Terrestrial Ecology

Plate tectonics

mobile plates floating on fluid mantle

mid oceanic ridges

Plates pull apart, creating a gap

magma rises from below to fill the gap

Magma cools in the water and turns to rock → new crust

subduction zones

Plates crash together

Heavier, colder plate gets forced under the lighter plate and melts into magma → deep ocean trenches, earthquakes, volcanoes

sahul

Consisted of mainland Australia, Tasmania, and New Guinea

Melting ice raised ocean levels and separated the landmass

laurasia

ancient northern supercontinent that broke away from the supercontinent Pangaea around 215 to 175 million years ago → Gondwana’s northern twin

Gondwana

South America, Australia, New Guinea, Antarctica, New Zealand, New Caledonia, Africa, and India

35 mya - end of Gondwana → Australia split away

wallace’s line

Meeting point of the Australian (Gondwanan heritage) and Asian (Laurasian heritage) tectonic plates

Imaginary line that separates wildlife from Asia and Australia

ratite distribution

Related group of giant ground birds restricted to the southern continents

evidence of gondwana

hotspot volcanoes

Australia sits in the middle of its plate far from mountain building activity that occurs on plate boundaries, resulting in no volcanoes or glaciers

hotspot volcanoes appear on eastern side of Australia (where great dividing range is)

occured as Australian tectonic plate drifted northward over a “hotspot” (upwelling of hot magma)

creates “islands” of high nutrient soil derived from basalt, supporting rainforest

great dividing range

eastern uplands are younger, more mountainous, better watered, and more fertile soil → more geological activity

mountains force warm, wet air from the ocean into the sky leading to rainfall (orographic)

rest of continent is in rain shadow (experiences much less rainfall)

why is australia old and flat

sits in the middle of its plate → geologically stable

has not experienced recent major mountain-building and tectonic activity

watering and erosion has worn down landscape

Old rocks + long-term erosion + relatively little recent uplift = old, flat landscape

how does australian landscape affect soil

Australia's old, relatively stable landscape has experienced very long periods of weathering → leaching of nutrients (phosphorous and nitrogen) and removal of soluble materials → nutrient-poor soils

5 factors of soil formation

1. climate

2. organisms

3. age

4. topography

5. parent rock

climate in soil formation

temperature and rainfall affect weathering, erosion, vegetation, decomposition

organisms in soil formation

plants, animals, and decomposers cycle nutrients and enrich soils with organic matter

age in soil formation

time for bedrock to erode, for soils to weather, and materials/nutrients to be transported

younger = more fertile

topography in soil formation

run-off slopes lose resources

run-on or depositional topographies accumulate them

mesa (flat-topped hills)

• top of hill experiences high run off and erosion leading to exposed rock and sparse vegetation

• bottom of hill accumulates resources leading to relatively fertile soil and supporting grassy, woodlands

parent rock in soil formation

bedrock types differ in the quality of soil they erode into

basalt = more fertile

rhyolite = less fertile

low pressure cells

warm, rising air

warm air evaporates readily and holds lots of water

brings rain as it rises and cools

warmer air = more energy = unstable, strong winds

rotates clockwise in southern hemisphere

high pressure cells

cool, descending air

drier and more unlikely to bring rain

cooler air = less energy = stable winds

rotates counter clockwise in southern hemisphere

isobars

link points of equal pressure

closeness of isobars indicates strength of winds

trough

elongated area of relatively low pressure

can draw up moist air to form long bands of clouds and can bring lots of rain and maybe flooding

hadley cell circulation

begins with warm, wet air (low pressure) rising over equator bringing clouds and rain to tropics around the equator

the now cooler and drier air is pushed by warmer, wetter air rising from below

the cooler and drier air decensds at around 30 degrees north and south, leading to deserts in these latitudes (where australia is)

orographic rainfall

rain caused by warm, wet air from the ocean being pushed into the sky by mountains

the mountain causes the rising air to cool and the excess moisture to be shed as rain

rainshadow

Area of reduced rainfall in the lee (sheltered side) of mountains

the dry air here has already shed its orographic rainfall (lost its moisture) on the way up

cold front

Mass of relatively colder, denser air

As it travels, relatively warmer, less dense air is pushed “up and over” as the cold front ploughs through underneath

As it rises, relatively warm air cools and sheds its excess moisture as rain
Rain can be expected along the leading edge of the front

what makes rain

warmer air holds more water vapour so as it rises and cools, clouds condense, and excess moisture may be shed as rain

la nina

1. high pressure pushes winds towards low pressure australia

2. trade winds blowing towards australia

3. winds blow the warm surface water towards australia

4. warm water pooling off eastern australia → evaporates easily → more rain and clouds

positive SOI

ENSO

Warming of sea surface temperatures off South America triggers a reversal of

trade winds and "flip" from La Niña to El Niño conditions →the El Niño Southern Oscillation

el nino

1. high pressure australia pushes winds toward central pacific

2. trade winds blow towards south america

3. winds blow warm surface water AWAY from australia towards South America

4. rain-making forces head east → dry season for australia

negative SOI

Southern Oscillation Index

difference in air pressure between Tahiti and Darwin

cooperative breeding

older family members (like brothers and sisters) assist their parents in raising the next generation instead of taking the oppurtunity to breed themselves

• kookaburras, magpies, noisy minors

wet sclerophyll forest

• transitional forest defined by fire

• sclerophyll trees (usually eucalypt) in the canopy

• rainforest plants growing in the understory

• high rainfall and fertile soil, but occasional fire that favors sclerophyll

• eucalypt seedlings cant regenerate under a shady rainforest understory, so without fire, wet sclerophyll eventually converts to rainforest

• fire temporarily wipes out rainforest understory, allowing eucalypts to regenerate

ecotone

a transitional boundary zone where two different ecological communities, ecosystems, or habitats meet and integrate

fire regime

defined by fire frequency, intensity, and season

fire frequency

after about 300 years without fire, wet sclerophyll turns into rainforest

highre fire frequency kills the rainforest understory and converts wet sclerophyll into a eucalypt forest

even higher fire frequency converts eucalypt forest into scrubland, then grassland

trees and shrubs need time to recover/establish in between fires

fire intensity

wind

• supply oxygen so flames burn faster and hotter

temperature

• temperature determines moisture content

• dry environment burns better than a wet one

fuel load

• amount of combustible material (leaf litter, fallen logs, dry/withered understory)

fire season

fires will be more intense in the drier, hotter, and windier seasons

dry lightning = natural ignition

controlled burning

northern australia = hot/wet summers so fires will occur in cold, but dry winter

southern australia = winter rains so fires have potential to be worse in the hot and dry summers

why sclerophyll burns well

• dry growing conditions

• foliage low in moisture and high in flammable woody tissue

• low rates of decompositon → fuel load builds up

• open canopy allows understory to dry out and wind to penetrate

• flammable eucalyptus oil

how do australian plants survive fire

resprouting and reseeding

resprouting

lost foliage is replaced by sprouting new leaves from protected meristems (epicormic buds, lignotubers)

reseeding

fire damages existing plants, but stimulates seed release for germination of next generation (serotiny)

epicormic buds

meristems insulated under bark

present in Eucalyptus, Banksia, and Acacia

lignotubers

mass of dormant underground meristem tissue

present in Eucalyptus, Banksia

serotiny

seeds protected in woody capsules (Banksia cones or Eucalyptus gumnuts)

fire burns foliage, but seeds are insulated

capsules open in response to heat and release seeds

reseeding - why germinate after fire?

less competition - other plants like grasses and other ground cover have been eliminated

space created - leaf litter and other debris have been burned away

available nutrients - fire recycles sparse nutrient from litter

fewer herbivores - populations supressed

firestick farming

used by aboriginal people

systematic and purposeful use of fire to reshape landscapes in ways that made
them more productive and convenient for people

burning a small patch of old, dry grass to allow new grass to reshoot

results in more open habitat, a mosaic of burnt and unburnt vegetation, low fuel loads, frequent but low intensity fires, fire-tolerant vegetation favored

controlled burnings

• fully suppressing fire = fuel load builds up = catastrophic fires

• fire favors some organisms, but harms others

how does sclerophyll vegetation conserve limited soil nutrients

• sclerophyll leaf has a high proportion of lignin (woody fibers), which is composed of abundant materials like carbon, hydrogen, and oxygen → this means less of the leaf is made of scarcer materials like nitrogen and phosphorous

• sclerophyll leaves are long, strappy, and tapering = less leaf area = less initial investment

• long lasting leaves

how does sclerophyll vegetation conserve water

• thickened leaves = wilt resistant → leaf retains strucutral integrituy in dry conditions

• drab grey-gray foliage → reflects back incoming light and heat

• thick, waxy cuticle → reduce transpiration

• reduced crown thickness and leaf area → less surface to evaporate from

• leaves held vertical to sun → minimized exposure at midday

• stomata is insulated → reduce transpiration

how does sclerophyll vegetation defend against herbivores

• woody sclerophyll leaves are physically harder to eat

• eucalyptus oil deters herbivores

xeromorphy

adaptations for low moisture availability

how do eucalypts have a thrifty investment in foliage

• vertical leaves

• low leaf area index = few canopy leaves produced per area of ground

• shedding leaves in difficult growing conditions

• dropping lower branches once they become shaded

tree hollows in eucalypts

susceptible to termite attack which create tree hollows

many vertebrates use tree hollows as shelter

mutualism → trees benefit from fertilizer from termite and vertebrate waste

Mycorrhizae

symbiotic fungi associated with plant roots

greatly improves nutrient uptake by increasing surface area

fruiting body (truffle) produced underground, eaten by some vertebrates

eucalypt flowers

blossom lacks petals, but has numerous stamens

form a showy display to attract pollinators

operculum

bud cap

covers the flower in bud

heathlands

low growing vegetation on low-nutrient and water-limited soils

trees replaced by woody shrubs

ericoid leaves

tiny, reduced sclerophyll leaves

small leaves = less investment

common in heathlands

dry heath

deep, porous, infertile soil where water drains freely

wet heath

seasonally waterlogged and stagnant soil caused by an impermeable soil layer

montane heath

exposed mountain tops, shallow soil over bedrock, poor drainage, high winds and exposure

root adaptations for nutrient-poor soil

• nitrogen fixation

• mycorrhizae roots

• cluster roots

nitrogen fixation

Root symbiosis with bacteria that “fix” atmospheric nitrogen

• acacia, casuarina, cycads

cluster roots

some plants make their own dense, branching root mats to increase root surface area instead of having mycorrhizae symbiosis

• Banksia

Melaleuca

sclerophyll wetlands

have sclerophyll leaves, insulating bark, and serotiny

seasonally flooded, but in the dry season, can dry out and burn

adapted to both waterlogging/flooding and drying/fire → advantage over rainforest

emergent

rainforest tree, old and tall enough to extend above the surrounding canopy

epiphyte

plant that grows on another plant for support

not rooted on the ground

liana

rainforest vine, usually thick and woody

rooted in the ground, climbs tree trunks to reach canopy

butchress roots

above-ground extensions of the root system

convergently evolved in many rainforests

provides stabilization in shallow rainforest soil

strangler fig

seeds dropped by birds, bats, and primates begin as epiphyte on tree branch, and then eventually “strangles” other tree

it encircles the host, eventually killing it, and leaving a hollow emergent tree

keystone species since it is in fruit for the entire year → providing resources to animals throughout the whole year

rain forest - light limiting

typically have high rainfall and fertile soils → light seeking leaf morphology → large and broad, dark green, held horizontal to the sun

dense growth of trees forming a closed canopy (>70%)

tree fall dynamics

1. a canopy tree falls and creates a light gap in the forest

2. rapid growth of juvenile trees: pioneer/secondary species from seeds and climax species from saplings

3. secondary rainforest forms: pioneer and secondary species dominate → closed canopy, but lower height and diversity

4. primary rainforest: mature, old growth with slow-growing, but long-lived climax species shading out the secondary rainforest trees

pioneer species

• smaller trees and shrubs

• grow fast and die young

• frequent, abundant reproduction

• seeds can germinate after disturbance (like tree fall event)

climax species

• long lived

• slow growing

• seed dispersal is relatively limited

• may persist as small sapling for decades, waiting for tree fall gap to open

fungi in rainforests

mycelium (fungal body) consists of tiny filaments called hyphae

digest carbon

the only thing that can digest lignin → essential decomposers

nutrient cycling in rainforests

nutrients between the biomass itslef and the topsoil/uppermost layers of litter are effectively cycled

shallow root systems

rainforests have high litter fall and decomposition rate

tropical rainforest

continuous growing season - always warm and wet

extremely high diversity

largest leaf sizes

subtropical rainforest

less optimal conditions and shorter growing conditions

high diversity, but less than tropical

large leaf sizes, but smaller than tropical

tall trees and multiple layers, but less than tropical

temperate rainforest

closed canopy forest, but with diversity and structure "held back" by less-optimal conditions

associated with EITHER more limited growing season or poorer soils

canopy and forest floor layers only

smaller trees

dry rainforest

rainforests dont need high rainfall

adapted to drier climate → small-leaved, drop leaves in response to drought

fertile soil, absence of fire → closed canopy

rainforest are pyrophobic

does not need fire to regenerate and is killed outright by fire

shaded and damp fuel loads repel fire

rainforest seed dispersal

have colorful, fleshy fruit

vital for rainforest plants to reach suitable growing conditions (tree fall gaps)

where are the big animals in rainforests

• rainforest vertebrates are usually either climbers (monkeys, possums, pythons) or fliers that move easily through canopy

• plant resources are concentrated in the canopy - where the light is

• rainforest floors offer fewer resources for larger vertebrates

the tertiary

• mammals diversify

• grasslands form

• beginning = warm and wet conditions

• long term cooling and drying trend

• glaciers → permanent antartic ice sheet

early tertiary

dominated by gondwanan rainforest

evidence of wetter and warmer climate

• fossil pollen of rainforest nathofagus and huon pine

• extant tropical plants found as fossils

birth of scleromorphy

• oldest eucalypt fossils from south america

• fossilized in proximty to rainforest taxa suggesting that their original habitat was an ecotone

• preadapted for drier climates, lower fertility, and fire that came later

the long drying

transition from rainforest to weathered, arid landscape

caused by circumpolar event, drift to 30 degrees latitude, and formation of new guinea

long drying circumpolar event

35 mya - australia seperates from antartica → allows southern ocean to circulate around antartica → circumpolar ocean current created → antartica becomes colder → southern ocean becomes colder, which means less evaporation → less rainfall → australia becomes cooler and drier

long drying - drift to 30 degrees latitude

35 mya - australia seperates → Australia drifts north into the 30 degree latitude belt dominated by the high pressure systems of the Hadley circulation → dry, descending air brings little rain

long drying - formation of new guinea

australia plate collides with south east asia → mountain building in new guinea puts australia in rainshadow

adaptations to dry climate

casuarina and banksia - stomata insulated to protect against excessive water loss

Quaternary

overall cooling trend, combined with cyclical oscillations between colder glacials and

warmer interglacials

quaternary climate change occurs in cycles

Most of the Quaternary has been spent in glacials – the warmer, wetter interglacials are relatively short

climate still fluctuates in a glacial, but with overall trend downwards to a

glacial maximum

holecene

present interglacial of the quaternary period

interglacial

a geological period of warmer global temperatures that lasts for thousands of years and separates cooler glacial periods within an ice age

glacial

the colder “ice age” between warmer interglacials

glacial maxima

coldest extreme of a glacial

ice age australia

cold and dry

cold oceans → less evaporation → less rain

hyper-aridity in central australia → more deserts

lower sea levels expose shallow continental shelf → vegetation retreats to refugia