Back To CourseBiology 101: Intro to Biology
24 chapters | 220 video lessons
Phil and Angie took a trip around the world together. They're so excited about all of the cool things that they saw, and they'd like to share some of their experiences with you!
The first stop on their trip was the temperate deciduous forests of the eastern United States. Temperate deciduous forests are forests in temperate climates that are characterized by broad-leaved deciduous trees. These forests are found at mid-latitudes in areas that get significant rainfall in the warm summer months, which can support fast-growing species like birch, hickory, maple, and sycamore trees.
However, at mid-latitudes, the winters are often too cold for the leaves of these trees to survive, so when the temperatures start to drop, the leaves of these trees die and fall off. The trees themselves then go into a dormant phase to survive the winter, and the lack of leaves helps to prevent the buildup of snow on the branches that could weigh them down to the point of breaking.
Trees that lose their leaves all at once in a seasonal cycle are called deciduous trees. Phil and Angie decided to start their trip in the autumn because the deciduous forests of the United States are famous for the spectacular display of color in the fall. As the leaves begin to die, the chlorophyll, which gives most leaves their green color, is broken down and disappears. This absence of chlorophyll allows us to see other pigments in the leaves, which can make the leaves appear red, yellow, orange, or brown.
The next stop on the trip was the tropical rainforest in South America. Tropical rainforests are forests in the tropics that receive over 100 inches of rainfall per year. Most types of forests can support large populations of plants and animals; however, tropical rainforests support the greatest number of species of any other type of biome on the planet. This incredible species richness is due largely to the combination of a tropical climate and high, year-round rainfall, which provide optimal growing conditions for the largest number of plant species. In turn, the high number of plant species can support a high number of animal species.
With such high productivity in the tropical rainforest, you might expect the soil to be rich with nutrients; however, it's just the opposite. The warm, wet conditions in the tropical rainforest cause rapid decomposition of any detritus, and because sunlight and water are plentiful, any nutrients released into the soil are rapidly used by the fast-growing vegetation, leaving the soil amazingly poor considering the high productivity of the biome. However, as long as the forest remains intact, nutrients will quickly cycle through the ecosystem. This rapid cycling produces a steady input of nutrients into the soil that plants can use, and that is how the poor soil can support such a massive amount of biomass.
After the tropical rainforests of South America, Phil and Angie hopped on a plane to Tanzania to visit the Serengeti National Park. Angie really likes giraffes, and although she has seen giraffes in zoos, she thought it would be really cool to see them in their natural habitat, the African savanna. Savanna is essentially grassland interspersed with trees. It is sometimes found in temperate climates, usually in areas that are transitional zones between grassland and forests. However, savanna is mostly found in tropical regions of the world where the climate changes in a seasonal pattern from cool and dry to hot and dry and then to warm and wet before starting the cycle again the following year. This is the type of savanna found in the Serengeti National Park, which is famous around the world for supporting so many large animals such as giraffes, elephants, rhinos, zebras, wildebeest, cheetahs, leopards, and lions.
While Phil and Angie were in Africa, they decided to take a few days to visit Lake Malawi, which is a very large lake located just South of Tanzania. Phil in particular wanted to visit this lake because he had an aquarium at home, and some of his favorite aquarium fish are found only in Lake Malawi. Lakes, ponds, streams, and rivers are all examples of freshwater aquatic biomes. Since lakes, ponds, streams, and rivers are often naturally isolated from each other in many ways, species of freshwater fish are often found only in one particular lake or river system or even in a single stream. These species are said to be endemic, or only found in one particular area.
Lake Malawi is a good example. It's the eighth largest lake in the world and is home to an estimated 1,000 different species of fish. There are so many different species in the lake that most of them haven't been fully described and identified. However, of the approximately 350 described species of rockfish or mbuna in the lake, only five of them are found in other bodies of water. Overall, it's thought that over 90% of the fish species in Lake Malawi are endemic and found nowhere else in the world.
The next leg of Phil and Angie's trip took them to Australia. One of Angie's life goals was to go on a walkabout in the Australian Outback, most of which is considered to be desert. Desert biomes are characterized by very little rainfall, so any landscape that gets less than 12 inches of rain per year can be considered desert. They occur at all latitudes, and although the popular depiction of deserts is a vast expanse of nothing but sand for miles, deserts can have a variety of soils, plant life, and animal life. In the Australian Outback, drought-resistant plants with small, leathery leaves are common, and some plants, like the desert bloodwood tree, store large quantities of water in their roots to survive prolonged periods of drought.
Animal density is not very high in deserts, but even so, insects, arachnids, lizards, snakes, mammals, birds, and even some amphibians can all be found in the Australian desert. Each of these animals has its own methods for conserving water and making use of specific food sources in what might seem like uninhabitable conditions.
And finally, what trip to Australia would be complete without visiting the Great Barrier Reef? Coral reefs occur in tropical marine environments where sunlight can reach the ocean floor or any other solid structure that corals can attach to. Coral reefs are pretty much the complete opposite of deserts. First off, coral reefs are the most productive biomes on Earth on a per-acre basis. We can compare this to deserts, which aren't quite the least productive but are pretty close to the bottom. There's also the obvious main difference that deserts contain very little water and coral reefs are submerged in water, and then there's the striking difference in the amount of visible animal life. Desert animals often remain hidden in burrows during the day, and many also use camouflage. In contrast, the fish, corals, and other animals of the coral reefs are abundant and include many of the most brightly colored species in the world.
However, while the animal life is prominent, plant life is strikingly absent. Sure, some corals look like plants, but they're actually animals. So where do all of these animals get their energy from - where are all the producers? It turns out that most of the producers in coral reefs are symbiotic dinoflagellates that live within the corals themselves. Dinoflagellates are single-celled organisms that are capable of photosynthesis. Dinoflagellates are fairly unique among organisms because they can thrive either as free-swimming ocean dwellers or as intracellular symbionts, while most other species have only one type of life cycle.
In summary, there are many types of ecosystems around the world that can be categorized into different biomes. Several factors determine what type of biome is present in a given area, but two of the most important factors are water abundance and latitude, which is basically how far a place is from the equator.
Temperate deciduous forests are forests in temperate climates that are characterized by broad-leaved deciduous trees. These forests are found at mid-latitudes in areas that get significant rainfall in the warm summer months.
Tropical rainforests are forests in the tropics that receive over 100 inches of rainfall per year. Tropical rainforests support the greatest number of species of any other type of biome on the planet.
Savanna is grassland interspersed with trees. It is sometimes found in temperate climates, usually in areas that are transitional zones between grassland and forests. However, savanna is mostly found in tropical regions of the world where the climate changes in a seasonal pattern from cool and dry to hot and dry and then to warm and wet before starting the cycle again the following year.
Lakes, ponds, streams, and rivers are all types of freshwater aquatic biomes. Since lakes, ponds, streams, and rivers are often naturally isolated from each other in many ways, species of freshwater fish are often endemic to a particular lake, river system, or even a single stream.
Desert is any landscape that gets less than 12 inches of rain per year. Deserts occur at all latitudes and can have a variety of soils, plant life, and animal life.
And finally, coral reefs occur in tropical marine environments where sunlight can reach the ocean floor or any other solid structure that corals can attach to. On a per-acre basis, coral reefs are the most productive biomes on Earth.
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Back To CourseBiology 101: Intro to Biology
24 chapters | 220 video lessons