Population Growth & Ecology: Exponential Growth, Capacity, & Human Impact, Exams of Environmental Science

Download Population Growth & Ecology: Exponential Growth, Capacity, & Human Impact and more Exams Environmental Science in PDF only on Docsity! 1 Announcements • Midterm exam begins today. Find it on the class web site. Complete in one sitting by 10AM Feb. 5th • Questions from review sheet? • Assignment 1: Review on Thursday • Assignment 2: Ecological Footprint – due Feb 12th at 10 AM Hierarchical structure of ecosystems • Hierarchy of ecological elements in the biosphere • Biotic elements: organism (species) → population → community ecosystem • Abiotic elements: resources, environmental conditions • ecosystem → landscape → biomes → biosphere Principles of population growth The world population has doubled in the last forty years – 1 billion in 1804 (many thousand years) – 2 billion in 1927 (123 years later) – 3 billion in 1960 (33 years) – 4 billion in 1974 (13 years) – 5 billion in 1987 (12 years) – 6 billion in 1999 (12 years) – 7 billion in 2013 (14 years - projected) 2 Principles of population growth • Topics for today – Exponential growth – Carrying capacity – Age distributions – Human population growth – Implications for the environment and society Principles of population growth • Definitions: – Births: • Natality: # births per time period • Birth rate: # births per 1000 individuals per year • Per-capita birth rate: # births per person per time period (# added / population size / time period) – Deaths: • Mortality: # deaths per time period • Death rate: # deaths per 1000 individuals per year • Per-capita mortality rate: # deaths per person per time period Exponential population growth Example: single-celled protozoa Generation N dN/dt r 1 1 2 2 1 0.5 3 4 2 0.5 4 8 4 0.5 Exponential Growth dN dt = rN N0: the initial population size e: Euler’s number ≈ 2.7183… rt: exponent Solution for time = t N = N0ert 5 Population growth and carrying capacity • Carrying capacity (K): # individuals that an area can maintain sustainably • Often set by one limiting factor (Leibig’s law of minimums) • Exponential Growth: • Logistic Growth: rN dt dN = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ −= K NrN dt dN 1 Logistic population growth 0 5 10 15 20 0 2 4 6 8 10 12 Carrying capacity Time (t) Po pu la tio n Si ze (N ) K = 10 r ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ −= K NrN dt dN 1 How do organisms cope with environmental resistance? • r-strategists: – Short life span – High birth rates – High dispersal rate • K- strategists: – Long life span – Good competitors for limiting resources – Few offspring, often parental care – Low dispersal rate ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ −= K NrN dt dN 1 6 Examples of r and K strategists r-strategist: K-strategist Cod fish Elephant - One million offspring - About one calf every 4 y per year! - Offspring dispersed by - Offspring remain close currents to mother USFWS Relationship between r- and K- strategists and community succession r strategists K strategists Implications: How are people affecting ecosystems? When populations exceed K Population crash: Rapid population growth rate Non-renewable resources 7 Population growth rates and age • Age distributions in human populations World population growth • Human populations have increased at greater than exponential rates- Why? – Reduced mortality rates – Sustained birth rates • What are the implications of this kind of human population growth? • Are human populations limited by the same kinds of resources as other animals? World population growth 10 Literacy, income and fertility What do the literacy data suggest? Education and fertility in the US US Census Bureau data 2006 0 500 1,000 1,500 2,000 2,500 N ot a h ig h sc ho ol gr ad ua te H ig h sc ho ol , 4 ye ar s So m e co lle ge , n o de gr ee A ss oc ia te de gr ee B ac he lo rs de gr ee G ra du at e or pr of es si on al de gr ee C hi ld re n bo rn p er 1 00 0 w om en 11 Incentives for high fertility • High infant mortality rates • Economic benefits of children • Improves future security • Women’s status • Motherhood in developing countries starts ~ 17 y • Average marriage age in developed world: 25-27y Reasons for declining death rates and high population growth rates • Causes of disease recognized • Improvements in nutrition • Discovery of antibiotics • Improvements in medicine • Increase in # of women who reach child-bearing age • Short generation times in some countries Summary: Continued high birth rates and short generation times with declining mortality rates lead to rapid population growth Demographic transition Epidemiologic transition Fertility transition Time 12 Countries in transition Figure from Wright (2005) Sustainable development • Developed countries helping developing nations to improve living conditions without sacrificing resources of future generations • Principles: 1: Education (literacy) 2: Health: nutrition, hygiene 3: Family planning 4: Enhance income 5: Resource management: sustainable use • One expected result: Reduced population growth rates by moving nations through the demographic transition Sustainable development and the World Bank • Loans money to developing countries to start money- making programs • Idea: Lend money → start a development project. Project makes money → repay the loan. • Problems: – If project fails, country’s debt increases. – If corrupt officials steal the money, debt increases. – If programs are not sustainable (e.g., cutting down rain forest for ranching), debt increases and natural resources diminish. • One solution: micro loans Complications to sustainable development