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3DE_The_Human_Animal - The Human Animal The Population...

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Unformatted text preview: The Human Animal The Population Dynamics and Population Sustainability Sustainability Milt Saier Dept Molecular Biology UCSD Factors that Limit Population Growth Growth Density-dependent Factors Predation Disease/ Parasites Food Supply Water Supply Social Mechanisms Density-independent Factors Temperature Weather Natural Disasters Natural Man-created Global Environmental Disasters Exponential Growth Exponential Occurs when organisms are Occurs density-independent. density-independent. Birth rate exceeds death rate. Both rates are constant. Both Both rates are proportional to the Both numbers of individuals present. numbers CAN THIS CONTINUE INDEFINITELY? Only as long as r is constant! as Mathematical requirements: Mathematical r=0, N does not change r>0, N increases without limit r<0, N decreases to 0 Exponential Growth in Nature Exponential Documented for: Documented Bacteria, yeast, insects, mice, humans, etc. Bacteria, However… However… Exponential growth can NEVER be sustained Exponential indefinitely. indefinitely. Populations are eventually limited by densityindependent factors if not by density-dependent independent factors. Population Dynamics Population The life span, number of offspring per adult, The and mortality rate at each stage of life affect the growth rate of a population. the Mortality Curves: Three Types: Type I: Organisms have few young and usually die Type of old age. of Type II: All organisms have an equal chance of Type dying throughout their lives. dying Type III: High mortality when young; the few Type adults that survive have relatively long life spans. adults Survivorship Curves Survivorship r-Strategists r-Strategists Many offspring Early maturity Short lifespan Reproduce once Small organisms Precocial young Little to no parental Little investment investment Type III survivorship Type pattern pattern K-Strategists K-Strategists Few offspring Later maturity Longer lifespan Reproduce more than Reproduce once in a lifetime once Larger organisms Altricial young Much energy is Much invested in raising young young Type I (or II) Type survivorship pattern survivorship What factors determine the survival pattern of K-strategists ? pattern Because of long life span, K-strategists have the Because opportunity to overexploit resources if limits are removed. Population growth is determined by: Population Reproductive rate, Reproductive Density of the previous generation, and Availability of resources, e.g., the food supply. If resources in the habitat are consumed faster than If the rate of replenishment, the population ALWAYS experiences an eventual crash. experiences Reindeer of St. Matthew Island Reindeer Reindeer were introduced on an island with no predators. The population grew exponentially. When the herd outstripped available resources, the population When crashed. crashed. Sustainable, K-strategist population oscillations were observed until the Sustainable, agricultural revolution (about 8000 BC; pop’n < one million). agricultural Then, with agriculture, the first increase of numbers occurred (pop’n at Then, 1 AD ~ 100 million; doubling time > 1000 yrs). AD The second increase resulted from the industrial/scientific revolution. We are still in near exponential growth (pop’n now at 7.0 billion; We doubling time ~ 30 yrs). doubling Overpopulation, Carrying Capacity, and Time Lags Time Humans (K-strategists) are designed to produce few Humans young on which they must lavish exceptional care for survival. survival. Now, worldwide, we produce lots of young Now, (250,000/day - births over deaths). (250,000/day While we have increased our carrying capacity with While technology, we have also increased our impact on the environment. environment. All K-strategist populations experience time lags: All exponentially growing populations overshoot their carrying capacity before experiencing population losses. losses. Promises of the Green Revolution of the 60s the Eliminate hunger and need. Increase the Earth’s carrying capacity. Increase productivity and yields. Increase technological knowledge. Distribute food and other necessities throughout the Distribute globe. globe. Indefinite prosperity for all!!! Indefinite THESE PROMISES WERE REASONABLE REASONABLE EXCEPT THAT THEY DIDN’T TAKE INTO ACCOUNT HUMAN POPULATION GROWTH, RESOUCE DEPLETION or HUMAN GREED. RESOUCE The Green Revolution failed to: Curb world hunger Fairly distribute resources Problems of the Green Revolution: Increased food supplies led to an increase in Increased population growth. population More mouths to be fed meant more would go More hungry. hungry. Increased living standards increased resource use. Negative impacts on the environment resulted. Impact of a Population on its Environment Environment Impact = P x A x T Impact P = population size A = per capita affluence (resource consumption) T = environmental disruptiveness of the environmental technologies used technologies Formula published by Ehrlich and Ehrlich, 1990 Differences in Resource Consumption Consumption 1 Child born in the US = 2 in Sweden or Switzerland 3 in Italy 13 in Brazil 35 in India 140 in Bangladesh 280 in Chad Information from Dr. Martha Groom, NCSU Zoology Department, 1998 Corrected Impact of a Population on its Environment on Impact = P x A x T x W P = population size A = per capita affluence T = environmental disruptiveness of the environmental technologies used technologies W = per capita wastage per Formula by Saier, 2005 (unpublished) Formula Human ecologists predicted a human population crash in the late 1900s. population Were they right or wrong? They were both right and wrong. They They were right to predict a population crash, but they got the time constant wrong. wrong. Skeptics took their error to mean that Skeptics the entire concept was wrong! They concluded we have nothing to worry about. We can live high on the hog!! BUT: BUT: The Human Animal The is subject to all of the laws of Nature, including those of Population Dynamics Population One and only one humane solution is available to save us from the pending disaster: POPULATION REDUCTION FOR FOR EARTH PRESERVATION 1, On what major issues did Darwin prove to be correct? Darwin 2, Plz describe the causes of an 2, organismal population crash. organismal 3, Why is it appropriate to refer 3, to humans collectively as “the Human Animal”? Human 4, Contrast a K-strategist with 4, an r-stategist. an QUIZ - QUIZ - QUIZ - QUIZ - QUIZ ...
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