Biology 141 Lewis & Clark College |
Ecological pattern and the environment: physical and chemical variables that influence life |
K.E. Clifton Dept of Biology |
What have we covered so far?
What is ecology and how do we do it (Chapter 1 of the text).
The scientific method and the importance of designing an effective study: replication, randomness, and a "control" .
Remember... ecology is often concerned about detecting "patterns"
Experiments often identify causal mechanisms... but be careful!
Now start to consider the outcomes of interactions between organisms and their environment: Pattern!
What do we mean by "ecological pattern" and what factors influence this pattern?
Think about how different parts of the world have different ecosystems.... is there pattern?
Climate represents a general and extremely important physical variable
Temperature varies spatially over different parts of the earth.
The earth's surface is warmed at a faster rate in lower latitutes
The earth's curved surface causes a beam of sunlight to have a larger "footprint" as you move away from the equator.
when sunlight strikes earth's surface at an angle (as at higher latitudes), it penetrates more atmosphere
local effects also important.
Temperature also varies temporally as the earth orbits the sun and tilts on its axis seasonally.
Precipitation varies over different parts of the earth.
to understand why, it's important to remember two things:
1) warm air rises, cool air sinks (cool air is denser)
2) air temperature affects the balance between evaporation and condensation. As air cools, condensation exceeds evaporation; as air warms, the reverse is true.
equatorial air is warmed more than other air
warm air rises
as it rises it expands (less atmospheric pressure) and cools
cooler air leads to the condensation of water vaport
this produces rain
the cooling air falls and spreads north and south of the equator
the falling air warms, evaporation gains the upper hand, creating deserts
these cells, called "Hadley Cells" occur both north and south of the equator. Ferrel cells and Polar Cells then occur at intervals of roughly 30° of latitude.
Here is a pretty nice animation of Hadley Cell dynamics
Collectively, these generate global patterns of airflow
An important outcome of this equatorial pattern of flow (i.e., spatial pattern):
Temporal pattern
Inter Tropical Convergence Zone (ITCZ) contributes to annual periods of rain and drought in the tropics.
There are also effects on smaller spatial scales
"Local" temperature and precipitation effects
Rainfall and rain shadows
when prevailing winds carry moisture-laden air toward mountains, the air is forced to riseit cools as it rises, water condenses; it rains
as the air drops down the other side, it warms, and water evaporates
thus the windward side of mountains is wet, the leeward side is dry
Oceanic influences
Water gains and loses heat more slowly than land does; thus the ocean is a reservoir of heat and coldin winter, areas near oceans are warmed by the ocean, and so are warmer than continental regions at the same latitudein summer, areas near oceans are cooled by the ocean, and so are cooler than continental regions at the same latitude
Patterns of temperature and precipitation allow us to predict the biomes that will occur in different parts of the world.
Don't forget the chemicals that are needed for life to persist....
Next: how might these patterns lead to limitations on different life forms... or, what does it mean to consider a "limiting resource"?
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