Predator-Prey Interaction

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Abstract Predators are animals that kill for their food; they must do this in order to survive. There has been controversy about predation in some areas including the re-introduction of wolves into the Yellowstone National park area and other areas. Predator-prey relationships are both beneficial and detrimental to some species. The weakest and unhealthiest become dinner for those predators and also become a positive thing for the species that only the strongest of the herd will survive and continue to reproduce. Some types of prey have defense mechanisms which fight off predators.

Survival of the fittest is the best explained phrase for this type of ecological interaction. Introduction Predator-prey relationships are a common interaction found in every type of ecosystems and communities. A predator is an organism that kills for their food. They must kill in order to survive. The prey is the organism being killed for food. Predation is an interaction where it is a +/- interaction. This could be related to animals killing animals, but the same concept is in other interactions such as bear eating berries or other insects eating leaves. If the predator doesn’t eat, it dies.

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Throughout the years, with evolution, animals have adapted to become better predators and prey has become harder targets. Predator-prey relationships are unstable. I will explain more about this throughout this essay in different species in different types of ecosystems, and the impacts of this type of interaction. Predator/Prey Interaction and Evolution Predator-prey relationships are a +/- interaction. The prey is killed and the predator gains energy and nutrients. Predators are the primary movers of energy throughout the food web. When prey is abundant, predator population increases. It is a cycle that is continuous.

When prey numbers decline, the predators also decline, therefore the cycle rebuilds itself. If the prey population of the primary choice of predators declines, they learn to move on to another species of prey to suffice their needs. When this runs out, they are forced to leave the area, the primary choice of prey population will then recover, and the predators will eventually come back to the area. There are positive and negative effects of this type of interaction in all ecosystems and throughout time, predators and prey have evolved in different ways. Throughout evolution, predators have evolved in ways that make them better hunters.

They have become faster runners, so they can chase and capture their prey. Predators have a very keen sense of smell, sight and hearing so they can target the unhealthy and the weak prey for their food. Animals that are prey to predators have also a keen sense of smell and hearing so they can avoid becoming dinner. Some species have ways of camouflaging themselves to be less visible to their predators. For example, the snowshoe hare is white and has a better chance of blending in with its environment, in the snow, so the chances may be slightly less for being consumed by a predator.

Other adaptations that have evolved in predators throughout the years were predators becoming better runners to chase their dinners. Some predators can run up to 70 mph, the cheetah of course, which helps for catching their prey. But other predators can run up to 40 mph as well. They also have great stamina for long periods of searching for food; they can travel for longer periods of time and scout out wider territories. (Phillips and Smith, 1996) Predators can be predators and prey to something else as well. There are many predators that aren’t on the top of the food web, and they can be prey themselves.

A spider could be on a web consuming an insect lunch. A lizard could have its tongue ready to strike and slurp up the spider; meanwhile there is a roadrunner behind the lizard, ready for a snack. And an hour later a coyote preys on the roadrunner. This is the food web of life in an ecosystem, and if a link is lost there could be a result of losing populations to a certain area. Predation and prey interactions keep the circle of life going. Benefits of Predation When a predator makes a kill, it feeds not only them, but other species as well.

For example, if there is an elk kill, this will feed other predators like bear, mountain lion, coyotes, eagles and others. Smaller rodents and other scavengers, like ravens will also benefit from a kill. We are predators ourselves we have to kill to eat, just most of us don’t do it ourselves, if we are meat-eaters. What we don’t eat can go to the dogs and feed them. Bacteria and other parasites can also join in on the fun. Other things we don’t eat, can go to compost, so there are many ways in which predation benefits the food chain.

It definitely feeds various links on the food web. Predation is also used to control populations of certain problematic species, such as snails, which pass certain types of diseases to other species including humans, as explained by Molles. They have used crayfish in some places such as Kenya and other East African countries to control a problematic snail population. (Molles, 343) This happens here at times also, with introducing species that will eradicate problem species or invasive species that are taking over watersheds and other ecosystems. Predator Body Systems

Predators can be birds of prey or carnivores or anything that must kill for their food. Predation is the interaction between the predator and the prey itself. All of life exists, because something else dies and predators kill to gain the food they need to survive. When predators seek their food, they target the easiest possible prey they can find. All predators have evolved with great skills of achieving this. They are great athletes, they are fast runners, they are strong and have specialized bodies and teeth needed to eat raw meat and claws and talons to delve into the skin and bodies of their prey.

For example, predators have longer, serrated teeth and canines for stabbing and killing their prey and they have cutting teeth called carnassials, which act as a shearing tool to cut up the meat. They don’t chew much; they swallow large chunks of meat whole. They must have a strong jaw and powerful muscles and heavy skulls to work into killing their prey and digging into feed also. For example, a jaguar has such strong powerful teeth; it can bite right through the shell of a turtle. Another example is of a hyena which can bite right through the bones of their prey to get to the marrow inside the bones. Phillips and Smith, 1996) Carnivore and predators digestive systems are rather simple. They have small stomachs and they are able to gorge themselves with a lot at one time and then not eat for days at a time. Most carnivore’s digestive systems are adapted for processing large amounts of food at one time quickly and efficiently. They end up processing most of the meat and fat into nutrients, excreting only fur and bones in their feces. For wolves, they will eat up to 20 pounds of food at one sitting, gorge themselves and sit and digest for hours after or go back to the den and regurgitate their dinner for the pups. DOW, 2009) Ocean Predators A starfish is one type of predator in their ecosystem. I have viewed this myself in my salt water aquarium that I have set up in my home. The starfish is the main predator in my aquarium and since I have owned it, it has eaten every one of the snails I put in the tank. They use their tube feet and move to where the snail is, suction to it with its mouth and suck the snails out of the shells. Sharks are the main predator in ocean ecosystems. In the Great Barrier Reef, there is a problem with the crown of thorns starfish.

They are eating away at the coral in their paths, they are eating machines and the reef is suffering from this species. An individual sea star can consume up to 6 square meters of the reef in one year, and that’s only one starfish doing that much damage. This is happening due to the fact that the predators that are preying upon these starfish are diminishing, the crown of thorns starfish’s predators include the hump head wrasse and the giant triton, the population of these have decreased due to overfishing. (Green Diary) Birds of Prey

Birds of prey including the bald eagle, vultures, hawks and the golden eagle are also considered predators. They usually take down young livestock, but are also capable of killing adult livestock. Most large animals that they feed upon were more than likely found and already dead. They have talons and curved beaks to rip into their prey and gorge themselves. They swoop down with talons out; they have three front talons and one in the back called the hallux. They hit their prey and clench their talons; they can puncture the lungs of the calves when the talon strikes the shoulder.

They will gorge themselves and not eat for a few days after. They eat slower than other predators and they tend to eat one side, flip the prey over and eat the other side. Said to be the most powerful of all, is the golden eagle. In Alaska, the golden eagle is known for preying upon Dall sheep lambs and even caribou calves. Golden eagles will team up to hunt sometimes and work together for their food. They also prey heavily on snowshoe hare and other rodents. It was actually observed that these eagles were taking down healthy calves, and not just the weak.

They basically are going for whatever is moving. The calf deaths usually happen within one week of life. If a mother sees an eagle coming she will try to defend her caribou calf by pushing the calf under her, and even striking at the eagle with her front feet. This has been observed on occasion; eagles have a hard time fighting back while stooping to try to fight for the calf. (Woodford, 2004) Defense Mechanisms Some organisms of prey have ways of “fighting back” against predators. Every organism has at least one type of defense mechanisms within their bodies.

They have very different defense mechanisms, some have poison, sharp quills, chemical defenses and some have other adaptations that aid in preventing predation. I find this extremely interesting and amazing, with some of the things that different organisms can do to avoid falling to prey. Some animals just run away and are very quick at it; wouldn’t that be your first response? Some fight back, and others have means of camouflage to hide into their surroundings to avoid predators, like chameleons, which can change their skin colors to match with their environment to avoid being seen.

Some organisms use trickery and have adaptations that may resemble those of an organism that a predator will avoid eating. Possums will “play dead” and even go into a semi-comatose state to trick the predator into not getting the excitement of the kill, or it can foam at the mouth to trick the predator into thinking its sick or toxic to avoid being eaten. Some species have sharp quills or other defenses, for example the porcupine has quills which make them hard to consume. Other species of ungulates have antlers and horns to try to defend themselves.

They can gore their opponents with their horns or antlers in order to survive. Some have hard outer protective shells, like turtles which make it harder to get to the turtle through the shell. Other species use chemical defense mechanisms to scare off predators. For example, the skunk has a powerful anal musk which it sprays on victims, and if sprayed directly into the eyes, the victim can go blind. Potato beetles will cover themselves in their own poop to defend themselves against predators. That is nasty, but effective! Another example of defense mechanisms is the horned lizard which already has the horns, but trangely fills up its sinus cavities with blood and squirts blood from its eyes to its attacker. Even a sea cucumber has some crazy defense mechanisms. It can actually change its body from hard to liquid and basically turn their bodies inside out; they have a toxic juice in their digestive tract to poison their enemies. It can actually go to liquid and seep through cracks and re-absorb water to inflate themselves again! It’s absolutely amazing how they try to defend themselves. Some species have strong feet to stomp their attackers, like kangaroos, they also use their tail for defense.

There is actually an ant, the Malaysian ant, which can explode when they are stressed. Their bodies actually explode under threat, and they die, but they sadistically wait for a victim to threaten them to do so. The Soldier ant has toxins that when threatened they excrete poison from their abdomen, their glands swell with this toxin and explode spraying their victim with this poison. And one last example is the hagfish, which when threatened, secretes this suffocating oozing slime from its pores and envelopes their predator in this suffocating goo.

But sometimes, the hagfish falls prey to its own goo, and ends up twisting itself into knots trying to escape its own oozing slime. (Web Ecoist, 2008) Predation Controversy Throughout the years, there has been much controversy with predation control. Even in 1975, according to Thefethen, it was said to “kill all grey wolves. ” (Trefethen, 1975) Farmers have lost numbers of livestock to predators because they would find areas where food wasn’t available, livestock would fall prey to predators in the area.

Cattle and other livestock have been lost for various reasons and according to the Defenders, there are many other reasons that cattle are dying, and that predation is low on the scale of causes. (DOW, 2005) See the graph below to see how the Defenders of Wildlife see how livestock is being killed in comparison to the USDA and farmers and producers. ? According to the USDA, who has a program that helps to recover costs lost on livestock lost due to disease and predation, $71 million is lost to ranchers and producers annually due to predation.

Sheep are most likely to fall prey to predation and coyotes are most likely to cause the most damage on livestock. Another study that was done through the USDA found that in the year 2000, coyotes were the biggest cause of most cattle and calf loss at 65% of the deaths from predation in the United States in livestock. The producers and farmers are not using proper methods of scare tactics to save their production, so with the help of the Wildlife Services, they help farmers and producers to use better tactics to retain their production.

The National Wildlife Research Center is testing non-lethal methods for preventing so much livestock loss for producers. They have used non-lethal methods such as lights and sirens and in Idaho where wolf predation is high, they have installed something called a “wolf-alarm” that is radio-controlled and used to scare off the wolves. (USDA, 2009) Yellowstone Wolves and More Controversy Back in the late 1800’s and early 1900’s, before the National park Service was formed, the Army was brought into Yellowstone and other areas to kill all predators.

It was thought that they were blood thirsty, ruthless man killing machines and all predators should die. In the years 1904 to 1908, a total of 63 mountain lions and 196 coyotes were killed by Army. Theodore Roosevelt sent letters asking the military to stop killing these predators in Yellowstone, his plea was ignored. In the next nine years, 23 mountain lions, 1,188 coyotes and 18 wolves were killed just in Yellowstone alone. It wasn’t until 1933 when the National Park Service took over, did the needless killing stop. A total of 132 wolves were killed during the wolf wars.

After many years of fighting for the reintroduction of wolves in Yellowstone, finally in 1995, wolves were reintroduced in the park. Eight wolves were introduced and throughout the years the population of elk and other species have benefitted from this, along with vegetation and other positive results from the introducing of this predator to this area once again. (Phillips and Smith, 1996) There is still controversy out there about wolves as killing machines, especially hunting outfitters and hunters are worried that the wolf population is doubling and are going to decimate the elk population.

Elk are the wolf’s primary prey, so this is a concern. How has the elk population changed since the reintroduction of wolves in 1995? According to the Montana fish, wildlife and park service in 2005, the elk population percentage in the area slightly increased in the years 2002 through 2005. The wolf populations in the park are being controlled through the U. S. Fish and Wildlife bureau. They have had to issue shoot-on permits and have shot wolves themselves to control the population, due to panic among agriculture and farming livestock, where there have been instances where wolves have come into farmland and killed livestock.

Observation based estimates, have concluded that there should be approximately 1. 4 to 2. 2 elk per wolf per 30 days. There is ongoing research being done through various organizations and only time will tell what the future will hold for the Yellowstone wolf population. (Preston, 2005) Conclusion Predation is a positive and negative interaction. Though there has been much controversy on this topic, hunting predators for predator control is being used in some areas with problems and other things are being done to prevent livestock from falling prey to predation.

There will always be controversy on this subject, because as this country and all countries grow, we are taking away space from everything that lives here as well. This makes it difficult to find a balance in these ecosystems and will continue to be an issue. And humans, as predators ourselves, we need to eat, just like everything else that lives, so we need to find a common ground where we can all live together in harmony. Molles MC. 2000. Ecology: Concepts and Applications, Fourth Edition. New York, NY: McGraw Hill Education. 343-344 p. Trefethen JB. 1975. An American Crusade for Wildlife.

New York, NY: Winchester Press. 409 p. Hausman L. 1948. Birds Of Prey. New Brunswick: Rutgers University Press. 165 p. Phillips MK, Smith DW. 1996. The Wolves of Yellowstone. Stillwater, MN: Voyaguar Press. 128 p. Preston, Charles R. , curator, Draper Museum of Natural History, Points West article. “Living on the Edge: Wolves and Human Communities in the Greater Yellowstone Area. ” Spring 2005 issue. http://www. bbhc. org/pointswest/PWArticle. cfm? ArticleID=179#top Accessed 25 July 2009. Defenders of Wildlife. “The basics of Wolf Taxonomy and Biology and Predation. ” 2009. Accessed 20 July 2009. http://www. efenders. org/programs_and_policy/wildlife_conservation/imperiled_species/wolves/wolf_facts/biology. php “Trophic Links: Predation and Parasitism” 2005. Accessed 26 July 2009. http://www. globalchange. umich. edu/globalchange1/current/lectures/predation/predation. html Woodford, Riley. “Alaska’s Most Powerful Bird of Prey. ” Alaska Wildlife Conservation News. 2004 December. Accessed 26 July 2009. http://www. wildlifenews. alaska. gov/index. cfm? adfg=wildlife_news. view_article&articles_id=94&issue_id=21 “Predator Starfish Wiping Out The Great Barrier Reefs Dramatically. ” Green Diary April 2007.

Accessed 26 July 2009. http://www. greendiary. com/entry/predator-starfish-wiping-out-the-great-barrier-reefs-corals-dramtically/ USDA. “Wildlife Services Protects Livestock. Assisting Ranchers and Farmers, Preventing Livestock Predation and Wildlife-borne Diseases Developing New Management Methods. ” Wildlife Services. FY 2004 report. Accessed 22 July 2006. http://www. aphis. usda. gov/ws/introreports/livestock. pdf “10 of the Most Bizarre Animal Defense Mechanisms” Web Ecoist. Nov 2008. Accessed 29 July 2009. http://webecoist. com/2008/11/04/9-of-the-most-bizarre-animal-defense-mechanisms/

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