Lecture_7 - Population biology today 7th 230 Ecology...

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Population biology today 7 th 230 Ecology lecture 5 November 2009 th Ed. In this lecture we will comment upon population issues/ideas that were covered in the 4 chapters of the Population section that are not driven by counts of total abundance and changes in abundance. The idea of a ‘stable age distribution’ is associated with sustainability in my mind. Sustainability is ‘going on forever’ and implies inputs equal outputs. The value of states (conditions) does NOT change despite the fact that there is change (system is dynamic) because inputs equal outputs. An alternative view is that biological systems never get close to equilibrium because they are dominated by events- special or unusual happenings. Things proceed along on a standard path (determined by normal or average conditions) and then an event occurs that resets the system – the event could be a large fire, a major flood, a major windstorm or even more catastrophic events. Such events often reset the biological community to all young individuals or even result in extinction. Many tree species grow in even age stands which normally have their origin in an event that reset succession. The word ‘regime’ as in fire regime is used to describe the historical pattern of events. While there is a lot of consistency of radiation from the sun, the revolution and rotation of the earth the resulting ‘nature’ is not constant. Part of the heterogeneity is scale dependent, other parts can be result of rare collisions such as with an asteroid. A large amount of rain can have a huge impact on a particular place and time even though on large temporal and spatial scales all is normal. Nature is not constant and the shorter the temporal and spatial scale the greater the inconsistency. People who live in nature eg farmers, appreciate its dynamic and changing nature. Tourists do not. Many ecologists do field work for short periods usually at the same time of year. Such patterns often miss the important event which usually occurs at times weather is considered unpleasant. While it is common to think of small population size as threatening extinction through demographic stochasticity or inbreeding, there are many examples of biological invasions that started with a very small number of individuals but ultimately grow to millions. Among those that started with a very small numbers are the introduction of the
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This note was uploaded on 01/23/2010 for the course BIOS 230 taught by Professor Gibbons during the Fall '08 term at Ill. Chicago.

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Lecture_7 - Population biology today 7th 230 Ecology...

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