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Monthly Archives: January 2018

Type B Kil­ler wha­les: Evo­lu­ti­on in Ant­ar­c­ti­ca

The­re are a lot of visi­tors to the Ant­ar­c­tic Pen­in­su­la every aus­tral sum­mer. Most of them are wat­ching wild­life and taking hundreds of pic­tures. Popu­lar sci­ence pro­jects like Hap­py Wha­le pro­vi­de a lot of digi­tal pho­to mate­ri­al for mari­ne mammal rese­ar­chers all over the world. So one could assu­me wha­le popu­la­ti­ons and their cha­rac­te­ristics espe­ci­al­ly in the fre­quent­ly visi­ted Ant­ar­c­tic Pen­in­su­la are well estab­lished. Howe­ver, natu­re can still sur­pri­se us.

Ame­ri­can mari­ne mammal sci­en­tists have been loo­king clo­se­ly at dif­fe­rent groups of Kil­ler wha­les in the South Polar Oce­an during the past deca­de. We now know about four dif­fe­rent eco­ty­pes of Kil­ler wha­les in Ant­ar­c­tic waters. The lar­gest Kil­ler wha­les belong to type A. They main­ly hunt Min­ke wha­les in the open sea. Type B Kil­ler wha­les live clo­se to the coast or the pack ice of the Ant­ar­c­tic Pen­in­su­la and type C ani­mals are fee­ding in the Ross Sea regi­on. The so far youn­gest and least known eco­ty­pe D roams in sub-ant­ar­c­tic waters, known bey­ond others to feed on fish of long lines.

Type B Killer whale, Antarctic Peninsula

Type B Kil­ler wha­le, Ant­ar­c­tic Pen­in­su­la.

Rese­ar­chers have been obser­ved dif­fe­ren­ces in body size within type B Kil­ler wha­les whe­re­as the body colou­ra­ti­on, such as the big eye patch and the dor­sal cape, does not show signi­fi­cant dif­fe­ren­ces. But appar­ent­ly, the­re are dif­fe­ren­ces in group size, fee­ding beha­viour and pre­fer­red habi­tat.

A com­plex habi­tat with abun­dant food resour­ces favour the spe­cia­li­sa­ti­on of pre­da­tors. Ani­mals might par­ti­ti­on resour­ces and habi­tats among­st them­sel­ves. This is cal­led “niche dif­fe­ren­tia­ti­on” in eco­lo­gy. Whe­re some spe­ci­es (or sub-spe­ci­es) have simi­lar food and habi­tat requi­re­ments, they are usual­ly sepa­ra­ted geo­gra­phi­cal­ly, e.g. Kil­ler wha­le type B and type C. Is the­re enough space and resour­ces available to per­mit coexis­tence within one area, niches can be dif­fe­ren­tia­ted local­ly by spe­cia­li­sa­ti­on. Like that, dif­fe­rent eco­ty­pes can deve­lop and even new spe­ci­es can evol­ve over time.

In future we might look at type B Kil­ler wha­les as two dif­fe­rent eco­ty­pes. The lar­ger are hun­ting seals in the pack ice or clo­se to the coast, whe­re­as the smal­ler feed on brush-tail­ed pen­gu­ins (Gen­too, Ade­lie, Chin­strap pen­gu­in) and fish. Like that both groups belong to a dif­fe­rent tro­phic level in the food web: the lar­ger are fee­ding on pre­da­tors of krill fee­ders, the smal­ler feed on the krill fee­ders them­sel­ves.

The­re seem to be small gene­tic dif­fe­ren­ces alre­a­dy. Indi­vi­du­als of type B can still mate with each other con­side­ring their bio­lo­gy, but mem­bers of the dif­fe­rent size groups obvious­ly rare­ly do so. Sci­en­tists sup­po­se that the gene­tic dif­fe­ren­tia­ti­on might have star­ted with the end of the last gla­cia­ti­on peri­od, when a lot of new space beca­me available due to the retre­at of the ice.


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