pg - Population biology Population density and dispersion...

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1 Population biology Population density and dispersion Life tables Life Histories Population growth – Exponential Logistic Human population growth Age structure Human population growth Density and Dispersion • Density – Is the number of individuals per unit area or volume • Dispersion – Is the pattern of spacing among individuals How to measure density? A. Count B. Count sample and extrapolate C. Proxy - nests, feeding damage, fecal droppings D. Mark - recapture

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2 How to measure density? C. Proxy - nests, feeding damage, fecal droppings African savanna elephants - count from a plane African forest elephants - notoriously hard to count, elusive Richard Barnes (UCSD) - developed 1st method to quantify forest elephant density using dung “A nose for wild things” Los Angeles Times, 11/13/2010 How to measure density? D. Mark-recapture capture 1st sample of animals mark those animals, release capture 2nd sample of animals how many are marked (recaptured)
3 D. Mark-recapture -How to mark animals in the field? Paint insects Band birds Metal rings around legs of invasive crabs Fish tag D. How to measure density? Mark - recapture Say you capture and mark 10 turtles in a lake On a 2nd visit, you capture 15 turtles 5 turtles are marked N = population size n 1 = # captured & marked n 2 - # captured in 2nd sample m - # re captured N = n 1 n 2 /m N = 10*15/5= 30 Patterns of Dispersion Organisms may be exhibit random , uniform , or clumped spatial distributions Environmental and social factors Influence the spacing of individuals in a population

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4 A clumped dispersion – Is one in which individuals aggregate in patches – May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory. A uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors. A random dispersion Is one in which the position of each individual is independent of other individuals Figure 52.3c (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.
5 Patterns of dispersion have many causes Creosote bush, mojave desert. Uniform distribution caused by competition for water Crows uniformly distributed in vineyard

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6 Dispersion patterns can vary, depending on scale at which you look Is the human population dispersion clumped or uniform?
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