Why Invasive Alien Species Increases And Decreases In The Ecosystem – Lab Report


            The purpose of this laboratory report was to investigate why invasive alien species increases and decreases in the ecosystem. The analysis involved the examination of the environmental hazard associated with these changes in an ecosystem. Two invasive alien species found in fresh water: zebra and quagga mussels were studied in this laboratory report


            The invasive species are generally transported from their indigenous ecosystem to the new environment through different means. Some species are introduced to the new accidentally or intentionally. For example, species that are used for ornamental purposes such as some gold fish in aquariums are normally introduced to new environment intentionally(Enger, et al., 2011). In the case of zebra and quagga mussels, they were accidentally introduced into United States freshwater lakes by cargo ships. As the cargo ship docks to empty the cargo, water is pumped into the ballast tanks to enhance balance of the empty cargo ship. The pumped water carries in it several diverse organism which are emptied into different parts of the world as the cargo ship is loaded.

Studies indicated that zebra and guagga mussels thrives in their new environment since they colonize the most-rigid abiotic rock layers underneath the lakes. This section of the fresh water lakes is underutilized by other organism hence becoming a perfect breeding ground for zebra guagga mussels. Due to lack of competition, disease causing organism and favorable conditions in terms of temperature and water quality, zebra and quagga mussels exhibits high survival and growth rate(Mc Cann, 2012). In addition, the ecosystem functions through inter twin balanced interactions between the organism. As a result, the population of the organisms increases and decreases based on the principle of food chain and interdependence. When an organism face little or competition in terms of food and breeding ground thrives, but as the competition increases, the population reduces accordingly.


            The introduction of zebra and quagga mussels into the United States fresh water lakes led to the decline of indigenous fresh water species.


            Six different species composed of producers and consumers were observed over a period of 20 years. The densities of zebra and quagga mussel, phytoplankton, zooplankton, cladophora biomass, foraging fish and lake trout were recorded in a tubular form as shown in the table below.



Zebra and Quagga Mussel (density/m2)

Phytoplankton (ug/ml)

Zooplankton (ug/ml)

Cladophora Biomass (g/m2)

Foraging Fish (kilotons)

Lake Trout (kilotons)

0 100 3 2 10 150 15
4 1000 2.5 1 100 100 10
7 2500 2 0.5 200 80 8
10 7500 1.5 0.25 600 50 5
13 15000 1 0.1 700 25 2.5
16 7500 1.5 0.2 243 40 4
20 5000 1.75 0.4 136 60 6



            The results observed in the study indicated that producer and consumers are directly related. As the number of producers increases, the number of consumers also increases due to high availability of foods. However, the population of consumers subsequently reaches a point where it cannot be supported by the producers. As a result, the population of the producers reduces and consumers also reduces.

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