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Chapter 3

BIOB50 Chapter 3 Review

Biological Sciences
Course Code
Marc Cadotte

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Chapter 3 The Biosphere
The American Serengeti – Twelve Centuries of Change in the Great Plains: A Case Study
-Great Plains located in central North America is different from Serengeti Plain of Africa
-low biological diversity in Great Plains
-genetically identical crop plants & few species of domesticated herbivores
-diverse wild animals in Serengeti
-latitudinal/ elevational shifts in biological communities & species composition
-vegetation followed retreating ice northward & colonized newly exposed area
-megafauna are animals larger than 45 kg
-these large mammals went extinct in Great Plains about 10.000-13,000 years ago
-changes in climate in extinction period were rapid
led to changes in habitat/ food supply that negatively affected animals
-arrival of humans increases the death rate of animals (still controversial)
-biosphere is zone of life on Earth located between lithosphere & troposphere
-lithosphere: Earth’s surface crust & upper mantle
-troposphere: lowest layer of atmosphere
Terrestrial Biomes
-large-scale biological communities shaped by physical environment
-reflect climatic variation
-categorized by most common forms of plants distributed across large geographic areas
categorization does not take taxonomic relationship among organisms into account
relies on similarities in morphological responses of organisms to physical environment
-biomes in different continents show similar responses to climatic forces
Tropical forests
-have multiple verdant layers
-high growth rates
-high species diversity
-vegetation reaches higher height
-greater aboveground biomass
Polar deserts
-harsh climate of high winds
-low temperatures
-dry soil
-tiny plants cling to ground
-low surface biomass
-terrestrial biomes are classified by:

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1) Growth form of dominant plants
-size & morphology
2) Characteristic of leaves
i) Deciduousness
-seasonal shedding of leaves
ii) Thickness
iii) Succulence
-development of fleshly water storage tissues
-plants instead of animals are used to categorize terrestrial biomes
-plants are immobile
-cope with environmental extremes & biological pressures (competition for water, nutrient, &
light) in order to occupy a site for a long time
-plant growth forms are good indicators of physical environment
-reflect climatic zones & rates of disturbance (fire frequency)
-mobility of animal allows them to avoid exposure to adverse environmental conditions
-composition of microbial communities reflects physical condition
-but tiny size of microorganisms along with rapid temporal & spatial changes in their composition
makes them impractical for classifying biomes
-plants develop different forms in response to selection pressures of terrestrial environment
-selection pressures include aridity, high & subfreezing temperatures, intense solar radiation,
nutrient-poor soil, grazing by animals, crowding by neighbour
-deciduous leaves help plants to face seasonal exposure, ranging from subfreezing temperatures to
dry periods
-woody tissues increase height & ability to capture sunlight & protect tissues from damage by
wind or large amounts of snow
Perennial grasses
-grow from bases of leaves
-keep vegetative & reproductive buds below soil surface
facilitate tolerance of grazing, fire, sub-freezing temperature & dry soils
-similar plant growth forms appear in similar climatic zones on different continents for plants that
are not genetically related
-this type of evolution is convergence when there are similar growth forms among distantly related
species in response to similar selection pressures
Terrestrial biomes reflect global patterns
-climatic zones determine distribution of terrestrial biomes
-high rainfall
-warm, invariant temperature
Subtropical region

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-border the tropics
-rainfalls become more seasonal with dry & wet seasons
-zones of high pressure
-rain-shadow effect of large mountain ranges
Temperate & polar zone
-subfreezing temperatures in winter
-North & South of 40̊
-amount of precipitation varies depending on proximity to ocean & influence of mountain range
-temperature affects distribution of plant growth form
has effect on physiological functioning of plants
-precipitation & temperature affect availability of water & its rate of loss
-water availability & soil temperature determine supply of nutrients in soil
-average annual precipitation & temperature graph can be used to show association between
climatic variation & terrestrial biome distribution
but, fail to include seasonal variation in temperature & precipitation
climatic extremes are more important in determining species distributions than mean annual
-soil texture & chemistry, proximity to mountains & large bodies of water can affect biome
distribution as well
The potential distributions of terrestrial biomes differ from their actual distribution due to human
-land use change is human effects of land conversion & resource extraction
-clear forest & enhance size of game populations
-land surface is altered by agriculture, forestry & livestock grazing
-a portion is turned into urban development & transportation use
-grasslands in temperate biomes have been transformed the most
-tropical & subtropical are experiencing rapid change as well
-climatic diagram shows characteristic seasonal pattern of air temperature & precipitation at
representative location in biome
period of water shortage is shaded in yellow
period of subfreezing temperature is shaded in blue
-each biome incorporates a mix of different communities
-boundaries between biomes are gradual
complex due to variations in regional climatic influence soil type, topography & disturbance
Tropical rainforests
-in low-latitude regions (between 10 N & S)̊
-precipitation exceeds 2000 mm annually
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