C The Impacts of Humans on Ecosystems

Question 1

what 3 main activities impact the ecosystem

Answer 1

1. introduction of alien species
2. pollution by humans leading to biomagnification
3. plastic pollution in the oceans

Question 2

what are endemic, alien and invasive species

Answer 2

endemic -native

alien - not native and introduced by humans

invasive - alien species increases in number and spreads rapdily

invasive often happens also often the normal limiting facctors in their original habitat are missing in a new area e.g. predators, diseases, competitiors - population number is not controlled

Question 3

why can an invasive species lead to extinction of a native species

Answer 3

1. act as a predator and eat many organisms in one particular species
2. release toxins and be harmful to native predators that try to consume it
3. introduce a disease to which native species are not resistant
4. compete with native species for the same resource (identical niche, competitive exculsion principle)

most successfully harmful if invasive species occupy the same niche, competitive exclusion principle, if they occupy the same niche then number will decrease or both or one species will narrow its niche

Question 4

example of an invasive species

Answer 4

grey squirrles ( alien) out compete red squirels (native)

grey - lack predators, grow, out compete

red - decrease, eradicated

Question 5

case study - introduction of alien specie sof cane toad to australia and the zebra mussle

Answer 5

cane toad introduced to act as a biological control

toad has become a generalist predator and competitor for food resources

toad has gland on head that releases toxins when eaten so is lethal to predators of the toad

zebra mussle is an invasive species in north america and black and caspian sea

empty cargo ships fill hulls with water to remain stable, transported to other locations and can lead to an invasive species if no measures are taken

have spread to river systems and covered the underside of docks and boats –> can grow so dense they block pipes, clogs and interfer with hydroelectric power generation

Question 6

what is biomagnification?

Answer 6

in the past humans relased pollutant into the environments, thinking low concentrations wouldn’t affect it

biomagnification occurs - lead to death of organism - process by which chemical substances becomes more concentrated in the organisms in each trophic level as you go up a food chain

this is because at each trophic level the pedator is eating many prey organisms and conusming toxins with each one so the toxins build up over time reaching higher and higher concentratoon

if the toxin is fat soluble it is more likely to accurmulate as it is not easily excreted

Question 7

benefits and risks of using DDT

Answer 7

used to control the malarial parasite but leads to pollution

insecticide - leads to ecological effects, magnifies so birds have thin shelled eggs so cannot reprodcue –> was banned for some purposes

but no other substitute so some countries have unbanned it

–> concerns over effect on human health

Question 8

how is pastic pollution affecting the oceans?

Answer 8

humans dispose of macroplastic in water systems that lead into oceans

chemical and physical degradation of this leads to formation of microplastics which disperse widely and are hard to see

ocean currents transport our garbage so it builds up in specific areas in the ocean called gyres

effects of this

• death of larger organisms due to microplastics and their toxins bioaccumulating as you go up the food chain
• death of orgnaism as they eat/ get tangled in plastic