Zebra mussel reduces diversity ~2 months ecological & economic damage reduces diversity loss of food & nesting sites for animals economic damage
Purple loosestrife 1968 1978 reduces diversity loss of food & nesting sites for animals
Logistic rate of growth Can populations continue to grow exponentially? Of course not! no natural controls K = carrying capacity Decrease rate of growth as N reaches K effect of natural controls What happens as N approaches K?
Number of breeding male Carrying capacity Time (years) 1915 1925 1935 1945 10 8 6 4 2 Number of breeding male fur seals (thousands) Maximum population size that environment can support with no degradation of habitat varies with changes in resources 500 400 300 200 100 20 10 30 50 40 60 Time (days) Number of cladocerans (per 200 ml) What’s going on with the plankton?
Changes in Carrying Capacity Population cycles predator – prey interactions At what population level is the carrying capacity? K K
Human population growth Population of… China: 1.3 billion India: 1.1 billion Human population growth adding 82 million/year ~ 200,000 per day! Doubling times 250m 500m = y () 500m 1b = y () 1b 2b = 80y (1850–1930) 2b 4b = 75y (1930–1975) 20056 billion Significant advances in medicine through science and technology What factors have contributed to this exponential growth pattern? Industrial Revolution The population doubled to 1 billion within the next two centuries, doubled again to 2 billion between 1850 and 1930, and doubled still again by 1975 to more than 4 billion. The global population now numbers over 6 billion people and is increasing by about 73 million each year. The population grows by approximately 201,000 people each day, the equivalent of adding a city the size of Amarillo, Texas, or Madison, Wisconsin. Every week the population increases by the size of San Antonio, Milwaukee, or Indianapolis. It takes only four years for world population growth to add the equivalent of another United States. Population ecologists predict a population of 7.3–8.4 billion people on Earth by the year 2025. Is the human population reaching carrying capacity? Bubonic plague "Black Death" 1650500 million
Distribution of population growth uneven distribution of population: 90% of births are in developing countries 11 10 high fertility uneven distribution of resources: wealthiest 20% consumes ~90% of resources increasing gap between rich & poor 9 8 There are choices as to which future path the world takes… medium fertility 7 low fertility 6 World total World population in billions What is K for humans? 10-15 billion? the effect of income & education 5 4 Developing countries 3 2 1 Developed countries 1900 1950 2000 2050 Time
individual at standard of living of population Ecological Footprint 30.2 15.6 6.4 3.7 3.2 2.6 USA Germany Brazil Indonesia Nigeria India Amount of land required to support an individual at standard of living of population 2 4 6 8 12 10 14 16 18 20 22 24 26 28 30 32 34 Acres over-population or over-consumption? uneven distribution: wealthiest 20% of world: 86% consumption of resources 53% of CO2 emissions A more comprehensive approach to estimating the carrying capacity of Earth is to recognize that humans have multiple constraints: We need food, water, fuel, building materials, and other requisites, such as clothing and transportation. The ecological footprint concept summarizes the aggregate land and water area appropriated by each nation to produce all the resources it consumes and to absorb all the waste it generates. Six types of ecologically productive areas are distinguished in calculating the ecological footprint: arable land (land suitable for crops), pasture, forest, ocean, built–up land, and fossil energy land. (Fossil energy land is calculated on the basis of the land required for vegetation to absorb the CO2 produced by burning fossil fuels.) All measures are converted to land area as hectares (ha) per person (1 ha = 2.47 acres). Adding up all the ecologically productive land on the planet yields about 2 ha per person. Reserving some land for parks and conservation means reducing this allotment to 1.7 ha per person—the benchmark for comparing actual ecological footprints. The graph is the ecological footprints for 13 countries and for the whole world as of 1997. We can draw two key conclusions from the graph. First, countries vary greatly in their individual footprint size and in their available ecological capacity (the actual resource base of each country). The United States has an ecological footprint of 8.4 ha per person but has only 6.2 ha per person of available ecological capacity. In other words, the U.S. population is already above carrying capacity. By contrast, New Zealand has a larger ecological footprint of 9.8 ha per person but an available capacity of 14.3 ha per person, so it is below its carrying capacity. The second conclusion is that, in general, the world was already in ecological deficit when the study was conducted. The overall analysis suggests that the world is now at or slightly above its carrying capacity.
Ecological Footprint deficit surplus A more comprehensive approach to estimating the carrying capacity of Earth is to recognize that humans have multiple constraints: We need food, water, fuel, building materials, and other requisites, such as clothing and transportation. The ecological footprint concept summarizes the aggregate land and water area appropriated by each nation to produce all the resources it consumes and to absorb all the waste it generates. Six types of ecologically productive areas are distinguished in calculating the ecological footprint: arable land (land suitable for crops), pasture, forest, ocean, built–up land, and fossil energy land. (Fossil energy land is calculated on the basis of the land required for vegetation to absorb the CO2 produced by burning fossil fuels.) All measures are converted to land area as hectares (ha) per person (1 ha = 2.47 acres). Adding up all the ecologically productive land on the planet yields about 2 ha per person. Reserving some land for parks and conservation means reducing this allotment to 1.7 ha per person—the benchmark for comparing actual ecological footprints. The graph is the ecological footprints for 13 countries and for the whole world as of 1997. We can draw two key conclusions from the graph. First, countries vary greatly in their individual footprint size and in their available ecological capacity (the actual resource base of each country). The United States has an ecological footprint of 8.4 ha per person but has only 6.2 ha per person of available ecological capacity. In other words, the U.S. population is already above carrying capacity. By contrast, New Zealand has a larger ecological footprint of 9.8 ha per person but an available capacity of 14.3 ha per person, so it is below its carrying capacity. The second conclusion is that, in general, the world was already in ecological deficit when the study was conducted. The overall analysis suggests that the world is now at or slightly above its carrying capacity. Based on land & water area used to produce all resources each country consumes & to absorb all wastes it generates
Any Questions? 2007-2008
Measuring population density How do we measure how many individuals in a population? number of individuals in an area mark & recapture methods Difficult to count a moving target sampling populations
Evolutionary adaptations Coping with environmental variation regulators endotherms homeostasis (“warm-blooded”) conformers ectotherms (“cold-blooded”)
Bright blue marble spinning in space Ecology
Studying organisms in their environment biosphere ecosystem community population organism