C.3 Impacts of humans of ecosystems Flashcards
What is an alien species?
Alien species are those that have been transferred (or arrive) from their natural habitat to a new environment.
To be contrasted with endemic species: those which are native to a defined geographic region
Invasive alien species
Often, an alien species is not well adapted to the new habitat and will not survive as it is to far outside its niche. However, if an introduced alien species should have a detrimental effect upon the pre-existing food chains, it is classified as invasive.
- Invasive species typically threaten the biodiversity of the ecosystem they are introduced into by displacing native species
Example of an alien species: cane toads in Australia
Case study 1
The cane toad was introduced in Australia in 1935 to control the spread of the sugar cane beetle that was damaging crops
- It failed to limit the beetle population (as the beetles live at the tops of sugar canes where the toads couldn’t reach them)
The cane toad has reproduced rapidly and is now classified as an invasive species that endangers the native wildlife
- It has a wide diet and has depleted the prey population for native insectivores
- It secretes a toxic chemical from its skin that has poisoned native predators
- It has carried diseases that have been transmitted to native species of frogs and fish
Since its introduction, the cane toad has spread across the northern fringes of Australia and has proven difficult to eradicate
- The cane toad has no natural predators in Australia to reduce its population size and now number in the millions
Example of an alien species: Wild rabbits in Australia
Case study 2
European rabbits were introduced to Australia with the arrival of the First Fleet
- Australian conditions promoted a population explosion (mild winters allowed rabbits to breed the entire year)
- It was the fastest spread ever recorded for any mammal anywhere in the world
Since their introduction, rabbits have had a devastating effect on native Australian ecology:
- They have killed native plant species by ringbarking (removing a strip of bark that prevents future growth beyond that point)
- The loss of native plants has left the topsoil exposed and vulnerable to extensive erosion from wind and rain
Various strategies have been employed to control rabbit populations with varying effect:
- ‘Rabbit-proof’ fences were built to try and contain rabbit populations
- Methods of hunting and poisoning have been utilised, along with efforts to destroy rabbit warrens
- Rabbit-borne diseases have been released with moderate success (e.g. myxomatosis virus)
Competitive exclusion and the absence of predators can lead to reduction in the numbers of endemic species when alien species become invasive.
Competitive exclusion principle: Two species cannot occupy the same niche in a community, as there will be competition for the same resources. When one species has even the slightest advantage or edge over another then the one with the advantage will dominate.
Invasive species possess several advantages that allow them to displace endemic species via competitive exclusion:
- They typically possess a large fundamental niche (can occupy a wider area than endemic species)
- They will often have faster reproduction rates (are capable of forming a larger population than endemic species)
- They commonly lack a predator capable of limiting their survival (due to being introduced into a foreign environment)
- They may possess certain features that are suited to the new environment (e.g. more aggression, better foraging, etc.)
What is biomagnification?
Biomagnification is the process in which chemical substances become more concentrated at each trophic level
- Biomagnification occurs because organisms at higher trophic levels must consume more biomass to meet requirements. This means higher order consumers will experience increased contamination from a chemical substance
Discussion of the trade-off between control of the malarial parasite and DDT pollution
DDT was widely employed as a chemical pesticide in the 1940s and 1950s to control insect-borne diseases like malaria
- Its use as an agricultural insecticide led to the complete eradication of malaria in many high socioeconomic world regions
- It was less effective in low socioeconomic tropical regions where eradication programs could not be sustained
Eradication programs were curtailed by the World Health Organisation in 1969 over safety and environmental concerns
- DDT can bioaccumulate to toxic levels and poses a significant threat to higher trophic levels (due to biomagnification)
- Current interventions for malaria now focus on non-spraying strategies (such as the use of bednets soaked in insecticides)
Arguments for DDT Spraying:
Malaria vs DDT
- DDT spraying is an affordable and effective means of killing mosquitos that carry disease (malaria, dengue fever, etc.)
- Where the use of DDT has been discontinued, the incidence of malaria and associated deaths have increased
- Health costs associated with the treatment of malaria are reduced when DDT spraying is implemented
- Alternative strategies are not as cost-effective or successful
Arguments against DDT Spraying:
- DDT spraying is associated with adverse health effects in humans (cancer, birth defects, reduced fertility, etc.)
- DDT persists in the environment for long periods of time (more than 15 years)
- DDT is biomagnified in higher order consumers, which has adverse consequences on ecosystems
Plastic pollution
sources and effects
Plastics are a type of synthetic polymer found in certain types of clothes, bottles, bags, food wrappings and containers
- Most plastics are not biodegradable and persist in the environment for many centuries
Organisms (such as marine animals), can consume both macro and micro plastics thinking it is food.
- This leads to the bioaccumulation and biomagnification of persistent organic pollutants within marine animals
Example: laysan albatross
Case study of the impact of plastic debris: Laysan albatrosses
Case study 1
- The Laysan albatross feed by skimming the top of the water and often pick up floating plastic garbage
- They they feed this to their children which don’t have the ability to regurgitate the plastic
- Consequently the mortality rate in albatross chicks is very high
Case study of the impact of plastic debris: Sea Turtles
- Sea turtles commonly mistake plastic bags for jellyfish (one of their primary food sources)
- Ingestion of the plastic can be fatal – the plastic can become lodged in the esophagus and cause future feeding problems
- Plastic debris can also become wrapped around the turtle, restricting movement and developmental growth
