POPULATIONS AND HOW THEY GROW

1. POPULATIONS AND HOW THEY GROW

2. Biosphere • Ecosystems • Community • Population ECOSYSTEM LEVELEucalyptus forest COMMUNITY LEVELAll organisms ineucalyptus forest POPULATION LEVELGroup of flying foxes ORGANISM LEVELFlying fox Brain Spinal cord ORGAN SYSTEM LEVELNervous system ORGAN LEVELBrain Nerve TISSUE LEVELNervous tissue CELLULAR LEVELNerve cell MOLECULAR LEVELMolecule of DNA Figure 1.1

3. Population-all of the individuals of a species that live together in one place at one time. Demography-the statistical study of populations. It is used to predict how the size of a population will change. POPULATIONS

4. direct observation-count indirect observation-estimate sampling-count small number in a small area and multiply to get the number in the large area mark and recapture studies-capture, mark, release Counting Populations

5. mark-recapture method depends on likelihood of recapturing the same individual Figure 35.2A

6. 1. Population size • is the number of individuals in a population. • had an important effect on the ability of the population to survive. A small population is more likely to become extinct: • in the case of random events or natural disaster • due to inbreeding where the population is more genetically alike. • with reduced variability it is harder to adapt to changes. KEY FEATURES OF POPULATIONS

7. 2. Population density – the number of individuals in a given area. – if they are too far apart they may only rarely encounter one another resulting in little reproduction. KEY FEATURES OF POPULATIONS, con’t

8. KEY FEATURES OF POPULATIONS, con’tPopulation size is limited by: density-dependent factors • Disease • Competition • Predators • Parasites • Food • Crowding • The greater the population, the greater effect these factors have. • Ex. Black plague in the Middle Ages – more deaths in cities density-independent factors • Volcanic eruptions • Temperature • Storms • Floods • Drought • Chemical pesticides • Major habitat disruption (as in the New Orleans flooding) • Most are abiotic factors

9. 3. Dispersion – the way in which the individuals are arranged. KEY FEATURES OF POPULATIONS, con’t Most common

10. Population Growth • Population Growth • Three factors can affect population size: • number of births (natality) • the number of deaths (mortality) • the number of individuals that enter or leave the population (immigration and emigration). * Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it

11. Immigration & Emmigration • Immigration • the movement of individuals into an area, is another factor that can cause a population to grow. • Emigration • the movement of individuals out of an area, can cause a population to decrease in size.

12. Nearly all populations will tend to grow exponentially as long as there are resources available. Two of the most basic factors that affect the rate of population growth are the birth rate, and the death rate. r(rate of growth)=birth rate – death rate PREDICTING POPULATION GROWTH, con’t

13. PREDICTING POPULATION GROWTH, con’t • Exponential growth curve: population growth plotted against time. • As a population gets larger, it also grows at a faster rate. • Maximum population growth under ideal circumstances. • Includes plenty of room, unlimited resources (food, water) and no predators. FACT: No population exhibits this type of growth for long.

14. Logistic model: This model accounts for the declining resources available to populations as they grow. It assumes the birth and death rates are not constant. As the population grows, births decline and death rises. Eventually birth=death so the population stops growing. Carrying capacity (K): The number of organisms of one species that an environment can support indefinitely. PREDICTING POPULATION GROWTH, con’t

15. PREDICTING POPULATION GROWTH, con’tTwo modes of population growth. The Exponential curve (also known as a J-curve) occurs when there is no limit to population size. The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the environment).

16. There are 2 ways a population can prosper: • Depends on the rate of growth (r) • Influenced by the carrying capacity (K) POPULATION GROWTH STRATEGIES

17. r-strategists: “boom and crash” characterized by exponential growth, which results in temporarily large populations, followed by sudden crashes in population size. Ex. Insects, bacteria, some plants • live in unpredictable and rapidly changing environments • Reproduce quickly when conditions are favorable • Many offspring: small, mature rapidly, no parental care • r= rate of growth POPULATION GROWTH STRATEGIES, con’t

18. K-strategists: characterized by a high degree of specialization. Ex. Trees, whales, tigers, etc. • Live in stable and predictable environments • Can compete effectively • Reproduce late in life • Few offspring: large, mature slowly, often much parental care • K = carrying capacity POPULATION GROWTH STRATEGIES, con’t

19. Human Populations: K- strategist characteristics But, recently, humans learned to expand carrying capacity of environment by increasing food supply, combating pests and curing diseases. Can Earth support this increase? POPULATION GROWTH STRATEGIES, con’t

20. THE HUMAN POPULATION • doubled three times in the last three centuries • about 7 billion and may reach 9.3 billion by the year 2050 • improved health and technology have lowered death rates

21. The history of human population growth Figure 35.8A

22. Will Earth Sustain All Life? Figure 2.10x