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Population Dynamics


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Population Dynamics

  1. 1. Natural Resources Population Dynamics
  2. 2. Carrying Capacity <ul><li>The supportable population of an organism, given the food, habitat, water and other necessities available within an environment </li></ul><ul><li>Biological capacity: what the environment can support </li></ul><ul><li>Cultural capacity: what people are willing to tolerate </li></ul>
  3. 3. Population Dynamics <ul><li>The study of the changes in the number and composition of individuals in a population and the factors that influence those changes </li></ul><ul><li>Needed for </li></ul><ul><ul><li>Harvest limits </li></ul></ul><ul><ul><li>Environmental impacts </li></ul></ul><ul><ul><li>Predicting endangerment </li></ul></ul><ul><ul><li>Interpopulation impacts </li></ul></ul><ul><ul><li>Indicate environmental quality </li></ul></ul><ul><li>Populations are always “dynamic”. They never stop changing . </li></ul>
  4. 4. Bobwhite Quail <ul><li>Bobwhites populations have experienced severe declines over the last 50 years </li></ul><ul><li>The primary reason is loss of agricultural areas as habitat. </li></ul><ul><li>Bobwhites do not survive well in woodlands </li></ul><ul><li>Quail need early succession habitat for nesting cover and brood range </li></ul><ul><li>Other bird species that are dependent on grasslands and shrub habitats have declined at similar rates. </li></ul><ul><ul><li>Henslow’s, grasshopper, and field sparrow </li></ul></ul><ul><ul><li>brown thrasher </li></ul></ul><ul><ul><li>yellowbreasted chat. </li></ul></ul>
  5. 5. Quail Population Changes <ul><li>Wildlife biologists track population dynamics for species of concern </li></ul><ul><li>Count by calls </li></ul><ul><li>Rural mail carriers </li></ul>
  6. 6. Factors causing population change <ul><li>Density: The number of animals per unit area (usually a hectare or sq kilometer) </li></ul><ul><li>Density Dependant </li></ul><ul><ul><li>As the density increases the amount of resources per animal decreases and the health of individuals decreases </li></ul></ul><ul><li>Density Independent </li></ul><ul><ul><li>Act on a population independent of the population size </li></ul></ul><ul><ul><li>Weather </li></ul></ul><ul><ul><li>Environmental catastrophe </li></ul></ul>
  7. 7. Birth rates <ul><li>Natality : # individuals born per unit of time </li></ul><ul><li>Fecundity : # young produced per female per unit of time </li></ul><ul><li>Factors affecting: </li></ul><ul><ul><li>Amount & quality of food </li></ul></ul><ul><ul><li>Age at first reproduction </li></ul></ul><ul><ul><li>Birth interval </li></ul></ul><ul><ul><li># young per birthing </li></ul></ul>
  8. 8. Population growth as a function of fecundity rate <ul><li>Assumes equal numbers male & female </li></ul><ul><li>1 litter per year </li></ul><ul><li>Age at sexual maturity 1 year </li></ul><ul><li>Logarithmic growth for unchecked populations </li></ul>
  9. 9. Quail Habitat <ul><li>Quail have low fecundity & natality rates </li></ul><ul><li>Need edge habitat with brood-rearing cover </li></ul><ul><li>Need overhead cover, but low density at the ground so chicks can move </li></ul><ul><li>Need lots of insects </li></ul><ul><li>Fescue fields are too dense at the ground </li></ul>
  10. 10. Mortality Rate <ul><li># animals that die per year divided by the # animals alive at the start of the year </li></ul><ul><li>Survival rate is the inverse </li></ul><ul><li>Longevity is the age at death. </li></ul><ul><li>Usually age & frequently sex related </li></ul><ul><li>Old & young die at higher rates </li></ul><ul><li>Males die at higher rates </li></ul><ul><li>Birds are exceptions – odds of surviving each year are about the same after they leave the nest </li></ul>
  11. 11. Bobwhite Quail Mortality <ul><li>Radio tracked birds used for study </li></ul><ul><li>Easy way to find out when & how they died </li></ul><ul><li>20% survival rate (annual) </li></ul>
  12. 12. Dispersal <ul><li>When animals leave the area where they are born and move to a new area where they reproduce. </li></ul><ul><li>Hard to measure scientifically </li></ul><ul><li>Male young often disperse at sexual maturity </li></ul><ul><li>Animals may disperse due to low resources and overcrowding </li></ul>
  13. 13. Age structure <ul><li>Divide into age classes, based on ability to reproduce. </li></ul><ul><ul><li>Juvenile </li></ul></ul><ul><ul><li>Subadult </li></ul></ul><ul><ul><li>Adult </li></ul></ul>
  14. 14. Sex ratio & mating <ul><li>Monogamous species have slower growth rates. Need 50:50 ratio to maintain growth rates </li></ul><ul><li>Polygamous species </li></ul><ul><ul><li>1 male : 4 females will produce 1.6X as many young as a 1:1 ratio. </li></ul></ul><ul><ul><li>4 males : 1 female will only produce 40% as many young </li></ul></ul><ul><ul><li>Hunter resistance to taking females can lead to a skewed sex ratio where there are not enough males to breed all of the females. Results in late season birth and increased mortality </li></ul></ul>
  15. 15. Limitations on resources <ul><li>Carrying capacity (K) </li></ul><ul><li>Density dependent breaking mechanism to the exponential growth equation </li></ul>
  16. 16. Survival strategies <ul><li>K - selected </li></ul><ul><li>Most endangered species </li></ul><ul><li>Low reproductive rates </li></ul><ul><li>Slow population growth rates </li></ul><ul><li>Low juvenile mortality </li></ul><ul><li>Long lives </li></ul><ul><li>Slow dispersal </li></ul><ul><li>Larger body size </li></ul><ul><li>r – selected </li></ul><ul><li>Adapt to change rapidly </li></ul><ul><li>High population growth rates </li></ul><ul><li>High mortality of young </li></ul><ul><li>Rapid dispersal </li></ul><ul><li>Short life spans </li></ul><ul><li>Most pest species </li></ul>
  17. 17. Source & sink population theory <ul><li>A model to describe how habitat quality and dispersal effect wildlife populations </li></ul><ul><ul><li>Source areas have high quality habitat and positive population growth </li></ul></ul><ul><ul><li>Sink areas have low quality habitat and negative population growth </li></ul></ul><ul><ul><li>Sink area populations are not eliminated because of proximity to source areas. </li></ul></ul>