Topic 5 (ECOLOGY AND EVOLUTION) IB Biology SL

Species: A group of organisms that can be interbred and produce fertile, viable offspring

Habitat: The environment in which a species normally lives or the location of a living organism

Population: A group of organisms of the same species who live in the same area at the same time

Community: A group of populations living together and interacting with each other in an area

Ecosystem: A community and its abiotic environment

Ecology: The study of the relationships between living organisms and between organisms and their environment.

Autotroph:

• An organisms that synthesizes its organic molecules from simple inorganic molecules

• Autotrophs are producers

Heterotroph:

• An organism that obtains organic molecules from other organism

• Heterotrophs are consumers

Consumers: An organism that ingest organic matter that is living or recently killed

Detritivore: An organism that ingests non-living organic matter

Saprotroph: An organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion

A food chain shows the linear feeding relationships between species in a community. The arrows represent the transfer of energy and matter as one organism is eaten by another (arrows indicate direction of energy flow). The first organism in the sequence is the producer, followed by the consumers.

ei.

Buffalo -> Grass -> Grasshopper -> Stick nest rat -> Black rat snake

Green algae -> Mosquito -> Dragonfly -> Horn frog

Phytoplankton -> Zooplankton -> Sardine Fish -> Tuna fish

The food web is a diagram that shows how food chains are linked together into more complex feeding relationships

The food web has a number of advantages over a food chains including:

• Shows the much more complex interactions between species within a community/ ecosystem

• More than one producer supporting a community

• A single producer being a food source for a number of primary consumers

• That a consumer may have a number of different food sources on the same or different trophic levels

• That a consumer can be an omnivore, feeding as a primary consumer and as a consumer at higher trophic levels

There are certain problems in drawing a complete food web as this would in most cases require a very complex study and identification of species. For this reason, food webs often reflect the interests of its author. The author will detail the species of interest by name but group other less interesting/ important species into larger family. order groups.

An organism's trophic level refers to the position it occupies in a food chain

Producers always occupy the first trophic level, while saprotrophs would generally occupy the ultimate trophic level of a given food chain or food web

The trophic levels in a community are:

Light is the initial energy source for almost all communities, and is absorbed by producers and used in photosynthesis to produce chemical energy. This energy is transferred to primary consumers when they consume the producer. However only 10% of this energy is available at each trophic level. Therefore 90% of energy is lost at each trophic level as heat due to cell respiration & metabolism as well as through undigested/uneaten matter that is not consumed and defecation. For this reason, there are less consumers as there are producers because energy transfers between trophic levels are not 100% efficient.

• Pyramids of energy shows inflow of energy at each trophic level, in kJ m-2 per year.

• Pyramids of energy are pyramid-shaped because energy transformations between trophic levels is never 100 percent efficient.

• 90 percent of energy lost at each trophic level due to cell respiration and undigested matter of organisms.

• Pyramids of energy cannot be inverted because matter (organic compounds) cannot be created nor destroyed.

• Thus organic compounds would have to be created for there to be more energy available at higher trophic levels than lower trophic levels.