Apex Predators

 

If you were to ever turn on your TV and watch the National Geographic channel you would most likely be bombarded with an extremely enthusiastic American narrating a documentary on sharks or lions. Words and phrases such as, ‘massive’, ‘deadly’, ‘teeth’, ‘no chance’, ‘can’t escape’, ‘torn limb from limb’ and ‘death’ make frequent appearances in the over-dramatised script. Another favourite is, ‘apex predator’… Yes apex predators are terrifying. I would rather not meet one late at night in a dark alley. If it were a killer whale I would have a few poignant questions before running away as fast as I possibly could. Despite their deadliness and rather almost because of it, apex predators have an extremely important role in the environment.

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Killer whale and her calf

Apex predators are organisms that are the top predators. Their only predator is usually humanity and the habitat destruction caused by said species. They have their pick of species to prey upon and do not have to settle for finding bugs under a log (Simba I’m looking at you). Well known apex predators are: lions, tigers and bears (oh no), great white sharks, crocodiles and killer whales. They are often referred to as, ‘the world’s most deadly predators’.

We all know that as beautiful and fascinating apex predators are, they scare the pants off any sane human but why is it that they are so important to the environment? People have written theses on small sections of that question. So as not to bore anyone to death, I will provide a few select examples that demonstrate the importance of apex predators whilst showing the extent of human influence on these organisms.

Village demolition by snowball

My apologies I know I said I’d talk about animals but first I really need to explain a critical part of theoretical ecology. When people argue against conservation or animal rights a common argument to hear is that, “man is the top of the food chain”. There isn’t the strongest argument because there isn’t really a food chain as such. Elton John was closer with there being a circle of life and a wheel of fortune. There is not really a top organism even when taking humans into account. A circle, whilst a better analogy than a chain, is still not quite right because a circle would imply that all parts of the circle are equal. Whereas, in the environment there are some factors that are more important than others. A clock with all of its beautifully machined cogs working together is beginning to near closer to the truth.

This brings me to the concept of trophic cascades. Do not panic at the new phrase. Trophic comes from the Greek, τροφή(trophē) which simply means food. A cascade is something that pours downwards often at a rapid rate. A trophic cascade passes down trophic levels (food level). Trophic levels are just another way that ecologists can group together organisms. The most basic trophic levels: producers (e.g. trees and herbs), consumers (e.g. deer, lions) and decomposers (e.g. bacteria and fungi).

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A trophic cascade is a reference to an event or circumstance that effects a specific trophic level (food level). The effect trophic level’s subsequent reaction then effects the corresponding trophic levels. Imagine you’re standing on top of a snow covered mountain and the conditions are perfect for the snow to stick to itself. You roll a snowball down the mountainside and as the snowball rolls down the mountain the snowball grows due to the snow it has gathered on its journey. That snowball grows to such a size that it wipes out the village at the base of the mountain. Highly unlikely event but that is a simplified version of what happens in a trophic cascade. The more important the organism in the environment and the greater the severity of the event the bigger the snowball. Another anaology would be the ripple effect. The bigger the stone and the greater the force behind it the bigger the ripples will be when it is thrown into the water. When humans manipulate the environment they are essentially rolling snowballs down a mountain or throwing rocks into a pond completely oblivious to the exact amount of damage we’re causing.

Why we can blame global warming and shark fin soup for all the red devils in the water

The humboldt squid (Dosidicus gigas) or diablo rojo (red devil) occupies the humboldt current off the coast of South America. They can grow up to 2m in length and weigh 50kg. Their Spanish name, diablo rojo, is rather apt due to their aggression and ability to flash red and white. They use this bioluminescence (flashing colours) to communicate with eachother and co-ordinate their attacks with deadly precision. They come equipped with a beak situated on the underside of their mantle. If you thought a cockatoo beak was menacing think again…. They’re highly intelligent and their behaviours are mostly a secret to humans due to their preference of lurking in the deep water whilst they are not hunting.

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Humboldt Squid

Humboldt squid are an apex predator but their populations are thought to be controlled by sharks. This control is thought to be possibly related to the short lifespan (up to two years) of Humboldt squid. Shark populations are currently under pressure due to multiple factors but primarily: over fishing (limited food supply for the sharks), shark fin trade and humans hunting them due to their infamy. With fewer sharks around to control humboldt squid numbers their population is booming. They have subsequently expanded their natural range. These changes have been aided by a rise in sea temperatures. If the sharks were in great enough numbers humboldt squid migration may have been slowed. With limited predation, they are sure to conquer their new territories quickly.

Cassowary drumsticks on steroids and Eagles on stimulants

Haast eagle (Harpagornis moorei) also known as the Pouakai, giant New Zealand eagle or Te Hokioi was the apex predator of New Zealand. The etymology of the genus Harapgornis is harpago + ornis. Harapago is a roman graplling hook that was shot by a catapault to aid in the boarding of enemy ships. Ornis is the ancient greek for bird. Therefore the Haast eagle is the grapling hook bird. In the 1870s the remains of a Haast eagle were discovered confirming the truth in the Maori legends of a giant man-eating eagle. It is thought that it became extinct around 1400.

 

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Haast eagle hunting moa

Why did the Haast eagle go extinct in 1400? There was nothing that could predate upon a live adult Haast eagle. There were no other extinction events at this time (e.g. meteor destroying all life on the face of the Earth). The answer lies in the remarkable migration that began a mere 150 years prior. This was the migration of the Maori.

 

The haast eagle was mind boggling big and probably lived on cliff edges when it was not soaring high above the forests. So it was a massive, massive creature that lived out of reach of humans. It is therefore considered unlikely that the eagles were hunted to extinction by the Maori. An alternate and much more plausible theory to the extinction of the Haast eagle was that they lost their prey source. Their main prey was the Moa which is a much larger and frankly much scarier version of the cassowary or emu. There were nine species of Moa endemic (simply put they’re not found anywhere else) to New Zealand. The Haast eagle was their only natural predator because the only creature to take down a cassowary on steroids is of course an eagle on stimulants twice as strong….

 

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Moa

The arrival of the Maori however changed this relationship. The Maori prolifically hunted the Moa. This could have been to utilise the resources of the Moa (i.e. massive drumsticks and wonderful feathers) or because the Moa are terrifying dinosaur birds and the Maori probably didn’t take to kindly to the idea of being eaten. Or perhaps the Maori hunted them for sport. It’s hard to determine why the Moa went extinct but they did which meant that the Haast eagle also became extinct and New Zealand lost its apex predator.

 

As previously mentioned there were nine separate species of Moa each differing in size and shape. However, on average just assume that they were larger and more solid than an Ostrich. The Haast eagle ate Moas…. They preyed on live, adult Moa…. Just think about that for a minute. A Haast eagle’s primary way of sourcing food was to take down a chunk of muscle bigger than an ostrich running through forest that would writhe and squirm until dispatched. Yet humans are responsible for its demise within 150 years. Keeping in mind that the rifle would not be invented for several hundred years.

Warty bags of poison (cane toads)

Cane toads are not apex predators. They are an excellent example of what happens when the apex predator is not around to control them. Cane toads take adaptation to the extreme. The little devils are able swim in salt water… You know how your fingers go wrinkly when you’ve been submerged in the water for a while? That’s because your body is losing water through a process referred to as osmosis. You, as a human, have a thick layer of skin that aids to slow this process down whereas a toad does not. They should be swivelled prunes pretty quickly but nope, they decide to be freaks of nature and swim in the ocean. Sorry back onto the topic… Toads can adapt to virtually any environment you put them in. The only thing that can really stop them taking over the globe is they are yet to make it to Antarctica alive (unless a scientist took one as a pet that I have not heard about) and predation. Their natural predators are: caiman (South America’s version of crocodiles); select species of catfish, eels and ibis; banded cat-eye snake and bullet ants.

If an animal can adapt to practically anything and has no predators there is nothing to stop it. Especially in the case of the cane toad where if anything tries to eat it they will die from ingesting the toad’s poison. This makes it very difficult for animals to become predators of the cane toad. Luckily for us Australian animals tend to be stubborn and rather persistent. Tawny and Papuan frogmouths have successfully eaten cane toads. Crows and ravens are well known for flipping the toads over and eating everything except the poison sacs. Keelbacks (a water snake) have small heads compared to their body which means that can only eat small cane toads that come with a smaller amount of poison. Due to their size they the keelbacks can endure these small doses of poison. The cane toads are at such high numbers that the likelihood of the Australian wildlife retaking their land is unfortunately unlikely without human influence.

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Tawny Frogmouth (Podargus strigoides)

New Zealand

You’re quite right New Zealand is not an apex predator. New Zealand is famous for: sheep, lots of birds and being the backdrop to Peter Jackson’s adaptation of Lord of the Rings and the Hobbit. From an environmental viewpoint, New Zealand is extremely fascinating for a number of remarkable reasons including the previously mentioned, ‘lots of birds’. Any island will always draw the eye of an ecologist. This is essentially because an island is nature’s version of a contained laboratory. The only organisms that can travel back and forth from an island have to be able to swim, fly, or cling expertly to driftwood.

New Zealand has no native mammal species bar three species of bat. In place of mammals, birds and reptiles have adapted to every possible environmental niche. Adult animals subsequently had few predators. One bird species in particular decided that it was so safe that it might as well give up on flying because it takes too much effort. I am of course referencing the kakapo. A bird so evolutionarily deluded that it forgets that it can no longer fly but this does not stop it jumping out of a tree and trying…

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Siroco the kakapo mating with Mark Carwardine’s head as Stephen Fry watches

What would happen to such innocent, naive species if you introduced cats? They get eaten… Or what about rats? They get eaten… What is there in the wild to control the introduced pests (e.g. brush-tailed possums, rats, cats, goats and rabbits)? Pretty much nothing because New Zealand wildlife has been closed off rest of the world while mammals and marsupials evolved. Any native organisms that are capable of preying upon these new pest species will have to learn that they can predate them.

Wolves equal more beaver dams

There is often news in the media about the latest drama in relation to the re-introduction of wolves to their native habitats. Being an Australian it is easy to remain distant to this issue and be unable to empathise with anti-wolf advocates. Wolves are beautiful, intelligent and marvellous creatures but it is important to remember they are also ever so slightly deadly… The facts tell us that you are unlikely to ever be a victim of a wolf attack even when living in wolf country and there are precautions you can take to lower even that small possibility. Precautions such as not wearing a suit of meat and running past a wolf den screaming, “come and get it!”. However, I can understand that even with this information people would be jittery at the idea of a pack of intelligent creatures with mouths filled with extremely sharp teeth wandering outside their home.

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Grey Wolves

Another reason for the negative view on wolf preservation and reintroduction is the fear they will predate upon livestock. Although, the areas in which wolves are being reintroduced tend to be more remote and within natural resource reservations such as National Parks which diminishes the chance of livestock predation. There is also a disbelief amongst the public that wolves never inhabited areas in which they are being re-introduced. The most contentious of these is Yellow Stone National Park. This belief has arisen due to the slow disappearance of the wolf from these areas leading to their inhabitance being lost from living memory.

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Anti-wolf sentiment

Why are wolves being reintroduced? If the media is to be believed it is an issue that many people feel extremely strongly about. Unfortunately, while people are screaming they can not hear the reasoning being delivered to them (that comment is for both sides of the argument).

Wolves are being reintroduced to their native territories primarily because they are living organisms and what right do humans have to take their existence away. The second reason is even more important. Wolves are apex predators. Their reintroduction to Yellowstone National park is a classic and wonderful example of the importance of apex predators.

Wolves were considered extinct in Yellowstone National Park in the 1930s. Up until this point they had preyed heavily upon elk. The remaining large, mammalian predators were the black and grizzly bears, coyote and cougars. These predators did predate the elk but not to the same extent as the wolf. The absence of wolves in the area allowed the elk population to boom. An increase in population meant there was an increase in consumable resource utilisation by the elk (i.e. food and water). This meant that less dominating animals in the same trophic level (require the same food as the elk) began to suffer as there was less food for them. This was particularly evident in the case of the beaver and its food sources of willow, aspen and alder. This effect was exacerbated because the elks were no longer being heavily predated, they had less inclination to migrate. The willow stands became severely effected by this heavy predation. Less willow means the beavers not only have less food but less timber to build their dams. Without a properly constructed dam the beavers natural behaviours such as reproduction are severely hampered.

When wolves are present elk behaviour changes. As mentioned before the elk move more frequently. They also break into smaller herd groups which places less stress on the environment. The elk feed less as they must remain constantly vigilant for wolf attack. If wolves are present to limit the elk numbers then the elk are less likely to destroy habitat due to their large population and resource requirements.

It is clear that the presence of wolves in Yellowstone National Park allows for a better functioning ecosystem. If elk numbers are controlled it is not only beaver populations that benefit but they are the most commonly used example.

 

Overall, apex predators are yes very scary but also very important. Without apex predators there is chaos. An over generalisation is that without wolves in Yellowstone there are fewer beavers and without sharks Humboldt squid might take over the Earth.

 

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