Variation in population size

Variation in population size

1. Population size - number of individuals in a population

2. Population density - the number of individuals per unit area

3. Population growth - a change in the number of individuals

4. Population growth rate - the change in number of individuals per unit time

5. S-shaped population growth curves

   • the population growth curve of a population colonizing a new habitat in which conditions are intially ideal has an s shape
     • Phase 1; Slow growth
     • Phase 2; exponential growth
     • Phase 3; decelerating growth
     • Phase 4; population stabilizers

6. Enviromental factors that limit popualtion size

   • Density dependant factors - as the popualtion density increases, density-dependant factors affect a larger proportion of the population. they are usually biotic and include intraspecific competition for space and other resources, availability of food, disease, and preditation
   • Density-independant factors - these facotrs affect the same proportion of the population no matter how great its density. they are usually abiotic. the most important are weather and climate