Ecological Consequences
Page 13 of 14
As we have seen, ecology is a science that studies how nature works by studying the interrelationships that exists in the Biosphere between its inhabitants and the nonliving environment that surrounds them. One important outcome of these studies is the knowledge that species do not live as isolated entities. They are connected to one another. These connections create dependence between species. Thus, the consequences of human activity can cascade through an ecosystem causing harm to many interconnected species. Here is an example!
Flathead Lake in western Montana is 28 miles (45 km) long and 365 feet (111 meters) deep. The opossum shrimp is a small crustacean that entered the lake after being introduced in other locations. They are considered to be a food source for sports fish. Prior to their invasion into Flathead Lake, phytoplankton (microscopic photosynthetic energy factories in the lake) were fed on by microscopic zooplankton (microscopic herbivores) that included several species of small crustaceans called cladocerans. Kokanee salmon fed on these zooplankton and thrived. In turn, grizzly bear and bald eagles fed on the salmon to meet their energy and nutrient needs.
It was thought that the opossum shrimp would be a further source of food for the salmon, thereby increasing fish stock and fishing revenue for the community. Thus, the entrance of the opossum shrimp into the lake appeared to be a good thing. However, the opossum shrimp is inhibited by light and stays at lower depths in the lake during the day when salmon are actively feeding. At night the opossum shrimp migrates to the surface and feed on the same zooplankton as the salmon, thereby becoming a competitor with the salmon (rather than a food source for them). This situation created a cascading effect in the Flathead Lake ecosystem. Some cladoceran populations were either completely destroyed or severely reduced by opossum shrimp. Without adequate food, the salmon population crashed and destroyed the Kokanee salmon industry. Grizzly bear and bald eagle populations also declined.
The Flathead Lake story illustrates how living things are connected and how human-induced alterations can have severe economic and ecological consequences.
Flathead Lake in western Montana is 28 miles (45 km) long and 365 feet (111 meters) deep. The opossum shrimp is a small crustacean that entered the lake after being introduced in other locations. They are considered to be a food source for sports fish. Prior to their invasion into Flathead Lake, phytoplankton (microscopic photosynthetic energy factories in the lake) were fed on by microscopic zooplankton (microscopic herbivores) that included several species of small crustaceans called cladocerans. Kokanee salmon fed on these zooplankton and thrived. In turn, grizzly bear and bald eagles fed on the salmon to meet their energy and nutrient needs.
It was thought that the opossum shrimp would be a further source of food for the salmon, thereby increasing fish stock and fishing revenue for the community. Thus, the entrance of the opossum shrimp into the lake appeared to be a good thing. However, the opossum shrimp is inhibited by light and stays at lower depths in the lake during the day when salmon are actively feeding. At night the opossum shrimp migrates to the surface and feed on the same zooplankton as the salmon, thereby becoming a competitor with the salmon (rather than a food source for them). This situation created a cascading effect in the Flathead Lake ecosystem. Some cladoceran populations were either completely destroyed or severely reduced by opossum shrimp. Without adequate food, the salmon population crashed and destroyed the Kokanee salmon industry. Grizzly bear and bald eagle populations also declined.
The Flathead Lake story illustrates how living things are connected and how human-induced alterations can have severe economic and ecological consequences.
Opossum shrimp lived at the lake's bottom during the day. At night (when salmon were inactive) they migrated to the surface of the lake and fed on cladocerans. Thus, instead of serving as a secondary food source for salmon, they contributed to the decline of various species of animals, including bald eagles and bears.
Credits: Bear, Bald Eagle (Dorling Kindersley) / Opossum Shrimp (Dennis J. Gemmell