bio unit 2 complete

What is a population?

A group of individuals of the same species living in the same area.

What is population size?

The total number of individuals in a population.

What is population density?

The number of individuals per unit area.

How do you calculate population density?

Population density = number of individuals ÷ area.

What is the density of 100 fish in a 20-square-meter pond?

5 fish per square meter: 100 ÷ 20 = 5.

What is population distribution?

The pattern of spacing of individuals across their geographic range.

How are population density and distribution different?

Density describes how many individuals live per unit area; distribution describes how they are spaced out.

What is a population's geographic range?

The area where the population lives; it can expand, shrink, or shift.

What four characteristics do ecologists use to describe populations?

Geographic range, density and distribution, growth rate, and age structure.

What is random distribution?

Individuals are spaced without a predictable pattern; one individual's location is largely independent of others. Example: some trees.

What is uniform distribution?

Individuals are evenly spaced. Example: nesting penguins.

What often causes uniform distribution?

Competition for resources or territorial behavior keeps individuals apart.

What is clumped distribution?

Individuals gather in groups. Examples: schools of fish and herds.

Why might a population have a clumped distribution?

Individuals may gather around resources or group together for protection from predators.

What is age structure?

The ages and numbers or proportions of males and females in a population.

Why does age structure help predict population growth?

It indicates how many individuals can reproduce now or may reproduce in the future.

What four processes directly change population size?

Births, deaths, immigration, and emigration.

What is immigration?

Movement of individuals into a population's area; it increases local population size. I = IN.

What is emigration?

Movement of individuals out of a population's area; it decreases local population size. E = EXIT.

What is the equation for population change?

Population change = births + immigration − deaths − emigration.

When does a population grow?

When births plus immigration exceed deaths plus emigration.

When does a population decline?

When deaths plus emigration exceed births plus immigration.

When is a population stable?

When births plus immigration equal deaths plus emigration; net population change is approximately zero.

Does a stable population have no births or deaths?

No. Births and deaths still occur, but total additions and losses balance.

Does birthrate equal to death rate always mean a stable local population?

No. Immigration and emigration must also balance.

What is the population change with 12 births, 5 deaths, 4 immigrants, and 3 emigrants?

An increase of 8 individuals: 12 + 4 − 5 − 3 = 8.

What is exponential growth?

Growth under ideal conditions with unlimited resources, in which a population adds more individuals per time interval as it gets larger.

What shape represents exponential growth?

A J-shaped curve that becomes increasingly steep over time.

Why does exponential growth speed up as population size increases?

More individuals reproduce, producing more offspring during each equal time interval.

Can slowly reproducing organisms grow exponentially?

Yes. Even slowly reproducing species can grow exponentially under ideal conditions.

Can a natural population grow exponentially forever?

No. Resources and other environmental conditions eventually limit growth.

If one bacterium doubles every 20 minutes, how many exist after one hour?

8 bacteria: three doublings give 1 → 2 → 4 → 8.

What is logistic growth?

Growth that slows and then stops near carrying capacity after a period of rapid, approximately exponential growth.

What shape represents logistic growth?

An S-shaped curve that levels off near carrying capacity.

What are the three phases of logistic growth described in the textbook?

Rapid growth, slowing growth, and approximately zero net growth near carrying capacity.

Why does logistic growth level off?

Limited resources and other limiting factors make population additions approximately balance losses.

Does slowing population growth mean the population is shrinking?

No. The population can still increase while adding fewer individuals each year.

What is carrying capacity, or K?

The number of individuals of a particular species an environment can support over time under its conditions.

What can happen when a population exceeds carrying capacity?

Resource shortages and competition may lower births or increase deaths and emigration, causing population decline.

Is carrying capacity always constant?

No. Changes in food, water, habitat, climate, and other limiting factors can raise or lower it.

Can different species in the same ecosystem have different carrying capacities?

Yes. Each species has different resource needs and interactions.

What resources limit barnacles, monarch butterflies, and buffalo in the textbook?

Barnacles: attachment space. Monarchs: food and host plants. Buffalo: edible grasses.

What do the axes usually show on a population growth graph?

The x-axis shows time; the y-axis shows population size.

What does a steep upward slope on a population graph mean?

The population is increasing rapidly.

What does a horizontal line on a population graph mean?

Population size is approximately constant; net growth is approximately zero.

What does a downward slope on a population graph mean?

Population size is decreasing.

What is a limiting factor?

Any factor that controls a population's growth; limiting factors together determine carrying capacity.

What is a density-dependent limiting factor?

A factor whose effects generally become stronger as population density increases.

Name density-dependent limiting factors from the textbook.

Competition, parasitism, disease, stress from overcrowding, predation, and herbivory.

Why is competition density-dependent?

More individuals must share limited resources, leaving less available per individual.

What resources can organisms compete for?

Food, water, space, sunlight, shelter, and access to mates or breeding territories.

Can competition occur within and between species?

Yes. Individuals of the same species or different species can compete for shared limited resources.

Why are parasitism and disease often density-dependent?

Crowding makes it easier for parasites and pathogens to spread between hosts.

How can stress from overcrowding limit a population?

It can increase fighting and disease susceptibility, lower birthrates, raise death rates, or increase emigration.

What is herbivory?

Feeding on plants by animals; it can limit plant populations, while plant availability limits herbivores.

What is a density-independent limiting factor?

A factor that can affect a population regardless of its density, such as a drought or hurricane.

Name environmental density-independent limiting factors.

Droughts, hurricanes, floods, wildfires, heavy rainstorms, and extreme heat or cold.

Can density-independent and density-dependent factors interact?

Yes. Drought can reduce food regardless of density, while a crowded population experiences greater competition for the remaining food.

What is a biotic factor?

A living component of the environment or an interaction involving organisms, such as predators or parasites.

What is an abiotic factor?

A nonliving environmental condition or resource, such as temperature, water, or sunlight.

How can habitat loss affect carrying capacity?

It reduces space and resources, often lowering carrying capacity; severe reductions can cause population loss or extinction.

What relationship exists between wolves and moose on Isle Royale?

Predation: wolves are predators and moose are prey.

How can an increase in moose affect wolves?

More moose provide more food, which can allow the wolf population to increase after a time lag.

How can an increase in wolves affect moose?

More wolves can increase moose deaths through predation, causing the moose population to decline.

What can happen to wolves after moose decline?

Food shortages can lower wolf birthrates and raise death rates, causing wolves to decline and allowing moose to recover.

Why do predator and prey populations often peak at different times?

Predators need time to survive and reproduce in response to increased prey availability.

What disease sharply reduced Isle Royale wolves after 1980?

Canine parvovirus; reduced predation helped moose increase.

What other factors affected Isle Royale moose besides wolves?

Plant availability, winter ticks, severe cold, and heavy snow that made food difficult to reach.

What should you check when reading the wolf–moose graph?

The two y-axis scales are different: one measures wolves and the other measures moose.

How did human hunting affect sea otters?

Hunting increased deaths beyond what births could replace, greatly reducing otter populations.

How do otters, sea urchins, and kelp interact?

Otters eat urchins, and urchins eat kelp. Fewer otters can mean more urchins and less kelp.

What is a trophic cascade?

An indirect effect through a food web, such as fewer otters leading to more urchins and less kelp.

Why can an introduced species grow rapidly in a new habitat?

It may find plentiful resources and escape predators, parasites, or diseases that limited it in its native range.

What is the difference between introduced and invasive species?

Introduced species are brought outside their native range; invasive species spread and cause harm.

How does the textbook classify hunting and trapping used against Australian rabbits?

As density-independent control efforts; they removed many rabbits but failed to control the invasion.

What density-dependent method was used to control Australian rabbits?

A virus causing myxomatosis was introduced; disease initially greatly reduced rabbit numbers.

Why did myxomatosis become less effective at controlling rabbits?

Rabbits evolved resistance, and less deadly virus strains evolved.

What is demography?

The scientific study of human populations, their characteristics, and how they change over time.

What drove rapid human population growth during the Industrial Revolution?

Improved nutrition, sanitation, medicine, and public health lowered death rates while birthrates remained high.

How can technology raise human carrying capacity?

It can increase food production and improve sanitation, medicine, and access to resources.

Are humans free from environmental limiting factors?

No. Humans still depend on food, water, soil, and other environmental resources.

What is the demographic transition?

A shift from high birthrates and death rates to low birthrates and death rates as social and economic conditions change.

What happens in stage 1 of this textbook's demographic transition model?

Birthrates and death rates are both high, so population growth is low.

What happens in stage 2 of this textbook's demographic transition model?

Death rates fall while birthrates remain high, causing rapid population growth.

What happens in stage 3 of this textbook's demographic transition model?

Birthrates fall as education and living standards improve, so population growth slows.

What happens in stage 4 of this textbook's demographic transition model?

Birthrates and death rates are both low and approach one another; growth slows toward stability.

What happens in stage 5 of this textbook's demographic transition model?

Birthrate equals death rate and population growth stops, assuming migration balances. Use this textbook's version for the test.

Which rate usually falls first during the demographic transition?

The death rate falls before the birthrate.

What does an age structure diagram show?

The numbers or percentages of males and females in different age groups.

What does a wide base on an age structure diagram suggest?

Many young individuals will reach reproductive age, suggesting future population growth.

What do similar-sized younger and middle age groups suggest?

Slow population growth or approximate stability.

What does a narrow base compared with older age groups suggest?

Fewer young people will replace older generations, suggesting population decline.

Why can a population keep growing after families start having fewer children?

A large generation of young people can create many future parents; this is population momentum.

What combination caused the Irish Potato Famine in the textbook?

Heavy reliance on one potato variety, potato blight, and unusually cool, wet weather that helped the disease spread.

How did the Irish Potato Famine affect population size?

Food shortages caused roughly 1 million deaths and 1.5 million emigrants, according to the textbook, reducing Ireland's population.

What lesson does the Irish Potato Famine illustrate?

Dependence on one vulnerable food crop can make human populations highly vulnerable to disease and environmental changes.

What human actions helped cause the Dust Bowl?

Farmers removed native prairie grasses and repeatedly cultivated crops, leaving soil without protective deep roots.

What natural processes helped cause the Dust Bowl?

Severe drought dried exposed soil, and strong winds eroded topsoil and created dust storms.

Why were native prairie grasses important?

Their deep roots held soil in place and helped the grassland withstand harsh conditions.

How did the Dust Bowl lower carrying capacity?

Water shortages, topsoil loss, crop failures, and livestock deaths reduced resources available to support people and other organisms.