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Plant Biology - Ecosystem Structure and Function

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    Study Guide Plant Biology – Ecosystem Structure and Function 1. Ecosystem Structure: Plant Communities Plants usually make up the most visible and important part of an ecosystem. In fact, ecosystems and plant communities are often named after the dominant plants — the plants that are most abundant or the largest. These dominant plants shape the environment around them. They influence things like light, temperature, soil conditions, and even which other organisms can live there. A plant community is not random . It is made up of populations of plants that can survive the specific conditions of that area. Each plant species has a tolerance range , which is the range of environmental conditions (such as temperature, moisture, and soil type) in which it can grow and survive. Only plants whose tolerance ranges match the conditions of the site can become part of that community. 1.1 Succession: How Plant Communities Change Over Time Even ecosystems that seem stable are always changing. One of the easiest ways to see this change is through ecological succession . Succession is the gradual change in plant species living in an area over time. There are two main types of succession : 1.1. 1. Primary Succession Primary succession happens on newly exposed land where no soil exists. This can occur after events like volcanic eruptions or landslides. Because there is no soil at first, plants and soil develop at the same time . Early plants help break down rock and add organic matter, slowly forming soil. 1.1. 2. Secondary Succession Secondary succession occurs when plants are removed from an area, but soil is already present . This can happen after forest fires, floods, farming, or logging. Plants grow back more quickly than in primary succession because the soil already contains nutrients. Over time, both the plant community and the soil continue to change as new species grow above ground and roots develop below ground.

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    Study Guide 1.2 Pioneer Species and Productivity The first plants to grow on bare ground are called pioneer species . These are usually weedy annual plants . Pioneer species are generalists , meaning they can survive under many different conditions. As they grow, they change the environment by adding organic matter, improving soil quality, and making the area suitable for other plant species. In the early stages of succession, productivity is high because plants grow quickly. However, as more species move in and total biomass increases, productivity begins to decrease. This is one reason why agricultural ecosystems are kept in early successional stages — it helps maximize crop production. 1.3 Disturbance: A Necessary Part of Ecosystems Disturbances play an important role in keeping ecosystems healthy. They help maintain diversity in species, ages, and habitats. Without disturbances, ecosystems could become less varied over time. Some disturbances are large and rare , such as hurricanes or tornadoes. Others are small and frequent , like a few trees falling and opening up sunlight in a forest, or rodents digging and bringing buried soil to the surface. Even though these events may seem destructive, they create opportunities for new plants and organisms to grow and thrive. 2. Ecosystem Functions Every ecosystem depends on the flow of energy. This energy moves through living organisms in an organized way. To understand this process, ecologists group organisms into three main levels based on how they get their energy: producers, consumers, and decomposers . Together, these organisms form complex food webs that connect all life in an ecosystem. 2.1 Producers: The Energy Starters At the base of every ecosystem are the producers , also called autotrophs . These include plants, algae, and some bacteria . Producers make their own food, usually through photosynthesis , using sunlight, carbon dioxide, and water. Because they create the organic material that all other organisms depend on, they are known as the primary producers of the ecosystem.

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    Study Guide 2.2 Consumers: Getting Energy from Others Next are the consumers , also called heterotrophs . These include animals, fungi, most protists and bacteria, and even a few non - green plants . Consumers cannot make their own food. Instead, they get both energy and carbon by eating producers or other consumers. Consumers are organized into trophic levels , which describe who eats whom. The Four Trophic Levels 1. First Level – Primary Producers 2. These are the autotrophs (plants, algae, and some bacteria). 3. Second Level – Primary Consumers 4. These are herbivores , or plant - eaters. They feed directly on producers. 5. Third Level – Primary Carnivores 6. These are meat - eaters that eat herbivores. 7. Fourth Level – Secondary Carnivores 8. These are top - level predators that feed on other carnivores. 2.3 What Happens to Energy at Each Level? As energy moves from one trophic level to the next, not all of it is passed on . • Some energy is used by organisms to carry out metabolic activities like movement, growth, and repair. • Some energy is stored in the organism’s body tissues. • A large portion of energy is released as heat into the environment. This heat is not truly wasted — it helps maintain Earth’s temperature balance and even plays a role in driving wind patterns and climate. 2.4 Decomposers: Nature’s Recyclers Another essential group in ecosystems is the decomposers . These organisms get energy from all trophic levels by breaking down dead plants and animals and their waste. Because they feed on detritus (dead organic matter), they are sometimes called detritivores . Although decomposers are usually tiny and live hidden in the soil, their role is incredibly important. Without them:

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