Ecology: organisms and their interaction

Each step is a trophic level, which represents the feeding position or level where an organ ism exists in a particular food chain or food web. The word trophic refers to feeding (or eating).

In each step of a food chain, only 10% of the energy moves from one trophic level to the next. If the grass represents 100% of the energy available, then the rabbit would only have 10% available, and the fox would then only have 1% available. In other words, it would take 100 pounds of grass to support ten pounds of rabbit and then one pound of fox. An herbivore is an animal that eats plants. Plants are producers in food chains, and any organism that eats plants is a consumer. Animals that eat other animals are also consumers. All animals are some kind of consumer because they cannot make their own food. First-order consumers such as herbivores are at the second level of a food chain (plants are at the first level), but they are the first level of consumer. Second-order consumers are other animals that eat herbivores. Third trophic-level organisms are another way of saying second-order consumers (they are at the third trophic level after herbivores and plants).

Food webs are complex groupings of interacting food chains. Organisms may play different roles in different food chains. Food webs with a number of diverse organisms are considered more stable than single food chains. Primary consumers are the first level of consumers, but also the second trophic level. The first trophic level contains the producers (plants).

Organisms interact with each other, and the most common interaction is within the structure of a food chain in which one organism is the food and energy source for another organism. All food chains start with plants as producers because they can photosynthesize and capture sunlight energy. Animals are consumers and eat either plants or each other. Several food chains can be interwoven to create a food web in which many organisms interact with each other.

1. The steps in a food chain or food web are called …….. and represent the …….. of an organism.

a) biomic levels; energy level c) trophic levels; feeding level

b) trophic levels; energy level d) energy levels; feeding level

2. In this food chain, grass → rabbit → fox how much of the energy captured in the grass’s tissue is available to the fox?

a) 100% b) 50% c) 10% d) 1%

3. Another term for herbivores is …….. .

a) plants c) first-order consumers

b) second-order consumers d) third trophic-level organisms

4. Several interacting food chains form a …….. .

a) food pyramid c) food column

b) food web d) food triangle

5. Herbivores are at the second trophic level and can also be called …….. .

a) primary producers c) secondary consumers

b) primary consumers d) secondary producers

6.17. Match the two parts of the sentences.

1. The largest extinction event occurred 250 million years ago, 2. The more we know about wild land biodiversity, 3. Contamination of the air, land and water results largely 4. Some species will need to be helped along artificially 5. Urban development can degrade a habitat 6. Forests not only harbour untold numbers of different species 7. The plant uses the sunlight energy to make food molecules, 8. Energy becomes a part of the animal communities

a) from the use of machines such automobile. b) because plants and soil are replaced with asphalt and concrete. c) when 95 percent of marine species died. d) which are stirred within the tissues of the plant. e) through those who eat plants. f) the more we can use it without damaging. g) by creating seed banks. h) but also play a critical role in regulating climate.

6.18. Match the titles with the notions.

1. Community 7. Food chain

2. Consumers 8. Genetic engineering

3. Decomposers 9. Habitat

4. Ecosystem 10. Natural selection

5. Evolution 11. Photosynthesis

6. Extinction 12. Producers

a) All green plants, which make food from simple materials by photosynthesis. They are the basis of all food chains.

b) A specific area, small or large, that is inhabited by a particular community of plants and animals.

c) A virtually self-contained system, consisting of a community of plants and animals in a given habitat, together with their environment.

d) The dying out of a species of living thing, and hence its complete disappearance from the earth.

e) The plants and animals within a certain habitat.

f) The means by which plants use the sun’s energy to build their food (carbohydrates) from water and carbon dioxide.

g) The theory of evolutionary processes first expounded by Charles Darwin. It suggests that those individual organisms within a species which have the best adaptations to their environment are the most likely to survive long enough to breed, hence these adaptations become established in later generations, and the species as a whole gradually “improves”.

h) Organisms that feed on other organisms.

i) Organisms that live by breaking down dead bodies, releasing the minerals they contain.

j) Altering genes to create organisms that are useful to man. Genes carry information about an organism’s basic characteristics.

k) The long-term process of change in organisms, often occurring over millions of years.

l) A chain of organisms, linked together because each is food for the next in line. Energy passes from one level (trophic level) to the next. All the food chains in an ecosystem are connected together in a complex food web.

6.19. Project work.

We are interfering with biodiversity on a great many levels, from the molecular (genetic modification) all the way through habitats and possibly global climate change as well. However, the many predictions made about species and habitats losses need to be carefully examined in each case and not just taken at face value. Many are based on computer simulations and emotions can get in the way of clear practical thinking. So, your project work may touch upon the following items:

1. Human activity could lead to extinction of a species by over-hunting, e.g. elephants, rhinos, whales, destruction of habitats, e.g. logging, farming, building, introduction of alien species, e.g. cats, rats, cane toads, pesticide use, e.g. honey bees, predatory insects.

2. We can attempt to protect species from extinction by making it illegal to kill the threatened animals or uproot or destroy the protected plants. Habitats of the species can be conserved. Breeding the endangered species in captivity and releasing them later can save a species from extinction.

3. Modern agriculture destroys the natural vegetation (e.g. woodland, hedgerows) on a site, which means a natural habitat is lost. A cultivated area has little biodiversity. The use of pesticides can destroy harmless or beneficial organisms as well as agricultural pests.

4. Biofuel can be obtained from sugar (sugar-cane), maize, sunflower oil, palm oil.

5. Biodiversity conservation is an international problem requiring international solutions and the role of international organisations is a vital one.

UNIT 7 WATER