Eco Chapter 9

What four processes determine the change in population size over time?

Birth, death, immigration, and emigration.

Which two processes add individuals to a population?

Birth and immigration.

Which two processes remove individuals from a population?

Death and emigration.

What is the definition of an open population?

A population that has immigration and emigration.

What is the definition of a closed population?

A population where immigration and emigration do not influence growth.

How do freshwater hydra primarily reproduce?

Asexually by budding.

In population notation, what does the symbol $N$ represent?

The number of individuals in the population.

What does $N(t)$ represent in population modeling?

The number of individuals at a specific time $t$.

How is the new population size $N(1)$ calculated for a closed population?

$N(0) + B - D = N(1)$.

The parameter b represents the _____ birthrate.

Per capita

What is the formula for the per capita birthrate b?

b = B / N(t)

What is the formula for the per capita death rate d?

d = D / N(t)

What does the equation N(t+1) = N(t) + bN(t) - dN(t) represent?

Geometric population growth.

The per capita growth rate of a population is defined by the variable _____.

$r$

What is the formula for the per capita growth rate r?

r = b - d

The equation $\Delta N / \Delta t = rN(t)$ defines the _____ of the line on a population size vs. time graph.

Slope

Under what condition is the geometric model of population growth used?

When birth and death are not continuous and occur in discrete time intervals.

Which population model is most appropriate for species with continuous births and deaths?

Exponential population growth model.

What is the differential equation for continuous exponential growth?

dN/dt = rN

In the equation N(t) = N(0)e^{rt}, what does the constant e represent?

The base of the natural logarithm, approximately 2.72.

If $r = 0$, what happens to the population size over time?

The population size remains constant.

What happens to a population when $r > 0$?

The population size increases exponentially.

What happens to a population when r < 0?

The population size decreases exponentially.

What two environmental conditions generally allow for exponential growth?

Favorable environments and low population densities.

How many reindeer were initially introduced to St. Paul Island in 1911?

25 (4 males and 21 females).

Which endangered bird species recovered from only 15 individuals in 1938 to over 300 in 2000?

The whooping crane.

What is a life table?

An age-specific account of mortality and survivorship within a population.

What is a cohort?

A group of individuals in a population born in the same period of time.

In a life table, the column $n_x$ represents the number of individuals _____.

Alive at age $x$.

What is the formula for survivorship l_x?

l_x = n_x / n_0

What does $d_x$ represent in a life table?

Age-specific mortality, or the number of individuals dying during an age interval.

What is the formula for the age-specific mortality rate $q_x$?

$q_x = d_x / n_x$.

A dynamic life table is also known as a _____ life table.

Cohort

How is a time-specific (static) life table constructed?

By sampling a population to obtain the distribution of age classes during a single period.

What assumption is made when constructing a time-specific life table?

Each age class is sampled in proportion to its numbers in the population.

How are life stages used in insect life tables (like the gypsy moth)?

They replace age classes as the x interval (e.g., eggs, instars, pupae).

In plant demography, for what purpose are life tables most useful?

Studying seedling mortality, perennial population dynamics, or annual life cycles.

A mortality curve plots mortality rates ($q_x$) against _____.

Age

A survivorship curve plots $l_x$ against age, typically using a _____ scale.

Log10

What does a Type I survivorship curve indicate?

High survival throughout the life span with most mortality at the end.

Which survivorship curve type indicates that survival rates do not vary much with age?

Type II (straight line).

What is the primary characteristic of a Type III survivorship curve?

Very high mortality early in life.

What kind of organisms typically exhibit Type III survivorship curves?

Oysters, fish, many invertebrates, and many plants.

Concept: Crude birthrate

Definition: Number of births during a period divided by the initial population size, multiplied by 1000.

The mean number of females born to each female in a specific age group is denoted as _____.

$b_x$

What is the gross reproductive rate?

The sum of age-specific birthrates ($b_x$) across all age classes.

A fecundity table combines $b_x$ with which other life table column?

The survivorship column ($l_x$).

What does the net reproductive rate $R_0$ represent?

The average number of females produced by a newborn female during her lifetime.

What is the mathematical formula for $R_0$?

$R_0 = \sum l_x b_x$.

If R_0 > 1.0, the population is _____.

Growing

If R_0 < 1.0, the population is _____.

Declining

How is the age-specific survival s_x calculated from mortality information?

s_x = 1 - q_x

What is the purpose of a population projection table?

To project future changes in population size using age-specific survival and birthrates.

What is a stable age distribution?

A state where the proportion of individuals in each age class remains constant over time.

The finite multiplication rate is represented by the Greek letter _____.

\lambda (Lambda)

What is the formula for the finite multiplication rate $\lambda$?

$\lambda = N(t + 1) / N(t)$.

What is the general equation to predict population size in a geometric growth pattern using $\lambda$?

$N(t) = N(0) \lambda^t$.

What is the mathematical relationship between \lambda and the instantaneous rate of growth r?

\lambda = e^r or r = \ln \lambda

What is the difference between deterministic and stochastic population models?

Deterministic models predict one exact outcome, while stochastic models incorporate random variation.

Concept: Demographic stochasticity

Definition: Variation in birth and death rates occurring in populations from year to year.

Concept: Environmental stochasticity

Definition: Random variation in the environment (e.g., climate, disasters) that influences birth and death rates.

Why are small populations more vulnerable to extinction?

Loss of genetic variability and increased vulnerability to stochasticity.

What caused the sharp decline of reindeer on St. Paul Island after 1938?

Overexploitation of resources and habitat degradation (overgrazing).

What is the leading cause of current global population declines and extinctions?

Habitat loss.

How do dams negatively affect freshwater fish migration?

They remove turbulent water sections and act as physical barriers to upstream movement.

What percentage of North American grasslands has been converted to other land uses since the mid-1800s?

More than 80 percent.

Why are migratory bird species particularly vulnerable to habitat decline?

They rely on multiple habitats (breeding, wintering, and stopover sites).

The decline of the cerulean warbler is primarily associated with the loss of _____ in South America.

Rainforest habitat

What is an endemic species?

A species found only in one specific geographic location.

Why does Madagascar have a high percentage of threatened animal species?

It has many endemic species and has lost over 90% of its original rainforest.

What specific ecosystem does the red-cockaded woodpecker depend on?

Mature longleaf pine savannas.

What social breeding system is used by red-cockaded woodpeckers?

Cooperative breeding (breeding pair plus nonbreeding helpers).

Why do red-cockaded woodpeckers abandon nest cavities if the understory grows too high?

Due to a decrease in food resources as hardwoods (like oaks) succeed.

What management tool is used to prevent hardwood succession in pine savannas?

Prescribed burning.

What was the purpose of building artificial nest cavities at Fort Bragg?

To test if a lack of suitable nesting habitat was limiting woodpecker populations.

What is an unintended negative consequence of prescribed burning in Florida pine savannas?

It can allow invasive cogongrass to establish, leading to excessively hot fires.

Why is cogongrass dangerous to native longleaf pine seedlings?

It causes fires to burn hotter and higher, increasing seedling mortality.

How did Hurricane Hugo impact red-cockaded woodpeckers in 1989?

It killed 70% of the birds in one population and destroyed many nest cavities.

What is the relationship between $\lambda$ and population stability?

If $\lambda = 1.0$, the population size is constant.

A population is declining if $r$ is _____.

Less than zero ($r < 0$)