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Chapter 2

BIOLOGY 2F03 Chapter Notes - Chapter 2: Tropical And Subtropical Dry Broadleaf Forests, Rainforest, Atmospheric Circulation


Department
Biology
Course Code
BIOLOGY 2F03
Professor
D R.Kajura
Chapter
2

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Chapter 2- Life on Land
Natural history is the study of how organisms in a area are influenced by climate, soils,
predators, competitors and evolutionary history
A good understanding of natural history provides the foundation for modern ecology and
conservation biology
Figure 2.1- A Guanacaste tree in Costa Rica provides large amounts of edible fruit which
requires large herbivores to disperse their seeds. This phenomenon of the Guanacaste tree
producing so much fruit was tackled by Daniel Janzen, who wanted to restore tropical dry forest to
Guanacastee National Park.
A common theme throughout the book is that people are not separate from ecological
processes.
Life of Land and Terrestrial Biomes
Life on land is very brutal as terrestrial organisms are essentially bags of water surrounded
by dry air and are affected by the cold and heat. Another stressor is gravity as terrestrial organisms
due not have the natural buoyancy that aquatic organism do have
Dealing with these stressors requires many specific traits, like sweating
Common abiotic conditions like precipitation and temperature result in predictable
characteristics in these species
Biomes- divisions of terrestrial environments. Distinguished by observed plant species, and
particular climate, Because biomes are very different from one another, they all have different
natural histories
Large Scale Patterns of Climate Variations
Uneven heating of the earths spherical surface by the sun and tilt of the earths axis produce
predictable latitudinal variations in climate
Understanding geographical and seasonal variations in temperature and precipitation Is
fundamental in studying ecology
Average temperatures are lower and more seasonal over the middle and high latitudes than
the equator. Deserts which are concentrated in narrow bands of latitude have very little
precipitation.
Average climatic conditions over a large geographic extent due not necessarily indicate the
typical climate for a given location in the area
Temperature, Precipitation, and Atmospheric Circulation
Earths climatic variation is from uneven heating of the surface by the sun. Since the earth Is
a sphere, the suns rays are concentrated where it is directly overhead and changes with seasons.
Since the tilted angle of rotation Is maintained throughout earths orbit, the amount of energy
received by the Northern and Southern Hemispheres changes seasonally. The sun is directly over
the Northern hemisphere on June 21 and directly over the Southern hemisphere on December 21.
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The sun is directly over the equator during autumn and spring where the southern and northern
hemisphere receives equal sunlight.
This shift in latitude in which the sun is overhead drives the various seasons
Heating of the earths surface and atmosphere drives circulation of the atmosphere and
influences patterns of precipitation
AS the sun heats the equator, air rises and expands and then cools forming clouds and
rainfall in the tropical environments. Then this equatorial air ceases to rise and spreads to the north
and south, as this air moves away from equator, it cools increasing its density and sinks to 30
degrees latitude where it then spreads to the North and south. This draws moisture from lands over
which it lows and creates deserts
There are 3 thermal loops (Hadley cell, ferrel cell and polar cells) which drive air movement
Figure 2.3a- solar cell air circulation, figure 2.3b- latitude and atmospheric circulation
Prevailing winds do not move north to south cause of the corolis effect. In Northern
hemisphere is causes deflection of wind to right and to the left in the southern hemisphere
The distribution of biomes are influenced by geographic variations in temperature and
precipitation
Climate Diagrams
Climate diagrams explore relationship between distribution of terrestrial vegetation and climate.
They summarize season variation in temperature and precipitation, length of wet and dry season
Months of year are plotted on horizontal axis beginning from January to December in (N.H) and July
to June in the (S.H)
Temperature is on the left vertical axis and precipitation is on the right vertical axis
The relative positions of temperature and precipitation reflect water availability
Adequate moisture for plants occurs when precipitation lies above temperature
When temperature exceeds precipitation, dry periods occur (potential evaporation rate exceeds
precipitation)
Mean temperature (top left) , precipitation and altitude (top right) are labeled
Figure 2.6- different climate diagrams
Climate diagrams efficiently summarize important environmental variables
Soil: Foundation of terrestrial biomes
Soil structure results form the long term interaction of climate, organism, topography and
parent mineral material
Soil is a complex mixture of living and nonliving material upon which most terrestrial life
depends on
Soils themselves are ecological systems
There is more organic carbon below ground than above ground
Much of what drives the worlds systems occurs below our feet
When soil is broken, you can see different layers or horizons.
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The majority of organic material is at the surface of soil. This is known as the O Horizon
where plant material is aquatic in nature, This layer is home to a lot of organism
The A horizon contains mixture of minerals like clay, silt and sand, this
zone also supports a lot of biological activity such as earthworms. With rain, this
horizon is leached of clays and humus (partially decomposed organic material)
B horizons has material leached from above resulting in a distinctive
banding pattern
C horizon below the b horizon has weathered parent material which is
broken down by frost which makes us soil, silt and clay
Underneath the C horizon is bedrock
Soil is in a constant state of flux due to the interactive actions of climate, and
organism
Plants secrete root exudates which serve as substrate for bacteria. Growth of the microbes
provides stability to the minerals allowing for the formation of canals in soil (air spaces)
Climate alters the rate of weathering (leaching, erosion). Climate also alters decomposition
Soil is dynamic and provides medium in which organisms grow, and these organisms affect
the soil structure
Natural History and Geography of Biome
The geographic distribution of terrestrial biomes corresponds closely to variation in
climate, especially in prevailing temperature and precipitation
Biomes change gradually along environmental gradients
Nearly everything determines where the different biomes are located. We will focus on how
climate and soils influence the distribution of vegetation
Tundra
Most northerly areas of vegetation, open landscape with moss and lichens. The air is filled
with birds during the small summer preying of the explosion of plant and animal prey
Arctic tundra covers most of the top of the globe extends from Northern Scandinavia across
Europe, Russia, Siberia and Alaska and Canada.
The tundra climate is mostly cold and dry with short summers; it does not get quite as cold
or warm as the boreal forests. Precipitation varies from 200mm-600mm. Precipitation exceeds
evaporation and tundra is soggy wet
Soil building is small, since rates of decomposition are slow and summer months are often
underplayed by permafrost (layer of soil even frozen during the summer months). One process that
occurs in the tundra , solifluction- slowly moves soil down slopes
Tundra is occupied by perennial herbivorous plants like grass, lichens are dominate and
eaten by caribou. Low growing shrubs predominate in the tundra and are slow growing. Tundra is
one of the last biomes that support a lot of native mammals like caribou
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