Where have all the sea otter gone

1
Population ecology

• Where have all the sea otter gone?

• Sea otters are smallest marine mammals

• Occur in coastal habitats in northern Pacific
  Ocean

• 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

• Where have all the sea otter gone?

• In late1700s, Americans, English and Russians
  hunting sea otters for pelts

• 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

• Where have all the sea otter gone?

• Current range of sea otters a portion of former
  range

Where have all the sea otters gone?
4
Population ecology

• Where have all the sea otter gone?

• Since 1990s, sea otter population has declined
  sharply in Aleutian Islands

• 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
Population ecology

• Distribution geographic range of a population

• Biotic and abiotic conditions determine where a
  population can survive and reproduce

• 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
Population ecology

• Distribution

• Metapopulations network of populations that
  interact occasionally by exchanging individuals

• 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
Population ecology

• Distribution

• Metapopulations

• Simple metapopulation contains populations in
  equally suitable habitats

• 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

• Demography statistical study of populations

• Population size number of individuals

• 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

• Demography

• Population pyramids show age structure

Where have all the sea otters gone?
12
Population ecology

• Demography

• Life tables describe mortality and fecundity of
  different age classes

• 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 x1

• 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

• Demography

• Example life table (Poa annua)

Where have all the sea otters gone?