APES Notes Ch. 9
Mrs. Sealy
Major Characteristics of
populations
–
–
–
–
–
size
density
Dispersion: clumped, uniform and random
age distribution:
Population dynamics: changes in size,
density, dispersion and age distribution of a
population
Clumped
(elephants)
Uniform
(creosote bush)
Random
(dandelions)
Fig. 9.2, p. 199
Limits on Population growth
•
•
•
•
A. Population change = (Births +
Immigration) – (Deaths + Emigration)
B. Carrying capacity (k) = biotic potential
+ environmental resistance
C. Biotic potential: capacity for growth of
a population. Example: flies – high biotic
potential, pandas - low
D. Environmental resistance: all those
things that limit the size of a population.
Examples: fire, predation, lack of
resources, disease
POPULATION SIZE
Growth factors
(biotic potential)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Abiotic
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites
Inability to migrate and live in other
habitats
Inability to adapt to environmental
change
Fig. 9.3, p. 200
Carrying capacity:
• E. the maximum number of individuals of a
given species that can be sustained in a
given area indefinitely. When the carrying
capacity of a population is exceeded, the
population will have a dieback or crash to
remove the excess animals. An example is:
• The Reindeer of Angel Island
Number of reindeer
2,000
1,500
1,000
500
1910
1920
1930
Year
1940
1950
Fig. 9.6, p. 201
Population size (N)
Population size (N)
K
Time (t)
Exponential Growth
Time (t)
Logistic Growth
Fig. 9.4, p. 201
Number of sheep (millions)
2.0
1.5
1.0
.5
1800
1825
1850
1875
Year
1900
1925
Fig. 9.5, p. 201
minimum viable population:
• F. minimum population that a species needs to
have to be sustained. You need a minimum
number of individuals to support a population
because:
•
1. Too few individuals causes interbreeding
•
2. They need to be able to find mates
•
3. Not enough genetic variability for the
population to adapt
G. Density and population
growth:
• 1. Density independent population controls are
things that affect the size of a population that
have nothing to with the density of a population.
For example: weather, natural disasters, seasons
• 2. Density dependent population controls are
things that affect the size of a population that
occur only as the density of the population
increases. For example: competition, predation,
parasitism, disease
H. Population fluctuation curves
Graph of population curves – stable, irruptive,
Irregular
cyclic, irregular
Number of individuals
Stable
Cyclic
Irruptive
Time
Fig. 9.7, p. 202
Population size (thousands)
160
140
Hare
120
Lynx
100
80
60
40
20
0
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
Year
Fig. 9.8, p. 203
5,000
Moose population
Wolf population
3,000
100
90
80
2,000
70
60
50
40
1,000
30
20
500
Number of wolves
Number of moose
4,000
10
0
1900 1910
1930
1950
Year
1970
1990 2000
Fig. 9.9, p. 204
1997
Reproductive Patterns and Survival
• III Asexual Reproduction: all offspring are
exact genetic copies (clones) of a single
parent. Example: bacteria, fungi
• Sexual Reproduction: all offspring are a
result of combining the sperm and ovum
from both parents. This produces offspring
that have traits from both parents. 97% of
all known organisms.
r-Selected Species
cockroach
dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching
reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
Fig. 9.10a, p. 205
K-Selected Species
elephant
saguaro
Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
Fig. 9.10b, p. 205
•
•
survivorship curves – life expectancy
curve: shows number of survivors of each
age group for a particular species
Graph Survivorship curve
Percentage surviving (log scale)
100
10
1
0
Age
Fig. 9.11, p. 206
Conservation Biology
–
–
Multidisciplinary science of that uses the
best information available to determine how
to best protect species from extinction.
Determine which species are in danger of
extinction, what the status of ecosystems is,
what measures can be taken to preserve
species.
Human Impacts on Ecosystems:
– fragmenting and degrading habitats
– simplifying ecosystems
– strengthening some populations of pest
species and disease causing bacteria
– eliminating predators
– introducing alien species
– over harvesting resources
– interfering with normal chemical cycling
Environmental Stress
Organism Level
Population Level
Population Level
Physiological changes
Psychological changes
Behavior changes
Fewer or no offspring
Genetic defects
Birth defects
Cancers
Death
Change in population size
Change in age structure
(old, young, and weak may die)
Survival of strains genetically
resistant to stress
Loss of genetic diversity
and adaptability
Extinction
Disruption of energy flow through
food chains and webs
Disruption of biogeochemical cycles
Lower species diversity
Habitat loss or degradation
Less complex food webs
Lower stability
Ecosystem collapse
Fig. 9.12, p. 208