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Lec 22 .docx

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Biology 1001A
Tom Haffie

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Lec 22: Community Ecology Human population growth • Most K-selected species show logistic growth… what about us? • No evidence that human population growth has been leveling off • Growth seems to be exponential • Humans have technology, this allows us to manipulate the environment and adjust the carrying capacity • Ex. Agriculture • Humans also don’t have any predators CLICKER: why is human population size worldwide still increasing? A) we are r-selected, not k-selected B) We have succeddes in increasing the carrying capacity, K C) We have succeedes in increasing per capita birth rates, b D) we have succeeded in decreasing the per capita death rates, d. Human populations vary in r - There is geographic variation - Different continents have different values for r - Red bar is projected populations for the year 2025. Certain continents (asia, africa) are projected to increase whereas, (eurpoe) population size tends to be stable r reflects age structure - Difference in whether a population will increase or not is majorly due to age structure. - Graph on the left (united states) seems like they will have a stable population because they have an equal age distribution \ - Graph on the right (mexico)- the population will increase because there are many prereproductive individuals. Increasing N, but decreasing r • Globally, r = 0.012 or 1.2% (per person per year) - Population will increase as long as r is above 0. - r is decreasing; however, the population is still growing because r is >0 (still positive) - When population size decreases (aprox 2050) the harmful effects on the environment (global warming, pollution) will decrease Demographic transition model • Over time, human societies get wealthier… - This is drawn from observation of birth and death rates in western europe. - Preindustrial- there is high death rates, high birth rate because the population is low early on- Low values of r - Transitional (stage 2)- decrease in death rates, happens before population responds by decreasing birth rates- High values of r- High rates of growth - Industrial- People choose to family plan (decrease birth rate) - Post Industrial- Birth rate falls below death rate - Extreme poverty can keep populations stuck in transitional phase; however, most countries will make it to industrial and post industrial stage. Population size isn’t everything! - Lower population puts less strain on the environment. All other things being equal, not all humans have an equal use of resourses. Not everyone has the same size carbon footprint. - U.S person has a footprint 50x bigger then someone in Guyana. Community ecology - Species interact with eachother (ecological community)- the assemblage of populations that interact in a given place. - Communities are composed of multiple species Why are populations distributed the way they are? • Some species limited by a single critical factor or resource (ex. Temp, soil moisture, the amount of salt in the water, food supply) • Many species have multidimensional tolerance limits. A particular species has more then one resource it requires Imagine this in n-dimensional space Ex. Temperature. @ optimal temperature, species are abundant @ upper and lower limit, species are infrequent as a result of physiological stress @ low/ high extreme temp
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