BIOMES

Different types of Biomes and its characterisitics

Aquatic biomes occupy the largest part of the biosphere.

·         Ecologists distinguish between freshwater and marine biomes on the basis of physical and chemical differences.

°         Marine biomes generally have salt concentrations that average 3%, while freshwater biomes have salt concentrations of less than 1%.

·         Marine biomes cover approximately 75% of the earth’s surface and have an enormous effect on the biosphere.

°         The evaporation of water from the oceans provides most of the planet’s rainfall.

°         Ocean temperatures have a major effect on world climate and wind patterns.

°         Photosynthesis by marine algae and photosynthetic bacteria produce a substantial proportion of the world’s oxygen. Respiration by these organisms consumes huge amounts of atmospheric carbon dioxide.

·         Freshwater biomes are closely linked to the soils and biotic components of the terrestrial biomes through which they pass.

°         The pattern and speed of water flow and the surrounding climate are also important.

·         Most aquatic biomes are physically and chemically stratified.

·         Light is absorbed by the water and by photosynthetic organisms, so light intensity decreases rapidly with depth.

°         There is sufficient light for photosynthesis in the upper photic zone.

°         Very little light penetrates to the lower aphotic zone.

·         The substrate at the bottom of an aquatic biome is the benthic zone.

°         This zone is made up of sand and sediments and is occupied by communities of organisms called benthos.

°         A major food source for benthos is dead organic material or detritus, which rains down from the productive surface waters of the photic zone.

·         Sunlight warms surface waters, while deeper waters remain cold.

°         As a result, water temperature in lakes is stratified, especially in summer and winter.

°         In the ocean and most lakes, a narrow stratum of rapid temperature change called a thermocline separates the more uniformly warm upper layer from more uniformly cold deeper waters.

·         In aquatic biomes, community distribution is determined by depth of the water, distance from shore, and open water versus bottom.

·         In marine communities, phytoplankton, zooplankton, and many fish species live in the relatively shallow photic zone.

·         The aphotic zone contains little life, except for microorganisms and relatively sparse populations of luminescent fishes and invertebrates.

·         The major aquatic biomes include lakes, wetlands, streams, rivers, estuaries, intertidal biomes, oceanic pelagic biomes, coral reefs, and marine benthic biomes.

·         Freshwater lakes vary greatly in oxygen and nutrient content.

°         Oligotrophic lakes are deep, nutrient poor, oxygen rich, and contain little life.

°         Eutrophic lakes are shallow, nutrient rich, and oxygen poor.

·         In lakes, the littoral zone is the shallow, well-lit water close to shore.

°         The limnetic zone is the open surface water.

·         Wetlands are areas covered with sufficient water to support aquatic plants.

°         They can be saturated or periodically flooded.

°         Wetlands include marshes, bogs, and swamps.

°         They are among the most productive biomes on Earth and are home to a diverse community of invertebrates and birds.

°         Because of the high organic production and decomposition in wetlands, their water and soil are low in dissolved oxygen.

°         Wetlands have a high capacity to filter dissolved nutrients and chemical pollutants.

°         Humans have destroyed many wetlands, but some are now protected.

·         Streams and rivers are bodies of water moving continuously in one direction.

°         Headwaters are cold, clear, turbulent, and swift.

§  They carry little sediment and relatively few mineral nutrients.

°         As water travels downstream, it picks up O₂ and nutrients on the way.

°         Nutrient content is largely determined by the terrain and vegetation of the area.

§  Many streams and rivers have been polluted by humans, degrading water quality and killing aquatic organisms.

§  Damming and flood control impairs the natural functioning of streams and rivers and threatens migratory species such as salmon.

·         Estuaries are areas of transition between river and sea.

°         The salinity of these areas can vary greatly.

°         Estuaries have complex flow patterns, with networks of tidal channels, islands, levees, and mudflats.

°         They support an abundance of fish and invertebrate species and are crucial feeding areas for many species of waterfowl.

·         An intertidal zone is a marine biome that is periodically submerged and exposed by the tides.

°         The upper intertidal zone experiences longer exposure to air and greater variation in salinity and temperature than do the lower intertidal areas.

°         Many organisms live only at a particular stratum in the intertidal.

·         The oceanic pelagic biome is the open blue water, mixed by wind-driven oceanic currents.

°         The surface waters of temperate oceans turn over during fall through spring.

°         The open ocean has high oxygen levels and low nutrient levels.

°         This biome covers 70% of the Earth’s surface and has an average depth of 4,000 meters.

·         Coral reefs are limited to the photic zone of stable tropic marine environments with high water clarity. They are found at temperatures between 18°C and 30°C.

°         They are formed by the calcium carbonate skeletons of coral animals.

°         Mutualistic dinoflagellate algae live within the tissues of the corals.

°         Coral reefs are home to a very diverse assortment of vertebrates and invertebrates.

°         Collecting of coral skeletons and overfishing for food and the aquarium trade have reduced populations of corals and reef fishes.

°         Global warming and pollution contribute to large-scale coral mortality.

·         The marine benthic zone consists of the seafloor below the surface waters of the coastal or neritic zone and the offshore pelagic zone.

°         Most of the ocean’s benthic zone receives no sunlight.

°         Organisms in the very deep abyssal zone are adapted to continuous cold (about 3°C) and extremely high pressure.

°         Unique assemblages of organisms are associated with deep-sea hydrothermal vents of volcanic origin on mid-ocean ridges.

§  The primary producers in these communities are chemoautotrophic prokaryotes that obtain energy by oxidizing H₂S formed by a reaction of volcanically heated water with dissolved sulfate (SO₄²⁻).

Climate largely determines the distribution and structure of terrestrial biomes

·         Because there are latitudinal patterns of climate over the Earth’s surface, there are also latitudinal patterns of biome distribution.

·         A climograph denotes the annual mean temperature and precipitation of a region.

°         Temperature and rainfall are well correlated with different terrestrial biomes, and each biome has a characteristic climograph.

·         Most terrestrial biomes are named for major physical or climatic features or for their predominant vegetation.

·         Vertical stratification is an important feature of terrestrial biomes.

°         The canopy of the tropical rain forest is the top layer, covering the low-tree stratum, shrub understory, ground layer, litter layer, and root layer.

°         Grasslands have a canopy formed by grass, a litter layer, and a root layer.

°         Stratification of vegetation provides many different habitats for animals.

·         Terrestrial biomes usually grade into each other without sharp boundaries. The area of intergradation, called the ecotone, may be narrow or wide.

·         The species composition of any biome differs from location to location.

·         Biomes are dynamic, and natural disturbance rather than stability tends to be the rule.

°         Hurricanes create openings for new species in tropical and temperate forests.

°         In northern coniferous forests, snowfall may break branches and small trees, producing gaps that allow deciduous species to grow.

°         As a result, biomes exhibit patchiness, with several different communities represented in any particular area.

·         In many biomes, the dominant plants depend on periodic disturbance.

°         For example, natural wildfires are an integral component of grasslands, savannas, chaparral, and many coniferous forests.

·         Human activity has radically altered the natural patterns of periodic physical disturbance.

°         Fires are now controlled for the sake of agricultural land use.

·         Humans have altered much of the Earth’s surface, replacing original biomes with urban or agricultural ones.

·         The major terrestrial biomes include tropical forest, desert, savanna, chaparral, temperate grassland, coniferous forest, temperate broadleaf forest, and tundra.

·         Tropical forests are found close to the equator.

°         Tropical rain forests receive constant high amounts of rainfall (200 to 400 cm annually).

°         In tropical dry forests, precipitation is highly seasonal.

°         In both, air temperatures range between 25°C and 29°C year round.

°         Tropical forests are stratified, and competition for light is intense.

°         Animal diversity is higher in tropical forests than in any other terrestrial biome.

·         Deserts occur in a band near 30° north and south latitudes and in the interior of continents.

°         Deserts have low and highly variable rainfall, generally less than 30 cm per year.

°         Temperature varies greatly seasonally and daily.

°         Desert vegetation is usually sparse and includes succulents such as cacti and deeply rooted shrubs.

°         Many desert animals are nocturnal, so they can avoid the heat.

°         Desert organisms display adaptations to allow them to resist or survive desiccation.

·         Savanna is found in equatorial and subequatorial regions.

°         Rainfall is seasonal, averaging 30–50 cm per year.

°         The savanna is warm year-round, averaging 24–29°C with some seasonal variation.

°         Savanna vegetation is grassland with scattered trees.

°         Large herbivorous mammals are common inhabitants.

§  The dominant herbivores are insects, especially termites.

°         Fire is important in maintaining savanna biomes.

·         Chaparrals have highly seasonal precipitation with mild, wet winters and dry, hot summers.

°         Annual precipitation ranges from 30 to 50 cm.

°         Chaparral is dominated by shrubs and small trees, with a high diversity of grasses and herbs.

°         Plant and animal diversity is high.

°         Adaptations to fire and drought are common.

·         Temperate grasslands exhibit seasonal drought, occasional fires, and seasonal variation in temperature.

°         Large grazers and burrowing mammals are native to temperate grasslands.

°         Deep fertile soils make temperate grasslands ideal for agriculture, especially for growing grain.

°         Most grassland in North America and Eurasia has been converted to farmland.

·         Coniferous forest, or taiga, is the largest terrestrial biome on Earth.

°         Coniferous forests have long, cold winters and short, wet summers.

°         The conifers that inhabit these forests are adapted for snow and periodic drought.

°         Coniferous forests are home to many birds and mammals.

°         These forests are being logged at a very high rate and old-growth stands of conifers may soon disappear.

·         Temperate broadleaf forests have very cold winters, hot summers, and considerable precipitation.

°         A mature temperate broadleaf forest has distinct vertical layers, including a closed canopy, one or two strata of understory trees, a shrub layer, and an herbaceous layer.

°         The dominant deciduous trees in Northern Hemisphere broadleaf forests drop their leaves and become dormant in winter.

°         In the Northern Hemisphere, many mammals in this biome hibernate in the winter, while many bird species migrate to warmer climates.

°         Humans have logged many temperate broadleaf forests around the world.

·         Tundra covers large areas of the Arctic, up to 20% of the Earth’s land surface.

°         Alpine tundra is found on high mountaintops at all latitudes, including the tropics.

§  The plant communities in alpine and Arctic tundra are very similar.

°         The Artic tundra winter is long and cold, while the summer is short and mild. The growing season is very short.

°         Tundra vegetation is mostly herbaceous, consisting of a mixture of lichens, mosses, grasses, forbs, and dwarf shrubs and trees.

°         A permanently frozen layer of permafrost prevents water infiltration and restricts root growth.

°         Large grazing musk oxen are resident in Arctic tundra, while caribou and reindeer are migratory.

°         Migratory birds use Arctic tundra extensively during the summer as nesting grounds.

Arctic tundra is sparsely settled by humans but has recently become the focus of significant mineral and oil extraction