2013年2月28日星期四
Sharks Are Color-Blind
Sharks have successfully prowled the oceans for millions of years, in part because of an impressive suite of sensory systems, including well-developed eyes and a large area in the brain devoted to vision.
But over the past few decades conflicting data have sparked a debate about whether sharks can see colors.
In a new study, scientists looked at the retinas of 17 shark species caught off the coasts of eastern and western Australia, including tiger sharks and bull sharks.
Retinas use two main types of light-sensitive cells to allow animals to see: Rod cells help measure brightness, while various types of cone cells help distinguish colors.
A technique known as microspectrophotometry had previously shown that rays and chimaeras, both close relatives of sharks, have color vision.
Using the same method, Nathan Scott Hart at the University of Western Australia and colleagues scanned shark retinas for pigments linked with rod and cone cells.
Rod cells were the most common types of photoreceptor found in all 17 shark species, which means the predators should be able to see within a wide range of light levels.
But no cone cells were observed in 10 of the 17 species, while only one type of cone cell appeared to be present in the other 7. This suggests that these sharks cannot tell different colors apart.
"We can't say hands down if sharks are color-blind yet, as there are over 400 different shark species," said shark biologist Michelle McComb at Florida Atlantic University's Harbor Branch Oceanographic Institute.
"But these findings are excellent, and a surprise, and definitely should spur more work," said McComb, who did not take part in the new study.
Color-Blindness to Save Rare Sharks?
It makes sense that sharks might be color-blind, the study team noted. Many aquatic predators—such as whales, dolphins, and seals—also appear to be color-blind, which may be because color vision isn't much use in their mostly blue-green environments.
If the discovery holds true for more shark species, it could be used to help reduce the numbers of endangered sharks accidentally caught by fisheries, as well as prevent shark attacks on humans.
"Our study shows that contrast against the background, rather than color per se, may be more important for object detection by sharks," study co-author Hart said in a statement.
"This may help us to design longline fishing lures that are less attractive to sharks, as well as to design swimming attire and surf craft that have a lower visual contrast to sharks and therefore are less attractive to them."
Oldest Giant Panda Relative Found in Spain
Dubbed Kretzoiarctos beatrix, the 11-million-year-old species was previously named Agriarctos beatrix based on a few fossil teeth found at a paleontological site near Zaragoza, Spain (map). Agriarctos is an extinct genus of European bear and a possible panda ancestor that lived eight to nine million years ago.
Earlier this year, scientists found a piece of A. beatrix's jaw, allowing them to compare it with that of another ancient Agriarctos bear from Hungary. In doing so, the team determined that A. beatrix is actually its own genus, which they called Kretzoiarctos.
The newly named K. beatrix pushes back the origin of giant pandas by a few million years, making it the oldest recorded giant panda relative, said study leader Juan Abella, a paleobiologist at the Museo Nacional de Ciencias Naturales in Madrid, Spain.
"Therefore, the origin of this group is not located in China, where the [giant panda] species lives, but in the warm and humid regions of [southwestern] Europe," Abella said in May.
New Bear Was Panda-Like?
For one, says Abella, the newfound jaw fragment shows the animal was likely an omnivore that fed on tough plants, like modern-day pandas. Also like them, and like most existing species of small bears, K. beatrix was probably a great climber. According to Abella, it would have had to scramble up trees to escape big predators of the day—such as extinct, doglike carnivores called bear-dogs—in the forests of what's now Spain.
But at 130 pounds (60 kilograms), K. beatrix was smaller than modern pandas and even more petite than the modern-day sun bear or spectacled bear.
An Epic Trek?
It's still unclear how panda ancestors made the epic trek from Europe to China.
Previous research suggests bears generally can migrate easily if the climate is mild enough, Abella said. Eleven million years ago, southwestern Europe was warm and humid-good conditions for starting out, he said.
The bears likely migrated mostly on land. One potential barrier—an ancient European sea called Parathetys—was already shrinking during the Middle Miocene, when K. beatrix lived, said Abella.
As for whether K. beatrix made it to China, "We don't really know, but no fossil remains of this species have been found outside Spain."
Whatever its history, the new research shows that K. beatrix was not your average bear.
The oldest panda relative study was published November 14 in the journal PLoS ONE.
Which Animals Sleep For A Long Time In A Day?
The sloths will be active during night times. The sleeping posture of sloths is very different where they bring their two legs together and their head on their hands and sleep on the trees. The sleeping posture of the sloths appears as if it is a part of the tree and they do not appear as an animal unless observed carefully. These sloths do not come down from the tree usually. Though if they come down from the tree they do not walk but crawl. During the time of floods , these animals can swim. The digestive system of the sloths is very big and the digestion process will go on like a snail. The digestion process takes one month of time to complete this process. That is the reason why, they sleep for a long time.
Things You Can Do To Protect Wildlife
Perhaps the greatest threat that faces many species is the widespread destruction of habitat. Deforestation, farming, over-grazing and development all result in irreversible changes—soil compaction, erosion, desertification, and alteration of local climatic conditions. Such land use practices vastly alter or even eliminate wildlife habitat. In areas where rare species are present, habitat destruction can quickly force a species to extinction.
By protecting habitat, entire communities of animals can be protected together and when communities are kept intact, less conservation intervention is required to ensure species survival. Parks, reserves, and other protected lands are too often the only habitats left untouched by habitat destruction.
2. Join a Conservation Organization
There is a wide range of conservation organizations working to protect endangered animals and habitats. Different organizations have different objectives—some work to protect a small plot of land or to protect whales, others focus on establishing good environmental policies in local government.
If you have a specific area of interest, you can often find an organization that is working to protect the species or habitats you're most concerned about. By joining in, you can support well-organized, ongoing efforts to protect species and habitats. And if you want to participate in conservation field work, you can often get involved in specific programs within many conservation organizations that rely to a great extent on help from volunteers.
3. Reduce the Threat of Invasive Species
The spread of non-native species has greatly impacted native populations around the world. Invasive species compete with native species for resources and habitat. They can even prey on native species directly, forcing native species towards extinction. Another way to reduce the threat of invasive species is to incorporate native plants in your garden and to welcome native animals into your yard.
4. Recycle and Reduce Energy and Goods Consumption
By recycling and (reusing as much as we can, we reduce our impact on the environment. Additionally, by reducing the energy we consume, we take a little of the burden off our natural resources (and our pocketbooks). You can also reduce your carbon footprint by first calculating your current carbon footprint and then reduce the amount of carbon you consume.
5. Minimize use of Herbicides and Pesticides
Herbicides and pesticides may keep yards looking nice but they are in fact hazardous pollutants that affect wildlife at many levels. Many herbicides and pesticides take a long time to degrade and build up in the soils or throughout the food chain. Some groups of animals such as amphibians are particularly vulnerable to these chemical pollutants and suffer greatly as a result of the high levels of herbicides and pesticides in their habitat.
6. Place Decals on Windows to Deter Bird Collisions
Daniel Klem Jr. of Muhlenberg College has estimated that as many as one billion birds in the United States die each year due to collisions with windows. You can help reduce the number of collisions simply by placing decals on the windows in your home and office. Other simple steps you can take to reduce the likelihood of collisions are to re-evaluate feeder placement, draw shades and curtains during brightest parts of day, install tilted window glass, and put screens on outside of windows.
7. Slow Down When Driving
Many native animals have to live in developed areas and this means they must navigate a landscape full of human hazards. One of the biggest obstacles to wildlife living in developed areas is that created by roads. Roads divide habitat and present a constant hazard to any animal attempting to cross from one side to the other. So when you're out and about, slow down and keep an eye out for wildlife.
8. Voice Your Concerns and Get Involved Locally
By letting local and national governments know that you're concerned about endangered species, you're increasing the likelihood that someone will do something about it.
9. Change Your Career
This may sound extreme but for some people getting involved in the protection of threatened and endangered animals is so important that a career change that enables you to work directly with species of concern may be the most rewarding way of doing so. If you're seeking more information on changing your career, you may want to check out The Working Zoologist.
10. Share Your Enthusiasm for Wildlife and Nature
Encourage others to learn about nature, enjoy watching wildlife, and value protecting habitats and species with which we share this planet.
Trade in Seal product
Seal hunting occurs in various parts of the world for commercial, subsistence and cultural reasons. Seal hunting is also carried out in some areas for the sustainable management of marine resources. At least 15 seal species are currently hunted, but the majority of hunted animals belong to five species: harp seals, ringed seals, grey seals, hooded seals and Cape fur seals.
The seal populations that are hunted for commercial purposes – an estimated 15 million animals – are generally not endangered. Some 900,000 seals are hunted each year around the globe, with the commercial hunt in Canada, Greenland and Namibia accounting for some 60% of the seals killed each year. Hunting for commercial purposes also takes place in Russia and Norway. Around one third of the world trade in seal products either passes through or ends up in the EU market.
Seal hunts around the world are governed by different rules and regulations. In some countries comprehensive systems are in place, while in others the seal hunt is regulated to a lesser degree. Within the EU, certain methods and means of capture and killing are prohibited in areas protected under EU nature law.
The Faroese Whale Hunt
The Faroese whale hunt, called the grind, is more than 1,200 years old, dating to the first settlement of the islands by Vikings in about 800 CE. It is a mark of the hunt’s traditional character that the methods used to trap and kill the animals are little different from those developed by the Vikings. When a pod of pilot whales is sighted near the islands or in the channels between them, the men of the local district (only men participate in the hunt) take to their boats to intercept the animals, forming a huge semicircle between them and the open sea. By making loud noises that frighten the whales, the hunters gradually herd them into a small bay or inlet, where they beach themselves or are trapped in the shallow water. There they are slaughtered with traditional knives whose blades are usually 16 to 19 cm (6.3 to 7.5 in) long. Usually two deep cuts are made on either side of the animal’s neck, just behind the blow hole, causing the head to drop forward; a third cut is then made through the middle of the neck down to the carotid arteries and spinal cord, which are severed. After a period of violent thrashing the animal is paralyzed and loses consciousness, dying of blood loss in most cases.
The whales that do not beach themselves or swim to water shallow enough for the hunters to stand in are dragged to shore, often by means of ropes attached to steel hooks that have been plunged into their sides, usually in the area of the head or neck. Because the animals are moving and because their skin is smooth, they often must be stabbed several times before the hooks become secure in their bodies.
The dead animals are lined up on wharves and butchered by hunters and by familes of the district. Each hunter and each family is entitled to an equal portion of the meat and blubber. Although the hunt is officially noncommercial, occasionally some portions are sold to local restaurants and hotels.
Naturally, the waters in which the whales are slaughtered become red with the animals’ blood—much as do the coves of Taiji, Japan, where each year some 2,500 dolphins are clandestinely stabbed to death (see Dolphin Slaughter in Japan). Even the Faroese government has described the hunt as “a dramatic and bloody sight.” Since the late 20th century, and especially since the advent of the Internet, images of hunters hacking at thrashing whales in a blood-red surf have been widely circulated. The images tend to convey the impression that the hunt is cruel.
The Faroe Island Whale Hunt
Nearly every year, usually during the months of July and August, several hundred pilot whales are killed for their meat and blubber by inhabitants of the Faroe Islands, a small, self-governing territory of Denmark in the far North Atlantic. Since the late 20th century numerous animal-rights, conservation, and environmental groups have condemned the hunt as cruel and unnecessary. The Faroese government has replied that the killing method used in the hunt—the severing of the spinal cord and carotid arteries by knife cuts to the animal’s neck—is actually humane and that the hunt is an integral part of traditional Faroese culture and a valuable source of food for the islands’ inhabitants.
Despite their common name, pilot whales are dolphins, constituting two species of the family Delphinidae of oceanic dolphins. Growing to a length of 4 to 6 metres (13 to 20 feet), they are distinguished by their round, bulging foreheads, their short snouts, and their slender, pointed flippers. Nearly all pilot whales are black. Pilot whales are highly gregarious, living in pods numbering several dozen to more than 200 animals and including extended-family groups. The short-finned pilot whale (Globicephala macrorhynchus) generally inhabits warmer waters than the long-finned pilot whale (Globicephala melas). The habitat of G. melas includes nearly the entire North Atlantic, from the eastern coast of Greenland to the western and northern coasts of Scotland and the Shetland Islands.
WWF
Project the wildlife is at the core of WWF’s mission. Why? Because animal populations are disappearing at an alarming rate. But even in the face of threats like poaching, habitat loss and overuse of natural resources, WWF is creating a better future for wildlife every day. Protecting these species also contributes to a thriving, healthy planet for people’s health and well-being-from forests that slow climate change and filter water to oceans that provide more than one-sixth of the world’s food.
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