Temporal Responses

Exploring the Vulnerability of Southern Ocean Seals to Climate Change

Previous research has documented the former existence of a large southern elephant seal (Mirounga leonina) breeding colony on the Victoria Land Coast of Antarctica, where conditions are too icy for them today. Radiocarbon dating of well-preserved mummified seal remains suggests that the colony was present from ~8000 to ~400 years ago. Analysis of ancient DNA from these samples shows that seals rapidly colonized the area once the habitat was released during a relatively warm period, but that there was a precipitous population decline about 1000 years ago, coincident with a period of cooling and a return to icy conditions.

In collaboration with Rus Hoelzel, Paul Koch, Brenda Hall, and Dan Costa, we are collecting more data from this time period for southern elephant seals, as well as Weddell (Leptonychotes weddellii), crabeater (Lobodon carcinophagus), and leopard (Hydryrga leptonyx) seals, which differ in their habitat requirements for ice. By combining next-generation sequencing of ancient DNA, stable isotopes, radiocarbon dating, and paleoclimatic data for these four species we are gaining a better understanding of their sensitivity and responses – in terms of both demography and foraging ecology – to major shifts in the Holocene climate over the last several thousand years.

Seal mummy, photo by Kristan Hutchison

Population and Ecological History of the Endemic and Endangered Hawaiian Petrel

Humans have had great impacts in the Pacific, and in Hawaii, human colonization has been associated with the extinction of nearly 75% of the endemic avifauna. The endemic Hawaiian petrel (Pterodroma sandwichensis) has escaped extinction, but colonies on at least two islands have become extirpated and population sizes across its range have declined dramatically.

The implications of this decline have been obscured by a lack of knowledge of this species, including a poor understanding of the potential for genetic and ecological differentiation between colonies. Since petrels are highly mobile, foraging from the waters off Hawaii to the Aleutian Islands near Alaska, no obvious barriers to dispersal exist between breeding colonies, which are separated by less than 500 km. Yet, at the same time, many petrel species demonstrate strong philopatry, and this can lead to genetic and/or ecological differentiation among populations.

In collaboration with Rob Fleischer, Helen James, Anne Wiley, Peggy Ostrom, and Craig Stricker we obtained genetic and stable isotope data from samples up to ~4000 years in age to investigate the historical dynamics of the Hawaiian petrel, as well genetic and ecological differentiation of populations of this endangered species. Previously Hawaiian petrels bred on all of the main islands of Hawaii. However, they were extirpated on Oahu prior to the arrival of Europeans, and have also (potentially) been extirpated recently on Molokai. Genetic work utilizing ancient DNA sequences from bones and museum skins suggest that prior to human arrival gene flow among populations was low. Similarly, levels of gene flow among extant populations today are low. However, there is evidence for high gene flow between the extirpated populations on Oahu and Molokai and the population on Lanai. This could be due to recent founding events, or potentially to dispersal away from the dwindling Oahu and Molokai colonies to the thriving colony on Lanai. Stable isotope data also suggest that birds today from Maui and Kauai have different foraging strategies than birds on Hawaii and Lanai. This genetic and ecological differentiation between colonies has important implications for the conservation of this species.