Chapter 53

• Population ecology is the study of populations in relation to their environment
• Populations evolve as natural selection acts on heritable traits that vary among individuals, resulting in a change in allele frequency over time.
• Population is a group of individuals of a single species living in the same general area.
• Density is the number of individuals per unit area or volume.
• Dispersion is the pattern of spacing among individuals within the boundaries of the population.
• Demography is the study of population characteristics such as birth, death, and migration rates, and how they change over time.
• A life table is used to summarize survival and reproductive rates of individuals in a specific age group within a population.
• A cohort is a group of individuals of the same age.
• Survivorship curve is a graphical way of representing survival rate data from a life table.
• What dispersion pattern does the picture show?

  Clumped

  A) Clumped

  
• What dispersion pattern does the picture show?

  A) Uniform

  
• What dispersion pattern does the picture show?

  Random

  A) Random

  
• Type I Survivorship Curve

  • fairly low death rates when young
  • death rates increase dramatically with older age
• Type III Survivorship Curve wip

  • high death rates when young
• Type II Survivorship Curve

  • common prey species for larger organisms
  • ex: rabbits
• All populations have the potential to expand exponentially. (Darwin observation)
• Plentiful food availability and access to reproductive opportunities are conditions that you might expect to see exponential growth in a population.
• If immigration and emigration are ignored, the change in population size equals births minus deaths
• Carrying capacity (K) is the maximum population size that a particular environment can sustain.
• Carrying capacity varies over space and time with the availability of limited resources.
• Crowding and resource limitation can influence the birth rate and the death rate in a population.
• Natural selection favors traits that improve an organism’s chances of surviving and reproducing.
• Trade-offs between survival and reproductive traits.
• Life history traits are traits that affect an organism’s schedule of reproduction and survival.
• Age at first reproduction

  loggerhead turtle (30 years)

  coho salmon (3-4 years)
• Iteroparity

  • repeated reproduction
  • example: loggerhead turtle, many birds and mammals, fish, trees, etc.
• Semelparity

  • a “one-shot” pattern or reproduction, reproduces once in a lifetime
  • examples: coho salmon, agave
• Agave is an example of semelparity.
• Bur oak is an example of iteroparity.
• Many parasites produce large numbers of offspring. This adaptation ensures that some will survive their complicated life cycle.
• K-selection (density-dependent selection)

  • selects for life history traits that are advantageous when density is high
  • common in long-lived species in a stable environment (i.e. hardwood forest trees, large mammals
• r-selection (density-independent selection)

  • selects for life history traits that maximize reproduction when density is low and there is little competition
  • common in short-lived species in disturbed habitats (i.e. weedy species, many insects
• From the logistic growth equation, K is carrying capacity, and r is the

  intrinsic rate of increase.
• In density-independent populations, birth rate and death rate do not change with population density.
• In density-dependent populations, birth rates fall and death rates rise

  with population density
• The effects of parental care in Eurasian Kestrels over 5 years. Researchers transferred chicks between nests to produce reduced broods (3-4 chicks), normal broods (5-6 chicks), and enlarged broods (7-8 chicks).

  A) Density-independent death rate (m)

  B) Density-dependent birth rate (b)
• Reproductive strategies among plants

  1. producing a large number of small seeds, ensuring that at least some of them will grow and eventually reproduce (ex. dandelion)
  2. produce a moderate number of large seeds that provide a large store of energy that will help seedlings become established (ex. brazil nut tree)
• Brood parasites lay their eggs in other bird nests.
• Mechanisms of Density-Dependent Regulation

  • competition for resources
  • territoriality
  • disease
  • intrinsic factors
  • toxic wastes
• Some populations undergo regular boom-and-bust cycles.