Types of Interactions

1. Types of Interactions Most living things produce more offspring than will survive. A female frog, for example, might lay hundreds of eggs in a small pond. In a few months, the population of frogs in that pond will be about the same as it was the year before. Why won’t the pond become overrun with frogs? An organism, such as a frog, interacts with biotic and abiotic factors in its environment that can control the size of its population

2. Types of ecological interactions competition predation symbiosis parasitism mutualism commensalism

3. Limiting Factors Populations cannot grow without stopping, because the environment contains a limited amount of food, water, living space, and other resources. A resource that is so scarce that it limits the size of a population is called a limiting factor.For example, food becomes a limiting factor when a population becomes too large for the amount of food available. Any single resource can be a limiting factor to a population’s size.

4. In Japan, green herons make interesting use of the biotic and abiotic parts o ftheir environment. They will drop sticks and even bread crumbs into the water to attract fish. Sometimes, they wil lcatch a fish within 2 or 3 seconds of dropping the bait

5. Keystone Species: Although all members of an ecosystem have important roles, some members are more important than others to the overall integrity of the ecosystem. Such species are called keystone species. In the same way that removing an arch’s keystone causes the arch to collapse, removing a keystone species can cause the whole ecosystem to collapse. This occurred when the sea otter was hunted to near extinction in the kelp forests of the Pacific Ocean. With the otters gone, nothing was left to eat the sea urchins, which multiplied and ate all of the kelp. The kelp was home to dozens of animals, all of which disappeared, as did most of the sea urchins. When the otter was reintroduced, populations of all of these organisms returned!

6. Carrying capacity The largest population that an environment can support is known as the carrying capacity. When a population grows larger than its carrying capacity, limiting factors in the environment cause individuals to die off or leave. As individuals die or leave, the population decreases. For example, after a rainy season, plants may produce a large crop of leaves and seeds. This large amount of food may cause an herbivore population to grow. If the next year has less rainfall, there won’t be enough food to support the large herbivore population. In this way, a population may become larger than the carrying capacity, but only for a little while. A limiting factor will cause the population to die back. The population will return to a size that the environment can

7. Competition – two species share a requirement for a limited resource  reduces fitness of one or both species

8. When two or more individuals or populations try to use the same resource, such as food, water, shelter, space, or sunlight, it is called competition.Because resources are in limited supply in the environment, their use by one individual or population decreases the amount available to other organisms. Competition happens between individuals within a population. The elks in Yellowstone National Park are herbivores that compete with each other for the same food plants in the park. This competition is a big problem in winter when many plants die. Competition also happens between populations. The different species of trees in at the right are competing With each other for sunlight and space. Some of the trees in this forest grow tall to reach sunlight, which reduces the amount of sunlight available to shorter trees nearby.

9. Predation – one species feeds on another  enhances fitness of predator but reduces fitness of prey herbivory is a form of predation

10. Predators and Prey • Predator Adaptations To survive, predators must be able to catch their prey. Predators have a wide variety of methods and abilities for doing so. The cheetah, for example, is able to run very quickly to catch its prey. The cheetah’s speed gives it an advantage over other predators competing for the same prey. Other predators, such as the goldenrod spider, shown at the right, ambush their prey. The goldenrod spider blends in so well with the goldenrod flower that all it has to do is wait for its next insect meal to arrive.

11. Predators and Prey • Prey Adaptations Prey have their own methods and abilities to keep from being eaten. Prey are able to run away, stay in groups, or camouflage themselves. Some prey are poisonous. They may advertise their poison with bright colors to warn predators to stay away. The fire salamander sprays a poison that burns. Predators quickly learn to recognize its warning coloration. Many animals run away from predators. Prairie dogs run to their underground burrows when a predator approaches. Many small fishes, such as anchovies, swim in groups called schools. Antelopes and buffaloes stay in herds. All the eyes, ears, and noses of the individuals in the group are watching, listening, and smelling for predators. This behavior increases

12. 1. Chemical Defense • There are two main ways animals can use chemicals to defend themselves. • Animals can synthesize toxin using their own metabolic processes, or they can accumulate toxin from the food they eat.

13. 1. Chemical Defense Many animals accumulate toxin from their food rather than synthesizing it from scratch. For example, the larvae of Monarch butterflies accumulate toxins from the plants they inhabit.  Birds that eat the Monarchs vomit and learn to avoid them in the future.  Their bright coloration allows birds to remember and avoid them.  Photo courtesy of T. W. Davies, Cal. Acad. of Sciences.

14. 1. Chemical Defense • Animals which synthesize their own toxin are able to convert chemical compounds in their body to a poison. • There are many amphibians that produce skin toxins. The skin toxins are produced by special poison glands, usually located on the animal's back or throughout the skin. Photo courtesy of Dr. John Daly The poison dart frog has poison glands scattered all over its body.

15. 2. Camouflage Animals that camouflage themselves pretend to be something they are not. Either their coloration, marking patterns, or entire body resembles something else in their environment, here a leaf, an owl.

16. 2. Camouflage Here an aptly named walking stick pretends to be a twig, in an attempt to avoid being seen by a bird or other predator. This is an example of cryptic coloration. Photo courtesy of Dr. Lloyd Glenn Ingles, Cal. Acad. of Sciences.

17. 2. Camouflage In this picture, a four-eyed butterfly fish uses deceptive markings. The large spot near the tail resembles an eye. When predators attack the wrong end, the butterfly fish can swim away in the other direction!

19. Symbiosis – two species live together can include parasitism, mutualism, and commensalism

20. Parasitism – one species feeds on anotherBenefits one species but hurts the other

21. Mutualism – two species provide resources or services to each other BOTH benefit

22. Commensalism – one species receives a benefit from another species  Benefits one species does nothing for the other.

23. Exploring Relationships: In India, the chital, a small deer, has trouble finding enough grass to eat during the dry season. This deer relies on a certain type of monkey to get enough to eat. • Can you guess how the monkeys benefit the deer? • Which species benefit from this relationship? These deer have keen eyesight, hearing, and sense of smell. They therefore warn the monkeys of predators. Which species do you think benefit?

24. The honeyguide, a small African bird, lives up to its name. The purpose of its song is to lure nearby creatures to a nest of honeybees it has found. Many animals have learned to listen for this bird! Baboons, mongooses, ratels (or honey badgers),and even people will follow the bird in order to claim the honey. Out of harm’s way, the bird waits for the leftovers: bee larvae. The bird’s unique digestive system allows it to eat wax as well. • Which animals in this story are in a mutualistic relationship? • Which animals are prey, and which are predators?

25. 1. Acacia ants live on the bullhorn acacia tree, which provides the ants with food and shelter. The ants deter grazing animals from eating the tree. What type of relationship is this? 2. Plants called epiphytes, such as certain orchids, live on other plants, which provide only a place to grow. Epiphytes absorb sunlight, water, and nutrients from their surroundings and make their own food. What type of relationship is this? 3. There is a tiny wasp that lays its eggs in a variety of other insects, such as caterpillars, spiders, aphids, and flies. The wasp larvae feed on the host insect and eventually kill it. What type of relationship is this?

26. a relationship between two organisms in which one benefits and the other is not affected • an organism that eats all or part of another organism • a relationship in which two different organisms live in close association with each other • an organism that is killed and eaten by another organism • a relationship where one organism benefits and the other is harmed • 6. a relationship between two species in which both species benefit Section Quiz: Match the correct word to the definition a.prey b.symbiosis c.mutualism d.commensalism e.parasitism f.predator

27. Write the letter of the correct answer. 7.The largest population an environment can support is its a. carrying capacity. c. population. b. limiting factor. d. symbiosis. 8. One type of competition involves individuals competing for resources. The other involves competition between different a. organisms. c. environments. b. populations. d. relationships. 9. Young wasps are eating the tomato hornworm that is their host. What is this an example of? a. commensalism c. parasitism b. mutualism d .competition 10. A bird eats a worm. Who is the predator? a. the worm b. the bird c. both the bird and the worm d. neither the bird nor the worm