53 1 and 53 2 Populations and Life History Population is the lowest level of organization in regards to Ecology The mark and recapture method m the of individuals originally marked in first sample n the of individuals in the second sample x the of individuals that were in both samples overlap N total population size x n m N Go out and sample population catch and mark each individual Then repeat process For this method to work 1 Must assume that population hasn t change much between the first and second sample so can t wait too long between first and second sample 2 Must be equally likely to sample each individual in the population so it s not only the slowest individuals being caught that would cause the results to be off Problems Trap shy once caught the animal may avoid possibility of being caught again and is less likely to be caught in second sample Trap happy once caught the animal learns there is free food and is more likely to be caught again FORCES THAT INFLUENCE POPULATION SIZE FORCES THAT INCREASE POPULATION SIZE Births Immigration individuals entering population FORCES THAT DECREASE POPULATION SIZE Deaths Emigration individuals leaving population How individuals are distributed in space Population density of individuals in a certain area High density spread out over large area Low density crammed into smaller area 1 Clumped Certain groups of individuals may need a particular environment or they may be in groups because they are social organisms 2 Even Individuals evenly distributed over area possibly due to defense of territory For example Penguins in a breeding colony are evenly dispersed because they are guarding their eggs and don t want other penguins too close 3 Random Common in plants because they grow wherever their seeds fall No patter in this type of distribution Survivorship Curves Type 1 extremely low death rate when young and then death rate begins to increase with age Good chance of offspring living if they re large and a lot of energy is invested in each individual offspring Ex Humans elephants Type 2 death rate is constant throughout whole life straight decreasing line relatively small animals that are never really out of danger Ex lizards squirrels Type 3 very high death rate when young and very few individuals live to be old But the few that do survive live to be extremely old because death rate is extremely small when old these organisms tend to have a ton of small offspring that require very little energy but grow to be very large as adults Ex trees oysters There is a trade off in offspring size and number If an organism has many offspring they are likely to be extremely small If an organism has large offspring there is likely to be only a few This is because large offspring require more energy therefore it wouldn t be smart or beneficial to have a ton of large offspring The more energy it takes to reproduce the less likely it is that the organism is going to survive and get the opportunity to do it again LIFESPAN A mouse that lives to be two years old is considered very lucky however a five year old elephant is considered to be a baby still and is expected to live a lot longer The elephant is large even as an infant so it is not at risk for dying young However a mouse is small throughout its whole life so there is always a risk of it dying
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