Ecology Chapter 3.docx

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University of Toronto Scarborough
Biological Sciences
Mark Kortschot

Ecology Chapter 3: The Biosphere  Terrestrial Biomes - Biomes are large-scale biological communities shaped by the physical environment where they are found - Biomes relies on similarities in the morphological responses of organisms to the physical environment - The tropics are characterized by high rainfall and warm, invariant temperatures - Subfreezing temperatures during winter are an important climatic feature of the temperature and polar zones - Terrestrial communities vary considerably, from the warm and wet tropics to the cold and dry polar regions - 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 (high winds, low temperature, and dry soils) - Terrestrial biomes are classified by the growth form (size and morphology) of the dominant plants - Plant growth are used to categorize terrestrial biomes over animal growth because they must cope with the environmental extremes as well as biological pressures (such as competition for water, nutrients, and light) so therefore plant growth is a good indicator of the physical environment - Deciduous leaves is one solution to seasonal exposure to subfreezing temperatures or extended dry periods - Trees and shrubs invest energy in woody tissues in order to increase their height - The same plants or the ones closely related grow in similar climatic zones on different continents even if the plants aren’t genetically related - Convergence is the evolution of similar growth forms amount distantly related species in response to similar selection pressures - The tropics (between 23.5 N and S) are characterized by high rainfall and warm, invariant temperatures - Temperature influences the distribution of plant growth - Locations of terrestrial biomes are correlated with these variations in temperature and precipitation - Land use change is the effects of and conversion and resource extraction by humans - There are 9 terrestrial biomes discussed: 1) Tropical Rainforests: - Experience warm, seasonally variant temperatures - Plants grow continually through the year - Seasonal climatic rhythms are absent - Characterized by broad-leaver evergreen and deciduous trees - Light is a key factor - Emergent trees rise up above the majority of the other trees that make up the canopy of the forest - Understory plants grow under the canopy further reducing the light that reaches the forest floor - Shrubs occupy the forest floor because they mostly rely on light flecks that move across the floor for photosynthesis - Rainforest nutrients are often nutrient poor 2) Savannas: - Shorter stature, lower tree densities and an increasing degree of drought deciduousness - The establishment of savannas is promotes by recurrent fires - Thorn woodlands typically occurs in regions with climates intermediate between tropical dry forests and savannas 3) Hot deserts: - Low populations of plants and animals because of high temperatures and low rainfall - The descending air creates zones of high pressure around 30 N and S - Low water availability is important on their form and function - Stem succulence occurs in both the cacti of the Western hemisphere and the Euphorbia family of the eastern hemisphere - Agricultural development in desert areas is dependent on irrigation (using or extracting water from deep grounds) - Desertification is long term drought that can result in loss of plant cover and soil erosion 4) Temperate Grasslands - Latitudes between 30 N and 50 N - Temperate climates have greater seasonal temperature variation than tropical climates, with increasing periods of subfreezing temperatures toward the poles - Precipitation in some grasslands is high enough to support forests - The rich organic matter accumulates in the soils and as a result enhances the fertility - Most human influenced biome on earth 5) Temperate Shrub lands and Woodlands - Occur in regions with a winter, rainy season - Precipitation falls primarily in the winter and hot weather occurs through later
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