An Introduction; Chapter 3 Ecosystem Ecology An Introduction; Chapter 3

Ecosystems A community of interdependent organisms and the interactions with the physical environment in which they live. It can also be defined as the abiotic and biotic factors and the interactions between them. The interaction between organisms and the environment is the key! Some ecosystems, such as a caves and lakes have very distinctive boundaries. However, in most ecosystems it is difficult to determine where one ecosystems stops and the next begins. Even though it is helpful to distinguish between two different ecosystems, ecosystems interact with other ecosystems.

Energy Flow Ecologists have to study how energy and matter flow within an ecosystem. Photosynthesis: Producers (autotrophs) use solar energy to convert carbon dioxide and water in to glucose a form of potential energy that can be used by a wide variety of organism. This reaction creates the oxygen that we breathe as a byproduct. 6CO2 + 6H2O ------> C6H12O6 + 6O2 Sunlight energy  

Energy flow cont. Respiration: a process that unlocks the chemical energy stored in the chemical energy stored in the cells of organisms. Respiration is the opposite of photosynthesis. All organism carry out respiration. C6H12O6 + 6O2 → 6CO2 + 6H2O

Niche vs habitat A habitat is wear an organism lives. The habitat must provide a source of food, water and shelter for the organism. Niche: The role of the organism. This is largely to do with the trophic level of the organism. For example: plants produce food for the rest of the food chain. Tigers keep herbivore populations under control.

Abiotic and Biotic factors Biotic Factor: A living, biological factor that may influence an organism or a system. Example: predation, disease, competition Abiotic factor: A non-living, physical factor that may influence an organism or a system Examples: Temperature, salinity, pH, light

Limiting factors An abiotic factor can limit the population size if there is too much or too little of it. Even if there is the right amount of other factors Examples to consider: Sunlight Precipitation Salinity Nutrients in the soil

Trophic levels Ecosystems are often broken up and described according to feeding relationships. Trophic level: The position of an organism in a food chain A group of organisms that occupy the same place in a food chain

Trophic levels in food chains Be able to give an example of each! Primary producers (autotrophs) Primary consumers (herbivores) Secondary consumers(carnivores) Tertiary consumers (top carnivores) Decomposers- complete the breakdown process by recycling the nutrients from dead tissue back to the environment Detrivores-specialize in breaking down dead tissue and waste products Scavengers-consume dead animals

Energy flow and material cycling

Producer lAutotroph - “self” + “feed” lAn organism that obtains organic food molecules without eating other organisms but by using energy from the sun or inorganic molecules to make organic molecules lRemember: This trophic level supports all of the others lThe role of producers is to convert energy into a form useable for other organisms

Producers lMost producers are photosynthetic (e.g. algae, mosses, diatoms, some bacteria, plants etc.) but some are chemosynthetic (e.g. hydrothermal vent bacteria) (H2)

Decomposer lAn organism that obtains energy by breaking down dead organic matter, including dead plants, dead animals and animal waste, into more simple substances lExamples include: bacteria and fungi Interconnects all trophic levels since the organic material making up all living organisms is eventually broken down Role of decomposers is to return valuable nutrients to the system so they can be used again

Compare detritus feeders to decomposers:

Consumer lHeterotroph - “other” + “feed” lAn organism that obtains its nutrition by eating other organisms lPrimary consumer (herbivore) - eats producers e.g. sea urchin, copepod lSecondary consumer (carnivore) - eats primary consumers e.g. wolf eel, herring lTertiary consumer - eats secondary consumers e.g. sea otter, seal lQuaternary consumer - eats tertiary consumers e.g. killer whale

Consumers The role of the consumer is to transfer energy from one trophic level to the next. Notice that consumers have different names, depending on what they eat: Herbivores: plant eaters Carnivores: meat eaters Omnivores: eat plants and animals

Food Chain- The sequence of consumption from producers through tertiary consumers. Food Web- A more realistic type of food chain that takes into account the complexity of nature.

Food Chains

Show energy flow through an ecosystem Food webs Show energy flow through an ecosystem An ecosystem’s trophic structure determines energy flow and nutrient cycling

Food webs

Trophic levels

Pyramid of biomass

Second Law of Thermodynamics There is a tendency for numbers and quantities of biomass and energy to decrease along food chains. The pyramids become smaller at the top because around 90% of the energy is “lost” between each level and only 10% is available in the body of the organism for transfer to the next level.

Energy transfer in a food chain: First law of thermodynamics

Flow of Energy When new matter appears into the ecosystem it appears in an orderly fashion over time to producers then cosumers and so forth. As new matter passes through the food chain, it gets more concentrated in organisms of each higher trophic level. This increase is called biomagnification. From the 1950’s to the 1970’s a pesticide called DDT was sprayed everywhere and while low doses were used it ended up getting maginified in many ecosystems and killed higher level species.

Ecosystem Productivity Gross primary productivity (GPP)- The total amount of solar energy that the producers in an ecosystem capture via photosynthesis over a given amount of time. Net primary productivity (NPP)- The energy captured (GPP) minus the energy respired by producers.

Energy Transfer Efficiency and Trophic Pyramids Biomass- The energy in an ecosystem is measured in terms of biomass. Standing crop- The amount of biomass present in an ecosystem at a particular time. Ecological efficiency- The proportion of consumed energy that can be passed from one trophic level to another. Trophic pyramid- The representation of the distribution of biomass among trophic levels.

Ecosystems respond to disturbance Disturbance- An event caused by physical, chemical or biological agents that results in changes in population size or community composition.

Resistance versus Resilience Resistance- A measure of how much a disturbance can affect its flows of energy and matter. Resilience- The rate at which an ecosystem returns to its original state after a disturbance. Restoration ecology- A new scientific discipline that is interested in restoring damaged ecosystems.

The Intermediate Disturbance Hypothesis The intermediate disturbance hypothesis- states that ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels.

Instrumental Values of Ecosystems Provisions- Goods that humans can use directly. Regulating services- The service provided by natural systems that helps regulate environmental conditions. Support systems- The support services that natural ecosystems provide such as pollination, natural filters and pest control. Resilience- Resilience of an ecosystem ensures that it will continue to provide benefits to humans. This greatly depends on species diversity. Cultural services- Ecosystems provide cultural or aesthetic benefits to many people.