6.6 Populations and sustainability

what is the carrying capacity?

the maximum number of organisms that can be sustained in a population.

what happens if the population exceeds the carrying capacity?

there will not be enough resources like food, water and space so the number of individuals will decline

what is the limiting factor?

the factor whose magnitude slows down the rate of a natural process

how can a population size change on a graph?

it can:

-remain stable

-rise or fall quite suddenly

-oscillate with a regular pattern

what determines the size of a population?

the balance between death rate (mortality) and the rate of reproduction

what are K-strategists and where are they found?

larger organisms that have longer life-spans and have fewer offspring, as they invest more in each offspring

often found in stable environments

e.g. birds, larger mammals and larger plants

K-strategists: lag phase = A

there may only be a few individuals, they are still acclimatising to their habitat

the rate of reproduction is low, and the growth in population size is slow

K-strategists: log phase = B

resources are plentiful and conditions are good

reproduction happens quickly exceeding mortality

K-strategists: stationary phase = C

the population has levelled out at the carrying capacity of the habitat

the habitat cannot support a larger population

in this phase, the rates of reproduction and mortality are equal

the population remains stable or shows very small fluctuations

what are limiting factors and what is there dependence on size?

the reason a habitat has a carrying capacity is because a factor is limiting further growth

some factors act just as strongly regardless of population size. (density independent) e.g. low temperatures will kill the same proportion of the population irrespective of its size

others are dependent on size (density dependent) and the factor’ influence increases with size

what are K strategists relationship with the carrying capacity?

K-strategist is when the population is determined by carrying capacity

for these populations the limiting factors exert a more and more significant effect as the population size gets closer to the carrying capacity leading to a levelling out

what are K strategists characteristics?

-low reproductive rate

-slow development

-late reproductive age

-long lifespan

-large body mass

what are R-strategists?

species where the population size often increases so quickly that it exceeds the carrying capacity before the limiting factors take effect

then there are no longer enough resources to allow reproduction or survival

the quick build up of waste can also poison the species

this model is often called boom and bust

what are R strategists characteristics?

-high reproductive rate

-quick development

-young reproductive age

-short life span

-small body mass

e.g. mice, insects, weeds and spiders

r-strategists population growth

boom- conditions are good and they get over the carrying capacity

bust- resources run out and they die off

what is the most important influence on population growth?

the physical rate at which individuals can reproduce

it is characteristic of species with short generation times and of pioneer species

what is interspecific competition?

competition between individuals of different species

what is intraspecific competition?

competition between individuals of the same species

what is a predator?

an organism that feeds on another living organism (prey) for its food

how does a predator act as a limiting factor on a prey’s population size?

1. when the predator population gets bigger more prey are eaten

2. the prey population then gets smaller, so there is less food for the predators

3. with less food, fewer predators can survive and their population size reduces

4. with less predators, fewer prey are eaten, and their population size increases

5. with more prey, the predator population gets bigger and the cycle starts again

when does competition happen?

when resources are in limited supply so organisms have to complete for this resource

as competition intensifies the reproduction rate decreases and death rate increases

why do predators and prey have to evolve together?

if this does not happened they would become extinct

what happens when predators and prey are brought together in a lab?

the prey is usually exterminated

this is due to the unnatural limited range of habitats available

outside of a lab the prey numbers can often drastically drop without becoming extinct

therefore, this must be studied in the wild whenever possible

what happens due to intraspecific competition?

within the species the best suited individuals survive and reproduce, while those not so suited fail to reproduce and/or die

this causes the population to enter a stationary phase

if the population size drops, competition will reduce and the population size can increase again

if the population size increases, more competition occurs leading to a drop

as factors become limiting, individuals compete for food

the individuals best adapted to obtaining food survive and reproduce, while those not so suited fail to reproduce or die

this causes the population growth to slow down and enter a stationary phase

how does intraspecific competition during the stationary phase keep the population size relatively stable?

if the population size drops, competition reduces and the population size increases

if the population size increases, competition increases and the population size drops

what does interspecific competition alter

the distribution of species in an ecosystem

who carried out the case study on interspecific competition and when?

a Russian scientist called Gause in 1934

what did Gause do for the case study for interspecific competition?

he grew two species of Paramecium both separately and together

when together they competed for food. P.aurelia obtained food more effectively than P.caudatum

over 20 days the P. caudatum died out

what did Gause find from the case study for interspecific competition?

when together, there was competition for food, with P. aurelia obtaining food more effectively than P. caudatum

over the 20 days, the population of P. caudatum reduced and died out, whereas the population of P. aurelia increased, eventually being the only species remaining

what did Gause conclude from the case study for interspecific competition?

that more overlap between two species’ niches results in more intense competition

what is the competitive exclusion principle?

it explains why particular species only grow in particular places

as if two species have exactly the same niche, one is out-competed by the other and dies out or becomes extinct in that habitat, because two species cannot occupy the same niche

why is the competitive exclusion principle is not always that simple?

other observations and experiments suggest that extinction is not necessarily inevitable

sometimes it simply results in one species simply being much smaller than the other with both populations remaining constant in size

as the environment is constantly changing it is rare for one species to be totally wiped out

how does the laboratory impact observations of interspecific competition?

in the laboratory it is easy to exclude the effects of other variables, so that the habitat remains stable

whereas in the wild a wide range of variables may act as limiting factors for different populations and can change daily or yearly

what experiments initially confirmed the competitive exclusion principle?

experiments on competition between flour beetles Tribolium confusum and T. castaneum

what was found from the flour beetles experiment?

the T. castaneum population size increased, whilst the T. confusum population died out

but even a small change in the temperature could change the outcome, so T. confusum would survive instead

what is conservation?

the maintenance of biodiversity, including diversity between species, genetic diversity within species, and maintenance of a variety of habitats and ecosystems

it is more active than preservation involving human intervention and improving biodiversity

a dynamic process that needs constant adaptation

what is preservation?

the maintenance of habitats and ecosystems in their present condition, minimising human impact and keeping things natural

what are some threats to biodiversity due to a steadily increasing human population?

over-exploitation of wild populations for food, sport or commerce

habitat disruption and fragmentation as a result of intensive agricultural practices, increased pollution or widespread building

what is over-exploitation?

when species are harvested at a faster rate than they can replenish themselves

what is reclamation?

conservation also involves:

managing areas of land

taking steps to encourage new habitats (e.g. controlled burning to clear forests and increase biodiversity)

removing animals to captivity

growing plants in cultivation

reclamation of damaged or destroyed ecosystems

what are ethical/ethological reasons for conservation?

species become extinct as a result of human action

humans have a responsibility to maintain species, ecosystems and habitats for future generations

all organisms have a right to survive and live in the way to which they have become adapted

what are social reasons for conservation?

people enjoy, visiting wild places

observing wildlife- the large animals are sustained by an interdependent web which includes a huge number of species

well-being- physical, intellectual and emotional health

what are economic reasons for conservation?

natural ecosystems provide services and products such as drugs

ecosystems also provide goods such as wood and fish for free

ecotourism

why is there a need for sustainable management?

because of potential conflict between the need for resources and conservation

what are three ways small-scale timber production manage sustainability?

coppicing, pollarding and rotational coppicing

what is coppicing?

the stem of a deciduous tree is cut close to the ground, once cut new shoots grow from the surface and mature into narrow stems

these can be used for fencing, firewood or furniture

after cutting them off, new shoots start to grow again and the cycle continues

what is pollarding?

it involves cutting the stem higher up, to prevent deer eating the emerging shoots

what is rotational coppicing?

it provides a consistent supply of wood, by dividing a wood into sections and cutting one section each year

by the time they want to coppice the first section again the new stems have matured and are ready to be cut

in each section some trees are left to grow larger without being coppiced

these are called standards and are eventually harvested to supply larger pieces of timber

why is rotational coppicing good for biodiversity?

when unmanaged woodland goes through succession and blocks out light from the woodland floor and reduces the number of species growing there

in rotational coppicing different areas of woodland provide different types of habitats

why is large-scale timer production bad for habitats?

it often involves clear felling of all trees in one area which can destroy habitats on a large scale, reduce soil mineral levels and leave soil susceptible to erosion

what is clear felling?

leaving each section of woodland to mature for 50-100 years before felling allows biodiversity to increase

what is a negative of clear felling?

the time scale is not cost effective

what does modern sustainable forestry do?

any tree harvested is replaced by another tree

the forest must maintain its ecological function regarding biodiversity, climate and mineral and water cycles

local people should benefit from the forest

what is selective cutting?

involves removing only the largest, most valuable trees, leaving the habitat broadly unaffected

how can trees be changed to sustainably manage forests?

if each tree supplies more wood, fewer trees ned to be harvested, so foresters

control pests and pathogens

only plant particular tree species where they know they will grow well

position trees an optimal distance apart

what is the Marine Stewardship Council?

fishing has to be done at a level which allows it to continue indefinitely

over-fishing must be avoided

it is ideal to maintain the fish population at the carrying capacity of their environment, so fishing harvests the excess of that capacity

there shouldn’t be permanent damage to the local habitat

what is aquaculture?

raising fish in controlled environments

can provide sustainable fish stocks

restricts the impact on oceanic fish stocks

what is the Terai region?

it is the in south of Nepal

made up of marshy grasslands, savannah and forests

densely populated and home to endangered species