Climate + Soil ® Plants ® Animals

Water Carbon dioxide Sugar Oxygen

Abiotic and biotic factors in ecosystems also interact with each other: climate and soil conditions determine which plants will live in a certain area. Plant life in turn affects the distribution of animals.

The influence of humans (anthropogenic factor) on abiotic variables may be substantial:

For example, increasing CO₂ output from the burning of fuels and deforestation may cause global CO₂ levels to increase so much that the world’s climate might change (so-called global warming).

Other anthropogenic changes include increased SO₂ (sulfur dioxide) output from fossil fuel burning (coal, oil, natural gas), leading to acid rain, acid lakes, and acid streams.

Biotic relationships:

Biotic factors interact in many ways: Competition, Predator – Prey system, Parasitism (Parasite–Host), Symbiosis.

Competition – a kind of antagonistic relationship within a community - a struggle between two or more groups for a limited resource such as light, food, or space.

Intr a specific – competition among members of the same species.

Int e rspecific – competition between members of different species.

Predation – a kind of relationship when one organism (predator) feeds directly upon another living organism (prey).

Parasitism – a kind of relationship when one organism (parasite) feeds on another living organism (host) or steals resources from it without killing it.

Symbiosis – the non-antagonistic relationship between different species living in close association with one another.

Mutualism – a type of symbiosis in which both organisms benefit from living together.

Commensalism – a type of symbiosis in which one member benefits and the other is neither benefited nor harmed.

2. Limiting factors: critical limiting factor and tolerance limits

Critical limiting factor – is the single factor closest to the survival limits, that determine area where a particular organism can live.

Liebig’s law of the minimum (1840):

The major environmental factor, affecting an organism is that one is inthe minimum.

Shelford’s principle of tolerance limits (1913):

Each environmental factor has both minimum and maximum levels called tolerance limits,beyond which a particular species cannot survive or is unable to reproduce.

Range of tolerance – the range of conditions to which an organism is adapted.

Environmental gradient includes:

- the optimum range, where organisms do best

- zones of physiological stress, where survival and reproduction are possible but not optimal

- zones of intolerance, where life for that organism is impossible.

Tolerance limits – limits of organisms stability to effect of ecological factors.

Any factor, which affects an organism, is either optimal or limiting depending on its strength.

Examples of limiting factors:

- for terrestrial organisms: temperature, moisture, and nutrient availability.

- for aquatic organisms: sunlight, oxygen supply, salinity, gradient (water current).

Sometimes the requirements and tolerances of species are useful indicators of specific environmental characteristics – environmental indicators (trout, lichens etc.).

Homeostasis – the biological balance between an organism and its environment.

Adaptation - an genetically determined structural, functional, or behavioural characteristic of an organism that increases its chance of survival in a particular environment.

Different ecological groups:

Ø Eyrobionts – are organisms with large range tolerance to an ecological factor.

Ø Stenobionts – are organisms with narrow range tolerance to an ecological factor.

Ø Xerophytes – are organisms that are adapted to drought and environmental water shortage.

Ø Homeothermics – are organisms with constant temperature not depending on environmental temperature.

Ø Poikilotehermics – are organisms with body temperature depending on environmental temperature.

Ø Endemics - species that are localized and may have just one population that inhabits a small area.

3. Ecosystems diversity: Earth’s biomes:

Biome - a large area of biosphere characterized by a distinct climate and by the presence of dominant plants and animals adapted to it.

The earth’s biomes are primarily controlled by temperature and precipitations.

q Terrestrial, or Land biomes:

· Polar – biomes found at the earth’s coldest extremes.

· Tundra – a treeless biome blanketed by snow in the winter.

The limiting factor is permafrost – a permanently frozen layer of ground over 500 m thick.

· Coniferous Forest – is a biome that is dominated by conifers, cone-bearing evergreen trees such as pines, firs, spruces, and cedars (boreal forest, or taiga).

· Deciduous forest – is a biome characterised by the presence of trees that lose their leaves in the fall.

· Grassland – is a biome dominated by grasses.

Grasslands are known by various names in different regions of the world:

Prairie (North America), Steppes (Asia), Pampas (South America), Veldt (South Africa), Savannah (grassland with scattered trees found in tropical and subtropical areas in Africa).

· Desert – is an area where rainfall averages less than 25 cm per year.

The limiting factor is low level of water.

· Rain forests

- Tropical rain forest biome – is found near the equator where rainfall and sunlight abound.

- Temperate rain forest extends along the west coast of North America.

q Aquatic, or Water biomes:

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