APES Unit 3

Specialists: Smaller range of tolerance, or narrower ecological niche makes them vulnerable

• Specific food requirements 

• Less ability to adapt 

Generalists: Larger range of tolerance, broader niche makes them less vulnerable & more likely to be invasive

• Broad food requirements

• High adaptability

3.2 K & r Selected Species

K-selected - “quality”

• Few offspring with lots of parental care

• Generally reproduce less often than r-strategists

  • Ex: most mammals, birds

• Long lifespan, long time to sexual maturity = low biotic potential 

  • More likely to be disrupted by environmental  change or invasives

    Biotic potential = maximum rate a population can grow

R-selected - “quantity”

• Many offspring, little to no care 

• Generally reproduce many times throughout lifespan

  • Ex: insects, fish, plants

• Shorter lifespan, quick to sexual maturity = high biotic potential 

• More likely to be invasive

  • Better suited for rapidly changing environmental conditions

Invasive Species Basics

💚  Species not native to an area, introduced often by human transport

• No natural predators to control population

• Highly competitive (aggressive feeders or fast growers) for resources

• Can thrive in their non-native habitats

r-selected, generalists

R-selected and generalist species are more likely to be invasive

Highly adaptable

• Diverse habitat & food needs

Invasives & k - selected species

💚 In areas of high competition, K - selected species are vulnerable to overcompetition with invasive species.

EX: Kudzu vine is an invasive species from China that has taken over many habitats in the southern US. It has overtaken the slow-growing K - selected tree species

3.4 Carrying Capacity

Carrying Capacity (k): the max. Number of individuals in a pop. that an ecosystem can support (based on limiting resources)

Carrying Capacity (k)

• Overshoot: when a population briefly exceeds carrying capacity

• Ex: deer breed in fall, give birth all at once in spring; sudden spike in pop. = overshoot

• Consequence of overshoot: resource depletion ex: overgrazing in deer

• Die-off: sharp decrease in pop. size when resource depletion (overshoot) leads to many individuals dying

  • Ex: many deer starve with too many new fawns feeding in spring

Die-off Example

• Reindeer of St. Paul Island

  • 25 introduced in 1910

  • Growth was gradual (10’-30’), then exponential (30’-37’)

  • Carrying capacity was overshot

  • Sharp die-off lead to pop. crash as food resource (lichen) were severely depleted

• Real populations don’t always fluctuate around carrying capacity. If resource depletion is severe enough, total population crash can occur

Predator - Prey

1. Hare pop. increase due to low predator (lynx)

2. Lynx pop. increase due to increase in food (hare)

3. Increasing lynx pop. limits hare pop; leads to die-off

4. Hare die-off decreases lynx food source, leading to die-off

5. Hare pop. increase due to low predator (lynx)

3.5 Population Growth & Resource Availability

Population Characteristics

• Size (N): total # of individuals  in a given area at a given time

• Density: # of individuals/area 

  • Ex: (12 panthers/km²)

  • High density = higher competition, increased disease 

• Distribution: how individuals in population are spaced out compared to each other

  • Random (trees)

  • Uniform (territorial animals)

  • Clumped (herd/group animals)

Pop. Characteristics & Growth Factors 

• Sex Ratio: Males to females the closer to 50:50, better for breeding

  • Die-off or bottleneck effect can lead to not enough females which limits population growth

• Density-Dependent Factors: factors that influence population growth based on size

  • Ex: food, competition for habitat, water, light, even disease

  • Larger impact the bigger the population size

• Density-Independent Factors: factors that influence population growth no matter their size

  • Ex: natural disasters (flood, hurricane, tornado, fire)

  • Equally impacts all independent of population size

Example of Density-Dependent Factor

• Food is a density dependent factor and a limiting resource

  • When twice as much food was added to the dish, both species increased carrying capacity by about 2x

Calculating Population Size:

(19+5) - (6+0) = + 18 elk

52 + 18 = 70 elk

Survivorship Curves

Survivorship Curve: line that shows survival rate of a cohort (group of same-aged individuals) in a pop. from birth to death

• Faster drop in line = quicker die-off of individuals

• Slower drop in line = longer avg. lifespan

Type I

Type I (mostly K-selected)

• High survivorship early in life due to high parental care

• High survivorship in mid life due to large size & defensive behavior

• Rapid decrease in survivorship in late life as old age sets in

  • Ex: most mammals

Type II

Type II (in between r & K)

• Steadily decreasing survivorship throughout life 

Type III

Type III (mostly r-selected)

• High mortality (low survivorship) early in life due to little to no parental care 

• Few make it to midlife; slow, steady decline in survivorship in mid life

• Even fewer make it to adulthood; slow decline in survivorship in old age

• Ex: insects, fish, plants

3.6 Age Structure Diagrams

Age cohorts = groups of similarly aged individuals

• 0-14 = pre-reproductive; 15 - 44 = reproductive age; 45 + = post-reproductive

• Size difference between 0-14 & 15-44 indicates growth rate

  • Larger 0-14 cohort = current & future growth

  • Roughly equal 0-14 & 15-44 = slight growth/stable

Larger 15-44 = pop. decline

• Extreme Pyramid shape = rapid growth

• Less extreme pyramid = slow, stable growth

• House = stable, little to no growth

Narrowest at base = declining population

Practice Reading Diagrams

 Highest to Lowest Growth Rate

Total Fertility Rate (TFR)

• Total Fertility Rate (TFR): average number of children a woman in a population will bear throughout her lifetime

  • Higher TFR = higher birth rate, higher population growth rate 

• Replacement Level Fertility: TFR required to offset deaths in a population and keep population size stable

  • About 2.1 in developed countries (replace mom & dad)

  • Higher in less developed countries due to higher infant mortality

TFR & Infant Mortality

• Infant Mortality Rate (IMR): number of deaths of children under 1 year per 1,000 people in a population

  • Higher in less developed countries due to lack of access to: health care, clean water, enough food

• Higher IMR = higher TFR, due to families having replacement children

Factors That Affect TFR

• Development (affluence): more developed or wealthy nations have a lower TFR than less developed nations 

  • More educational access for women

  • More economic opportunity for women

  • Higher access to family planning education & contraceptives

  • Later age of first pregnancy

  • Less need for children to provide income through agricultural labor

Factors That Affect TFR

• Government Policy: can play a huge role in fertility by coercive (forceful) or noncoercive (encouraging) policies

  • Forced or voluntary sterilization (can’t reproduce)

  • China’s 1 (now 2) child policy

  • Tax incentives to have fewer children

  • Microcredits or loans to women without children to start businesses

Affluence & TFR

• More access to contraceptives & family planning

• Ed./econ. opportunities require time, leaving less for raising children

• Lower IMR = lower TFR

Female Education & TFR

• More education = fewer unplanned pregnancies

• More education = more job opportunities for women

  • Alternative to marrying young

Demographic Transition

• Industrialization: the process of economic and social transition from an agrarian (farming) economy to an industrial one (manufacturing based)

• Pre-industrialized/Less developed 

  • A country that has not yet made the agrarian to industrial transition

  • Typically very poor (low GDP)

  • Typically high death rate & high infant mortality

  • High TFR for replacement children & agricultural labor

• Industrialization: the process of economic and social transition from an agrarian (farming) economy to an industrial one (manufacturing based)

• Pre-industrialized/Less developed 

  • A country that has not yet made the agrarian to industrial transition

  • Typically very poor (low GDP)

  • Typically high death rate & high infant mortality

  • High TFR for replacement children & agricultural labor

• Industrializing/developing

  • part way through this transition

  • Decreasing death rate & IMR

  • Rising GDP

• Industrialized/developed: completed the transition

  • Very low DR & IMR

  • Very High GDP

  • Low TFR

Stage one - preindustrial

•  High IMR & high death rate due to lack of access to clean water, stable food supply, and healthcare 

• High TFR due to lack of access to:

  • Ed. for women

  • Contraceptives/family planning

• Need for child agricultural labor

• Little to no growth due to high CBR & CDR balancing each other out  

Ex: Virtually no country is in phase 1

Stage 2 - Industrializing/ Developing

• Modernizations brings access to clean water, healthcare, stable food supply  

  • IMR & CDR decline

• TFR remains high due to 

  • Lack of ed. for women & contraceptives/family planning

  • Need for child agricultural labor

  • Generational lag ( takes time for ed. & societal change to spread

• Rapid growth, due to high CBR and declining CDR

Stage 2 - Industrializing/ Developing

• Economic /societal indicators

  • Low per capita GDP

  • Shorter life-expectancy

  • High infant mortality

  • High TFR

  • Low literacy rate & school life expectancy for girls

Stage 3 - Industrialized/ Developed

• Modernized economy and society increase family income, so TFR declines significantly due to

  • More ed. opportunities for women

  • Delayed age of marriage & first child to focus on ed./career

  • Access to family planning & contraceptives

• Slowing growth rate as CBR drops closer to CDR

• Economic /societal indicators

  • High per capita GDP

  • Long life-expectancy

  • Low infant mortality

  • TFR, near replacement level (2.1)

  • High literacy rate & school life expectancy for all

Stage 4 - Post-Industrialized/ Highly Developed

• Highly modernized countries that are very affluent

  • TFR declines even further as families become more wealthy and spend even more time on educational & career pursuits

  • Increased wealth & education brings even more prevalent use of family planning & contraception

• CBR drops lower that CDR & growth becomes  negative(pop. decline)

Stage 4 - Post-Industrialized/ Highly Developed

• Economic / societal indicators

  • Very high per capita GDP

  • Longest life-expectancy

  • TFR, below  replacement level (2.1)

  • Highest contraceptive use rates

Stages & Development

• 1 = pre-industrial

• 2 = developing

• 3= Developed

• 4 = Highly developed

Human Population Dynamics

Does Earth have a human carrying capacity?

Malthusian Theory (what Malthus theorized):

• Earth has a human carrying capacity, probably based on food production

• Human population growth is happening faster than growth of food production

• Humans will reach a carrying capacity limited by food

Technological Advancement

• Humans can alter earth’s carrying capacity with technological Innovation

  • Ex: synthetic fixation of nitrogen in 1918 leads to synthetic fertilizer, dramatically increasing food supply

Birth Rate, Death Rate & Growth

• Growth Rate (r) = % increase in a population (usually per year)

  • Ex: a growth rate of 5% for a population of 100 means they grow to 105

• Crude Birth Rate & Crude Death Rate (CBR & CDR)

  • Births & deaths per 1,000 people in a pop.

    • Ex: Global CBR = 20 & CDR = 8

  • Calculating Growth Rate (r)

(CBR- CDR)/ population size   *100

(20-8)/ 1000 * 100 = 1.2%

Doubling Time (Rule of 70)

• Rule of 70: The time it takes (in years) for a population to double is equal to 70 divided by the growth rate

Ex: Global growth rate = 1.2%

70/1.2 = 58.3 years

Global pop. will double in 58.3 years

Calculating Population Change

• Practice Problem: A country has a CDR of 9 and a CBR of 18. 

  • Calculate the annual growth rate, and the doubling time

• Solution: (18-9)/10 = 9/10 = 0.9% growth rate 

70/0.9% = 77.77 years to double

Factors Affecting Human Pop. Growth

• Factors that decrease population growth rate

  • High death rate

  • High infant mortality rate

  • Increased development (education & affluence)

  • Increased education for women

  • Delayed age of first child 

  • Postponement of marriage age

Standard of Living Indicators

• Standard of Living

  • What the quality of life is like for people of a country based 

• Gross Domestic Product (GDP) = key economic indicator of standard of living

  • Total value of the goods & services produced 

  • Per capita GDP is total GDP/total population

Standard of Living Indicators

• Life expectancy = key health indicator of standard of living

  • Average age a person will live to in a given country

  • Increases with access to clean water, health care, stable food sources

High GDP & life expectancy are both indicators of development & low population growth

Specialists vs. Generalists

Specialists

• Characteristics:

  • Specialists possess a smaller range of tolerance and a narrower ecological niche, which makes them more vulnerable to environmental changes. This particularity leads them to have strict specific food requirements, limiting their adaptability to varied habitats and resources.

  • Due to their specialized traits, these species often find it challenging to compete when environmental conditions change or when facing invasive species that may exploit resources more efficiently.

Generalists

• Characteristics:

  • Generalists have a broader ecological niche and a larger range of tolerance, making them less vulnerable to environmental fluctuations, and much more likely to thrive in diverse habitats.

  • These species typically possess broad food requirements, allowing them to utilize various resources effectively and adapt to changes in availability.

  • Their high adaptability contributes to their potential to become invasive species in new environments, often outcompeting specialists.

K- and R-Selected Species

K-Selected Species

• Definition: K-selected species focus on quality over quantity in reproduction.

• Reproductive Strategy:

  • They produce few offspring and invest significant parental care in nurturing them.

  • Reproduction occurs less frequently compared to R-selected species.

  • Examples: Most mammals and birds.

• Life Traits:

  • Generally exhibit longer lifespans and a prolonged period to reach sexual maturity, which results in a low biotic potential. This makes them more susceptible to disruptions caused by environmental changes or invasive species due to their slower reproductive rates.

R-Selected Species

• Definition: R-selected species emphasize quantity over quality in their reproductive strategy.

• Reproductive Strategy:

  • They produce a high number of offspring with little to no care, allowing them to reproduce multiple times throughout their lifespan.

  • Examples: Many insects, fish, and certain plants.

• Life Traits:

  • Exhibit shorter lifespans and reach sexual maturity quickly, which results in a high biotic potential. This reproductive trait allows them to thrive in rapidly changing environmental conditions and adaptability to various habitats, increasing their likelihood of becoming invasive.

Invasive Species Basics

• Definition: Invasive species are organisms not native to a particular area and are often introduced through human activities, such as transportation.

• Impact on Ecosystems:

  • They typically lack natural predators in their new environment, which allows their populations to grow unchecked.

  • These species are often highly competitive, either through aggressive feeding habits or rapid growth rates, allowing them to monopolize available resources.

  • Invasive species are generally r-selected and generalists, enabling them to adapt to various situations and thrive in their non-native habitats.

• Example: The Kudzu vine is an invasive species from China that dramatically affects southern U.S. ecosystems, often outcompeting the slow-growing K-selected tree species, disrupting local biodiversity.

Carrying Capacity

• Definition: The carrying capacity (K) of an ecosystem is defined as the maximum number of individuals of a population that can be supported over time, considering the limiting resources available.

• Overshoot and Die-Off:

  • Overshoot occurs when a population temporarily exceeds the carrying capacity, potentially leading to resource depletion, as seen in deer populations that breed in fall and see a spike in numbers during spring.

  • Die-off follows when resource depletion causes a sharp decline in population size, often resulting in starvation or death of individuals due to insufficient resources.

• Example: The reindeer population on St. Paul Island demonstrates this concept, where an overshoot led to a significant die-off as lichen, their primary food source, became severely depleted.

Predator-Prey Dynamics

• Understanding predator-prey relationships is crucial for grasping how populations regulate themselves:

  • For instance, an increase in the hare population due to decreased predation can subsequently lead to a rise in lynx populations, which then puts pressure back on the hare population, leading to cycles of increase and decrease (die-off) in numbers.

Population Growth and Resource Availability

• Population Characteristics:

  • Size (N): Total number of individuals in a specific area.

  • Density: Number of individuals per unit area, affecting competition levels and disease spread.

  • Distribution: Spatial arrangement of individuals, which can be random, uniform, or clumped.

Density-Dependent and Density-Independent Factors

• Density-Dependent Factors: Influence population growth based on size ( e.g., food, competition, disease).

• Density-Independent Factors: Affect growth regardless of population size (e.g., natural disasters).

Survivorship Curves

• Illustrate survival rates over time for a cohort, categorized into three types:

  • Type I: High early-life survivorship, typical of K-selected species.

  • Type II: Steady survivorship across life stages.

  • Type III: High early mortality, common in R-selected species.

Age Structure Diagrams

• Cohorts categorize individuals by age:

  • 0-14: Pre-reproductive (potential growth indicator).

  • 15-44: Reproductive age.

  • 45 and older: Post-reproductive.

Total Fertility Rate (TFR)

• TFR indicates the average number of children a woman will bear, affected by various factors including healthcare access and education levels.

• Replacement Level Fertility: The TFR required to maintain a stable population, typically about 2.1 in developed countries.

Demographic Transition Stages

• Stage 1: Pre-Industrial: High birth and death rates, limited growth.

• Stage 2: Industrializing: Declining death rates, high birth rates, rapid growth.

• Stage 3: Industrialized: Declining birth rates, slowed growth due to increased education and economic opportunities.

• Stage 4: Post-Industrialized: Very low birth rates with potential population decline due to high affluence and educational pursuits.

Human Population Dynamics

• Malthusian Theory encapsulates the idea of a natural carrying capacity limited by food production with growth occurring faster than available nourishment. Human innovations, such as technological advancements in agriculture, can impact this balance.