A biome
/ˈbaɪoʊm/ is a formation of plants and animals that have common
characteristics due to similar climates and can be found over a range of
continents.
Biome
From Wikipedia, the free encyclopedia
A map of different biomes around the world.
A
biome is a formation of
plants and
animals that have common characteristics due to similar climates and can be found over a range of continents.
[1] Biomes are distinct from
habitats, because any biome can comprise a variety of habitats.
A biome contrasts with a
microbiome. A microbiome is also a mix of organisms that coexist in a defined space, but on a much smaller scale. For example, the
human microbiome is the collection of bacteria, viruses, and other microorganisms that are present on a human.
Classification
Biomes are defined by climate regimes and
biogeography.
A 1978 study on North American grasslands
[2] found a positive
logistic correlation between
evapotranspiration in mm/yr and above-ground net primary production in g/m
2/yr. The general results from the study were that precipitation and water use led to above-ground primary production, while
solar irradiation
and temperature lead to below-ground primary production (roots), and
temperature and water lead to cool and warm season growth habit.
[3]
These findings help explain the categories used in Holdridge’s
bioclassification scheme (see below), which were then later simplified
by Whittaker. The number of classification schemes and the variety of
determinants used in those schemes, however, should be taken as strong
indicators that biomes do not fit perfectly into the classification
schemes created.
Holdridge
Holdridge classified climates based on the biological effects of
temperature and rainfall on vegetation under the assumption that these
two
abiotic
factors are the largest determinants of the types of vegetation found
in a habitat. Holdridge uses the four axes to define 30 so-called
"humidity provinces", which are clearly visible in his diagram. While
this scheme largely ignores soil and sun exposure, Holdridge
acknowledged that these were important.
Whittaker's biome-type classification scheme
The distribution of vegetation types as a function of mean annual temperature and precipitation.
Whittaker
classified biomes using two abiotic factors: precipitation and
temperature. His scheme can be seen as a simplification of Holdridge's;
more readily accessible, but missing Holdridge's greater specificity.
Whittaker based his approach on theoretical assertions and empirical
sampling. He was in a unique position to make such a holistic assertion
because he had previously compiled a review of biome classifications.
[4]
Key definitions for understanding Whittaker's scheme
- Physiognomy
- The apparent characteristics, outward features, or appearance of ecological communities or species.
- Biome
- A grouping of terrestrial ecosystems on a given
continent that are similar in vegetation structure, physiognomy,
features of the environment and characteristics of their animal
communities.
- Formation
- A major kind of community of plants on a given continent.
- Biome-type
- Grouping of convergent biomes or formations of different continents, defined by physiognomy.
- Formation-type
- A grouping of convergent formations.
Whittaker's distinction between biome and formation can be
simplified: formation is used when applied to plant communities only,
while biome is used when concerned with both plants and animals.
Whittaker's convention of biome-type or formation-type is simply a
broader method to categorize similar communities.
[5]
Whittaker's parameters for classifying biome-types
Whittaker, seeing the need for a simpler way to express the
relationship of community structure to the environment, used what he
called "gradient analysis" of ecocline patterns to relate communities to
climate on a worldwide scale. Whittaker considered four main ecoclines
in the terrestrial realm.
[5]
- Intertidal levels: The wetness gradient of areas that are exposed to
alternating water and dryness with intensities that vary by location
from high to low tide
- Climatic moisture gradient
- Temperature gradient by altitude
- Temperature gradient by latitude
Along these gradients, Whittaker noted several trends that allowed him to qualitatively establish biome-types:
- The gradient runs from favorable to extreme, with corresponding changes in productivity.
- Changes in physiognomic complexity vary with how favorable of an
environment exists (decreasing community structure and reduction of
stratal differentiation as the environment becomes less favorable).
- Trends in diversity of structure follow trends in species diversity;
alpha and beta species diversities decrease from favorable to extreme
environments.
- Each growth-form (i.e. grasses, shrubs, etc.) has its characteristic place of maximum importance along the ecoclines.
- The same growth forms may be dominant in similar environments in widely different parts of the world.
Whittaker summed the effects of gradients (3) and (4) to get an
overall temperature gradient, and combined this with gradient (2), the
moisture gradient, to express the above conclusions in what is known as
the Whittaker classification scheme. The scheme graphs average annual
precipitation (x-axis) versus average annual temperature (y-axis) to
classify biome-types.
Walter system
The eponymously-named Heinrich Walter classification scheme considers
the seasonality of temperature and precipitation. The system, also
assessing precipitation and temperature, finds nine major biome types,
with the important climate traits and
vegetation types.
The boundaries of each biome correlate to the conditions of moisture
and cold stress that are strong determinants of plant form, and
therefore the vegetation that defines the region. Extreme conditions,
such as flooding in a swamp, can create different kinds of communities
within the same biome.
- I. Equatorial
- II. Tropical
- III. Subtropical
- Highly seasonal, arid climate
- Desert vegetation with considerable exposed surface
- IV. Mediterranean
- Winter rainy season and summer drought
- Sclerophyllous (drought-adapted), frost-sensitive shrublands and woodlands
- V. Warm temperate
- Occasional frost, often with summer rainfall maximum
- Temperate evergreen forest, somewhat frost-sensitive
- VI. Nemoral
- Moderate climate with winter freezing
- Frost-resistant, deciduous, temperate forest
- VII. Continental
- Arid, with warm or hot summers and cold winters
- Grasslands and temperate deserts
- VIII. Boreal
- Cold temperate with cool summers and long winters
- Evergreen, frost-hardy, needle-leaved forest (taiga)
- IX. Polar
- Short, cool summers and long, cold winters
- Low, evergreen vegetation, without trees, growing over permanently frozen soils
Bailey system
Robert G. Bailey nearly developed a
biogeographical
classification system for the United States in a map published in 1976.
He subsequently expanded the system to include the rest of North
America in 1981, and the world in 1989. The Bailey system, based on
climate, is divided into seven domains (polar, humid temperate, dry,
humid, and humid tropical), with further divisions based on other
climate characteristics (subarctic, warm temperate, hot temperate, and
subtropical; marine and continental; lowland and mountain).
[6]
- 100 Polar Domain
- 120 Tundra Division (Köppen: Ft)
- M120 Tundra Division – Mountain Provinces
- 130 Subarctic Division (Köppen: E)
- M130 Subarctic Division – Mountain Provinces
- 200 Humid Temperate Domain
- 210 Warm Continental Division (Köppen: portion of Dcb)
- M210 Warm Continental Division – Mountain Provinces
- 220 Hot Continental Division (Köppen: portion of Dca)
- M220 Hot Continental Division – Mountain Provinces
- 230 Subtropical Division (Köppen: portion of Cf)
- M230 Subtropical Division – Mountain Provinces
- 240 Marine Division (Köppen: Do)
- M240 Marine Division – Mountain Provinces
- 250 Prairie Division (Köppen: arid portions of Cf, Dca, Dcb)
- 260 Mediterranean Division (Köppen: Cs)
- M260 Mediterranean Division – Mountain Provinces
- 300 Dry Domain
- 310 Tropical/Subtropical Steppe Division
- M310 Tropical/Subtropical Steppe Division – Mountain Provinces
- 320 Tropical/Subtropical Desert Division
- 330 Temperate Steppe Division
- 340 Temperate Desert Division
- 400 Humid Tropical Domain
- 410 Savanna Division
- 420 Rainforest Division
WWF system
A team of biologists convened by the
World Wildlife Fund (WWF) developed an
ecological land classification system that identified fourteen biomes,
[7] called
major habitat types, and further divided the world's land area into 882
terrestrial ecoregions
(includes new Antarctic ecoregions by Terrauds et al. 2012). Each
terrestrial ecoregion has a specific EcoID, format XXnnNN (XX is the
ecozone, nn is the biome number, NN is the individual number). This classification is used to define the
Global 200 list of
ecoregions identified by the WWF as priorities for conservation. The WWF major habitat types are:
- 01 Tropical and subtropical moist broadleaf forests (tropical and subtropical, humid)
- 02 Tropical and subtropical dry broadleaf forests (tropical and subtropical, semihumid)
- 03 Tropical and subtropical coniferous forests (tropical and subtropical, semihumid)
- 04 Temperate broadleaf and mixed forests (temperate, humid)
- 05 Temperate coniferous forests (temperate, humid to semihumid)
- 06 Boreal forests/taiga (subarctic, humid)
- 07 Tropical and subtropical grasslands, savannas, and shrublands (tropical and subtropical, semiarid)
- 08 Temperate grasslands, savannas, and shrublands (temperate, semiarid)
- 09 Flooded grasslands and savannas (temperate to tropical, fresh or brackish water inundated)
- 10 Montane grasslands and shrublands (alpine or montane climate)
- 11 Tundra (Arctic)
- 12 Mediterranean forests, woodlands, and scrub or sclerophyll forests (temperate warm, semihumid to semiarid with winter rainfall)
- 13 Deserts and xeric shrublands (temperate to tropical, arid)
- 14 Mangrove (subtropical and tropical, salt water inundated)
Freshwater biomes
According to the WWF, the following are classified as
freshwater biomes:
[8]
Realms or ecozones (terrestrial and freshwater, WWF)
Marine biomes
Marine biomes (H) (major habitat types), Global 200 (WWF)
Biomes of the coastal and
continental shelf areas (
neritic zone –
List of ecoregions (WWF))
Realms or ecozones (marine, WWF)
- North temperate Atlantic
- Eastern tropical Atlantic
- Western tropical Atlantic
- South temperate Atlantic
- North temperate Indo-Pacific
- Central Indo-Pacific
- Eastern Indo-Pacific
|
- Western Indo-Pacific
- South temperate Indo-Pacific
- Southern Ocean
- Antarctic
- Arctic
- Mediterranean
|
Other marine habitat types
Major habitats, nonglobal 200 (WWF)
Summary – ecological taxonomy (WWF)
Example
Anthropogenic biomes
Humans have altered global patterns of biodiversity and ecosystem
processes. As a result, vegetation forms predicted by conventional biome
systems can no longer be observed across much of Earth's land surface
as they have been replaced by crop and rangelands or cities.
Anthropogenic biomes
provide an alternative view of the terrestrial biosphere based on
global patterns of sustained direct human interaction with ecosystems,
including agriculture, human settlements, urbanization, forestry and
other uses of land. Anthropogenic biomes offer a new way forward in
ecology and conservation by recognizing the irreversible coupling of
human and ecological systems at global scales and moving us toward an
understanding of how best to live in and manage our biosphere and the
anthropogenic biomes we live in.
Major anthropogenic biomes
- Dense settlements
- Croplands
- Rangelands
- Forested
- Indoor[10]
Dermal biome
The dermal biome is the living
ecosystem that animals (including humans) have evolved, that permits them to live symbiotically and in balance with the
microbes on and in them (the
microbiome). This ecosystem consists of
skin,
follicles,
hair,
sebaceous glands,
sweat glands,
arrector pili muscles,
peptides,
proteins, lipids and its associated
microbiota. A healthy dermal biome has several functions: it resists infection of
pathogens,
protects against moisture loss and water damage, dynamically regulates
body temperature and supports the healthy renewal of skin through the
epidermal cell life cycle.
- Infection Resistance: Commensal
microbiota assist the dermal biome resist infection for pathogenic
bacteria by i] out-competing pathogens for resources, ii] training or
stimulating the host’s immune system to defeat the pathogen, or iii] expressing substances that are directly hostile to the pathogen.
- Water-barrier regulation: The dermal biome regulates the water
barrier – preventing moisture from escaping (except when expressed as
sweat) and preventing environmental water from permeating the skin.
Because environmental water can have a chilling effect to mammals and warm-blooded animals when kept in close proximity to the epidermis, the dermal biome also produces hydrophobic lipids that repel water.
- Temperature regulation: The dermal biome is responsible for thermoregulation.
To regulate excess heat, the dermal biome activates the sweat glands,
allowing for evaporative cooling as sweat evaporates. To regulate cooler
temperatures, the arrector pili muscles contract, causing hairs to
“stand up” (goosebumps), and thereby trap an insulating blanket of air
close to the skin.
- Skin renewal: a healthy biome supports the replacement of skin
through the life cycle of epidermal cells as they proliferate in the
basal layers of the epidermis until they die and are shed (desquamation).
Other biomes
The
endolithic biome, consisting entirely of microscopic life in rock
pores
and cracks, kilometers beneath the surface, has only recently been
discovered, and does not fit well into most classification schemes.
Freshwater biomes
The drainage basins of the principal oceans and seas of the world are marked by continental divides. The grey areas are
endorheic basins that do not drain to the ocean.
See also
References
A biome /ˈbaɪoʊm/ is a formation of plants and animals that have common characteristics due to similar climates and can be found over a range of continents.[1] Biomes are distinct from habitats, because any biome can comprise a variety of habitats.A map of different biomes around the world.
Whittaker classified biomes using two abiotic factors: precipitation and temperature. His scheme can be seen as a simplification of Holdridge's; more readily accessible, but missing Holdridge's greater specificity.The distribution of vegetation types as a function of mean annual temperature and precipitation.
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