6.3.2 populations and sustainabiltiy Flashcards
What is a population?
all the members of ONE species in a given area
what is the carrying capacity?
The carrying capacity is the maximum population size that a given habitat/ecosystem can sustain. The carrying capacity is determined by the limiting factors present.
what is a limiting factor
A limiting factor is something which stops a process or population increasing any further
what happens if the carrying acapacity is exceeded?
the limiting factors present will tend to bring the population size back down (negative feedback)
what does the population size do arround the carrying capacity?
it fluctuates around the carrying capacity
Sketch a graph showing how the population of newly‐introduced species may change over time, in a habitat with a fixed carrying capacity
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what are density-dependenty limiting factors?
limiting factors that have an increasingly significant effect on the population
growth rate as the population size increases
give 4 examples of Density‐dependent limiting factors
Limited food availability
Inadequate space
Presence of infectious disease
Intraspecific and/or interspecific competition
what are Density‐independent limiting factors?
These are limiting factors that have a consistently significant effect on the population growth rate regardless of the present population size.
give 2 examples of Density‐independent limiting factors
Temperature (too high or too low)
Factors that determine photosynthesis rate
intraspecific competition definition and example
Intraspecific competition occurs when members of the same species compete for the same resource.
example: Lions in the same habitat are in competition for the same food sources
interspecific competition definition and example
Interspecific competition occurs when two (or more) different species compete for the same resource
example: Buzzards and barn owls compete for small mammals
what is a Predator–prey relationships, give an exmaple, what does it mean?
when a specific predator has one principal (main) prey species on which it feeds and when that prey species has no/few other predators
example: Lion and gazelle
the population size of each species can strongly affect the population size of the other species: the two populations show a high level of interdependence
Sketch a graph showing how the relative sizes of a predator population and its prey population may vary over time
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explain this graph
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- When predator numbers are low, the prey population increases as few are eaten by predators. Most prey offspring survive to breed themselves. Birth rate of prey is higher than death rate.
- However, the increasing prey population now means there is more readily available food for predators. If the prey population has increased beyond its carrying capacity, some prey individuals may be weakened by lack of food (as intraspecific competition for limited food may lead to starvation) or by the increased presence of disease or pathogens spreading through the crowded population. These factors plus the high prey density mean that predators can catch prey more easily, with low energy expenditure themselves.
- Predators therefore now have increased growth rates (enabling them to breed sooner), higher fertility and more offspring that survive to breed themselves. Hence, after a time delay, the previous increase in prey population is now followed by an increase in the predator population. The delay between the two will be longer in species where the predators are slow to reach maturity and have long gestation periods: it could then take several years before an increase in prey actually translates to bigger predator population.
- Now the predator population is increasing (with their birth rate higher than their death rate), they will be killing and feeding on more prey. This results in the prey population declining. Death rate has now exceeded birth rate in the prey.
- However, if the prey population is falling, this means food is less readily available to the predators. The predators may have to expend more energy to catch the increasingly scarce prey. The prey may be stronger (less weak) and so better at evading capture as they have less intraspecific competition for their own food sources (hence they are better nourished); they may have fewer diseases and parasites (as these don’t spread readily in a sparse population).
- The predator population may now fall as the predators struggle to get enough food: they may reach breeding age later due to poor nutrition and fewer offspring may survive to breed themselves. If the predator population has exceeded carrying capacity, its numbers may also be declining due to increased disease or parasite transmission. Death rate of predators now exceeds birth rate.
- As the predator population falls, there are fewer predators killing prey. Hence the prey population has the opportunity to increase again: the above sequence of events will restart and repeat. Both populations will oscillate over time, but the changes in the predator population always lag behind those in the prey population.
what is preservation?
Preservation is the prevention of any human activity in a pristine ecosystem, in order to avoid its damage or modification
examples of preservation
keeping humans out
banning tourism, mining, deforestation, hunting, industry, housebuilding
why is preservation hard?
Most ecosystems have been subjected to modification or exploitation by humans already, therefore it cannot be preserved
what is an example of preservation?
Antarctica
what is conservation?
Conservation is the active management of a habitat/ecosystem (by humans)
with the aim of maintaining or increasing its biodiversity
what are the aims of conservation?
increase or maintain the diversity of habitats, the species diversity and the genetic diversity of one or more species
What are the three catagories for conserving biological resources?
Economic reasons
Social reasons
Ethical reasons
what are the economical reasons for conserving biological resources?
high biodiversity = avoid problems relating to soil mineral depletion
avoid large‐scale deforestation = less soil loss via erosion by wind/water
ecotourism
protects jobs
genetic resource for future selective breeding or genetic engineering
new materials for manufacturing or new medicines
what are the social reasons for conserving biological resources?
Sustainable fishing helps coastal communities remain viable by protecting jobs
considered beautiful and many people experience a better sense of wellbeing
what is the ethical reasons for conserving biological resources?
Humans have a moral responsibility to protect ecosystems and avoid causing extinctions. In particular, given the interdependence of organisms in a food web, keystone species should be identified and conserved (since their presence significantly affects all others in the ecosystem, e.g. via predation or via the modification of the habitat).
what does it mean for a resource to be used in a sustainable manner?
the resources we harvest from the ecosystem will continue to be available at predictable levels into the future
the resources are being replenished at (at least) the same rate as they are being harvested.
what are the two examples we must learn for sustainable management of ecosystems?
Sustainable timber production
sustainable fishing
what are the aims of sustainable timber?
predictable yield of timber can be harvested every year into the future, achieving sustainability
increase the biodiversity
ecotourism
what are the three management strategies for sustainable timber?
rotational coppicing, pollarding and selective felling and replanting
what are the 5 steps of rotational coppicing?
- The woodland is divided into (for example) nine sections of equal size;
- In one section only, suitable trees (e.g. hazel, sweet chestnut) are cut down close to ground level, leaving a coppice stool or stump;
- Over the next nine years, the stumps will grow new shoots from their remaining meristem tissue;
- Each year, a different section of the woodland is coppiced, i.e. the scheme is rotational;
- By the time all nine sections have been coppiced, the trees in the original section have regrown sufficiently that their timber can be harvested again.
what are the benefits of rotational coppicing?
The timber from rotational coppicing is a sustainable resource: it will remain available into the future, since the rate of regeneration of the resource (at least) matches its rate of harvest
There is an ongoing economic benefit to the landowner, who has a predictable yield of timber to sell each year: the timber from coppicing (called ‘small wood’ due to the relatively narrow diameter of the logs) is used for making fences, garden furniture, charcoal etc;
Biodiversity is increased due to there effectively being nine different habitats in the ecosystem, each with different light intensities and different stages of tree (re)growth: different species of plants, insects and birds will thrive in the particular conditions present in each section.
The high biodiversity may attract visitors to the woodland (ecotourism): they may psychologically benefit from spending time there, and may provide economic opportunities for the landowner e.g. a pay‐and‐display carpark or a café.
what is pollarding?
Pollarding is similar to coppicing but the tree is cut much higher up the trunk (e.g. at least 2m
above ground level). The new shoots which grow from the meristem tissue in the trunk
why use pollarding?
Pollarding is used in areas where deer are common. The new shoots which grow from the meristem tissue in the trunk are safely out of reach of deer.
what is Selective felling and replanting
the occasional cut down and replanting of trees.
benefits of Selective felling and replanting
The timber from a standard (which may be a 200 year old oak tree) will be of very high value, as it provides wide planks that can be used for making high quality furniture; there is a significant economic gain from the felling of a standard;
Felling of only a small number of trees minimises the disruption to the whole woodland, as there is only a limited amount of disturbance by heavy machinery and its noise (that would disturb wildlife);
The ‘gap’ left in the woodland where the standard used to grow will be a new microhabitat: additional light reaches ground level in the gap, hence biodiversity may be increased.
what should be considered during Selective felling and replanting?
Plant tree saplings of fast growing native species, as these will immediately play a beneficial role in the ecosystem, supporting insects and birds
Protect saplings with plastic cylinders or wire mesh, so that they are not eaten by herbivores
Avoid a high planting density (i.e. too many trees in a given area) as trees strongly compete for light, water and mineral ions and their growth will be stunted if they’re too close together
Be prepared to carry out pest and disease control if necessary, e.g. use of insecticides.
strip felling
cutting down trees in a narrow strip through the forest
clear felling
the removal of all trees and other vegetation from a large area of forest
why strip felling over clear felling?
Strip felling causes less significant disruption to the ecosystem since it doesn’t involve destroying a large area of the habitat
Strip felling leaves some vegetation (including roots) in place, so avoids significant soil erosion occurring; in contrast, clear felling often leads to loss of topsoil via erosion by wind and water
Since strip felling maintains the topsoil in situ, minerals are retained to support future plant growth
Following strip felling, the habitat often generates quite rapidly because seeds fallinto the area from the surrounding intact woodland (essentially resulting in a secondary succession process); this doesn’t happen if the area was clear felled.
how is fishing sustainable?
the rate of removal of fish must not exceed the rate of reproduction in the remaining populations
why should fishing be sustainable?
If fish populations remain at a level at which commercial fishing remains viable into the future, jobs in the fishing industry are maintained and fish will continue to be available to humans as widely‐available, affordable, healthy protein source
If a balanced ecosystem is maintained, this helps conserve marine biodiversity. If overfishing occurred and the population of a particular fish species fell sharply in a given area, there would be a knock‐on effect to other species in the marine ecosystem, e.g. a lack of food for that species’ predators.
what are the strategies for sustainable fishing?
larger Mesh size of fishing net
fishing Quotas
No take’ zones and Marine Conservation Zones
Seasonal restrictions
large scale Fish farming
give an example of an ecosystem where there is a Balancing conflict between conservation and meeting human needs
Peat bog
give an example of an ecosystem where the effects of human activities has had an impact on the ecosystems
Antarctica
describe Antartica
What happenning:
global warming
hunting of whales and seals
soil contamination
discharging of waste intoi sea
whats being done:ecotourism
protected areas
conservation and preservation
protection of environment
cooperation between governments
describe peat bogswet
wet spongy ground cotaining decomposing vegetation
what is a niche?
the role an organism plays in a community
what happens if two or more species share a niche?
out‐compete the other
The successful species will be the one best adapted to the niche
what happens if niches overla[p? example
two different bird species may require some of the same food sources (e.g. specific seeds or insects) and so compete for these, whilst having different nesting requirements and so not competing in that regard
what does interspeciofic competition play a key role in?
determining where particular species are found in their ecosystem and the times at which they are active
what to remember when reading predator prey realtionship gaphs?
On graphs, to highlight the interdependent relationship between the population sizes, the lines for each species may be drawn on the same axes but using a different numerical scale for each species. Pay close attention in exam questions to check whether this is the case!