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TOPIC 4: ECOLOGICAL SYSTEMS, BIODIVERSITY & CONSERVATIONS
4.1: Discuss how ecosystems function as dynamic systems.
BIOTIC AND ABIOTIC FACTORS
Ecosystems are complex networks that consist of interactions between biotic and abiotic factors:
Biotic factor
Note
Predation
Where one organism hunts and eats another. This helps control several populations in
the food web.
Competition
Where multiple organisms occupy similar niches and must vie for limited resources.
Symbiotic
relationships
A relationship where at least one organism benefits. These include:
 Parasitism, where one benefits from harming the other (e.g. ticks and dogs)
 Commensalism, where one benefits while the other is unaffected (e.g.
remora fish and shark)
 Mutualism, where both benefit (e.g. pea plants and Rhizobium)
 Altruism, where organisms cooperate for a common goal (e.g. ant colonies)
Abiotic (non-living) factors include:
Abiotic factor
Note
Light intensity
Impacts the rate of photosynthesis and animal habits.
Temperature
Impacts the rate of evaporation and water supply; type of vegetation; and the
metabolism of organisms;
Gas concentrations
O2 impacts rate of respiration and CO2 impacts rate of photosynthesis; on a
larger scale, CO2 affects climate change and acidification of water biomes.
pH
Measurement of acidity or alkalinity of soil or water; impacts habitat.
Soil characteristics
Also known as edaphic factors. Soil aeration and soil pH affects subterranean
life; particle size affects drainage; contains inorganic ions such as nitrates; soil
pH affects type of terrestrial life and vegetation.
Water characteristics
Availability of water supply affects flora and fauna for sustenance and some
for habitat; turbidity (muddiness) of water affects visibility; salinity and pH
affects type of aquatic life.
Wave action
Helps with movement of nutrients and gases; continuous wave action can
result in erosion or damage, e.g. to shorelines or coral reefs.
Humidity
High humidity decreases rates of evaporation and transpiration.
Wind speed
High wind speed increases rates of evaporation and transpiration.
Topography
The land‟s physical features, which impacts layout of habitats, and allows
animals and vegetation to reside at multiple altitudes.
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EXAMPLE OF AN ECOSYSTEM – The Aripo Savannah Scientific Reserve in Trinidad
Left: Marshy area in Aripo Savannah; Middle: Student (J. Awong) in open savannah
Right: (Top) A parasitic Cassytha vine. (Bottom) A carnivorous sundew plant (Drosera capillaris)
For the CAPE Unit 2 syllabus, you are required to describe a model ecosystem. In this manual, that
ecosystem will be the Aripo Scientific Reserve.
The Aripo Reserve is situated has contains numerous biomes, including an open savannah and a marsh
forest. In the savannah, the topography is very flat with small depressions caused by the burrowing of
earthworms and termites. Since it is situated in a tropical climate, there is a high annual rainfall
average of 2500mm, a stable medium-high temperature of 20 – 25oC, and a high humidity more than
50%. Since the open savannah has a constant high wind speed, it promotes rapid evaporation and
transpiration in the plants. Grass growth is sparse in areas of acidic pH caused by domestic runoff.
Since the soil mostly consists of low-drainage clay and has an impermeable clay layer at the surface, the
land becomes easily flooded during the rainy season. The small depressions act as irrigation channels,
which lead to soil becoming very dry, leading to water supply shortages to plants. Plants, as a result, have
adapted to have XEROPHYTIC characteristics, such as reduced leaves and succulent tissues to retain
water. Some of their roots have bulbs that store water. They also have stilted roots to keep them anchored
during flooding.
In terms of biotic factors, the Aripo Reserve contains over 250 species of plants, including many grasses,
shrubs, mosses, orchids and tall woody trees. These plants exhibit numerous facets of symbiosis.
Parasitic orange love vines (Cassytha) lack chlorophyll and thus must sap nutrients from other plants,
harming them. Commensalistic epiphytes grow atop the woody trees to obtain sunlight. A common
example of mutualism would be the nitrogen-fixing Rhizobium bacteria that live in the nodules of
leguminous plants. Carnivory is observed in sundew plants, which trap and digest insects.
Fauna in the Aripo Reserve include grass mice, agouti, opossum, numerous birds, insects and reptiles,
such as iguanas, frogs and lizards. These exhibit typical feeding relationships.
Human interference in the Reserve include squatting, quarrying, agricultural and industrial runoff,
poachers setting fires, and illegal removal of timber from Galba trees and cocorite palms.