5.1 Communities and ecosystems

Definitions

Species - a group of organisms that can interbreed and produce fertile 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 and interacting with each other in an area.

Ecosystem - a community and its abiotic environment.

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

Autotroph and heterotroph

Autotroph - an organism that synthesizes its organic molecules from simple inorganic substances.

Heterotroph - an organism that obtains organic molecules from other organisms.

Consumers, detritivores and saprotrophs

Consumer - an organism that ingests other organic matter that is living or recently killed.

Detritivore - an organism that ingests non-living organic matter.

Saprotrophs - an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

Food chain

Food chain - a feeding relationship in which a carnivore eats a herbivore which itself has eaten plant matter; indicates the direction of energy flow.

Carrot Plant -> Eastern Cottontail Rabbit -> Red Fox -> Golden Eagle

Grass -> Grasshopper -> Snake -> Hawk

Grass -> Grasshopper -> Shrew -> Owl

Food web

Food web - individual food chains may be temporary, and are interconnected so that they form it; shows all the feeding relationships in a community with arrows which show the direction of the energy flow.

 

Trophic level
Trophic level - the level at which an organism feeds in a food chain.

Deduce trophic levels of organisms in a food chain and a food web
(enchantedlearning.com)

(msu.edu)

Food web with 10 organisms
(ibguides.com)

(exclude one organism as there are 11 here).

Light as an energy source
Light is the initial energy source for almost all communities.

Energy flow in a food chain
Green plants (producers) transfer light energy into chemical energy of sugars in photosynthesis; some is reflected, some transmitted and some lost as heat energy.
Heat is the waste product of reactions of respiration and of the plant's metabolism, as sugar is converted into lipids and amino acids.
Some of these metabolites are used in growth and development of the plant, and by these reactions, energy is locked up in the organic molecules of the plant body.
Energy transfer from plant to primary consumer once consumer eats plant.
When plant dies, remaining energy is passed to detritivores and saprotrophs when dead plant matter is broken down and has decayed.
Consumer eats producers or primary or secondary consumers. Energy transferred to consumer and the consumer uses this energy into muscular movements (hunting, feeding, escaping from predators); some food is undigested and some is lost in feces.
Heat energy is lost when consumer grows and develops.
When another consumer eats a consumer, the dead consumer passes remaining energy to detritivores and saprotrophs when dead matter is broken down and decayed.

Energy transformations
Energy transformations are never 100% efficient.

Shape of pyramids of energy

Only 10% of the energy is passed onto the higher tertiary levels, much energy is used for cell respiration to provide energy for growth, movement, feeding, and all other essential life processes. Not all food that is eaten can be digested (bones, hair, feathers), and not all organisms as each trophic level are eaten.
For pyramid of numbers, it is evident that grass and plants are much more numerous than the higher trophic levels.
For pyramid of biomass, finding the biomass is the dry weight, and it would seem plausible that because grass and plants take up the most numbers, then it must weigh the most.

Energy and nutrients in an ecosystem
All organisms are made of carbon, hydrogen and oxygen, together with mineral elements nitrogen, calcium, phosphorus, sulphur and potassium.
When organisms die, their bodies are broken down and decomposed, mainly by bacteria and fungi, and the nutrients are released.
Elements may become part of the soil solution, and some may react with chemicals of soil or rock particles, before becoming part of living things again by being reabsorbed by plants.
The cycling processes by which essential elements are released and re-used are called biogeochemical cycles because the cycle of changes involve both living things and the non-living environment, consisting of atmosphere, hydrosphere (oceans, rivers and lakes) and the lithosphere (rocks and soil).
When organisms die, their bodies are broken down to simpler substances by a succession of organisms.
Scavenging actions of detritivores often begin the process, but saprotrophic bacteria and fungi always complete the breakdown processes.
There is a limited supply of many of the chemical elements required as nutrients, so recycling is essential.

Saprotrophic bacteria
Saprotrophic bacteria and fungi (decomposers) recycle nutrients.