Properties of Populations Density: The number of individuals per unit area or volume
Properties of Populations Dispersion: Is the relative distribution or arrangement of individuals within a given amount of space
Dispersion Pattern Clumped – Organisms are aggregated in patches – Most Common – Associated with uneven food distribution Uniform – Organisms are evenly dispersed – Plants Random – VERY VERY Rare in nature
Sex Ratio Def: Proportion of Males to Females A 50/50 Ratio maximizes population growth An uneven ratio leads to negative population growth
REMEMBER THIS??? Developing Countries – Lower average incomes – Simple and agricultural based economies – Rapid population growth Developed Countries – Higher average incomes – Slow population growth – Diverse, industrial economies
Age Structure Def- the distribution of ages in a specific population at a certain time. Is shown visually in Population Pyramids
#2.2 Aim: How do we describe populations? Agenda QOD (5) Lesson: populations (15) Activity: (15) Summary (5) HW #9 5. Age structure – relative #’s of organisms of each age within a population Mostly younger organisms positive growth Even age distribution stable population Mostly older organisms negative growth Age (years)
Population Pyramids A double-sided bar graph Ex: Countries that have high rates of growth usually have more younger people than older people
Age Structure Cont. Mostly Younger: Positive Growth Even Age: Stable Population Mostly Older: Negative Growth
Survivorship Def: The percentage of members of a group that are likely to survive to any given age. Used as a way to predict population trends.
Survivorship Curves TYPE I: Most people live to be very old TYPE II: Similar death rates at all ages TYPE III: Many children die
Fertility Rates Def: The number of babies born each year per 1,000 women in a population Total fertility rate: The average number of children a women gives birth to in her lifetime.
Imagine a population with positive growth… 1. Describe the size, density, distribution, sex ratio, age structure, and birth/death rates of your population. 2. Work in pairs to make a mini-poster showing a picture and a diagram of either the age structure or the survivorship type. For example…
#2.2 Aim: How do we describe populations? Agenda QOD (5) Lesson: populations (15) Activity: (15) Summary (5) HW #9 Example: Subway rats Size: about 1,000 organisms and increasing (positive growth) Density: medium (not high or low). Not a lot of competition for resources, not too hard to find mates. Distribution: clumped. The rats like to be near the stations where they find more food. Sex ratios: even. Since there are just about as many males as females, the population is increasing at a rapid rate. Age structure: mostly young. Since most of the rats in the population are in their reproductive prime years, the population is increasing at a rapid rate. Birth and death rates: The birth rate is higher than the death rate. The rats have Type 1 survivorship where they don’t usually die until old age.
#2.2 Aim: How do we describe populations? Agenda QOD (5) Lesson: populations (15) Activity: (15) Summary (5) HW #9 Example: Subway rats Rats have Type 1 survivorship
Direct Counting – Method to estimate the size and density of population – Impractical due to size of ecosystem, the number of plants involved, and the movement of animals
Sampling Technique A more practical way Enables us to estimate the total population size of the organism 1: Quadrat Sample Method 2: Mark and Recapture Sampling
The Quadrat Sample Used for estimating the size of plant population and immobile animals A quadrat: A wooden frame which forms a square of a known area (1 m 2 ). Placed randomly in a population where sampling is carried out.
Quadrat Sampling Used to find DENSITY: The mean number of organisms per unit area.
Quadrat Sampling Used to find PERCENT COVERAGE: an indication of how much the area of quadrat is occupied by a species.
The Capture, Mark, Release, and Recapture Technique Used to estimate mobile animals Procedure: – First Capture: A random sample of animals is selected. – Mark: Each animal is marked in a distinctive way – Release: The marked animals are released back into nature – 2 nd Capture: Only a proportion of the 2 nd capture sample will have animals that were marked in the 1 st capture.