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BIOL 1010 Introduction
to Biology: The
Evolution and Diversity
of Life. Spring 2011
Sections A & B
Steve Thompson: [email protected]
http://www.bioinfo4u.net
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Wednesday, April 6, 2011
OK, on to the easiest
part of the course . . .
Stuff you’ve actually been
learning all your life, perhaps
even without realizing it.
I’m talking about ‘green’
stuff . . . the theories and
methods of ecology.
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Wednesday, April 6, 2011
We’ll start with population ecology.
Population – a group of organisms of one
species occupying a geographic location
at the same time, such that they can
potentially interbreed.
Habitat – the physical location where
members of a population live.
Community – all of the organisms in a
given habitat.
Ecology – the study of the relationships
among organisms and the environment.
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Wednesday, April 6, 2011
a. Random
Population density – the number of individuals of a
species per unit area or unit volume of habitat.
Different distribution patterns:
Random – evenly distributed resources, no
territories;
Uniform – evenly distributed resources, strong
territories;
Clumped – unevenly distributed resources.
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Wednesday, April 6, 2011
Population dynamics
is the . . .
Study of the factors that influence
changes in a population’s size:
Immigration – the movement of
individuals into a population; and
Emigration – migration out of a
population.
Births and deaths affect this too, duh!
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Wednesday, April 6, 2011
Growth rates are affected by . . .
Birth rate – the number of new
individuals produced per unit time.
And . . .
Age structure – the distribution of age
classes. This determines whether a
population is growing, stable, or declining.
For example, if a population is mainly of
prereproductive age, it will grow; and . . .
If it is mainly of postreproductive age it
will remain stable or shrink.
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Wednesday, April 6, 2011
This can be seen graphically . . .
In population-age pyramids.
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Wednesday, April 6, 2011
Death rate
– the
number of
deaths per
unit time.
Life table –
a chart
showing the
probability
of surviving
to any given
age.
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Wednesday, April 6, 2011
A survivorship cur ve is a . . .
Graph of the proportion of surviving individuals at
any given age. There are . . .
Three general patterns:
Type I – invests a great deal of energy and time into
their offspring, and mortality is highest as
individuals approach their maximum life span; e.g.
many large mammals like humans and elephants.
Type II – there’s an equal probability of dying at any
age; e.g. many medium sized birds and mammals.
Type III – produce many offspring but invest little
in each one, and most offspring die at a young age;
e.g. many fish, and plants, and most invertebrates.
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Wednesday, April 6, 2011
You can plot this graphically:
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Wednesday, April 6, 2011
And some of
the factors
that make it
happen . . .
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Wednesday, April 6, 2011
Population growth
The per capita rate of increase of a
population is “r”.
It is the difference bet ween the birth rate
and the death rate.
If it is negative, the population is shrinking.
If it is positive, the population is growing.
G = rN This is exponential growth.
G is the number of individuals added per
unit time. And . . .
N is the number of individuals at the start
of a given time inter val.
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Wednesday, April 6, 2011
Exponential growth
The number of new individuals is
proportional to the size of the
population at any given time. A . . .
J-shaped curve emerges. This is . . .
Growth resulting from repeated
doubling (exponential).
Organisms not native to an area may
proliferate exponentially for a time,
because there is no natural population
controls when they arrive.
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Wednesday, April 6, 2011
Exponential
growth –
think
bacteria in
complete
(everything
they need)
media . . .
t wo, four,
eight,
sixteen . . .
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Wednesday, April 6, 2011
However, . . .
Exponential growth cannot continue
indefinitely; something will run out . . .
Environmental resistance – the combination
of factors that keeps a population from
reaching its maximum growth rate.
Carrying capacity – the maximum number
of individuals that a particular habitat can
support indefinitely.
As a population approaches its carrying
capacity, growth slows and eventually
stops.
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Wednesday, April 6, 2011
This
makes
sense —
it’s
called
logistic
growth
and is Sshaped
when
plotted.
See http://
www.youtube.com/
watch?
v=NWqNKwwkB4k
bad sound, but a
good overview.
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Wednesday, April 6, 2011
G= rN(K-N)/K describes the curve.
G is the number of individuals added per unit time.
r is the per capita rate of increase.
N is the number of individuals at the start of the
given time interval.
K is the carrying capacity of the population in a
particular habitat.
rN is the growth rate without limiting resources.
N(K-N)/K factors in increasing environmental
resistance.
However, in reality the carrying capacity is not
fixed, e.g. an extended drought may be followed by
several wet years.
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Wednesday, April 6, 2011
There are limits to population size!
Density-independent factors – exert effects
unrelated to population density. These are usually
catastrophic, such as . . .
Flood, volcanic eruption, earthquake, severe
weather, etc.; versus . . .
Density-dependent factors – conditions whose
effects increase as a population grows.
For example, infectious disease spreads faster in a
larger population (makes sense).
Competition for space, nutrients, and light can
also limit population growth in a densitydependent manner. Ya think . . . .
A population may even crash given limited resources.
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Wednesday, April 6, 2011
E.g. A
population
crashes –
introduced
Reindeer
on St.
Matthew
Island ate
up all their
food,
especially
lichen, and
then died
off.
Wednesday, April 6, 2011
see http://dieoff.org/page80.htm
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Reproductive strategies are called . . .
Life histories – all events in a species’
existence that influence its reproduction.
This includes . . .
Whether a species reproduces sexually
and/or asexually; its . . .
Life span; its . . .
Age at maturity; . . .
When and how often it reproduces;
and . . .
The number and size of its offspring.
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Wednesday, April 6, 2011
r-selected species:
Individuals tend to be short-lived, reproduce
at an early age, and have many offspring
that receive little care.
This is typical of species with a type III
sur vivorship cur ve.
Weeds, crop pests, and many invertebrates
are r-selected species.
Populations can explode in favorable
conditions, but . . .
Density-independent factors tend to limit
growth in the long run.
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Wednesday, April 6, 2011
K-selected species:
Individuals tend to be long-lived, late-maturing,
and to produce a small number of offspring
that receive extended parental care.
Therefore, they typically have a . . .
Type I or II survivorship cur ve.
Density-dependent factors, such as
competition, limit growth; keeping populations
close to their carrying capacity.
This is typical of many birds and most large
mammals.
Both selection strategies are extremes; most
organisms fall somewhere in bet ween.
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Wednesday, April 6, 2011
Guppies (Poecilia reticulata) illustrate
the importance of selection.
Experiments show that natural selection directly
influences the details of life history.
Here’s what a group of scientists did:
They collected guppies from 16 sites —
4 with low predation intensity; . . .
5 with moderate predation intensity; and . . .
7 with high predation intensity.
They predicted that guppies from streams with high
predation intensity would reach reproductive
maturity at a younger age and devote more energy to
reproduction than guppies from the other streams.
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Wednesday, April 6, 2011
Here’s a Guppy.
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Wednesday, April 6, 2011
The results confirmed their
hypothesis.
Guppies from the high intensity predation
stream did mature earlier, had more and
smaller offspring, and reproduced more
frequently, than the guppies in the other
streams.
The differences were proven to be genetic.
And the predators there were responsible
(not some other stream condition).
Natural selection had shaped their life
history.
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Wednesday, April 6, 2011
And remember back . . .
To the first part of the course. Those
null-model equations of HardyWeinberg and Wright-Fisher, and lots
of fancy mathematics, and powerful
computer programs, all allow us to . . .
Estimate these sort of population
parameters, such as growth, migration,
and selection, based on samples of
organisms’ DNA from the populations
of interest.
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Wednesday, April 6, 2011
Told ya’ – it’s the big picture
that matters. Next . . .
We’ll continue to learn about ecology and
talk about communities, succession, and
ecosystems — the foundation of the global
biome — starting with the tropical
rainforest. And we’ll start that right now.
Unfortunately we can’t do the Exam III
review until later because my graduate
assistant had some schedule conflicts that
prevented her from being able to grade
them right away.
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Wednesday, April 6, 2011