Populations What is a population Group of individuals

Populations

What is a population? Group of individuals of same species inhabiting an area

Population Characteristics 1. 2. 3. 4. 5. 6. • Natality Mortality Sex Ratio Age Distribution Population Density Spatial Distribution A population has all six of these characteristics, individuals do not

1. Natality • # of individuals added through reproduction Birth rate = __# born____ 1000 individuals Example: population size = 100, 000 # born = 1, 000 What is birth rate for this population?

2. Mortality • # of deaths per year Death rate = ___# die____ 1000 individuals What criterion must be met for population to grow?

Population Growth Example Birth rate = 25/1000 Death rate = 5/1000 Assuming an original population of 1000, what will this population’s size be in 5 years? 2009 data for U. S. : birth rate = 13. 5/1000 death rate = 8/1000

3. Sex Ratio • Relative # of males to females in a population • Usually close to 50/50 • Sex ratio does not apply to plants, earthworms and anything else that has both kinds of reproductive organs • Other anomalies: bees, more females- most are sterile. Deer more females than males, what is a good buck: doe ratio?

4. Age Distribution • # of individuals of each age in a population • cohort- all individuals of a same age in a population • For deer, we use hunting season to separate cohorts. Deer is 6 months old in December.

Age Distribution in Deer Fawn- 6 months old, typically do not reproduce 1 -1/2 2 -1/2 3 -1/2 4 -1/2 5 -1/2 If more individuals are pre or post-reproductive adults, population will not grow as fast

Age Distribution in Human Populations Fast Growth Slow Growth Zero Growth

5. Population Density • # of organisms per unit area Ex: Deer in Pennsylvania Seedling/sapling= 60 deer/sq. mile Pole timber= 10 deer/sq. mile Saw timber= 20 deer/sq. mile

How can we calculate deer population in Pennsylvania? 1. Count them (census) 2. Estimate (capture-mark-recapture) 3. Estimate using density– best for deer Example: N= population estimate m= # caught at time 1 t= # caught at time 2 p= # caught @ time 2 that were also caught @ time 1

6. Spatial Distribution • How organisms are arranged A. Random- not too common B. Uniform- unusual (each individual is a set distance apart) C. Clumped- Most common in nature

Population Growth Curves • Influenced by sex ratios and age distribution 4 Main Phases to Population Growth 1. Lag Phase- growth is slow 2. Exponential- Fast growth birth > death 3. Stable Equilibrium- birth = death 4. Death phase- death > birth

Carrying Capacity (k) • # of individuals of a species that can survive in an area 4 Factors that Impact Carrying Capacity 1. Availability of raw materials 2. Availability of energy 3. Accumulation of waste products 4. Interactions among organisms

Carrying Capacity • Remember, limiting factors: Density dependent vs. independent Ex: hare and lynx populations Cyclical, “boom and bust” What causes these fluctuations?

k-strategists • Type I Survivorship Curve • Examples: humans, bears • Larger animals, live longer, few offspring, much care for offspring, reproduce several times

r-strategists • Type III Survivorship curve • Ex: fish, insects • Smaller organisms, shorter lives, many offspring at one time, little or no care, maybe only reproduce 1 time, don’t reach k

Human Population Growth • Very long lag phase • Currently in exponential growth phase • Why?

What is Carrying Capacity for Humans? • Must consider limiting factors: 1. 2. 3. 4. Availability of raw materials Availability of energy Accumulation of waste products Interactions among organisms

Human Carrying Capacity • With all of our advancements in technology and medicine, why can’t we stabilize the global population?