4.1 Species, Communities and Ecosystems

Define a species

A species is a group of organisms that can potentially interbreed to produce fertile, viable offspring

• Members of a single species are unable to produce fertile, viable offspring with members from a different species

• When two different species do produce offspring by cross-breeding, these hybrids are reproductively sterile (e.g. liger, mule)

  • Due to the difference in chromosome numbers

Define a population

A group of organisms of the same species that are living in the same area at the same time

• Organisms that live in different regions (i.e. different populations) are reproductively isolated and unlikely to interbreed, however are classified as the same species if interbreeding is functionally possible

Define a species

A species is a group of organisms that can potentially interbreed to produce fertile, viable offspring

• Members of a single species are unable to produce fertile, viable offspring with members from a different species

• When two different species do produce offspring by cross-breeding, these hybrids are reproductively sterile (e.g. liger, mule)

  • Due to the difference in chromosome numbers

Define a population

A group of organisms of the same species that are living in the same area at the same time

• Organisms that live in different regions (i.e. different populations) are reproductively isolated and unlikely to interbreed, however are classified as the same species if interbreeding is functionally possible

Define a community

• A group of populations living together and interacting with each other within a given area

Define a habitat

• The environment in which a species normally lives, or the location of a living organism

Define an ecosystem

A community and its abiotic environment (i.e. habitat)

Define ecology

The study of the relationship between living organisms, or between living organisms and their environment

State abiotic and biotic factors

Abiotic factors:

Non-living factors, such as pH, salinity, wind speed, type of soil, etc.

Biotic factors:

Living factors in an ecosystem, such as the plants and animals.

State the levels of an ecosystem (smallest to biggest)

Species → P opulation → C ommunity → E cosystem → Biome → Biosphere.

Define heterotrophs

• Obtains organic molecules (Carbon compounds) from other organisms (either living / recently killed or their non-living remains and detritus)

• Because heterotrophs cannot produce their own organic molecules and obtain it from other sources, they are called consumers

List the types of heterotrophs

• Saprotrophs

  Saprotrophs live on (or in) non-living organic matter, secrete digestive enzymes into it and absorbing the products of digestion

  • Unlike other types of heterotrophs, saprotrophs do not ingest food but use enzymatic secretion to facilitate external digestion

  • Because saprotrophs facilitate the breakdown of dead organic material, they are commonly referred to as decomposers

  • Examples of saprotrophs include bacteria and fungi

• Detritivores

  Detritivores are a type of heterotroph that obtains nutrients from non-living organic sources, such as detritus and humus

  • Detritus is dead, particulate organic matter – such as decaying organic material and fecal matter

  • Humus is the term given specifically to the decaying leaf litter intermixed within the topsoil

  • Detritivores include dung beetles, earthworms, woodlice, snails and crabs

Define mixotrophs

• Certain unicellular organisms may on occasion use both forms of nutrition, depending on resource availability

• Euglena gracilis possess chlorophyll for photosynthesis (autotrophic) but may also feed on detritus (heterotrophic)

State how to classify different modes of nutrition

• Consumers ingest organic molecules from living or recently killed organisms

• Detritivores ingest organic molecules found in the non-living remnants of organisms (e.g. detritus, humus)

• Saprotrophs release digestive enzymes and then absorb the external products of digestion (decomposers)

Define a mesocosm

Mesocosms are enclosed environments that allow a small part of a natural environment to be observed under controlled conditions

• A terrarium is a small transparent container (e.g. glass or plastic) in which selected plants (or animals) are kept and observed

• The container should be transparent to enable sunlight to reach producers inside the mesocosm

• Autotrophs should be included so that light energy can be converted into chemical energy inside the mesocosm

• Small primary consumers such as zooplankton or other small invertebrates could be included, but it is important to consider whether the mesocosm is likely to be large enough to support them

• Do not include secondary consumers in a mesocosm because there will not be enough energy in the food chain to sustain them for long, and it could be considered unethical to allow the primary consumers to be eaten in this way

List the 4 main components for a sustainable ecosystem

• Energy availability – light from the sun provides the initial energy source for almost all communities

• Nutrient availability – saprotrophic decomposers ensure the constant recycling of inorganic nutrients within an environment

• Recycling of wastes – certain bacteria can detoxify harmful waste byproducts (e.g. denitrifying bacteria such as Nitrosomonas)

Outline the nutrient cycle