Transcript E3_Construction_2011Part 1

Niche Construction
E3: Lecture 18
Entropy and Life
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Roughly, entropy is a measure of disorder, or how
evenly energy is distributed in a system.
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Second law of thermodynamics:
– In a closed system, entropy will not decrease.
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At first glance, organisms (with their exquisitely
ordered subsystems) seem to break the second law,
however,…
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…the order within organisms originates through
creation of disorder elsewhere.
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At a fundamental level, to live is to affect your
environment.
Construction
• A process whereby an organism
“actively changes one or more of the
factors in its environment, either by
physically perturbing factors at its
current location… or relocating to a
different [place], thereby exposing
itself to different factors.”
relocation
(Odling-Smee et al. 2003)
• An organism affects its environment
through:
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artifact construction
constructing artifacts
competing for resources
generating waste and by-products
moving within its habitat
following developmental pathways
interacting intra- and interspecifically
modulation of light
space competition
• Such effects may feed back to affect
further evolution of the constructing
species, as well as other species in
its web of construction.
excreted
products
affecting the welfare
of other organisms
Niche Construction
Lecture Outline
• Introduction to niche construction
• Niche construction and adaptive landscapes
• Rekindling an old flame
• Experiment on mutual niche construction
• Summary
Niche Construction
Lecture Outline
• Introduction to niche construction
• Niche construction and adaptive landscapes
• Rekindling an old flame
• Experiment on mutual niche construction
• Summary
Adaptation versus Construction
• No niche construction
– “Fitting a niche”
– Here, the environment
sifts through available
phenotypes and picks that
type best adapted.
• Relocation niche
construction
– “Finding a niche”
– Here, the environment
must be heterogeneous in
order for relocation to be
meaningful
• Perturbation niche
construction
– “Forging a niche”
– Here, the dynamics
between the organism
and environment are
coupled.
Construction as a Complimentary Process
• Construction as the compliment to
natural selection:
– The norm of reaction describes
phenotype as a function of
environment.
– Niche construction involves the
inverse function: environment as
a function of phenotype.
N.C.
N.S.
Environment
PLASTICITY
CONSTRUCTION
environment
phenotype
• Construction as the compliment to
plastic development:
Organism
phenotype
– Natural selection is often
considered as a process where
organisms “solve” problems
“posed” by the environment.
– Thus, selection can be seen as a
process where the form of the
organism follows from the form of
the environment.
– Niche construction is a process
where the form of the environment
follows from the form of the
organism.
environment
environment
phenotype
A New View of Evolution
• The form of the environment
influences this process (via
natural selection)
environment (t)
• The “new view” of evolution
recognizes mutual influence
between environment and
organism.
population (t)
niche construction
natural selection
environment (t+1)
genetic
inheritance
environment (t)
ecological
inheritance
• The “old view” of evolution
focuses on how a population
changes over time.
population (t+1)
• The “new view” also sees two
channels of inheritance.
Take 5 minutes to talk to your neighbor about the following:
Do you think that the incorporation of niche construction into evolutionary
theory is necessary? How does niche construction relate to:
Coevolution? Cultural evolution? Anthropogenic effects on environment?
Kinds of Niche Construction
• How does the organism change
its environment?
– Relocation: Organism moves
to a new place in a
heterogeneous habitat
– Perturbation: Organism
physically changes one or
more factors in its habitat.
seasonal migration of birds
earthworms aerate soil
• How does the change modify
selective pressures?
– Inceptive: Change introduces
a new selective pressure.
– Counteractive: Change
reverses or neutralizes a prior
change in selective pressure.
oviposition on novel host
behavioral thermoregulation
bowerbird constructs bower
trees use nutrients, space, light
• What are the feedback effects
on the organism?
– Positive: Activities feed back
to increase fitness of organism.
– Negative: Activities feed back
to decrease fitness of
organism.
Mini Case Study: Niche Construction and Cognition
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Much of the research in early psychology
and ethology focused on how behavior
depended on properties of the environment;
thus, this research did not explicitly
incorporate niche construction.
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However, it is often the case that behavior
changes the environment (e.g., a stimulus
could be prey, an offspring, or a mate).
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This niche construction takes various forms:
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Antagonistic relations between an organism
and its stimulus is a form of negative NC.
Mutualistic relations is a form of positive NC.
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Previously, we discussed how a changing
environment might favor learning.
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Negative NC may produce a changing
environment, whereas positive NC may
yield a static environment.
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Models show that negative NC can favor
learning and positive NC can favor innate
behavior.
Learner
Stimulus
Niche Construction
Lecture Outline
• Introduction to niche construction
• Niche construction and adaptive landscapes
• Rekindling an old flame
• Experiment on mutual niche construction
• Summary
Niche Construction and the Adaptive Landscape
fitness
• The adaptive landscape is a map
from genotype to fitness.
• Since the environment defines the
landscape, environmental change
will affect evolution. Consider:
– No change
– Exogenous change
– Endogenous change
Figure 2 from Wright (1932)
EXOGENEOUS
STATIC
Evolution in Changing and Changed Environments
• When the landscape
is rugged (e.g., due
to genetic epistasis),
the population can
become trapped on a
sub-optimal peak.
• A changing
environment can
move a population to
a new peak (perhaps
a higher one).
• An environment
changed by
organisms can also
move a population to
new places.
• In particular, negative
niche construction
may encourage
continual
diversification.
reference
environment
reference
environment
alternate
environment
altered
environment
reference
environment
reference
environment
The Experimental System
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We explored these topics using the digital
evolution platform AVIDA.
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An evolving population of digital
organisms (Avidians) vie for space.
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The genome of an Avidian is a selfreplicating computer program.
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The instructions of the genome are
processed by a virtual CPU, such that
data (bit strings) are read, stored,
manipulated and written.
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Josh
Nahum
Luis
Zaman
Jevin
West
Data
I/O
Q buffer
&A
nop-A
add
inc
push
nop-C
Some types of manipulation (tasks) are
rewarded, increasing fitness.
We can control how tasks are rewarded;
thus, Avida is suited for our questions:
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0 1 0 1 Question:
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Static landscape: unchanging rewards
Changing landscape: exogeneously
changing rewards
Changed landscape: endogeneously
changing rewards
Ben
Charles
Althouse Ofria
0 0 0 1
Are the elements of
these strings equal?
1 0 1 1 Answer
if Q/A is rewarded
CPU
Data
memory