Transcript Population ecology

Unit 3 Ecosystems
Topic 6: Population ecology
Populations
• All of the individuals of a species in a given area at the same
time
Clumped
• Characteristics of populations
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Size (N)
Density
Distribution
Sex ratio
Age structure
Uniform
Random
Population Size
is affected by:
• Additions:
– Birth
– Immigration
• Subtractions
– Death
– Emigration
Change in population size:
N=(birth+immigration)-(death+emigration)
Population growth
Change in population size:
N=(birth+immigration)-(death+emigration)
• Growth occurs if inputs are greater than outputs.
• Under ideal conditions, the intrinsic growth rate is observed.
• This is the maximum potential for growth of a population.
• It is essentially the maximum amount of offspring that a population
could have, if all females of reproductive age give birth to the maximum
number of offspring they are capable of.
Population growth: Exponential
• Exponential growth is
defined as a rate
greater than 1.
• Occurs in populations…
– That are introduced to a
new area
– That are rebounding
from a catastrophe
• Cannot be sustained
indefinitely. Why?
Logistic rate of growth
• So, can populations continue to grow exponentially?
K = carrying capacity
Max. size that environment can
support with no degradation of
habitat.
Varies with changes in resources.
Exceeding Carrying Capacity
• Members of populations which exceed their resources will die or
move to an area with more resources.
Figure 8-6
Population growth general patterns
Predator/prey population cycles
Predator/prey population cycles
What do you think the
primary producer graph
looks like?
Predator/prey population cycles
Population regulation
• Limiting factors control population growth
• Density independent
– Abiotic (precipitation,
temperature, acidity, salinity,
etc.)
– Catastrophic abiotic (flood, fire,
volcanic eruption, tsunami,
earthquake)
• Density dependent
– Biotic (food supply, disease,
parasites, competition,
predation)
Regardless of pop. density,
these factors are the same
for all individuals.
The effects of these factors are
influenced by population density.
Organisms that are more crowded:
•Compete more for resources
•Are found easily by predators
•Spread disease and parasites more
readily
What determines reproductive capacity
of a population?
– sex ratio (how many females vs. males?)
– generation time (at what age do females reproduce?)
– age structure (how many generations reproduce?)
Reproductive strategies
• K-selected
– late reproduction
– few offspring
– invest a lot in raising offspring
• primates
• coconut
• r-selected
– early reproduction
– many offspring
– little parental care
K-selected
• Invertebrates
• many plants
r-selected
More generalized characteristics
of r and K selected species
Survivorship curves
What do these graphs tell
about survival &
strategy of a species?
(Generalized strategies)
Survival per thousand
1000
Human
(type I)
I. High death rate in
post-reproductive
years
Hydra
(type II)
100
II. Constant mortality rate
throughout life span
Oyster
(type III)
10
1
0
25
50
75
Percent of maximum life span
100
III. Very high early
mortality but the few
survivors then live long
(stay reproductive)
Populations of r and K strategists
Pop.
Number size
of individuals
Populations of k strategists tend to
grow exponentially when initially
established and then become stable
around a carrying capacity.
Populations of r strategists tend to
r strategist
k strategist
have
periods of rapid growth (births)
followed by sharp declines (most
young do not survive).
Which is which?
Time
Populations over time
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Evolution occurs at the level of the population.
What is survival of the fittest?
How can community dynamics create biological diversity?
How can climatic changes create biological diversity?