Biology test prep

• Rural areas to cities

  Cities have more dense populations, while rural areas have more widely dispersed, or scattered, populations
• Population density

  The number of individuals living in a defined space
• Changes in population density over time

  Studying whether causes are due to environmental changes or natural variations in the life history of the species
• Using population data

  Deciding whether it is necessary to make changes to maintain a healthy population
• Clumped dispersion occurs when resources are spread unevenly within an ecosystem
• Clumped dispersion helps protect individuals from predators and makes finding a mate easier
• Uniform dispersion occurs when individuals of the same species must compete for limited resources and territory
• Random dispersion is the least common pattern of distribution
• Random dispersion occurs when resources are evenly distributed within an ecosystem
• Quadrat sampling is a method used by ecologists to collect data about population numbers in an ecosystem using square or rectangular grids of a known size
• Quadrat sampling works best with species that do not move, such as plants and corals
• The mark-recapture technique is a method used to measure the size of a population of animals by capturing, tagging, and releasing individuals, then recapturing and counting tagged individuals as well as any newly captured animals
• Biologists may fit animals with radio collars or GPS devices to track their movements
• Locker ecosystem


  • Apple left in locker over winter break leading to a cloud of fruit flies
• When left, the fly population in the locker was zero, but upon return, it was at least 100
• Changes in population sizes and densities in ecosystems are normal responses to changes in resource availability
• Tracking population size of a species like elephants

  Accounting for immigration, emigration, births, and deaths
• Immigration and emigration

  Individuals entering and leaving a population
• Disturbance in a nearby habitat

  Some elephants might immigrate to a new population, while others might emigrate to a new area due to increased competition
• Births and deaths


  Change a population size over time
• Growth rate of a population can be measured with the equation: r= (b + i) - (d + e)
• In the equation, r= population growth rate, b = birth rate, i = immigration rate, d = death rate, and e = emigration rate
• Application of population growth factors to locker ecosystem example

  Immigration of fruit flies, birth of new flies, emigration of flies that were swatted and thrown away
• Reproductive strategies


  • Behaviors that improve chances of producing offspring or increase survivorship rate of offspring after birth
• Reproductive strategies


  • Parental care
• Parental care


  • Important for species with offspring that cannot take care of themselves, helps ensure young stay alive until they can survive on their own
• Assessment of a population's reproductive strategies

  Using a survivorship curve
• Survivorship curve

  • A simplified diagram showing the number of surviving individuals over time from a measured set of births, gives information about the life history of a species
• Type I survivorship curve

  • Mammals and other large animals
• Type III survivorship curve

  • Many invertebrates, fish, and plants
• Some species have a small number of offspring, and many of the offspring live long enough to reach old age
• Type I survivorship curve

  Mammals and other large animals generally exhibit this curve where many offspring survive to old age
• Type III survivorship curve

  Many invertebrates, fish, and plants exhibit this curve where many offspring do not survive long enough to reproduce
• Species exhibiting Type III survivorship

  • Fish
• Type II survivorship curve

  Organisms such as birds, small mammals, and some reptiles exhibit this curve where survivorship rate is roughly equal at all stages of life
• Exponential Growth


  Population growth that occurs rapidly in ideal conditions of available resources, space, and other factors
• Exponential growth occurs when a population size increases dramatically over a relatively short amount of time
• Exponential growth is represented by a J-shaped curve on a graph
• Real-world example of exponential growth occurred in 1859 when an Australian landowner introduced 24 rabbits into the country, leading to a population explosion
• Logistic Growth occurs when a population faces limited resources and shows a pattern of slow growth, followed by exponential growth, before leveling off at a stable size