Transcript Population density - Napa Valley College

Fig. 52-2
Organismal
ecology
Population
ecology
Community
ecology
Ecosystem
ecology
Landscape
ecology
Global
ecology
Introduction to Ecology
Populations
• Population ecology
– Abundance
– Dynamics
Density, dispersion,
demographics,
interrelationships with
other populations
Population density
• The number of individuals
per unit area or volume
Pattern of dispersion
• Refers to how
individuals are
spaced relative to
one another
(a) Random dispersion
Fig. 52-1a, p. 1128
Pattern of dispersion
• Patchiness in
resources
• Family groups
• Reduce risk of
predation
(b) Clumped dispersion
Fig. 52-1b, p. 1128
Pattern of dispersion
• Aggressive
interactions
• Competition
(c) Uniform dispersion
Fig. 52-1c, p. 1128
Population dynamics
• 4 primary factors that influence population
size
– Births
– Deaths
– Immigration
– Emigration
• How do these factors affect the rate at which
populations change?
Fig. 53-3
Births
Births and immigration
add individuals to
a population.
Immigration
Deaths
Deaths and emigration
remove individuals
from a population.
Emigration
Fig. 53-3
Births
Births and immigration
add individuals to
a population.
Immigration
Deaths
Deaths and emigration
remove individuals
from a population.
Emigration
Life History
– The age at which reproduction begins
– How often the organism reproduces
– How many offspring are produced during each
reproductive cycle
• evolutionary outcomes reflected in the
development, physiology, and behavior of an
organism – based on trade-offs
A survivorship curve is a graphic way of representing the data in a life table
Number of survivors (log scale)
1,000
100
Females
10
Males
1
0
2
4
6
Age (years)
8
relatively constant death rate
10
Fig. 53-6
Number of survivors (log scale)
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
Fig. 53-9
(a) Dandelion
(b) Coconut palm
Number of bacteria (N)
Dynamics - Population growth
Hours
r = unchecked population growth
Fig. 52-2, p. 1130
Human population (billions)
2006: 6.5 billion
Black Death
Time (years)
Fig. 52-13, p. 1139
Number of individuals (N)
Carrying capacity of the
environment (K)
Time
Fig. 52-3, p. 1131
The Logistic Model and Life Histories
• Life history traits favored by natural selection may
vary with population density and environmental
conditions
• K-selection, or density-dependent selection, selects
for life history traits that are sensitive to population
density
• r-selection, or density-independent selection,
selects for life history traits that maximize
reproduction
Factors influencing population size
• Density-dependent
– Density of population alters the affect of an
environmental condition
• Density-independent
– Effect of an environmental factor is not affected
by the density of a population
Density-dependent factors
Density-dependent factors
• Competition – interaction
in which individuals try to
use the same resource
– Intraspecific
– Interspecific
Density-independent factors
Metapopulations
• Environments are
heterogeneous
– Resources are patchy
– Several small
populations rather
than 1 large
• Not all patches are
equal
– Less desirable may
result in lower b or
higher d
– More productive may
lead to higher b and
lower d
Fig. 52-12, p. 1138