Chapter 14: Climate and other niche axes

species ranges

species have ranges of tolerance along environmental gradients

• lethal zone

• survive

• growth

• reproduce

• optimal

the ecological niche

• combination of physiological tolerance and resource requirements of a species

• more casually, a species’ place in the world - what climate it prefers, what it eats, etc

• a concept with a long history in ecology…

the Hutchinsonian niche

the niche is an n-dimensional hyper volume in which each axis is an ecological factor important to the species being considered

Global gradients

• temp → mostly a function of latitude

  • high latitude = colder (summer-winter)

  • lower latitude = warmer (dry season - wet season)

• rainfall → mostly depends on atmospheric circulation, offshore ocean currents, rain shadow

• seasonality → function of temp + rainfall

*these factors determine biome

earth’s tilt = produce seasons

• 90degree = light directly concentrated to one area → hottest

• higher angle (60degrees) =light covers small area → more intense light → warm

• lower angle (30 degrees) = light spread over large area → less intense light → cold

• when northern hemisphere is tilted toward the sun

  • northern hemisphere = lower angle = warmer (summer) , days = longer (longer orbit)

  • Southern hemisphere = lower angle = colder (winter), days = shorter (shorter orbit)

• when norther hemisphere is tilted away from the sun

  • northern hemisphere = higher angle = colder(winter), days = shorter (shorter orbit)

  • southern hemisphere = lower angle = warmer (summer), days = longer (longer orbit)

Hadley cells make equatorial regions rainy

Hadley cell = large, looping air circulation systems in earth’s atmosphere that help move heat from the equator toward the poles (0-30 degree latitude)

1. heated air rises → air cools as it rises, 5-10 degrees celsius/km

2. as air cools, water vapour condenses and fall as rain near equator

3. air warms again as it falls

4. Hadley cells moves air toward equator, which gets heated by intense sun

*dry, high-pressure areas at ± 30 degrees latitude

Other atmospheric cells interlock like a gear train

• Hadley cell (0 - 30) : warm air rises at 0, cold air sinks at 30

• Ferrel cell (30 - 60) : warm air rise at 60, cold air sinks at 30

• Polar cell (60 - 90) : warm air rise at 60, cold air sinks at 90

Intertropical convergence zone (ITCZ)

belt of low pressure that circles he earth near the equator, where the trade winds from Northern and Southern hemisphere converge

1. warm air rises at equator because it’s heated by intense, direct sunlight

2. rising air causes low pressure at the surface

3. as air rises, it cools, condenses, form thick clouds → lead to frequent rain + thunderstorm

4. air moves poleward at high altitudes as part of the Hadley cells

*intertropical convergence = shows as line of rain clouds across the Pacific

• hot, humid, stormy weather, tropical rainforest, monsoon climates

*intertropical convergence zone shift seasonally, producing rainy and dry seasons in some parts of tropics → solar equator moves as earth orbit around the sun

• July → sun is over Tropic of Cancer (23.5N) → ITCZ shifts north

• January → sun is over Tropic of Capricorn (23.5S) → ITCZ shifts south

• ITCZ moves over a region → warm, moist air rises

• ITCZ moves away from a region → sinking dry air dominates

Coriolis effect

earth’s rotation deflects winds

• even though the whole planet spins together, diff latitudes move at diff speed → earth rotates on its axis, and radius diff

  • equator = move fastest (longest distance per rotation)

  • poles = move slowest (shortest distance per rotation)

• so when air or water moves north or south, it travels into regions at diff rotational speed → curved path

  • in northern hemisphere → rightward(east) deflection)

  • in southern hemisphere → leftward (west) deflection

Coupled cells + Coriolis effect = prevailing wind patterns

• trade winds: blows east→ west, 0-30

• westerlies: blow west→ east, 30-60

• polar easterlies: blow east→west, 60-90

roaring forties (40) = strong winds

• few landmasses resistance

• strong pressure gradients

land masses vs oceanic winds

• friction difference

  • landmasses → more rough surface → more friction → slow down wind

  • ocean → smooth surface → less friction → fast wind

• temp difference

  • landmasses → land = low heat capacity → land heats + cools faster → variable wind

  • ocean → water = high heat capacity → water heats + cools slower → steady wind

general trends of terrestrial vegetation with climatic variables

• more vegetation growth(primary productivity), more moisture, high temp

• vegetation stature also increases → so regions with certain combinations of moisture + temp develop predictable, characteristic types of vegetation = biomes

• seasonality = secondarily important

*deserts = near 30N, 30S

additional climate patchiness overlaid on basic latitudinal belts

• temperature = land changes temp more readily than water; maritime climates are moderate, continental climates are extreme, ocean provide thermal inertia

• precipitation = where does atmosphere get laden with moisture? where does it condense?

  • evaporation high from water bodies of water, low from cold bodies of water

  • prevailing winds

  • orographic precipitation = air forced up mountainsides undergoes cooling, precipitates on upper windward slopes

  • rain shadows created on leeward slopes of mountain ranges

  • seasonality of moisture

orographic precipitation

happens when moist air is forced to rise over mountains, causing rain on one side and dry conditions on the other

rain shadow

a dry region found on the leeward side of mountain range

e.g. grasslands = rain shadow because of rockies

land masses vs temp

• northern hemisphere = more land = low heat capacity = change temp easily = large range of temp

• southern hemisphere = more water = high heat capacity = steady temp = small range of temp

ocean currents vs precipitation

driest deserts occur inland of cold-water upwellings

• cold water → dry air → less rain→ desert climate

niche limits vs geographical range limit

• niche limits = where species could survive

• geographical range = where species are actually living

• animal’s geographical range corresponds to biomes → limited by climate or vegetation

  • geographic range <= niche limits

• but sometimes not. possibilities include: → why geographic range might differ from niche limits, (e.g. sometimes species are not living in all regions where it is suitable for them to live)

  • transcend biomes (ecological versatility, super generalists) → some species have broad ecological tolerance allowing them to live in various niches → niche limit > geographical range

  • not a limit because of recent history (e.g. limited dispersal) → have not reached to all places yet due to barriers → niche limit > geographical range

  • limited by other organisms (enemies, friend) → species might be biotically limited → predators that live elsewhere, mutualists that only live there → niche > geographical range

ecological niche modelling

• use data from a species present distribution to predict where a species can live

• useful for modelling

  • biological invasions

  • how species range may shift as climate changes

  • spread of vector-borne diseases

• usually relies on climate data (more rarely on other niche axes such as resources)

climate warming - observed range shifts

• in 2003, a study of 1046 species estimated that species are moving poleward at a rate of 6.1km per decade

• in 2011, a study of 1367 species estimated that species are moving pollards even faster, at a rate of 16.9km per decade

*although many factors influence a species range, there is considerable evidence that numerous species are doing polewards to track recent changes in climate