13.1 ECOLOGISTS STUDY RELATIONSHIPS KEY CONCEPT Ecology is the study of the relationships among organisms and their environment. Ecology is the study of interactions among living things, and between living things and their surroundings. The term ecology was coined in 1866 by Ernst Haeckel, a German biologist, who wanted to encourage biologists to consider the ways in which organisms interact. Ecologists typically study nature on five different levels: Organism an individual living thing Population a group of the same species that lives in one area Community a group of different species that lives together in one area Ecosystem all of the organisms as well as the climate, soil, water, rocks, and other non-living things in a given area Biome a major regional or global community of organisms Ecological research methods include observation, experimentation, and modeling. Observation is the act of carefully watching something over time. Scientists often use surveys to observe and monitor species populations. Surveys may be direct or indirect. Direct surveys involve observing the actual animal, while indirect surveys involve looking for signs of the animal s presence, such as the presence of feces or fresh kills. Experiments may be conducted in the field or in the lab. Models are used when the questions scientists wish to answer cannot be easily answered by observation or experimentation. Models are often used to project what might happen in the future. 1. What is ecology? 2. What are the five levels of organization used by ecologists to study nature? 3. What are the three research methods typically used by ecologists? 4. When might a scientist choose to create a model to answer a research question? 4 Unit 5 Resource Book
13.2 BIOTIC AND ABIOTIC FACTORS KEY CONCEPT Every ecosystem includes both living and nonliving factors. All ecosystems are made up of living and nonliving parts. The living parts are called biotic factors, such as plants, animals, fungi, and bacteria. The nonliving parts are called abiotic factors, such as moisture, temperature, wind, sunlight, and soil. An ecosystem is formed from a complex web of connected biotic and abiotic factors. Biodiversity refers to the variety of living things in an ecosystem. The amount of biodiversity found within an ecosystem depends on many abiotic factors, such as moisture and temperature. A change in a single biotic or abiotic factor can have a significant impact on an ecosystem. One biotic factor that greatly impacts an area s biodiversity is the presence of a keystone species. A keystone species is a species that has an unusually large effect on its ecosystem. 1. What is a biotic factor? List two examples. 2. What is an abiotic factor? List two examples. 3. What is biodiversity? 4. Why might it be important to preserve areas with high biodiversity? 8 Unit 5 Resource Book
13.3 ENERGY IN ECOSYSTEMS KEY CONCEPT Life in an ecosystem requires a source of energy. All organisms must have a source of energy in order to survive. Producers get their energy from nonliving resources, meaning they make their own food. Producers are also called autotrophs. Consumers get their energy by eating other living or once-living resources. Consumers are also called heterotrophs. Photosynthesis is the two-stage process that green plants, cyanobacteria, and some protists use to produce energy in the form of carbohydrates. These chemical reactions form carbohydrates from carbon dioxide and water. Other producers use chemicals to form carbohydrates in a process called chemosynthesis. Chemosynthetic producers are found in deep-sea vent communities as well as in sulfur-rich salt marsh flats and hydrothermal pools. 1. What is the difference between a producer and a consumer? 2. Whydoallecosystemsdependonproducers? 3. How are consumers dependent on the Sun? 4. What is the difference between photosynthesis and chemosynthesis? 12 Unit 5 Resource Book
13.4 FOOD CHAINS AND FOOD WEBS KEY CONCEPT Food chains and food webs model the flow of energy in an ecosystem. A food chain is a model that shows a sequence of feeding relationships between a producer and consumers. There are several types of consumers. Herbivores eat only plants. Carnivores eat only animals. Omnivores eat both plants and animals. Detritivores eat detritus, or dead organic matter. Decomposers are detritivores that break down organic matter into simpler compounds. Food chains are very helpful to explain the feeding relationships of very selective eaters. Specialists are consumers that mainly eat only one specific organism or a very small number of organisms. In contrast, generalists are consumers that have a varying diet. Trophic levels are the levels of nourishment in a food chain. Energy flows up the food chain from the lowest trophic level to the highest. Primary consumers (herbivores) are the first consumer above the producer trophic level. Secondary consumers (carnivores) eat primary consumers. Tertiary consumers (carnivores) eat secondary consumers. A food web is a model that shows the complex network of feeding relationships and the flow of energy within and sometimes beyond an ecosystem. At each link in a food web, some energy is stored within an organism, and some energy is dissipated into the environment. 1. What are the four main types of consumers? 2. What is the difference between a specialist and a generalist? 3. What are the trophic levels in a food chain? 4. What is the difference between a food chain and a food web? 5. What happens to energy at each link in a food web? 16 Unit 5 Resource Book
13.5 CYCLING OF MATTER KEY CONCEPT Matter cycles in and out of an ecosystem. The hydrologic cycle is the circular pathway of water on Earth from the atmosphere, to the surface, below ground, and back. Water falls to Earth as precipitation such as rain or snow. Some droplets of water reenter the atmosphere through evaporation, or from transpiration, which is evaporation that occurs between plant leaves and the atmosphere. Water vapor in the atmosphere condenses and forms clouds, from which precipitation falls. A biogeochemical cycle is the movement of a particular chemical, such as oxygen, carbon, nitrogen, or phosphorus, through the living and nonliving parts of an ecosystem. In the oxygen cycle, oxygen flows into the atmosphere as a byproduct of photosynthesis. Organisms take in this oxygen and release it as carbon dioxide through respiration. Photosynthesis and respiration also figure heavily in the carbon cycle. The cycling of carbon is important because it is the building block of life. During the nitrogen cycle, bacteria convert gaseous nitrogen into ammonia in a process called nitrogen fixation. Nitrifying bacteria change ammonium into nitrate through the process of nitrification. These nitrates areusedbyplantstomakeaminoacids. The phosphorus cycle begins when phosphate is released by the erosion of rocks. Plants and fungi can take up the phosphate with their roots. Phosphorus moves from the producers to consumers via the food chain. Phosphorus is returned to the soil through the decomposition of plants and animals. Phosphorus may leach into groundwater from the soil, settling in sediment. Over time this sediment forms into rocks. When these rocks erode, the cycle begins again. 1. What is the hydrologic cycle? 2. Why is the cycling of elements and nutrients important? 3. What two major processes are involved in the oxygen cycle? 4. What is nitrogen fixation? 20 Unit 5 Resource Book
13.6 PYRAMID MODELS KEY CONCEPT ecosystem. Pyramids model the distribution of energy and matter in an An energy pyramid shows the distribution of energy among trophic levels. Biomass is a measure of the total dry mass of organisms in an ecosystem. When a consumer incorporates the biomass from a producer into its own biomass, some of the energy is lost as heat and waste. The loss of energy between trophic levels can be as much as 90 percent, meaning only 10 percent of the available energy is transferred from one trophic level to another. A typical energy pyramid has a very large section at the base for the producers, and tiers that become smaller the higher the trophic level. Two other pyramid models are biomass pyramids and pyramids of numbers. A biomass pyramid compares the biomass of different trophic levels within an ecosystem. This pyramid model shows the mass of producers needed to support primary consumers, the mass of primary consumers needed to support secondary consumers, and so on. A pyramid of numbers shows the numbers of individual organisms at each trophic levelinanecosystem. 1. What is an energy pyramid? 2. What is biomass? 3. Describe the flow of energy from one trophic level to another. 4. What is the difference between a biomass pyramid and a pyramid of numbers? 24 Unit 5 Resource Book