Transcript Population ecology

Population Ecology
Chapter 4
Population
• An interacting group of individuals of a
species that use common resources and
are regulated by the same natural
phenomena, such as temperature, water
and food supply, and predation
• Population density-the number of
individuals of a species per unit area or
volume
Key Concepts
 Factors affecting population size
 Species reproductive patterns
 Species survivorship patterns
 Conservation biology and human
impacts on ecosystems
Spatial Distribution
Dispersion – the pattern of spacing
of a population within an area
Population ranges- not all
species occupy all
habitats in the
biosphere: limited and
vast ranges
Dispersion Patterns
Uniform is even pattern of
Dispersion that results in
Interactions among
Individuals of a population
Creosote bush and black
Bears are examples
Clumped is when individuals
are aggregated into patches,
is the most common in nature.
Elephants and the American
Bison are clumped in groups or
herds.
Random occurs when
Individuals are spaced,
in a patternless, unpredictable way. Dandelions
And white-tailed deer
are examples.
Density Independent Factors Limit
Population Growth
• Density Independent – density of the
population doesn’t matter, the population will be
affected
• Natural disasters (climate, weather);
environmental factors (fire, floods, storms); and
habitat disruption by human activity
Density Dependent Factors Limit
Population Growth
•
Density Dependent – when population-limiting
factors depend on the density of the population
•
Competition for resources
•
Predation
•
Parasitism
•
Disease
What Limits a Population?
• Birth
• Death
• Immigration
• Emigration
 Population =
(Birth + Immigration) - (Deaths + Emigration)
Growth Models
• Exponential Growth Model -gives an idealized
picture of the unregulated growth of a population
• Equation is G= rN describes the J-shaped curve,
which is typical of exponential growth; G=growth,
r=intrinsic rate of increase, N=population size
• The bigger the value of N, the faster the population
increases
• The lower part of the J results from the relatively
slow growth when the population is small
• The steep, upper part of the J results from N being
large
Growth Models
• Logistic Growth Model-a description of idealized
population growth that is slowed by limiting factors;
results in a sigmoidal or “S” shaped curve
• Describes the effect of population-limiting factors as
well as population growth
• Equation is more complicated than exponential; (KN)/K; K is for “carrying capacity”
• Carrying Capacity is the number of individuals in a
population that the environment can maintain “carry”
without a net increase or decrease.
Population Growth Curves
Exponential - J
curve, starts
slow then fast
Logistic - s curve,
exponential growth,
environmental effects,
then leveling
Population size (N)
Population size (N)
K
Time (t)
Time (t)
Exponential Growth
Logistic Growth
What affects K? (Carrying
Capacity
• competition
• immigration & emigration
• natural & human
caused catastrophes
• seasonal fluctuations
affect food, water,
shelter
Reproductive Patterns
• Depends on several factors
• Species vary in the number of births per reproduction cycle, in
the age reproduction begins, and in the life span of the
organism
• R-strategy is an adaptation for living in an environment where
fluctuation of biotic and abiotic factors occur (availability of
food or changes in temperature)
• R-strategist is usually a small organism such as a fruit fly,
mouse or locust. Generally have short life spans and produce
many offspring.
– Expend little or no energy in raising their young to adulthood
– Controlled by density-independent factors
– Do not maintain a population near its carrying capacity
Reproductive Patterns
• K-strategy or carrying capacity is an
adaptation for living in predictable
environments
• K-strategist is generally a larger organism with
a long life span
– Produces few offspring whose population reaches
carrying capacity
– Have a better chance of survival because energy,
resources and time is invested in caring for the
young
– Controlled by density-dependent factors
Survivorship Curves
• Type 1 survivorship curve: ex. Whales,
elephants, humans
High survival rates until old age.
Example:
humans
% of
survivors
% of maximum life span
Survivorship Curves
• Type 2 survivorship curve: mortality
constant over the life span; ex. Hydras,
squirrels
Intermediate between the extremes.
Example:
% of
survivors
squirrel
% of maximum life span
Survivorship Curves
• Type 3 survivorship curve:
High mortality (death) rates as larvae/very
young but decreased mortality at later
ages.
Example:
% of
survivors
oysters
frogs
insects
% of maximum life span
Survivorship Curves
Percentage surviving (log scale)
100
10
1
0
Fig. 9.11, p. 206
Age
Trends in Human Population
Growth
Demographic transition is a change in a
population from high birth and death rates
to low birth and death rates
If (Birth + Immigration) = (Deaths +
Emigration)
then it’s called
ZERO POPULATION GROWTH
Age Structure Diagrams
• Gives the proportion of individuals in different
age groups
Demography
• The study of the human
population size, density,
distribution, movement and
birth, and death rates