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Black Mangroves (<i>Avicennia germinans), Genovesa Island, Ecuador Black Mangroves (Avicennia germinans)
Genovesa Island, Galápagos Islands, Ecuador
May 14, 2007


Red Mangroves (Rhizophora mangle), Fernandina Island
Red Mangroves (Rhizophora mangle)
Fernandina Island, Galápagos Islands, Ecuador
May 15, 2007

Palo Santos Trees (Bursera graveolens), Baltra Island
Palo Santos Trees (Bursera graveolens)
Genovesa Island, Galápagos Islands, Ecuador
May 14, 2007

Dry Forest Teeming with Lichen, San Cristobal Island
Dry Forest Teeming with Lichen
San Cristobal Island, Galápagos Islands, Ecuador
May 19, 2007

Tiquilia Plant (Tiquilia nesiotica), Bartolome Island
Tiquilia Plant (Tiquilia nesiotica)
Bartolome Island, Galápagos Islands, Ecuador
May 16, 2007

Giant Tortoise (Geochelone elephantopus), San Cristobal Island Giant Tortoise (Geochelone elephantopus)
Española Island, Galápagos Islands, Ecuador
May 19, 2007
Cactus Pad (Opuntia echios), San Cristobal Island
Cactus Pad (Opuntia echios)
San Cristobal Island, Galápagos Islands, Ecuador
May 19, 2007

Lush, Green Tree Tops in the Highlands, Santa Cruz Island
Lush, Green Tree Tops in the Highlands
Santa Cruz Island, Galápagos Islands, Ecuador
May 17, 2007

Question #2
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It is currently estimated that about 875 species of plants inhabit the Galápagos, relatively few when contrasted with approximately 20,000 species in Ecuador. Of the 875 Galápagos species, 228 have been found to be endemic (about 250 of the 875 species were introduced by humans!). Discuss reasons for the relatively low number of plant species and the relatively high rate of speciation. Speculate on the impact of introduced species, whether agricultural or non-cultivated.

There are several reasons the Galápagos Islands have a low number of plant species, some of which contribute to the high rate of speciation found there. These reasons include the fact the islands are relatively far from the mainland where seeds are likely to have originated, the harsh and inhospitable environment the islands offer for seeds that did arrive and the likely problem of the lack of pollinators on the island needed for reproduction of many plants.

The Galápagos archipelago is 1,000 km (600 mi) from the mainland of South America, providing the initial barrier for the arrival of plants that might successfully reproduce on the islands. Although the distance is relatively great for most plants to transport their seeds or spores, it is not an impossible feat. It is likely that some of the first arrivals were the mangrove trees, black mangrove (Avicennia germinans) and red mangrove (Rhizophora mangle), plants adapted to live in harsh environments with a reproduction strategy where their seedlings can float in salty waters for up to a year before germinating and beginning to grow. All these seeds had to do was to get caught up in the strong currents of the Humboldt or Panama flows which would carry them to the islands fairly quickly. Driftwood from the mainland would offer another source of seeds or spores that may have caught a ride on the dead wood floating along the currents.

Another avenue available for seedlings or spores to arrive in the islands is the wind. The light spores of ferns and seeds of some trees easily get caught up in winds that carry them to a high altitude where they float along the currents. If they happen to drift toward the Galápagos Islands, they could very likely get caught up in the garua clouds where the air becomes much denser causing them to fall to the islands.

Yet another form of seed transportation to the island chain could be through the feathers or stomachs of birds or other animals. Many birds carry seeds in their stomachs that will only germinate after being passed in the feces. Other seeds get attached to feathers where they can easily make their way to the islands on birds that visit them.

While getting to the islands is difficult, it is certainly not impossible. The bigger problem is arriving on the islands and having suitable resources such as humus and other nutrients necessary to begin growth. When the islands first appeared as volcanoes pushing lava up above the surface of the water, there was nothing but lava rock on which to grow. In addition, the weather patterns in the area were not hospitable mostly arid lacking a source of fresh water. Hence, the ability of the mangroves to grow in salty water was a plus for those species. Likewise, lichens that arrived had the ability to establish themselves on the lava rocks and were able to grow and ultimately produce the nutrient rich base needed by other plants to grow.

Even if other species of seeds or spores arrived and were lucky enough to land on bird guano or dead lichen materials giving them the necessary nutrition for survival and happening to arrive during the garua season where moisture was available, reproduction would be a problem for many flowering species needing pollinators to spread the pollen for fertilization. For example, plants that rely on hummingbirds for pollination would not survive even today because there is a complete absence of these birds on the islands. However, a species of carpenter bee and some wasps along with a few land birds did arrive that made it possible for the angiosperms to survive.

For the lucky plants that arrived and were able to germinate and grow, some of them still found themselves in an environment differing from their parent plants. Because of the climatic difference, these plants had to find ways of adapting to their new environment in order to survive and reproduce. It is this fact that has caused the high rate of speciation found in the Galápagos today.

For instance, the crinklemat plant, or tiquilia (Tiquilia nesiotica), common in Ecuador made its way to the islands where it established itself on the volcanic ash that settled onto the terrestrial surface of some islands. However, because of the heat and dryness of the environment it found itself in it had to adapt or face extinction. The plant ultimately adapted by sending its roots horizontal over greater distances in order to absorb more water when it was available and it found a way to use its leaves and stems to reflect the hot sunlight and decrease the damage from radiation of its chloroplasts, which gives it a gray appearance instead of green.

When herbivorous animals such as the giant tortoise (Geochelone elephantopus) began to arrive they presented another problem for plants, new predators. For plants that had finally established themselves on the islands and adapted to the climate a new problem now existed where they would have to adapt again in order to eliminate the possibility of extinction. One example of this force is that of the tree-like opuntia cactus (Opuntia echios). Due to their low growth and high predation by the giant tortoise, they adapted by growing taller and out of reach from the hungry creatures.

All of the struggles mentioned above have been going on for thousands of years and the successful pioneer plants that arrived and established themselves ultimately helped create a more hospitable place for plant life. These plants helped retain soil by holding it with their roots and by helping to make it when they died and regenerated into fertile matter. Because of this natural process the introduced non-native plants brought by man have a head start in getting established on the islands. In addition, those purposely brought for cultivation receive extra care in the form of nutrients and water given them by man himself.

The introduced plants present yet a new problem for the native plants established on the islands. The non-native plants can and do reproduce naturally away from the cultivated areas man set up. It is likely that many of the native plants in adapting to their new environment may have lost defensive abilities they once had on the mainland when they were in the company of many other species because they did not need them on the islands. Now with other species being introduced they find themselves at a disadvantage and facing extinction yet again.

When man came and began cultivating the land on islands such as Santa Cruz and San Cristobal, they cleared the land in order to plant. This action itself eliminated many plants from the natural occurrences and then replaced them with the non-native plants. Again, the new plants have a much greater head start in getting established. Once established these foreign plants become competitors to the native species taking over their resources such as territory, sunlight by blocking the rays to low growing plants and by taking up more water than their native counterparts.

Today many of the native species are being threatened by the introduced species. Unless the native plants learn to adapt and better compete with the non-native species or man himself steps in and eliminates them, they may very well face extinction.

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