Nancy Black

Publications (2)7.83 Total impact

• Article: Evolution of population structure in a highly social top predator, the killer whale.

  A Rus Hoelzel, Jody Hey, Marilyn E Dahlheim, Colin Nicholson, Vladimir Burkanov, Nancy Black
  [show abstract] [hide abstract]
  ABSTRACT: Intraspecific resource partitioning and social affiliations both have the potential to structure populations, though it is rarely possible to directly assess the impact of these mechanisms on genetic diversity and population divergence. Here, we address this for killer whales (Orcinus orca), which specialize on prey species and hunting strategy and have long-term social affiliations involving both males and females. We used genetic markers to assess the structure and demographic history of regional populations and test the hypothesis that known foraging specializations and matrifocal sociality contributed significantly to the evolution of population structure. We find genetic structure in sympatry between populations of foraging specialists (ecotypes) and evidence for isolation by distance within an ecotype. Fitting of an isolation with migration model suggested ongoing, low-level migration between regional populations (within and between ecotypes) and small effective sizes for extant local populations. The founding of local populations by matrifocal social groups was indicated by the pattern of fixed mtDNA haplotypes in regional populations. Simulations indicate that this occurred within the last 20,000 years (after the last glacial maximum). Our data indicate a key role for social and foraging behavior in the evolution of genetic structure among conspecific populations of the killer whale.
  Molecular Biology and Evolution 07/2007; 24(6):1407-15. · 5.55 Impact Factor
• Source

  Available from: Douglas G Burrows

  Article: Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales.

  Margaret M Krahn, David P Herman, Craig O Matkin, John W Durban, Lance Barrett-Lennard, Douglas G Burrows, Marilyn E Dahlheim, Nancy Black, Richard G LeDuc, Paul R Wade
  [show abstract] [hide abstract]
  ABSTRACT: Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers-stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles-were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n=84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.
  Marine Environmental Research 04/2007; 63(2):91-114. · 2.28 Impact Factor