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Hood Mockingbird (Nesomimus macdonaldi) Prying for Insects, Española Island
Hood Mockingbird (Nesomimus macdonaldi)
Prying for Insects

Española Island, Galápagos Islands, Ecuador
May 18, 2007

Night Sergeant Damselfish (Abudefduf concolor), Bartolomé Island
Night Sergeant Damselfish (Abudefduf concolor)
Bartolomé Island, Galápagos Islands, Ecuador
May 16, 2007

Galápagos Whitetail Damselfish (Stegastes leucorus beebei), Bartolomé Island
Galápagos Whitetail Damselfish
(Stegastes leucorus beebei)

Bartolomé Island, Galápagos Islands, Ecuador
May 16, 2007

Question #5
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Of the 11 extant sub-species of tortoise in the Galápagos, 5 are located on one island (Isabela). Each of these sub-species is located at a higher elevation of 5 separate volcanoes, kept apart by features that make it impossible for the tortoises to cross (mainly rough lava fields). Identify and discuss this method of speciation. Find one other example of this type of speciation in the Galápagos. Find an example and discuss the contrasting type of speciation (without separating barriers). If possible, use organisms you have directly observed.

The Galápagos mockingbirds (Nesomimus) are another example of geographically isolated speciation both as a group and as individual species and subspecies. The genus Nesomimus includes four species and six subspecies, all of them are endemic to the Galápagos archipelago. Initially, when the mockingbird first arrived in the Galápagos it diverged from its continental cousin to become a new genus. Then after establishing themselves on the islands a closer scale geographical isolation occurred multiple times producing the multiple species and subspecies.

Being a land bird it would be rare for this species to fly long distances over water. So, having arrived 1,000 km from its nearest relative, isolation would occur preventing the mixing of the two population's genes. Then by going through the process of adaption to their new environment in isolation, speciation occurred. Moreover, individuals of this species over time populated other islands becoming geographically isolated from each other allowing speciation to occur differentiated adaptation strategies in the various climates of each of the islands.

Damselfish in the genera Abudefduf found in the shallow rocky waters around the islands have diverged to form separate species. The species panamic sergeant major (A. troschelii) and night sergeant (A. concolor) both occupy the same area but have carved out differing ecological niches. A. troschelii primarily feeds on plankton near the surface of the water while A. concolor primarily feeds on sessile bottom dwelling mollusks and invertebrates. Both species also graze on algae at the bottom, however, this difference of feeding habits causes an ecological isolation allowing speciation to take place. Furthermore, A. troschelii feeds during the day and A. concolor feeds during the night increasing the isolation between the species further isolating the two species ecologically.

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