Primary Connections: Linking science with literacy

Impacts on environments: Natural

Natural environmental changes affect the kinds and numbers of organisms in an area at any given time.

Short-term
Some environmental factors experience regular cyclic changes causing short-term variations in conditions and populations.

Tides cause changes in water availability and temperature, salt concentration, and food.
Day/ night variation affects temperatures, and light intensity (eclipses occasionally disrupt this!). Changes in day length stimulate flowering in some plants.
Seasons alter weather and often trigger hibernation, or migration (to follow food sources), or life cycles.

Medium-term
Floods, drought and fire are natural factors impacting on environments but which, over a longer time frame, are still part of the natural, stable ecosystem.

Floods
Extreme variations in rainfall causing floods usually occur in late winter, increasing in spring with snow-melt. This inundates wetlands promoting aquatic life to breed and provide food for nesting waterbirds. Loss of topsoil and erosion can harm burrowing animals and wash away plants. Ultimately, floods can change river courses isolating some areas, and silt is deposited further downstream, e.g. the fertile delta of the Nile.
Drought
Conversely, prolonged absence of rain causes plants to die, leaving no food or water for animals. Without the roots' anchoring effects, topsoil is lost, and the Earth becomes cracked and wind-eroded. Desertification increases (e.g. spreading sand-dunes of the Sahara). Many seeds and eggs can remain dormant for years until water is once again available and germination can begin. Analysis of global annual rainfall shows patterns of extreme drought in some areas while others suffer storms and floods. This cycle which occurs every seven years or so is linked to the warming of currents in the southern oceans (El Nino).
Fire
Fires are natural ecological occurrences, often started by lightening during thunderstorms. Some plants (e.g. wattles) are adapted to germinate only after being burnt in a fire. When the undergrowth has been burnt, it no longer competes with the germinating seedlings for light, space and water. Most eucalypts also have dormant buds under the fire resistant thick bark. They sprout after the other leaves are burnt by fire.

Long-term
Some natural impacts are extreme and have very long-lasting effects.

Volcanoes
Volcanic action is devastating to natural ecosystems, with all living things in the path of the lava buried and killed by heat and suffocation. In time, however, life will return to the area as simple life forms grow and alter the environment making it more suitable for other organisms. This is called succession. (see Ecosystems and foodwebs)
Meteor impact
Evidence suggests that, at various times in the Earth's history, large meteors have collided with Earth creating huge dust-storms. One such event is suggested to have been the cause of the dinosaurs' extinction through low light intensity and subsequent reduced plant growth.

Continental Drift
The gradual shifting of the world's continents over hundreds of millions of years (due to upwelling of magma) is believed to have greatly influenced the distribution of plants and animals. Fossils of temperate zone organisms now found in the Antarctic suggest that this area was once much further north than at present as part of the great landmass of Gondwanaland.

Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission.


	FAQ:
			How do plants know when to flower? What is the El Nino effect?


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			Impact on environments: Human Introduced species: "Not in my backyard"


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	Glossary

		Hibernation Migration Gondwanaland