The Land Massive

Life is hard for wild animals, being fraught with the perils of predation, starvation and sickness. Only the strongest manage to survive into adulthood and breed, which means that only the best genes are passed into the next generation. This is the major driving force behind evolution and is responsible for the staggering diversity of life on our little planet.

One of the most obvious adaptations that some species have is their tendency to grow to enormous sizes. This is typically a defense against predators and takes advantage of the 'ten times larger' rule. Simply put, this rule states that a terrestrial animal becomes safe from predation if it can grow ten times heavier than their largest predator, since their predators are unable to develop jaws strong enough to kill them.

Obviously, this rule is not absolute. It doesn't take mankind in account, as our technology and sentience allowed us to overcome it as cavemen, nor does it take into account predators growing larger themselves. If all of the prey species in an area begin to grow larger, this will itself drive a size increase in predators. Bigger prey means more meat per kill, which is able to fuel more muscle mass and only the largest predators will be able to make kills (so only the genes for a bigger body size will be passed down into subsequent generations).

This means that predators and prey are locked in a constant arms race where each is trying to become bigger. Over time, the size of each species will grow bigger until size becomes limited by another factor - such as the availability of food - and is therefore no longer advantageous (where upon it's selected against and a 'maximum' size of the species has been reached).

Animals have reached unbelievable sizes in the past, both in the oceans and on land. Dinosaurs are the obvious example of megafauna, with some species becoming so heavy that the ground used to tremble as they walked! Sadly, there aren't animals this impressive anymore (certainly not on land, anyway), but we do have some truly huge beasts roaming our continents. Here's a list of the top ten largest animals that are alive today (sorted by average weight):

10: Wild (Asian) water buffalo: 770kg/3.5m long (max weight: 1, 250kg)

Also called the Asian or Asiatic buffalo, the wild water buffalo, Bubalus arnee,  is endemic to Southeast Asia. As well as its obvious bulk, the bovid is famed for having the widest horn-span in its family, which can be as wide as 2m from tip-to-tip in large males.

Wild water buffaloes are gregarious and live in tight, matriarchal groups as a defense against predators. Each group is called a 'clan' and is made up from related females and their young offspring. A clan can be as large as 30 individuals and often band together with other clans to form large herds (for further defense) that can consist of more than 500 individuals!

To avoid inbreeding, young males actually leave their clan once they become sexually mature and form small 'bachelor' groups. These groups consist of about 10 males and generally spend the dry season away from females. In breeding season, the young males rejoin a herd where they are polygynous and mate with multiple females.

9: Black rhino: 1, 150kg/3.5m long (max weight: 1, 900kg)

Black rhinos have two horns on their snout, which are made from keratin - the same protein as hair and nails. Their horns can grow as much as 3 inches a year and individuals have been found with horns that are longer than five feet! Sadly, their horns have been their downfall as it is coveted for Asian herbal medicines and ornaments in the Middle East, meaning that the black rhino is now classified as 'Endangered' by the IUCN.

There are four species of black rhinos (of the genus Diceros), which are actually grey. Their skin looks darker because they frequently wallow in mud to help keep cool through the hottest parts of the African day. Their size and rotund shape means that they actually retain body heat, so black rhinos are usually inactive during the hottest hours and rest beneath shade if the cannot find shallow water. During gloaming, when it's cooler, the rhinos feed by browsing shrubs and the lower branches of trees.

8: Walrus: 1, 200kg/3.4m long (max weight: 2, 150kg)

Odobenus rosmarus - the Latin taxonomic name for the walrus - literally means "tooth-walking sea-horse". This name stems from the tendency of walrus' to drag themselves onto pack ice using their tusks for purchase. It should be noted, however, that walrus tusks are actually elongated canines. These teeth are so large that they can grow as long as 1 meter in big males!

Walrus' are found throughout the Northern Hemisphere in the Arctic Circle and some subarctic regions. Walrus' once covered most of the frigid north, but their numbers were decimated by hunting in the 19th Century and their populations are now discontinuous; being limited to certain regions. That being said, they can still be found through most areas of shallow water, where they like to dive and crawl across the bottom of the sea bed to feed off crustaceans, molluscs, amphipods and slow-moving fish.

7: Giraffe: 1, 400kg/6m tall (max weight: 2, 150kg)

There are nine distinct species of giraffe, which are classified under the genus Giraffa. Growing to heights of 5 - 6m, giraffes are the tallest living animal and have unique patterns of spots in their fur. Their spotting is very similar to human fingerprints and can used to identify an individual. Interestingly, their spots also reveal the relative age of a giraffe as they grow darker as throughout their lives.

Giraffes are herbivores and use their long necks to reach leaves that are high up in the canopies of trees. This allows them to access food that many animals are unable to get at, thus allowing them to exploit a very specific niche. Despite this being an obvious use of their long neck, many scientists are skeptical that this is why it first evolved. Their neck is simply too exaggerated for access to slightly more food to have driven its appearance and many scientists now believe that the length of their neck was initially a sexually selected trait.

During mating season, male giraffes fight for the right to mate with females. They have an interesting way of dueling called 'clubbing', where they literally use their heads as bludgeons to strike their opponent with. As explained by the mechanisms of physics, a giraffe's head will hit harder the longer its neck is. Thus, having a longer neck would have given a giraffe an advantage in battle, meaning that it is more likely to win and pass on the 'long neck' gene so becomes selected for. Being able to reach an abundance of previously unattainable food would have then acted as a secondary use of their long necks and would have helped to reinforce its selection.

6: Gaur: 1, 600kg/4m long

Gaur, Bos gaurus, are characterised by a very prominent dorsal hump and have a long dewlap that hangs from their chin. Other than mankind and tigers, their large size means that they are rarely preyed upon and their lives are relatively safe for a herbivore.

Gaur are typically diurnal, gregarious animals where the females live matriarchal herds with their close relatives and offspring. To avoid inbreeding, a young male leaves its herd once it has sexually matured and spends much of the year in solitude. During the breeding season, polygynous males rejoin herds where they compete for mates by showcasing their size and emitting loud calls. 

Interestingly, scientists have noticed that many gaur become nocturnal in areas with high levels of human activity. But whatever hours gaur keep, their behaviour remains the same and they seem to actively avoid water, going to sources only sparingly to drink. They rarely wash or wallow and spend much of their time browsing on a wide variety of shrubs, flowers and grasses. 

5: Hippopotamus: 2, 500kg/1.2m long (max weight: 3, 400kg)

The hide of the hippopotamus, Hippopotamus amphibius, is so thick it can make as much as a half a ton in large males! Interestingly for an animal that lives in an extremely hot environment, hippos have neither sweat nor sebaceous glands. Instead, they have unique glands that secrete a viscous red fluid. This has given rise to the urban myth that hippos 'sweat blood'.

Due to their weight, which makes them cumbersome and ungainly on land, hippos spend much of their time in water where their body weight is decreased. Hippos mainly venture onto land to feed at night, where they are able to climb even very steep banks in their search for grass. Most hippo attacks on humans happen during the night, when a person accidentally walks between the hippo and water. The hippo panics and then charges, bulling over the person as it tries to get back to safety.

Hippos are actually the most dangerous animal to humans in Africa and should be avoided if ever seen in the wild. They are extremely territorial and (in addition to what was mentioned above) may attack people on shores and knock us from boats if we venture into their 'space of water'. With hugely powerful jaws that can open almost 180 degrees, hippos are reportedly able to bite animals as big as Nile crocodiles clean in half with a single bite!

4: White rhino: 2, 350kg/3.8m long (max weight: 3, 850kg)

The white rhino, Ceratotherium simum, spends large amounts of its day wallowing in the wet mud around rivers, streams and lakes. The mud acts as a natural 'sun cream' and helps to deter parasitic insects.

Unlike their cousins, black rhinos, white rhinos are grazers and have differently shaped mouths that are adapted to trimming grass off the ground. They have poor eyesight, but have excellent hearing and even better smell. Due to this, they often walk in single file so they can follow the scent trail of the rhino ahead of them.

3: Southern elephant Seal: 3, 000kg/5m long (max weight: 4, 000kg)

There are actually two types of elephant seal, but it is the southern elephant seal, Mirounga leonina, that grows the largest. Surprisingly, their name does not stem from their enormous size, but rather from their inflatable trunk-like snouts!

Living in the brutal Antarctic waters, Southern elephant seals are superb divers and can go as deep as 1.5 miles, staying submerged for up to 2 hours at a time. While underwater, southern elephant seals hunt fish and squid, which form the staples of their diet. Both male and female seals spend months at sea at a time, where they migrate vast distances in search of food.

Elephant seals return to rookeries during their breeding season, where males compete with each in other in brutally violent displays for the right to mate with females. Successful males can form harems that consist of 40 - 50 females, whom they mate with exclusively!

2: Asian elephant: 4, 200kg/6m long (max weight: 5, 200kg)

Like their African cousins, the Asian elephant, Elephas maximus, has an extremely long gestation period and their pregnancies last for 22 months! Although this isn't surprising really, considering newborn calves can weight as much as 90kg!

Asian elephants have been domesticated by humans over thousands of years for a variety of tasks. Most often, the elephants are used to carry or move heavy objects and as taxis, where they carry people around on saddles or carriages called howdahs. Less commonly, but perhaps more famously, the elephants have been used for combat on occasion by warlords such as Hannibal, who took the elephants over the Pyrenees and the Alps in his campaign against the Roman Empire!

1: African  elephant: 8, 500kg/6.7m long (max weight: 13, 000kg)

Although African elephants are noticeably bigger than their Asian cousins, you can also use the shape of their ears to tell them apart. Rather bizarrely, the shape of an African elephant's ear looks similar to the continent of Africa, while the shape of an Indian elephant's ear looks a bit like India! 

There are actually two types of African elephant of the genus Loxodonta: the African bush elephant and the slightly smaller African forest elephant. Both are larger than the Asian elephant and can roam huge distances in search of food. The elephants eat roots, grasses, fruit and bark, which they attain using their deceptively dextile trunk and their tusks, which they use for scraping trees and digging.

Unfortunately, as with Asian elephants, their trunks have also proved to be their downfall and they were almost hunted almost to extinction by those in the ivory trade. Since the international trading ban on ivory that was placed in 1990, elephant numbers have recovered somewhat (although illegal poaching is still a problem). It's estimated that there are now as few as 700, 000 elephants left in Africa and they are officially classified as 'threatened' by the IUCN. Sadly, less than 20% of the elephants' known range is under formal protection (which is largely due to budget constraints and the instability of many Africa governments). 

Mountain gorillas seen disarming poachers traps!

Everyday, animal trackers set out from the Karisoke Research Center into an isolated area of Rwandan rainforest aiming to find and disarm as many of the dangerous and illegal traps set by poachers as they can find. The trackers efforts are crucial in helping to protect the extremely rare mountain gorillas (Gorilla beringei beringei) that inhabit the region, which are classified as being 'Critically Endangered' by the IUCN and are predicted to become extinct within 10 years if we fail to conserve them.

When tracker John Ndayambaje set out one morning he was fully expecting to see poachers traps. Sure enough, he located a clan of gorillas and spotted a snare trap nearby. Although many poachers don't set snare traps to catch gorillas, as adults of the species are easily strong enough to break free, they are capable of killing juveniles so he knew that he must disarm it.

When John moved to approach the trap however, a silverback called Vubu grunted at him, presumably warning him to stay away. As John watched, two younger gorillas named Rwema and Dukore made their way over to it and carefully broke it, working confidently and quickly, which suggests that they've had extensive experience with the traps in the past. Rwema and Dukore then searched the surrounding foliage, joined by a third member of the Kuryama Clan called Tetero, and disarmed several more traps that John hadn't yet seen.

Rwema and Dukore work together to disarm a snare trap set by poachers.

This remarkable ingenuity has undoubtedly arisen in response to the very real dangers that the traps pose and is a superb example of mountain gorilla intelligence and their ability to learn. Researchers at the Karisoke Research Center believe that the gorillas watched human trackers tackling the traps and copied how they disarmed them. Although fascinating to watch, Veronica Vecellio (the Centre's gorilla program coordinator) was not surprised by the events and said that she is "always amazed and very proud when we [the Centre's researchers] can confirm that they are smart".

Ocean Giants

Throughout its history Earth has been home to animals of epic proportions. These monsters have included dragonflies the size of small planes, dinosaurs that were so big that the very ground trembled when they walked and huge land mammals such as the woolly mammoth, which were actually seen by early man! Most of these colossal animals are now extinct however, with only the occasional over-sized fossil being found as the the only indication that they ever even existed. Despite the loss of these species, Earth is still filled with giants and none are bigger and heavier than the whales. 

10: Gray whale - 45 feet/40 tonnes

The gray whale, Eschrichtius robustus, is the only surviving member of its family,  Eschrichtiidae, which first appeared  over 30 million years ago. Gray whales were nicknamed devil fish during the whaling era because of their violent behaviour when hunted.

Gray whales are famous for their 14, 000 mile (22, 000 kilometre) migration route that takes them from the Bering and Chukchi Seas in the summer to Mexico over the winter. This route was once believed to have been the longest migratory journey undertaken by any animal, but recent evidence now suggests that some humpback whales can travel even further!

9: Sei whale - 48 feet/45 tonnes

The sei whale, Balaenoptera borealis, is one of the fastest species of cetaceans (the family of whales, dolphins and porpoises) and has been recorded swimming at speeds of 30 mph (50 kph).

Sei whales need to consume nearly 1, 000 kilograms of copepods (small crustaceans), krill and zooplankton every day in order to meet their energy requirements. Sei whales are a type of baleen whale, which means that they eat by filtering the organisms out of the water as they swim. Sei whales can be found in most of the world's oceans, although they are not found in polar waters.

8: Humpback whale - 45 feet/48 tonnes

The humpback whale, Megaptera novaeangliae, is easily identifiable by its  knobbly head and unusually long pectoral fins. Male humpbacks produce one of the most complex songs out of any whale species, which can last for as long as 20 minutes and are often repeated for hours at a time. Although the function of their songs is not conclusively known, it is believed that they have a role in attracting a mate.

Humpback whales are one of the most wide-spread species of whale and can be found throughout the world's oceans. They have an intensive migration route and travel over 16, 000 miles (25, 000 kilometres) a year from the cold polar waters where they spend their summer to the tropical or subtropical waters where they breed and give birth in the winter.

7: Sperm whale - 50 feet/60 tonnes

The sperm whale, Physeter macrocephalus, is the largest living species of toothed animal and has the  largest brain of any animal in the world.

Sperm whales feed predominantly on giant squid, which they dive for to depths of up to 3 kilometres. This feat makes them the deepest diving animal and they navigate in the complete darkness using echolocation. The clicks that they produce  for their echolocation have a range of 60 kilometres and are the loudest sound produced by any animal.

6: Bowhead whale - 55 feet/75 tonnes

The bowhead whale, Balaena mysticetus, lives in the frigid waters within the Arctic Circle. In order to keep warm here the whale has a huge layer of blubber that accounts for up to 50% of its total body mass.

Bowhead whales are unique among mammals because their bones never fuse. This means that they keep growing throughout their entire lives and individuals as long as 70 feet have been found (although this post uses the average length of each species, else it would be higher up the list). Remarkably bowhead whales are believed to live for over 200 years due to their low body temperature and females have been found over the age of 100 that are still fertile!

5: North Atlantic right whale - 52 feet/100 tonnes

With only 400 individuals of the species left in existence, the North Atlantic right whale (Eubalaena glacialis) is one of the most endangered whales in the world. This is despite its protection under the Marine Mammal Protection Act of 1972 and the U.S. Endangered Species Act of 1973.

Like all right whales, North Atlantic right whales can be distinguished by their broad back that lacks a dorsal fin and the callosities (thickened skin) above its eyes.  They continuously feed on copepods and other small invertebrates such as krill, pteropods and larval barnacles by skimming them out of the water and migrate from the Gulf of Maine to their calving areas off Georgia and Florida in the winter.

4: Finback whale - 90 feet/74 tonnes

The finback whale, Balaenoptera physalus, is also called the fin whale, razorback whale or  the common rorqual.  It is  the second longest animal in the world, but its thin body means it is lighter than some species of much shorter whale.

Finback whales feed off schooling fish, squid, crustaceans and krill and are unbelievably fast. So fast in fact, that they are faster than the quickest ocean steamship! This attribute has earned them the esteemed title of being the 'greyhounds of the sea'.

3: Southern right whale - 58 feet/110 tonnes

The Southern right whale, Eubalaenna australis, is recovering well since it became protected in 1937 and is now classified as being of 'Least Concern' by the IUCN, with its population growing by an estimated 7% each year.

Southern right whales spend much the summer close to Antarctica where their calves are safer from being predated by killer whales and great white sharks. During the winter, when the conditions of Antarctica become too harsh for them to remain there, they migrate north to the warmer waters of Argentina and seem to spend many hours in a unique behaviour called 'sailing'. This behaviour is believed to be recreational and consists of the whales catching the wind in their flukes and letting it propel them through the water like  boats!

2: North Pacific right whale - 60 feet/120 tonnes 

The North pacific right whale, Eubalaena japonica, feeds mainly on copepods that it constantly filters out of the water while swimming. Its prey is so small that it needs to consume millions of them each day in order to provide the energy that it needs to survive.

Unlike many other species of whale, the North Pacific right whale does not seem to have a clear migratory pattern and the only notable annual difference in their distribution is when they are breeding, where they tend to move closer inland.

1: Blue whale - 100 feet/190 tonnes

The blue whale, Balaenoptera musculus, is a peaceful whale that eats krill - one of the smallest organisms on the planet. Although there were once believed to have been 200, 000 blue whales in the oceans, it is estimated that there are now only 10, 000 left due to their historical over hunting. Sadly, and despite now being protected, their numbers are not expected to recover due to their slow life cycles.

As far as we know the blue whale is the largest animal that has ever lived on this planet and is twice the weight of the biggest known dinosaur. In fact, blue whales are so big that their tongues alone can weigh as much as an elephant and their hearts as much as a small car!

Watching from the waters

The Nile crocodile, Crocodylus niloticus, is one of the most feared animals in the world and is undisputedly the most dangerous species of crocodilian to humans - being estimated to kill around 200 people each year. This is mainly due to its close proximity to our settlements and its indiscriminate diet - with it hunting anything that moves! Growing as long as 16 feet (5 metres) and weighing up to 225kg (500lb), the Nile crocodile can be found through central and south-east Africa and on the western shores of Madagascar. 

This is believed to be one of the largest specimens of Nile crocodile ever caught! Its huge size makes it no wonder why many Ancient Egyptians incorporated the beast into their belief system and worshipped Sobek, the crocodile god that lived in Crocodilopolis - a great city of crocodiles!

Probably one of the main reasons that the crocodile is such a proficient predator and is so lethal to humans is because it is a silent ambush predator - its flat body allows it to remain completely submerged, even in the shallow waters by river banks; and it has slightly raised nostrils and eyes that can be poked above the surface while keeping everything else hidden underwater, allowing it to see and breath virtually unnoticed. This allows the crocodile to get within yards of its prey (including humans), completely unnoticed and once it is ready, it lunges out of the water. Once the crocodile has lunged it is normally too late for its victim due to the speed of the attack and the animal is then crushed in the crocodile's vice-like bite and dragged into the water. After it has bitten an animal, Nile crocodiles (as with most crocodilians), have an overwhelming instinct to role - this is commonly known as 'death rolling' and, by spinning like a corkscrew, the crocodiles tear huge chunks of flesh out of their prey. This helps to compensate for their ineffective teeth, which are unusually blunt for a predator.

A Nile crocodile that has caught a gazelle. Nile crocodiles can eat up to half their body weight at a time and their bite force has been measured to be as high as 5, 000 lbf (22N), which is like being hit by a very fast-moving truck! Like most crocodiles, N. niloticus has a primary and secondary bite where an individual bites its prey once and then re-bites it without relaxing their first bite, helping to drive its blunt teeth even further into the flesh of the animal.

Ambushing their prey in this manner means that they can remain motionless in the water for very long periods of time and so, can conserve enormous amounts of energy. Crocodilians can also reduce their energy expenditure even further by slowing down their breathing and reducing their metabolism using a sophisticated cardiac shunting system that diverts blood away from their heart. Although cardiac shunting mechanisms are found in many species of reptile none have one as advanced as crocodiles. This, along with the fact that they have the most advance heart physiology in the world, has led many scientists to believe that crocodiles were once endothermic (warm blooded) like mammals and birds! Such scientists believe that their warm blooded ancestors slowly evolved back into being ectotherms (cold blooded) when they began to ambush their prey from water since a cold blooded body-plan would be much more beneficial for such a strategy; mainly because it wastes much less energy than trying to maintain a body temperature that is hotter than the surrounding water - just think about how cold you get if you spend too long in a cool bath or pool!

Thus, crocodiles can remain even in fairly cool water for long periods of time and wait for a potential meal to come to them! This is usually when an animal ventures too close to the waters edge for a drink... Nile crocodiles don't even have to use their muscles to hold their head up so can save even more energy while they wait! Their lungs act as ballast tanks and when they are inflated with air, actually push the crocodiles snout and eyes up above the water level! In fact, crocodiles can slow down their energy expenditure so much that they can hold their breath underwater for up to 2 hours when they inactive; often, lying in little 'dens' that they've dug out of the riverbed with their arms.

Certain species of bird, such as the spur-winged plover (Vanelus spinosus), have been seen picking scraps of meat from between crocodile teeth. It is not known for certain whether the birds are merely 'running the gauntlet' to obtain food at great personal risk or whether crocodiles are allowing them to this; forming a mutualistic relationship where the birds are fed while keeping the crocodile's mouth and teeth clean.

Although Nile crocodiles often hunt via ambushing their prey, they can also hunt with a much more proactive and energetic approach - chasing after fish and eating them underwater. It is believed that Nile crocodiles prefer to eat larger terrestrial game that they hunt with surprise attacks preferentially and switch to smaller fish when they aren't available or during then night when their mammalian prey is less active. Nile crocodiles are thought to prefer to ambush mammals for two main reasons: firstly, since it is less energetically expensive as mentioned above; and secondly, because crocodiles are far-sighted underwater due to the closure of their protective nictitating, or 'third', eyelids. Closing their third eyelid helps to protect their eye from underwater debris but also bends the light that passes through it so that the lenses in their eye can't refract the light enough to focus on close-up objects. Obviously, this will severely reduce their ability to hunt underwater and hunting in such a manner would probably be impossible if they didn't have many sensory papillae around edge of their lower jaw. These papillae act a bit like whiskers in dogs and cats and are able to detect even very minute vibrations in the water, allowing the crocs to sense fish that are close to their mouth! Crocodiles use much more energy when hunting fish in such a manner and as a result, can only hold their breath underwater for about 15 minutes since their muscles require more oxygen.

Their ruthless ability to surprise their prey and the fact that they eat humans has undoubtedly earned the Nile crocodile a fearsome reputation as a heartless monster. Oddly however, this isn't true and Nile crocodiles are one of the few crocodilians that care for their young - with mothers watching over their nests from when they lay their eggs to when they hatch! Most crocodilians abandon their nests as soon as they have lain their eggs and leave their offspring to fend for themselves. Furthermore, many crocodilians are cannibalistic and will eat juvenile crocodiles so that they may actually kill their own young unknowingly...

The gender of crocodiles is determined by the temperature that the eggs are at during their incubation, with temperatures of 32 - 33C producing males. Anything warmer or cooler than this narrow temperature range produces females, which is of great concern to conservationist biologists since global warming may result in more females being born and less males! The small size of the baby crocodiles makes them very vulnerable to predation early in life, but as they grow bigger and, if all goes well, the crocodiles can live for up to 100 years!

The Nile crocodile then, is a brutal and ruthless predator that preferentially hunts by ambushing unsuspecting animals from water. It accomplishes this using a range of physiological and behavioural adaptations and techniques which allow them to get within yards of their prey, gliding through the water causing barely a ripple... Despite their danger to man and the polluting effects that our lifestyle has on the waters of their habitats, the Nile crocodile is thriving and is classified as being of 'Least Concern' by the IUCN. This is not surprising really, since crocodilians are ancient animals that even trod the world with the dinosaurs! Their famed resilience allowed them to survive through the catastrophe that killed off the once mighty dinosaurs; and maybe, will even mean that they will survive for long after man has disappeared...

How effective are captive breeding programs?

One of the most amazing attributes that humans have is our unprecedented ability to alter our surrounding environment so that it is more suitable for our daily needs; with the most obvious of such alterations being the clearing of land to make room for housing and agricultural crops. Whilst we are not the only animals to alter our habitat (many other species such as beavers and termites also build large structures), we are the only species to build and destroy at such a large scale. The fact is that we have now spread onto every continent - even having science stations of Antarctica - and wherever we go, deforestation soon follows. The result of this is that there is very little true 'wilderness' left on Earth and many animals have lost their habitats due to our destructive ways and face imminent extinction in the near future as a result.

'Slash and burn' agriculture is an ancient way of clearing land that dates back to our earliest endeavours of farming 12, 000 years ago and involves setting blaze to, sometimes, vast acres of forest. Obviously this technique is highly destructive and displaces all of the resident organisms that were previously living there, destroying their homes. The problem is made worse by the fact that land gained in such a way is very infertile so that farmers need to create new plots of land every year.

In fact, the problem is now so bad that research undertaken during the Millennium Ecosystem Assessment (MEA) has found that in the past 50 years humans have changed ecosystems more rapidly and extensively than at any other comparable time throughout our entire history! This has resulted in a huge and irreversible loss of Earth's biodiversity and the MEA found that we have already destroyed over half of the planet's forests, 20% of its coral reefs and 35% of its mangroves - all of which are essential ecosystems for providing habitats to animals, providing ecosystem services to us and in preserving the planet's future evolutionary potential. To make matters even worse, the MEA has predicted that the degradation of ecosystems is likely to get considerably worse during the first half of this century at the very least! This loss of habitat has had profound implications on the survival of many species, which are now already extinct or are endangered and this destructive human behaviour is unlikely to change any time soon. The question then, is whether or not we should try to preserve at least some of the species and ecosystems that we are threatening and of course, many people believe that we should. As the result of this, there are countless specialised conservation organisations across the globe like the WWF and the IUCN.

One of the methods that we can use to preserve endangered species then, is via captive breeding programs in which we take animals from the wild and breed them ex-situ in institutes such as zoos and aquariums. Captive breeding programs have been very successful in the past and have been sufficient to restore the natural populations of endangered species back to relatively 'safe' numbers. A good example of this is the black-footed ferret (Mustela nigripes), which has now made a remarkable recovery after its entire population was removed from the wild and bred in captivity, with reintroduction schemes running since the early 90's. In addition to breeding rare animals in an environment that is safe from illegal poaching, captive breeding programs also allow the animals to be studied by scientists; allow the public to see foreign and exotic animals in zoos, which is both interesting and may help to raise their awareness of the importance of conservation; and furthermore, helps to maintain a 'stock' population against unforeseeable events like natural disasters (which become a huge problem if all the individuals of a particular species are only found in one place!).

These elephant tusks were seized after an anti-poaching raid in Tanzania. Sadly, despite the great efforts to protect wild elephants, illegal poaching for their highly valuable ivory tusks still goes on as is very difficult to protect wild populations. Bringing endangered species, such as elephants, into captivity however makes this much easier.

However, even though captive breeding programs sound like a good idea at first glance and definitely have their good points, are they really feasible on a large scale? The IUCN has estimated that 2, 000 - 3, 000 species of terrestrial vertebrates will have to be captive bred in the near future in order to save them from extinction and sadly, the space and money that is available globally is nowhere near sufficient enough  to cope with such an epic undertaking. Thus, we may have to decide to save some species at the expense of others - decisions that would undoubtedly be both unpleasant and controversial: why is one species more important than another?

Obviously then some animals will be more suitable for captive breeding programs than others: mainly, small creatures that can be kept and maintained cheaply in small enclosures. Amphibians are a great example of such animals and furthermore, can be easily released back into the wild because they don't have any learnt behaviours that must be taught to them in order for them to survive. This is one of the main problems with reintroduction schemes, which is particularly evident in predators - without learning how to hunt and kill their prey, captive-bred animals cannot survive in the wild and thus depend on humans for their entire lives! The fact that amphibians make such good candidates for breeding in captivity is very fortunate, as over a half of all amphibians are now endangered due to the Chytid Fungus that is killing them in large numbers across the globe and due to their extreme susceptibility to anthropogenic environmental pollutants.

The endangered black-eyed tree frog, Agalychnis moreletti, is currently being bred in captivity in Chester Zoo. The zoo is participating in an international effort called the Amphibian Ark (AArk) program that aims to preserve amphibian life and safe-guard them against their global decline.

The lack of space that is available in zoos however, sadly makes the captive breeding of large animals much less feasible than programs that incorporate smaller species. This is particularly true for large predatory mammals such as lions and tigers, which need very large territories to thrive and do not respond well to being kept in captivity. In addition, they require so much space and cost so much to keep that zoos can only afford to keep relatively small numbers of them in captivity. This means that only a small number of individuals can be bred from so that the captive populations would become vulnerable to inbreeding depression and would suffer from low genetic diversity and have reduced fitness as a consequence. To explain this further, a small breeding population rapidly becomes inbred because simply put, there are no animals available for a individual to breed with that they are not related to. Over time the population becomes more and more inbred and deleterious alleles build up in individuals. Usually such maladaptive alleles are recessive and are masked in outbred individuals who have a 'normal' and healthy allele for the gene so that they don't suffer from its effects, even if they are carrying it. However inbreeding increases the chances of an individual having two copies of the deleterious allele (which are then are said to be homozygous for the allele) so that they suffer from its ill effects - a phenomenon known as inbreeding depression.

The lion, Panthera leo, is one of the most majestic predators in the world. Sadly however, captive lions usually have extremely low sperm counts and a very high percentage of what little sperm they do produce is abnormal. This problem, due to inbreeding depression, is very common in species of big cat and is exacerbated even further by the fact they they rarely even try to mate when in captivity! Problems that makes them very unsuitable for captive breeding programs.

As well as inbreeding depression, captive breeding programs have two other serious problems. The first is that keeping many animals of the same species in a small confined space that often has poorer than desirable hygiene means that the spread of infectious diseases becomes very likely (unless a vaccination against the disease is available). This can be disastrous for the recovery efforts of a species, which is highlighted in the case study of the before-mentioned black-footed ferrets where canine distemper killed all of the first ferrets that were taken into captivity! Sadly this could easily have led to the extinction of the species as more individuals had to be removed from the wild - an example that highlights the final disadvantage of captive breeding programs: removing individuals from an already dwindling population could actually push the species into extinction in the wild, as there may be too few left to breed successfully! Unfortunately, there is no way around this problem and all conservationist biologists can do is make a decision on what they think would be best for a species in its own specific case of circumstances and hope that it's the right one!

So in conclusion, captive breeding programs are undoubtedly very effective measures for preventing species from becoming extinct. However, due to the lack of space that is available and the unsuitability of some species for such schemes, they cannot be used to save every endangered species of animal so we must also take measures to preserve them in-situ in the wild. Often, this is accomplished by protecting animals from hunting under law and by setting up designated animal reserves or parks that specifically aim to protect them and conserve nature (click here for a recent example of a national park).