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1 Ecology Notes TEK 8.11 (B) Investigate how organisms and populations in an ecosystem depend on and may compete for biotic and abiotic factors such as quantity of light, water, range of temperatures, or soil composition. Vocabulary: community, population, competition, limiting factor POPULATIONS Populations and Communities A population is all the organisms of a single species living in the same area at the same time. A community is all the populations of different species living in the same area at the same time. Competition Competition is the demand for resources that are in limited supply in an environment, such as food, water, and shelter. If the available resources in an environment diminish, competition among the organisms living in the environment increases. Population Sizes The largest number of individuals of one species that an environment can support is called its carrying capacity, and it is determined by various limiting factors. Those factors include the amount of food and shelter for animal species and the amount of sunlight and growing space for plants. CHANGING POPULATIONS How Populations Change The population size of a species can vary. Its population will increase if the birth rate of the species surpasses the death rate. Its population will decline if deaths surpass births. When a species experiences ideal conditions, with almost unlimited resources, its population increases exponentially until limiting factors stop its growth. Movement The population size of a species in an environment also can change when members of the species move from place to place. For example, animals sometimes move to a new area in search of more food. The seasonal migrations of some species, such as geese, also change in population sizes. Human Population Change The human population has increased dramatically in recent centuries. A thousand years ago, there were about 300 million people in the world; today there are more than 7 billion. This huge and growing population is placing great demands on Earth s resources and is leading to the widespread clearing of tropical rain forests to make room for crops and livestock.

2 COMMUNITIES Communities, Habitats, and Niches A community is all the populations of different species living in the same area at the same time. The part of an environment in which an organism lives is its habitat. Aniche is the role a species fills in an environment what it does to survive. For example, butterflies feed on flower nectar. Energy Roles How an organism obtains the energy it needs to survive is an important part of its niche. Organisms are either producers or consumers. Producers use energy of sunlight. Consumers are animals that get their energy by eating other organisms either producers or other consumers. Energy Flow The way energy moves through an ecosystem can be modeled by food webs and food chains. A food chain shows how energy flows through a community. It has one producer and multiple consumers that feed upon each other. A food web is an interconnected group of food chains. Predator Prey Relationships Many of the animals in a community are involved in predator prey relationships, with larger animals eating smaller ones. The harpy eagle, for example, is a predator that feeds on squirrel monkeys. Cooperative Relationships The members of some populations work together in cooperative ways that enhance their chances of survival. Leaf cutter ants, for instance, work together to cut leaves apart and carry the pieces to their underground nest. Symbiotic Relationships Some species are almost always found living together. A close relationship between two or more organisms of different species that live in direct contact is called symbiosis. Three kinds of symbiosis are mutualism, in which both partners benefit; commensalism, a relationship that benefits one species and neither benefits nor harms the other; and parasitism, a relationship that benefits one species and harms the other. INHERITANCE AND TRAITS What is inheritance? The passing of traits from one generation to the next is called inheritance. Since many traits are inherited, offspring resemble their parents and grandparents. However, acquired traits, such as a learned skill or a lost limb, are not passed on to the next generation. For a trait to be passed on, it must be encoded in the organism s genes.

3 DNA and Genes Genes are made of a molecule called deoxyribonucleic acid, or DNA, which looks like a twisted zipper. A gene is a segment of a DNA molecule. In many cases, a gene is a code for a single trait, but inheritance can be more complicated than that. Many involved in more than one trait. Scientists are uncertain how many human genes there are, but most estimates fall between 25,000 and 30,000. Chromosomes Genes are carried on structures called chromosomes, located in the cell nucleus. The number of chromosomes in each cell varies by species. Chromosomes come in pairs. Humans have 23 pairs of chromosomes. Combining Genes The pairs of chromosomes in the cell nucleus contain genes that also can be paired up. Different genes for the same trait are called alleles. Which alleles are passed onto offspring is a matter of chance. It is determined by meiosis, in which egg and sperm cells are created. These cells have a single set of chromosomes. When an egg is fertilized by a sperm, those single sets of chromosomes come together to form pairs of chromosomes. All the body cells of the offspring have that complete set of paired chromosomes. Genotype and Phenotype An organism s complete set of genes is called its genotype; it remains the same throughout the organism s life. Phenotype is a set of observable traits. An organism s phenotype is determined by its genotype, but the expression of these traits can change during its lifetime. Some changes can be due to environmental factors, such as diet. Phenotype and Mutations The genes in egg and sperm cells sometimes undergo mutations, or changes in the DNA sequence of a gene. Mutations can be caused by chemicals or radiation or can occur spontaneously during DNA replication. If a sex cell with a mutation is passed on to an offspring, the offspring may have a different phenotype from the parents. Variations and Adaptations Slight differences in inherited traits among individual members of a species are called variations. Variations are caused by mutations. Sometimes a variation helps an organism survive. If a beneficial variation spreads through a species, it is called an adaptation. Natural Selection In the wild, adaptations arise through the process of natural selection. Organisms with a particular beneficial variation are more likely to survive and reproduce and pass on the beneficial trait to offspring. Over a number of generations, more and more members of the

4 species inherit the trait until the entire population has it. The trait has then become an evolutionary adaption. Selective Breeding For thousands of years, humans have accelerated evolution by using selective breeding to improve crops and livestock. Selective breeding is similar to natural selecting. Selecting plants or animals with desired characteristics produces improved organisms in much less time than is required for natural selection. Types of Adaptations There are three main categories of adaptations: structural, behavioral, and functional. A structural adaptation is a physical trait, such as color or shape. A behavioral adaptation is a way of behaving, such as migrating or hunting at night. A functional adaptation is a biochemical change, such as hibernating in winter months. Maintaining Homeostasis Some adaptations help species maintain homeostasis, a stable internal environment in response to changing external conditions. For example, sweating in response to increased heat is an adaptation. Protection from Predators In order to survive, organisms must be able to protect themselves from predators. There are many adaptations that species have evolved for this purpose. Some animals, such as the stonefish, have developed camouflage that helps them blend in with their surroundings. Other animals, like the gazelle, avoid many predators by running very fast. Mimicry is another adaptation. The scarlet king snake, for instance, is a nonvenomous snake that looks much like venomous coral snake. Food Gathering Many adaptations help organisms obtain food. An anteater, for example, has a long nose and tongue that it uses to gather ants from their nests. The powerful bodies and sharp claws of big cats enable them to bring down running prey. DEPENDENCE ON OCEANS Ocean Pollution Most ocean pollution originates from human activity on land. Solid wastes, excess sediments, and excess nutrients can damage ocean systems. Excess nutrients can cause algal blooms that kill fish and other marine organisms. Increasing atmospheric carbon dioxide lowers ph as it mixes with ocean water. This weakens the shells and skeletons of marine animals. Climate Change and Oceans

5 Global increases in air temperature and atmospheric carbon dioxide threaten oceans in many ways. Temperature increases cause coral bleaching and melting of glaciers and ice sheets.