Have you ever wondered how an ecosystem functions? Why do there exist so many mosquitoes and so few tigers? What makes the numbers of diverse species? Now scientists have figured out mathematical models of food webs, noting who eats whom and how much each one eats.

Drawing upon the models, scientists have discovered some key principles operating in food webs. Most food webs, for instance, consist of many weak links rather than a few strong ones. When a predator (掠食动物) always eats huge numbers of a single prey (猎物), the two species are strongly linked; when a predator lives on various species, they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species, it can survive the extinction of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare, the switch allows the original prey to recover. The weak links may thus keep species from driving on another to extinction.

Mathematical models have also revealed that food webs may be unstable, where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s, scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species — including species they did not directly attack.

And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean, we fished for predators such as cod on an industrial scale, while on land, we killed off large predators such as wolves. These actions have greatly affected the ecological balance.

Scientists have built an early-warning system based on mathematical models. Ideally, the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key, scientists say because once ecosystems pass their tipping point (临界点), it is remarkably difficult for them to return.

Nothing is more American than blue jeans. The blue denim pants(牛仔裤) were invented in 1871 and were initially made for miners and cowboys but became a popular fashion among youth in the 1950s and 1960s. Denim soon became accepted by most people, making jean pants, jackets, skirts, and more a big part of western culture.

Now, Wrangler which has been making jeans since 1947, is greening the industry by dyeing denim with indigo—the deep blue color used for jeans-foam(泡沫), instead of the traditional way of using vats of Indigo liquid dye.

While indigo is a natural compound and has been used to dye cloth for centuries, most of the indigo dyes used today are manmade, and dyeing thread for the production of blue jeans is very wasteful. The thread has to be pulled through multiple dye boxes filled with around 2,000 liters of liquid dye and water, and the process has to be repeated several times for the dye to hold according to Fast Company.

The new eco-friendly foam dyeing method was developed at Texas Tech and uses over 99 percent less water than the traditional method. In 2017, Wrangler, the Walmart Foundation, and Lee, another blue jeans brand• invested in new technology to make the industry more sustainable.

In the new “Indigo good” methods the process saves more than just water; it is expected to use 60 percent less energy and produces 60 percent less waste.

“While we have been able to reduce 3 billion liters of water in product finishing during the past 10 years, we know that more needs to be done across the entire supply chain.” Wrangler president Tom Waldron told Fashion Network. “Foam technology reduces water consumption and pollution further upstream.”

Australian scientists have successfully tested a new method for freezing and storing coral larvae(珊瑚幼虫), which they say could eventually help restore the wild coral reefs(珊瑚礁) threatened by climate change. They are struggling to protect coral reefs as rising ocean tem peratures damage ecosystems.The Great Barrier Reef has suffered four events of becoming white in the last seven years including the first one during a La Nina phenomenon, which typi-cally brings cooler temperatures.

Frozen coral can be stored and later reintroduced to the wild, but the current process requires some modern equipment including lasers(激光). The scientists say a new lightweight   “cryomesh(冷冻网)” can be produced cheaply and better protect coral. In a December lab tri- al,the world’s first with Great Barrier Reef coral, they used the “cryomesh” to freeze coral larvae at the Australian Institute of Marine Sciences(AIMS). “If we can protect the coral, we’ll have tools for the future to really help restore the reefs, and this technology for coral reefs in the future is a real game-changer,” said Mary Hagedorn, Senior Research Scientist at AIMS.

The “cryomesh” was previously tested on smaller and larger kinds of Hawaiian corals. Some trials on the larger kinds failed. But then other trials are continuing with larger varieties of Great Barrier Reef coral. The trials involved scientists from AIMS, the Smithsonian National Zoo and Conservation Biology Institute,the Great Barrier Reef foundation and the Taronga Conservation Society Australia as part of the Reef Restoration and Adaptation Program.

The technology,which will help store coral larvae at - 196 ℃, was invented by a team from the University of Minnesota’s College of Science and Engineering. It was first tested on corals by PhD student Nikolas Zuchowicz. “This new technology that we’ve got will allow us to do that, and it can actually help to support the growing and restoration of wildlife in water,” said Jonathan Daly of the Taronga Conservation Society Australia.