BIOLOGY 220 LECUTRE #28 - 12-11-07

BIOLOGY 220 LECUTRE #28 - 12-11-07 - BIOLOGY 220 LECTURE...

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BIOLOGY 220 – LECTURE #28 – LIFE HISTORY, ENERGY ALLOCATION, AND REPRODUCTIVE STRATEGIES POPULATION ECOLOGY - 5 Age Pyramids o Bottom of pyramid might shift in over time as the baby boomers grow older and pass the post-reproductive point. POPULATION ECOLOGY – 6 We can use this information (like the pyramids) to predict what’s going to happen over time. Based on what we know about a particular region (like Pakistan), we can make predictions about mortality Most of the people in the bottom will shift upwards in the pyramid over time (because they are growing older!) o Most of those individuals will be reproductive – more individuals will be added to the bottom of the pyramid, so the whole pyramid becomes wider over time POPULATION ECOLOGY – 7 Survivorship – How well organisms survive from one age level to the other o This is usually measured based on: 1.) Who survives at what stage during the life cycle? Survivorship curves – represents what happens over time – logarithmic y-scale We can chart out how many individuals are living 25% of the way through the life cycle, half-way, 75%, and at the end of the life span o We use the % of maximum life span because we can’t compare between organisms if we don’t scale for the differences between each species’ life span (meaning, the lifespan of an earthworm vs. that of a human are very different)
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3 different types of survivorship (3 different curves) o Type 1 – Humans Many mammals are type 1; any species that has a strong societal component tends to have a type 1 curve (even bees have a type 1 curve) 2 nd most common o Type 2 – Hydra has constant mortality over entire life span Is fairly rare o Type 3 survivorship – When these types of organisms are born, there is a very good chance that they will not survive, but if they do, then the chances of living to the maximum amount of lifespan is very good. THE MOST common survivorship POPULATION ECOLOGY – 8 Take proportions and combine them with our knowledge about who is going to survive when, and we can mix this information with info about how much offspring something has, and come up with a life-history table A Life-history table – Tells us how organisms are going to survive from one stage in their life to another. POPULATION ECOLOGY – 9 Life Table – survivorship and fecundity of a cohort It’s hard to take a census of “everybody” Cohort – A group of organisms born during a certain time period (a sampling of the population) o In other words, group of persons sharing a particular statistical or demographic characteristic That characteristic could be that the sample was taken of birds all born in the spring of 2005 in a certain area. X = Age interval (age at the start of period) (defines age class)
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BIOLOGY 220 LECUTRE #28 - 12-11-07 - BIOLOGY 220 LECTURE...

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