Biodiversity and the distribution of Life
Summary
Biology N4/5
Biomes and ecosystems
Biodiversity is the variety of living organisms present in an area.
Biomes are regions of the planet with specific climate, fauna and flora.
The global distribution of biomes is influenced by factors including temperature and light and.
There are a variety of ways to classify biomes. Examples of biomes include aquatic, desert, forest,
grassland and tundra.
Other factors like soil type, latitude and altitude can have an influence on biome distribution.
Fauna are the animals present in an area. Flora are the plants present in an area.
A biome can be made up of many ecosystems.
An ecosystem consists of all the organisms living a in particular habitat and the non-living components
with which the organisms interact. The non-living components include light, temperature, pH, CO2, O2
and other chemicals.
Ecosystems are many and varied. In ecosystems the organisms are inter-linked in many ways. Shelter is
provided by plants for animals, plants are food for animals and animals are food for other animals.
The organisms are linked by their feeding
relationships. If there is a change to on organism it will
affect others in the food web.
These changes could be natural or could be
man-made.
Niche
A niche is the role an organism has within a
community.
A niche includes the use organisms make of their resources including light, temperature and nutrients.
The interactions include other organisms in the community including competition, parasitism and
predation. Communities are the made up of all the different living organisms present in an area.
Plants are the producers in an ecosystem. They can photosynthesise and make their own food.
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Animals have a variety of niches depending on their feeding level. Primary consumers are animals that
feed directly on plants, they are herbivores. Secondary consumers are animals that feed on primary
consumers. Tertiary consumers feed on secondary consumers. Carnivores eat other animals to get
their energy. Omnivores eat both plants and animals to get their energy. Decomposers break down
waste and dead material to get their energy.
Feeding relationships in ecosystems can be represented in food chains and food webs.
Algae
tadpoles
dragon fly larvae
The arrows represent the flow of energy. Food webs are many food chains joined together to
represent the complicated interlinking of organisms in an ecosystem.
Changes to one type of organism in a food web will affect others.
Relationships between organisms
Organisms are influenced by their relationships with other organisms. If organisms require the same or
similar resources they will need to compete for them.
Plants often compete for light, space and available nutrients. Animals often compete for food, space
and reproductive mates. As a result of competition between organisms their success in the ecosystem
will be affected.
Parasites are organisms that live on or in another organism. The parasite will gain benefit from the
relationship while the host will lose out in some way.
Predators get their food by eating other animals their prey. Predator and prey numbers are closely
linked and affect each other.
Factors affecting Biodiversity
Biotic and abiotic factors that affect biodiversity include grazing, predation, pH and temperature.
Human activities and natural hazards can also affect biodiversity.
Biotic factors
These are the living factors including disease, predation, competition (for space, light, nutrients,
reproduction) and grazing.
Grazing is when animals get their food (energy) by eating plants. Sheep are selective grazers. They
select the more dominant competitive species (by chance). This means that other weaker species get
the opportunity to grow so biodiversity is kept high. Too many sheep would overgraze an area and
reduce biodiversity. Rabbits are relatively unselective grazers. They eat all types of plants and help
maintain a high biodiversity. Too many rabbits would overgraze an area and reduce biodiversity.
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Abiotic factors
These are non-living including light, moisture, pH, temperature, O2 and CO2. Temperature affects the
enzyme controlled reactions so could speed up or slow down activity or growth. pH influences the
working of chemical reactions. Aquatic organisms are particularly affected by these.
Humans influence biodiversity in a number of ways including habitat destruction, introducing alien
species, farming practices and pollution.
Natural hazards such as storms, excessive rainfall, earth quakes and volcanoes can also influence
biodiversity.
Measuring abiotic and biotic factors
Abiotic factors can be measured with simple apparatus. Light intensity is measured using a light meter,
pH with a pH meter, soil moisture with a moisture meter and temperature with a thermometer.
Errors to avoid when measuring include not shading the light meter, wiping the probe between
readings for moisture and pH and leaving the thermometer long enough to adjust.
Also make sure enough readings are taken, repeats make for more reliable results.
Biotic factors are usually sampling the number or type of organisms present in an area. Quadrats are
subdivided squares used to estimate the abundance of plants in an area. They can be used randomly to
sample an area or on a transect line. They give a representative sample if enough repeats are done.
Pitfall traps can be used to sample the small organisms moving along the soil surface.
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