PREDATION AND PARASITISM

A symbiosis (SIM-bie-OH-sis) is a close, long-term relationship between two organisms. Three examples of symbiotic relation- ships include: parasitism, mutualism, and commensalism. Parasitism (PAR-uh-SIET-IZ-UHM) is a relationship in which one indi- vidual is harmed while the other individual benefits. Mutualism (MYOO-choo-uhl-IZ-uhm) is a relationship in which both organisms derive some benefit. In commensalism (kuh-MEN-suhl-IZ-uhm), one organism benefits, but the other organism is neither helped nor harmed. Parasitism Parasitism is similar to predation in that one organism, called the host, is harmed and the other organism, called the parasite, benefits. However, unlike many forms of predation, parasitism usually does not result in the immediate death of the host. Generally, the parasite feeds on the host for a long time rather than kills it. Parasites such as aphids, lice, leeches, fleas, ticks, and mosquitoes that remain on the outside of their host are called ectoparasites. Parasites that live inside the host’s body are called endoparasites. Familiar endoparasites are heart- worms, disease-causing protists, and tapeworms, such as the one shown in Figure 20-5. Natural selection favors adaptations that allow a parasite to exploit its host efficiently. Parasites are usually specialized anatomically and physiologically for a par- asitic lifestyle. Parasites can have a strong negative impact on the health and reproduction of the host. Consequently, hosts have evolved a variety of defenses against parasites. Skin is an important defense that prevents most parasites from entering the body. Tears, saliva, and mucus defend openings through which parasites could pass, such as the eyes, mouth, and nose. Finally, the cells of the immune system may attack para- sites that get past these defenses. parasite from the Latin word parasitus, meaning “one who eats at the table of another” Word Roots and Origins Tapeworms are endoparasites that can grow to 20 m or greater in length. Tapeworms are so specialized for a parasitic lifestyle that they do not have a digestive system. They live in the host’s small intestine and absorb nutrients directly through their skin. Tapeworms reproduce by producing egg-filled chambers, which are released in their host’s feces to be unknowingly picked up by a future host. FIGURE 20-5 Copyright © by Holt, Rinehart and Winston. All rights reserved. 404 CHAPTER 20 Mutualism Mutualism is a relationship in which two species derive some benefit from each other. Some mutualistic relation- ships are so close that neither species can survive without the other. An example of mutualism, shown in Figure 20-6, involves ants and some species of Acacia plants. The ants nest inside the acacia’s large thorns and receive food from the acacia. In turn, the ants protect the acacia from herbi- vores and cut back competing vegetation. Pollination is one of the most important mutualistic rela- tionships on Earth. Animals such as bees, butterflies, flies, beetles, bats, and birds that carry pollen between flowering plants are called pollinators. A flower is a lure for pollina- tors, which are attracted by the flower’s color, pattern, shape, or scent. The plant usually provides food—in the form of nectar or pollen—for its pollinators. As a pollinator feeds in a flower, it picks up a load of pollen, which it may then carry to other flowers of the same species. Commensalism Commensalism is an interaction in which one species benefits and the other species is not affected. Species that scavenge for leftover food items are often considered commensal species. However, a relationship that appears to be commensalism may simply be mutu- alism in which the mutual benefits are not apparent. An example of a commensal relationship is the relationship between cattle egrets and Cape buffaloes in Tanzania. The birds feed on small animals such as insects and lizards that are forced out of their hiding places by the movement of the buffaloes through the grass. Occasionally, the cattle egrets also feed on ectoparasites from the hide of the buffaloes, but the buffaloes gen- erally do not benefit from the presence of the egrets.

1. What is intraspecific competition? a. A relationship between predator and prey b. Competition between individuals of the same species for limited resources c. Interaction between two different species in an ecosystem d. A form of predation where herbivores consume plants 2. How does interspecific competition affect ecosystems? a. It leads to an increase in biodiversity b. It causes one species to always become extinct c. It can change population sizes and species distribution d. It has no effect on ecosystems 3. Which of the following is an example of true predation? a. A cow grazing on grass b. A lion hunting a zebra c. A bee pollinating flowers d. A bird building a nest 4. What role do parasitoids play in ecosystems? a. They are primary producers b. They help control pest populations c. They are a type of prey d. They compete with herbivores for plants 5. Which of the following best describes a predator? a. An organism that is hunted and consumed b. An organism that feeds on plants c. An organism that hunts and consumes another organism d. An organism that lays eggs inside a host 6. How does grazing affect plant communities? a. It allows a single plant species to dominate b. It helps maintain diverse ecosystems c. It eliminates all plant life d. It has no impact on plant communities 7. What is the main difference between intraspecific and interspecific competition? a. Intraspecific involves different species; interspecific involves the same species b. Intraspecific involves the same species; interspecific involves different species c. Intraspecific competition is always beneficial; interspecific is not d. Intraspecific competition occurs only in aquatic environments 8. What is a common consequence of predation in ecosystems? a. Increase in prey population b. Overpopulation of predators c. Regulation of prey populations d. Extinction of all predators 9. Which interaction involves herbivores consuming plants? a. True predation b. Intraspecific competition c. Grazing d. Parasitism 10. How can interspecific competition influence natural selection? a. It does not influence natural selection b. It leads to cooperation among all species c. It can drive adaptation and evolutionary change d. It eliminates the need for adaptation

Create a review game for 9th grade biology students using the following topics Levels of Organization in an ecosystem- population, community, ecosystem, biome, biosphere Abiotic and Biotic Factors Differences between Food chains and food webs Trophic Levels Producers vs Consumers, Autotrophs vs. Heterotrophs Effects of Greenhouse gases and their effects on global systems. Biome examples Photosynthesis vs cellular respiration Types of Consumers Ecological Pyramids 10% rule Cycles of Matter/ Nutrient Cycles- Water Cycle, Carbon Cycle, Nitrogen Cycle, Phosphorus Cycle (note on the diagrams… the bigger the arrow, the larger amount of matter that moves through the cycle from that point to the next. Macromolecules- Carbohydrates, Lipids, Proteins, Nucleic Acids Nitrogen fixation Denitrification Eutrophication The usable form on nitrogen for plants is nitrate Population density and distribution-random, dispersed and clumped Birth rate and death rate Survivorship curves- Type I, II, and III Density dependent factors Density independent factors Exponential growth- J curve = unlimited resources, no limiting factors Logistical Growth-S curve= limiting factors, carrying capacity Symbiotic Relationships- Competition, predation, Herbivory, mutualism, parasitism, commensalism What is an invasive species? Why might countries limit certain species to coming into a new country or area? What is mycorrhizal? Succession- Primary vs Secondary Pioneer Species Climax community Biodiversity Climate change

As long as the birth rate of a population exceeds the death rate, the population size will continue to increase. At a steady, positive per capita growth rate, the population will add a larger number of indi- viduals with each generation. So, a population can increase rapidly with even a small growth rate. A pattern of increase in number due to a steady growth rate is called exponential growth. The observa- tion that populations can grow in this pattern is called the exponential (EKS-poh-NEN-shuhl) model of population growth. One way to understand the exponential model is to study a graph of population size over time. A graph of exponential growth makes the characteristic J-shaped curve shown in Figure 19-6. With expo- nential growth, population size grows slowly when it is small, but growth speeds up as individuals join the population. The exponen- tial model leads us to predict that the population size will increase indefinitely and by a greater number with each time period. Applying the Exponential Model A scientific model is useful if it helps to predict or explain pat- terns that can be observed in reality. Indeed, the exponential model matches observed patterns of growth of real populations, but only under certain conditions and for limited periods of time. For example, a population of microorganisms can grow exponen- tially if provided with an abundance of food and space and if waste is removed. Figure 19-7 shows the growth of bacteria in a laboratory. However, the exponential model does not apply to most popu- lations. In natural environments, populations cannot grow indefi- nitely because the resources they depend on become scarce and harmful wastes accumulate. Any factor, such as space, that restrains the growth of a population is called a limiting factor. All populations are ultimately limited by their environment.SPECIES INTERACTIONS Just as populations contain interacting members of a single species, communities contain interacting populations of many species. Many species have specific types of interactions with other species. This chapter introduces the five major types of interactions among species: predation, competition, parasitism, mutualism, and commensalism. These categories are based on whether each species causes any benefit or harm to the other species in a given relationship. PREDATION In predation (pree-DAY-shuhn), an individual of one species, called the predator, eats all or part of an individual of another species, called the prey. Predation is a powerful force in a community. The relationship between predator and prey influences the size of each population and affects where and how each species lives. Examples of predators include carnivores—predators that eat ani- mals—and herbivores—predators that eat plants. Many types of organisms can act as predators or prey. All heterotrophs are either predators or parasites or both. Predator Adaptations Natural selection favors the evolution of predator adaptations for finding, capturing, and consuming prey. For example, rattlesnakes have an acute sense of smell and have heat-sensitive pits located below each nostril. These pits enable a rattlesnake to detect warm- bodied prey, even in the dark. Many snakes use venom to disable or kill their prey. A venomous rat- tlesnake is shown in Figure 20-1. Other predator adaptations include the sticky webs of spiders, the flesh-cutting teeth of wolves and coyotes, the speed of cheetahs, and the striped pat- tern of a tiger’s coat, which provides camouflage in a grassland habitat. Many herbivores have mouthparts suited to cutting and chewing tough vegetation. A predator’s survival depends on its ability to capture food, but a prey’s survival depends on its ability to avoid being captured. Therefore, natural selection also favors adaptations in prey that allow the prey to escape, avoid, or otherwise ward off

2.2 Study Guide [ 2.2 Sequence Assessment 1/21 and 1/22] Ecosystems and Ecological Relationships Invasive Species ● An invasive species is a plant, animal, or organism that is not native to a specific area and causes harm to the environment or human health. Why are they harmful? Invasive species often outcompete native species for food, water, and space. They can spread quickly because they lack natural predators in the new environment. What is their impact on the ecosystem? Invasive species can reduce biodiversity by pushing native species to extinction or by changing the habitat in which native species live. Biodiversity and Its Importance to Ecosystems Biodiversity refers to the variety of life in a specific area, including different species of plants, animals, and microorganisms, and the ecosystems they form. ● Stability: Biodiversity makes ecosystems more resilient to changes such as climate change, diseases, and natural disasters. ● Food chains and webs: A greater variety of species means more sources of food for different animals, helping maintain a balanced food web. For example, a forest with many species of plants and animals can recover from a drought more easily than a forest with fewer species. Predator-Prey Relationships In a predator-prey relationship, one organism (the predator) hunts and eats another organism (the prey). The predator benefits by getting food, while the prey loses its life.The population sizes of predators and prey are often linked. If there are more prey, the predator population may grow, but if too many predators eat the prey, the predator population will decrease. This relationship can be shown in the graph below. ● For example: Lions hunt zebras for food. When there are many zebras, lions have more food and their population can grow. However, if too many lions eat the zebras, the zebra population can decrease. Predator-prey relationships help keep animal populations balanced, preventing one species from becoming too numerous and harming the environment. Ecological Relationships There are several types of relationships between organisms in an ecosystem. These include commensalism, parasitism, and mutualism. Commensalism In commensalism, one organism benefits from the relationship while the other is neither helped nor harmed. An example would be Barnacles and Whales. Barnacles attach to the skin of whales. The barnacles get access to nutrient-rich water while the whale swims, but the whale is not affected by their presence. Parasitism In parasitism, one organism (the parasite) benefits at the expense of the other organism (the host), which is harmed. For example, fleas live on dogs and feed on their blood. The fleas benefit, but the dog may suffer from itching, infections, or even anemia. Another example are tapeworms and humans. Tapeworms live in the intestines of humans and absorb nutrients, leaving the human host malnourished. Mutualism In mutualism, both organisms benefit from the relationship. An example would be bees and flowers: Bees collect nectar from flowers to make honey, while helping the flowers by transferring pollen, which helps them reproduce.

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