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Population ecology

Population ecology Sea otters are smallest marine mammals Occur in coastal habitats in northern Pacific Ocean Where have all the sea otter gone? Feed on variety of fish and marine invertebrates Gregarious; live in ‘rafts’ of about 100 individuals Where have all the sea otters gone?

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Population ecology

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  1. Population ecology • Sea otters are smallest marine mammals • Occur in coastal habitats in northern Pacific Ocean • Where have all the sea otter gone? • Feed on variety of fish and marine invertebrates • Gregarious; live in ‘rafts’ of about 100 individuals Where have all the sea otters gone?

  2. Population ecology • In late1700s, Americans, English and Russians hunting sea otters for pelts • Where have all the sea otter gone? • By 1911, when International Fur Seal Treaty enacted, sea otters nearly extinct • Currently, about 150,000 sea otters Where have all the sea otters gone?

  3. Population ecology • Current range of sea otters a portion of former range • Where have all the sea otter gone? Where have all the sea otters gone?

  4. Population ecology • Since 1990s, sea otter population has declined sharply in Aleutian Islands • Where have all the sea otter gone? • In next several lectures we will explore why Where have all the sea otters gone?

  5. Population ecology • Population = groups of individuals of a given species that occur together • Members of a single species make up a population • But a species may be represented by many populations • Major properties of populations: • Distribution • Dispersion • Demography Where have all the sea otters gone?

  6. range shift of red spruce after glacier retreated • range expansion of cattle egret Population ecology • Biotic and abiotic conditions determine where a population can survive and reproduce • Distribution = geographic range of a population • Population distributions can change over time • Most population distributions are declining because of habitat destruction by humans • Others expand or contract naturally Where have all the sea otters gone?

  7. glanville fritillary butterfly in Finland Population ecology • Metapopulations = network of populations that interact occasionally by exchanging individuals • Distribution • Occur when habitat is patchily distributed and separated by unsuitable habitat • Characterized by suitable habitat patches going extinct and getting recolonized over time Where have all the sea otters gone?

  8. Source-sink metapopulation 3 separate populations sink Source 3 populations of simple metapopulation (arrows =migration of individuals) Population ecology • Metapopulations • Simple metapopulation contains populations in equally suitable habitats • Distribution • Differences in habitat suitability produces a source-sink metapopulation • Sources = populations in high-quality habitat; continually produce ‘surplus’ individuals that colonize new habitats • Sinks = populations in low-quality habitat; can not persist without continuous input from neighboring populations Where have all the sea otters gone?

  9. Population ecology • Dispersion = spacing between individuals in a population • Random • Individuals do not interact with each other or non-uniform habitat conditions • Uniform • Usually result of competitive interactions or territories • Clumped • Individuals cluster in response to uneven resources Where have all the sea otters gone?

  10. Population ecology • Population size = number of individuals • Demography = statistical study of populations • Population growth = size of population over time • Population structure = proportion of individuals in different age classes • Population growth strongly influenced by age structure • Populations with large number of young individuals grow rapidly because an increasing proportion of individuals are reproductive • Populations with equal numbers of individuals in different age classes usually maintain same population size Where have all the sea otters gone?

  11. Population ecology • Population pyramids show age structure • Demography Where have all the sea otters gone?

  12. Population ecology • Life tables describe mortality and fecundity of different age classes • Demography • Mortality = number of individuals that die in a given period • Survivorship (lx) = proportion of individuals that survive from birth to age x • Mortality (Mx) = proportion of individuals that die between age x and age x+1 • Fecundity = number of offspring produced in a given period • Age-specific fecundity (mx) = average number of offspring produced by females at age x Where have all the sea otters gone?

  13. Population ecology • Example life table (Poa annua) • Demography Where have all the sea otters gone?

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