Transcript Population Dynamics


Populations can be described by
 Distribution
 Numbers
 Age structure
 Density

Populations cannot grow indefinitely (r)
because there are limited by resources and
habitats (k= carrying capacity).



Clumping
Uniform dispersion
Random dispersion
 i.e., Plethodon sp. salamanders are found
clumped under fallen logs in the forest
 the night lizard Xantusia sp. is found
clumped within fallen Joshua trees in the
Mojave desert
 Plants often clump because their seeds fall close
to the parent plant or because their seeds only
germinate in certain environments. Impatiens
capensis is an example.
This generally happens because of interactions
between individuals in the population.
 Competition: Creosote bushes in the Mojave
desert are uniformly distributed because
competition for water among the root systems of
different plants keep them separated.



Territoriality: The desert lizard Uta sp.
maintains somewhat regular distribution via
fighting and territorial behavior
Human Intervention: I.e., the spacing of
crops.

This pattern occurs in the absence of strong
attraction or repulsion among individuals.
 It is uncommon.
 For example, fig trees in the amazon rain forest.
This random distribution might be due to seed
dispersal by bats.

Simply the number of individuals in the
population at any given time. Sometimes
called abundance.

This is the relative number of individuals
at different ages.

Broken down by:
 Prereproductive age
 Reproductive age
 Postreproductive age



Which population structure would lead to
stable growth?
Which leads to an increase in population?
Decrease?
Which types of countries do you think follow
a stable growth? Increasing? Decreasing?

The number of individuals in the population
per unit area or unit volume.
 For many organisms, it is the density of a
population rather than its actual numbers, that
exerts a real effect on the organism.

There are 10,400 mice living in a 1000m x
1000m field. What is the density of this
population?


The area of the field is 1,000,000 square
meters (m2).
The density of mice is therefore 10,400
mice/1,000,000m2=.0104/m2.





Birth (Natality)
Death (Mortality)
Immigration
Emigration
Population change= (B+I) – (D+E)

This is probably the best, simple, model of
population growth…it predicts the rate of
growth, or decay, of any population where
the per capita rates of growth and death are
constant over time.
 In exponential growth models, births, deaths,
emigration and immigration take place
continuously.
 What must exist for populations to grow in
this way?




Density
independent
Results from
sudden crash in
population size
Outstrip resource
limit
catastrophe

Populations tend to grow to the
maximum extent possible given
environmental conditions
 Intrinsic rate of increase (r)= rate of
population growth if unlimited
resources available
 Also called biotic potential
 Biotic potential cannot be
sustained
 Environmental resistance
 Negative feedback
▪ Snowshoe hare and lynx

Populations grow until one or several limiting
resources become rare enough to inhibit
reproduction so that the population no longer
grows.

Eventually, every population reaches its
carrying capacity, this is the maximum
number of individuals a given environment
can sustain.



Density dependent
Recycling and
renewal of
resources
Establishes
equilibrium around
carrying capacity






A: lag phase
B: acceleration
phase
C: exponential
growth
D: deceleration
phase
E: equilibrium
G: dynamic
fluctuations



Adaptive traits
Technological advances
How have we changed the carrying capacity
for human population growth to continue?

Density- dependent factors
 Intraspecific competition
 Predation
 Disease
 Density-independent factors
 Natural disasters
 Pollution
 Habitat destruction (deforestation)

What is an example of a density dependent
and independent factor?

Examples: For Neodiprion sawflies, winter
surviorship is greatly affected by the weather,
which is density-independent.
 During the summer, however, parasitic wasps
impose very high density-dependent mortality.

Pacific mussels, Mytillus sp., are largely
limited by density-dependent competition
for space on rocky outcrops. Occasionally,
density -independent disturbance by floating
logs decimates populations.

Stable
 Rainforest species

Irruptive
 Insects

Cyclic- (boom and bust)
 Lemmings
▪ http://www.youtube.com/watch?v=pDqlZjpSJCc
 Wolf-moose interactions

Irregular
 Due to catastropies



Why are deer referred to as an “edge
species”?
What are controls to deer population?
What is the deer dilemma?

Delayed density
dependence


SEXUAL
What are pros and
cons to this type of
reproduction?


ASEXUAL
What are pros and cons
to this type of
reproduction?
r-selected
 Reproduce early and put
most of their energy into
reproduction
 Many small offspring
 High growth rate
Population size fluctuates
wildly around carrying
capacity
 Low ability to compete
 Most offspring die before
reaching reproductive age
K-selected
 Fewer, larger offspring
 High parental care
 Most offspring survive to
reach reproductive age
 Lower growth rate
 High ability to compete
 Population size fairly stable
around carrying capacity
 Positive: enhance population
growth
 Negative: reduce population
growth
 Predators
 Diseases
 Pheromones
Type I (Late Loss): large
animals immune to
predation, live to old
age
 Type II (Constant Loss):
mostly prey, predation
is constant throughout
lifespan
 Type III (Early Loss):
large numbers of young
because most will be
eaten, only few adults
survive
