c.3- impacts of humans on ecosystems

Question 1

what is the problem with alien species being introduced?

Answer 1

they can escape into local ecosystems and become invasive.

Question 2

endemic species

Answer 2

species native to an area

Question 3

alien species

Answer 3

species that are not native but are introduced by humans

Question 4

what is an invasive species?

Answer 4

a species that increases in number and spreads rapidly

Question 5

why are many alien species invasive?

Answer 5

because the normal limiting factors in their original habitat are missing (eg predators, diseases, competitors).

Question 6

give 2 examples of harmful impacts of alien species

Answer 6

• excessive predation of native species
• interspecific competition due to niche overlap with native species

Question 7

—– —— and the —— – —— can lead to a reduction in the numbers of endemic species when alien species become invasive

Answer 7

competitive exclusion; absence of predators

Question 8

define the competitive exclusion principle

Answer 8

two species with overlapping niches cannot continue occupying overlapping niches indefinitely

Question 9

give 2 possible effects of competition between endemic and alien species

Answer 9

• either or both species may occupy smaller realised niches
• the ability of a new ecosystem to resist an alien species can prevent it from becoming invasive

Question 10

define bioaccumulation

Answer 10

the build up of toxins in the body of organisms

Question 11

when is bioaccumulation most likely to happen?

Answer 11

when the toxin is fat-soluble and not easily excreted

Question 12

define biomagnification

Answer 12

the process by which chemical substances become more concentrated at each trophic level

Question 13

why does biomagnification happen?

Answer 13

at each stage in a food chain, the predator consumes large quantities of prey during its lifetime and bioaccumulates the toxins that they contain.

Question 14

——– AND ——- have accumulated in marine environments

Answer 14

microplastic; microplastic debris

Question 15

describe the causes and effects of plastic accumulation in the ocean

Answer 15

causes:
- direct disposal from ships and platforms
- litter being blown into water systems
effects:
- degradation of the plastic at sea releases persistent organic chemicals that can bioaccumulate/magnify
- plastics absorb other persistent organic chemicals and thus concentrate these toxins
- animals eat/become tangled in plastic

Question 16

give two examples of when biological control can go wrong

Answer 16

Cane toad
- introduced to Australia to control the cane beetle
- has become a generalist predator and competitor for food resources
- big ecological impact on predator that consume the toad (as it is lethal to consume)
Zebra mussel:
- invasive species of the North American Great Lakes system that is native to the Black/Caspian Sea.
- brought by empty cargo ships
- populations can grow so dense that they block pipes, municipal water systems or interfere with hydroelectric power generation

Question 17

define biological control

Answer 17

involves using a living organism (or a virus) to control an invasive species

Question 18

define eradication programmes

Answer 18

involve application of herbicides or selective harvesting of invasive plants, and trapping/culling of invasive animals

Question 19

describe the uses, benefits and risks of DDT

Answer 19

Insecticide used to control vector diseases and in agriculture.

• DDT pollution is biomagnified up food chains, and leads to birds of prey having thin-shelled eggs and failing to reproduce successfully.
• in humans it can cause reduced fertility, genital birth defects, cancer, damage to developing brains, and its metabolite, DDE can block male hormones
• accumulates in body fat/breast milk and persists in the environment for decades.

It is very good for malaria vector control- when the use of DDT was discontinued for malaria vector control, malaria rates climbed.

Question 20

Give 2 case studies for plastic pollution

Answer 20

Laysan albatross:
- nests on islands found in the North Pacific gyre, where large amounts of plastic debris is found
- feeds by skimming the ocean surface with their beak, causing them to ingest large quantities of plastic
- adults can regurgitate the plastics they have swallowed, but chicks are unable to – as such it fills up their stomachs
- mortality rate is high

Sea turtles:
- commonly mistake plastic bags for jellyfish
- ingestion of the plastic can be fatal – the plastic can become lodged in the esophagus and cause future feeding problems
- debris can also become wrapped around the turtle, restricting movement and developmental growth