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 breast-feeding 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 pesticide-

resistant 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 paper-mill workers.

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

to spray?

… loggers, lumber and paper-mill 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 egg-laying 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 minnows

. Zooplankton

phytoplankton