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POPULATION GROWTH What determines the size of a population and where a population can live? Available resources Land, food, Shelter, Predators, Competitors When these factors are ideal, populations thrive, when they are not, populations decline and can become endangered. Population graphs show how populations of organisms change over a period of time. What is different about the 2 population graphs below? GRAPH A: EXPONENTIAL GROWTH This shows a population of bacteria over a time period of 4 h. The bacteria reach a maximum population of4000 bacteria in 4 h. REGION DESCRIPTION REASON C OF GROWTH A Increasing Few animals so slowly reproduction is B slow B C Increasing at a More bacteria to faster rate reproduce Increasing Large numbers rapidly of bacteria reproducing (eg. 1000 reproduce 2000) A This is called EXPONENTIAL GROWTH. The bacteria appear to be growing rapidly and do not seem to be limited by resources. However, most ecosystems have limited resources and therefore, it is not possible for populations to grow exponentially forever. Graph B: LOGISTIC GROWTH This shows a population of water fleas over a time period of 160 days. The water fleas reach a maximum population of 135 fleas in 90 days and maintain this population. C B A REGION GROWTH A Few organisms reproducing slow growth B More organisms reproducing rapid growth C # Organisms born = # organisms dying stable (no increase or decrease in population) This is known as a balance or equilibrium. A population will remain stable but fluctuate slightly at C, the CARRYING CAPACITY the number of organisms that an ecosystem can support (without causing harm to the environment) A population will remain stable but fluctuate slightly at the CARRYING CAPACITY. LIMITING FACTORS Factors that place an upper limit to the size of a population. They can be abiotic or biotic. FOOD, SPACE and other important resources (sunlight, water, nutrients in the soil) DECREASE because they are shared between more organisms increases death rate decreases population. COMPETITION between organisms with the same niche increases increases death rate decreases population. PREDATION increases because it becomes easier to hunt and catch prey increases death rate decreases population. DISEASE spreads more easily in crowded environments.