Tropical Thursday

The rainforest is teeming with dynamic relationships!

There are many dynamic relationships in the rainforests of the world. Which is expected as they are home to up to 40 percent of known plant and animal species. Within the forest there are a widely variety of symbiotic relationships, which means there are interactions between two species. For some species the relationship is beneficial for both parties, this is call mutualism. For example the Brazil nut trees (Bertholletia excelsa) produces a nut that is an only be cracked by a few species, one of which is various agouti (Dasyprocta sp.) which is a small rat like animal. The tree benefits as it’s seeds are dispersed and the agouti receives a free meal.

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Description
English: A Central American Agouti (Dasyprocta punctata) in Panama experimenting with a western diet.
Source BirdPhotos.com
Author Tomfriedel

In some cases one species is unaffected and the other benefits, this is commensalism. A example of this would be a frog sheltering itself from a storm event under the leaves of a plant. The plant is un effected but the frog benefits. Lastly, parasitism is when one species is harmed and the other benefits. Bot flies are a common tropical parasite that lay their eggs on a mammal host. The eggs then hatch and the larva develop in the skin of the host animal.

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A frog in the rain in Belize. Image by Lauren Schramm

Competition is a symbiotic relationship in while two species use the same resources. Because it requires an energy investment both species are harmed, but the harm may be unequal. Many rainforest plants are animal pollinated or their seeds are dispersed by animals. Resource partitioning occurs when a resource is divided among species in some way like time or place. One way plants reduce their competition against each other is by targeting different animal groups. For example flowers pollinated by bats are often white making them easier to see at night, while flower pollinated by other animals are red, orange, and yellow. Bat pollinated flowers also contain a musky smells, while flower pollinated by moths, bees, and other insects have a strong fragrance. Plants also reduce competition by flowering and fruiting at different times. This is one reason there are always flowers and fruits available in the rainforest at any given time.

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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.

 

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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.

 

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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. 

 

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

 

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Tropical ecosystems: savannas, rainforests and reefs

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.

 

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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.

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Marine ecosystems of Belize- corals and mangroves

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 photosynthesis. This 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.

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

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