C.3 Impacts of Humans on Ecosystems

Question 1

Alien species

Answer 1

Competitive exclusive principle: when the alien species has even the slightest advantage over another then the invasive species will dominate:

• Higher reproductive rate
• Large size/more aggressive
• Faster/more efficient forager
• Absence of predator and competitors: invasive species often lack a natural predator in the new area due to initially belonging to a foreign environment

Question 2

Impacts of introducing alien species

Answer 2

• Excessive predation of native species
• Interspecific compeition with native species which constitute similar niches
• Reduces biodiversity

Question 3

Biological control

Answer 3

Can be used to limit an invasive species by introducing antural predators of the invasive species to limit its spread.

Question 4

Risks of biological control

Answer 4

The newly introduced species as biological control itself may become invasive –> requires verification by tightly controlled experiments in approved facilities.

Question 5

Cane toad

Answer 5

Introduced to Australia with the aim of it acting as a biological control for the cane beetle (agricultural crop pests feeding sugar canes)
The toad is native to central and S America.
Becomes a generalist predator and a competitor for food resources.
Toxin secreted by a gland behind its head when being disturbed –> lethal to predators
Toxic skin
Very high reproductive rate
Very large in size (up to 1 kg) and try to eat “almost any terrestrial animals”

Underdevelopment of biological control mechanisms based on viruses and parasites specific to the cane toad.

Question 6

Zebra mussel

Answer 6

Native to the Black Sea
Introduced to North America Great Lakes system by ballast water by cargo ships.
Spread to many N America river systems
Covered the underside of docks and boats.
The population growth is too rapid and density is too high that they block pipes, clog water systems and interfere with hydroelectric power generation.

Suggested biological control: a bacteria which produces toxin specific to zerba mussels

Question 7

Controlling alien species

Answer 7

• Using herbicides
• Selective harvest of invasive plants
• Trapping and culling of invasive animals
• Removal of invasive mammal species from islands

Requires:

• Removing the invador faster than it can reproduce
• Ongoing commitment until completion
• Support from local communities
• Preventing re-invasion

Question 8

Biomagnification

Answer 8

The process by which toxins become more concentrated at higher trophic levels.
This is because organisms at higher trophic levels need to consume large quantities of prey, and the toxins they contain during their lifetime.
May varry depending on the toxin: fat-soluble, how easily it can excreted?

Ex: DDT caused falls in the populations of some birds or prey (e.g. falcons and ospreys) between 1950s and 1960s

Question 9

Bioaccumulation

Answer 9

Toxin builds up in the body of organisms in a trophic level, partcularly if the toxin is fat-soluble and not easily excreted.

Question 10

DDT

Answer 10

An insecticide widely used in the mid 20th century, initially to control disease vectors (e.g. ticks and mosquitos) and later on as agricultural insecticide.

Question 11

Bioaccumulation and biomagnification of DDT

Answer 11

DDT was washed away into waterways from agricultural fields in low concentrations, where it is biomagnified up the food chain.

Caused:
Falcon and ospreys having thin-shelled eggs –> failure to reproduce successfully

Question 12

Pros of using DDT

Answer 12

• Affordable and effective at killing mosquitoes that carry malaria
• Where the use of DDT is continuef for malaria vector control, malaria rates and deaths decreased
• Alternative strategies were not successful
• Health costs of treating malaria are greatly reduced

Question 13

Cons of using DDT

Answer 13

• Human exposure to DDT may cause serious health effects: reduced fertility, cancer and damage to developing brains
• Persists in the environment for long periods of time (> 15 years)

Question 14

Macroplastic

Answer 14

Large visible debris (e.g. nets) that has not degraded yet.

Question 15

Microplastic

Answer 15

Fragments formed by physical and chemical degradation of macroplastic (

Question 16

Gyres

Answer 16

Where plastic debris is concentrated as ocean currents transport macro and microplastic to these 5 areas.

Question 17

Consequences of marine plastic pollution

Answer 17

1. Degredation –> release of organic chemicals –> bioaccumulation and biomagnification;
2. Plastic can absorb other persistent organic materials and thus concentrate these toxins
3. Eaten by animals –> blocks intestine/stomach
4. Suffocation: if inhaled or wrapped around the throat
5. Animals being tangled up in plastic pollution

Question 18

Laysan Albatross

Answer 18

Marine bird living on an island on the Pacific ocean.
On the island, the North Pacific gyre contacts the shore and trasport large Q of plastic onto the bleaches.
Parent Laysan Albatross feed their chicks with plastic pieces –> high mortality rate