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UMass Amherst BIOLOGY 152 - Population Growth

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Lecture 29 Outline of Last Lecture I. A Population Ecology continued a. Population Growth i. Exponential Growth Model Outline of Current Lecture ii. Exponential Growth Model continued b. What Limits Population Growth? c. Experiment on Intrinsic Factors Current Lecture Population Growth Continued What is the value of the carrying capacity for the blue population shown at right? -around 50,000 because that’s where the blue line starts to level out If growth doesn’t fit the data, then we look for why: -does r vary? -does the carrying capacity vary because of something like climate? The logistic growth curve isn’t just something we see with population growth, it also describes how many complex systems work (like the product vs. time curve for an enzyme) **Clicker Question** When is the rate of growth highest? The change in population per unit time, not the rate of growth per capita -C is the point where it stops getting faster every generation and starts getting slower (still growing but not growing as fast) So how are logistic curves used for hypothesis testing? **Clicker Question’s** The red line shows the growth predicted by the logistic model, and the black dots show the measured growth of the population. Does the measured growth match the predicted growth pattern? Bio 152 1st EditionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. !Edited with the trial version of Foxit Advanced PDF EditorTo remove this notice, visit:www.foxitsoftware.com/shopping-black dots don’t follow exactly along the red line, but does it match the predicted one or is completed different? this is the difference between answers B and C -answer key = C but both of the answers seem perfectly reasonable -you would need to do a statistical analysis and see if the numbers lie within a certain distance that would decide whether they were the same or not What is the predicted carrying capacity of the Daphnia culture? -135 Daphnia/50 mL (where the line starts to level off) Did the Daphnia population ever experience a negative growth rate? -From about day 70 to day 105 the population decreased in size, indicating a negative growth rate What is the most plausible biological explanation for why the population became neg? -The population’s death rate was greater than the birth rate during that period (D) -C could be an explanation but not supported by the data (because the population increased after that) What Limits Population Growth? -where does K come from? 2 basic categories of limitations on pop. growth 1. Density dependent 2. Density independent Density Independent = doesn’t matter how many individuals of the population are there, it will inhibit growth ex: drought (oscillations in amount of precipitation, when amount precipitation goes down, it causes loss of population) Density Dependent = factors limiting population growth (gets worse as population increases) -referred to as a type of negative feedback -death rate rises as pop. goes up -as population of the kelp perch goes up, the kelp bass eats more so the death rate of kelp perch goes up ex: as the sparrow population increases, their clutch (# of eggs they lay) decreases Density dependent negative feedback controls: -competition for resources -disease: as population goes up, much more likelihood of disease -predation -territoriality: limit the # of organisms because there isn’t enough space for everyone -intrinsic factors: most populations of animals have some sort of societal norm (hierarchy) and as these get too big, populations will break down -toxic wastes: more organisms, more chance for lots of waste *Thomas Malthus started thinking about this first, he had seen population growth in the US (human population growth exponential) — started thinking that if a population was given enough food it would grow to a certain point, and once it hit that point then the population would collapse*density dependent limitations tend to lead to fluctuations around the carrying capacity **Clicker Question** Classic study on the snowshoe hares and lynxes. Are we seeing a density dependent effect on hare populations? -Yes, the hare population increases, so does the lynx population immediately afterwards, hare population goes down, and the lynx population decreases as well (this trend continues) Which of the following processes is NOT likely to supply density-dependent neg. feedback on a population’s growth? -seasonal climate change (density independent) -you’re going to have parasites no matter what but they’re going to be worse in more crowded conditions TL;DL Experiment on Intrinsic Factors -created “mouse utopia”, provided enough food and water for 4,000 comfortably living mice -put in 8 mice (disease free) and allowed them to live normally — they mated & created more mice -observed a growth curve: -in the beginning there was exponential growth (doubling time of 55 days) which lasted until day 315 after colonization with 620 mice -then he noticed a change — slowed down (doubling time went to 104 days) which continued to grow until day 560 (now there’s 2,200 mice in there, still below carrying capacity) -the last mouse was born and after that the population began to decline — well before it exceeded the theoretical carrying capacity -20% of nest boxes totally unoccupied, and overcrowded into certain nest boxes (not using resources uniformly) -mouse society broke down, mothers stopped caring for young by kicking them out of nest, male mice stopped attempting to mate and began congregating in the center in masses that would fight with each other -group of mice that would find the unoccupied part of mousetopia and only eat, groom and sleep — they were examined and were no longer like normal mice -by the end of the experiment there were only 27 mice left (23 females and 4 males) — after 1500 days -shows that when there are too many, society breaks down -his argument was that this was a mental factor — they stopped trying to


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UMass Amherst BIOLOGY 152 - Population Growth

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