Ecosystems and sustainability
Ecosystem: Any group of living organisms and non-living thins occuring together, and the interrelationships between them, eg, african grassland or a pond
They are dynamic:
-Population sizes rise and fall, because the community of living things interact with eachother and with their physical environment, so any small changes affect each other, eg:
-if predator's pop. rises, they prey pop. will fall (more predators to eat prey)
-the nitrogen levels in the soil can affect the pop. sizes there- only nitrogen fixing plants would grow in nitrogen-deficient soil, increasing the nitrogen levels and therefore more plants to grow there.
Habitat: place where organism lives
Population: all of the organisms of one species, who live in the same place at the same time+can can breed together
Community: all the populations of different species that live in the same place at the same time and can interact with eachother.
The role that each species plays in an ecosystem is its niche- it is hard to work out its niche because of the many interactions between living and non-living things.
Abiotic factors are non-living factors/components in an ecosystem, eg pH, temp and soil type
Biotic factors are living factors/components in an ecosystem, eg, food supply, predation and disease
Producers: photosynthetic organisms eg, plants, such as algae or bacteria, supply chemical energy to all other organisms
Primary consumers: herbivores who feed on the plants, and they are eaten by secondary consumers, who are eaten by carnivorous tertiary consumers.
Some living things called decomposers (bacteria, fungi, some animals) feed on waste material or dead organisms
Trophic level: hierarchical levels in an ecosystem, consisting of organisms sharing the same function in the food chain and the same nutritional relationship to the primary sources of energy.
Understanding energy transfer
Efficiency of energy transfer:
At each trophic level some energy is lost and therefore unavailable to the organism at the next level:
-At each trophic level, living organisms need to carry out processes such as respiration that releases energy from organic molecules, eg glucose. Some of this energy is eventually converted to heat.
-Energy remains stored in dead organisms and waste material, and so is only available to decomposers-it contains parts of animals and plants that cannot be digested.
Because of this lost energy there is less available to sustain living tissue at higher levels of the food chain, and so less living tissue can be kept alive-ecologists drew a pyramid of numbers to represent this idea.
Pyramid of numbers
Measuring the efficiency of energy transfer
Pyramids of biomass:
Each area of the bars in the pyramid is proportional to the dry mass of all the organisms at that trophic level. To do this properly the ecologist would have to collect all of the organisms and put them in an oven at 80degrees-this is destructive, so measure the wet mass of the organisms and then calculate the dry mass.
Pyramids of energy:
Biomass pyramids can cause issues if different species release different amounts of energy per unit. They may use a pyramid of energy instead, where they burn the organisms in a calorimeter and work out how much heat energy is released by calculating the temp rise of a known mass of water. This is however time consuming and destructive, and so biomass pyramids are more commonly used.
Measuring efficiency- productivity
Pyramids of energy have limitations:
-they only take a snapshot of an ecosystem at one moment in time
-pop sizes can fluctuate-this may provide a distorted idea of the efficiency of energy transfer
-Because of this, ecologists often work out the rate at which energy passes through each trophic level-pyramid of energy flow-this rate is called productivity
-Productivity gives an idea of how much energy is available to the organisms at a particular trophic level, per unit area in a given amount of time (usually per year) -itis measured in MJ or kJ
-at the base of the food chain, the productivity of plants is called the primary productivity
-the gross primary productivity is the rate at which plants convert light energy into chemical energy, after respiration, the energy transferred to the primary consumer is reduced. This energy left over to them is net primary productivity (NPP).
Manipulating energy transfer
Improving Primary productivity:
Humans can increase NPP making energy conversion more efficient, reducing energy loss and increasing crop yields.
-light levels limit rate of photosynthesis+hence NPP-some crops planted early to provide longer growing season to harvest even more light-others grown under light banks
-lack of water is important in many countries-drought resistant barley developed in N. Africa, wheat in Australia and sugar beet in UK
-temp limits photosynthesis-greenhouses can provide warmer temps for growing plants and therefore increase NPP-planting field crops early to provide a longer growing season also helps avoid the impact of temp on final yield
-Spraying crop w pesticides-reduces loss of biomass from pests removing biomass and energy stored in crop
-Herbicides-kill weeds and reduce competition-more crop-more NPP
Manipulating energy transfer
Improving secondary productivity:
It is possible for humans to manipulate enery transfer from producer to consumer:
-young animal invests a larger proportion of energy into growth than adult ones-harvesting animals just before adulthood minimises loss of energy from the food chain
-Selective breeding- produce breeds with faster growth rates, increased egg production+milk production
-Animals treated w antibiotics to avoid unnecessary loss of energy to pathogens+parasites
-Mammals and birds lose a lot of energy walking around to find food+keeping their body temp stable-zero grazing for pig and cattle maximise energy allocated to meat production, and by supplying food to animals means they do not have to look for food. Maintaining a constant environmental temp also reduces energy lost in homeostasis.
Succession: directional change in a community of organisms over time
Example no1: Surtsey in Iceland- created by volcanic eruption but now home to a community of plants: this kind of development is succession:
-algae+lichens begin to live on the bare rock-PIONEER COMMUNITY
-erosion of rock+the build-up of dead/rotting organisms produces enough soil for larger plants like mosses+ferns to grow-these succeed the algae+lichens
-larger plants succeed the smaller plants until a final, stable community is reached-this is the CLIMAX COMMUNITY.
Succession on sand dune- see pg 199
- Pioneer plants such as sea rocket and prickly sandwort colonise the sand just above the water mark-these can tolerate salt water spray, lack of fresh water and unstable sand
- Wind-blown sand builds up around the base of these plants forming sand dunes that get bigger and bigger with the decay of plants-larger dunes =other species such as sea sandwort can colonise it
- With more stability+accumulation of more nutrients plants like sea-spurge and marram grass can grow-marram grass shoots trap wind-blown sand and as the sand accumulates, the shoots grow taller above the sand, trapping more sand.
- as the sand dune+nutrients build, more plants colonise the sand, eg bird's foot trefoil, whose bacteria in their root nodules convert nitrogen into nitrates, with nitrates, more species can colonise the dunes. This stabilises them further- CLIMAX COMMUNITY.
DISTRIBUTION: the presence or absence of the species
ABUNDANCE: estimate or count the number of individuals of each species
-use random sampling to make sample more representative of the whole habitat (use random numbers to plot co-ordinates) or take samples at regular distances across the habitat
-use pilot study to determine how many quadrats to use: make cum. freq. table and plt c.f. against quadrat number- where the curve tails off this is the number of quadrats to use, and ecologists usually double this number.
-do the same as above w quadrat size plotting quadrat area aginst the number of species found in each one
pop size of species = mean number of individuals of the species in each quadrat/fraction of the total habitat area covered by the quadrat
Line transect: at regular distances taking note of which species are touching the tape
Belt transect: at regular distances place quadrat along the transect (interrupted belt transect) or just use the same quadrat and move it along the line (continuous belt transect)
Decomposers and Recycling
-excrete enzymes onto waste material
-the enzymes break down the material into smaller molecules which are absorbed by the organism
-used for respiration and energy stores
-Nitrogen needed to make proteins and nucleic acids
-Nitrogen in unreactive and so it must be fixed in order to be taken in by plants - fixed by nitrogen-fixing bacteria
-e.g. Rhizobium, lives in root nodules of beans and has mutualistic relationship with them, it fixes nitrogen and gets glucose from the plant in return
-Proteins such as leghaemoglobin absorb O2 and keep conditions anaerobic, allowing the Rhizobium to use an enzyme, nitrogen reductase, that reduces nitrogen gas to ammonium ions so that it can be used.
Decomposers and Recycling
This happens when chemoautrophic bacteria absorb ammonium ions:
-bacteria involved in the putrefaction of proteins in waste material release ammonium ions
-chemoautotrophic bacteria get energy from oxidising ammonium ions to nitrites or by oxidising nitrites to nitrates
-this oxidation requires O2 and so only happens in aerated soil
-nitrates can be absorbed by the plant to make nucleotide bases and amino acids
Other bacteria convert nitrates back into nitrogen gas.
-bacteria in anaerobic conditions must use nitrates as a source of oxygen to respire, and release nitrogen gas and nitrous oxide.
What affects population size
Carrying Capacity+ limiting factors:
The carrying capacity is the maximum size in population that can be maintained over a period of time in a specific habitat- it usually occurs when the reproduction rate equals the mortality rate. Once carrying capacity has been reached the pop. size may fluctuate slightly due to changes in conditions.
Limiting factors can have a significant effect on pop.size once it has reached carrying capacity- these are called k-strategists
Some species adopt different pop. growth where their pop. size is able to exceed the carrying capacity, and then due to the inability to reproduce anymore and an increase in waste products, they all begin to die. These are known as boom+bust and r-strategists- limiting factors do not have an effect on these.
Limiting factors are the ones that hinder the rate of process and are usually the ones in short supply. They can be food, light, water shelter, and can also be the effects of other species, eg competition, parasites and predators.
Predators and Prey
-Predator pop. size increases and this means more prey eaten
-low prey pop. size so less food and a decrease in predator pop. size
-less predators so more prey
-more prey so more predators...cycle continues
however realistically predators will eat lots of different types of prey, not just one- this would make the graph less well-defined. Also pop. size can be determined by other limiting factors!
Intraspecific- happens within a species, and those most adapted to obtain the food will survive and those less adapted will die and fail to reproduce. It maintains pop. size because when the pop gets low, there is less comp and more resources and so it will increase again. When the pop size is high, there is more comp and the size will decrease.
Interspecific-between different species.
Gause studied with 2 species of paramecium. When grown together there was more comp for food with paramecium aurelia obtaining food more effectively-over 20 days paramecium caudatum died out. It was the overlap of these two species' niches which caused one to be out-competed by another and died out/extinct. This was called the competitive exclusion principle and can used to explain why some species only grow in some areas.
However it is not that simple; interspecific could just lead to a smaller pop size of one species -lab experiments do not take into account other limiting factors in the wild
Small scale timber production:
Coppicing- cutting deciduous trees at the base, whilst several new shoots grow from the cut area, which can be used for fencing/furniture, and once these have been cut more shoots grow and and the coppice cycle continues
Pollarding is the same as coppicing but instead, u take wood from the top so that deer do not eat the new shoots
Rotational coppicing is dividing the wood into sections and cutting one section a year, this allows time for other sections to grow back- some trees are left to grow for longer, these are called standards, and are used for larger pieces of timber
Rotational coppicing is good for biodiversity- it allows different habitats to develop within a wood, allowing more light in and a greater diversity of species
Large scale timber production:
often involves clear felling but this is widely destructive and rarely happens in the UK. It can reduce soil mineral levels and leave soil susceptible to erosion-it may run into water ways polluting them, because the trees usually- remove water from soil and stop soil being washed away by the rain, and maintain soil nutrient levels through the trees' role in the carbon+nitrogen cycles
Leaving each section to mature for 100 yrs is not cost effective, and modern sustainable forestry works on these principles: any tree which is harvested is replaced by another tree, even with timber extraction the forest but maintain its ecological function regarding biodiversity, climate and water cycles, and local people should be benefited from the forest.
Selective cutting means only removing specific trees and so the habitat is broadly unaffected
The balance between harvesting wood and conserving wood is made easier by each tree giving MORE wood. This is achieved by controlling pests+pathogens, only planting particular tree species that will grow well, and planting trees at the optimum distance apart
Conservation: maintenance of biodiversity, including diversity between speices, genetic diversity within species and maintenance of a variety of different habitats and ecosystems
A steady increase in human pop can threaten biodiversity by...
-over-exploitation of wild populations, e.g. cod for food, sharks for sports and pearls for commerce
-habitat disruption bc of more agricultural practices, polluction and building
-species introduced to an ecosystem by humans, which may out-compete native species which could become extinct
-Some people believe every species have a value in their own right, regardless of their economical value to humans
-many species provide a valuable food source +were originally domesticated from wild species - genetic diversity may be needed for disease resistance, drought tolerance or improved yield
-natural environments are a valuable source of potentially beneficial resources - many of the drugs used today were discovered in wild plant species
-natural predators of pests used as biological control agents-this can have advantages over synthetic chemicals but they are only a few of these predators!
-wild insect species are responsible for pollinating crops-without them harvests would fail+farmers out of business- others also maintain water quality, protect soil+break down waste products
-ecotourism and recreation also have economic and social value, deriving from aesthetic value
-preservation involves protecting areas that have been untouched by humans whereas conservation is maintaining areas that have been interferred with.
Humans and the Galapagos
50% of species endangered-the population on the islands has increased as an increase in endangered species has occurred too, due to an expanding demand for marine products such as lobster, a developing tourist trade and economic problems in mainland Ecuador. In just 25 years, the island's population number multiplied by more than 5 times, and the number of tourists multiplied by more than 20 times.
The dramatic increase in population has caused an increase in pollution and waste on the islands, with a high demand for water, energy and oil. An oil spill in 2001 had a negative effect on marine ecosystems and the increased pollution and building has destructed habitats. This is seen in the near eradication of Scalesia trees and shrubs due to removal of land for agriculture.
Over-exploitation of resources:
Whaling boats and fur-traders harvesting whales and seals to sell internationally have caused a catastrophic effect on populations, with species harvested faster than they could reproduce. Giant tortoises were also taken because they could survive off little food in the hold of a ship for a long time, before being killed and eaten. This caused a huge knock to tortoise populations, with 200,000 being taken in the last half century.
Humans and the Galapagos
Species such as goats, cats and vegetable plants were deliberately brought onto the island by the humans that moved over. Other species such as insects were accidentally introduced to the islands. These new species can compete with or eat other pre-existing species, as well as threatening their habitats, bringing diseases such as bird flu and malaria to the islands.
The goat is an example of an introduced species that has caused damage to the islands. It eats Galapagos rock purslane, a species that is specifically unique to the island. It out-competes with the giant tortoise for grazing, by ruining and feeding on the tortoises' food supply, and therefore changes the habitat by reducing the tortoise population. On Northern Isabella Island, the goats have also transformed forests into grassland, leading to soil erosion.
Introduced species are now the focus of conservationists' attention, with strategies put into place to prevent them coming into the island:
A quarantine system, where they search arriving boats and tourists for any foreign species
Natural Predators exploited to try and reduce the damage caused to ecosystems by pest populations, e.g. a controlled release of ladybirds wiped out a scale insect which was damaging plant communities
Culling has been successful against feral goats on Isabella Island
Any conservation plan must take the concerns of the local people seriously, and plan for their economic livelihood. Finding a balance between environmental, economic and social concerns is therefore key in order for conservation to be successful.
It is also important to teach those residents who were not born on the island about the unique nature of the islands. This can be a challenge, and strong leadership combined with compromises between organisations is essential.