Ecosystem roles in tropical rainforests

Primary producers in all of these ecosystems vary. In rainforests, the primary producers include trees, shrubs, and epiphytes. An epiphyte is a plant that grows on another plant but it not directly parasitic. In mangroves, they are epiphyte and mangroves. The term mangrove describes how the trees live, it is not a taxonomic term. It simply describes a tree that lives in salt water. In a reef, the primary producers are corals, seagrass, and macroalgae (seaweed). Interestingly corals are also predators of the reef. The algae they are in a symbiotic relationship (zooxanthellae) with undergoes photosynthesis during the day. At night they hunt small organisms in the water and spear them with tiny barbs.


A view of Guatemala primary producers. Captured by Lauren Schramm


Herbivores (or primary consumers) in the mangroves, rainforest, and reefs all vary. In rainforests, these include birds, monkeys, agouti, tapir, butterflies, and sloths. In the mangroves there are fewer herbivores, these include mollusks and crabs. In the reef system, most organisms are herbivores. These include coral, smaller fish, sponges, plankton, and mollusks.


An Agouti (Dasyprocta punctata )


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North Point Bahamas

The following is adapted from my field notes on a research trip to San Salvador Bahamas. 

North Point is made of eolianites which are made of wind deposits of calcium-rich sand from the island mainland. The wet carbonate turns sold. A crust (caliche) forms on the surface and the then rest solidifies. These dunes are less than 500 years old. My professor, Fred said that sometimes the crust of the eolianites breaks and then is filled with sand which cements. It is harder than the rest of the eolianites so while the rest erodes it stays behind. Off of North Point, there is a shipwreck of a gas tanker. Fred saw a grey catbird (Dumetella carolinensis).These birds are named after their cat-like meowing sounds. Non breeding birds can be found as far south as the Bahamas. We also saw white-tailed tropic birds (Phaethon lepturus). They have very elegant long whitetails. They can be found in Hawaii as well. They don’t build nests and instead lay eggs on the bare ground. I saw several really small hermit crabs, which are also called soldier crabs (Coenobita clypeatus) taking advantage of old snail shells. This crab is one of two species that is commonly sold as pets. They are both herbivores and scavengers. 


North Point with the old gas tanker visible. Captured by Lauren Schramm.


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Tropical ecosystems

The one common characteristic that the tropics have in common is that the temperature is warm. The daily temperature usually changes more than the temperature average of the year. This is because the sun falls more directly on the topics than on other regions. However, depending on the region there will be changes in rainfall. Rainforest receives more rain than tropical savannas (more than 200 cm a year). Because of this savannas are more suitable to fires in the dry season. Some plants have adapted to be able to survive these fires, and often have visible scarring from fires. The animals have also adapted to the dry conditions. Because droughts are localized the animals migrate around the savanna. The soils are often acidic and are poor in nutrients. The soils are sandy and coarse textured. In addition, some savanna may become waterlogged during the year so the plants have to be adapted. For this reason, there is less plant diversity in savannas.

Trees in Kiang West/The Gambia

Rainforests, on the other hand, have to deal with excess moisture. Moisture can cause fungus and molds to grow. Some plants have developed drip tips because of this. Drip tips are sharp points on the end of a leaf that let water drip off the leaf. Leaves are concavely shaped so that water will run off of them. Leafs also have smooth edges rather than teeth to prevent water build up. Water build up would cause fungi and molds to grow on the leaf which would block sunlight and decompose the leaf. The soil is often moist and clay-like. Many monkeys are well adapted to live in the rainforest. They rely on the fruit which is in constant supply. In addition, new world monkeys have developed tails so they can easily navigate the tall canopy. Other animals have adapted to the heat by becoming nocturnal. Bats are an excellent example of this adaptation.


Belizan Rainforest. Captured by Lauren Schramm.


Like the savanna and the rainforest, coral reef requires fairly specific environmental factors in order to exist. The temperature is usually between 21-29 degrees Celsius. The reason this range is idea is that coral is actual a mutualistic relationship with algae called zooxanthellae. If the temperature increases too much then the zooxanthellae starts to produce toxic compounds to the coral and so the coral has to kick it out. Nutrient levels must be low because otherwise, microalgae will out-compete the corals. This is why the coral must be in a relationship with zooxanthellae because it lives in nutrient-poor water. In order for the zooxanthellae to undergo photosynthesis, the water must have a high light availability. Plating coral has evolved its shape so that it can absorb more light because it has a large surface area. In addition, the water cannot be too acidic or the rate of decalcification will be too great for the coral to form. The coral reefs provided great nursing habitat for dolphins, and whales raising their young. However, they do not have much food. Therefore these animals have adapted to use the reef as nursery habitat but migrate north to waters with more food. Because coral reefs have nooks many animals, particularly fish have adapted to live in these. They have flat bodies that are highly maneuverable.


Marine ecosystems of Belize

The following post is a reflection on a field trip I took to Belize as part of my tropical ecological class. In the marine environments, there were three main ecosystems that we explored; seagrass and sand flats, coral reefs, and mangrove forests. Of all of these, the coral reefs had the highest species richness due to their high primary productivity. This is due to the dual nature of coral, that of a producer and a predator. Coral itself is a tiny animal that hunts plankton with tiny barbs. Most coral tissue also contains an algae called zooxanthellae which provides energy to the coral via photosynthesisThis creates available energy for others, like parrotfish that eat corals. It also allows the coral to create a structurally complex area. The mangroves have the next highest level of primary production and are almost as structurally complex as the coral reefs. On the other hand, the sandy and grassy flats have little structure to them. When snorkeling there very few species besides 3 species of ray were seen.

Belize contains the 2nd largest coral reef in the world and is notable for this feature called a blue hole

Mangroves are a group of woody plants that grow in areas that are exposed to salt water. The species we saw the most of were the red mangrove (Rhizophora mangle). These trees often have prop roots. The served as great habitats for a large variety of sponges. The roots were also the ideal habitats for baby fish. We saw smaller versions of many of the species we saw at the reef. The water was also slower in this area. This is important because it allows for silt to settle out, and the roots of mangroves need soft sediments to grow well. The area inside of the barrier reef is ideal for these types of environments to develop because the reef crest was able to decrease the wave action in the area. The roots were also very lightweight. This was a result of the aerenchyma tissue in the roots which are sponge-like root tissues that allow for the transportation of oxygen. The roots also provide habitats for young fish, increase friction between the wave and the tree, and trap sediments. The decrease water speed due to increased friction was very noticeable, as we traveled deeper into the mangroves the waves lessened until it was almost still.

Red mangrove trees (Rhizophora mangle)

The species richness of the coral reef appeared to be heavily affected by niche speciation in spatial terms. We saw a variety of fish that used the different spatially regions of a coral reef. The nurse sharks and rays feed on the bottom. Some fish like black hamlets (Hypoplectrus nigricans) preferred to live on the top of the coral mounds. Other larger fish like the queen angelfish (Holacanthus ciliaris) live near corals in isolated pockets. Lastly, some fish such as the squirrelfish (Holocentrus sp.) prefer to live underneath the coral mounds. Species evenness did change because the availability of certain structures was greater than others. For example, there was lots of space for black hamlets, but there were fewer isolated pockets for French angelfish (Pomacanthus paru). These are also examples of specialization which happens when a species becomes uniquely adapted to a narrow resource. This reduces competition between species in the reef which allows more species to live there.

The coral reef in some areas was clearly more subject to top-down forces than others. Often corals are in competition with algae, in the last reef we snorkeled this was partially noticeable with the brown algae growing in some areas. This is kept in check by the fish that prey on the algae in these areas. If the fish are removed then the coral will not be able to compete with the algae. The reef where the algae were seen growing was also where the local fishermen like to fish. The increase in fishing for these species has been linked to an increase in the number of algae in an area. It is possible that overfishing is or could affect the reef in this area. Many of the fish caught were served to tourist on the island so it is possible that eco-tourism could harm the reef if more fishing regulations are not put in place.

There was bleaching in some areas of the reef. Bleaching usually occurs when the temperature of the water is too great and the algae in a symbiotic relationship with the coral start to produce toxic compounds to the coral. Because of this, the coral ejects these cells, and since the cells coral the coral the coral then appears white. It is possible for a coral to survive this event but this depends on its resilience. Some species of coral are more resilient than others so the biodiversity of species is highly important. The species that appeared to be maintained the most by bleaching were the branching corals. These also were the corals that were washed up on shore the most.


The area effect was also witnessed in the reef. This says that there is increased species richness with increased area. The larger the patches of reefs the great the size of the fish, and the species richness. I would also argue that the area effect could explain why some habitats contained fewer species, particularly if you compared the available space to organisms in the reefs, mangroves and sea flats. The more surface area available the more species our class found. As the more of a type of ecosystem, we explored the more species we found. In smaller areas, there were fewer species than in larger areas.