Transcript Populations
POPULATIONS Chapter 20 Lab Biology Chapter 26 Honors Biology Anticipatory Set: Count the number of dolphins in this picture… Does this represent a population of dolphins? PROPERTIES OF POPULATIONS Grp. Of organisms of the same species in a particular place at the same time. Population Size no. of individuals it contains (how do we measure it?) Population Density measures how crowded a population is (indiv. Per unit of area or volume) Dispersion spatial distribution of individuals within the population Clumped Even random POPULATION DISPERSION POPULATION DYNAMICS (CHANGE OVER TIME) Birth rate – no. of births occurring in a period of time Death rate – number of deaths in a period of time Life expectancy –how long on average an individual is expected to live Continue… Age Structure the distribution of individuals among different ages in a population Patterns of Mortality tends to conform to one of three curves on a graph called survivorship curves they show the likelihood of survival at different ages throughout the lifetime of the organism. POPULATION GROWTH RATE Growth rate the amount by which a population’s size changes in a given time This depends on 4 processes: Birth Death Emigration immigration FORMULAS FOR GROWTH RATE!! Loss… Birth rate – death rate = growth rate (per capita use 1,000) Gain… To find the no. of new indiv. That will be added to the population in a yr. Multiply the per capita growth rate by the no. of indiv. In the popul. EXPONENTIAL MODEL Exponential Model describes a population that increase rapidly after only a few generations Exponential Growth the larger the population gets the faster it grows PREDICTIONS BASED ON THE EXPONENTIAL MODEL View population growth over time Represented by a J – shaped curve LIMITATIONS OF THE EXPONENTIAL MODEL Exponential growth occurs only under rare conditions and for short periods of time Why: resource get depleted and waste builds up Limiting factor – a factor that restrains the growth of a population LOGISTIC MODEL A population growth builds on the exponential model but accounts for the influence of limiting factors Carrying capacity: the no. of indiv. The environment can support over a long period of time. Logistic growth ENVIRONMENTAL RESISTANCE Environmental resistance can be classified into two broad categories Density-independent factors Density-dependent factors POPULATION REGULATION 2 Kinds of limiting factors control population size: 1. Density-independent factors: limit populations regardless of their density Examples: climate, weather, floods, fires, pesticide use, pollutant release, and overhunting 2. Density-dependent factors: can cause birth rates to drop and/or death rates to increase Population growth slows resulting in an S-shaped growth curve (or S-curve) DENSITYINDEPENDENT FACTORS Some species have evolved means of limiting their losses Examples: seasonally migrating to a better climate or entering a period of dormancy when conditions deteriorate DENSITY-DEPENDENT FACTORS Density-dependent factors can cause birth rates to drop and/or death rates to increase Population growth slows resulting in an S-shaped growth curve (or S-curve) DENSITY-DEPENDENT FACTORS Carrying capacity is determined by the continuous availability of resources DENSITY-DEPENDENT FACTORS Include community interactions Predation Parasitism Competition HISTORY OF HUMAN POPULATION GROWTH 1. Development of Agriculture – “agricultural revolution” stabilized and increase available food supply 2. Population Explosion – 3. Population Growth today – - developed countries - developing countries