Imagine you are in a forest on a dark still night. You travel along a path, you feel the intense gaze on your back, a bush rustles, a twig snaps. The sounds follow you as you continue; you decide to run back to camp. Within seconds you hear a scream behind you. You pick up your pace. Something crashes through the thick forest behind you. You turn around and see glowing green eyes. Then it goes black as its body collides with yours.

That is one of the worst nightmares a person has: The fear of falling prey to a predator. It has been ingrained into the brain since the first-eyed prey could see predators coming. Predator/Prey interactions are driving forces of evolution. Native prey will always tend to be harder for the native predators to hunt. The predator/prey interaction plays a crucial role in biodiversity and psychology, as well as how invasive predators are disrupting the natural balance of ecosystems.

All species have been affected by predator/prey interactions. In many organisms there are physical defenses such as camouflage, spines and venom. There is also a psychological defense in the form of habits and tactics that can save prey from a predator's jaws. Take humans, for example, we are physically weak - no fangs, fur, large muscles, protective fat, in contrast to the strength many animals related to us have. However, psychologically we are very strong as group animals: Tool constructors and problem solvers.

Research claims that before wolves were released back into western Wyoming the elk herds were fat, dumb and happy, unaware there was anything out there to prey upon them. The elk herds became so large; they devastated native flora thus cracking and unstabilizing the other fauna as well. Within decades of wolf reintroduction, the elk populations have decreased, and the affected flora and fauna are recovering. Now the once slow and unafraid elk are fast and fearing creatures, much more jumpy and always on the look out for predators.

According to one study, a few small parts of the brain control fear. If these areas are tampered with, mice will show little or no fear.

A group of neuroscientists led by Larry Swanson of the University of
Southern California studied the brain activity of rats and mice exposed to cats, or to rival rodents defending their territory. Both experiences activated neurons in the dorsal premammillary nucleus, part of an ancient brain region called the hypothalamus. Swanson's group then made tiny lesions in the same area. Those rodents behaved far differently.

"These animals are not afraid of a predator," Swanson said. "It's almost like they go up and shake hands with a predator."


A similar thing appears to happen with the teenage brain. As many know teenagers may act as if they are invincible. This has to do with small parts of the brain not functioning properly.


An examination of the brain activity in the adolescent mice showed that the two areas of the brain associated with processing experiences of fear — the basal amygdala and the hippocampus — were exhibiting lower levels of activity.

This is the key to understanding fear.

In theory, the fear response can be stopped by altering certain parts of the brain. However, fear is what keeps us alive. If I am too afraid to jump out of a plane or go off a waterfall in a barrel, then my chances of survival are greater than if I do not fear those things and actively do them. But with too much fear, I will go nowhere. This is how natural selection, or evolution, works with fear: If I have no fear, I die, if I have too much, I die, but if I can strike a balance, then I can live.

The physical and psychological sides of fear impact evolution. Depending on where a creature is located, the physical and mental needs differ. Species that share a common ancestor but are on separate land masses, with different predators and environments, will differ. This creates biodiversity.

Biodiversity is the variation of life. Predator/prey interactions drive this as the predators eat those who are physically weak. For example, if two geckos live on a tropical green island, one gecko looks like bark and almost invisible and the other is dark blue and obvious. The dark blue ones will be eaten more often than the bark ones because they are easier to find. The blue ones evolve to be smaller and quicker than their counterparts to avoid being eaten. The bark-like gecko just cannot be easily found therefore, their will likely be more bark geckos than blue ones.

Prey is an evolutionary step ahead of the predator, but the predator is close behind. It is an ongoing tug-of-war. If the prey can out smart or outrun the predator, the prey wins. If the prey is caught, then the predator wins. The stakes are also unequal: If the prey wins the predator misses a meal, if the predator wins, the prey loses its life. This is what keeps a species healthy. Predators weed out the weak, sick, injured, or physically unsuitable allowing the healthy ones to live and pass on their genes. Killing a sick prey helps stop the disease from reaching healthy animals.

A good example of this is the relationship between tuna and mako sharks. These are two of the fastest fish in the sea. Tuna try to out swim makos and the mako is always evolving to be faster. This has shaped the two species. The tuna's and mako's muscles have evolved similarly and so have their tails. These two fish have been racing against each other for million of years, so over time each has gotten faster.

What happens when the perfect balance is disrupted? When new predators just show up without giving any time for prey to adjust? Native animals begin to loose ground and can become endangered or extinct. This happens when invasive species arrive in a new ecosystem. Invasive species must be removed to preserve native species of flora and fauna. Islands are perfect examples because each is like a miniature world, different from each other, with unique life, and unique ecosystems. Guam and New Zealand are two islands struggling against invasive species.

Guam is a small island near the Marianas and the Philippines. It is a US territory. It was and is a home to unique birds, reptiles, and insects. During World War II ships from New Guinea brought a "weapon of mass destruction." Not the atomic bomb, but a long, thin, aggressive, and scaly creature, the Brown Tree Snake. These snakes are perfectly adapted for killing birds. The birds that had no clue these snakes were bad. Guam was reduced to a nearly bird-less rock in the Pacific. The snakes now thrive, by eating other invasive species because they have decimated the native ones.

The main victim was the Guam Rail, or Coco Bird. Guam Rails are flightless and were found nowhere else but Guam. These rails are now extinct in the wild. Effort has been put into moving rails onto nearby islands. However, the rails are not returning to Guam. Fortunes may yet turn for these birds as quite a few live in captivity. But until Guam's snakes go, these birds cannot return.

New Zealand is much larger than Guam. It is the ultimate land of birds. There are no mammals with the exception of several bat and seal species. The world's largest bird once roamed New Zealand's forests, the Giant Moa (like an 11 foot tall Emu). It is a land of living fossils. From the last member of sphenodontia family, the Tuatara, to giant cricket-like insects known as wetas. It is home to many unique plants. Since the arrival of man, New Zealand has been constantly bombarded with invaders. Almost half of New Zealand's plants are now invasive, and non-native animals roam freely, this includes koi carp, Himalayan Tahr, Acacias, and many weeds. Deer and other herbivores have ruined forests and grasslands, displacing native animals.

Many animals lost out in this invasion. Native birds of New Zealand have evolved to hide from eagles and falcons which hunt by sight. Camouflage and standing still kept them alive when there were no carnivorous mammals around. These tactics which were designed to help the animal stay out of the reach of birds of prey, but mammals hunt based on smell, for example bloodhound follow scent trails to find prey. Several birds on New Zealand have interesting smells so the invasive mammals can easily find them.

Of New Zealand's birds that remain, the Kakapo, or Night Parrot (in Maori), is the best example of invasive mammal predation. Kakapo live on two small, predator free, islands. That number is due to the hard work over the past forty years by the Kakapo Recovery Team and New Zealand Department of Conservation. The Kakapo's native predators are the New Zealand Falcon and several extinct avian predators. Kakapo have very cryptic camouflage and can disappear into their surroundings. They are nocturnal so they can avoid contact with eagles and falcons. However, they smell like old violin cases, because of this, Kakapo are very susceptible to invasive predator attack, mostly cats and stoats. Kakapo also have a habit of jumping out of trees when threatened to get out of a raptor's way. Kakapo, in theory, could defend themselves from cats and stoats, as they are rather large birds. However, Kakapo has never had to defend themselves against mammals in the recent past.

Removing invasive species is hard. Although they do great damage to native ecosystems, some people oppose it. Even if people want them removed, they may oppose the means if they think it is cruel. Also, killing every individual of an invasive species in a large area is nearly impossible. For small scale eradications, live trapping is the humane and least controversial way. One of the best ways to get rid of invaders, and make money at the same time is to get a market for it. Such as fur coats made from an invasive mammal or sell an invasive fish for food at markets. If invasive species cannot be eradicated, then biosecure areas may be these animals' only hope for survival of the species. Biosecure areas are refugee camps for biodiversity, designed to keep out unwanted invaders. Fences keep out predatory mammals. Small islands are good biosecure areas because, surrounded by the sea, it is difficult for non-native predators to invade. Hopefully invasive species can be controlled and biodiversity of islands and elsewhere can be preserved.

Elk in Wyoming are not endangered by the reintroduction of wolves because they were still physiologically adapted to escape predators. However, island birds have not interacted with mammalian predators for millions of years and were not prepared for the invasion.

Fear is an evolved behavior. Without it, survival is questionable. Animals that are introduced to unfamiliar predators have not evolved to fear that animal, thus making it easy prey for the new predator. Fear protects biodiversity.

Quotes from:
"New Perspective on What Part of the Brain Controls Fear." THE MEDICAL NEWS | from News-Medical.Net - Latest Medical News and Research from Around the World. 10 Mar. 2009. Web. 22 Oct. 2011. <http://www.news-medical.net/news/2009/03/10/46704.aspx>.

"Brain Changes Explain Why Teens Have No Fear." PhysOrg.com - Science News, Technology, Physics, Nanotechnology, Space Science, Earth Science, Medicine. 10 Jan. 2011. Web. 22 Oct. 2011. <http://www.physorg.com/news/2011-01-brain-teens.html>.