EVERY MORNING in Africa, a lion wakes up and

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1 Understanding the Food Chain and Natural Selection EVERY MORNING in Africa, a lion wakes up and knows that it must run faster than the slowest gazelle or it will starve. Every morning in Africa, a gazelle wakes up and knows it must run faster than the fastest lion or it will be eaten. This African proverb illustrates the food chain and natural selection. Objective: Describe food energy reliance and adaptations for survival. Key Terms: anatomy asexual reproduction biotic pyramid circulatory system class cover digestive system excretory system family food chain genus integumentary system invertebrates kingdom muscular system natural selection nervous system nutrients order phylum physiology respiratory system scientific name sexual reproduction skeletal system space species vertebrates Food and Survival The food chain and natural selection are important forces in biology. The food chain can be described as the relationships between organisms in which energy is transferred from one to another. For example, plants harness energy from the sun. Rabbits consume plants and are then eaten by predators (e.g., fox). Energy flows from the producer to the consumer. Natural Page 1

2 selection is the process in which inheritable traits that favor species survival are passed on to succeeding generations; unfavorable traits are less likely to be passed on. The plants, animals, and people that are better adapted to the environment are more likely to pass on their genetic material. SCIENTIFIC CLASSIFICATION AND NAMING FIGURE 1. The grizzly bear is at the top of the North American food chain. (Courtesy, U.S. Fish and Wildlife Service) Scientific classification is based on carefully obtained information about organisms. A system of taxonomy is used consistently worldwide. Modern classification uses seven divisions or stages: kingdom, phylum, class, order, family, genus, and species. The kingdom is the first and broadest classification. All living things belong to one of five kingdoms: animalia, plantae, fungi, monera, and protista. The phylum is the second division in classification. The three most important phyla in studying wildlife are chordate phylum, arthropoda phylum, and mollusca phylum. The class is the third division in classification. Some important classes in the chordate phylum of animals are mammalian, reptilian, and aves. EXPLORING OUR WORLD SCIENCE CONNECTION: Natural Selection The term natural selection was introduced by Charles Darwin in his 1859 book The Origin of Species. In the book, he described natural selection as the process by which species adapt to their environment. In the process, favorable heritable traits become more common in successive generations of a population of reproducing organisms. At the same time, unfavorable heritable traits become less common. Natural selection leads to evolutionary change. Some individuals have certain characteristics that give them a greater survival or reproductive rate than other individuals in a population. These characteristics are passed to their offspring. Natural selection influences an organism s physical characteristics or phenotype, which is determined by its genetic composition and the environment in which the organism lives. Over time, natural selection of certain characteristics may result in specialized adaptations that allow organisms to occupy ecological niches. It can also result in the emergence of new species. Page 2

3 The order consists of organisms that are more alike than the class. Orders are based on feeding characteristics. The family is composed of organisms that are more alike than the orders and are often based on anatomical features. The genus is made of similar groups that do not naturally breed with each other. The species contains very similar creations within the same genus. They are capable of breeding with each other and are sometimes divided into subspecies. Scientific Names Every identified organism has a scientific name. Scientists use these names worldwide based on information about a species. The scientific name of an organism is a combination of the genus and species. The genus is the first capitalized word followed by the species name. The scientific name is always written in italics or underlined. Scientific names are not changed unless information results in a new name for the species. LIFE-SUSTAINING PROCESSES All organisms have body systems that carry out life processes. Anatomy (the study of the form, shape, and appearance of organisms) and physiology (the study of the functions of parts of the anatomy) influence how organisms live and experience life processes. The differences are obvious to our eyes and make it possible for each species to sustain itself in its environment. Organ Systems The way in which functions are carried out is influenced by the form of the organ systems. Animal organ systems include skeletal, digestive, respiratory, muscular, circulatory, excretory, nervous, and integumentary. The skeletal system is the body framework that gives the body shape and protects the organs. Wildlife animals have skeletal systems made of bone, cartilage, or chitin. Animals with backbones are vertebrates, and animals without a backbone or an internal skeleton are invertebrates. The digestive system prepares food for use by the body. The major parts of the digestive system are the mouth, esophagus, stomach, intestines, and anus. The respiratory system is responsible for taking in oxygen and giving off carbon dioxide. Many animals have lungs to breathe, but fish have gills to filter oxygen from the water. The muscular system creates bodily movement and support with special tissues called muscles that are attached to the skeletal system by ligaments. FIGURE 2. Bears are categorized as vertebrates. Page 3

4 The circulatory system is a network of vessels that move blood throughout the body. The major organ in the circulatory system is the heart. The excretory system rids the body of wastes (e.g., carbon dioxide, water, nitrogen, and undigested solid food materials). The nervous system conducts impulses back and forth from the brain to the muscles. Vertebrates have a spinal column that contains a spinal cord. The integumentary system is the skin, which protects the internal organs and gives shape to the body. It helps regulate temperature. Hair, fur, and scales are part of the integumentary system. WILDLIFE REPRODUCTIVE PROCESS Reproduction is the process by which a species produces new organisms to perpetuate the species. The process of reproduction is accomplished sexually or asexually. Sexual Reproduction Sexual reproduction involves the union of the sperm (the male sex cells produced in the testes) with the eggs (the female sex cells produced in the ovaries). Mating involves a male and a female joining together for the male to release sperm on or near the egg(s) of a female. Fertilization may occur internally or externally. Asexual Reproduction Asexual reproduction is producing new organisms without the sexual union of male and female cells. Asexual reproduction is common in plants, not in animals. Cloning is an approach to producing identical offspring. MAJOR NUTRIENT NEEDS Animals need food to grow into healthy organisms and to live a long life. Nutritious food provides nutrients chemical substances in food that support life. Types of Nutrients Nutrient types are essential, energy, protein, minerals, and vitamins. Essential nutrients are needed to properly provide for an FIGURE 3. This egret obtains nutrients by eating fish. (Courtesy, U.S. Fish and Wildlife Service) Page 4

5 organism, depending on the life stage. Energy nutrients are needed for an animal to be active and carry out life processes (e.g., starches, sugars, and plant oils). Protein is needed for growth, maintenance, and reproduction; it is used to build strong, new tissue and to repair old tissue. In addition, minerals are needed for growth, reproduction, bones, shells, hooves, teeth, and horns. Vitamins are present in many foods and are needed to regulate body functions. The health of an animal depends largely on adequate vitamins (e.g., vitamins A, D, E, K, and B complex). Food Sources Most animal food comes from plants and other animals. Plants are eaten by herbivores, which are at the bottom of the food chain. Animal food sources are consumed by carnivores and omnivores. These animals tend to be at the middle to the top of the food chain. HABITAT REQUIREMENTS Wildlife animal species have life requirements that must be met by the habitat for a healthy existence. A habitat is a physical area in which members of a wildlife species live. The habitat supports life processes. All organisms require food, and a key component of food is energy. The sun is the source of energy for all living things. The biotic pyramid is a series of transfers of food energy from one organism to another; it is a graphical way of showing a food chain. Water is a basic need to sustain life. It is not a food nutrient because it does not supply energy. The amount of water, or lack thereof, determines the species of plants that will grow in an area and, therefore, determines the wildlife species that reside there. Some examples of water sources for wildlife animals are lakes, streams, rivers, and creeks. Cover is the vegetation or other material that provides safety in a habitat. Animals use cover for nesting, resting, and escaping dangerous predators. Cover needs vary throughout the year. Space is the area or territory around an organism. Space provides air, food sources, and cover. Space requirements vary from year to year and according to the habitat quality. Summary: The food chain is the relationship between organisms in which energy is transferred from one to another. Natural selection is the FIGURE 4. Habitat for these elk must include food, water, space, and cover. (Courtesy, National Park Service) Page 5

6 process in which inheritable traits that favor species survival are passed on to succeeding generations and unfavorable traits are less likely to be passed on. A system of taxonomy uses seven divisions: kingdom, phylum, class, order, family, genus, and species. The scientific name is composed of the genus and species. Anatomy is the study of the form, shape, and appearance of organisms. Physiology is the study of the functions of parts of the anatomy. Organ systems include skeletal, digestive, respiratory, muscular, circulatory, excretory, nervous, and integumentary. Reproduction is accomplished sexually and asexually. A nutrient is a chemical substance in food that supports life. Nutrient types are essential, energy, protein, minerals, and vitamins. Wildlife animal species have life requirements that must be met by the habitat. Checking Your Knowledge: 1. What is a food chain? 2. What is natural selection? 3. How do organisms reproduce? 4. What role do nutrients play in the food chain and in natural selection? 5. How does habitat relate to the food chain and to natural selection? Expanding Your Knowledge: Diagram a food chain for an ecosystem in your area. Include as many species as possible. Indicate the flow of energy within the chain. Web Links: Food Chain Food Chains Natural Selection Natural Selection Page 6