Models of Population Growth Chapter 8

Carrying Capacity Carrying capacity (K) is the number of individuals that can be sustained in a given space.

Growth Curves Two population growth curves: J-shaped (exponential) S-shaped (logistic)

Unlimited Growth Model Unlimited resources. Not realistic due to carrying capacity. J

Density-dependent Growth Model Resources become more and more limiting. S

Environmental resistance Carrying capacity (K) Population size (N) Biotic potential Exponential growth Time (t)

Logistic Growth Model Population growth is SLOWED by limiting factors: Density-dependent Density-independent

Density-Dependent Factors Factors include: Competition, Predation, Disease

Pause and Think What’s going on here? Exponential increase in population size (number of bacteria). Doubling every 20 min. This assumes resources are unlimited. J-shaped curve – unrealistic due to carrying capacity

Pause and Think What’s going on here? P. aurelia and P. caudatum both show exponential growth early on, then their growth slows down. Resources are becoming more and more limited, which in turn affects growth. Carrying capacity is reached. In a mixed culture, P. aurelia becomes a dominating species after 5 days. The growth of P. caudatum declines at this time. P. aurelia must be a better competitor for resources.

Predator-Prey Cycles Low # predators = high # prey As # prey increase, # predators increases High # predators = low # prey As # prey decrease, # predators decrease

Which population peaks first in each cycle — Think-Pair-Share Which population peaks first in each cycle — predator or prey? Why?

Population Curves in Nature

What is happening to the populations? Think-Pair-Share What is happening to the populations?

How/why did this lead to a population explosion? Activity 1 How/why did this lead to a population explosion? Industrial Revolution (1800)

How did this lead to a population decline? Activity 2 How did this lead to a population decline? WWII (1939-1945)

How did this lead to a population increase? Medicine and Sanitation Activity 3 How did this lead to a population increase? Medicine and Sanitation

Pause and Think What’s going on here?

Reproductive Strategies Organisms can be divided into two categories of "strategies" for reproduction and survival: r–strategist species K–strategist species © Brooks/Cole Publishing Company / ITP

r–strategist species r–strategist species tend to live in environments where resources are not limiting. Such species tend to have high intrinsic rates of growth (high r).

‘Quick and Many’ r-selected species are short-lived and produce very large numbers of offspring. r-selection is directed to quantity of offspring (they put most of their energy into numbers). The letter ‘r’ comes from the equation for population growth where r = rate of increase per generation.

K–strategist species K–strategist species tend to do well in competitive conditions and live in environments where resources are limiting. They tend to have lower intrinsic rates of growth and characteristics that enable them to live near their carry capacity (population size near K).

‘Slow and Few’ K-selected species produce small numbers of offspring at less frequent intervals In general, K-selection is for quality of offspring (they put most of their energy into development). The letter ‘K’ comes from the equation for population growth where K = carrying capacity of a habitat.

Carrying capacity K K species; experience K selection Number of individuals r species; experience r selection Time

Revisual

Revisual

Revisual

Characteristics of r–Strategist Species © Brooks/Cole Publishing Company / ITP

Characteristics of K–Strategist Species Fig. 10–7b © Brooks/Cole Publishing Company / ITP

Biozone 146 – Factors Affecting Population Size 147 – Calculating Change in Population Size