POPULATION ECOLOGY CH 53 Study of the growth, abundance and distribution of populations

I. POPULATION ABUNDANCE AND DISTRIBUTION A. Population size and density Population size = N = Total number of individuals in the population Population Density = Number of individuals per unit area

Calculating population size: Mark recapture method Capture and tag a population then release it Recapture a population a count number tagged N-= population size m = #captured and tagged n = #second capture x = #tagged in 2nd capture x/n = m/N

B. Population dispersion: how is the population dispersed in an area Clumped is often due to availability of resources or social behavior

Uniform is often due to territoriality Random dispersion is due to no real interaction between members

Age structure The abundance of individuals of each age Pyramid shaped curves indicate a rapidly growing population Rectangular shaped curves indicate a stable population

Survivorship curves Describes the mortality of individuals during their lifetime Type I species: most survive to middle age or older tend to be large mammals that produce few offspring but provide a lot of care

Type II species: length of survival is random. Equal likelihood of death at any age example rodents Type III species: most of the individuals die young Tend to be organisms that produce a lot of offspring with very little care example oysters

II. POPULATION GROWTH Population growth rate 1. exponential growth: Maximum growth rate of a species under IDEAL conditions dN/dt = r max N Results in J shaped curve R max = biotic potential

Factors that affect the r max of a species Age at which they reproduce Average # offspring produced in each breed How frequently they reproduce How long they can reproduce How many offspring survive to reproduce Greater r max fly or elephant?

2. Logistic Growth Exponential growth is often seen in very small, newly established populations but can’t be sustained for long As the population reaches the carrying capacity of the environment, growth decreases and approaches zero

Represented by the following formula: dN/dT = r max N(K-N/K) K = carrying capacity (maximum # individuals environment can support) N= #individuals K-N = #of new individuals the environment can support K-N/K = fraction of K that is still available for population growth

The smaller N is the closer K- N/K is to 1 and the growth rate approaches the maximum rate (exponential) The larger N is the closer K-N/K is to zero and the closer the growth rate approaches zero What happens if N>K?

Carrying capacity: the maximum number of individuals of a population that the environment can support Some populations overshoot carrying capacity before stabilizing at a certain density Some populations fluctuate greatly

Factors that limit the carrying capacity and biotic potential of a population Parasites and disease Resources Toxic effects of waste Stress of too many individuals inhibits reproduction predators These are density dependent. What does that mean?

III. REPRODUCTIVE PATTERNS ARE THE RESULT OF NATURAL SELECTION Any trait that would enhance an organism’s chances to survive and reproduce is favorable However, there are tradeoffs between survival and reproduction Reproduction requires an investment of energy

The greater the chance of survival, the more energy can be invested in reproduction o Species whose young have a high rate of survival like primates tend to produce few larger young and invest energy in their care

The lower the chance of survival the less energy will be invested in reproduction o Species whose young have a lower chance of survival, like insects, produce a lot of smaller young and don’t invest energy in their care

reproductive strategies can be k- selected or r-selected K-selected strategies Tend to operate in a stable environment and is under the influence of density dependent factors Selects for traits that are sensitive to population density

Organisms that are extreme k- strategists tend to have the following reproductive characteristics : o Fewer larger offspring o Lots of parental care o Slower maturity o Often reproduce more than once o Most offspring survive to reproduce Because most offspring survive they can invest a lot of energy in their young

R-selected strategies Tend to operate in an unstable environment and subject to density independent factors Select for traits that maximize reproduction

Characteristics of r-strategists : o many small offspring o little or no parental care o early reproductive age o often reproduce only once o most offspring die before they reproduce because survival of offspring is low they tend to invest little energy in their young