The tiny, diligent gardeners of the Amazon

The gardeners described here are not concerned with trimmed topiaries or manicured lawns—though, like designers of landscape gardens, these workers are exceptionally picky. And they have to be if they are going to survive. That is, ants such as Myrmelachista schumanni and Camponotus femoratus of South America depend on certain plants for shelter, and in return, they offer these plants nutrients and protection from predators. As a result, they have developed a mutualistic relationship that has led to an incredible resilience for both species. For example, the ant M. schumanni has kept the plant Duroia hirsute alive in one area of the Amazon, known as a devil’s garden to locals, for more than 800 years. This particular type of ant-plant dependency is plentiful in the Amazon and it creates eerie patches of monoculture gardens amidst the rest of the lush, diverse rainforest. As biologist and photographer Alex Wild described in a recent Myrmecos blog post (complete with photos): I had been following an army ant raid for half an hour through dense tropical forest when the trees unexpectedly parted to reveal a small clearing. Sun broke through the canopy and fell on a low tangle of furry plants. It was a monoculture, looking as though planted by a reclusive sort of gardener. I had stumbled into a Devil’s Garden. Local lore holds that malevolent forest spirits create these unnatural crop circles, but the truth is just as weird. Devil’s Gardens are [cultivated] by ants. The plant species that compose these gardens—mostly in the genera Tococa, Clidemia, and Duroia—sport swollen structures filled by the nests of tiny Myrmelachista ants no more than 3 millimeters long. The ants are meticulous about caring for their hosts, removing [pesky] herbivores and injecting formic acid into the saplings of competing plants. Another ant species, C. femoratus, gathers the seeds of particular plants to cultivate in its nests, called ant gardens, and made of a mixture of animal feces, digested plants and other organic material. These nests are attached to vines, the sides of trees and even high up in the tree canopy. As Elsa Youngsteadt explained in the podcast Curiouser and Curiouser, ants followed chemical signals given off by seeds of certain plants, collected the seeds, carried them back and embedded them in the walls of the nests. The plants benefitted from the fertilizer mixed in the nest, and in turn, the roots helped to add structure to the ant garden. In addition, the leaves protected it from heavy rains that would otherwise have caused the material to disintegrate. “There are about ten plant species that are in ant gardens regularly that you don’t...

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Can birds affect tree growth?

Growing conditions, such as water and nutrient supply, are the major determinates of tree growth, but insectivorous birds can also play an important role, say scientists in a study published in the January issue of Ecology. Under the right conditions, birds contribute to whole tree growth by preying on herbaceous arthropods, such as leafhoppers, caterpillars and grasshoppers…

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Master-of-one caterpillars dodge bird predation

Insect herbivore species often specialize on the host plants that they eat, evolving adaptations to use a plant’s unique set of resources.  But like any time you throw all your eggs in one basket, these caterpillars put themselves at risk. Michael Singer of Wesleyan University gave a talk today at the ESA Annual Meeting that evaluated these tradeoffs in caterpillars. “A lot of evolutionary ecologists have pondered the advantages of being a specialist, and there are presumably tradeoffs,” he said. “Specialists have a smaller resource base, but they might be better adapted to their niche.” Singer and his colleagues wondered if there could be other advantages to specialization than better utilization of host plants as food. Specialists might also be more adept than generalists at, for example, using their host plants for defense or refuge from predation, specifically by birds. The team tested this idea by excluding birds from experimental plots in a temperate forest in Connecticut and surveying the density of generalist and specialist caterpillar species inside and outside the exclosures. In the exclosures, his team observed a surge in generalist density compared to natural areas. The number of specialists, however, only increased slightly. The conclusion? Bird predators were preferentially targeting generalists. The difference is likely due to the specialists’ ability to take better advantage of their host plants, says Singer. Specialists can use chemicals from their host plant’s tissue to make themselves toxic.  While Singer’s caterpillars don’t do this, they might be more adept at camouflaging themselves by finding the best places to hide or to blend in. Singer says that the interactions among the three trophic levels – plants, herbivores and predators – are the key to understanding the species’ ecology and evolution. “Food webs are complex, and that complexity is fundamental to understanding ecological specialization and diversity in natural ecosystems,” he...

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