53.1 and 53.2: Populations and Life HistoryPopulation is the lowest level of organization in regards to Ecology. The mark and recapture method: m = the # of individuals originally marked in first samplen = the # of individuals in the second samplex = the # of individuals that were in both samples (overlap) N = total population sizex/n=m/NGo 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 resultsto 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: BirthsImmigration: individuals entering population*FORCES THAT DECREASE POPULATION SIZE:DeathsEmigration: individuals leaving populationHow individuals are distributed in space:Population density: # of individuals in a certain areaHigh density: spread out over large areaLow density: crammed into smaller area1. ClumpedCertain groups of individuals may need a particular environment or they may be in groups because they are social organisms. 2. EvenIndividuals evenly distributed over area possibly due to defense of territory. For example, Penguins in a breeding colony are evenly dispersedbecause they are guarding their eggs and don’t want other penguins too close. 3. RandomCommon 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 organismis 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
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