Question

Three years ago, a 5 km³ section of the Great Lakes was studied and approximately 89 000 zebra mussel colonies were found. Each colony produced 120 colonies over a three-year period. However, only 2% of the new colonies survivedpast the first year.

Over the three years, there were 97 000 dead colonies that were washed ashore in the Great Lakes. Many of the zebra mussels attach themselves to hard surfaces, such as boats and trailers. It was estimated that approximately 85 000 colonies attached themselves to boats and left the area. Many of these zebra mussels died, but some managed to hitchhike on boat equipment and enter other waterbodies. Negligible numbers of zebra mussels migrated from other lakes.

1. Calculate the population density at the end of the third year

Answer 1

Let's find out population at the start of the 3 years.

Total 89000 colonies gave rise to 120 colonies in 3 years , in 1 year 40 colonies and out of those only 2 % will survive ie, 2.4 colonies in 3 years by each 89000 colonies is produced.

So, total colonies = 89000× 2.4 = 213600 colonies.

Now,97000 became dead , colonies left = 213600-97000= 116600

Out of this 85000 colonies left the area

So population density left after 3 years = 116600-85000 = 31600 colonies.