Like the islands of Hawaii, and many others, the Galapagos are created due to a mantle plume. The hot rock in the mantle plume is hotter than the surrounding rock, thus causing it to be less denser, which causes it to rise just beneath the surface of the earth. Any magma that does break the surface causes a volcano, which are seen on the islands. Because the tectonic plates, specifically the Nazca plate, moves along the plume, more islands can be formed - it's like one of those 3D printing pens, but instead of the pen moving, the platform moves instead. Due to this movement, islands located in the south and southeast are older than the other islands. As stated above, the hotter rock in the plume is less dense and will rise, as such, the opposite is true as well. Older islands have sunk due to being cooled by the surrounding water (thermal contraction).
Back onto the topic of volcanoes, due to the lithosphere having various thicknesses, the islands have different types of volcanoes. For example, islands in the west have an "inverted soup-bowl" feature (aka calderas), while islands in the east are smaller shield volcanoes that have gentle slopes. I remember learning in Physical Geology that calderas are formed when the magma chamber collapses, and that they are some of the most dangerous types of volcanoes (Jeff would be so proud of me!). The Sierra Negra volcano is the most accessible volcano of the western islands. The Sierra Negra has a large discharge rate and voluminous eruptions, which cause the development of a coastal apron.
How Did Animals Get to the Islands?
Interesting to learn that the species of the islands are "unbalanced". There are plenty of reptiles, but no amphibians. Many land and sea birds, but few mammals. Plants are excluded either, with most being grasses and ferns, while few have large flowers and big seeds.
It is theorized that one of the mechanisms by which organism came to the Galapagos is via sea. Some animals, like the turtles and penguins swam, while some land animals came via vegetative rafts. The raft theory explains why there are mostly reptiles on the islands, since reptiles can withstand intense salty and sunny conditions for weeks at sea better than mammals and amphibians. Additionally, some plant seeds are also adapted to salty conditions, such as mangroves.
The second mechanism is air. Many plant seeds and spores are theorized to have just flown here via the wind, with some seeds specifically designed to fly, like those helicopter seeds. Small insects and small birds could have been assisted by the wind, while larger birds could have easily flown there.
Today, humans are introducing new species that can have potentially disastrous effects on biodiversity , like donkeys, pigs, and blackberries.
Galapagos Biodiversity
Plants: The Galapagos has three major vegetation zones: 1) coastal, 2) arid, and 3) humid highlands. Due to the low elevation of most of the islands, many do not have a humid highlands, which are lush and green and allow for dense forests. Vegetation in the coastal zone are adapted and have high tolerance to salty conditions, such as mangrove trees. The arid zones contain plants that are adapted to low-water conditions, such as cacti. While mainland Ecuador has about 20,000 plant species, the islands only has about 600 native species, and 825 introduced species.
Giant Tortoises: The tortoises have been hunted, not only by humans for their oils and flesh, but also by other animals, such as rats and even ants. Because the tortoises can survive a year without food or water, humans began to bring them on their ships during long voyages as a source of fresh protein. This, alongside their oils which were used for lamps, led to the loss of more than 100,000 tortoises! I found it interesting that the tortoises spend about 16 hours resting, that slow metabolism definitely is a good survival mechanism, so long as humans aren't around/don't find out...I also think it is interesting that when the females lay their eggs, they don't see where they are digging the holes, laying the eggs, and covering them up because she uses her hind legs. I thought it was VERY funny that the only times the tortoises make vocal noises is when the males mate and make "a bellowing, periodic 'groan' that sounds similar to a loudly mooing cow". Lastly, it is interesting that the tortoises and birds have a mutualistic relationship, I wonder how the first bird and tortoise established said relationship, "Yo, let me eat your neck-skin-flap bugs."
Iguanas and Lizards: I found it interesting that the lizards' colors are dependent on the islands that they are on, ie if the island has dark lava, then the lizards will be darker in color. The islands are known for their discussion on evolution, but most discussions are focused on the finches and tortoises, it was interesting to learn about other animals. Once again, I wonder how the first relationship between the finches and the iguanas and tortoises began, most likely some finches started to eat the ticks/bugs and the animals stopped getting irritated. It was interesting to learn about the marine iguanas' ability to shrink and grow accordingly to the boom and bust cycles of the El Nino. Still love the Plant Earth video of the iguanas sneezing out the salt.
Mammals: I've heard of harems to describe herds of female animals, but never bachelor colonies (when I hang out with my single guy friends, is that also a bachelor colony? :thinking face emoji:). Interesting to learn about how the rice rats got to the islands, but sad to learn about the black rats out-competing the rice rats. I had assumed that dolphins and whales would go to the islands, since they are located in warmer areas on the earth, nice to see that it is true.
Land, Sea, and Shore Birds: Of the endemic 22 species of land birds, 13 are the famous Darwin's finches. Even though they hunt young iguanas, I think it would be funny watching an iguana get scooped up by one. There are eight land bird species listed an vulnerable or higher on the IUCN Red List: Mangrove Finch, Floreana Mockingbird, San Cristobal Mockingbird, Galapagos Hawks, Medium Tree Finch, Galapagos Rails, the Espanola Mocking bird, and the Galapagos Martin. There are only six endemic seabirds: the Galapagos Penguin, Flightless Cormorant, Waved Albatross, Galapagos Petrel, Lava Gull (as opposed to Lava Girl), and the Swallow-tailed Gull. The penguin is unique in that it is the only penguin species to live at or above the equator. Some shore birds include the Galapagos Flamingo, Great Blue Herons, Lava Herons, and Oystercatchers (I myself am an oyster eater).
Marine Life: 20% of all marine life in the Galapagos is endemic. Interesting that the only marine iguana and most northern-living penguin are located there. Won't lie, most of the time when I hear coral bed/reefs I don't imagine seals in the picture, since I mostly picture the Coral Reef.
Life in the Mangroves
Some mangroves can block salt from entering their roots, while others metaphorically sweat out the sweat from their leaves. red mangroves are some of the first organisms to colonize a new habitat. Interesting to learn that mangrove seeds can 1) survive for a year, and 2) attach to substrate at the bottoms of waterbodies. The symbiotic jellyfish with photosynthesizing algae is super cool, it lives upside-down so the algae can photosynthesize! Mangrove serve as a nesting habitat for not only fish, but also birds. Interesting to learn that it wasn't the direct hunting of birds that caused a slow in births, but the noise prevented/scared the birds. Sad to learn that 35% of mangroves throughout the world have been removed, and over 80% of Florida's have been deforested. Just like marshlands near us, mangroves buffer coastal storms, and prevent/slow down erosion. Funny, yet sad to learn that light bulbs are a common trash item found in the mangroves. Fortunately, mangrove forests can be very easily restarted!