CHAPTER 3 THE BIOSPHERE

3.1 What is Ecology?

Studying Our Living Planet Biosphere- consists of all life on Earth and all parts of the Earth in which life exists, including land, water and the atmosphere. The biosphere extends from about 8 kilometers above Earth’s surface to as far as 11 kilometers below the surface of the ocean.

The Science of Ecology Ecology- is the scientific study of interactions among organisms and between organisms and their physical environment. Organisms in the biosphere interact with one another and their environment. Interactions within the biosphere produce a web of interdependence between organisms and the environment in which they live.

Ecology and Economics Economics is concerned with human interactions based on money and trade. The Greek word oikos is the root of the word economics. Humans live in the biosphere and depend on ecological processes to provide essentials to be bought and sold or traded.

Levels of Organization Species – can breed and produce fertile offspring. Population – same species that live in the same area. Community – collection of different populations that live in the same area. Ecosystem – a community plus the non-living physical environment. Biome – group of ecosystems with the same climate and similar dominant communities.

Biotic and Abiotic Factors Environmental conditions include biotic and abiotic factors. The word environment refers to all conditions surrounding an organism.

Biotic Factors Biotic factor- any living part in the environment. The biological influences on organisms are called biotic factors. Biotic factors relating to a bullfrog can be algae, herons, and insects.

Abiotic factors Abiotic Factor- any nonliving part in the environment. Physical components of an ecosystem are called abiotic factors. Abiotic factors relating to a bullfrog can be water, temperature, and humidity.

Biotic and Abiotic Factors Together Physical factors can be influenced by activities of organisms. The mix of biotic and abiotic factors shapes every environment. For example, trees can help to make the soil around them richer.

Ecological Methods Ecologists use observing, experimenting, and modeling to understand complex processes. Ecologists also use measuring tools to assess changes in plant and wildlife communities.

Observation This is the first step in asking ecological questions. Some observations are simple, other are complex. These questions can be the first steps in creating experiments and models.

Experimentation Experiments are used to test hypotheses. Experiments can be carried out by creating artificial environments. Some experiments alter conditions in selected parts of natural ecosystems.

Modeling Models help scientists explain phenomena’s. Many consist of mathematical formulas gathered through observation and experimentation. Further observations by ecologists can be used to test predictions based on those models.

3.2 Energy, Producers, and Consumers

Primary Producers Autotrophs- organisms that capture energy from sunlight or chemicals and convert it into forms that living cells can use. Primary Producers- another name for autotrophs.

Energy from the Sun Photosynthesis- plants use sunlight to convert carbon dioxide and water into oxygen. 6CO2 + 6H2O à C6H12O6 + 6O2 Plants are the main photosynthetic producers on land.

Life Without Light Chemosynthesis- chemical energy is used to produce carbohydrates. Mainly found deep down in the ocean where light is not present. Many live in deep sea ocean vents.

Consumers Heterotrophs- organisms that acquire energy from other organism. Consumers- another word for heterotrophs.

Types of Consumers Herbivores – eat only plants (cows) Carnivores – eat only animals (snakes) Omnivores – eat both plants and animals (humans) Detritivores – eat dead matter or wastes (earthworms) Decomposers – break down organic matter (fungi)

Beyond Consumer Categories Organisms do not always stay in the categories they are placed in. Some animals like hyenas for example will scavenge if they need to. Energy and nutrients always move through the ecosystem so animals move between categories.

3.3 Energy Flow in Ecosystems

Food Chains and Food Webs Food Chain- series of steps in which organisms transfer energy by eating or being eaten. Phytoplankton- mixtures of floating algae.

Food Webs Food Web- a network of feeding interactions. Food webs contain numerous food chains within them. Many organisms die without being eaten so decomposers and detritivores play a big role.

Food Webs and Disturbance It is difficult to determine how food webs will react to changes in the environment. Zooplankton- small swimming organisms that feed off of marine algae. Natural disasters also play a huge role in food web disturbances.

Trophic levels and Ecological Pyramids Trophic level- each step in a food chain or food web. Ecological Pyramids- show the relative amount of matter or energy contained within each trophic level in a food chain or food web.

Pyramids of Biomass and Numbers Biomass- the total amount of living tissue within a given trophic level. Ecologists interested in the number of organisms at each trophic level uses a pyramid of numbers. A pyramid of numbers shows the relative number of individual organisms at each trophic level in an ecosystem.

3.4 Cycles of Matter

Recycling in the Biosphere Biogeochemical Cycles- elements pass from one organism to another and among parts of the biosphere through closed loops. Processes involved in the biogeochemical cycle are biological processes, geological processes , chemical and physical processes, and human activity.

The Water Cycle Water continuously moves between the oceans, atmosphere, and land. Water is evaporated, precipitated, and then goes through the cycle again and again.

Nutrient Cycles Nutrients- chemical substances that organisms need to sustain life. Every organism needs nutrients to survive.

The Carbon Cycle Carbon is a major component of all organic compounds. Some carbon containing compounds that were once part of ancient forests have been buried and transformed by geological processes. Geologic forces can turn accumulated carbon into carbon-containing rocks or fossil fuels.

The Nitrogen Cycles Nitrogen gas (N2) – 78 % of earth’s atmosphere. Decomposers convert dead matter and nitrogen back into soil. Denitrification – bacteria convert nitrates back to N2 gas.

Phosphorus cycle Phosphorus is found in rocks and ocean sediments. Forms a part of vital molecules such as DNA and RNA. As rocks gradually wear down, phosphorus is released.

Nutrient Limitation Limiting nutrient – is either scarce or cycles slowly in an ecosystem. If ample sunlight and water are available the primary productivity of an ecosystem may be limited by the availability of nutrients.

Nutrient Limitation in Soil The growth of crop plants is typically limited by one or more of the nutrients that must be taken up by plants through their roots. Most fertilizers contain large amounts of nitrogen, phosphorus, and potassium. All nutrient cycles work together like gears.

Nutrient Limitations in Aquatic Ecosystems The open oceans of the world are nutrient-poor compared to many land areas. After heavy rains aquatic systems can receive large levels of nutrients. Algae blooms are when algae covers the water’s surface and disrupt the functioning of an ecosystem.