).

In the late 1990s, I set out to find out just how many animal species eat figs. The answer is an astounding 1,200-plus species, including ten per cent of all birds and six per cent of all mammals – see Who eats figs? Everybody). That’s the variety of life that stands to suffer in some way if fig-wasps disappear. Now, in a new study in the journal Biology Letters, Nanthinee Jevanandam of the National University of Singapore and colleagues provide a chilling insight into what a warmer world could mean for these wasps.

In a laboratory, they exposed the pollinators of four Ficus species to temperatures between 25°C and 38°C and to a various levels of humidity. The lifespan of all four species fell steadily as the temperature rose. By 36°C, the lifespan of three of the species had fallen to just two hours. In the wild this would give the wasps hardly any time to find a fig of the right species in which to pollinate and lay its eggs. It would hurt both wasp and fig species. This is the Achilles heel of a partnership that has existed for 80 million years. It is here that we might expect to see the relationship break down, with consequences for other species.

This has happened before. In the 1990s, fig-wasps in northern Borneo went locally extinct after a severe drought, and in Florida they disappeared when a hurricane wiped them out. In both cases, fig-wasp populations eventually bounced back — thanks to the fact they can disperse for tens of kilometres in the day or two they live. But a sustained temperature increase — like that which climate scientists predict will be a reality worldwide by the end of the century — is a different matter. As we turn up the global temperature we change the chemistry of life.

I asked Nanthinee whether she thought fig-wasps could adapt to a rise in temperature, either in their physiology or their behaviour — by flying at a cooler time of day for instance. “Fig wasps can produce up to 12 generations in a year in the aseasonal tropics, and so acclimation or genetic adaption is a possibility,” she said. “But more research has to be carried out to ascertain this. As to the possibility flying at different times, it is difficult to predict.”

The wasp species she and her colleagues studied came from distinct branches of the fig-wasp family tree, so they think their results will be relevant to hundreds of other fig-wasp species, the trees they pollinate and the animals that eat their figs. But these little wasps might have surprises in store for us yet. After all, they survived the mass extinction that saw off the dinosaurs, 65 million years ago. They might outlive us too.

Their story is a reminder that we are just new here, and that between our kisses, our fights and our smiles, we tend to stumble about breaking things before we know how they work.

Photo credit:
Valisia malayana fig-wasps at a fig of their host tree Ficus grossularioides (Nanthinee Jevanandam)

Related posts:
The humbling history of the tiny wasps that upset a Jurassic Park narrative.

Reference:
Jevanandam, N., Goh, A.G.R. & Corlett, R. 2013. Climate warming and the potential extinction of fig wasps, the obligate pollinators of figs. Biology Letters 9: X-X.  Published online March 20, 2013 doi: 10.1098/rsbl.2013.0041