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Colonization of a site:
dispersal adaptations
requirements
sequence
r and K strategy
Consequences
More examples
Dispersal and colonization of habitats
Example
Location: present
Indonesia, island of
Krakatoa
The explosion destroyed completely life on the volcano and adjacent
islands.
A new cone formed and its ecological development was monitored, with
decent ecological surveys made as early as 1897.
The 1883 eruption
ejected more than 25
cubic kilometers of
rock, ash, and pumice
Example
Only fraction of
the surface is
alive …
Colonization
and
development of
communities
was interrupted
several times
2
Krakatoa (Krakatau) – dispersal types
After Whittaker et al. 1997
Ridley„s dispersal classification on the then known floras on
Krakatau (up to 1919 only), Christmas Island and Cocos-
Keeling
Dispersal type Krakatau
Christmas Cocos
Sea borne 60 44 17
Wind 34 9 0
Berry or drupe 34 36 0
Adhesive 9 15 5
Mud on birds 3 0 0
Doubtful 4 7 0
Total 144 129 22
Pteridophyta 48 25 0
Timing
Hawaii (more isolated):
• one plant species every 30 000 years,
• one land snail every 200 000 years and
• one bird species every 350000 years These estimates are based on the average age of the
islands being 5 million years
The colonization of the
newly built Krakatoa
island by plants &
animals took 50 years;
First:
Timing of
arrival
Category 1897 1924 1989
Sea dispersed
flowering plants
23 53 59
Animal dispersed
flowering plants
2 48 110
Wind dispersed
flowering plants
14 48 75
Ferns (all wind-
dispersed)
13 51 81
A shift from “sea” to “animals”
3
5-20 years
Ferns appear to dominate first settlers. Why?
Empty space: primary sites Primary sites –
where no prior
communities
existed
Empty space: secondary sites Secondary
sites – where
new „space‟
opens at the
partial
expense of an
old community
Implications: modified physical habitat, propagules
New
secondary site
Primary sites – who arrives first?
- transient animals
- seeds or spores carried by wind or
transient animals
- small seeds before large ones
Two steps: arrival and settlement
What are typical properties of early arrivals?
- small
- resistant to high temperature, low humidity
- adapted to fast or delayed germination
- adapted to transport (burs, wings, hairs)
- require light, i.e., no shade from other plants
4
Dispersal adaptations
Fur Wind Consumer
Wate
r
Non-consumers Hoarders
Ocean
currents
Requirements
Ability to survive travel in a physically
demanding environment (rock, air, ocean, dry
and hot mineral soil)
Ability to survive germination or birth in the
above
Ability to reach reproductive maturity, or
reproduce vegetatively, or parthenogenetically
(animals)
High reproductive rates, colonial nature
(examples ….?) e.g., beach creepers (vine like
plants)
Differential performance
Who (plants)
stays on site?
Plant Characteristic Value
Photosynthesis light saturation efficiency at low light photosynthetic rates
High
Low
High
Water use efficiency transpiration rates
high
Seeds number size dispersal distance viability induced dormancy
High Small Large Long common
Root/shoot ratio low
Mature size small
Growth rate high
5
r and K strategy
Time (t)
N
rNdt
dN
K
NKrN
dt
dN
Recall:
r = net rate of N increase (speed). Thus:
K = carrying capacity (~max N). Thus, if there is a limit:
Invading plants grow quickly, and make lots of seeds ( “r” strategists). “K” strategists focusing their energy and resources on growth and long-term survival (usually come in later in the settlement of new habitat).
From this:
If N is small, a species must grow fast; if N is near K, it should keep it without large fluctuations
Pioneer communities
Mature communities
Dispersal limitation: limitation of distribution or abundance
because of either constraints on dispersal or inadequate
production of dispersing individuals.
Recruitment limitation: limitation of distribution or abundance because
of either constraints on survival of individuals that arrive or were born at
a site (local filter). How would we demonstrate it empirically?
Initial
community
Resultant
community
General concepts
http://www.logos-verlag.de/cgi-bin/buch/isbn/423 Just for fun
Things may become complicated
6
Things may become complicated
Propagules (young, seeds) are often easy,
nutritious and abundant food for other
organisms
Their survival should thus depend on: • Kinds of predators
• Number of predators
• Pattern of foraging
• Payoffs from foraging (number of propagules
predator can find)
Attalea butyracea
Distance from parent tree Number of seeds
Pre
dat
ion
rat
e
Theory
Distance from parent tree
See
dli
ng
s
However …
See
ds
7
Results
Distance from parent tree
See
dli
ngs
Distance from parent tree Number of seeds Pre
dat
ion
rate
See
ds
squirrels inverts agoutis
Invertebrates
Seed density
or health
Thus, a complex system emerges
Seedling density
Red-tailed
squirrel (attack
low densities)
-
+
-
-
Agouti (attack
high densities)
- +
What is a site anyway?
8
Who arrives in greatest numbers? - those that are close - those that are more numerous - those that more mobile
Differential performance
Likely candidates Small insects and arachnids (young spiders, mites) Also, small birds and mammals if site is not very isolated
3 months old lava flow
10 years
15 year old lava flow
20 year old lava flow
Effects of scale
What if the site is large (relative to dispersal distance?
Diagrammatically ..
Role of monkeys,
parrots
9
Effects of scale
What if the site is large (relative to
dispersal distance?
spatial waves; short distances from
the source site if:
a) dispersed by tree animals
(monkeys, birds, bats) that do not
enter open areas)
b) seeds belong to K-strategists
(heavy, adapted to germinate in
shady understory)
These are patterns produced by dispersal limitation
Effects of scale
What if the site is small (relative to dispersal distance?
Recolonization will
be synchronous
throughout the
site
Rich structure, multiple
levels
Same age; simpler
structure
Other consequences of new sites
Consider the case of forest regeneration after logging
10
Site availability
Initial coarse disturbance
Agents Landscape
Species availability
Size Severity Dispersion
Dispersal
Decay rate Land use
Propagule pool
After Pickett et al.
Dispersal
initiates
another
process
(succession)
Resource availability
Consumers
Climate Prior occupants
Germination Assimilation Growth rate
Eco- physiology
Identity Cycles Defenses Patchiness
Stress
Soils Microbes Neighbors
Competitors
Species
performance
Life history Allocation Reproductive timing Reproductive mode
Identity Consumers Fine-scale disturbance Resources
Allelopathy
Soil Microclimate
Inspection of right-hand lists alerts to the fact that all these phenomena, factors, or constraints depend on the area and time considered (scale-dependence)
Vegetation
dynamics