Evolution
Behavioural Ecology is the scientific study of
behavioural phenomena in the light of
ecological and evolutionary theory
1. A refresher in evolution by natural selection
2. What is behaviour in the light of
evolutionary theory
3. How did behavioural ecology develop as a
discipline?
4. There is evolution in action all around us
PSYCH 3T03
Lecture 02
Animal Behavior – Chapter 1
Common misunderstandings in evolution
1. Evolution is not random – mutation is random, selection is not
2. There is no ‘aim’ to evolution – whatever survives survives
3. What survives is not necessarily what is ‘best’ for long term survival of the species
4. No species is ‘more evolved’ than any other – same ~3.7 billion years of evolution
5. Evolution is not necessarily slow – big changes can occur in few generations
6. Not all evolutionary change is adaptive – neutral processes such as drift
Three things that behavioural ecology is not
1. Behavioural Ecology is not behavioural genetics
2. Behavioural Ecology is not behavioural determinism
3. Behavioural Ecology is not primarily about humans
* This course will not be about humans
Three things that behavioural ecology is
1. Behavioural Ecology is Adaptationist
We will be looking at adaptive traits
2. Behavioural Ecology is Selectionist
Natural selection is the force driving adaptation
3. Behavioural Ecology is Comparative
We will be comparing across different taxa and sexes
Adaptation
The evolutionary process by which organisms fit better into
their environments or habitats.
A physical or behavioual trait maintained
and evolved by natural selection that enhances the
probability of survival and reproduction
Adaptation- Bird Flight
Wings – large chest muscles
Bones – hollow, lightweight
Aerodynamic – body structure
Feathers – help birds fly
Powerful heart and respiratory system –
extract more oxygen and power flight
Why study Behavioural Ecology?
1. Behavioural Ecology benefits us
We use animals and plants in many different ways
Protect our crops from pests, improve the welfare of pets/livestock, find food etc.
2. Behavioural Ecology benefits the natural world
Know what animals need and when/where they need it
Monitor how ecosystems are changing due to habitat and climate change
3. Behavioural Ecology is interesting
>5000 mammals, >30,000 fishes, >40,000 spiders, >400,000 beetles, etc.
Who studies Behavioural Ecology?
Evolutionary Biologists
Population and Community Ecologists
Zoologists
Psychologists
Physiologists
Geneticists
Neuroscientists
Endocrinologists
Anthropologists
Conservation Biologists
Wildlife Resource Managers
Animal Breeders
And where do they publish?
Nature
Science
Proceedings of the Royal Society
Animal Behaviour
Behavioral Ecology
Behavioural Ecology & Sociobiology
Hormones & Behavior
Ethology
Behavior
Ecotoxicology
Neuroscience
Experimental Physiology
And many more….
How did the field develop?
Behavioural Ecology unites two fields:
1. Ethology
The study of behaviour under natural conditions
2. Evolutionary Biology
The study of how life develops through natural selection
Ethology – studying behaviour
Niko Tinbergen
Konrad Lorenz
Karl von Frisch
Nobel Prize in 1973
The great insight of the classical ethologists was that they realized that just as each
animal species has its characteristic anatomy, physiology, biochemistry so too each
species has its characteristic behaviour.
Behavioural traits can be analyzed in the same way as physical traits, including the study
of their evolution.
A curious naturalist
Obliged to the public
Valued communication
Science is a social effort
Richard Dawkins
Marian Stamp Dawkins
Iain Douglas Hamilton
Desmond Morris
How did the field develop?
Behavioural Ecology unites two fields:
1. Ethology
The study of behaviour under natural conditions
2. Evolutionary Biology
The study of how life develops through natural selection
Evolutionary Biology
Charles Darwin
On the Origin of Species 1859
Alfred Russell Wallace
Natural selection occurs because
1. The is variation within populations
Individuals differ in traits that affect their chance of survival / reproduction
2. Variation is heritable
Successful traits can be passed on to the next generation
3. Reproductive success can differ within a population
Some individuals will have more offspring that others
Gregory 2009. Evo Edu Outreach. 2: 156-175.
Remember…. when differential survival and
reproduction are related to individual differences
and these individual differences are heritable,
evolution can ensue.
We say evolution "can" ensue, not that it will ensue,
because even if all 3 conditions are fulfilled,
selection is often stabilizing: if a trait's is already
optimal (because of past selection), current
selection tends to prevent it from evolving
("drifting") away from that optimum.
Evolution in action
Anyone know of any examples of
contemporary examples of evolution?
Share them in the chat
Pollution adapted peppered moths
SARS-COV-2 variants
Running cane toads in Australia
Antibiotic resistant ‘superbugs’
Anolis lizards adapted to urban substrates
Shrinking fish
because of over
fishing
Tuskless elephants
Darker owls in Finland due to
climate change
Evolution in action – Darwin’s Finches
This is the adaptive radiation that most influenced Darwin :
By standard morphological criteria of taxonomy, these 11 species are one another’s
closest relatives (now confirmed by molecular methods), but they are much more diverse
in bill morphology, diet and behaviour than is typical within a genus of songbirds.
Arriving first at the newly formed volcanic islands of the Galapagos, they “radiated” to
fill unoccupied ecological niches that other songbird genera occupy in South America
and elsewhere.
The Grants in
The
Galapagos
50 km
Rapid evolution of beak
morphology in the medium
ground finch (Geospiza fortis)
G. fortis has been studied on
Isla Daphne for > 50 years
by Rosemary & Peter Grant
Unusual aspects of this study
1. Long term study.
2. Every individual was marked and tracked. So LRS
was known and the traits beneficial for fitness could be
assessed.
3. Natural environmental perturbations in the form of
droughts were “naturalistic experiments” or
manipulations allowed the Grants to observe natural
selection in a relatively short time period.
Excellent popular account of their
work:
J Weiner (1994)
The beak of the finch. NY: Knopf.
Beak size/depth
Birds with large beaks eat
large hard seeds
Birds with medium beaks eat
both small soft
and large hard seeds
Birds with small beaks eat
small soft seeds
1976 was an unusually dry year on Isla Daphne; 1977 was worse.
Over < 2 years, finch food (seed) abundance plummeted, and the finch population crashed.
Not only were seeds rarer, but
species composition of the
seed bank changed.
Before the drought the most
abundant were small, soft
Portulaca seeds.
After the drought, most of
what remained were large
hard Tribulus seeds… which
not all G. fortis were capable
of cracking open.
Result : Directional selection on beak size in G. fortis
as a result of differential survival of the drought
N of birds
751
90
1976 population
1978 survivors
1976
Number of individuals
9.4 mm
10.2 mm
5
7
9
11
Beak depth (mm)
1978
13
Average beak depth
9.4 mm
10.2 mm
Recall : When differential survival and reproduction are nonrandomly related to individual differences and these individual
differences are heritable, evolution can ensue.
Survival (hence reproduction) was obviously selective with respect to
beak dimensions.
But is beak size demonstrably heritable?
Yes, it is
All the necessary conditions for
evolution were met, and
evolution of bill size indeed
occurred: ensuing generations
of Daphne Island G. spiza had
bigger bills than the 1976
pre-drought population.
Boag & Grant 1981. Science
Review
Evolution
Is a change in the genetic
composition of a population over
successive generations. Driven by
natural selection acting on the
genetic variation in reproductive
success among individuals (resulting
from a heritable trait). Results in new
species.
Review
Evolution-long term process
Natural Selection
1976
9.4 mm
Number of individuals
is a process by which traits become
more or less common in a population
because these inherited traits lead to
differential survival and reproduction
of individuals possessing them.
1978
10.2 mm
5
7
9
11
Beak depth (mm)
13
Review
Adaptation
is a change in a state or a trait that increases the reproductive
success of individuals that have it.
Important to Remember
1. Evolution is not Natural Selection
Evolution is gene frequency change - Evolution occurs across generations.
Individuals do not evolve.
2. The major causes of evolution are mutation, genetic drift and natural selection.
3. Natural selection is differential reproduction
Differential reproductive success is called FITNESS
4. Natural selection is the only evolutionary force predictably leading to
adaptation (or the fit between an organism and its environment).
Important to understand the following terms:
Evolution
Natural Selection
Fitness
Adaptation
Evolution in Action:
The Story Continues
Grant PR & Grant BR (2006) Evolution of character displacement in
Darwin’s finches. Science 313 : 224-226.
Result : Directional selection on beak size in G. fortis
as a result of differential survival of the drought
N of birds
751
90
1976 population
1978 survivors
1976
Number of individuals
9.4 mm
10.2 mm
5
7
9
11
Beak depth (mm)
1978
13
Average beak depth
9.4 mm
10.2 mm
Review
MEDIUM GROUND FINCH WITH A SMALL BEAK
1982
NEW COMPETITOR:LARGE GROUND FINCH
MEDIUM GROUND FINCH WITH A BIG BEAK
Review
Grant PR & Grant BR (2006) Evolution of character displacement in Darwin’s
finches. Science 313: 224-226.
Figure 2.
Year-by-year
variation in
Geospiza fortis
beak size on
Daphne Major.
The 1977 and 2004 “selection events” were both droughts that led to seed bank
depletion and crashing finch populations due to starvation.
But the selective effects on G. fortis beak dimensions were opposite in direction.
The Grants argue that the critical difference was the presence of G. magnirostris in
2004 cf. absence in 1977.
“Character displacement”
Divergence in traits that is
caused by competition between
species
(interspecific competition).
CD means that the differences
are exaggerated in sympatry,
presumably as a result of a
recent selective history of
interspecific competition.
CD caused bigger differences in
beak dimensions between the
medium ground finch (G. fortis)
and the large ground finch (G.
magnirostris)
G. fortis- MGF
G. magnirostris - LGF
After 2005
40
20
%
Individuals 8
In
Each
Size 40
class
20
8
10
12
1
4
Before 2004
10
12
Beak size (mm)
1
4
Review
“Character release”
In the absence of competition
from the small ground finch,
(G. fulginosa), the medium
ground finch (G. fortis), on
Daphne had smaller beaks
than is typical on other
islands.
Greater overlap in beak size
when each species found
alone (allopatric).
In the past, the medium
ground finch was released
from competition and had
unusually small beaks.
Any Questions?
PSYCH 3T03
Lecture 02