# Chapter 53 (Final Exam)

population ecology
explores how biotic and abiotic factors influence density, distribution, size, and age structure of populations

For example, the number of loggerhead turtle hatchlings that survive their first journey to the ocean is affected by both biotic and abiotic factors

Biological processes influence…
DDD

population density, dispersion, and demographics

population
a group of individuals of a single species living in the same general area
populations are described by…
their boundaries and size
density
the number of individuals per unit area or volume
dispersion
the pattern of spacing among individuals within the boundaries of the population
determining population size using the mark-recapture method
Scientists capture, tag, and release a random sample of individuals (s) in a population

Marked individuals are given time to mix back into the population

Scientists capture a second sample of individuals (n), and note how many of them are marked (x)

Population size (N) is estimated by… N = (M1 x C) / M2

environmental and social factors influence…
the spacing of individuals in a population
clumped dispersion
individuals aggregate in patches
uniform dispersion
one in which individuals are evenly distributed
territoriality
the defense of a bounded space against other individuals

influences dispersion

random dispersion
the position of each individual is independent of other individuals

occurs in the absence of strong attractions or repulsions

demography
the study of the vital statistics of a population and how they change over time
life table
an age-specific summary of the survival pattern of a population

best made by following the fate of a cohort

cohort
group of individuals of the same age
life table of Belding’s ground squirrels
it provides data on the proportions of males and females alive at each age

The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate

survivorship curve
a graphic way of representing the data in a life table
3 types of survivorship curves
type 1, 2, and 3

many species are intermediate to these curves

type I survivorship curve
Low death rates during early and middle life and an increase in death rates among older age groups
type II survivorship curve
A constant death rate over the organism’s life span
type III survivorship curve
High death rates for the young and a lower death rate for survivors
reproductive rates
For species with sexual reproduction, demographers often concentrate on females in a population

Ecologists use many approaches to estimate the number of breeding females

For example, DNA profiling was used to determine the number of female loggerhead turtles laying eggs in a season

reproductive table
or fertility schedule, is an age-specific summary of the reproductive rates in a population

describes the reproductive patterns of a population

The exponential model describes…
population growth in an idealized, unlimited environment
idealized populations
exponential model

It is useful to study population growth in an idealized situation

Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth

population growth rate
Births and deaths can be expressed as the average number of births and deaths per individual during the specified time interval

B= bN
D=mN
b is the annual per capita birth rate, m
(for mortality) is the per capita death rate, and N is population size

per capita rate of increase
If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate
zero population growth
occurs when the birth rate equals the death rate (r = 0)
Change in population size can now be written as _________
Instantaneous growth rate can be expressed as ________
where r_inst is the instantaneous per capita rate of increase
exponential population growth
population increase under idealized conditions

Under these conditions, the rate of increase is at its maximum, denoted as r_max

exponential population growth.
equation is ___________
exponential population growth results in
a J-shaped curve

The rate of increase is constant, but the population accumulates more new individuals per unit time when it is large than when it is small

The logistic model describes
how a population grows more slowly as it nears its carrying capacity

Exponential growth cannot be sustained for long in any population

a more realistic population model limits growth by incorporating carrying capacity

carrying capacity (K)
the maximum population size the environment can support

Carrying capacity varies with the abundance of limiting resources

logistic population growth model
the per capita rate of increase declines as carrying capacity is reached

The logistic model starts with the exponential model and adds an expression that reduces per capita rate of increase as N approaches K

The logistic model of population growth produces a sigmoid (S-shaped) curve

New individuals are added to the population most rapidly at intermediate population sizes

The population growth rate decreases as N approaches K

ΔNΔt=rMmaxN(K−N)K

Some populations overshoot…
K before settling down to a relatively stable density
Some populations fluctuate greatly and
make it difficult to define K
Allee effect
individuals have a more difficult time surviving or reproducing if the population size is too small
life history traits
products of natural selection

evolutionary outcomes reflected in the development, physiology, and behavior of an organism

life history of an organism
comprises the traits that affect its schedule of reproduction and survival
3 main variables of life history
1. The age at which reproduction begins
2. How often the organism reproduces
3. How many offspring are produced per reproductive episode
semelparity
or big-bang reproduction, species that reproduce once and die
iteroparity
or repeated reproduction, species that produce offspring repeatedly
Highly variable or unpredictable environments likely favor…
semelparity
dependable environments may favor
iteroparity
some plants produce a large number of small seeds, ensuring that…
at least some of them will grow and eventually reproduce
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
the concepts of K-selection and r-selection are
oversimplifications but have stimulated alternative hypotheses of life history evolution
Many factors that regulate population growth are…
density dependent
two general questions about regulation of population growth
What environmental factors stop a population from growing indefinitely?

Why do some populations show radical fluctuations in size over time, while others remain stable?

density-independent populations
birth rate and death rate do not change with population density
density-dependent populations
birth rates fall and death rates rise with population density
density-dependent birth and death rates are an example of…
negative feedback that regulates population growth
Density-dependent birth and death rates are affected by…
many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors
Figure 53.18
know this!
study of population dynamics
focuses on the complex interactions between biotic and abiotic factors that cause variation in population size
long-term population studies have…
challenged the hypothesis that populations of large mammals are relatively stable over time
Both weather and predator population can affect
population size over time

For example, the moose population on Isle Royale collapsed during a harsh winter, and when wolf numbers peaked

Some populations undergo…
regular boom-and-bust cycles
Figure 53.20
Lynx populations follow the 10-year boom-and-bust cycle of hare populations
Two main hypotheses have been proposed to explain the hare’s 10-year interval
Figure 53.20
Hypothesis: The hare’s population cycle follows a cycle of winter food supply
If this hypothesis is correct, then the cycles should stop if the food supply is increased
Additional food was provided experimentally to a hare population, and the whole population increased in size but continued to cycle
These data do not support the first hypothesis
Hypothesis: The hare’s population cycle is driven by pressure from other predators
In a study conducted by field ecologists, 90% of the hares were killed by predators, including lynx, coyotes, hawks, and owls
These data support the second hypothesis
The availability of prey is a major factor influencing predator population dynamics
When prey become scarce, predator species begin to prey on one another, accelerating the collapse of predator populations
To maintain population stability, a regional human population can exist in one of two configurations
Zero population growth = High birth rate – High death rate

Zero population growth = Low birth rate – Low death rate

demographic transition
the move from the first state to the second state of zero population growth

The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women

Most of the current global population growth is concentrated in developing countries

Age structure diagrams can predict a…
population’s growth trends

they can illuminate social conditions and help us plan for the future

infant mortality and life expectancy at birth
vary greatly among developed and developing countries but do not capture the wide range of the human condition
global carrying capacity
how many humans can the biosphere support?

the carrying capacity of Earth for humans is uncertain

population ecologists predict a global population of 8.1-10.6 billion people in 2050

ecological footprint
summarizes the aggregate land and water area needed to sustain the people of a nation

one measure of how close we are to the carrying capacity of Earth

Countries vary greatly in footprint size and available ecological capacity

Ecological footprints can also be calculated using energy use

Our carrying capacity could potentially be limited by
food, space, nonrenewable resources, or buildup of wastes
Unlike other organisms, we can regulate…
our population growth through social changes
Both weather and predator population can affect
population size over time
life history of an organism
comprises the traits that affect its schedule of reproduction and survival
3 main variables of life history
1. The age at which reproduction begins
2. How often the organism reproduces
3. How many offspring are produced per reproductive episode
semelparity
or big-bang reproduction, species that reproduce once and die
iteroparity
life history of an organism
comprises the traits that affect its schedule of reproduction and survival
3 main variables of life history
1. The age at which reproduction begins
2. How often the organism reproduces
3. How many offspring are produced per reproductive episode
life history of an organism
comprises the traits that affect its schedule of reproduction and survival
3 main variables of life history
life history of an organism
Ignoring migration, the age structure of a human population likely to increase in size will have what shape?
pyramid
Ignoring migration, the age structure of a human population likely to decrease in size will have what shape?
inverted pyramid
Ignoring migration, the age structure diagram of a human population likely to maintain a relatively stable size will have what shape?
a rectangle tapering toward the top
A newly mated queen ant founds a nest in an unoccupied patch of suitable habitat. Assuming that no disasters strike the nest, which of the following types of equations is likely to best describe the population growth of the new colony?
Logistic
A population that grows rapidly at first and then levels off at carrying capacity can be modeled __________.
by a logistic equation
A graph that plots the numbers of individuals who are alive at particular ages is called _________.
survivorship curve
density dependent factor
affected percentage increases as the population density increases
density independent factor
affected percentage remains the same, regardless of increase/decrease in population density
Fluctuations in the numbers of individuals in a population from year to year are called _________.
population dynamics
territorial behavior leads to what kind of dispersion?
uniform
The concept that summarizes the aggregate land and water area required by each person to produce all resources he or she needs and absorb all waste he or she produces is called the _________
ecological footprint
Life history traits that are favored in uncrowded environments are known as _________.
r-selection
density independent
distribution of a resource results in what kind of distribution?
clumped
immigration
influx of new individuals (NOT POPULATIONS) from other areas
emmigration
the movement of individuals (NOT POPULATIONS) out of an area
Although there are organisms whose life histories fall somewhere between iteroparity and semelparity, life history always represents a trade-off. Why is this?
The energy cost of reproduction is high, so there are not enough resources to reproduce often, produce many offspring, and take care of them.
Mechanisms of density-dependent selection doesn’t include…
the size of a brood
Mechanisms of density-dependent selection includes
competition for resources
disease
predation
territoriality
Chimpanzees have a relatively low birth rate. They care for their young, and most chimps live a long life. The chimp survivorship curve would look like ___________.
a relatively flat line that drops steeply at the end
A population that is growing logistically __________.
grows fastest at an intermediate population density
The selective pressures of having a large brood of offspring to care for, as in the kestrel experiment, _________.
lower the survival rates of the parents
The difference between density and dispersion is that __________.
density is the number of individuals of a population in a unit area whereas dispersion is the pattern of spacing of individuals of the population
Life history traits that are favored at high population densities are known as _________
K-selection
When the per capita birth rate equals the per capita death rate, __________.
a population remains constant
A population will always grow exponentially under what circumstances?
if there are no limiting factors
If you wanted to determine what percentage of the population of Thailand is less than 10 years old, you could look at __________.
the population’s age structure
An ecologist would suspect a population to be growing rapidly if it __________.
contains many more prereproductive than reproductive individuals
To calculate the __________ of a nation, researchers summarize arable land, pasture, fossil energy land, and several other factors appropriated by each nation to produce all of the resources it consumes and to absorb all the waste it generates.
ecological footprint