Biology Final

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A human eats a deer. Which of these terms applies to the relationship between the human and the deer?


Humans and sharks both eat fish. Which of these terms applies to the relationship between the human and the shark?


Humans who have pets tend to be healthier than humans who do not have pets. Which of these terms applies to the relationship between a human and a pet?


Which of these terms applies to the relationship between a dog and a blood-sucking tick?


An egret eats insects stirred up by grazing animals. Which of these terms applies to the relationship between the egret and the grazing animal?


In an ecosystem, phytoplankton are _____.


An earthworm that feeds on the remains of plants and animals is acting as a _____.


secondary consumer

When a human eats a steak, the human is acting as a _____.

A cow eating grass is an example of a _____.

primary consumer

A human who just ate a hamburger is eaten by a shark while swimming. The shark is acting as a _____.

tertiary consumer

Which of these is a starting point for primary succession?

surface exposed by retreating glacier

Plants use _____ as a source of energy.


What element is found in all organic compounds?


What name is given to organisms that convert the carbon in organic compounds into carbon in carbon dioxide?


What name is given to the process by which detritivores return carbon to the atmosphere?


removes carbon from the atmosphere?


Detritus is composed of _____.

dead organic matter and excretory wastes

Nitrifying bacteria convert _____ to _____.

ammoinium __ nitrates

_____ removes nitrogen from the atmosphere.

Nitrogen fixation

Denitrifying bacteria convert _____ to _____.

nitrates __ nitrogen gas

The study of the interaction of organisms with each other and their environment involves non-living factors, also called _________________, and living factors, which are referred to as __________________.

abiotic components; biotic components

Which of the following options lists the ecological hierarchy in the correct order, from largest to smallest?

biosphere; ecosystem; community; population; organism

A scientist is studying how sea slugs respond to predators. Which hierarchical level of ecology does this represent?


Desert owls are inactive during the day and active at night. They also have small bodies. This describes _____ adaptation to the hot and dry desert.

anatomical and behaviora

Horned lizards are desert animals that are active during the day. Their skin and kidneys are efficient at conserving water; when they get hot, they move to the shade so they can cool off. This describes _____ adaptation to the hot and dry desert.

anatomical, behavioral, and physiological

The benthic zone of aquatic environments is defined as the _____.

substrate at the bottom of the body of water


The _____ biome is the largest of Earth’s biomes.

A(n) _____ is a region where fresh water and salt water mix.


What are the two major factors determining the distribution of terrestrial biomes?

temperature and light

Which of these biomes is characterized by little rainfall?


Which of these is the largest terrestrial biome on Earth?

confierous forest

Which biome is characterized by an extensive canopy that allows little light to penetrate to the ground and by the presence of epiphytes?

tropical rain forest

Which biome is characterized by the presence of permafrost?


Which location on Earth receives the most solar radiation per unit area?


what is a biodiversity hotspot?

number of endemic species, number of species, degree to which the species are threatened to extiction

A sink habitat is where a subpopulation’s death rate is _____.

greater than its reproductive rate

Fertilizer runoff can result in _____ a lake.

the eutrophication of

Most biodiversity hot spots are in the _____.


A group of individuals of a single species that occupy the same general area defines a


Which of the following is an example of a population?

all students in classroom

The pattern of distribution for a certain species of kelp is clumped. We would expect that the pattern of distribution for a population of snails that live on the kelp would be


Assume that there are five alligators per acre in a swamp in northern Florida. This is a measure of the alligator population’s


You drive through Iowa in the spring and notice that along a stretch of several kilometers, every third fence post has a male redwing blackbird perched on it defending its nesting territory. This is an example of

uniform disperstion

A Type I survivorship curve is the result of which of the following life history traits?

parents providing extended care for their young

A survivorship curve

is a graph that plots an individual’s likelihood of being alive as a function of age.

The maximum number of individuals a habitat can support is called its

carrying capacity

In the logistic growth model, as population size increases, birth rates

rates decline and/or death rates increase.

An ecological footprint

is a means of understanding resource availability and usage.

The human population on Earth is expected to reach 9.5 billion people by


A community is composed of

potentially interacting populations of different kinds of organisms.

An owl and a hawk both eat mice. Which of these terms describes the relationship between a hawk and an owl?


When two different populations in a community benefit from their relationship with each other, the result is called


The sum total of a population’s use of the biotic and abiotic resources of its habitat constitutes its


In an ecosystem, you would expect to find interspecific competition between

populations of two species that occupy the same niche.

Dinoflagellates are important to coral and coral-dwelling animals because they

produce energy that is used by coral animals through photosynthesis.

One mechanism that prey populations evolve to avoid predation is


Some herbivore-plant interactions evolved through a series of reciprocal evolutionary adaptations in both species. The process is called


Most plants have a variety of chemicals, spines, and thorns because the plants

cannot run away from herbivores.

In addition to environmental factors, community composition of plants can be severely compromised by

parasites and pathogens

The primary decomposers of a community are called


In a hypothetical food chain consisting of grass, grasshoppers, sparrows, and hawks, the grasshoppers are

primary consumers

On Earth, most organic molecules are produced by


Within an ecosystem, a tree is a


reduction in the number of mice

In a certain ecosystem, field mice are preyed on by snakes and hawks. The entry of wild dogs into the system adds another predator of the mice. Of the following, the most likely short-term result of this addition is

The number of species in a community is called the

species richness

Which of the following statements regarding food webs is true?

Several species of primary consumers may feed on the same species of producer.

During ecological succession, the species composition of a plant community generally

changes gradually because each species responds differently to the changing environment.

Biological control is defined as

the intentional release of a natural enemy of a pest population.

Non-native species that are introduced in new environments, spread far beyond the original point of introduction, and cause damage are called

invasive species.

The flow of ________ into ecosystems occurs in one direction only, while ________ are recycled within the ecosystem itself.

energy ___ chemicals

Which of the following processes does not occur in ecosystems?

The energy source that powers the system is used by consumers to make organic compounds.

For a given area and time period, the amount of solar energy converted to chemical energy is called

primary production.

Carbon mainly cycles between the biotic and abiotic worlds through the processes of

respiration and photosynthesis.

The primary goal of conservation biology is to

counter the loss of biodiversity.

The three greatest current threats to biodiversity, in order starting with the greatest, are

habitat destruction, the introduction of invasive species, and overexploitation.

CO2 flooding into the atmosphere is absorbed by ________ and converted into biomass.

photosynthetic organisms

An important change in populations and species in response to climate change is


An organism’s responses to climate change that result in phenotypic variation is called

phenotypic plasticity.

The study of the interaction of organisms with each other and their environment involves non-living factors, also called _________________, and living factors, which are referred to as __________________.

abiotic components; biotic components

Which of the following options lists the ecological hierarchy in the correct order, from largest to smallest?

biosphere; ecosystem; community; population; organism

A scientist is studying how sea slugs respond to predators. Which hierarchical level of ecology does this represent?


Which hierarchical level is represented by a survey of students and their habits?


What is the largest hierarchical level that global warming affects?


Population Ecology

the study of factors that affect population density and growth


a group of individuals of a single species that occupy the same general area

population density

the numer of individuals of a species per unit area of volume of habitat

age structures

the distribution of individuals in different age-groups

Life Tables

track survivalship, and mortality the chance of an individual in a given population surviving to various ages

Survivorship curve

a plot of the number of individuals still alive at each age in the maximum life span -use percentages

Type I

produce few offspring, but give them good care, increasing the likelihood hat they will survive to maturity

Type III

low survivorship for the very young, followed by a period when survivorship is high for those few individuals who live to a certain age

Type II

intermediate, there are no more vulnerable at one stage of the life cycle than another

Life history

the set of traits that affect an organism’s schedule of reproduction and survival

opportunistic life history

Type III, one that enables the plant or animal to take immediate advantage of favorable conditions

Equilibrial life history

pattern of developing and reaching sexual maturity slowly and producing few, well-cared-for offspring

exponential population growth

describes the expansion of a population in an ideal, unlimited environment, -J shaped curve

limiting factors

environmental factors that hold population growth in check

carrying capacity

the maximum population size that a particular environment can sustain

logistic population growth

the growth rate decreases as the population size approaches carrying capacity, -s shaped

intraspecific competition

competition between individuals of the same species for the same limited resources

density-dependent factor

a population-limiting factor whose effects intensify as the population increases in density

density-independent factor

a population limiting factor whose intensity is unrelated to population density

threatened species

species that are likely to become endangered in the foreseeable future

invasive species

non-native species that has spread far beyond the original point of introduction and causes environmental or economic damage by colonizing an dominating suitable habitats

biological control

the intentional release of a natural enemy to attack a pest population


evolutionary changes in which an adaptation of one species leads to the counter adaptation in a second species

population momentum

the increased proportion of women of child bearing age in the population

ecological footprint

an estimate of the amount of land required to provied the raw materials an individual or a population consumes


the scientific study of the interactions between organisms and their environments

Biotic Factors

all of the organisms in the area that make up the living component of the environment

Abiotic factors

make up the environment’s nonliving component ndinclude chemical and physical factors, such as temp, light, water, minerals, and air.


the specific environment it lives in, -biotic and abiotic

Organismal ecology

concerned with the evolutionary adaptions that enable individual organisms to meet the challenges posed by their abiotic environments.


a group of individuals of the same species living in a particular geographic area

population ecology

concentrates mainly on factors that affect population density and growth


consists of all the organisms that inhabit a particular area

community ecology

focus on how interactions between species such as predation and competition affect community structure and organization


includes all the abiotic factors in addition to the community of species in a certain area

ecosystem ecology

questions concern energy flow and the cycling of chemicals among the various biotic and abiotic factors


the global ecosystem, the sum of all the planet’s ecosystems

Abiotic factors of the biosphere

energy source- sunlight, temperature, water, nutrients, other aquatic factors, other terrestrial factors-wind

How are the fiels of ecology and evolution linked?

the process of evolutionary adaptation via natural selection results from the interactions of organisms with their environments


a physiological response that is a gradual, thought still reversible, physiological adjustment that occurs in response to an environmental change

anatomical response

a response to an environmental challenge that results in a change in body shape or structure


a major terrestrial or aquatic life zone, characterized by vegetation type in terrestrial biomes or the physical environment in aquatic biomes

photic zone

shallow water near shore and the upper layer of water away from the shore, -light is available for photosynthesis

aphotic zone

where light levels are two low to support photosynthesis

benthic zone

the bottom of all aquatic biomes made up of sand and organic sediments


a transitional biome between an aquatic ecosystem and a terrestrial one

benthic realm

sea floor

pelagic realm

all open water


photosynthetic algae and bacteria


free-floating animals, including many microscopic ones

coral reef

occurs in the photic zone of warm tropical waters in scattered locations around the globe


a transition area between a river and the ocean


the region from the tropic of cancer to the tropic of Capricorn

temperate zones

latitudes between the tropics and the arctic circle in the north and the antarctic circle in the south

Why is there so much rainfall in the tropics?

air at the equator rises as it is warmed by direct sunlight. as the air rises, it cools. this causes cloud formation and rainfall because cool air holds less moisture than warm air

Why are climbing plants common in rain forests?

climbing is a plant adaptation for reaching sunlight in a closed canopy, where little sunlight reaches the forest floor

tropical forest

occur in equatorial areas where the temperatures is warm and days are 11-12 hours long year round


dominated by grasses and scattered trees. temp is warm year round. rainfall varies dramatically with season


form from cool ocean currents circulating offshore, producing mile, rainy winters and hot, dry summers.

temperate grassland

some of the characteristics of tropical savannas but are mostly treeless, except along rivers or streams , and are found in regions of relatively cold winter temperatures

temperate broadleaf forests

occur throughout midlatitudes where there is sufficient moisture to support the growth of large trees.

coniferous forests

cone-bearing evergreen trees such as pine, spruce, fir, and hemlock


northern coniferous forest- largest terrestrial biome

temperate rain forests

coastal North America area that are coniferous forests


covers expansive areas of the artic between the taiga and polar ice


bitterly cold temperatures and high winds are responsible for the absence of trees and other tall plants

polar ice

covers the land at high latitudes north of the arctic tundra in the No. Hemisphere


the goal of developing, managing, and conserving earth’s resources in ways that meet the needs of people today without compromising the ability of future generations

greenhouse gasses

co2, water vapor, and methane

green house effect

the natural heating effect

carbon footprint

the amount of greenhouse gas emitted as a result of the actions of a single individual


biological diversity

How does the loss of genetic diversity endanger a population?

A population with decreased genetic diversity has less ability to evolve in response to environmental change

Main causes of declining biodiversity

habitat destruction, fragmentation, invasive species, overexploitation, pollution


an assemblage of species living close enough together for potential interaction

Interspecific Interactions

interactions between species

Ecological niche

the sum of its use of the biotic and abiotic resources in its environment

Competitive Exclusion Principle

if the ecological niches of two species are too similar, they cannot coexist in the same place


+/+, both species benefit from an interaction




+/-, an interaction in which one species kills and east another

Cryptic Coloration

makes potential prey difficult to spot against its background


(+/-) the consumption of plant parts of algae by an animal


lives on or in a host from which it obtains nourishment

Trophic Structure

the feeding relationships among the various species in a community

Food Chain

the sequence o food transfer between trophic levels


the bottom of the food chain, -plants, -phytoplankton


all organisms in tropic levels above the producers, -heterotroph

Primary consumers

herbivores- eat plants, algae, or phytoplankton


eat the consumers from the level below


the dead material left by all trophic levels


scavengers, consume detritus


consisting of prokaryotes, fungi, and protists, secrete enzymes that digest molecules in organic material and convert them to inorganic forms

how much solar energy is converted to chemical energy



the amount of living organic material in an ecosystem

species diversity

the variety of species that make up the community

species richness

the number of different species in the community

relative abundance

the proportional representation of a species in a community

The scientific study of the interactions between organisms and their environments is called


Abiotic components consist of

nonliving chemical and physical factors, such as temperature, light, water, minerals, and air.

Biotic components include

the living factors—all the other organisms that are part of an individual’s environment.


test hypotheses in the laboratory and in the field, use computer simulations of large-scale experiments that might be impossible to conduct in the field, and pose and test hypotheses.

Organismal ecology

is concerned with the evolutionary adaptations that enable individual organisms to meet the challenges posed by their abiotic environments. The distribution of organisms is limited by the abiotic conditions they can tolerate. For example, organismal ecologists study. (1) whale adaptations for deep diving or (2) how earthworms are restricted to moist environments because their skin does not prevent dehydration.

The population

is a group of individuals of the same species living in a particular geographic area. Population ecology concentrates mainly on factors that affect density and growth. For example, what factors limit the number of striped mice that can inhabit a particular area?

A community

consists of all the organisms that inhabit a particular area. It is an assemblage of populations of different species. Community ecology focuses on how interactions among species, such as predation, competition, and symbiosis, affect community structure and organization. For example, what factors influence the diversity of tree species that make up a particular forest?

An ecosystem

includes all the abiotic factors and the community of species in a certain area. Ecosystem ecology is concerned with the energy flow and the cycling of chemicals among the various biotic and abiotic factors. The biosphere is the global ecosystem—the sum of all the planet’s ecosystems, or all of life and where it lives. (1) It is the most complex level of ecology. (2) Isolated in space, the biosphere is self-contained, or closed, except that its photosynthetic producers derive energy from sunlight, and it loses heat to space.


Solar energy powers nearly all ecosystems. In aquatic environments the availability of sunlight: (1) has a significant effect on the growth and distribution of algae, and (2) most photosynthesis occurs near the surface of the water. In terrestrial environments, light is often not the most important factor limiting plant growth.


Aquatic organisms face problems of water balance if their own solute concentration does not match that of their surroundings. Terrestrial organisms have adaptations to prevent dehydration. (1) Many land species have watertight coverings that reduce water loss. (a) A waxy coating on the leaves and other aerial parts of most plants help prevent dehydration. (b) Mammals have an outer layer of dead skin containing a waterproofing protein.(2) Mammalian kidneys excrete very concentrated urine to eliminate urea with minimal water loss.


Environment influences metabolism. (1) Few organisms can maintain a sufficiently active metabolism at temperatures close to 0 ̊C (32°F), and (2) temperatures above 50 ̊C (122°F) destroy the enzymes of most organisms. Extraordinary adaptations enable some species to live outside this temperature range. For example: (1) some North American frogs and turtles can freeze during the winter months and still survive, (2) prokaryotes living in hot springs have enzymes that function optimally at extremely high temperatures, and (3) mammals and birds can remain considerably warmer than their surroundings.


has diverse effects. Some organisms such as bacteria, protists, and many insects that live on snow-covered mountain peaks, depend on nutrients blown to them by winds. Many plants depend on wind to disperse their pollen and seeds. Local wind damage often creates openings in forests, contributing to patchiness in ecosystems. Wind also increases an organism’s rate of water loss by evaporation. The consequent increase in evaporative cooling can be advantageous on a hot summer day but can cause dangerous wind chill in the winter. Wind can also affect the pattern of a plant’s growth

Rocks and Soil

The physical structure and chemical composition of rocks and soil limit the distribution of plants and of the animals that feed on the vegetation. Soil variation contributes to the patchiness we see in terrestrial landscapes. The composition of the substrate can affect water chemistry, influencing the resident plants and animals in streams, rivers, and marine environments.

Periodic Disturbances

Catastrophic disturbances, including fires, hurricanes, tornadoes, and volcanic eruptions, can devastate biological communities. After the disturbance, (1) the area is recolonized by organisms or repopulated by survivors, but (2) the structure of the community undergoes a succession of changes during the rebound. Several communities actually depend on periodic fire to maintain them.

Three types of adaptations enable plants and animals to adjust to changes in their environments

physiological, anatomical, and behavioral. These changes occur during the lifetime of an individual, so they do not qualify as evolution (a change in a population over time)

Physiological Responses

Short-term responses in a cat include- the contraction of tiny muscles attached to the hairs and the constriction of blood vessels in the skin.


Longer-term responses are called acclimation. An example is the gradual increase in the number of red blood cells in an animal that moved to a higher elevation (with less oxygen). Acclimation can take days or weeks. This is why high-altitude hikers—such as those attempting to scale Mount Everest—need extended stays at a base camp before proceeding to the summit.


use their metabolism to regulate internal temperature


are more limited in the climates they can tolerate.

Anatomical Responses

Many organisms respond to environmental challenges with some type of change in body shape or anatomy (structure).

Behavioral Responses

In contrast to plants, most animals can respond to an unfavorable change in the environment by moving to a new location. Such movement may be: fairly localized, such as a lizard shuttling between sun and shade, or over great distances, such as migratory birds.

The distribution of the biomes largely depends on

latitudinal patterns and climate.

Most biomes are

named for major physical or climatic features and for their predominant vegetation and characterized by microorganisms, fungi, and animals adapted to that particular environment


is a major terrestrial or aquatic life zone characterized by vegetation type or the physical environment ; it is a type of biological community, not a collection of certain species of organisms.

Aquatic biomes

consisting of freshwater and marine ecosystems, occupy the largest part of the biosphere.

photic zone

Shallow water near shore and the upper stratum of water away from shore make up the photic zone, so named because light is available for photosynthesis. (a) Phytoplankton (microscopic algae and cyanobacteria) grow in the photic zone,

aphotic zone

If a lake or pond is deep enough or murky enough, it has an aphotic zone where light levels are too low to support photosynthesis.

benthic zone

At the bottom of all aquatic biomes, the substrate is called the benthic zone, occupied by communities of organisms, including a diversity of bacteria, collectively called benthos.


A major source of food for the benthos is detritus, dead organic matter that "rains" down from the productive surface waters of the photic zone.

Nitrogen and phosphorus

are the mineral nutrients that usually limit the amount of phytoplankton in a lake or pond.

A river or stream changes greatly between

its source and the point at which it empties into a lake or the ocean. Near a source, the water is usually cold, low in nutrients, and clear, with a narrow channel and swift current. The current also inhibits the growth of phytoplankton. Most of the organisms are supported by the photosynthesis of algae attached to rocks or organic material (such as leaves) carried into the stream from the surrounding land. The most abundant benthic animals are insects that eat algae, leaves, or one another.


are often the predominant fishes, locating their food, including insects, mainly by sight in the clear water.


The area where a freshwater stream or river merges with the ocean is called an estuary. Most estuaries are bordered by extensive coastal wetlands called mudflats and saltmarshes. Nutrients from rivers enrich estuarine waters, making estuaries one of the most biologically productive environments on Earth.

Major Oceanic Zones

Marine life is distributed according to depth of the water, degree of light penetration, distance from shore, and open water versus ocean floor.

intertidal zone

The area where land meets sea. This environment is alternately submerged and exposed by the twice-daily cycle of tides. Intertidal organisms are therefore subject to huge daily variations in: (a) the availability of seawater, (b) the nutrients it carries, (c) temperature, and (d) mechanical forces of wave action.

pelagic realms/ zone

It supports communities dominated by motile animals such as fishes, squids, and marine mammals, including whales and dolphins. Microscopic algae and cyanobacteria—the phytoplankton—drift passively in the pelagic zone.


are the ocean’s main photosynthetic producers . Zooplankton: are animals that drift in the pelagic zone.

benthic zone

The seafloor is the benthic zone. Depending on depth and light penetration, it consists of attached algae, fungi, bacteria, sponges, burrowing worms, sea anemones, clams, crabs, and fishes.

photic zone

Marine biologists often group the illuminated regions of the benthic and pelagic communities together as the photic zone. aphotic zone: the most extensive part of the biosphere. Photosynthetic organisms do not live here. Sea urchins, polychaete worms, and some fishes scavenge organic matter that sinks from the lighted waters above. hydrothermal vent: communities, powered by chemical energy from Earth’s interior rather than sunlight.

Coral Reef Biome

The coral reef biome occurs in the photic zone of warm tropical waters, in scattered locations around the globe.

Terrestrial biomes are primarily determined by

Temperature and Rainfall

Temperate zones

occur in latitudes between the tropics and the Arctic Circle in the north and the Antarctic Circle

Mountains affect climate in two major ways

air temperature drops as elevation increases. mountains can Block the flow of cool, moist air from a coast

Terrestrial Biomes

Terrestrial ecosystems are grouped into biomes primarily on the basis of their vegetation type.


is a visual representation of the differences in: Precipitation, Temperature ranges that characterize terrestrial biomes, Tropical Forest

Tropical forests

occur in equatorial areas, where the temperature is warm, and where days are 11-12 hours long year- round.


Are dominated by grasses and scattered trees, Are warm year-round, Experience rainfall (roughly 12-20 inches per year) with dramatic seasonal variation


Are the driest of all biomes, May be very hot or very cold


has a climate that results from cool ocean currents circulating offshore and producing mild, rainy winters and hot, dry summers.

Temperate grasslands

are mostly treeless, Have 10-30 inches of rain per year, Experience frequent droughts and fires, Are characterized by grazers including bison and pronghorn in North America

Temperate Broadleaf Forest

Occurs throughout midlatitudes where there is sufficient moisture to support the growth of large trees, Includes dense stands of deciduous trees in the Northern Hemisphere

Coniferous forests

Are dominated by cone-bearing evergreen trees. Include the northern coniferous forest, or taiga, the largest terrestrial biome on Earth

Temperate rain forests

Are found along coastal North America from


Covers expansive areas of the Arctic between the taiga and polar ice. Is characterized by Permafrost (permanently frozen subsoil). Bitterly cold temperatures. High winds . Polar ice covers the land at high latitudes north of the arctic

Population ecology focuses on the factors that influence

a population’s size (number of individuals), growth rate, and density (number of individuals per unit area).

Population density

is the number of individuals of a species per unit area or volume, for example, the number of oak trees per square kilometer (km2) or the number of earthworms per cubic meter (m3) in the forest’s soil.

How is population density measured?

Rarely are all individuals counted in a defined area. Sample plots are often used instead.

The mark-recapture method

is commonly used to estimate wildlife populations. Animals are trapped within the boundaries of the population. The trapped animals are marked and released. After a few days or a few weeks, enough time for the marked individuals to mix randomly with unmarked members of the population, animals from the same population are trapped again. From these data, the total number of individuals in the population can be estimated.

Clumped patterns

occur when individuals are aggregated in patches. Clumping is the most common pattern in nature. Clumping often results from an unequal distribution of resources in the environment or with mating or other social behavior. Examples are schooling fish and mosquitoes swarming to increase chances for mating.

Uniform patterns

result from interactions among individuals of a population. Creosote bushes in the desert tend to be uniformly spaced because their roots compete for water and dissolved nutrients. Birds nesting on small islands often exhibit uniform spacing.

Random dispersion

results when individuals in a population are spaced in a patternless, unpredictable way. This only occurs in the absence of strong attractions or repulsions among individuals in a population. Clams living in a coastal mudflat might be randomly dispersed at times of the year when they are not breeding, when resources are plentiful and do not affect their distribution.

The age structure

of a population is the proportion of individuals in different age groups. Age structure can help us predict the future growth of populations in different countries. The combination of the birth rate and immigration exceeds the death rate. Immigration (legal and illegal combined) now contributes about 40% of the current growth of the U.S. population. Researchers predict that the U.S. population will continue to grow from about 280 million today to about 390 million by 2050.

A life table

tracks survivorship and mortality (death) in a population .

A survivorship curve

is a plot of the number of people still alive at each age. We can classify survivorship curves for diverse organisms into three general types.

Type I survivorship curves

have low death rates during the beginning and middle of life but increasing steadily in old age, and are characteristic of humans and many other large mammals that produce relatively few offspring but provide them with good care.

Type II survivorship curves

have even mortality over the life span, and are characteristic of species such as several invertebrates, including hydras, and certain rodents, such as the gray squirrel.

Type III survivorship curves

have high death rates for the very young but lower rates for those few individuals who survive, and are characteristic of species such as oysters that produce large numbers of offspring but provide little or no care for them.

Some key life history traits affecting population growth are

the age at which reproduction first occurs, the number of offspring produced for each reproductive episode, the amount of parental care committed to offspring, and the overall energy cost of reproduction.

Opportunistic life

histories usually have a Type III survivorship curve. Individuals reproduce when young and produce many offspring. Populations typically live in an unpredictable environment and are controlled by density- independent factors such as the weather. The life histories of many insects fit this pattern.

Equilibrial life histories

usually have a Type I survivorship curve. Individuals usually mature later and produce fewer offspring but care for their young. The population size may be quite stable, maintaining the carrying capacity by density-dependent factors. The life histories of many large terrestrial vertebrates, such as polar bears, and the coconut palm tree fit this model.

The Exponential Growth Model

The Ideal of an Unlimited Environment, The rate of expansion of a population under ideal, unregulated conditions is described by the exponential growth model, in which the whole population multiplies by a constant factor during constant time intervals. The constant factor for the bacterial population represented in Figure 18.18 is 2, because each parent cell splits to produce two daughter cells. The generation time for these bacteria is 20 minutes. The progression for bacterial growth—2, 4, 8, 16, and so on—is the number 2 raised to a successively higher power (exponent) each generation (that is, 21, 22, 23, 24, and so on). A key feature of the exponential growth equation is that the rate at which a population grows depends on the number of individuals already in the population. Exponential growth is rare in the real world. Where it is found, it is generally a short-lived consequence of organisms being introduced to a new or underexploited environment

The Logistic Growth Model

The Reality of a Limited Environment, The logistic growth model is a description of idealized population growth that is slowed by limiting factors.

Carrying capacity

is the number of individuals in a population that the environment can just maintain ("carry") with no net increase or decrease. (1) For the fur seal population in Figure 19.6, for instance, the carrying capacity is about 10,000 mated males. (2) At carrying capacity, the population is as big as it can theoretically get in its environment.

intraspecific competition

competition between individuals of the same species for the same limited resources. As the population size increases, the competition becomes more intense, and growth rate declines in proportion to the intensity of competition. The population growth rate is density-dependent.

A density-dependent factor

is a population -limiting factor whose effects intensify as the population increases in size. Such factors depress a population’s growth rate by increasing the death rate, decreasing the birth rate, or both. Examples are: (1) limited food supply and (2) a build-up of poisonous wastes.

Density-Independent Factors

Population-limiting factors whose intensities are unrelated to population density are called density-independent factors. Examples include weather, fires, and freezing temperatures/killing frosts.

Population ecology is used to

Increase populations of organisms we wish to harvest, Decrease populations of pests, Save populations of organisms threatened with extinction

An endangered species

as one that is in danger of extinction throughout all or a significant portion of its range

A threatened species

as one that is likely to become endangered in the foreseeable future A major factor in population decline is habitat destruction or modification.

An invasive species

Is a non-native species that has spread far beyond the original point of introduction. Causes environmental or economic damage by colonizing and dominating suitable habitats

Biological control

Is the intentional release of a natural enemy to attack a pest population, Is used to manage an invasive species


Evolutionary changes such as these, in which an adaptation of one species leads to a counter adaptation in a second species

Population momentum

is the continuation of population growth as girls in the prereproductive age group reach their reproductive years.

An ecological footprint

is an estimate of the amount of land required to provide the raw materials an individual or a population consumes, including, Food, Fuel, Water, Housing, Waste disposal

species richness

the total number of different species in the community and the relative abundance of the different species.

species diversity

as used by ecologists, considers both diversity factors—richness and relative abundance

Biodiversity has three main components

the genetic variation within each species, the variety of species that make up the biological community of any ecosystem, the diversity of ecosystems—each ecosystem has- a unique biological community and characteristic patterns of energy flow and chemical cycling. Some ecosystems are being erased from the biosphere at an astonishing rate.

The Four Main Causes of the Biodiversity Crisis

Habitat Destruction, Introduced Species, Overexploitation, Pollution

Vegetation has two properties

the type of plants that are dominant and the structure of the plants.

A community’s stability refers to the ability to

resist change and return to its original species composition after being disturbed.

Stability depends on

the type of community and the nature of disturbances.

The trophic structure

is the feeding relationships among the various species making up the community.

A community’s trophic structure determines

the passage of energy and nutrients from plants and other photosynthetic organisms to herbivores and then to carnivores.

Interspecific interactions

are interactions between species. Interspecific competition may result when populations of two or more species in a community rely on similar limiting resources.

limiting resource

As a population’s density increases and nears carrying capacity, every individual has access to a smaller share of some limiting resource (food and water for example)

G. F. Gause

In 1934, Russian ecologist G. F. Gause studied the effects of interspecific competition. He used laboratory cultures of two closely related species of protists, Paramecium aurelia and Paramecium caudatum. When cultured separately, each population grew rapidly and then leveled off at the apparent carrying capacity. But when cultured together, P. caudatum was driven to extinction. Gause concluded that: (1) When two species so similar that they compete for the same limiting resources cannot coexist in the same place. This is known as the competitive exclusion principle.

The Ecological Niche

The sum total of a species’ use of the biotic and abiotic resources in its environment is the species’ ecological niche.

Resource Partitioning

There are two possible outcomes of competition between species having identical niches- either the less competitive species will be driven to local extinction, or one of the species may evolve enough to use a different set of resources. The differentiation of niches that enables similar species to coexist in a local is called resource partitioning.


the consumer is called the predator, and the food species is the prey.


the eating of plants by animals, is a form of predation, even in cases such as grazing when the animal does not kill the whole plant. strychnine: produced by a tropical vinecalled Strychnos Toxifera:


from the opium poppy;


produced by the tobacco plant;


from peyote cactus; and


from a variety of plant species.


is a common antipredator response, though it can be very expensive energetically.

Other behavioral defenses include

alarm calls, mobbing, and distraction displays.

Camouflage, or cryptic coloration

is a passive defense that makes potential prey difficult to spot against its background.

Animals with chemical defenses

are often brightly colored, a caution to predators known as warning coloration.

In Batesian mimicry

a palatable or harmless species mimics an unpalatable or harmful model.

In Müllerian mimicry

two or more unpalatable species resemble each other.

keystone predator

is a species that: reduces the density of the strongest competitors a community. The predator helps maintain species diversity by preventing competitive exclusion of weaker competitors.


exists if one organism, the parasite, benefits at the expense of the other, which is harmed in the process. Parasitism is a specialized form of predation. There are internal and external parasites. Tapeworms and the protists that cause malaria are internal parasites. Mosquitoes and aphids are external parasites. Natural selection has refined the relationships between parasites and their hosts. Many parasites have adapted to specific hosts, often a single species. Natural selection has also favored the evolution of host defenses. In humans and other vertebrates, an elaborate immune system helps defend the body against specific internal parasites. The eventual outcome is usually a relatively stable relationship that does not kill the host quickly.


is a symbiosis that benefits both partners. the root-fungus associations called mycorrhizae, the specific interactions between certain pollinators and flowering plants, and the relationship between acacia trees and ants that protect these trees from herbivorous insects and competing plants.

Primary succession

occurs when a community arises in a virtually lifeless area with no soil.

Secondary succession

occurs where a disturbance has destroyed an existing community but left the soil intact.

Energy flow

is the passage of energy through the components of the ecosystem. Energy enters most ecosystems as light. Producers convert the light energy to the chemical energy of food. Other organisms feed on plants or organisms that eat plants. Decomposers consume the dead remains of life. In using their chemical energy for work, all organisms dissipate heat energy to their surroundings.

Chemical cycling

is the use and reuse of chemical elements, such as carbon, within the ecosystem.

Plants and other producers

acquire their carbon, nitrogen, and other chemical elements from the air and soil and convert these inorganic elements into organic compounds (carbohydrates and proteins) using photosynthesis. Animals feed on these organic compounds. The metabolism of all organisms returns some of the chemical elements to the abiotic environment in inorganic form. Decomposers finish recycling.

Conservation biology

is a goal-oriented science that seeks to counter the loss of biodiversity.

Conservation biologists

recognize that biodiversity can be sustained only if the evolutionary mechanisms that have given rise to species and communities of organisms continue to operate. Thus, the goal is- not simply to preserve individual species, but to sustain ecosystems, where natural selection can continue to function, and to maintain the genetic variability upon which natural selection acts.

A biodiversity hot spot

is a relatively small area with an exceptional concentration of species. nearly 30% of all bird species are confined to only about 2% of Earth’s land area, and about 50,000 plant species, or 20% of all known plant species, inhabit 18 hot spots that make up only about 0.5% of the global land surface. (1) include rain forests and dry shrub lands that total less than 1.5% of Earth’s land but are home to1/3 of all species of plants and vertebrates.

Landscape ecology

is the application of ecological principles to the study of land-use patterns.


between ecosystems are prominent features of landscapes, both natural and human-altered. Edges may have their own- (1) sets of physical conditions, (2) type and amount of disturbance, and (3) communities of organisms. Edges can have both positive and negative effects on biodiversity. They can be important sites of speciation but human-produced edges often- have fewer species and are dominated by species, such as cowbirds, that are adapted to edges.

movement corridor

is a narrow strip or series of small clumps of quality habitat connecting otherwise isolated patches.

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