APES Unit 3

Unit 3.1: Generalist and Specialist Species 

• Populations change over time as a reaction to a variety of factors

• Why is it that some species can adapt quickly to changes in environments but other species are not? 

• Generalist Species

  • Live in a variety of environments

  • Eat a variety of food

  • Broad ecological tolerance for environmental conditions 

  • Have an advantage when the environment changes

  • Have a wide niche and can use a variety of resources

  • Quickly reproduce 

• Specialist Species

  • Require a specific habitat 

  • Limited diet

  • Narrow ecological tolerance for environmental conditions 

  • Have an advantage in constant habitats

  • Have a narrow niche and can use limited resources  

• Specialist species are advantaged in habitats that remain constant, generalist are more advantaged in constantly changing habitat 

Unit 3.2: K-Selected and r-selected Species 

• K-selected Species

  • Tend to be large

  • Have few offspring/reproduction event

  • Expend significant energy for each offspring

  • Mature after many years of parental care; have long life spans

  • Reproduce more than once in their lifetime

  • Can better regulate reproduction 

  • Can maintain its population near carrying capacity

  • Live in stable environments 

  • High competition 

  • TEND TO BE SPECIALIST

• r-selected Species

  • Tend to be small

  • Have many offspring 

  • Expend or incest minimal energy for each offspring

  • Mature early; have short life spans

  • May reproduce only once in their lifetime

  • Are able to thrive in disturbed environments

  • Low competition 

  • High rates of growth and reproductive 

  • TEND TO BE GENERALIST

• Populations have in their capacity for growth 

• Biotic potential- the maximum reproductive rate of a population in ideal conditions

• Classifying Species 

  • Many organisms cannot be categorized as strictly r-selected or K-selected

  • Example: turtles have traits of both r-selected and K-selected species 

• Most invasive species are r-selected species because they have a high reproductive and biotic potential, growing and maturing very quickly. As a result, they can colonize area more easily and can out compete native specialist species.

• K-selected species are more adversely affected by invasive species because they are typically specialists that have a low population growth rate. Invasive species are generalists that can quickly reproduce and take over a habitat. r-selected species are minimally affected by invasive species because they can easily switch to a different resource to avoid competition.

Unit 3.3: Survivorship Curves 

• Shows a graph of time VS percent of organisms surviving

  • Type I: Late Loss

    • A large % of the population survive from birth to death

    • They survive because they care for the young, thus increasing chances of survival to old age.

  • Type II: Constant Loss

    • Death rate constant from birth to death

  • Type III: Early Loss

    • A large % of the population dies early life, a small amount make it to adulthood

    • There is no parental care, so there is a high infant mortality rate 

• These curves give us insight to K and r-selected species 

Unit 3.4: Carrying Capacity 

• Biotic Potential - the maximum reproductive rate under ideal conditions

• Carrying Capacity (K) - the maximum number of organisms that an environment can support without degradation of resources 

  • Gets its name from K - selected species (represented by a dotted line and the letter K)

  • It is not constant - it can go up or down depending on the resources available in an ecosystem

    • When a population exceeds carrying capacity, it results in resource depletion 

  • Factors that determine carrying capacity are complex and interconnected, they can completely change an ecosystem 

• Overshoot - when a population exceeds carrying capacity 

• Dieback - bringing an art overshot population back to its carrying capacity due to depletion of resources from overpopulation 

  • Can be catastrophic 

    • Example: a reindeer population exploded in 1845 on St. Matthew’s Island, and then had a very devastating dieback where many, many reindeer died 

• R-species more likely to overshoot carrying capacity (high rates of growth and reproduction) while K-species tend to maintain population close to carrying capacity (able to regulate)

Unit 3.5: Population Growth and Resource Availability 

• Environmental Resistance - factors that limit growth

• Density Dependent Resistance Factors

  • Tend to be biotic

  • Have a strong influence when the number of organisms per unit area reaches a certain level

  • Competition for resources

  • Predation

  • Parasitism/Disease

• Density Independent Resistance Factors

  • Tend to be abiotic 

  • Have an affect on all populations, regardless of size of density

  • Natural disasters, severe weather events

  • Drought

• Exponential Growth - unlimited resources 

  • When a species first begins to evolve in an ecosystem, the growth will be exponential until any species hits its carrying capacity

• Logistic Growth - limited resources, competition is present 

• Fecundity- the ability to produce offspring 

Unit 3.6: Age Structure Diagrams

• Age structure diagram = population pyramid 

  • Show the distribution of ages in a certain population 

  • Divided by male and female

  • Not always pyramidal 

  • Come in many shapes 

    • Bottom heavy - population is growing quickly

      • Younger age groups are are the largest percent of the population 

      • They are reproducing longer

      • Usually an indicator of a developing population

    • Middle Heavy - population growth is stable

      • Rectangular shape 

      • All reproductive groups seem to have similar percentages 

        • Not as many younger groups for reproduction

        • Nations in this shape are developed and well off

• Top Heavy - population may be negative/declining

• Inverted pyramid shape

• Largest percentage of the population is closer to post-reproductive 

  • Economically and socially developed, higher education common

    • Many women delay having children

  • Long term social services may be impacted 

• Population pyramids are graphs:

  • X axis = number of individuals, each side being male or female

  • Y axis = usually center of diagram, shows age groups

    • Age groups divided by reproductive ability:

      • Pre-reproductive: 0-14 years

      • Reproductive: 15-45

      • Post: 46-100+

• Population Growth rates can be interpreted from age structure diagrams by the shape of the structure

• A rapidly growing population will, as a rule gave higher proportion of younger people compared to stable or decline populations 

Unit 3.7: Total Fertility Rate

• Total Fertility Rate - the average number of children a woman will have during her child bearing years

  • These years are ages 15-45

  • The world average for TFR is currently 2.5

    • Globally, TFR has been lowering over time.

  • Developing Nations: TFR above 2.1

    • Could be as high as 6 or 7

    • Democratic Republic of Congo: 6.3

    • Uganda: 6.2

  • Developed Nations: TFR at or below 2.1

    • The lower the TFR, the slower the growth

    • United Kingdom: 2.0

    • Japan: 1.4

    • USA: 1.8

• Factors of TFR

  • Age of first pregnancy 

  • Educational opportunities

  • Family planning

  • Governmental policies 

    • Can be done by tax increases, not necessarily limiting the number of children a family can have

  • Infant mortality and rates related to healthcare to access 

  • Economics, cost of raising children

Unit 3.8: Human Population Dynamics 

• Factors that can affect whether a population is growing or declining:

  • Birth rates

    • High rate: speeds population growth

    • Low rate: slows population growth

  • Death rates

    • High rate: speeds population growth

    • Low rate: speeds population growth 

  • Education in Women

    • High rate: slows population growth

    • Low rate: speeds population growth 

  • Infant mortality

    • High rate: slows population growth 

    • Low rate: speeds population growth

  • Age of Marriage

    • Early: speeds population growth

    • Late: slows population growth

  • Nutrition 

    • High rate: speeds population growth

    • Low rate: slows population growth

• Human Populations Have Limits

  • Human populations also experience carrying capacity

  • According to Thomas Malthus, all populations have a carrying capacity

  • Human populations are limited by density-independent factors and density-dependent factors

  • Human populations have to deal with many environmental issues

    • Example: Hurricanes from 1980-2012 led to high density countries having a drop in their human population 

      • Reasoning being damage to homes, economic loss, and better opportunities elsewhere

  • When women are educated longer, they will not have the same availability to have children, therefore having less children

• Density-Independent Factors

  • Storms

  • Fires

  • Heat waves

  • Drought

• Density-Dependent Factors

  • Disease transmission 

  • Territory size

  • Food availability 

  • Access to clean air and water

• Unlike non-human populations, societal and economic factors also play a role in human population growth 

• The Rule of 70 - used for calculating doubling time

  • Doubling Time - the amount of time for a population to double at a constant growth rate

  • 70/r = Doubling time

    • r = growth rate of a population

    • For these calculations r needs to be a number percentage for example 1.55%, not 0.0155

Unit 3.9: Demographic Transition

• Demographic Transition - a model that shows trends in 3 key factors for a nation

  • Birth rate

  • Death rate 

  • Total population 

    • Derived from historical data as a developmental of a nation progresses

• Nations tend to move towards industrialization: 

  • Change from agricultural to industrial economics 

  • Shown through 4 stages

  • Those in Stages 1-2 

    • Younger nations/populations usually have higher infant mortality 

    • Children are needed in the workforce

• Demographic transition is a model showing how a nation’s population, birth and death rate are historically correlated 

• Less developed countries are in the later part of stage 2, early part of stage 3, undergoing industrialization

• Under the demographic transition model, population starts growing slow, speeds up in the middle and ends with little to no growth.