BIO120H1 Chapter Notes - Chapter 3: Streams, Ocean Acidification, Northern Hemisphere

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5 Feb 2013

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Chapter 3: The Biosphere
The Great Plains, bears little resemblance to the Serengeti
If not for a series of important environmental changes, however, the two ecosystems might
superficially look very similar
Temperate and high latitude biological communities have been subjected to natural, long term
climate change, leading to latitudinal or elevational shifts in their positions and species composition
The animal inhabitants of those earlier grasslands were strikingly different from today‘s
As the extensive grasslands of the Great Plains were developing, many of the large mammals of
North America suddenly went extinct
Nearly all the animals that went extinct belonged to the same group: large mammals
Hypotheses have been proposed to account for the disappearance:
- Changes in the climate during the extinction period were rapid and could have led to
changes in habitat or food supply that would have negatively affected the animals
- Arrival of humans in North America may have hastened the demise of the animals
Living things can be found in remarkable places
However, most living things occur in a range of habitats that cover a thin veneer of Earth‘s
surface, from the tops of trees to the surface soil layers in terrestrial environments and within
200m of the surface of the oceans
Biosphere the zone of life on Earth, is sandwiched between the lithosphere, Earth‘s surface
crust and upper mantle, and the troposphere, the lowest layer of the atmosphere
Biomes a large scale terrestrial biological community shaped by the regional climate, soil, and
disturbance patterns where it is found,
usually classified by the growth form of the dominant plants
Concept 3.1 Terrestrial Biomes are Characterized by the Growth Forms of the Dominant Vegetation
Biomes are the large scale biological communities shaped by the physical environment in which they
are found
- They reflect the climatic variation
- Categorized by the most common forms of plants distributed across large geographic areas
- Categorization of biomes relies on similarities in the morphological responses of organisms to
the physical environment
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- Provides a useful introduction to the diversity of life on Earth, the biome concept provides
a convenient biological unit for modelers simulating the effects of environmental change on
biological communities as well as the effects of vegetation on the climate system
Tropical forests have multiple verdant layers, high growth rates, and tremendous species diversity
Polar deserts have a scattered cover of tiny plants clinging to the ground, reflecting a harsh
climate of high winds, low temperatures, and dry soils
Terrestrial biomes are classified by the growth form (size and morphology) of the dominant plants
- Characteristics of their leaves such as deciduousness (seasonal shedding of eaves), thickness
and succulence (dev. Of fleshy water storage tissues) may also be used
Plant growth forms are good indicators of the physical environment, reflecting the climatic zones
Trees and shrubs invest E in woody tissues in order to increase their height and ability to capture
sunlight and to protect their tissues from damage by wind or large amounts of snow
Perennial grasses can grow from the bases of their leaves and keep their vegetative and
reproductive buds below the soil surface, which facilitates their tolerance of grazing, fire, sub-
freezing temp. and dry soils
Convergence the evolution of similar growth forms among distantly related species in response to
similar selection pressures
Climatic zones are major determinants of the distribution of terrestrial biomes
The tropics are characterized by high rainfall and warm, invariant temperatures
- Subtropical regions rainfall becomes more seasonal, with pronounced dry and wet seasons
- Major deserts zones of high pressure at about 30° N and S and with the rain shadow
effects of large mountain ranges
- Temperate and Polar zones subfreezing temperatures during winter
- The amount of precipitation N and S of 40° varies depending on proximity to the ocean
and the influence of mountain ranges
The locations of terrestrial biomes are correlated with variations in temperature and precipitation
- Temperature influences the distribution of plant growth forms directly through its effect
on the physiological functioning of plants
- Precipitation and temperature act in concert to influence the availability of water and its
rate of loss by plants
- Water availability and soil temp. are important in determining the supply of nutrients in
the soil, which is also an important control on plant growth form
While these 2 factors predict biome distributions reasonably well, this approach fails to
incorporate seasonal variation in temperature and precipitation
Climatic extremes are sometimes more important in determining species distributions than mean
annual conditions
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Factors such as soil texture and chemistry as well as proximity to mountains and large bodies of
water can influence biome distribution
Land Use Change the alteration of terrestrial surface, including vegetation and land forms, by
human activities such as agriculture, forestry
and mining
As a result of human influences, the potential and the actual distributions of biomes are markedly
- Found in low latitude regions
- Precipitation exceeds 2 000 mm
- Seasonal climatic rhythms are generally absent
- Plants grow continuously throughout the year
- Include the most productive ecosystems on Earth
- Characterized by broad-leaved evergreen and deciduous trees
- Light is a key environmental factor determining the vegetation structure of
this biome
- Emergent trees rise above the majority of the other trees that make up the
canopy of the forest
- Below the canopy, plants that utilize trees for support and to elevate their
leaves above the ground are found draped over or clinging to the canopy and
emergent trees, including lianas (woody vines) and epiphytes (plants that grow
on tree branches)
- Understory plants grow in the shade of the canopy, further reducing the light
that finally reaches the forest floor
- Shrubs and forbs occupy the forest floor, where they must rely on light flecks
that move across the forest floor during the day for photosynthesis
Tropical Seasonal
Forests and
- Rainfall is seasonal, with pronounced wet and dry seasons associated with shifts
in the ICTZ
- This region is marked by a large gradient in climate primarily associated with
the seasonality of rainfall
- Vegetation: shorter stature, lower tree densities, and an increasing degree of
drought deciduousness, with leaves dropping from the trees during the dry
season, greater abundance of grasses and shrubs and fewer trees relative to
- Vegetation types: tropical dry forests, thorn woodlands, and tropical savannas
- The frequency of fires, which increases with the length of the dry season,
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