Introduction to Ecology

Transcription

1 Introduction to Ecology Ecology is the scientific study of the interactions between living organisms and their environment. Scientists who study ecology are called ecologists. Because our planet has many diverse plants, animals, and environments, ecologists tend to study small areas called ecosystems. An ecosystem consists of the physical environment (abiotic) and all of the living (biotic) things within it. Examples of abiotic components of an ecosystem include water, sunlight, oxygen, soil, nutrients, and temperature. Examples of biotic factors include the plants, animals, fungi, and bacteria that live within the ecosystem. Each type of living organism in an ecosystem has a place in which it lives. This is known as its habitat. The combination of an organisms habitat and the role it plays in the ecosystem is called its niche. Food Chains All living things require energy to live. The ultimate source of that energy is the Sun. Producers, such as plants and algae, capture the Sun s energy and transform it into organic compounds. These compounds are used to build plant parts and to store energy in roots and seeds. Unlike producers, consumers are unable to directly transform sunlight into organic compounds. Instead, consumers receive their energy by consuming other organisms. Primary consumers, also known as herbivores, feed directly on plants. Secondary consumers feed on primary consumers. Most secondary consumers are carnivores, meaning they feed on other animals. Some, however, may be omnivores who feed on both plants and animals. Tertiary consumers, sometimes referred to as apex predators, feed on both primary and secondary consumers. Tertiary consumers can be carnivores or omnivores. Decomposers, also known as detritivores, are organisms that break down dead or decaying organisms. A scavenger is a carnivore that feeds on dead animals. A food chain is a representation of the predator-prey relationships between species within an ecosystem or habitat. A sample food chain is shown below.

2 Each step in this series of feeding relationships is known as a trophic level. Trophic levels are numbered, starting at level one with plants. Other trophic levels are numbered according to how far the organism is along the food chain. Level 1: Plants and algae make their own food and are called primary producers. Level 2: Herbivores eat plants and are called primary consumers. Level 3: Carnivores which eat herbivores are called secondary consumers. Level 4: Carnivores which eat other carnivores are called tertiary consumers. Level 5: Apex predators, which have no predators, are at the top of the food chain. Since decomposers recycle nutrients, leaving them so they can be reused by primary producers, they are sometimes regarded as occupying their own trophic level. Food Webs In real world ecosystems, most organisms eat more than one kind of food or are eaten by more than one type of predator. A diagram which sets out the intricate network of intersecting and overlapping food chains for an ecosystem is called its food web. A sample food web is shown below. Because plants and animals die at all points in the food chain, decomposers are found at all trophic levels in ecosystems.

3 Ecological Pyramids Ecologists use a variety of pyramid models to describe the energy flow among the trophic levels. Pyramid of Energy A pyramid of energy, for example, allows us to visualize the total amount of energy at each trophic level of an ecosystem. The area at the bottom of the pyramid represents the greatest amount of energy in the ecosystem. As the energy passes to increasingly higher trophic levels, less and less energy is available. This is because all of the energy that an organism takes in is not transformed into food. Some is used by the organism for things like breathing, movement, reproduction, etc. As a result, only about 10 percent of the energy taken in at one trophic level is passed on to the next level. This loss of available energy as you move up the food chain explains why there are seldom more than four or five trophic levels in an ecosystem.

4 Pyramid of Biomass A pyramid of biomass shows the total amount of living material (biomass) available at each trophic level of an ecosystem. The area at the bottom of the pyramid represents the producer level. This level contains the greatest amount of living material. In each subsequent trophic level, the amount of biomass decreases. It should be noted that a pyramid of biomass does not follow the 10 percent rule that a pyramid of energy does. In a typical ecosystem, it takes a large amount of producers (grass) to support a small number of herbivores (insects). The number of carnivores (birds) that can be supported by the insects is even smaller still.

5 1. How does a niche differ from a habitat? Worksheet 2. What would happen to an ecosystem if all the decomposers were destroyed? 3. One student argues that humans are producers because they produce their own food by growing crops and raising livestock. Do you agree? Explain. 4. Define and give an example of each of the following: a) herbivore b) carnivore c) scavenger d) omnivore 5. Why is it more energy efficient for humans to eat grains and vegetables rather than meat? 6. Why is sunlight needed to maintain an ecosystem?