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SO, we have an idea of what a population is….

SO, we have an idea of what a population is…. “Individuals of a single species living within a given area”. HOW DO WE DESCRIBE IT?. Some Useful Information:. Population structure. How many individuals? How old are they? How long do they live? How many young do they have?

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SO, we have an idea of what a population is….

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  1. SO, we have an idea of what a population is…. “Individuals of a single species living within a given area” HOW DO WE DESCRIBE IT?

  2. Some Useful Information: Population structure • How many individuals? • How old are they? How long do they live? • How many young do they have? • What is the genetic makeup of the group? • What is their distribution? Note that these can vary through space and time…

  3. More Useful Information: • Density • Spacing patterns among individuals • Territory size • Distance between conspecific plants • Movement patterns These too may vary through space and time…

  4. 10 individuals/km2 Boundaries are often hard to determine…. If boundaries unclear, or if population is very large, density may be the descriptive tool we most need

  5. Density is particularly useful for plants and other sessile organisms Examples: barnacles sagebrush

  6. Density can give clues aboutenvironmental quality or ecological processes Environmental quality (what does it mean?) Blue tits in southern Europe nest in both deciduous and evergreen oak forests, habitats that differ in environmental quality

  7. Environmental quality and blue tits Parus caeruleus

  8. Density can give clues aboutenvironmental quality or ecological processes Ecological processes High densities of an intertidal algae, Enteromorpha, occur in tide pools where they are sheltered from grazing by the snail Littorina littorea. Lubchenco 1978

  9. Changes in density assumed to reflect changing local conditions Example: Burrowing owls in California, 1996-2001

  10. Many owl populations are tied to the abundance of their prey J.A. Gervais Clair de Beauvoir Burrowing owls at Lemoore NAS live within the Air Operations area and in small easements surrounded by industrial agriculture

  11. Changes in density of owl nests and voles found in pellets 9 8 7 6 Vole biomass/Pellet Nest Density 5 4 3 2 1997.5 1998.0 1998.5 1999.0 1999.5 2000.0 2000.5 1997 1998 1999 2000

  12. Plants and Density “The Law of Final Constant Yield” Yield = total biomass of vegetation per unit area (single species) Total yield is independent of plant density above a certain threshold

  13. Yield Density Relationships:Examples

  14. Spacing of individuals Patterns of individuals within a population give clues to the processes affecting that population

  15. General spacing patterns: Clumped • Social interactions • Resource availability • Dispersal patterns

  16. Gray wolves (social) Burrowing owls (resources)

  17. General spacing patterns: Evenly Spaced • Social antagonism • Competition for resources in plants

  18. Chinstrap penguins

  19. General spacing patterns: Random Positions not influenced by positions of other individuals in population

  20. Movement We are primarily concerned with movements among populations (not within them) This type of movement is called dispersal Measuring and modeling dispersal is a major challenge in population biology We will discuss this further in the next lecture

  21. SUMMARY • Populations can be described by a number of characteristics: • Size • Density • How long individuals live • Reproductive rate • Distribution of individuals • Distribution of populations

  22. Density is especially useful • Can indicate environmental quality and ecological processes • Changes in density can indicate changes in environmental conditions • Most sensible way of describing populations for: • Sessile organisms • Populations without clear boundaries • Very large populations

  23. Plants and density: • The law of final constant yield • Increasing density eventually does not increase the yield, or plant biomass

  24. Spacing patterns Clumped Evenly Spaced Random Result from interactions among individuals and patterns of resource occurrence

  25. UNGRADED WRITINGASSIGNMENT • What is the law of constant • final yield? 2. What are the three basic spacing patterns?

  26. Self-thinning in Plants As final yield approached, some individual plants die, while the survivors get bigger

  27. This characteristic has also beenreferred to as the –3/2 thinning law-However, the –4/3 ratio appearsto more accurately reflect whatis happening.

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