Please switch to ‘slide show’ mode (press F5)
This is a presentation by
Roderick Hunt, Ric Colasanti & Andrew Askew
University of Sheffield
It is all about
SAM
A model involving self-assembling
modular plants
This is what a community of
virtual plants looks like
Contrasting tones show patches
of resource depletion
This is a single propagule of a
virtual plant
It is about to grow in a
resource-rich above- and
below-ground environment
The plant has produced abundant
growth above- and below-ground
and zones of resource depletion
have appeared
Above-ground binary tree ( = shoot system)
Each plant is
structured like
this
A branching module
Above-ground array
Above-ground binary tree base module
Below-ground array
Below-ground binary tree base module
This is only a
diagram, not a
painting !
An end module
Below-ground binary tree ( = root system)
The end-modules capture resources:
Light and carbon dioxide from above-ground
Water and nutrients from below-ground
The branching (parent) modules can pass
resources to any adjoining modules
In this way whole plants can grow
The virtual plants interact with their
environment (and with their neighbours)
just like real ones do
They possess most of the properties of real
individuals and populations
For example …
S-shaped growth
curves
Biomass (modules per plant)
3000
2500
2000
1500
1000
Light
Light
Light
Light
500
1 Nutrient
2 Nutrient
1 Nutrient
2 Nutrient
6
6
8
8
0
0
20
40
60
80
Time (iterations)
100
120
140
Partitioning towards the resource-poorer half
of the environment
1.3
Root/shoot allometric coefficient
1.2
Maintaining a functional equilibrium
above-and below-ground
1.1
1 Light unit
2 Light units
1
0.9
0
5
10
15
Units of nutrient per cell
20
Foraging towards resources in a
heterogeneous environment
And when many plants are grown
together in a dense population …
Biomass (modules) per plant
10000
… they exhibit self-thinning
1000
Slope -2/1
100
but as the plants are
2-dimensional
the thinning
slope is not –3/2
10
1
1
10
Planting density
100
All of these plants have the same
specification (modular rulebase)
But this specification can easily be changed
if we want the plants to behave differently…
For example, we can recreate J P Grime’s
system of C-S-R plant functional types
For this, the specifications we need to
change are those controlling morphology,
physiology and reproductive behaviour …
Combinations of plant attributes for seven C-S-R functional types
—————————————————————————————
Functional
Module
Module
Propensity to
type
size
longevity
flowering
—————————————————————————————
C
High
Low
Low
S
Low
High
Low
R
Low
Low
High
SC
Medium
Medium
Low
SR
Low
Medium
Medium
CR
Medium
Low
Medium
CSR
Medium
Medium
Medium
—————————————————————————————
With three levels possible in each of three
traits, 27 simple functional types could be
constructed
However, we model only 7 types; the other
20 include Darwinian Demons that do not
respect evolutionary tradeoffs
Let us see some competition between
different types of plant
Initially we will use only two types …
Small size,
rapid growth
and fast
reproduction
Medium size,
moderately fast
in growth and
reproduction
(Red enters its 2nd generation)
White has won !
Now let us see if white always wins
This time, its competitor is rather different …
Medium size,
moderately fast
in growth and
reproduction
Large size,
very fast
growing, slow
reproduction
The huge blue type has out-competed
both of the white plants, both above- and
below-ground
And the simulation has run out of space …
So competition can be demonstrated
realistically …
… but most real communities involve more
than two types of plant
We need seven functional types to cover
the entire range of variation shown by
herbaceous plant life
To a first approximation, these seven types
can simulate complex community
processes very realistically
For example, an equal mixture of all seven
types can be grown together …
… in an environment which has high levels
of resource, both above- and below-ground
The blue type has eliminated almost
everything except white and green types
And the simulation has almost run out of
space again …
Now we grow the equal mixture of all seven
types again …
… but this time the environment has low
levels of mineral nutrient resource, as
indicated by the many grey cells
(a gap has appeared here)
(red tries to colonize)
(but is unsuccessful)
White, green and yellow finally predominate …
… blue is nowhere to be seen …
… and total biomass is much reduced
Environmental gradients can be simulated
by increasing resource levels in steps
Whittaker-type niches then appear for
contrasting plant types within these gradients
% Biomass in mixture
100
80
60
C
S
40
SC
(types)
20
0
0
5
10
15
20
25
Resource (= 1/stress)
30
Next we grow the equal mixture of all seven
types again …
… but this time under an environmental
gradient of increasing mineral nutrient
resource
Number of plant types
surviving (max 7)
5
Greatest biodiversity is
at intermediate stress
4
3
2
1
0
0
5
10
15
20
25
Resources (= 1/stress)
30
35
Now, environmental disturbance can be
defined as ‘removal of biomass after it has
been created’
For example, grazing, cutting, burning and
trampling are all forms of disturbance
In our model, ‘trampling’ can be applied
simply by removing shoot material from certain
sizes of patch at certain intervals of time and
in a certain number of places
Other forms of disturbance can be simulated
by varying each of these factors
So we grow the equal mixture of all seven
types again …
… but this time under an environmental gradient
of increasing ‘trampling’ disturbance
Number of plant types
surviving (max 7)
2
Greatest biodiversity is at
intermediate disturbance …
… but the final
number of types is low
1
0
0
0.2
0.4
0.6
0.8
Probability of disturbance
1
Environmental stress and disturbance can, of
course, be applied together
This can be done in all forms and
combinations
Again we grow the equal mixture of all
seven types …
… but with one of seven levels of stress and
seven levels of disturbance in all factorial
combinations
Number of plant types
surviving (max 7)
Greatest biodiversity is at intermediate productivity
5
R 2 = 0.534
4
3
2
1
0
0
2000 4000
6000
8000 10000 12000
Total biomass (productivity)
The biomass-driven humpbacked relationship
is one of the highest-level properties that
real plant communities possess
Yet it emerges from the model solely because
of the resource-capturing activity of modules
in the self-assembling plants
Number of plant types
surviving (max 7)
5
R 2 = 0.534
4
3
2
1
0
0
2000 4000
6000
8000 10000 12000
Total biomass (productivity)