GENERAL BIOLOGY - POPULATION ECOLOGY
A SHORT TRIP
FROM 500,000 TO 7.4 BILLION
PEOPLE ON EARTH
FROM 500,000 TO 7.4 BILLION
PEOPLE ON EARTH
POPULATION ECOLOGY
OFFLINE STUDY GUIDES
POPULATION ECOLOGY - Study Guide
Population Ecology
Population ecology (or autecology) is a sub-field of ecology that deals with
1) the dynamics of species populations
2) how these populations interact with the environment
3) how the population sizes of species change over time and geographic location
Population Ecology Facts You Should Know:
1. The term population ecology is often used interchangeably with population biology or population dynamics.
2. The development of population ecology owes much to demography and actuarial life tables.
The human population is growing at an exponential rate and is affecting the populations of other species in return.
1. Examples
This principle in population ecology provides the basis for formulating predictive theories
Population density
Dispersion pattern - The way individuals are spaced within an area
Dispersion pattern details
1. Clumped dispersion pattern
Life Tables and Survivorship Curves
Life tables
Survivorship curves
How do we make a survivorship curve? Plot the log of the percentage of survivors by the percent maximum lifespan to get the “survivorship curves”.
There are 3 types of survivorship curves
1. Type I survivorship curve
2. Type II survivorship curve
3. Type III survivorship curve
Idealized models
Idealized models give Predictions of population growth
In biology, population growth is the increase in the number of individuals in a population.
Two idealized patterns of population growth:
Population growth models
Exponential Growth Model
•When a population is introduced to a new environment, it will often display Exponential Growth.
•After some time, this will change to a logistic growth model.
Logistic Growth Model
•Carrying capacity (K) (the limitations of that environment)
Limiting factors that contribute to the logistical growth model are …
“Boom-and-bust” population cycles
- These are dramatic fluxuations in population
Boom-and-Bust cycles occur when the population growth of one species is closely tied to a limiting factor that may be expended.
The Boom-and-Bust cycle has two-phases:
Example of Boom-and-Bust cycle - Lynx and snowshoe hare population cycles
Evolution shapes life histories
There are different kinds of evolutionary selectivity
1. r-selection
2. K-selection
A. r-selection is…
B. K-selection is
The two evolutionary "strategies" are termed r-selection, for those species that produce many "cheap" offspring and live in unstable environments and K-selection for those species that produce few "expensive" offspring and live in stable environments.Of course, the animal or plant is not thinking: "How do I change my characteristics?" Natural selection is the force for change, not the individual's conscious decision. But, natural selection has produced a gradation of strategies, with extreme r-selection at one end of the spectrum and extreme K-selection at the other end.
The following table compares some characteristics of organisms which are extreme r or K strategists:
r
Unstable environment, density independent
K
Stable environment, density dependent interactions
small size of organism
large size of organism
energy used to make each individual is low
energy used to make each individual is high
many offspring are produced
few offspring are produced
early maturity
late maturity, often after a prolonged period of parental care
short life expectancy
long life expectancy
each individual reproduces only once
individuals can reproduce more than once in their lifetime
type III survivorship pattern
in which most of the individuals die within a short time
but a few live much longer
type I or II survivorship pattern
in which most individuals live to near the maximum life span
The terms "r-selected" and "K-selected" come from a description of the population growth regimes of the two types of organisms.If you are in an unstable environment, you are unlikely to ever have population growth to the point where density dependent factors come into play. The population is still at low values relative to the carrying capacity of the environment and thus is growing exponentially with intrinsic reproductive rate r (when it is not subject to environmental perturbations.), hence the name r-strategist.
An extreme K-strategist lives in a stable environment which is not seriously affected by sudden, unpredictable effects. Thus the population of a K-strategist is near the carrying capacity K.
Surviorship curves give us additional insight into r and K-selected strategies. Notice that the vertical axis of the survivorship plots is on a log scale and that horizontal axis is scaled to the maximum lifetime for each species.
One of the interesting differences between r and K strategists is in the shape of the survivorship curve. We can generate a survivorship curve by ploting the log of the fraction of organisms surviving vs. the age of the organism. To compare different species, we normalize the age axis by stretching or shrinking the curve in the horizontal direction so that all curves end at the same point, the maximum life span for individuals of that species. Notice that the vertical axis is on a log scale, dropping from 1.0 (100%) to 0.1 (10%) to 0.01 (1%) to 0.001 (0.1%) in equally spaced intervals.
Extreme r-strategists, such as the oyster, lose most of the individuals very quickly, relative to the maximum life span for the species. But, a very few individuals do survive much longer than the rest. But, for extreme K-strategists, such as man, most individuals live to old age (again relative to the maximum life span for the species).
These survivorship data are very valuable when studying the ecology of various organisms. Two components are involved in reproduction: 1) How many females survive to each age and 2) the average number of female offspring produced by females at each age. By using these data, we can compute the intrinsic rate of reproduction, r, a key parameter in models of population growth.
Population ecology (or autecology) is a sub-field of ecology that deals with
1) the dynamics of species populations
2) how these populations interact with the environment
3) how the population sizes of species change over time and geographic location
Population Ecology Facts You Should Know:
1. The term population ecology is often used interchangeably with population biology or population dynamics.
2. The development of population ecology owes much to demography and actuarial life tables.
- Population ecology is important in conservation biology, especially in the development of population viability analysis (PVA) which makes it possible to predict the long-term probability of a species persisting in a given habitat patch.
- Although population ecology is a subfield of biology, it provides interesting problems for mathematicians and statisticians who work in population dynamics.
The human population is growing at an exponential rate and is affecting the populations of other species in return.
1. Examples
- chemical pollution
- deforestation
- irrigation
- desertification
- waste
- resource depletion
This principle in population ecology provides the basis for formulating predictive theories
Population density
Dispersion pattern - The way individuals are spaced within an area
- Clumped dispersion – grouped in patches
- Uniform dispersion
- Random dispersion
Dispersion pattern details
1. Clumped dispersion pattern
- grouped in patches
- most common type of dispersion
- Is often the result of an unequal distribution of resources
- Examples:
- Humans
- Sea stars group where food is abundant
- Mushrooms grow where rich soil is
- Uniform dispersion pattern – evenly spread out over a given area
- Is often the result individual interactions of a population
- Examples:
- People in a lecture hall tend to spread out
- Some plants secrete chemicals and inhibit germination and growth of nearby plants that would be in competition for resources
- Territorial behavior
- Random dispersion pattern – spread out in an unpredictable way
- Is often due to…
- Social interactions
- Varying habitat conditions
- Examples:
- Dandelions
Life Tables and Survivorship Curves
Life tables
- Life tables track survivorship
- Survivorship is the probability (or chance) of an individual to survive (or live past) a certain age.
- Another way to look at it is that it is a table which shows, for each age, what the probability is that a person of that age will die before his or her next birthday ("probability of death"). In other words, it represents the survivorship of people from a certain population
Survivorship curves
How do we make a survivorship curve? Plot the log of the percentage of survivors by the percent maximum lifespan to get the “survivorship curves”.
There are 3 types of survivorship curves
- Type I
- Type II
- Type III
1. Type I survivorship curve
- For a Species that exhibits a type I survivorship curve – Most of the individuals of that species will survive until they reach “old age”
- Examples
- Humans
- Large mammals
2. Type II survivorship curve
- For a Species that exhibits a type Ii survivorship curve – the survivorship of that species remains relatively constant over the lifespan.
- Examples:
- Hydra
- Invertebrates
- Lizards
- Rodents
3. Type III survivorship curve
- For a Species that exhibits a type IIi survivorship curve – Most of the individuals of that species will die young, but the ones that live on to adulthood will live a relatively long time.
- Animals who have large numbers of offspring, but provide little care for them
- Examples:
- Fish
- Oysters
Idealized models
Idealized models give Predictions of population growth
In biology, population growth is the increase in the number of individuals in a population.
- Notes about the human population
- Global human population growth amounts to around 75 million annually, or 1.1% per year.
- The global population has grown from 1 billion in 1800 to 7 billion in 2012.
- The human population is expected to keep growing.
- estimates have put the total population at 8.4 billion by mid-2030
- estimates have put the total population at 9.6 billion by mid-2050.
- The nations with rapid population growth generally have low standards of living, whereas those nations with low rates of population growth have high standards of living.
Two idealized patterns of population growth:
- Exponential (or “geometric” for discrete version)
- Logistic (s-shaped)
Population growth models
Exponential Growth Model
- In the exponential model of population growth, you do not see the effect of limiting factors.
- Population undergo rapid and explosive growth of population.
- This equation expresses rate of change
- the intrinsic rate of increase “r” is assumed to be constant
•When a population is introduced to a new environment, it will often display Exponential Growth.
•After some time, this will change to a logistic growth model.
Logistic Growth Model
•Carrying capacity (K) (the limitations of that environment)
Limiting factors that contribute to the logistical growth model are …
- Predation
- Parasites
- Food sources
- Illness
- Change in environment
- Predation
- Territory
- Illness
- Change in environment
- Intraspecific competition – when members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals.
- Interspecific competition - when members of different species compete for a shared resource.
“Boom-and-bust” population cycles
- These are dramatic fluxuations in population
Boom-and-Bust cycles occur when the population growth of one species is closely tied to a limiting factor that may be expended.
- The predator populations increase and decrease as the prey numbers change.
- Predation may be an important cause of density-dependent mortality for some prey.
- Boom-and-bust cycles: Prey populations rapidly increase.
The Boom-and-Bust cycle has two-phases:
- Boom – rapid population increase is followed by a…
- BUST – population falls back to minimal levels
Example of Boom-and-Bust cycle - Lynx and snowshoe hare population cycles
- Lynx and snowshoe hare population cycles have a period of rapid population increase followed by a sudden precipitous decline in numbers.
- The increase is prey is then followed by an increase in the predator population.
- As predators eat the prey, the prey population goes down.
- As the predator’s food source becomes scarce, the predator population decreases.
- As the predator population decreases, The prey population can increase again
- —the cycle repeats; for example, the snowshoe hare and lynx have a 10-year cycle.
Evolution shapes life histories
There are different kinds of evolutionary selectivity
1. r-selection
2. K-selection
A. r-selection is…
- r-selection is a density-independent selection –
- This means the selection is due to density-independent factors that operate when an increase in population density lowers the survival odds for an individual, such as
- predation
- parasites
- disease
- competition for resources.
- This means the selection is due to density-independent factors that operate when an increase in population density lowers the survival odds for an individual, such as
- Rapid reproduction
- Takes advantage of new or open environments
- High biotic potential
B. K-selection is
- Density-dependent selection –
- This means the selection is due to density-dependent factors that exist regardless of the population density.
- These factors may cause more deaths or a lower birth rate or both.
- Example of density-independent factors include temperature, precipitation, and natural disturbances.
- Efficient use of limited resources
- Subject to competition
- lower rates of reproduction
- low biotic potential
- r-selection and K-selection
- Organisms are subject to each of these at varying degrees.
- We usually do not see a species which is solely R-Selection or solely K-selection.
- Life history traits
- Life history characteristics are traits that have been shaped through natural selection. Traits that are more desirable or advantageous, are more likely to persevere.
- life history traits include:
- Reproduction
- development
- Behavior
- life span
- Post-reproductive behavior
The two evolutionary "strategies" are termed r-selection, for those species that produce many "cheap" offspring and live in unstable environments and K-selection for those species that produce few "expensive" offspring and live in stable environments.Of course, the animal or plant is not thinking: "How do I change my characteristics?" Natural selection is the force for change, not the individual's conscious decision. But, natural selection has produced a gradation of strategies, with extreme r-selection at one end of the spectrum and extreme K-selection at the other end.
The following table compares some characteristics of organisms which are extreme r or K strategists:
r
Unstable environment, density independent
K
Stable environment, density dependent interactions
small size of organism
large size of organism
energy used to make each individual is low
energy used to make each individual is high
many offspring are produced
few offspring are produced
early maturity
late maturity, often after a prolonged period of parental care
short life expectancy
long life expectancy
each individual reproduces only once
individuals can reproduce more than once in their lifetime
type III survivorship pattern
in which most of the individuals die within a short time
but a few live much longer
type I or II survivorship pattern
in which most individuals live to near the maximum life span
The terms "r-selected" and "K-selected" come from a description of the population growth regimes of the two types of organisms.If you are in an unstable environment, you are unlikely to ever have population growth to the point where density dependent factors come into play. The population is still at low values relative to the carrying capacity of the environment and thus is growing exponentially with intrinsic reproductive rate r (when it is not subject to environmental perturbations.), hence the name r-strategist.
An extreme K-strategist lives in a stable environment which is not seriously affected by sudden, unpredictable effects. Thus the population of a K-strategist is near the carrying capacity K.
Surviorship curves give us additional insight into r and K-selected strategies. Notice that the vertical axis of the survivorship plots is on a log scale and that horizontal axis is scaled to the maximum lifetime for each species.
One of the interesting differences between r and K strategists is in the shape of the survivorship curve. We can generate a survivorship curve by ploting the log of the fraction of organisms surviving vs. the age of the organism. To compare different species, we normalize the age axis by stretching or shrinking the curve in the horizontal direction so that all curves end at the same point, the maximum life span for individuals of that species. Notice that the vertical axis is on a log scale, dropping from 1.0 (100%) to 0.1 (10%) to 0.01 (1%) to 0.001 (0.1%) in equally spaced intervals.
Extreme r-strategists, such as the oyster, lose most of the individuals very quickly, relative to the maximum life span for the species. But, a very few individuals do survive much longer than the rest. But, for extreme K-strategists, such as man, most individuals live to old age (again relative to the maximum life span for the species).
These survivorship data are very valuable when studying the ecology of various organisms. Two components are involved in reproduction: 1) How many females survive to each age and 2) the average number of female offspring produced by females at each age. By using these data, we can compute the intrinsic rate of reproduction, r, a key parameter in models of population growth.
