D2.3 Changing Populations

Overgrowth in Human Populations Recall, sustainability is: the ability for a population (or ecosystem) to be maintained at a certain rate or level, by also ensures the availability of resources in the future. If a human population grows beyond its capacity, it will experience problems such as: overcrowding outbreaks in disease water, food and housing shortages pollution and waste accumulation

Overgrowth in Human Populations New Delhi, capital of India Ottawa, capital of Canada Pop India: 1,170,938,000 in 3,287,590 km² = 356 ppl/km2 vs. Pop Canada: 34,108,752 in 9,984,670 km² = 3.50 ppl/km2

Growth Rates The two main growth rate patterns are: Exponential growth Logistic Growth population growth at an increasingly rapid rate in proportion to the total population size. Logistic (or constant) growth population growth that is continuously growing and decreasing over time, as a result of balance within the population.

Growth Rates Bacteria are an example of a population that grows exponentially Bacteria are single-celled organisms that reproduce by splitting in two. the doubling time is the amount of time it takes for a population to double in size For bacteria that happens in one generation. For populations that DO NOT grow exponentially it takes considerably longer. 2  4 4 8

Growth Rates a population that experiences exponential growth will continue to grow at a faster and faster rate. for these populations, growth will continue until a limiting factor slows or stops the population’s expansion in the Ancient Rome example; limiting factors were disease, lack of clean water, food and shelter. for bacteria; limiting factors would be lack of food, increase in temperature and presence of toxin (antibiotics)

Please copy the completed graph into your notes Growth Rates a population that experiences exponential growth will continue to grow at a faster and faster rate. When exponential growth is graphed, the shape of the line is like the letter “J” thus, these graphs are also referred to as J-curves Please copy the completed graph into your notes

Factors that Support Exponential Growth species that are able to grow exponentially: have short life spans reproduce often produce numerous offspring do little to care for young

Factors that Support Exponential Growth exponential growth can only occur in some organisms, under ideal conditions most often seen in micro-organisms (e.g. bacteria) small animals (e.g. insects) certain plants (e.g. weeds)

Factors that Limit Exponential Growth Scarcity of resources, such as: food water living space / shelter availability of mates Predation Disease

Population Explosions & Crashes a population explosion is a sudden exponential growth in a population …so the explosions are usually followed a population crash: a rapid drop in population size most ecosystems cannot tolerate exponential population growth for very long… Please copy the completed graph into your notes This is generally due to the limiting factors in the ecosystem, acting on the population.

Factors affecting populations Most populations experience logistic growth, by definition, these populations fluctuate in size, in responses to environmental conditions: Factors that increase population size births immigration (movement into the population)

Factors affecting populations Most populations experience logistic growth, by definition, these populations fluctuate in size, in responses to environmental conditions: Factors that decrease population size deaths emigration (movement out of the population) If all four of these factors can occur in a population, it is called an open population. If conditions prevent immigration and emigration, the population is said to be closed

Equilibrium Carrying Capacity the carrying capacity of a population is the maximum number of individuals that can be sustained in an ecosystem While some populations will alternate between explosions and crashes, most will find an equilibrium

Carrying Capacity the curve for a population that is being limited by its carrying capacity is called an S-curve

Human Population Growth explosive growth of the human population is linked with advancements in agriculture, industry, science/medicine specifically the Industrial Revolution of the 18th century living conditions improve (better hygiene linked with higher education) death rate lowered due to advancements in medicine for most of its history, the human population has been stable or grown very slowly

Human Population Growth the 21st century is the first time in the world’s history that the elderly will out number the youth the carrying capacity of the Earth depends on: food and resource supply waste disposal pollution access to clean water distribution of populations

Human Population Growth The current population of the world is about 7,237,851,917 (~7 billion) growing at an annual rate of 1.7%, will add approximately 93 million people / year The carrying capacity of the Earth is estimated to be around ~12 billion If the human population growth continues at its current rate of growth, scientists estimate it will reach the earth’s carrying capacity in ~ 53 years Recall the term “sustainability” The human population is NOT currently growing in a sustainable way.

Human Population Growth Recall the term “sustainability” Will the the human population be an S-curve… …or a J-curve?

Assignment: PRACTICE PROBLEMS # 7, 8, 10 & 11 (pg 484) 18-22 (pg 485) 2.3 Summary Q. 5 (pg 487)