Ecosystem
What is an Ecosystem?
An ecosystem is a
community of organisms that interact with each other and non living components
for sustainable development and adaptation to changing conditions. There are
different type of ecosystems around us which involves living organisms and non
living organisms. If we combine all the ecosystems present on earth, it is
called Biosphere.
Components of an
Ecosystem:
There are two
components of an ecosystem;
·
Biotic (living) components .
·
Abiotic (non living) components.
Abiotic
Components
The
abiotic components of a grassland ecosystem are the non-living features
of the ecosystem that the living organisms depend on. Each abiotic component
influences the number and variety of plants that grow in an ecosystem, which in
turn has an influence on the variety of animals that live there. The four major
abiotic components are: climate, parent material and soil,
topography, and natural disturbances.
Climate
includes
the rainfall, temperature and wind patterns that occur in an area, and is the
most important abiotic component of a grassland ecosystem. Temperature, in
tandem with precipitation, determines whether grasslands, forests, or some
combination of these two, form. The amount and distribution of the rainfall an
area receives in a year influences the types and productivity of grassland
plants.
The
climate in our grassland ecosystems is usually hot and dry in the spring and
summer growing season, and cool or cold in winter dormant season. Precipitation
in the winter falls mostly as snow rather than rain. During the hottest months
of the year (the height of summer) more water evaporates from parts of the grasslands
than falls as rain, creating a moisture deficit.
Parent Material and Soil
Parent
material
is
the geological material that lies on top of the bedrock and is the foundation
on which soil has developed. Much of the parent material underlying BC's
grasslands was deposited as the last ice sheets melted away. The actual
composition of the material at any specific location depends on how and where
it was deposited in relation to the ice. In the Rocky Mountain Trench, for
example, some material was deposited under a moving glacier, while on the
Chilcotin plateau some was deposited under a stationary ice sheet; in many
places throughout the grasslands material was carried and deposited by water
on, in, or under the ice.
The
material dropped in place under the ice varies in thickness from a thin veneer
to several metres, and contains all sizes of rocks and particles from boulders
to silts. Rivers and streams that flowed on, under and beyond the ice left
hummocky ridges of water-rounded materials of all sizes. Material deposited in
ice-damned lakes formed layers of fine silts. Winds picked up fine particles
and blew them across the newly ice-free land surface, depositing thick layers
of the particles in some places. These wind-blown materials are called aeolian
deposits.
Soil develops in the
upper portion of the parent material and is a mixture of abiotic and biotic
components: minerals, organic matter, water and air. The type of parent
material in a particular area influences the texture of the soil, how well
water flows through it, and hence the chemistry and nutrients of the soil. This
combination of texture, water flow and chemistry determines the vegetation that
grows in the area.
The
fine silt soils found on the terraces of the Okanagan, Kootenay and Thompson
valleys hold water near to the surface where it either evaporates or is soaked
up by the dense fine roots of grasses; trees are not common in these areas. By
contrast, in areas with gravelly soils water moves quickly down to depths below
the grass roots to levels where tree roots grow. As such, more trees are likely
to be found in these areas.
Grasslands
have a rich layer of organic matter that forms the top surface of the soil.
This layer has developed largely as a result of the breakdown of plant roots.
Roots form as much as half the volume of a grass plant and up to 50% are
replaced every year.
Biotic
Components
The biotic components of a grassland ecosystem are the living organisms that exist in the system. These organisms can be classified as producers, consumers or decomposers.
Producers
are
able to capture the sun’s energy through photosynthesis and absorb nutrients
from the soil, storing them for future use by themselves and by other
organisms. Grasses, shrubs, trees, mosses, lichens, and cyanobacteria are some
of the many producers found in a grassland ecosystem. When these plants die
they provide energy for a host of insects, fungi and bacteria that live in and
on the soil and feed on plant debris. Grasses are an important source of food
for large grazing animals such as California Bighorn Sheep, Mule Deer and Elk,
and for much smaller animals such as marmots, Pocket Gophers and mice.
Consumers
are
organisms that do not have the ability to capture the energy produced by the
sun, but consume plant and/or animal material to gain their energy for growth
and activity. Consumers are further divided into three types based on their
ability to digest plant and animal material:
- Herbivores eat only plants,
such as the elk that graze the grasslands of the Columbia valley,
or an insect nibbling on the leaf of a sticky geranium.
- Omnivores eat both plants
and animals, such as the black bear.
- Carnivores eat only
animals, such as the red-tailed hawk or western rattlesnake.
Decomposers
include
the insects, fungi, algae and bacteria both on the ground and in the soil that
help to break down the organic layer to provide nutrients for growing plants.
There are many millions of these organisms in each square metre of grassland.
Soil
has
many biotic functions in a grasslands ecosystem. It provides the material in
which plants grow, holds moisture for plants to absorb, is the "recycling
bin" for plant and animal matter, and provides an important habitat for
soil organisms. Soil is a vital link between the biotic and abiotic parts of a
grassland ecosystem.
Ecosystem
Processes
Energy Flow
Refer
to the yellow
arrows in the diagram to help you understand
the way that energy moves through an ecosystem.
Plants
only capture about one percent of the energy that reaches the earth from the
sun. In grasslands, that small amount of energy is used by the grasses and
other plants, or producers. Some animals eat only these plants. Other
animals eat both grasses and other plants, and animals, while yet other animals
only eat animals. Animals are called consumers.
Food Chain
This
movement of energy from producers to consumers is called a Food Chain.
The
"grazing" food chain has a number of steps that start with the
producers, or the plants, and flows through a series of levels of consumers. At
each step only about 10% of the energy is passed up through the chain. The rest
is passed back into the atmosphere as heat through breathing and decomposition.
In
the first step plants convert the sun’s energy to chemical energy through a
process called photosynthesis. The chemical energy is stored both as
food and as structural elements in the plant.
The
next step involves the primary consumers, animals that eat only plants.
In a grassland ecosystem this includes animals such as California Bighorn
Sheep, Mule Deer, Elk, marmots, Pocket Gopher and mice. At step three are the secondary
consumers, also called predators; these animals eat primary
consumers. In a grassland ecosystem this includes a Coyote eating a mouse, a
woodpecker eating an ant, or a frog eating an insect. At step four are the tertiary
consumers that eat secondary consumers, and sometimes primary consumers as
well. In a grassland ecosystem this includes a snake eating a frog.
The
"detritus" food chain is a system where the energy produced by
the breakdown of dead plant and animal matter is cycled into the
"grazing" food chain. Detritus is organic matter formed by decaying
animal or plant tissue, or fecal matter. Detritus eaters (or
detritivores) such as insects, worms and other small organisms feed on
dead plants, waste products from animals and dead animals. Decomposers
are fungal or bacterial organisms that work within the dead material to help
break it down, activating decay and decomposition. This important part of the
ecosystem takes the last of the energy that was originally absorbed by the
plants and returns it to the soil.
Carbon can be traced
through the ecosystem in a cycle that is similar to the water cycle. Plants
take in carbon in the form of carbon dioxide from the atmosphere through respiration.
Through a process called photosynthesis, the carbon dioxide combines with
oxygen to form carbohydrates that range from simple sugars to the
complex carbohydrate cellulose, which forms cell walls. When plants are eaten
the carbon is transferred to the consumers. As plant material is broken
down in the digestive system of an animal, carbon is absorbed as a nutrient for
use by that animal. It is released back into the atmosphere as carbon dioxide
through respiration and through the decomposition of dead animals and fecal
matter. Grassland fires also release carbon dioxide into the atmosphere.
Water Cycling
All
organisms require both water and nutrients (food) to survive.
Where
do the water and nutrients come from and how do they move around a grassland
ecosystem?
The
water cycle is
illustrated by the blue parts of
the diagram.
Water exists in three
forms: solid (ice and snow), liquid and gas (water vapour). Water is the vital
link between the ecosystem and the weather or climate.
Water
falls from clouds onto the grasslands as rain or snow.
Rain runs off plants and
rocks onto the ground, where some water is absorbed into the soil. The rest
runs over the surface of the ground and collects in low areas to form into
wetlands, lakes and rivers. Finally, some water that reachs the ground is
evaporated back into the atmosphere.
Snow, which is
crystallized water droplets, may form a blanket over the grasslands during the
winter. Snow undergoes similiar processes to rain when it reaches the ground.
Some of it evaporates back into the atmosphere, and as snow melts, the water
produced is absorbed into the soil, or runs over the ground into wetlands,
lakes and rivers.
Plants
take up some of the water contained in the soil through their roots. Other
water that permeates (soaks through) the soil flows into wetlands, lakes, and
rivers. The rest becomes part of the water table. The water table is water that
remains in the soil, filling the pores between rocks and soil particles. Water
is returned to the atmosphere as water vapour through evaporation and
transpiration. Transpiration is a process performed by plants whereby water
molecules leave the plant's surface through evaporation.
The
water that reaches wetlands, lakes and rivers flows eventually to the ocean,
with some of it evaporating along the way. Evaporation provides the moisture in
clouds that condenses to form droplets of rain or snow. These droplets of water
return to the earth as precipitation, and the cycle starts again.
The
portions of grassland ecosystems that occur in low elevations and especially on
south-facing slopes suffer from a water deficit during the hottest and
driest months of the year. The amount of water that is released into the
atmosphere through transpiration and evaporation is larger than the amount that
falls as rain at this time of year. Grassland plants have adopted a variety of
ways to survive under these difficult growing conditions.
Bright
yellow sagebrush buttercups are some of the earliest flowers to be seen in the
grasslands early spring. They start to grow before all the snow has left the
grasslands, their shallow roots take advantage of all the water stored in the
thawed upper layers of the soil. By the end of May the available moisture is
well below the reach of the roots of the plants, and little remainsof the
sagebrush buttercup but some dried out leaves.
Plants
such as low pussytoes and silky lupine start growing a little later in the
spring and bloom before the summer drought begins. They may grow again as soil
moisture increases after fall showers. Some of the bunchgrasses have a similar
early growth habit but become semi-dormant during the summer drought. They put
on a significant amount of growth when fall rains arrive. Deeply-rooted shrubs
such as big sagebrush and rabbitbrush start growing later in the year and are
covered with yellow flowers in the fall.
Nutrient Cycling
The
nutrient cycle follows the green parts of
the diagram below.
Nutrients
combine with water in the soil and are transported through the roots of the
plant to those parts that need them. They are then passed through the food
chain as the consumers eat the plants and each other. The final
decomposition of both producers and consumers returns the nutrients back to the
soil.
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