Lecture 17

  • Rapid environmental changes may lead to extinction - unless they can adapt
  • Great tits
  • Extremely resilient
  • Vulnerable species
  • Golden toad

Species likely to go Extinct

  • Endemic species (small geographic distribution)
  • Small populations (lack of genetic diversity)
  • Specific habitat requirements
  • Slow growth potential (slow maturation, few offspring, etc)

Extinction is a Natural Process

  • Extinction is forever
  • Humans profoundly affect rates of extinction
  • Are we in the 6th mass extinction?

Wildlife Decline Between 1970 and 2010

  • 76% freshwater species
  • 39% terrestrial species
  • 39% marine species
  • 52% overall decline in wildlife population

Species are Made up of Populations

  • Populations are individuals of same species

Population ecology

  • How populations interact with the environment
  • How population sizes change over time and space
  • Populations differ in their spatial distribution
  • Random, uniform, clumped

Population Dynamics

  • How pops change over time
  • Not enough to just count individuals - characteristics of individuals and species matter
  • Sex ratio: What is the ratio of males to females?
  • Age structure: What are the relative numbers of individuals of different ages?

Patterns of Age-specific Survival

  • At what age are you at greatest risk of dying?
  • For birds the risk of dying is the same at any age
  • Sturgeon, probability of dying decreases with age

Patterns of Age-specific Survival

  • Type 1 (older is more death)
  • Type 2 (same all ages)
  • Type 3 (younger has a higher chance of death)

Reproductive Patterns

  • How old are you when you reproduce for the first time? How often do you reproduce over life? How many at a time
  • Patterns of survivorship and reproduction are called life history patterns
  • Many classifications: one way is the r-K continuum

R-Selected Species

  • Small
  • Fast development
  • Short lived
  • Reproduce early in life
  • Many offspring
  • Fast pop growth
  • No parental care
  • Weak competitive ability
  • Variable pop size, often well below carrying cap
  • Unpredictable mortality

K-Selected Species

  • Big
  • Slow development
  • Long-lived
  • Reproduce later
  • Few large offspring
  • Parental care
  • Strong competitive
  • Less resilient to extinction
  • Knowing the life history patterns of a species; the sex ratio & age distro of a population allows you to predict the growth of the pop

Population Growth

Balance of 4 processes -

  • Natality - Births
  • Mortality - Deaths
  • Immigration - Arrival from outside
  • Emigration - Departure to outside

2 ways at looking at growth rate -

  • Per capita rate - (birth rate + immigration) - (mortality rate + Emigration rate) / pop size negative - shrinking population 0 - no change in size

Absolute rate -

  • Size of pop at a given time/size of pop in earlier time
  • < 1 - shrinking pop
  • 1 no change
  • > 1 growing

If the Per Capita Rate is Constant

  • Absolute rate will increase exponentially

Exponential Growth cannot be Sustained

  • Populations eventually run out of resources

Logistic Growth

  • Growth rate decreases as the population reaches carrying capacity

Carrying capacity can change depending on environment change

Carrying Capacity

  • Max pop size of a species that its environment can sustain



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