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Medium ground finch
The medium ground finch (Geospiza fortis) is a species of bird in the family Thraupidae. It is endemic to the Galápagos Islands. Its primary natural habitat is tropical shrubland. One of Darwin's finches, the species was the first which scientists have observed evolving in real-time.
Many studies and research have been conducted on medium ground finches: there are the most famous studies conducted by Charles Darwin and more recent studies conducted in relation to the changes revolving around the medium ground finches due to natural selection. Due to an increase in urbanization on the Galápagos Islands, droughts and climate change, character displacement, changes in the finch's habitat and range, inbreeding and nesting, parasites, and viruses, medium ground finches have gone through changes. Changes that have been observed are beak size, behavior in feeding, behavior in inbreeding, behaviors in nesting, antibody development and more. The changes in the Galápagos Islands are factors that affect the medium ground finches.
Like the other members of its genus, the medium ground finch is strongly sexually dimorphic; the female's plumage is brown and streaky, while the male's is solid black, with white tips to the undertail coverts. The bird measures 12.5 cm (4.9 in) in length—which falls between the lengths of the small and large ground finches. The bill of this species is quite variable in size, though the length of the upper mandible is always greater than the depth of the bill at its base. The wing shape, on average, seems to change with ecological shifts. Different selective pressures act on the wing shape of the finches, such as natural and sexual selection. The males have shorter, rounder wings, which help with maneuvering around a female during sexual displays.
The Galápagos Islands are famous for plant and animal life; they are also famous due to the studies conducted by Charles Darwin, which led to the development of his theory of evolution by natural selection. The Galápagos Islands have now changed and has been an area of rapid urbanization. These changes have caused an impact to the life on the island. Since the 1990s, Galápagos tourism has increased by 9.4% per year and resident populations have increased by about 6.4% per year. Rural areas on the islands, which were privately owned, had wetlands suitable for agriculture. This agriculture brought about invasive plant species, which included guava, passion fruit, etc. The urban areas had more human activity like roads, shops, and pollution. This area brought invasive species to the island like fire ants, black rats, etc. With these changes in the environment, medium ground finches with short/stubby beaks adapted due to the seeds and food preferences.
Food is the main driver of beak size and shape in Darwin's finches. For medium ground finches to be able to survive in urban areas, they had to adapt to new environments. Studies have shown that medium ground finches' phenotypes have been more variable than of small ground finches on Santa Cruz Island, being consistent with previous findings that medium ground finches adapt more rapidly to local conditions than small ground finches. The speed of how medium ground finches have been able to change beaks' sizes and shape may be centered around epigenetics. A research team led by Ms. McNew on the Galápagos Islands has measured the physical traits of wild birds and the genetics and epigenetics of two Darwin's finch species living at El Garrapatero, a rural area. They then compared the findings to urban finches living near Puerto Ayora; the two sites were not far apart. Some of the earlier studies showed that only one female out of 300 medium ground finches that were marked and used in the research relocated between both sites. Later on, Ms. McNew then captured more than 1,000 small ground finch and medium ground finch specimens, taking blood samples from females, sperm from males, and physical characteristics from each finch. Researchers realized that there was a difference between urban and rural finches' feeding preferences. The finches living in urban areas preferred human foods while the rural living finches did not. They then discovered that medium ground finches from the urban living area were larger in beak size than those living in the rural area. As for the small ground finches living in urban areas, they did not have any morphological differences from the ones living in rural areas. After conducting research, Ms. McNew and her team looked for evidence through genetics and found no evidence that can prove these phenotypic changes occurred through mutations. But when looking at epigenetics, there was significant evidence. In the finches studied, epigenetic alterations between the populations were dramatic, but minimal genetic changes were observed. The evidence showed that in medium and small ground finches, most of the epigenetic mutations were related to beak size and shape.
Urbanization is not the only factor affecting medium ground finches; drought and character displacement can also act as a selective pressure that can drive evolution of medium ground finches. In 1977, a severe drought reduced the supply of seeds in the Galápagos. The finch on Daphne Major, which normally preferred small and soft seeds, was forced to turn to harder, larger seeds. This strong selective pressure favoring larger beaks, coupled with the high heritability of traits relating to beak size in finches, caused the medium ground finch population to experience evolution by natural selection, leading to an increase in average beak size in the subsequent generation. A second drought of 1984–1986 caused a similar change, made more apparent by having smaller birds with bigger beaks.
Evidence of evolution through character displacement has been found in a population of medium ground finches on the Galápagos island of Daphne Major. During a drought in 2004, overlap in the diets of the medium ground finch population and a recently settled population of large ground finches (Geospiza magnirostris, five founding birds in 1982) led to competition for a limited supply of seeds on which the medium ground finch population normally fed. Because the large ground finches were able to out-compete the medium ground finches for these seeds due to both a larger beak and body size, the medium ground finch population experienced a strong selective pressure against large beaks to avoid competition, ultimately leading to dramatic evolutionary change favoring smaller beaks in the subsequent generation.
The Big Bird lineage occurred through hybrid speciation between Daphne Major G. fortis and an immigrant G. conirostris. The group underwent a severe bottleneck (down to two members) during the 2004 drought.
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Medium ground finch
The medium ground finch (Geospiza fortis) is a species of bird in the family Thraupidae. It is endemic to the Galápagos Islands. Its primary natural habitat is tropical shrubland. One of Darwin's finches, the species was the first which scientists have observed evolving in real-time.
Many studies and research have been conducted on medium ground finches: there are the most famous studies conducted by Charles Darwin and more recent studies conducted in relation to the changes revolving around the medium ground finches due to natural selection. Due to an increase in urbanization on the Galápagos Islands, droughts and climate change, character displacement, changes in the finch's habitat and range, inbreeding and nesting, parasites, and viruses, medium ground finches have gone through changes. Changes that have been observed are beak size, behavior in feeding, behavior in inbreeding, behaviors in nesting, antibody development and more. The changes in the Galápagos Islands are factors that affect the medium ground finches.
Like the other members of its genus, the medium ground finch is strongly sexually dimorphic; the female's plumage is brown and streaky, while the male's is solid black, with white tips to the undertail coverts. The bird measures 12.5 cm (4.9 in) in length—which falls between the lengths of the small and large ground finches. The bill of this species is quite variable in size, though the length of the upper mandible is always greater than the depth of the bill at its base. The wing shape, on average, seems to change with ecological shifts. Different selective pressures act on the wing shape of the finches, such as natural and sexual selection. The males have shorter, rounder wings, which help with maneuvering around a female during sexual displays.
The Galápagos Islands are famous for plant and animal life; they are also famous due to the studies conducted by Charles Darwin, which led to the development of his theory of evolution by natural selection. The Galápagos Islands have now changed and has been an area of rapid urbanization. These changes have caused an impact to the life on the island. Since the 1990s, Galápagos tourism has increased by 9.4% per year and resident populations have increased by about 6.4% per year. Rural areas on the islands, which were privately owned, had wetlands suitable for agriculture. This agriculture brought about invasive plant species, which included guava, passion fruit, etc. The urban areas had more human activity like roads, shops, and pollution. This area brought invasive species to the island like fire ants, black rats, etc. With these changes in the environment, medium ground finches with short/stubby beaks adapted due to the seeds and food preferences.
Food is the main driver of beak size and shape in Darwin's finches. For medium ground finches to be able to survive in urban areas, they had to adapt to new environments. Studies have shown that medium ground finches' phenotypes have been more variable than of small ground finches on Santa Cruz Island, being consistent with previous findings that medium ground finches adapt more rapidly to local conditions than small ground finches. The speed of how medium ground finches have been able to change beaks' sizes and shape may be centered around epigenetics. A research team led by Ms. McNew on the Galápagos Islands has measured the physical traits of wild birds and the genetics and epigenetics of two Darwin's finch species living at El Garrapatero, a rural area. They then compared the findings to urban finches living near Puerto Ayora; the two sites were not far apart. Some of the earlier studies showed that only one female out of 300 medium ground finches that were marked and used in the research relocated between both sites. Later on, Ms. McNew then captured more than 1,000 small ground finch and medium ground finch specimens, taking blood samples from females, sperm from males, and physical characteristics from each finch. Researchers realized that there was a difference between urban and rural finches' feeding preferences. The finches living in urban areas preferred human foods while the rural living finches did not. They then discovered that medium ground finches from the urban living area were larger in beak size than those living in the rural area. As for the small ground finches living in urban areas, they did not have any morphological differences from the ones living in rural areas. After conducting research, Ms. McNew and her team looked for evidence through genetics and found no evidence that can prove these phenotypic changes occurred through mutations. But when looking at epigenetics, there was significant evidence. In the finches studied, epigenetic alterations between the populations were dramatic, but minimal genetic changes were observed. The evidence showed that in medium and small ground finches, most of the epigenetic mutations were related to beak size and shape.
Urbanization is not the only factor affecting medium ground finches; drought and character displacement can also act as a selective pressure that can drive evolution of medium ground finches. In 1977, a severe drought reduced the supply of seeds in the Galápagos. The finch on Daphne Major, which normally preferred small and soft seeds, was forced to turn to harder, larger seeds. This strong selective pressure favoring larger beaks, coupled with the high heritability of traits relating to beak size in finches, caused the medium ground finch population to experience evolution by natural selection, leading to an increase in average beak size in the subsequent generation. A second drought of 1984–1986 caused a similar change, made more apparent by having smaller birds with bigger beaks.
Evidence of evolution through character displacement has been found in a population of medium ground finches on the Galápagos island of Daphne Major. During a drought in 2004, overlap in the diets of the medium ground finch population and a recently settled population of large ground finches (Geospiza magnirostris, five founding birds in 1982) led to competition for a limited supply of seeds on which the medium ground finch population normally fed. Because the large ground finches were able to out-compete the medium ground finches for these seeds due to both a larger beak and body size, the medium ground finch population experienced a strong selective pressure against large beaks to avoid competition, ultimately leading to dramatic evolutionary change favoring smaller beaks in the subsequent generation.
The Big Bird lineage occurred through hybrid speciation between Daphne Major G. fortis and an immigrant G. conirostris. The group underwent a severe bottleneck (down to two members) during the 2004 drought.