Environmental Systems and Societies Topic 2

• A species is a group of organisms that share common characteristics and that interbreed to produce fertile offspring.
• A habitat is the environment in which a species normally lives.
• A niche describes the particular set of abiotic and biotic conditions and resources to which an organism or population responds.
• The fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce.
• The realized niche describes the actual conditions and resources in which a species exists due to biotic interactions.
• The non-living, physical factors that influence the organisms and ecosystem—such as temperature, sunlight, pH, salinity, and precipitation—are termed abiotic factors.
• The interactions between the organisms—such as predation, herbivory, parasitism, mutualism, disease, and competition—are termed biotic factors.
• Interactions should be understood in terms of the influences each species has on the population dynamics of others, and upon the carrying capacity of the others’ environment.
• • A population is a group of organisms of the same species living in the

  same area at the same time, and which are capable of interbreeding.
• S and J population curves describe a generalized response of populations

  to a particular set of conditions (abiotic and biotic factors).
• Limiting factors will slow population growth as it approaches the carrying

  capacity of the system.
• • A community is a group of populations living and interacting with each other in a

  common habitat.

  • An ecosystem is a community and the physical environment with which it

  interacts.

  • Respiration and photosynthesis can be described as processes with inputs,

  outputs and transformations of energy and matter.

  • Respiration is the conversion of organic matter into carbon dioxide and water in

  all living organisms, releasing energy. Aerobic respiration can be represented by

  the following word equation.

  glucose+oxygen  carbon dioxide + water
• During respiration, large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling organisms to maintain relatively low entropy and so high organization.
• Primary producers in most ecosystems convert light energy into chemical energy in the process of photosynthesis.
• The photosynthesis reaction can be represented by the following word equation: carbon dioxide + water  glucose + oxygen.
• Photosynthesis produces the raw material for producing biomass.
• The trophic level is the position that an organism occupies in a food chain, or the position of a group of organisms in a community that occupy the same position in food chains.
• Producers (autotrophs) are typically plants or algae that produce their own food using photosynthesis and form the first trophic level in a food chain.
• Chemosynthetic organisms, which produce food without sunlight, are exceptions to the rule that producers are typically plants or algae.
• Feeding relationships involve producers, consumers and decomposers.
• Ecological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that are usually measured for a given area and time.
• In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore, the pyramids become narrower towards the apex.
• Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down.
• Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants along a food chain.
• Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy.
• Pyramids of numbers can sometimes display different patterns; for example, when individuals at lower trophic levels are relatively large (inverted pyramids).
• A pyramid of biomass represents the standing stock or storage of each trophic level, measured in units such as grams of biomass per square metre (g m–2) or Joules per square metre (J m-2) (units of biomass or energy).
• Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass present at a fixed point in time, although seasonal variations may be marked.
• Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that stock/storage is being generated.
• Pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain.
• Pathways of radiation through the atmosphere involve a loss of radiation through reflection and absorption.
• Pathways of energy through an ecosystem include: conversion of light energy to chemical energy, transfer of chemical energy from one trophic level to another with varying efficiencies, overall conversion of ultraviolet and visible light to heat energy by an ecosystem, and re-radiation of heat energy to the atmosphere.
• The conversion of energy into biomass for a given period of time is measured as productivity.
• Net primary productivity (NPP) is calculated by subtracting respiratory losses (R) from gross primary productivity (GPP).
• Agriculture impacts energy flows as well as the carbon and nitrogen cycles.
• Gross secondary productivity (GSP) is the total energy or biomass assimilated by consumers and is calculated by subtracting the mass of fecal loss from the mass of food consumed.
• Net secondary productivity (NSP) is calculated by subtracting respiratory losses (R) from GSP.
• Maximum sustainable yields are equivalent to the net primary or net secondary productivity of a system.
• Matter also flows through ecosystems linking them together.
• The carbon and nitrogen cycles are used to illustrate this flow of matter using flow diagrams.