Predators and prey
edyong | January 21, 2009If the sound of eating dung all your life doesn't sound that appealing to you, you're not alone. A beetle called Deltochilum valgum shares your distaste, which is quite surprising given that it's a dung beetle.
There are over 5,000 species of dung beetle and almost all of them feed mainly on the droppings of other animals (and more specifically, on the rich supply of bacteria they contain). D.valgum is the black sheep of the family, the only one that has abandoned the manure-based diet of its fellows and taken to hunting live meat for a living.
D.valgum lives in the lowland rainforests of…
edyong | January 13, 2009As a species, our unflinching obsession with size is just as apparent in our dealings with other animals as it is in our personal lives. Fishermen prize the biggest catches and they're are obliged to throw the smallest specimens back in. Hunters also value the biggest kills; they provide the most food and make the flashiest trophies. This fixation isn't just a harmless one - by acting as a size-obsessed super-predator, humans are reshaping the bodies of the species we hunt, at a remarkable pace and to a dramatic degree.
Predators already put a lot of pressure on their prey to evolve new ways…
edyong | December 18, 2008This post is part of a celebration of the 2-year anniversary of open-access journal PLoS ONE.
Gathering in large numbers is usually a good way of protection yourself against predators, and it's no surprise that mass defence is a common strategy in the natural world. But it doesn't always work. There is one hunter that has found a way to use group defence to its advantage. It allows its prey to gather in large numbers and then freezes them in place with a chemical weapon, providing it with a bountiful banquet to eat at its leisure. It's called Dictyostelium caveatum.
D.caveatum is a member of…
edyong | December 10, 2008Pity the small fish snagged by a sea anemone. Blundering into the waving tentacles, the fish is stung by hundreds of tiny harpoons shot out from stinging cells, each one loaded with potent venom. It is paralysed and moved towards the anemone's 'mouth', which lies in the centre of its tentacles and also doubles as its anus. The fish is swallowed and , but its ignominious fate doesn't end there. The anemone's internal cavity (which passes for its stomach) is also lined with thousands of stinging cells so that even after it's been swallowed, the fish continues to be stung.
The sea anemone is a…
edyong | November 29, 2008
As Charles Darwin learned several centuries ago, islands are havens for evolution. Newcomers to these isolated worlds find themselves unshackled from the predators that dogged them on the mainland. They celebrate their freedom by diversifying into a great variety of species. But predators still have ways of tracking them down, and following the footsteps of sailors is one of them. By killing adults and eating eggs, introduced predators such as rats, cats and stoats are responsible for nine in ten of the bird extinctions since 1600.
Now, conservation agencies are getting serious about…
edyong | November 8, 2008On the surface, plummeting populations of sharks do not seem like much cause for concern for humans or, for that matter, other sea life. But this simple viewpoint relies on splitting animals into two groups - predators and prey. In practice, this distinction is far too crude. Too put it bluntly, there are predators and there are predators. Those at the top kill those in the middle, and stop them in turn, from killing those at the bottom. As the old saying goes, the enemy of my enemy is my friend.
The rise in shark fishing is mainly driven by a growing market for their fins. Shark fins soup…
edyong | October 22, 2008
Humans are a funny lot. While we seem to be relentless voyeurs, we generally frown on eavesdropping as an invasion of privacy. But in the animal world, eavesdropping can be a matter of life or death. Animals rarely communicate in isolation. Often it pays for one species to monitor the dialogues of others, particularly when predator warnings are involved.
Small animals in particular do well to pay attention to the alarms of other species, as they are often preyed upon by the same larger hunters. Even very unrelated species can listen in and understand each other's signals. Vervet monkeys…
edyong | October 13, 2008
Many animals use poisonous secretions to protect themselves from predators. But poisons are complex chemicals and can take a lot of energy to make. Why invest in them, when you can steal someone else's?
Poison thieves are well-known in the animal kingdom. Many species of brightly coloured poison arrow frogs acquire their poisons from beetles, while some sea slugs make a living by hunting for jellyfish, transporting their stinging cells into their own limbs. Now, another species joins this guild of thieves - the tiger keelback snake, Rhabdophis tigrinis (image right, by Deborah…
edyong | September 10, 2008The forests of east Asia are home to giant honeybees. Each one is about an inch in length and together, they can build nests that measure a few metres across. The bees have an aggressive temperament and a reputation for being among the most dangerous of stinging insects. Within mere seconds, they can mobilise a swarm of aggressive defenders to repel marauding birds or mammals. But against wasps, they use a subtler and altogether more surprising defence - they do a Mexican wave.
Wasps, and hornets in particular, are major predators of bees and the largest ones can make even the giant bees…
edyong | August 5, 2008Thanks to Hollywood, the jaws of the great white shark may be the most famous in the animal kingdom. But despite its presence in film posters, the great white's toothy mouth has received very little experimental attention. Now, Stephen Wroe from the University of New South Wales has put the great white's skull through a digital crash-test, to work out just how powerful its bite was.
A medium-sized great white, 2.5m in length and weighing in at 240kg, could bite with a force of 0.3 tonnes. But the largest individuals can exert a massive 1.8 tonnes with their jaws, giving them one of the most…
edyong | July 19, 2008
In April 1998, an aggressive creature named Tyson smashed through the quarter-inch-thick glass wall of his cell. He was soon subdued by nervous attendants and moved to a more secure facility in Great Yarmouth. Unlike his heavyweight namesake, Tyson was only four inches long. But scientists have recently found that Tyson, like all his kin, can throw one of the fastest and most powerful punches in nature. He was a mantis shrimp.
Mantis shrimps are aggressive relatives of crabs and lobsters and prey upon other animals by crippling them with devastating jabs. Their secret weapons are a pair…
edyong | July 3, 2008Spider silk is a most amazing and versatile material, and spiders put it to all sorts of uses. It helps them to climb, to travel from place to place and most famously, to ensnare their prey. But one group of spiders, the uloborids, use their silk in a unique way - as a murderous garbage-compactor.
Most spiders kill with venom and even those that pose no threat to humans pack enough poison to deal with insect prey. Their famous webs are simply elegant traps, designed to immobilise prey so that the spider can deliver a fatal bite. But the uloborid spiders have uniquely lost their venom…
edyong | June 27, 2008For humans, sight is the most important of senses but only after we are born. Within the womb, surrounded by fluid, muscle and darkness, vision is of limited use and our eyes remain closed. But not all animals are similarly kept in the dark.
Cuttlefish develop inside eggs that are initially stained black with ink, but as the embryo grows and the egg swells, the outer layer slowly becomes transparent. By this time, the developing cuttlefish's eyes are fully formed and we now know that even before they are born, they can use visual information from the outside world to shape their adult…
edyong | June 26, 2008I've written two news stories in this week's New Scientist. One is on the different tactics of four-year-old boys and girls as they compete for animal puppets. The other is on the webs spun by black widow spiders. The article on the venomous, evil, little critters is longer so I'm going to use this space to talk about the black widows instead...
Black widows are notorious for both the toxicity of their venom and the cannibalistic nature of their sex, but their webs are equally interesting and less well known.
The basic design - the "sheet-based" web - consists of a well-defined horizontal…
edyong | March 13, 2008
Many animals have cunning ways of hiding from predators. But the larva of the sand dollar takes that to an extreme - it avoids being spotted by splitting itself into two identical clones.
Sand dollars are members of a group of animals called echinoderms, that include sea urchins and starfish. An adult sand dollar (Dendraster excentricus) is a flat, round disc that lives a sedate life on the sea floor. Its larva, also known as a pluteus, is very different, a small, six-armed creature that floats freely among the ocean's plankton.
A pluteus can't swim quickly, so there is no escape for one…
edyong | March 10, 2008
The story of evolution is filled with antagonists, be they predators and prey, hosts and parasites, or males and females. These conflicts of interest provide the fuel for 'evolutionary arms races' - cycles of adaptation and counter-adaptation where any advantage gained by one side is rapidly neutralised by a counter-measure from the other. As the Red Queen of Lewis Carroll's Through the Looking Glass said to Alice, "It takes all the running you can do, to keep in the same place."
The Red Queen analogy paints a picture of natural foes, wielding perfectly balanced armaments and caught in a…
edyong | February 25, 2008Humans have explored the entire face of the planet, but we haven't done so alone. Animals and plants came along for the ride, some as passengers and other as stowaways. Today, these hitchhikers pose one of the greatest threats to the planet's biodiversity, by ousting and outcompeting local species.
Islands are particularly vulnerable to invaders. Cut off from the mainland, island-dwellers often evolve in the absence of predators and competitors, and are prone to developing traits that make them easy pickings for invaders, like docile natures or flightlessness.
Two years ago, I wrote about…