Population Dynamics, Carrying
Capacity, and Conservation Biology
G. Tyler Miller’s
Living in the Environment
13th Edition
Chapter 9
Dr. Richard Clements
Chattanooga State Technical Community College
Key Concepts
Factors affecting population size
Species reproductive patterns
Species survivorship patterns
Conservation biology and
human impacts on ecosystems
Population Dynamics and Carrying
Capacity
 Population dynamics: changes in a population
due to environmental stress and changes in
environmental conditions
Change in
Size: numbers of organisms in population
Density: organism per area
Dispersion: spatial patterns
Age distribution: proportion of individuals of
age in a population
Population Dynamics and Carrying
Capacity
 Variables for changes in population size:
1. Birth
3. Death
2. Immigration
4. Emigration
Relationship:
(birth + immigration) – (death + emigration) =
population change
Zero Population Growth: increases in
population cancel out decreases
Population Dynamics and Carrying
Capacity
 Biotic potential (intrinsic rate of increase
[r]): capacity for growth; [r] is the rate at which
population would grow with no limit in resources
 Environmental resistance: factors that limit
population growth
 Carrying capacity (k): determined by biotic
potential and environmental resistance
 Minimum viable population (MVP):
minimum population to maintain the intrinsic rate of
increase. If not maintained population loses genetic
diversity due to lack of mates and interbreeding
Population Dispersion
Clumped is the most common due to resources being
found in patches
Fig. 9-2 p. 191
Factors Affecting Population Size
biotic factors
increase population
growth and
environmental
factors decrease
population growth.
Balance of the two
determines the
population size.
Fig. 9-3 p. 192
Exponential and Logistic Growth
• Exponential growth: few if any resource
limitations on growth
– Starts out slow and then increases exponentially
as the population grows
– Yields a J-shaped exponential growth curve
•Logistic growth: growth that has resource
limitations
•Starts out slow and then progresses to a period of
exponential growth until environmental resistance is
encountered and the population levels off at the
carrying capacity.
•Yields an S-Shaped logistic growth curve
Exponential and Logistic Growth
Fig. 9-4 p. 192
Fig. 9-5 p. 193
Fig. 9-6 p. 193
Exponential and Logistic Growth
Populations do not stay constant in size over
time many shifts in resources will effect how a
populations growth continues.
Fig. 9-5 p. 193
Fig. 9-6 p. 193
Population Density Effects
Density-independent controls:
Affects population size equally regardless of
their density. natural disasters.
Density-dependent controls: density of
the population determines the overall affect.
Competitions for resources, predation,
parasitism, and disease
Natural Population Curves
Stable: fluctuates above and below carrying capacity
Irruptive: population erupts to a high peak and then crashes
Irregular: populations change irregularly for unknown
reasons
Cyclic: sharp increases in population followed by crashes
over fairly regular intervals.
Fig. 9-7 p. 194
The Role of Predation in Controlling
Population Size
 Top-down control: predator controls the cyclic
fluctuations of the prey
 Bottom-up control: herbivore-plant interaction
influences the cyclic fluctuations of the predator
Fig. 9-8 p. 195
Reproductive Patterns and Survival
 Asexual reproduction: produces exact genetic
copies (clones) of a single parent.
 Sexual reproduction: produces offspring by
combining gametes (sex cells; egg or sperm) from
both parents. Combinations of traits (from the
parents) seen in the offspring
Reproductive Patterns and Survival
 Sexual reproduction: disadvantages
Females have to produce twice as many
offspring to maintain the same number of young
in the next generation as an asexually
reproducing organism because males do not give
birth.
Increase in genetic errors
Mating costs: time for courtship and mating,
disease transmission, and injury inflicted by
males during mating
Reproductive Patterns and Survival
 Sexual reproduction: Advantages
Why do 97% of organisms sexually
reproduce???
It provides a greater genetic diversity
in the offspring
Males provide for females and
offspring in many species.
Reproductive Patterns and Survival
r-Selected species: high intrinsic
rate of increase ( r ). Opportunistic
species.
K-Selected species: competitor species
due to their populations surviving in highly
competitive conditions when their population
size is near the carrying capacity (k). Much
more stable species.
Reproductive Patterns and Survival
Fig. 9-10
p. 196
Survivorship Curves
• Way of representing the age structure of a
population is a survivorship curve.
• Survivorship curves show the number of
survivors of each age group for a particular
species. (rate of mortality)
• Types:
– Early loss: r-selected species
– Late loss: K-selected species
– Constant loss curve: organisms with
intermediate reproductive patterns and constant
rate of mortality in all age classes.
Life Tables
• Shows the number of individuals at each
age from a survivorship curve.
• It illustrates the projected life expectancy
and probability of death for individuals at
each age.
• Used by life insurance companies to
determine policy costs.
Survivorship Curves
Fig. 9-11 p. 198
Conservation Biology: Sustaining
Wildlife Populations
 Conservation biology: a multidisciplinary
science, originated in the 1970’s that uses the best
available science to take action to preserve species
and ecosystems.
 Ideas for maintaining biodiversity
 Endangered species management
 Bioinformatics: a new discipline that provides
tools for storage and access to key biological
information and builds data bases that contain the
needed biological information
Human Impacts on Ecosystems
 Habitat degradation and fragmentation
 Ecosystem simplification: monoculture
 Genetic resistance: overuse of pesticides and
antibiotics
 Predator elimination
 Introduction of non-native species
 Overharvesting renewable resources:
overgrazing
 Interference with ecological systems:
chemical cycling and energy flow
Learning from Nature
 Interdependence: everything is connected to
everything else
 Diversity:helps maintain the sustainability and
ecological functioning of ecosystems
 Resilience: most populations are naturally
resilient however we need to allow them to
rebound
 Adaptability: driven by biodiversity and aids
in the sustainability when environments change
 Unpredictability: human interference often
has unpredictable side effects
 Limits: all populations have limits to growth
and resource consumption