Forest ecosystems are
dominated by trees that can mature to at least 2 m in height and provide a
canopy of at least 20% cover, together with all the native wildlife, including
birds, mammals, marsupials, amphibians, reptiles, insects, plants, as well as
moss, fungi, micro-organisms and non-living things such as water, soil and air interacting
within the same area.
Grassland ecosystem: A
biological community that contains few trees or shrubs, is characterized by
mixed herbaceous (non-woody) vegetation cover, and is dominated by grasses or
grass like plants. Mixtures of trees and grasslands occur as savannas at
transition zones with forests or where rainfall is marginal for trees. About
1.2 × 108 mi2 (4.6 × 107 km2) of the Earth's surface is covered
with grasslands, which make up about 32% of the plant cover of the world. Grasslands
occur in regions that are too dry for forests but that have sufficient soil
water to support a closed herbaceous plant canopy that is lacking in deserts.
Thus, temperate grasslands usually develop in areas with 10–40 in. (25–100 cm)
of annual precipitation, although tropical grasslands may receive up to 60 in. (150
cm). Grasslands are found primarily on plains or rolling topography in the
interiors of great land masses, and from sea level to elevations of nearly
16,400 ft (5000 m) in the Andes. Because of their continental location they
experience large differences in seasonal climate and wide ranges in diurnal
conditions. In general, there is at least one dry season during the year, and
drought conditions occur periodically. Significant portions of the world's
grasslands have been modified by grazing or tillage or have been converted to
other uses. The most fertile and productive soils in the world have developed
under grassland, and in many cases the natural species have been replaced by
cultivated grasses (cereals).
Desert ecosystem: Deserts, like forests and
grasslands, occur all around the world. Symmetrical clusters of deserts are
found around the Tropic of Cancer and the Tropic of Capricorn - the two
latitudes that define the area where the sun's angle at solar noon is closest
to ninety degrees overhead at the Equinox. Deserts are formed in the driest of
environment. The temperature of deserts may vary from very hot as in hot
deserts, to a very cold as in cold deserts. The most important hot deserts of
the world is the Sahara-Arabia-Gobi which extends from Africa to Central Asia.
It has a highly irregular an insignificant rainfall and low humidity. Hot
deserts also occurs in India such as Sindh-Rajasthan desert South America,
North America and Australia, cold deserts occurs in Ladakh regions of Himalayas
and Tibet. Desert plants which are adapted to drought conditions through
reduced leaf size and the dropping of leaves in any conditions both reducing
loss via evapotranspiration. The roots of most desert plants remain well
developed and occur in the top of the soil in order to take maximum possible
advantage of any rainfall. The animals present in the desert are reptiles,
insects and rodents. All these animals have special morphological,
physiological and etiological adaptations for desert. Some desert animals are
newly adapted for high extremes of temperatures. In general large animals are
very uncommon except male deer. Some desert plant closes their petals at night
while many plants blossom only at night. There are some insects which remain
active during the day while some insects are active at night. Some reptiles and
insects are well adapted for their survival in deserts and excrete dry matter;
kangaroo, rat and pocket mouse are able to live without drinking water. They do
so by extracting the moisture from the seed they eat. The camel and the desert
birds (ostrich) have an occasional drink of water but can go for long periods
of time using the water stored in the body. Most insects of the deserts are
herbivores. The species composition of desert ecosystem is much more varied and
typical. The biotic components of deserts ecosystem are summarized as under:
(1) Producers: These are shrubs, bushes and some
grasses and a few trees. The shrubs have widespread, branched root system. Some
lower plants like xerophytes mosses may also be present.
(2) Consumers: The most common animals are reptiles
and insects which are able to live under xeric conditions. These are also
present some nocturnal rodents and birds. The camel feed on tender shoots of
the plants.
(3) Decomposers: They are very few due to poor
vegetation. The amount of dead organic matter is correspondingly less. There
are also some fungi and bacteria most of which are hemophilic.
Aquatic ecosystems: An aquatic
ecosystem is an ecosystem in a body of water. Communities of organisms that are
dependent on each other and on their environment live in aquatic ecosystems.
The two main types of aquatic ecosystems are Marine ecosystems & Freshwater
ecosystems Aquatic ecosystems include oceans, lakes, rivers, streams, estuaries,
and wetlands. Within these aquatic ecosystems are living things that depend on
the water for survival (fish, plants & microorganisms). These ecosystems
are very fragile and can be easily disturbed by pollution.
Marine Ecosystems: Marine
ecosystems cover approximately 71% of the Earth's surface and contain
approximately 97% of the planet's water. They generate 32% of the world's net primary production. They are distinguished from
freshwater ecosystems by the presence of dissolved compounds,
especially salts.
Approximately 85% of the dissolved materials in seawater
are sodium
and chlorine.
Seawater has an average salinity of 35 parts per
thousand (ppt) of water. Actual salinity varies among different
marine ecosystems. Marine ecosystems can be divided into many zones depending
upon water depth and shoreline features. The oceanic zone is the vast
open part of the ocean where animals such as whales, sharks, and tuna live. The
benthic
zone consists of substrates below water where many invertebrates live. The intertidal
zone is the area between high and low tides; in this figure it is termed the
littoral zone. Other near-shore (neritic) zones can include estuaries,
salt marshes,
coral reefs,
lagoons
and mangrove
swamps. In the deep water, hydrothermal
vents may occur where chemo synthetic
sulfur
bacteria
form the base of the food web. Classes
of organisms found in marine ecosystems include brown algae,
dinoflagellates,
corals,
cephalopods,
echinoderms,
and sharks.
Fish caught in marine ecosystems are the biggest source of commercial foods
obtained from wild populations. Environmental problems concerning marine
ecosystems include unsustainable exploitation of marine resources (for example overfishing
of certain species), marine pollution, climate change, and building on coastal
areas.
