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1C7 Ecology
OB60 to OB64
Biodiversity means the number of kinds of different things in a particular environment. A field
planted with a single species of grass (monoculture) has a very low biodiversity, whereas a wild
meadow with a variety of grasses and clovers as well as weeds has a high biodiversity.
There are many reasons why biodiversity is important but they can be divided into three
categories: Usefulness, “we need it”, Aesthetic, “I like it” and Ethical, “It exists”.
There are thought to be about 10 million species (a species is a collection of all the individuals
that may potentially breed with one another to produce fertile offspring), but less than 20% of
those have been described and named. It is thought that one species in a million became extinct
each year in the pre-human age. It is estimated that extinctions for the last 400 years are about 5
times that rate. It is reported by the International Primatological Society that nearly a quarter of
the 625 primate species are endangered. This is mainly due to human influence; cutting trees for
timber and to make agricultural land, eating bushmeat and using body parts as exotic medicine.
Useful functions of ecosystems
All life on earth is based on plants and algae that can photosynthesise. This provides all the food
for these primary producers and for all consumers, including humans.
All our clothing comes directly (cotton, wool, leather) or indirectly (via fossil fuels) from living
species.
Very many species have an important role in the water cycle. Plants move water from the ground
to the air in the transpiration stream. It is thought that all of the rainfall in some parts if West
Africa comes from local transpiration and evaporation rather than from the oceans. Deforestation
in these circumstances can lead to a cycle in which reduction in plant cover leads to less rainfall.
This will lead to less plant growth and eventually to desertification.
Plants roots also bind soil particles together to prevent erosion. If perennial plants are replaced
by crops then soils can be completely eroded in wet weather after harvest time.
Aquatic species filter water. Oyster beds filter all the water in some bays every few days but
over-fishing and pollution have drastically reduced oyster numbers and reduced water quality.
Most waste water and sewage treatments involve biological digestion of nutrients.
Responses by living things to their environment range from the rotation of a sunflower so that it
is facing the sun all day to hibernation of bears when it is extremely cold and food is scarce to
the change in behaviour of foxes that allow them to live in urban environments.
The numbers of any plant or animal in an ecosystem depends on, among other things, the
availability of its food source and on predation. Cod in the North Atlantic were once very
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abundant. Over-fishing drastically reduced their numbers but it was assumed that if fishing was
curtailed their numbers would gradually increase.
Cod is a large predatory species that eat smaller fish. Some of these smaller fish have cod fry as
part of their diet. Adult cod keep their numbers in check so that there was a balance between
species. This cycle was brought into imbalance by over fishing of cod so that the smaller fish
rose in population and ate a greater proportion of cod fry. This is thought to have caused the cod
numbers to remain low.
Competition
Competition occurs at different levels; between animals of the same species competing for a
mate; between similar species for a scarce resource. The grey squirrel was introduced to Ireland
in 1911 and has spread slowly. It has succeeded in replacing the red squirrel in many places as it
can out-compete the native red squirrel for scarce pine seeds.
Adaptation
Camels are adapted to living in conditions that are very warm and where food and water are very
scarce. They need very little water if their regular diet contains good, moisture-rich pasture. They
can withstand severe dehydration, but can drink as much as one third of their weight of water in
10 minutes. This water is stored in its bloodstream.
A camel’s hump is used as a fat store and it will decrease in size as the food is used up when
fresh food is not available. Their feet are broadened to make it easier to walk in sand and their
eyelids are adapted to protect their eyes from windblown sand.
In local habitats in Ireland the beaks of most birds are adapted to the particular food source.
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