Differences Between Generalist and Specialist Species in Populations

Specialist species

Species that tend to be advantaged in habitats that remain constant, have narrow niches, may live in only one type of habitat, use one or few types of food, and can tolerate a narrow range of climatic environmental conditions.

Generalist species

Species that tend to be advantaged in habitats that are changing, have broad niches, live in many different places, eat a variety of food, and tolerate changes in the environment.

K-selected species

Species that tend to produce later in life, have a small number of offspring with fairly long life spans, and live in stable environments.

r-selected species

Species that have many small offspring with little or no parental care and tend to be opportunistic.

Biotic potential

The maximum reproductive rate of a population in ideal conditions.

K-selected species characteristics

Large size, reproduce later in life, have few offspring per reproduction event, expend significant energy for each offspring, mature after many years, have long life spans, reproduce more than once in their lifetime, and have high levels of competition for resources.

Examples of K-selected species

Large mammals (elephants, whales, humans), birds of prey, large and long-lived plants (cactus, tropical rain forest trees), some ocean fish (orange roughy, swordfish, and sharks).

r-selected species characteristics

Small size, have many offspring, expend minimal energy for each offspring, mature early, have short life spans, may reproduce only once in their lifetime, and have low levels of competition for resources.

Examples of r-selected species

Algae, bacteria, rodents, frogs, turtles, annual plants (dandelions), and most insects.

Population size dynamics of r-selected species

Population size may crash due to unfavorable environmental conditions or invasion by a more competitive species, and most r-selected species go through irregular and unstable boom-and-bust cycles in their population sizes.

Reproductive strategies

Many species have reproductive strategies that are not uniquely r-selected or K-selected, or they change in different conditions at different times.

Example of a species with mixed strategies

Trees have longevity and strong competitiveness (K-strategy) and also produce thousands of offspring and disperse them widely with no parental care (r-strategy).

Example of sea turtles

Large organisms with long lifespans (K-strategy) but produce large numbers of unnurtured offspring (r-strategy).

Impact of invasive species

K-selected species are typically more adversely affected by invasive species than r-selected species, which are minimally affected by invasive species.

Typical characteristics of invasive species

Most invasive species are r-selected species.

Survivorship curve

A line that displays the relative survival rates of a cohort in a population, from birth to the maximum age reached by any one cohort member.

Cohort

A group of individuals of the same age in a population.

Type I curve

High survivability in early and middle life, followed by a rapid decline in survival in later life - K-strategists, ex: humans.

Type II curve

Constant mortality rate regardless of age - ex: some birds and some lizards.

Type III curve

Greatest mortality early in life with high survivability for those that do survive - typically r-selected strategists, ex: marine invertebrates.

Carrying capacity (K)

The maximum population of a given species that a particular habitat can sustain indefinitely without being degraded.

Biotic potentials

Capacity for population growth under ideal conditions.

Intrinsic rate of increase (r)

The rate at which the population of a species would grow if it had unlimited resources.

Limiting factors

Anything that limits the size of the population.

Environmental resistance

The combination of all factors that act to limit the growth of a population.

Exponential growth

Accelerated growth that slows but increases as the population size increases.

J shaped curve

A representation of exponential growth showing a doubling of the population.

Logistic growth

Rapid exponential growth followed by a steady decrease in population growth until carrying capacity is met - S shaped curve.

Overgrazing

The process that reduces the overall carrying capacity for cattle by allowing sagebrush to thrive and outcompete grass.

Southern sea otter

A species that does not have a high biotic potential, reaching sexual maturity between 2 and 5 years old and typically producing 1 pup per year.

Decline of southern sea otter population

Caused by killer whales feeding on them more due to climate change, cat litter causing parasites, and toxic algae blooms.

Biomagnification

The process by which toxic chemicals released by humans accumulate in the food chain.

Oil spills

An environmental disaster that can lead to the decline of certain species, including the southern sea otter.

Intrinsic rate of increase

Individuals with a high intrinsic rate of increase typically reproduce early in life, have short generation times, can reproduce many times, and have many offspring each time they reproduce.

Minimum population size

There is a minimum population size where if the number of individuals goes below that number they may not be able to find mates or interbreed to produce weak offspring with little genetic diversity.

Doubling of the population

A doubling of the population occurs during exponential growth.

Carrying capacity

Carrying capacity is the maximum population of a given species that a particular habitat can sustain indefinitely.

Population overshoot

When a population exceeds its carrying capacity, overshoot occurs, leading to a dieback or crash in the population numbers caused by resource depletion.

Dieback

A major ecological effect of population overshoot is dieback of the population, often severe to catastrophic, due to lack of available resources leading to famine, disease, and/or conflict.

Natality

Natality refers to the birth rate in a population.

Mortality

Mortality refers to the death rate in a population.

Immigration

Immigration is the movement of individuals into a population.

Emigration

Emigration is the movement of individuals out of a population.

Population change

Population change is calculated as (birth + immigration) - (death + emigration).

Zero population growth

Zero population growth means there is no population change.

Resource availability

Resource availability and the total resource base are limited and finite over all scales of time.

Fecundity

Fecundity is the ability to produce an abundance of offspring.

Age structure

Age structure is the distribution of males and females among age groups in a population.

Baby Boomers

Baby Boomers refers to the generation born between 1946 and 1964, which added 79 million people to the US population.

Retirement impact

Starting in 2011, when the baby boomers began turning 65, there was an increase in retirees, projected to create a shortage of workers by 2043 when about 25% of the US population will be over 65.

Public policy and age structure

Age structure diagrams can be used to guide public policy, particularly in relation to the aging population.

Crude birth rate

The number of live births per 1,000 people in a population in a given year

Crude death rate

The number of deaths per 1,000 people in a population in a given year

Fertility rate

The number of children born to a woman during her lifetime

Replacement-level fertility rate

The average number of children that couples in a population must bear to replace themselves

Total fertility rate

Average number of children born to women in a population during their reproductive years

Infant mortality rate

The number of children per 1,000 live births who die before the age of 1

Life expectancy

The average number of years a newborn infant can expect to live

Rapidly declining population countries

Japan, Russia, Germany, Bulgaria, the Czech Republic, Hungary, Poland, Ukraine, Greece, Italy, and Spain

Prereproductive age

Ages 0-14

Reproductive age

Ages 15-44

Postreproductive age

Ages 45 and older

Population growth indicators

A rapidly growing population will have a higher proportion of younger people compared to stable or declining populations

Impact of prereproductive individuals

The more prereproductive individuals in a population, the higher growth that population will experience

Major cause of population increase

Decline in crude death rates

Replacement level fertility in developed countries

2.1

Replacement level fertility in developing countries

Up to 2.5

Delay in population growth reduction

Having fewer children does not immediately lower the population growth due to older individuals still being alive

Countries with largest populations in 2008

China - 1.5 billion, India - 1.4 billion, US - 357 million, Indonesia - 292 million, Pakistan and Brazil (tied) - 229 million

Factors affecting total fertility rate

Age at which females have their first child, education opportunities for females, access to family planning and government acts and policies

Total Fertility Rate (TFR)

In developed countries, it costs more to raise children.

Pensions

In developed countries, parents don't need as many children to support them in their old age if there is a system in place for when they retire.

Urbanization

Children are not needed to carry water or raise crops.

Education and employment for women

Typically, higher educated women tend to marry later and have fewer children.

Age at marriage / age for first child

Women typically have fewer children when they have their first child later.

Access to birth control

This allows women to control and space out their children.

Religious beliefs / traditions / cultural norms

Some countries favor larger families, oppose abortions, and are against birth control.

Factors affecting death rates

Better nutrition, better healthcare, improved sanitation.

Migration

Migration impacts population size.

Replacement level fertility

If fertility is at replacement levels, a population is considered relatively stable.

Annual rate of population change formula

To calculate annual rate of population change = (CBR - CDR) x 100 / 1,000.

Population momentum effect

If replacement level fertility was reached worldwide, the population would still increase for the next 50-60 years.

Demographic transition

As countries become industrialized, first their death rates decline and then their birth rates decline.

Empowering women and population growth

Educated women that can read can work outside the home, freeing them from poverty and leading to fewer children.

China's population control measures

Discouraged premarital sex, urged people to marry later, and provided incentives for couples with one child.

Surplus of men in China

Chinese culture prefers male children, leading to a surplus of men with not enough women.

Average age of China's population

With fewer children being born, the average age is increasing, leading to a declining workforce.

Problems in India due to population growth

Poverty, malnutrition, and environmental problems.

Reasons for large families in poverty

Poor couples continue to have a large number of children because they need children to work and care for them in old age.

Stages of demographic transition

Demographic transition occurs in 4 distinct stages: Preindustrial, Transitional, Industrial, and Postindustrial.

Stage 1 of demographic transition

Population grows very slowly with high birth rates and high death rates.

Stage 2 of demographic transition

Population grows rapidly because birth rates are high and death rates drop due to improved food production and health.

Stage 3 of demographic transition

Population growth slows as both birth and death rates drop due to improved food production, health, and education.

Stage 4 of demographic transition

Population growth levels off and then declines as birth rates equal and then fall below death rates.

Characteristics of developing countries

Higher infant mortality rates and more children in the workforce than developed countries.