Population Ecology & Ecology of Aging
Population Ecology & Ecology of Aging BIOL 1001-001
U of M
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This 5 page Class Notes was uploaded by Mickayla Notetaker on Monday December 7, 2015. The Class Notes belongs to BIOL 1001-001 at University of Minnesota taught by Annika Moe and Craig Packer in Summer 2015. Since its upload, it has received 32 views. For similar materials see Evolution and Ecology in Biology at University of Minnesota.
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Date Created: 12/07/15
Lecture 22 Population Ecology Tuesday December 12 2 15 913 AM Ecology What influences the abundance and distribution of organisms in space and time Population How pop size of a particular species varies through time Community relations between interacting species Ecosystem Effects of physical environment on communities r intrinsic growth rate of a population rbide bbirth rate iimmigration rate ddeath rate e emigration rate Predicting population growth Island population with no migration Each pair has a litter of two each year no one ever dies Birth rateb2 babies2 adults yr 1yr Immigration rate0 Death rate 0 Emigration rate 0 Growth rater 10 1 Nt1rNtNt Linear vs Exponential growth Populations usually grow geometrically or exponentially which usually doubles every year barring any mass extinction event Exponential growth assumes that r will remain constant generation after generation Density dependent factors in population growth growth slows as population density increases Density of dependence in song sparrows population density is low there are only a few females laying eggs there are many more young that are raised per female When population density is high and there are 60 females laying eggs only a couple of the eggs are raised per female Density dependent food limitation in voles The growth rate of the voles increases with more food available even when the population density increases Densitydependent limitation of space In species that are colonial they only live in certain areas When they run out of space in their area they will lay eggs in an unsafe area causing the eggs to be destroyed There is only so much space for the living population Parasites thrive more in higher population densities As the host species goes up so does the number of parasites Population has a clear limit and as it approaches K the quotcarrying capacityquot the growth looks exponential but then plateaus when it gets closer to K Both behave the same at lower densities but slow down as it approaches its limitation Every organism has some upper limit of its population39s growth DensityDependent Equations Change in population through time dNdtNrkNK KNK proportion of unexploited resources When NO KNK 1 and growth is exponential When NK KNKO and growth comes to a halt When NgtK KNKltO and the population declines New Section 1 Page 1 Logistic growth equation dNdtNrKNK Low population densities the growth rate is essentially exponential but is halted as it approaches K when r is small the population eases toward K If the population growth is more rapid the population may overshoot K but the next generation will see a decrease and fall back down to K When population growth is very rapid the population overshoots K so far that it constantly bounces back below K to above K Cyclical Population oscillations f population is any more rapid the population growth can seem very random and is classified as chaos Chaotic population growth is seen in measles and also weeds Smaller faster species have higher r and exhibit the chaotic growth rate Densityindependent factors perturbations that affect population size regardless of density Population rarely approaches the carrying capacity especially in smaller species Species vary in their intrinsic growth rate and their exposure to density dependent population limitation Ecological time Time spans measured in months or years long enough for population sizes to change Evolutionary time Time spans measured in generations long enough for gene frequencies to change Evolutionary responses to population growth Some species are very density independent they are limited by fire or flood while others are density dependent limited by food space Those that are density independent have been selected for r and competition is low lots of food to eat and space whereas the density dependent species are k selected and competition is high not a lot of food or space available The R selected species are more likely to have a smaller body size and they develop rapidly have very rapid reproduction tend to have large litters and have short lifespans The K selected species on the other hand have a large body size slow development slow reproduction rhinos have a gestation period of 1 year small litters and a long lifespan Persistent differences in shortterm ecology have predictable effects on longterm evolution Human population Growth Population size of Homo sapiens increased 399 fold within the first 10000 years in Europe essentially crowding out the Neanderthals Transition from huntergathering to agriculture occurred quot11000 yrs ago and human family size increased by 392 additional children per woman The human population has exploded in the last 200 yrs and now we have 7 billion people on our planet What will happen to us 25 reindeer were introduced to St Paul Island AK in 1910 At first they had an exponential growth rate but instead of leveling out they have almost gone extinct Lichen was the primary food source for reindeer and it grows very slowly in such a harsh environment So once all the reindeer ate all the lichen it was all gone and there was nothing else to eat Could this happen to us Malthus calculated that as the population grows exponentially that our means of food would not grow as quickly and that we might overpopulate with not enough to eat but that technology could help produce more food Ehrlich using Malthus39 ideas about population growth he predicted that 4 billion people would starve between 19801989 including 65 million in the US By 2000 the world would run out of oil copper iron aluminum and coal On the other side some guys have said that we can subsist forever The limit of human growth will be reached it is only a matter of time and we already have signs that we are reaching the limit of what our planet can support so the growth can39t go on forever Human populations must someday reach an upper limit Easter island 2000 miles from South America 1250 miles from nearest habitable island People colonized from East Polynesia in 400800 AD Population peaked at about 9000 in 1550 AD In 1722 New Section 1 Page 2 Dutch Admiral visited on Easter Sunday and found quot2000 people living in huts or caves and engaged in almost perpetual warfare Population continued to decline and conditions worsened all but 110 people were removed in 1877 Classical ecological disaster caused by humans When Easter Island was first colonized it had been a tropical paradise They had a lot of palm trees and plants they could eat on the island but the island didn39t have any reefs so they would have to go out further to fish porpoises and tuna The moai which are the large faces on the island were so large that to be able to move them from the quarry to their places it would have took large logs to move them They used the palm trees for rollers and the demand for the timber was so great that one day someone chopped down the last tree When that happened there were no more boats to be made so there was no more food from the sea The families went to war At this point the most abundant source of meat was each other they became cannibals and after that the island never recovered The Earth is technically an island there is no one coming into it and no one can leave to live elsewhere What can we do Causes of current human population growth Developing countries have the highest fertility rate and have the most babies that is causing the worldwide growth rate to increase Age structures in different countries Nigeria there are very few older men and women The most abundant people in Nigeria are babies India It is also a pyramid with very few older people and mostly babies but it is curved more towards the ends because population growth has slowed down over recent years USA The age pyramid is not a pyramid at all It starts as the others with few older people but stretches out sooner because there were a lot of fertile people In the 195039s and the rest is variable Meaning it is not predictable like the other pyramids Russia There is no structure to the pyramid and people have stopped having babies Population momentum people in India are starting to have smaller families but the population will continue to grow as the younger generations reach reproductive age Unwanted fertility the fertility in women in S America Latin America and East Asia has decreased rapidly from the 1960s to the 1990s this can be directly attributed to the use of contraceptives in those countries High desired family size ask women in Senegal how many children they wanted in 1980s they wanted on average 8 kids The preferred family size has fallen worldwide but remains high in sub Saharan Africa What encourages people to have a large family while others don39t want that many children Demographic transition as infant survival increases people want to have less children If there is a low infant survival rate people will have more children almost as an insurance that some of those children will grow up and survive Poverty Alleviation the best solution to population growth Richer countries have a slower population growth rate than do poorer countries Economic development is essential for controlling population growth especially by empowering women Better educated women have smaller families Universal highquality primary and secondary education is achievable within 25 years A difference of one child per woman from now until 2100 would affect the global population by 9 billion people Population can be stabilized by educating every man and woman on the planet New Section 1 Page 3 Lecture 23 Evolutionary ecology of Aging Thursday December 3 2 15 1 218 AM Why do we age Adwaitya lived 255 years a tortoise Some humans can live up to 110 while others die around 80 A disease called Progeria where the victims grow old 8X faster than normal with an average life expectancy of 13 years Everyone grows old but some grow old faster than others Physiological basis of aging Chromosomal shortening 0 Mature cells can only survive about 50 cell division and this is because of the shortening of telomeres O Telomeres prevent chromosomes from binding to each other DNA cannot be replicated to the end of each chromosome Telomeres shorten by 20100 base pairs at each cell division Telomeres are expended by 50 cell divisions further replication removes functional DNA 0 Children born with progeria are born with shortened telomeres However there is an enzyme that lengthens the telomeres O Telomerase restores the telomere after each cell division This treatment has worked in mice who are genetically engineered for shorter telomeres They start growing telomeres Prematurer aged mice can be rejuvenated by restoring their telomeres 0 Some cells in our bodies have telomerase germ cells in particular But cancer cell also has telomerase which allows cancerous cells to proliferate Damaged DNA caused by metabolic products 0 Free radicals bind to our DNA and cell membranes Study nematodes to learn about aging When they gave the normal strain of nematodes an enzyme they reduced the amount of free radicals and extended the lifespan of that strain Mutant strain that accumulated excess free radicals was treated with the enzyme and the lifespan was also extended 0 There are mechanisms in our cells that repair damage P53 responds to DNA damage as an emergency brake It can either halt the cell cycle or activate DNA repair Cells lacking p53 are very unstable and can become cancerous Proximal mechanisms of aging mostly involve DNA damage There is a relationship between body size and age Those animals with larger body size tend to live longer Extrinsic mortality dead by some outside force predation starvation Want to know the senesce or the physiological aging of organisms Iteroparity repeated breeding Semelparity quotexplosivequot or suicidal breeding African Elephants they are sexually mature by age 15 and they have a calf every 5 years iteroparity Pacific Salmonspends 5 years at sea then makes a journey upstream and spawn a bunch of times then they drop dead semelparity The salmon are less likely to survive another round trip so they invest everything into reproducing With Atlantic Salmon some journey a long way inland and those that do lay more eggs and put more into their offspring than those who travel only a little ways inland Suicidal reproduction is favored whenever an asexual female thereby produces gt1 additional offspring Elephants are essentially immune to predation but calves are not So elephants should invest more in adult survival New Section 1 Page 1 0 Agespecific patterns of mortality determine whether to invest more in adult survival or reproduction f mortality is highest in infancy adults should invest more in looking after themselves than in reproducing f mortality is higher in adults adults should get their genes into the next generation 0 Natural selection shapes life history patterns Evolutionary theories of aging 0 Antagonistic pleiotrophy genes that enhance reproduction but reduce survival Testosterone increases attractiveness in younger men but is actually harmful to the immune system 0 Especially likely to evolve if gene enhances reproduction of young and only harms the old since so few will still be alive to suffer the costs Sex is inherently costly 0 Fruit flies that are secluded from females have a higher survival rate than those who were reproducing Marsupial mouse females live 2 years and have an average litter size of 68 The rut lasts 11 days and the competition for access to breeding females is intense After the rut every male drops dead of old age about 2 days after They have suffered a lethal cocktail of testosterone and stress hormones 0 Sex hormones appear to interfere with the immune response intact men and women suffer from more infectious diseases 0 Mutation accumulation too few individuals are still alive for selection to weed out mutations that only harm the elderly 0 Two mutations one that kills the elderly and one that kills children The one that affects the elderly would persist more than one that affects children because the elderly that die from the mutation have already had time to reproduce and pass on the mutation Natural selection favors genes that confer youthful vigor despite sideeffects at advanced ages Selection cannot remove purely harmful mutations that only hurt the elderly 0 Species with low extrinsic mortality should show a delayed onset of senescence 0 Tortoises that live for many years live on islands where there aren t a lot of predators and low extrinsic mortality 0 Naked mole rats live entirely underground so there are no predators and no diseases their average lifespan is 26 years NMR39s produce high levels of telomerase their telomeres never shorten and they also possess a gene that prevents cancer Improved nutrition and health care have greatly reduced our risk of death from extrinsic mortality 0 Life expectancy has risen so fast that society faces an quotepidemicquot of agerelated disorders Alzheimer39s is an agerelated disorder where the brain shrinks All of the agerelated macular degeneration heart disease and osteoporosis are genetic but none are pleiotrophic 0 Dietary restriction only known method for extending lifespan Rhesus monkeys that one was given a restricting diet and the other as much to eat as he wants the one that had the restricting diet looked better younger and more fit than the monkey with the other diet 0 In order for this to work the diet has to be 30 less than normal which in turn results in a complete loss of desire It extends their lifespan by shutting down reproduction Mitochondria are the main sites of freeradical production within the cells Mitochondria can be revitalized by exercise New Section 1 Page 2
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