Every living being is part of a food chain. Food and the animals that eat the food make up a food chain. There are many different food chains in an ecosystem. All together, the food chains in the ecosystem make a food web.
In this article, we'll delve into the intricate dynamics of the Serengeti grassland ecosystem, exploring food web examples and highlighting the crucial roles played by various species. We will examine the Serengeti grassland ecosystem of Tanzania from the perspective of a number of recent theoretical and empirical studies of food webs.
The Serengeti has been studied as a fully functioning natural ecosystem for over 50 years and still retains an almost complete set of plant and animal species. Developing a food web for the Serengeti is a formidable undertaking, yet sufficient work has been done on the major plant and mammalian groups that we can begin to see the outlines of the structure of an intact terrestrial food web dominated by vertebrate herbivores and carnivores.
Trophic Levels in a Food Web
Organisms in food webs are grouped into categories. These categories are called trophic levels.
Producers
Organisms in the first trophic level are called producers. Plants are producers. Algae and some bacteria are also producers. Each producer makes its own food. Most producers use photosynthesis. This is a series of chemical reactions. Plants use these reactions to make energy from sunlight, carbon dioxide, and water.
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Consumers
The next trophic levels are animals that eat producers. These animals are called consumers. Consumers can be carnivores or omnivores. Carnivores only eat meat. Omnivores eat both meat and plants.
The first level of consumers is made of herbivores. These animals are also called primary consumers. They eat plants, algae, and other producers. Deer, mice, and elephants are herbivores. They eat grasses, shrubs, and trees. In the desert, a mouse is a primary consumer. It eats seeds and fruit. In the ocean, many fish and turtles are herbivores. They eat algae and seagrass.
Secondary consumers eat herbivores. In a desert, a secondary consumer may be a snake. It eats mice. In underwater kelp forests, sea otters are secondary consumers. They hunt sea urchins.
Animals in the next level are called tertiary consumers. They eat secondary consumers. In the desert, an owl or eagle may hunt snakes.
Top predators are also called apex predators. They eat other consumers. No other consumers eat them. Lions are apex predators on the grasslands of Africa. In the ocean, the great white shark is an apex predator. In the desert, bobcats and mountain lions are top predators.
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Detritivores and Decomposers
Detritivores and decomposers make up the last part of food chains. Detritivores eat plants and animals that are not alive. For instance, vultures eat dead animals.
Some organisms, like fungi and bacteria, are decomposers. They turn decaying plants into soil. Decomposers allow food chains to start over. For example, grass makes its own energy through photosynthesis. A rabbit eats the grass. Then a fox eats the rabbit. When the fox dies, worms and fungi break down its body. The body returns to the soil. There, it leaves nutrients for plants to grow.
The Role of Scavengers
Scavengers are animals that eat dead animals. In the Maasai Steppe Ecosystem where the Wild Nature Institute's scientists work, there are many scavengers which feed on the numerous animals that die from natural causes, or clean up the carcasses after a predator is finished. Vultures, hyenas, jackals, and even predators like lions often scavenge food.
Hyenas are the undisputed top scavengers of the African savanna, with specialized jaws that can crush bones. These spotted hyenas can drive a leopard or lion off its kill. Black-backed jackals are often spotted at the scene of a lion kill. Avian scavengers like White-backed Vultures and Marabou Storks have no feathers on their heads - otherwise, their heads would get covered with blood and tissue from a carcass, which would then become a source of disease. The White-backed Vulture is listed as Endangered on the IUCN Red List. The massive Marabou Stork may have the largest wingspan of any living bird, and can weigh up to 20 pounds!
Scavengers also provide another service. Dead animals would pile up and take a long time to decompose, especially in drier climates where there are fewer decomposers such as fungi. Therefore, scavengers play an important role in the savanna ecosystem.
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Key Scavengers in the African Savanna:
- Hyenas
- Jackals
- Vultures (e.g., White-backed Vulture)
- Marabou Storks
Seasonal Rainfall Patterns
The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators.
At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation.
Nested Structure of the Serengeti Food Web
The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem.
The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year.
The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species.
Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web.
The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web.
Threats to the Serengeti Ecosystem
If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem. The best way to do this is by controlling the external forces that threaten the boundaries of the ecosystem and by balancing the economic services the park provides between local, national and international needs.
The Food Chain
The resilience of different ecosystem services provided by natural ecosystems depends upon food-web structure and is likely to be sharply dependent upon the trophic level of the species that deliver these services. Aesthetic and spiritual services that require pristine intact ecosystems will be less resilient to species loss than services such as carbon storage, or prevention of erosion, which may still be accomplished in ecosystems that are reduced to mixtures of native and invasive plants and herbivorous insects.
Bioaccumulation and Its Impact
Sometimes, pesticides can affect food chains. Pesticides get into the soil and water. Animals eats plants that are covered in pesticides. The pesticides stay in the animals' fat. When a carnivore eats that animal, it also eats the pesticides. This is called bioaccumulation.
Bioaccumulation happens in water ecosystems, too. Runoff from cities or farms can be polluted. Algae, bacteria, and seagrass absorb the pollutants. Sea turtles and fish eat the seagrass. Then, sharks or tuna eat those fish. When people finally eat the tuna, that meal is full of pesticides.
In the 1940s and 1950s, bald eagles began disappearing. One major cause was a pesticide called DDT. The name DDT stands for dichloro-diphenyl-trichloroethane. It was used to kill insects that spread diseases. DDT builds up in soil and water. Worms, grasses, algae, and fish ate organisms with DDT. Bald eagles ate the fish. They had high amounts of DDT in their bodies. They got it from their prey. These eagles started laying eggs with thin shells. government decided to ban DDT. Food webs have come back in most parts of the country.
Biomass
Biomass is the energy in living organisms. Producers use the sun's energy to create biomass. The higher the trophic level, the lower the biomass. There is more energy in lower trophic levels than in higher ones.
There are always more producers than herbivores in a healthy food web. A healthy food web has many producers and many herbivores. It only has a few carnivores and omnivores.
Every part of a food chain is connected to other food chains. When one part is in danger, others are also at risk. If plants are destroyed, herbivores don't have enough to eat. Their numbers go down. The number of plants can decrease because of drought or disease.
Humans can also destroy food chains by destroying habitats. People cut down forests. We use the lumber for buildings. We also pave over grasslands to build shopping malls or parking lots.
