Download ecosystem poster

Published by: Jacaranda Designs
P.O Box 1202-00606 Nairobi Kenya
+254(0)20 374-4737
[email protected]
A
healthy ecosystem has a balance among all its elements—
plants, animals (including humans), soil, air and water.
If one of the elements is changed in some way, the
whole ecosystem is affected. Human activities often change
ecosystems.
back to the atmosphere
How we affect our ecosystems
People damage ecosystems through actions like cutting down trees,
polluting the air, overfishing and overgrazing, and replacing many plant
species with one crop. However, not all our actions are bad. When we
manage ecosystems well, they can stay healthy.
Dead plant
material falls
to ground
Nutrients taken
to other parts
of plants
Four ecosystem processes
Four basic processes support ecosystems and allow us to measure the
health of the land. They work together to make a healthy ecosystem. If
one of these processes is altered, they will all change because they are
closely linked.
Energy flows through an ecosystem in the food chain—from the sun
to green plants (1), to herbivores (plant eaters—2), to carnivores
(meat eaters—3), to detritivores (eaters of dead plants and
animals—4). Plants make foods from sunlight using their green
pigment—a process called photosynthesis. At each step, most
energy is lost in the form of heat. Only 10 % of the energy
received from the previous level moves on to the next level.
Sunlight is converted into energy for the food cycle when it
falls on green growth, but not when it falls on dead plants or
bare ground.
100–200 years
25–100 years
1. Evaporation—warm water evaporates and rises into the
air as water vapour
2. Transpiration—plants give off water vapour
3. Condensation—Water vapour cools as it rises, turns into
water droplets and clouds.
4. Precipitation—when the clouds become dense and heavy,
the water falls as rain, hail or snow.
5. Runoff—rain, snow and hail run off the land into lakes,
rivers and seas or fall directly into them.
6. Seepage—Water seeps into the ground.
7. Groundwater flow (percolation)— Water moves through
the soil. Some of it remains underground as groundwater.
8. Groundwater discharge—Water moves from the ground
into rivers, lakes and oceans. There the cycle begins again.
The water cycle varies from one ecosystem to another. In a
healthy ecosystem, rain sinks into the ground, nourishing plants
and recharging underground water. In an unhealthy one, it may
run off the land, causing erosion.
Arid and semi-arid ecosystems
The species in arid and semi-arid ecosystems in
East Africa are adapted to hot, dry conditions.
However, change caused by human activities and
climate change has affected arid and semi-arid
ecosystems.
If you live in an arid or semi-arid
region, use the table to find out
whether your ecosystem is healthy
or unhealthy.
These hills look green but the exposed soils on the
plain are being eroded.
Abundant green vegetation protects the soil around
this river.
0–10 years
Plant roots
absorb minerals
from the soil
animals eat
plants
rain washes
minerals into soil
animals excrete
minerals in dung
and urine
minerals
in the soil
Detritivores break
down dead matter and
return minerals to soil
In a healthy ecosystem, soil organisms quickly break down plant
and animal waste, making mineral nutrients available for plants
and animals. Rain carries minerals into the soil. In an unhealthy
ecosystem, organic matter may be washed away by rain or
burned in fires before the nutrients can enter the soil.
An ecosystem is a particular area or environment
with the community of plants and animals that
live in it. Everything in an ecosystem, both the
living organisms and the physical elements like
soil and water, interacts with (affects and is
affected by) everything else.
10–25 years
A community consists of different plant and animal species adapted
to the conditions in their ecosystem. Some plant and animal species
are more dominant than others—there are more of them because
the conditions suit them best. Communities usually change very
slowly. When conditions change, previously dominant species may
become fewer while members of other species increase and new
species move in.
In a healthy ecosystem the populations of different plants and
animals are very diverse (=biodiversity). Sudden changes in
populations may indicate that the ecosystem is in trouble.
Healthy Ecosystem
Look for signs of how the 4 processes are working in your
ecosystem:
• Water cycle—does rain sink into the soil to feed plants and
recharge groundwater or does it run off the land and cause
erosion? Do rivers and springs flow seasonally or perennially
(year-round)? Do rivers that used to flow year-round now
flow only seasonally? Do dams and ponds always have water?
• Mineral cycle—how healthy is your soil? Does it contain many
organisms? Do plants look healthy? Does plant and animal
waste rot or stay around for a long time? Are nutrients
burned or eroded before they can re-enter the soil?
• Energy flow—how much green vegetation is around to turn
sunlight into food for the ecosystem? How much of the sun’s
energy is wasted as it falls on dead plants or bare ground?
• Community dynamics—are there many plant and animal
species? Do their populations stay stable or do they grow and
shrink a great deal?
Unhealthy Ecosystem
Water cycle
Rain sinks into the ground and replenishes groundwater.
Rainy seasons follow their normal regular pattern.
Rain runs off the bare ground and carries away seeds and soil,
causing gully erosion.
Rainy season are irregular, either too heavy, leading to floods, or
too low, leading to drought.
Energy flow
Sunlight can be converted into energy for the food cycle,
as enough green vegetation is available.
Only a little green vegetation is available to convert sunlight into
energy. Most of the sunlight falls onto bare ground.
Community
dynamics
(succession)
There is a high diversity (large range) of plant and animal
species living together.
There is a low diversity (small range) of plant and animal species
live in the same ecosystem.
Mineral cycle
Soil organisms break down plant and animal waste, making
minerals available. Rain carries nutrients in the soil where
they can be used by animals and plants.
Plant and animal waste is washed away or burned in fires before
the nutrients can go back into the soil.
Pastoralist
system
Pastoralists traditionally move with their herds in search of
water and pasture depending on the season—dry or rainy.
They have access to their traditional dry season and wet
season grazing areas.
Access to traditional dry season and wet season grazing areas
has become limited due to increased human population and
settlements.
The limited resources available are not sufficient for all the
people and animals living in an area.
The number and length of time of animals grazing in a
particular area is planned and controlled.
Pasture left behind has enough time to recover and to
re-grow.
Too many animals spend too much time in one area. The plants are
grazed to the point where they cannot grow again. The ground
becomes bare and the bare topsoil dries in the sun and is blown
or washed away.
Rain can seep into the ground and replenish the
groundwater.
Rain runs off the ground, causing flash floods, and carries away
seeds and soil, causing gully erosion.
Proper management of natural resources supports a
healthy ecosystem.
Overuse and mismanagement leads to land degradation and causes
an unhealthy ecosystem.