BIO120H1 Lecture Notes - Lecture 14: Ecological Niche, John Hutchinson (Writer), Four-Dimensional Space
Lecture 14 – Climate and other Niche Axes
Outline:
- What determines local gradients in climates
o How this determines where species live
- Ecological niche
- Climatic variables as important niche axes
- Global gradients in temperature and rainfall
- Biomes
- Sources of climatic variation beyond latitudinal belts (oceans, mountains)
- Ecological niche modeling
o Predict where species can live and how this may change
- Climate warming and range shifts
Ecological Niche:
o Concept with a long history
o Niche: a place of the world (location)
▪ Species niche: what place a species prefers, etc.
- Idea meant to describe for each species the combination of physiological tolerance, tolerances and resource
requirements
o What kind of resources that species need to survive and reproduce
o What kind of climate the species prefers
- Hutchinsonian Niche - Hutchinson
o The niche is “an n-dimensional hypervolume” in which each axis is an “ecological factor”
important to the species being considered.
▪ Described ecological niche in multiple dimensions
Example:
- 2 Dimensions of Niche Axes (2 environmental gradients compared) – easier to plot
- Dark blue: optimum
values for the 2 gradients for
the performance of the
species.
- Light blue – white:
conditions not suitable for the
survival and reproduction of
the species
Global gradients:
temperature, rainfall, seasonality
- What determines climate?
- Temperature is mostly a function of latitude
o Colder at high latitudes and warmer at the equator
- At higher latitudes where it is colder, seasonality is a function of temperature (summer – weather)
- At lower latitudes (at equator) where it is warmer, seasonality is a function of rainfall (dry season – wet
season) because there isn’t much change in temperature.
- Rainfall mostly depends on the atmospheric circulation, offshore ocean currents and rain shadows
All of these factors determine biomes – important feature to understand why species live in certain places
Temperature in Equator vs. Poles
- As sunlight shines down to the earth at the equator, the photons that are being emitted from the sun warm
that area up
- Near the poles, sunlight that’s shining at down to the earth hits the poles at the lower angles thus spread
over a larger area towards the poles.
- Seasons are due to the fact that the earth is tilted.
Hadley Cells – PATTERNS OF RAINFALL
The earth’s tilt isn’t only important because it produces patterns of seasons and temperature but also because it
drives major patterns of atmospheric circulations
- The fact that the earth is warmest at the equator and coldest at the poles, this sets up Hadley cells
o Hadley cells: important cells at atmospheric circulation that are responsible for certain patterns of
rainfall.
- Because hot air cools and
water vapor condenses and falls as
rain, this is why it rains more near
the equator (tropical places)
- Because Hadley cells only
cover a certain area; as air warms
again as it falls, this results in dry
areas such as deserts.
Ferrell Cells & Polar Cells
- At the equator, there’s hot air rising from the lower to
upper atmosphere and moving north and south of the
equator
o This results in rainfall in the equator because as air
cools, water vapor condenses.
- Air then warms again as it falls back down from the
upper to lower atmosphere to the north or south (closer
to the poles) which then results in deserts (dry/hot airs)
The Hadley cell sets up the return of air from the upper
to the lower atmosphere
- This then sets up the Ferrell cells in which air will
then move from 30 deg N to 60 deg N in latitude and
moving over the earth’s surface (red arrows).
- The air then moves 60 deg N again and this cycle
repeats and goes in the opposite direction of Hadley cells
The Ferrell cell sets up the Polar cell between 60 deg – 90 deg N (north pole) in which air then moves in the
opposite direction of the Ferrell cell.
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BIO120H1 Full Course Notes
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