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Populations- distribution and abundance (2).docx

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October 3 , 2012 Biology 2F03: Fundamental and Applied Ecology Populations: distribution and abundance (2) Distribution of two barnacles within the intertidal zone - balanus larvae settle throughout intertidal zone but survive to adults only below mean high neap tide - chthamalus larvae settle in middle and upper zones but survive to adults mainly in upper zone - why: The two species of barnacles differ in ability to survive exposure to air - barnacle mortality in the upper tidal zone - warm weather and calm seas produced much higher mortality among Balanus balanoides than among Chthamalus stellatus in upper intertidal zone - Chthamalus survives longer in warm weather without wave spray - This explains why it remains in higher intertidal zones - But why is it missing from deeper locations: chapter 13 Question - does a pattern of distribution provide information on what individuals do Microscale distribution can reveal species interactions - pattern – random: an individual has an equal probability of occurring anywhere in an area - processes: neutral interactions between individuals and between individuals and local environment - pattern regular – individuals are uniformly spaced through the environment - processes: antagonistic interactions between individuals or local depletion of resources - pattern – clumped: individuals live in areas of high local abundance which are separated by areas of low abundance - processes: attraction between individuals or attraction of individuals to a common resource Regular and random distribution of stingless bee colonies in the tropical dry forest - colonies of the stingless bee, trigona fulviventris which interact aggressively, are distributed regularly across this tract of forest - t. fulviventris from rival colonies battled daily for 2 weeks for possession of this potential nest - the less interactive stingless bee, T. dorsalis, is distributed randomly across the same tract of forest Interactions may change over time, with growth of individual (shrubs in the hypothetical situation below) - circular patterns - young, small shrubs clumped: small shrubs establish in high densities and produce a clumped distribution - mortality as the shrubs grow reduces clumping and produces a random distribution among medium shrubs - competition enforces a regular distribution among large shrub Creosote bush root distributions: hypothetical vs actual root overlap - excavated root systems: the root system
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