An ecosystem is a community of living organisms and the nonliving components of the environment. energy flows in an ecosystem in one direction through food chains, and a food web is made up of all the food chains within a community of organisms. biodiversity refers to the variation in species found within an ecosystem, and it is measured in two ways: (1) species richness, which is the total number of different species in an ecosystem; and (2) relative abundance, which is a measure of how common each species is within the ecosystem. the alewife, found in the blue banded row of fish in this food web, is an invasive species found in the great lakes. in fact, there have been about 25 invasive species of fish found in the great lakes over the last century. yet the ecosystem of the great lakes has remained relatively stable. according to the passage and the model, what factor(s) contribute to the lake ecosystem's long term sustainability? a biodiversity and complex feeding relationships b effective methods to eradicate invasive species c low number of invasive species; high native species number d high number of organisms in the producer and primary consumer levels