6.6 Populations and sustainability

carrying capacity

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

if the population number increases above the carrying capacity, there will not be enough resources like food, water and space.

the number of individuals will decline

limiting factor

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

population size and carrying capacity

population size of a species can:

-remain stable

-rise or fall quite suddenly

-oscillate with a regular pattern

the balance between death rate (mortality) and the rate of reproduction determines the size of a population

K-strategists

A= lag phase → there may only be a few individuals, they are still acclimatising to their habitat. at this point, the rate of reproduction is low, and the growth in population size is slow

B=log phase → resources are plentiful and conditions are good. reproduction happens quickly exceeding mortality

C=stationary phase → 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

limiting factors

-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

K strategist

-this 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

-birds, larger mammals and larger plants are K-strategists

K strategists- characteristics

-low reproductive rate

-slow development

-late reproductive age

-long lifespan

-large body mass

R-strategists

-some species adopt a different type of population growth

-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

R strategists- characteristics

-mice, insects, weeds and spiders

-high reproductive rate

-quick development

-young reproductive age

-short life span

-small body mass

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

bust- resources run out and they die off

interspecific competition

competition between individuals of different species

intraspecific competition

competition between individuals of the same species

predators and prey 1

a predator is an organism that feeds on another lviving organism (prey) for its food

prey is def on by predators

with time predators evolve to become better adapted for capturing their prey; faster movement, more effective camouflage, better means of detecting/tracing prey

prey have also become better adapted otherwise the entire species of predators that feed on them would die

predators and prey 2

both the predator and the prey evolve together if this had not happened they would have become extinct

when a population of 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

predator and prey- the relationship

predators eat their prey reducing numbers

with fewer prey available the predators are in greater competition with each other

the predator population is reduced as some individuals are unable to obtain enough prey

with fewer predators left, fewer prey are eaten

the prey population increases

predator numbers increase

competition

this happens when resources are in limited supply

organisms have to complete for this resource

as competition intensifies the reproduction rate decreases and death rate increases

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

interspecific competition

in this case the competition can alter the distribution of species in an ecosystem

interspecific competition- case study I

two species of Paramecium were grown separately and together in a lab

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

over 20 days the P. caudatum died out

interspecific competition- case study II

the scientist concluded that the more overlap between two species’ niches the more intense the competition

if 2 species have the same niche, one will be totally out-competed by the other

two species cannot occupy the same niche

this idea is known as the competitive exclusion principle

interspecific competition- case study III

it is often not quite so extreme with one species simply being much smaller than the other with both populations remaining constant in size

in a lab other variables are often excluded

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

the Terai region

these groups created forest corridors between the national parks, which are essential to the dispersal and survival of tigers

they also started initiatives to counteract poachers nad

…………….

they also:

• constructed waterholes

• monitored endangered species

• eradicated invasive species

Maasai Mara 1

this region of Kenya is famous with wildlife watcher due to the large numbers of antelope and other large mammals

the region combines high endemic poverty and abundant wildlife population that attract many tourists it is a prime area to develop conservation- compatible land use that rewards the locals financially

Maasai Mara 2

in 1945 some areas were made into national parks and others held in trust until 1968 where they became designated ‘group ranches’

worried about ownership the Maasai took over titles to small portions of land and started intensive agriculture

this limited the areas for wildlife and reduced mobility

by reducing the wet-season range of wildlife the wildebeest population shrank from 150000 (1977) to 40000 (2010)

the density of other wildlife has dropped 65% over the last 30 years

in 2005 several land owners in the north consolidated their land forming conservancies to generates tourist income

partnerships between these and tourism operators have developed payments for wildlife conservation schemes

they are paid proportionally to the amount of land set aside for conservation

they work because they have a positive social outcome as well

there are also some negative consequences

land-owners need to move livestock during the tourist season leading to increase stock density outside the reserve where no one receives the extra money

peat forms in the absence of oxygen so complete decomposition cannot occur

it often occurs in waterlogged areas

it forms over thousand of years so can also contain information of historical interest

over time the rainfall removes the nutrients creating ideal conditions for Sphagnum moss to grow

these areas retain lots of moisture

these wet lands support high biodiversity

however, its ability to retain moisture had lead to its widespread use in compost, leading to mass removal

only 1/10 of the original bogs are left

conservation

the protection and management of an ecosystem so that the natural resources (biodiversity) can be used without running out and are still available for future generations

it is a dynamic process- needs constant adaption to changed within the ecosystem

involves:

• maintaining genetic diversity within a species

• the maintenance of habitats

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

preservation

preservation is the protection of ecosystems so they are kept exactly as they are

nothing is removed from a preserved area

commonly used to preserve sensitive resources

visitation is limited

examples: newly discovered caves, Galapagos islands and nature reserves

reasons for conserving species

economic- trade and finance

ethical- morally right or wrong

social- affect lifestyle

ecological- for animals and plants

economic reasons

natural ecosystems provide services

ecosystems also provide goods such as wood and fish for free

ecotourism

ethical reasons

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

social reasons

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

sustainable management of ecosystems

in our quest to manage the ever increasing human population we have been using intensive methods to exploit the environment

such approaches can disrupt or destroy ecosystems, reduce biodiversity and even remove the resource- this is not sustainable

conflict can occur between out need for resources and conserving the resource e.g. wood and timber production and fish production

sustainable management allows the use of resources whilst maintaining biodiversity

small scale timber production

coppicing provides a sustainable supply of wood

the stem of a deciduous tree is cut back close to the ground

new shoots grow from the cut surface and mature into narrow stems

these narrow stems can be used for fencing, firewood and furniture

each cut back leads to new growth so the cycle continues

the Terai region

these groups created forest corridors between the national parks, which are essential to the dispersal and survival of tigers

they also started initiatives to counteract poachers nad

they also:

• constructed waterholes

• monitored endangered species

• eradicated invasive species

it appears to have been successful due to the combined work of governmental and non governmental leadership

recent research shows rising numbers