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5-2 Limits to Growth Limiting Factors • Remember, primary productivity of an ecosystem can be reduced by limiting nutrients • Limiting factors can determine carry capacity – Density Dependent Factors – Density Independent Factors 1. Density-Dependant Factors • Limiting factors that depend on population size • Density-dependent factors become limiting only when population density reaches a certain level • Does not affect small, scattered populations 1a. Competition • Occurs when populations become crowded • When 2 species compete for same resource, they are under pressure to change – Over time, evolve to occupy diff. niches 1b. Predation • Populations in nature are controlled by predation – Known as predator-prey relationship • Isle Royale in Lake Superior 1c & 1d Parasitism & Disease • Parasites are similar to predators – weaken and kill hosts • Large populations can be under stress making them more susceptible to diseases • More members = easier to pass “things” around 3. Density-Independent Factors • Factors that affect populations regardless of their size • Examples: – Unusual weather (Draught, Hurricanes) – Season cycles – Human activities (damming rivers, forest cutting) 5-3 Human Population Growth • Like the populations of many other living organisms, the size of the human population tends to increase with time. • For most of human existence, the population grew slowly • Until fairly recently, only half the children in the world survived to adulthood. • What caused human populations to suddenly grow rapidly? • Agriculture • Industry/Medicine • About 500 years ago, the human population began growing more rapidly because of agriculture and industry. • With these advances, the human population experienced exponential growth Patterns of Population Growth • English economist Thomas Malthus observed that human populations were growing rapidly. • Malthus predicted that such growth would not continue indefinitely. • Malthus- war, famine, and disease would limit human population growth. Demographic Transition • The scientific study of human populations is called demography • Demographic transition, a dramatic change in birth and death rates. • Ex: U.S., Japan, Europe What are the 4 densitydependent limiting factors? • • • • Predation Disease Competition Parasitism What are examples density independent limiting factors? • Storms • Natural Disasters • Human activity What caused the human population to grow rapidly? • Agriculture • Industry • Medicine