module 2 Flashcards
why are there so few native species to Britain?
- glaciers have advanced south several times (clean slate each time)
- English Channel formed only 7500 years ago. sea levels rose and formed a barrier to plant migration.
- narrow range of habitats as no climatic variation and np great altitudes.
two types of fossils
- MACROFOSSILS - sometimes find charcoal remains, seeds and fruits, leaf impressions.
- MICROFOSSILS (pollen and spores) - have a very resistant outer coat, called exile, made up of sporopollenin.
Silurian fossils
They are about 7 mm tall.
◆ They all have names and a
taxonomic place
◆ They have spore bodies on
the end of stalks
◆ They do not have roots or
leaves
devonian fossils
- A reconstruction of the Rhynie chert fossils
- Very famous, because so well preserved – probably vertically in a swampy peat bed.
- Chert is a soil type – fine crystalline quartz
- They have primitive vascular systems.
- This is how we know the age of vascular plants
the quaternary period
- 2.5 million years ago to the present
- at least 21 cycles of cold and warm
four major interglacials in the quaternary period
cromerian
hoxnian
ipswichian
flandrian (present)
names of glacial periods
the devensian - Britain
the weichselian - Northern Europe
the wurm - the alps
the wisconsinan - North America
what causes major changes in climate?
- change in eccentricity - oval orbit
- periphelion changes - suns distance to earth
- obliqueness - tilt
principle of uniformity
assumes that the ecology of a species in the past was similar to its present ecology
what factors can influence pollen assemblage?
- species differ in how well they preserve
- pollen and spores are tiny (some more easily transported than others, so may be deposited far away from where they wee produced)
- some species produce more pollen than others - relative abundance of plants difficult to assess.
- more pollen produced by wind pollinated species
what does a pollen diagram display?
how vegetation has developed through the ages due to changes in climate
first Godwin zone
pre temperate zone
sea buckthorn and grasses present at the end of the previous glaciation.
Godwin zone 2
early temperate zone
mixed oak forest with some thermophiles species present
Godwin zone 3
late temperate zone
expansion of forest trees
godwin zone four
post temperate zone
boreal trees dominate again: betula and pinus
thinning of the forest occurs and non-tree pollen is frequent.
birk’s climate stages
- cryocratic
- protocratic
- mesocratic
- oligocratic and telocratic
Cryocratic phase
– Glacial stage, cold and dry
– Vegetation sparse, species poor arctic-alpine or steppe on thin skeletal mineral soils
– Frequent frost disturbance
(permafrost)
Protocratic phase
– Rising temperatures
– Species-rich grassland, scrub and open woodland
– Base-rich and fertile soils with low humus content and
little leaching
Mesocratic phase
– Climatic optimum
– Closed temperate deciduous woodland with
increasing species richness.
– Brown earth soils of high base status.
Oligocratic and Telocratic phases
– Climate warm at first, but begins to deteriorate.
– Soils become leached to podzols or acid peats
leading to acid, nutrient poor conditions.
– Vegetation becomes dominated by conifers,
heathers and plants of open sites.
the devensian glaciation
the last glaciation
began 73 ka bp to 14 ka bp
part of the country that wasn’t covered in ice had periglacial conditions (-20/30 degrees winters and 10 degrees summers. mineral soils)
sea level was 130-160 m below current
holocene interglacial
current interglacial
began 14 km bp.
glacial periods starting with lower dryas.
lower dryas
allerod
upper dryas
pre-boreal
boreal
atlantic
sub-boreal
sub-atlantic
lower dryas
14 - 12 ka bp.
ice retreated, still cool.
vegetation - low tundra grassland, grass, plantain and weeds.
allerod period
12,000 to 10,800 years bp
warmer - continental climate.
vegetation dominated by birch scrub, grasses and weedy species.
upper dryas
10,800 - 10,300 yearsbp.
cold period.
ice re-advanced causing decline in birch and increase in some tundra.
pre-boreal
10,300 to 9000 years bp.
warmer.
birch forest with increasing pine, elm, oak and hazel. decreasing grasses and herbs.
canopy closes.
boreal period
9000-7500 years bp.
warm dry continental period.
elm, oak, hazel woodland.
pine and birch declining.
atlantic period
peat accumulated because it was wetter.
7500 - 5000 years bp
warm wet oceanic climate.
sub-boreal
5000 to 2500 years bp.
significant decline of elm.
sub-atlantic period
2500 bp to present
progressive disturbance of the forest.
culture is neolithic crops of rye and barley planted and sheep and goats kept.
tephra
volcanic air-fall material
radiocarbon dating
when an organism dies, the proportion of c14 (radiocarbon) declines because it decays to normal nitrogen.
the ratio of radiocarbon to normal carbon gives the approximate age.
what is succession and what three processes does it involve?
Succession is a directional non-seasonal
cumulative change in the types of plant
species that occupy a given area through time
- colonisation
- establishment
- extinction
steps in primary succession
- denudation
- immigration of species
- ecesis
- competition and interaction
- reaction
- stabilisation
denudation (in primary succession)
pre-biotic changes occur before plant establishment can begin e.g. weathering of rock faces
immigration of species (in primary succession)
arrival of species depends on:
- dispersal mechanism (wind dispersal etc)
- seed or spore size
- distance to source of propagules
- chance
ecesis (in primary succession)
germination and early phase of establishment - depends on suitability of habitat.
competition and interaction (in primary succession)
earliest colonists find little competition
populations expand exponentially until a resource is limiting
then interaction - stronger competitors may eliminate the earliest colonisers
reaction (in primary succession)
presence of organisms changes the environment for others - creates new environments allowing the ecesis of other species
stabilisation (in primary succession)
rate of change in the environment slows down
- little immigration
- little ecesis
sere
the pathway of a succession. a successional sequence of communities.
three types of lichen
- crustose - like a crust
- foliose - turned up edges like foliage
- fruticose - shrubby
why are lichens often early colonisers
- need little water
- need no soil
- are very hardy.
example of succession in the lithosphere starting with lichen
lichen increases water retention allowing moss to invade.
moss breaks down rock and soil increases. moss penetrates rock cracks.
annual herbs and grasses
pioneering shrubs/trees
mixed deciduous forest
sequence of succession on psammosere
COASTAL SAND DUNES
25 year old dunes
- marram grass is main plant
100 year old
- prairie bunch grass
150 year old
- conifer trees
225-400 year old
- mixed forest of pines
more than 400 years old
- deciduous trees
sequence of succession in the hydrosphere
micro organisms.
submerged leaved macrophytes establish
floating leaved macrophytes
marsh
swamp
sedges
pond floor is raised by debris
Carr, willow and alder establish.
mixed oak woodland
walkers hydrosphere succession
- Biologically unproductive open water
- Open water with micro-organisms
- Open water with submerged macrophytes
- Open water with floating leaved macrophytes
- Reedswamp
- Tussock Sedge swamp
- Fen (herbs on organic soil)
- Swamp carr (trees on
unstable peat) - Fen carr (trees on stable
peat) - Aquatic sphagnum species
- Sphagnum bog
- Marsh (herbs on mineral soil)
why is there no progression to forests in the hydrosphere?
- low nutrient content
- low pH
- anoxia
secondary succession
The progression of communities where pre-existing vegetation has
been disturbed or destroyed and a soil (and possibly a seed bank) is already developed on the site.
secondary succession stages
- pioneer species - various annual plants
- perennials and grasses
- shrubs
- softwood trees and shrubs
- hardwood trees
early successional plants (secondary succession)
pioneer species
high growth rate
small size
wide dispersal
fast population growth
late successional plants (secondary succession)
lower rates of dispersal
lower rates of colonisation
slower growth rates
larger sizes
longer lives
super-organism
Clements view of vegetation as one being. the whole was greater than the sum of the parts.
it is born, it develops and it reaches maturity.
it heals itself with secondary succession.
climax community
slow rates of change
not static (not still)
autogenic changes
succession driven by organisms themselves. organisms alter the habitat.
allogenic changes
succession driven by changes in the environment
more common than autogenic changes.
five main problems with Clements
- concept of suer-organism
- facilitation model
- climactic climax
- stable climax
- autogenic succession
Gleasons individual model
individual species are struggling to maintain themselves not facilitating others.
species behave individualistically
composition determined by the availability of species locally.
succession does not lead to definite climax
tolerance model
all species can colonise early on, but the most rapid colonisers and fastest growers dominate.
poor colonisers tolerate fast growers.
inhibition model
each plant inhibits the establishment of other species by site pre-emption (do it before them)
4 main sources of evidence of succession
direct observations through time
historical evidence
preserved biological evidence
spatial sequences
