Biology: Chapter 5,6,7 Flashcards
(112 cards)
1
Q
Human Impact of biodiversity and ecosystem ( ningaloo reef)
A
can impact on the magnitude, duration and speed of ecosystem change
eg. Ningaloo reef
2
Q
What is an ecosystem?
A
an ecosystem consists of a community and it environment ( the biotic and abiotic factors in a given area ) and the interactions between them
3
Q
What is a stable ecosystem? Def
A
Can be sustained over long periods of time
4
Q
Signs of an healthy ecosystem:
A
stress in the form of extreme conditions:
- flood
- droughts
- invasive species
- disease
- overexploitation
> overall shows resilience
5
Q
Human Population Increase ->
A
human impact on biodiversity and ecosystem increase
6
Q
Biodiversity Hotspots must include: (2)
A
- it has a minimum of 1500 vascular plants that are not found in any other region on earth
- it has suffered at least a 70% reduction in its original natural vegetation
7
Q
Habitat def
A
habitat are environments in which species normally live
8
Q
Why are habitats being destroyed?
A
- urbanisation
- manufacturing
- agriculture
- forestry
- mining
- fishing
9
Q
what is habitat destruction ?
A
is a human activity that greatly impacts ecosystems
10
Q
what is habitat loss ?
A
is a human activity and is the greatest threat to biodiversity
11
Q
what is urbanisation?
A
Urbanisation is the extreme modification of an ecosystem by humans to support a human population of gradually increasing density; often, this happens as more people migrate to towns and cities from rural areas.
12
Q
What do urban ecosystem have ?
A
Urban ecosystems have reduced biodiversity and are dominated by people
13
Q
Communication between communities in urban ecosystems:
A
There is little recycling of matter between the community (the living things present) and the non-living surroundings.
Additional inputs of energy and matter are needed from other ecosystems to maintain modern standards of living
14
Q
what is agriculture?
A
Agriculture is the practice of farming; cultivating soil, growing crops, raising animals, preparation of plant and animal products for market
15
Q
what has happened due to agriculture ?
A
Many animals and plants have lost their habitat due to land clearing
16
Q
what is habitat fragmentation?
A
Habitat fragmentation – some parts of the habitat of an ecosystem are separated into isolated sections
17
Q
Human Activities: Urbanisation and Agriculture
A
Create: Habitat Fragmentation
- isolation of animal groups
- habitat in fragments
No interbreeding between sub-populations:
- no sharing of genetic diversity
- loss of resilience
18
Q
the gondwana link
A
The Gondwana Link program has been working to reconnect fragmented habitats across the south-west of Australia. If the Gondwana team reach their goal, 1000 km of continuous habitat will reconnect habitats from the dry woodlands of the inner region to the tall wet forests of the far south-west corner. Traditional land managers, organisations, farmers and conservation scientists have worked together to strategically revegetate gaps of cleared land to restore the fragmented habitat.
19
Q
Land and Soil Degradation examples
A
Overgrazing and the hard hooves of farm animals are factors that lead to land and soil degradation.
Shallow rooted plants have more of an opportunity to grow on degraded land.
With significantly reduced tree cover and an increase in shallow-rooted grasses, the topsoil becomes more exposed to the effects of abiotic factors such as wind and rain.
Past land clearance practices, the move to shallow-rooted pastoral grasses and the overuse of fertilisers that have affected soil organisms have placed enormous pressures on the structure of the soil and the ability of the land to hold its topsoil.
20
Q
Dry Salinity
A
Salinity’ refers
to the concentration of salt in the soil. If the
concentration of salt in soil becomes too high,
plants such as crops will no longer grow and the
soil is infertile.
21
Q
why is a significant problem?
A
Salinity is a significant problem that can happen when natural vegetation is replaced with crops that require irrigation
In many agricultural areas of WA, the
underlying reason behind the rising water table
is the removal of deep-rooted, perennial (long lived),
usually native, vegetation.
22
Q
The Steps leading to dryland salinity:
A
Step 1:
human population increases, leading to increased food consumption and need
Step 2:
farming increases, with further clearing of deep-rooted trees
Step 3:
removal of deep-rooted native perennial species and planting shallow-rooted annual crops. Deep-rooted native plants remove water from underground aquifers and use in transpiration: this balances the input and output of aquifers. The root of shallow-rooted crops do not grow down far enough to reach the watertable to access water for transpiration or evaporation
Step 4:
watertable rises.As it rises , salt from surrounding soil dissolves into the water
Step 5:
water evaporates at the soil surface, leaving behind soil that is too salty for most plants to survive.
23
Q
Introduced species def
A
Introduced species are species that humans have intentionally or unintentionally moved from their native location to a new ecological region.
24
Q
Why are invasive species a problem?
A
In their new location, they are without their natural predators, parasites and pathogens, which would usually limit their growth.
The rate at which they have been introduced has increased with the increase in human travel by ship and air.
Many introduced animals and plants become invasive species if they manage to establish populations in new areas; out-competing natives.
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Examples of WA's invasive species declared pest:
- Fox
- Feral Camels
- Cane Toad
- Rabbit
-
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Environmental Management: Chemical Control
The use of chemical pesticides (chemical control ) is a quick and effective method of getting rid of pests, but there is a downside: pesticides can be ecologically damaging as well as costly.
A chemical control is a chemical such as a pesticide or poison, such as a bait, used to control the population of a pest/invasive species.
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Environmental Management: Biological Control
Biological control is another method of management, in which a species is used to control the population of a pest species.
Biological control agents exploit relationships between organisms.
Sometimes an integrated approach (using two or more measures) when rapid response is needed in the early stages of a pest reaching a new area.
It combines the use of biological measures with the use of chemicals limited to narrow-spectrum agents that target specific species.
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Four Kinds of biological control agents
- general predators
- specialised predators
- parasites
- microbial diseases eg caused by a virus
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Precautions to the release of biological control agents
Field trials must be conducted in an isolated area to discover any unexpected effects before wide release, especially to check the risk of the biological control species becoming a pest itself.
To be released more widely, the biological control species must:
only target the pest species and not impact on other populations
decrease in number as the pest species decreases in number
not compete with native species for a resource (e.g. food or habitat).
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Biological control agents: Lady birds
Ladybirds have been introduced to Australia to battle aphids on citrus trees. This reduces the use of expensive chemical pesticides and limits the impact of these chemicals on other species.
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Environmental management: culling
Under strict regulations, invasive organisms are culled (killed) eg Australian red and grey kangaroos out-compete other species for resources in some ecosystems. Each year, more than 2 million kangaroos are culled. A small proportion of the meat is processed for human consumption, most of it for export
32
Environmental management: reintroducing populations
Some species are released from breeding programs back into their original or a disease/pest free environment for the purpose of building up their population. For example, Galaxias is a genus of native freshwater fish whose numbers have suffered since the introduction of the mosquitofish. Introducing Galaxias back into the wild is through finding uninfested waterways or artificially created ponds that have no links with infested water bodies.
33
What is unsustainable use of natural resources ? def
Unsustainable use of natural resources – using resources more quickly than they can naturally be restored – has a huge effect on biodiversity.
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what is overharvesting ?
Overharvesting means harvesting a species at a rate that exceeds the replenishing rate of the population
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why is overharvesting a problem ?
Organisms that have low reproductive rates, such as the African elephants (often poached for their ivory tusks), are especially vulnerable to overharvesting.
This is because the sum of new individuals from births and immigration does not exceed the total individuals lost to death plus emigration.
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Sustainability and Fishing
There is competition for their use: for food, recreation, transport, commercial livelihood and as a repository for our wastes.
Particularly by over-harvesting, commercial fishing has reduced the populations of many species, some almost to extinction.
Shark numbers, for example, are at an all-time low.
The reduction in populations of these and other fish affects other species through disruptions to food chains. Penguins and seals, for example, now compete with the fishing industry for food.
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Sustainability and fishing: by-catch and bottom trawling
PROBLEM: by-catch
The by-catch (undersized and over-sized fish caught and discarded) poses problems for species that are fished commercially.
As populations of fish (such as the valuable snapper) decrease, there are fewer fish reaching reproductive age to sustain population growth
PROBLEM: bottom trawling
Destructive to ocean ecosystems; involves dragging a large net across the seafloor.
Deep-sea fish species are targeted globally, but bottom trawling is known to also remove vast amounts of non-target species, including habitat forming deep-sea corals and sponges.
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Management strategies: creating and monitoring protected areas
In WA, recreational fishing licences and fishing seasons are compulsory and are used to control fishing levels
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what is eutrophication?
Eutrophication is a process that occurs when excess nutrients, particularly nitrogen and phosphorus, enter a body of water and become highly concentrated, leading to excess growth of organisms such as algae.
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Farmer dealing with nutrient-deficient soil use fertilsers
2. The fertilisers are usually enriched in nitrogen and phosphorous
3. Excess nitrogen and phosphorous not absorbed by roots are often leached from the soil by run-off (rain water or irrigation).
4. The run-off can reach local water bodies such as lakes and cause algal blooms
5. An algal bloom is a rapid increase in the population of algae or other microorganisms at the surface of a water body that blocks sunlight from entering. When this happens, autotrophs that live under the surface die.
6. Algae die and are decomposed by bacteria.
7. As bacteria consume the dead algae, they use large amounts of oxygen from the water, which depletes oxygen levels. The water can become hypoxic (low in oxygen) and possibly anoxic (completely devoid of oxygen).
8. The low oxygen levels do not meet the respiration needs of aquatic organisms, so fish and other populations die.
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what is Biomagnification ?
Biomagnification is the sequence of processes in an ecosystem by which higher concentrations of a particular non-biodegradable chemical are reached in the tissues of organisms higher up the trophic levels
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what does biomagnification do ?
Biomagnification occurs because the biomass at any given trophic level is produced from a much larger biomass ingested from the trophic level below.
The concentration of the chemical increases in the tissue at each trophic level.
A classic example of biomagnification is DDT, a pesticide
43
The impact of pollution: plastic
Large amounts of the world’s plastic rubbish enter waterways. Many aquatic animals mistake plastic for food. Turtles frequently ingest plastic bags, confusing them with their prey, jellyfish.
Plastic can be consumed by wildlife, causing disease and death
44
What is climate ?
the average long-term, predictable atmospheric weather conditions at a site over a period ranging from months to many thousands of years). Climate is made up of such variables such as rainfall (precipitation), temperature, intensity of sunlight and wind.
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what is weather ?
the atmospheric conditions in an area over a short time, usually 2–3 days. Weather forecasts or predictions can be very unreliable. Weather is not a gauge for climate change, because it is too short term.
46
what is climate change?
a significant change in the global climate that can be identified by changes in the average and variability of such features as temperature and precipitation, and that lasts for a long time, typically decades or longer.
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Evidence for Global Warming: Ice Cores
Scientists are able to analyse samples from ancient ice cores extracted from polar ice. The layers of ice in the ice core contain bubbles of gas trapped long ago and other factors that reveal data about past carbon dioxide levels and temperature data.
Scientists have been able to collect and analyse data from Antarctic ice cores to calculate estimates of average global temperatures and carbon dioxide levels spanning 400 000 years.
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Evidence for Global Warming: Atmospheric Concentration
Atmospheric concentration of carbon dioxide has also risen and fallen in cycles. The cycles in carbon dioxide concentration and temperature appear to coincide.
There is evidence to support a relationship between the sudden rise in concentration of carbon dioxide in the atmosphere in the last few hundred years and the rise in average global temperature.
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The causes of climate change:
greenhouse gasses
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what is greenhouse gases ?
Greenhouse gases (gases that trap heat) are probably the most significant drivers of our climate.
The human activities of burning fossil fuels and deforestation are increasing the concentrations of carbon dioxide and other greenhouse gases in the atmosphere.
51
what is greenhosue effect ?
The greenhouse effect is the insulating effect of these gases in the atmosphere, which prevent some of the solar radiation from escaping Earth’s atmosphere. The gases trap and absorb some of the heat originating from the Sun, which keeps Earth warm.
The natural greenhouse effect is an essential process for maintaining Earth’s average global temperature within a range that is warm enough for humans to survive. Concentrations of greenhouse gases have increased and too much heat is being retained – the enhanced greenhouse effect.
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The Greenhouse Effect: Natural
essential process for maintaining Earth's average global temperature at a warm enough range for human to survive
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The greenhouse effect: Enhanced
concentration of greenhouse gases are increased and too much heat is retained resulting in an increase in average global temperatures
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The Greenhouse Effect ( Summary)
diagram
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Observable factors related to climate change
Climate change is causing increased melting of glaciers and polar ice sheets, resulting in a gradual increase in sea level.
Plants and animals are also affected by global climate change when the timing of seasonal events, such as flowering or pollination, is affected by global warming.
As the abiotic and then biotic factors change in an ecosystem, some species experience different selective pressures affecting their survival. These could include habitats becoming unsuitable, not enough food or conditions that require fast migration. As we lose individuals and species, biodiversity declines and the result is a decline in the resilience of ecosystems.
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Event increased by climate change: Heat waves
- increase in death rates in elderly and poor
- increase heat stress in livestock
- changes in tourist destination
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Event increased by climate change: Storms
- increase in property and infrastructure loss
- increase in infections disease epidemics
- increase in risk to human life
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International Biodiversity Projects: World Heritage Site
the united nations educational, scientific and cultural organisation, globally supports the idenification, protection and preservation of cultural and natural heritage that is of outstanding value to humanity.
eg. Ningaloo cost or the great barrier reef
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International Biodiversity Projects: Biodiversity HotSpots
the program targets regions that are rich in unique biodiversity ( inclusion of those rules ). There are 36 hotspots around the worlds in need of conservation
eg. South-west WA
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International Biodiversity Projects: Protection of international migration routes and areas used for breeding
projects are undertaken to protect migrating species such as whales and bird. Several whale species migrate north from the Southern Ocean into the warm tropical waters off northern Australia to breed during the winter months.
eg. the conservation management plan for blue whales
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Numbat captive breeding program at Perth Zoo
Numbats are now restricted to two small wild populations in south-west WA at Dryandra Woodland and the Tone-Perup Nature Reserve. The species is listed as endangered and there may be as few as 1000 numbats left in the wild.
The numbat captive-breed-for-release program is designed to provide additional animals for release into the wild to establish new populations or to augment existing ones.
Perth Zoo has been involved in the
captive breeding for release of numbats since 1992.
During that time, 268 captive-bred
numbats have been released into the wild at
nine locations in two states, resulting in the
establishment of four new self-sustaining
populations; three in Western Australia and
one in New South Wales.
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Ecosystems can change dramatically over time: Continent
They were joined to form a super continent called Pangaea.
Pangaea split into Laurasia (north) and Gondwana (south).
Gondwana split to form the southern land masses, South America, Africa, India, Australia and New Zealand.
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The origins of australia's unique fauna and flora
65 million years ago a catastrophic event destroyed most of life on earth.
Dinosaur extinction led to the occupation of the vacant niches by vertebrates.
40 million years ago Australia parted from Antarctica and was isolated.
Isolation and harsh Australian conditions led to development of unique species.
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The evidence of past ecosystem: ice or sediment cores
Changes in past ecosystems can be understood by studying regions with abundant fossils
Studies on geological features can help uncover clues to the past environmental conditions
Ice or sediment cores provide an excellent record of changes that have occurred over thousands, perhaps millions, of years
Scientists can analyse changes in trapped gas composition to understand temperature change
Organic matter – abundance of foods
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What is succession?
Communities change progressively over time, one community being replaced by the next in the process of succession.
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what is nudation ?
Catastrophic events such as volcanic eruptions, cyclones, earthquakes and tsunamis can cause the development of bare sites with no organisms inhabiting the affected area. This process, called nudation, starts a long-term process of change, involving three stages in general.
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aspects of ecological succession:
- Changes in abiotic factors means the environment becomes more suitable for survival of new species
- During succession there are changes in population
- Biomass increases at each stage of ecological succession
- When a stable community is established it is know as climax community
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what is primary succession ?
when succession begin in a virtually lifeless area where soil has not formed
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Steps of Primary Succession:
Pioneer plants arrive to colonise the area.
For example:
- lichens colonise rocks
-mosses inhabit soils
- bacteria and fungi form simple communities.
2. These r-selected species are characterised by:
- effective seed dispersal
- rapid growth
- rapid reproduction
- producers.
3. Small herbivores move in and new communities form
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what is secondary Succession def?
Through fire and flood, or human intervention by logging and land clearing for agriculture, dramatic changes to ecosystems occur. The cycling of matter and the flow of energy are interrupted as the components of the ecosystems are affected. Organisms can recolonise recently disturbed communities via secondary succession, regaining equilibrium although the number and kinds of organisms present may be different from the original ecosystem.
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Primary Succession ( Summary)
Begins with: a new area with no life: barren
Soil: no soil to begin with
Plants: pioneer plants
Primary Productivity: lower productivity due to fewer plants ( biomass or energy )
Biodiversity: low biodiverisity for a long time
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Secondary Succession ( Summary)
Begins with: begins with disturbance of an already established ecosystem/begins after primary succession
Soil: soil is present at the beginning
Plants: seeds and roots of established vegetation already present
Primary Productivity: higher productivity due to ther being more plants and faster regrowth
Biodiversity: faster development of wider biodiversity
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what is a climax community?
Slow-growing, long-lived
K-selected species:
live in more stable environments
than r-selected species
outcompete other species
are often tall established trees
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Natural disturbances can lead to succession
events (Negative )
A fire or tsunami can cause:
a loss of vegetation
a reduction of leaf litter
a decrease in animal numbers
an impact on abiotic interactions in a community.
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Fire Impact
Fire impacts the abiotic interactions in a community. It opens up spaces and creates a nutrient-rich seedbed resulting in secondary succession.
Fire damage stimulates regrowth in other species smoke particles signal growth in others. The proliferation of new growth in a post-fire community attracts many mobile species such as wallabies, birds, small mammals and insects.
The new growth sustains animals such as wombats and echidnas that may have survived the fire in underground burrows.
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Natural disturbances can lead to succession
events: Fire Regimes
Fire regimes are determined by:
- the season
- the intensity of fires
- how frequently fires occur
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the purpose of fire-stick farming:
Fire-stick farming was used by the First Australians to clear areas of
land as an aid for hunting.
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Human influence on biodiversity: negative changes to australia
Humans have inhabited Australia for the past 20 000 years.
Human impacts have included:
species extinction through hunting and loss of habitat
changes to the landscape through farming practices.
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Human impact on ecosystems today
Urbanisation
Habitat destruction
Land and soil degradation
Salinity
Monoculture practices
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Human activities put pressure on resources
Disruption of water flow
Eutrophication
Marine ecosystems
Introduced species can become pests
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Models can be used to predict the impact of change
Ecosystem models are useful representations of elements within the ecosystem, the relationship between the elements and the relationship with surrounding ecosystems.
Ecosystem models are very useful for simulating and analysing the long-term dynamics and properties of complex ecosystems. They allow the use of information from different disciplines as well as analysing, interpreting and understanding field observations. This provides a basis for predictions of the impacts of changes in real ecosystems, the development of tools for management support and policy advice.
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what is population ?
A population is a group of individuals belonging to the same species living in a particular area at the same time.
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Populations in unstable environments are filled with what species
r-selected species are early colonisers in
disturbed environments.
As they fill the previously open spaces, they change the abiotic and biotic conditions of the environment and are soon overtaken by competitors.
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Populations in stable environments
K-selected species
Larger, longer-lived species dominate
Fewer offspring
Outcompete r-selected species
Close to carrying capacity of environment
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Growth of populations: Open ecosystem
Open ecosystem: migration occurs freely
in response to environmental changes
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Growth of Population: Closed
Closed ecosystem: migration does not occur, but births and deaths still impact population size
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Population Growth Rate Formula
Pop growth rate = (birth rate + immigration rate) - (death rate + emigration rate)
= (br + ir) - (dr + er)
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Determining Growth: Population Pyramid
A useful method of representing collected data is the construction of population pyramids. Figure 5.3 shows population pyramids for two different human populations. You can see that the pyramid for population A is wider at the bottom indicating a healthy future reproduction rate, with the number of children quite high. Population A has a greater proportion of children than does population B. What is the significance of this?
Scientific data about age distribution and sex ratios can assist in the management of populations. Each year federal, state and local governments collect and collate information on the state of wild fish stocks. It is this information that is used to determine the level of both recreational and commercial sustainable fishing. Sustainability ensures that over-fishing does not drain the stocks, and that young (smaller) fish are able to contribute to the populations in the future. This information can be used to plan how to ensure sufficient numbers of young live to reach reproductive age, how to develop strategies for protecting endangered species and maintaining ecosystems, and how to restore degraded ones.
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Measuring Distribution : Clumped
* Clumped (grouped) distribution: a number of individuals is grouped together and the groups make up the population as a whole. This is sometimes to do with social behaviour as in schools of fish, or clumping of vegetation in mini-habitats where biotic and/or abiotic factors are favourable.
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Measuring Distribution: Uniform
Uniform (continuous) distribution: organisms are evenly spaced; the presence of one organism determines how close or distant another will be. It is common in relatively high-density populations of some animals that set up breeding territories
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Measuring Distribution: Random
Random distribution: organisms are spaced irregularly; the location of an organism does not affect the location of another (more common for plants than for animals).
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Measuring abundance: Direct Observation
Direct observation
Direct observation involves:
Sighting, or
Counting, or
sampling a population
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Measuring Abundance: Quadrats
For each quadrat:
the number of individuals of each species is counted and recorded, or
* the relative numbers of each species is estimated using a scale from abundant (3) to absent (0), or
* percentage cover is estimated, and
* the totals of the quadrats are averaged.
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Density Quadrat
The density can also be calculated.
Estimating total population size of area under study
Average density of members of species (estimated)
= total number of individuals counted / area of each quadrat x number of quadrats
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Measuring abundance: Transect
A transect is a line drawn through a community and the information gathered is used to determine the distribution of species within that community
Data gathered using transects offers fairly accurate information regarding distribution of individuals and/or species; whereas quadrats offer a comprehensive picture of species abundance, but not distribution.
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Measuring abundance: Capture-mark-recapture def
Capture–mark–recapture is used to sample mobile species. A random sample of individuals of a species is taken and an overall estimation of the abundance of the species is made.
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Capture- Mark- Recapture Steps
Step 1 Capture: animals are caught randomly and in such a way that they are unhurt. Small animals are trapped in cages or pitfalls in the ground, birds are trapped in fine nets and some animals are caught easily when they ‘freeze’ in spotlights. Flying insects are attracted to light traps.
Step 2 Mark: each captured animal is marked so that the mark is not obvious to predators or harmful to the organism. Insects are usually marked with a blob of paint, whereas birds are tagged on the leg or wing. The animals are returned to their habitat and left to mix with the unmarked individuals.
Step 3 Recapture: later, a random sample is taken and the number of marked individuals counted. The timing of recapture needs to be appropriate to again capture a random mixture of individuals, but without leaving it so long that many of the original marked individuals have died. From this information the total population can be estimated. The procedure has to be planned carefully so that the chances of each individual being caught are equal. Sometimes ‘trap happy’ individuals will be sampled over and over.
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Measuring abundance: Telemetry ( Remote Tracking )
Species distribution modelling is used to predict future needs and resource management and is a more recent technology used for conservation and management.
Little Penguins on Phillip Island fitted with GPS transmitters could be used to plot their movements as they search for food. This data helps monitor their season movements in time and space.
GPS tracking is also used to track the movements of migrating animals such as birds and caribou, and is most efficient when tracking water animals such as whales, sharks, sea turtles and many sea birds. The signal is received by a satellite which ensures the animals are tracked when not in sight.
Radio tracking is older technology than the GPS tracking systems. In this instance, the signal is transmitted from the unit attached to the animal to a receiver, much like a home transistor radio. The animals are physically followed by the scientists who will have the receiver in a car, truck or aeroplane. The data collected determines the movements of the animals and their destination. The information is then used to determine the best management strategy to ensure the safe movement of the animals involved.
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Density Def
Density: the number of individuals in a given area
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Carrying Capacity Def
Carrying capacity: the maximum population size of a species that can be supported in a given environment
Knowing the density of populations can help assess an ecosystem’s ability to provide sufficient resources to support its populations
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Population Growth:
Factors in the environment, collectively referred to as environmental resistance, act on a population. If the population rises above the equilibrium or set point, competition for resources such as food and space begins to take effect. The increased ability of disease-causing organisms and parasites to spread also increases deaths and possibly reduces breeding. This could be to such an extent that the population falls. If it falls below the set point, there is less competition and the population begins to rise again. This kind of negative feedback process, or homeostatic control, keeps the population more or less constant (Figure 5.13).
Is this scenario an example of K-selection or r-selection?
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Population Growth: Diagram Explaining
Equilibrium Population:
Increase in Population -> raised environment resistance -> negative feedback -> falls in population -> population returns to norm near to the carrying capacity of the environment
Fall in population -> lowered environmental resistance -> negative feedback -> increase in population -> population return to norm near to the carrying capacity of the environment
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Density-dependent factors Def
Density-dependent factors include competition, disease, parasites, predation and food supply. The greater the density of a population, the more individuals die or fail to reproduce.
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Density-independent factors Def
Density-independent factors, such as severe weather conditions, volcanic activity or habitat destruction by clearing or fire, are those that affect all individuals in a population regardless of age or stage. These factors are seen
vividly following a catastrophic event such as a bushfire or flooding. Populations of all living things usually decrease quite drastically due to either death or emigration to a habitat that is better able to meet their needs.
In some cases, populations of species are not able to recover from such extreme environmental resistance and disappear from that ecosystem, which may eventually result in widespread extinction.
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How does Population survive?
Population survival. A combination of factors, working together, determines the survival of populations.
There are patterns in survivorship of various species. Species can be classified according to their probability of survival. This can be represented in a graph.
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Controlling Populations
The rate of species lost is alarming, but there are examples of species being restored through:
natural cycles of population change
careful management
legal protection of species.
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Controlling populations: Chemical and Biological Control
There are four kinds of biological control agents.
1. General predators: organisms that consume a great variety of pest species; e.g. ladybugs, target aphids, caterpillars, mites and small beetles
2. Specialised predators: organisms that target one pest species, e.g. dragonflies target all life stages of mosquitoes
3. Parasites: e.g. wasps lay their eggs in the bodies of hosts, leading to the host’s death.
4. Microbial diseases: caused by bacteria, fungi and viruses that target species and cause death.
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Controlling Populations: Culling
Culling ensures the:
sustainability of ecosystems
viability of native species.
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Reintroducing populations
Invasion of pest species devastates native populations.
Native populations decline due to:
-a lack of resources
- a loss of habitat
- predation.
Eradication of pest species; e.g. through quarantine from protected stock.
Reintroduce native species; i.e. restocking in captivity.
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1) Define the term "Cool burn in ecology".
Cool burning is a practice where the fire burns at a much lower heat intensity than wildfire or a modern large scale fuel reduction burn. This sophiscated use of fire burned at such a low intensity that the tree canopy remained protected. The fire only burned the undergrowth.
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2) Define the term "Hot burn in ecology".
The intensity of a fire depends on the amount of fuel available, the stage of plant growth and climate conditions. High intensity fires consume most of the above ground material and favour germination of certain plants species.. However, the rate of seedling survival may be high
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3) What are the features of a cool burn? List as many as you can find, for example the Fire temperature, height of burn, etc
- small blazes are aet alight to clear the underbrush
Generates patch
