1. Chapter 7 Population Concepts Population - a group of individuals of the same species occupying an area and capable of interacting with each other. Natality-# of individuals added to population through reproduction. “birthrate”—born per 1000 individuals per year Mortality -# of individuals removed from population through death. “deathrate”—die per 1000 individuals per year

2. Chapter 7 Ability of a population to grow is a function of: sex ratio:number of males to the number of females. age distribution: number of individuals in each “age bracket” –pre-reproductive age <15 –reproductive age 15-44 –post-reproductive age >44 -survivorship curves -population pyramids

3. Chapter 7 Population size influenced by dispersal –Movement from dense population to new areas emigration - outward migration –Pressure (competition) is typical reason individuals leave a population. –Typically juveniles leave, relieve overcrowding immigration - inward migration –Enter a population where pressure is less severe. –Bring genetic/cultural characteristics

4. Chapter 7 Population Growth Curve A population’s inherent reproductive capacity is called its biotic potential. –Plant versus animal Typically, biotic potential is higher than that need to simply replace the parents.  most (many) offspring die, with few surviving to be reproductive adults. Usually more than 2 survive.  population size grows.

5. Chapter 7 Growth is typically “exponential”, until a stable size is reached. Lag phase –It takes time for the first mating pairs to reach sexual maturity, mate, and produce offspring. Exponential growth phase –As more and more individuals mature, more offspring are produced. –Continues as long as birth rate exceeds death rate Stable equilibrium phase –Birth rates and death rates become equal. –Typically, death rate increases first. Often followed by a decrease in birth rate.

6. Chapter 7 Carrying Capacity –The number of individuals that can be supported in an area over time. Determined by environmental resistance. Limiting Factors –Key components to limiting size of population availability of raw material availability of energy accumulation of waste products (can result in “death phase”) interactions between individuals –If fix one, carrying capacity can increase, but new primary limiting factor emerges

7. Chapter 7 K-strategist Start 2/25/02 Have long lives, few offspring and provide much care for each offspring. –Usually large organisms Strategy:exert much energy into a few offspring that have a good chance of surviving. –Examples—lion, deer, human Limited by density-dependent factors. –Becomes more severe as size of population grows

8. Chapter 7 r-strategist Have short lives, many offspring and provide little or no care for the offspring. –Usually smaller organisms Strategy:If only a very small percentage of offspring survive, produce MANY offspring. –Examples: frogs, fish, dandelions –Oyster may produce millions only couple survive Typically limited by density-independent factors and do not reach carrying capacity. Changing weather Pond dries up Destruction of food source

9. Chapter 7 Human Population Growth Current rate of increase is 1.4%. Current population size is around 6 billion. –Very long lag time. –Explosive growth in last 200 years. –Currently in exponential growth phase Major reason for continuing increase is reduction in death rate –Method of reduction shared throughout the world No change in birth rate

10. Chapter 7 Environmental Resistance for Humans raw materials available energy waste disposal interactions with others We will, with absolute certainty, reach our carrying capacity. What that level is, nobody knows. Earth’s population will double again by 2050.