2.2 Pesticides Casestudy

Pesticides Casestudy

(a) … in what circumstances would each organism (fig3) be considered a pest, if any. •Dandelions - unsightly. •Grasshopper / Mice – numbers increase to become a pest •Deer – consume all the grasses

(b) … how might the removal of one of the pests affect the food web? •…

lead to an insufficient food supply for their consumers.

(c) … short-term benefits of using pesticides: • an

increase in crop yield.

•Preventing loss of stored grains •Preventing allergies (moulds, mildews)

(d) … why might chemical taken from plants be less risky to humans and the ecosystem? • they

might be less dangerous because they are more easily broken down; and do not build up in the bodies of consumers (bioamplification)

(e) … the difference between a pyramid of biomass and a pyramid of bioamplification. • the

biomass graph would have a large base and gradually decrease in width. The pyramid of bioamplification would have a narrow base and increase in width each step upwards.

(f) … predict how scavengers might be affect by bioamplification. … if the scavenger consumes from dead organisms from higher trophic levels, there would be a greater amount of bioamplification.

(g) Why is the fact that other countries have not banned DDT of concern to Canadians? … DDT can be transferred to organisms in Canada by migrating fish, sea mammals, and birds. Also by imported foodstuffs.

(h) … how might breastfeeding affect the DDT levels in mother & baby? … DDT is fat-soluble and can be found in breast milk and would be passed to the baby.

(i) Why are newer pesticides less harmless to ecosystems than DDT used in the 1950s and 60s?

… the newer pesticides are water-soluble (not fat-soluble) and does not accumulate in fat tissue.

(j) … how does less competition for food help increase the reproductive success the insects that remain after the use of pesticide?

… as there is more food for those remaining, they will more likely breed and more of their offspring would survive.

(k) … which decade shows the greatest increase in pesticideresistant species? Why?

… between 1970 and 1980 … because the # of resistant species increases with length of time the pesticide is used.

(l) … why haven’t the spruce bud worm been eliminated after 40 years of spraying?

… the budworms have become resistant to all available pesticides.

(m) … why haven’t they used extremely high concentrations of insecticide?

… this would kill not only the budworms but also kill other possibly helpful organisms.

(n) … what groups have benefited from the NB spray program?

… loggers, lumber and papermill workers.

(o) … what groups might have suffered from the NS decision not to spray?

… loggers, lumber and papermill workers … First Nation groups who use the forest.

(p) … what are the benefits of not spraying?

… the ecosystem adjusted and a natural recovery occured.

(q) … why is DDT more dangerous to freshwater ecosystems than the newer water-soluble pesticides?

… DDT builds up in fat tissues (bioamplication) causing problems in top predators (falcons). The newer pesticides are broken down the kidneys and passed in urine.

(r) … female eagles have slightly lower levels of toxins than male eagles - why? … fat-soluble toxins are released from the female during egg-laying. Males have no means to release toxins during their 25-year lifespans.

Continued (r) … compare egglaying in eagles to breast-feeding in humans? … human mothers will release toxins stored in fat tissues in their breast milk. However, these toxins would move to their babies.

(s) Draw a food web, showing the movement of pesticides in a lake ecosystem from aquatic insects to the bald eagle? Herons

ducks

hawks

gulls

Larger fish Medium-size fish Insects .

shellfish Zooplankton phytoplankton

minnows