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population ecology

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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

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Biological processes influence...

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DDD population density, dispersion, and demographics

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population

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a group of individuals of a single species living in the same general area

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populations are described by...

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their boundaries and size

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density

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the number of individuals per unit area or volume

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dispersion

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the pattern of spacing among individuals within the boundaries of the population

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determining population size using the mark-recapture method

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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

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environmental and social factors influence...

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the spacing of individuals in a population

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clumped dispersion

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individuals aggregate in patches

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uniform dispersion

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one in which individuals are evenly distributed

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territoriality

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the defense of a bounded space against other individuals influences dispersion

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random dispersion

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the position of each individual is independent of other individuals occurs in the absence of strong attractions or repulsions

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demography

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the study of the vital statistics of a population and how they change over time

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life table

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an age-specific summary of the survival pattern of a population best made by following the fate of a cohort

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cohort

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group of individuals of the same age

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life table of Belding's ground squirrels

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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

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survivorship curve

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a graphic way of representing the data in a life table

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3 types of survivorship curves

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type 1, 2, and 3 many species are intermediate to these curves

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type I survivorship curve

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Low death rates during early and middle life and an increase in death rates among older age groups

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type II survivorship curve

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A constant death rate over the organism's life span

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type III survivorship curve

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High death rates for the young and a lower death rate for survivors

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reproductive rates

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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

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reproductive table

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

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The exponential model describes...

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population growth in an idealized, unlimited environment

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idealized populations

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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

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population growth rate

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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

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per capita rate of increase

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If immigration and emigration are ignored, a population's growth rate (per capita increase) equals birth rate minus death rate

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zero population growth

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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

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exponential population growth

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

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exponential population growth.

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equation is ___________

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exponential population growth results in

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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

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The logistic model describes

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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

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carrying capacity (K)

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the maximum population size the environment can support Carrying capacity varies with the abundance of limiting resources

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logistic population growth model

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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 ?N?t=rMmaxN(K?N)K

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Some populations overshoot...

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K before settling down to a relatively stable density

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Some populations fluctuate greatly and

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make it difficult to define K

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Allee effect

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individuals have a more difficult time surviving or reproducing if the population size is too small

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life history traits

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

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life history of an organism

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comprises the traits that affect its schedule of reproduction and survival

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3 main variables of life history

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1. The age at which reproduction begins 2. How often the organism reproduces 3. How many offspring are produced per reproductive episode

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semelparity

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or big-bang reproduction, species that reproduce once and die

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iteroparity

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or repeated reproduction, species that produce offspring repeatedly

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Highly variable or unpredictable environments likely favor...

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semelparity

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dependable environments may favor

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iteroparity

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some plants produce a large number of small seeds, ensuring that...

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at least some of them will grow and eventually reproduce

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K-selection

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or density-dependent selection, selects for life history traits that are sensitive to population density

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r-selection

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or density-independent selection, selects for life history traits that maximize reproduction

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the concepts of K-selection and r-selection are

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oversimplifications but have stimulated alternative hypotheses of life history evolution

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Many factors that regulate population growth are...

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density dependent

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two general questions about regulation of population growth

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What environmental factors stop a population from growing indefinitely? Why do some populations show radical fluctuations in size over time, while others remain stable?

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density-independent populations

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birth rate and death rate do not change with population density

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density-dependent populations

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birth rates fall and death rates rise with population density

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density-dependent birth and death rates are an example of...

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negative feedback that regulates population growth

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Density-dependent birth and death rates are affected by...

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many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors

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Figure 53.18

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know this!

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study of population dynamics

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focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

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long-term population studies have...

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challenged the hypothesis that populations of large mammals are relatively stable over time

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Both weather and predator population can affect

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

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Some populations undergo...

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regular boom-and-bust cycles

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Figure 53.20

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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

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To maintain population stability, a regional human population can exist in one of two configurations

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Zero population growth = High birth rate - High death rate Zero population growth = Low birth rate - Low death rate

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demographic transition

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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

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Age structure diagrams can predict a...

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population's growth trends they can illuminate social conditions and help us plan for the future

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infant mortality and life expectancy at birth

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vary greatly among developed and developing countries but do not capture the wide range of the human condition

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global carrying capacity

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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

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ecological footprint

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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

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Our carrying capacity could potentially be limited by

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food, space, nonrenewable resources, or buildup of wastes

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Unlike other organisms, we can regulate...

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our population growth through social changes

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Both weather and predator population can affect

answer

population size over time

question

life history of an organism

answer

comprises the traits that affect its schedule of reproduction and survival

question

3 main variables of life history

answer

1. The age at which reproduction begins 2. How often the organism reproduces 3. How many offspring are produced per reproductive episode

question

semelparity

answer

or big-bang reproduction, species that reproduce once and die

question

life history of an organism

answer

comprises the traits that affect its schedule of reproduction and survival

question

3 main variables of life history

answer

1. The age at which reproduction begins 2. How often the organism reproduces 3. How many offspring are produced per reproductive episode

question

life history of an organism

answer

comprises the traits that affect its schedule of reproduction and survival

question

Ignoring migration, the age structure of a human population likely to increase in size will have what shape?

answer

pyramid

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Ignoring migration, the age structure of a human population likely to decrease in size will have what shape?

answer

inverted pyramid

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Ignoring migration, the age structure diagram of a human population likely to maintain a relatively stable size will have what shape?

answer

a rectangle tapering toward the top

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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?

answer

Logistic

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A population that grows rapidly at first and then levels off at carrying capacity can be modeled __________.

answer

by a logistic equation

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A graph that plots the numbers of individuals who are alive at particular ages is called _________.

answer

survivorship curve

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density dependent factor

answer

affected percentage increases as the population density increases

question

density independent factor

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affected percentage remains the same, regardless of increase/decrease in population density

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Fluctuations in the numbers of individuals in a population from year to year are called _________.

answer

population dynamics

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territorial behavior leads to what kind of dispersion?

answer

uniform

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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 _________

answer

ecological footprint

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Life history traits that are favored in uncrowded environments are known as _________.

answer

r-selection density independent

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distribution of a resource results in what kind of distribution?

answer

clumped

question

immigration

answer

influx of new individuals (NOT POPULATIONS) from other areas

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emmigration

answer

the movement of individuals (NOT POPULATIONS) out of an area

question

Although there are organisms whose life histories fall somewhere between iteroparity and semelparity, life history always represents a trade-off. Why is this?

answer

The energy cost of reproduction is high, so there are not enough resources to reproduce often, produce many offspring, and take care of them.

question

Mechanisms of density-dependent selection doesn't include...

answer

the size of a brood

question

Mechanisms of density-dependent selection includes

answer

competition for resources disease predation territoriality

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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 ___________.

answer

a relatively flat line that drops steeply at the end

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A population that is growing logistically __________.

answer

grows fastest at an intermediate population density

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The selective pressures of having a large brood of offspring to care for, as in the kestrel experiment, _________.

answer

lower the survival rates of the parents

question

The difference between density and dispersion is that __________.

answer

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

question

Life history traits that are favored at high population densities are known as _________

answer

K-selection

question

When the per capita birth rate equals the per capita death rate, __________.

answer

a population remains constant

question

A population will always grow exponentially under what circumstances?

answer

if there are no limiting factors

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If you wanted to determine what percentage of the population of Thailand is less than 10 years old, you could look at __________.

answer

the population's age structure

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An ecologist would suspect a population to be growing rapidly if it __________.

answer

contains many more prereproductive than reproductive individuals

question

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.

answer

ecological footprint

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