materials life sciences 1. population fluctuation and regulation carrying capacity – maximum...

MATERIALS

Life Sciences

1

Population fluctuation and regulation

Carrying capacity – maximum number of individuals of a species that an ecosystem can continually supply resources to.

Certain factors prevent a population from unlimited growth and exceeding its maximum growth rate – limiting factors and together are called environmental resistance.

Seasonal fluctuations – Swallows fly from the cold European winter to Southern Africa where the summer temperature is more favourable.

Annual fluctuation – Migration of millions of wildebeest in East Africa. This phenomen is determined by the availability of grazing which is also dependant on rainfall.

J Gerber and J Goliath2

Growth patterns/forms – Geometric or J – shaped curve

Population size increases unrestricted and rapidly with time.

A population can reach its full reproductive potential because of enough food, water and no predators.

Environmental resistance increases when numbers of population increase.

Number of population can decrease rapidly due to limiting factors.


Graph of repeated growth pattern


Logistic growth form (S - shaped)

Lag phase: Population acclimates, individuals

become sexually mature and seek partners for mating.

Accelerating growth phase Population grows rapidly and

reaches its maximum growth rate.Deceleration growth phase Growth rate decreases due to an

increase in environmental resistance.

Equilibrium phase Population numbers reach the

carrying capacity.


Geometric and logistic growth phase


Methods to determine population size - direct technique (census)

Count of all individuals in a population and includes human population census.

Aerial photography may be used in the counting of larger animals in nature reserves.


Indirect technique – simple sampling (quadrated method)

A square frame (quadrat) is used Place it on the ground and count the individuals

inside the quadrat It gives the number of individuals (density) per unit

area Repeat in different places at random and calculate

the average density Method is used for plants and slow moving animals


Mark-recapture technique (Peterson)

Demarcate a specific area. Capture a number of individuals, count and mark them (first

sample). Set the marked individuals free in the area. Allow the marked individuals enough time to mix with unmarked

individuals in the area. Capture a second number of individuals and count them

(second sample). Count the number of previously marked individuals in the

second sample.


Mark-recapture technique

Use this information to calculate the total size of the population by means of the following formula:

P = m x s

t P = estimated population size. m = total number of animals captured and marked in first

sample. s = total number of animals captured in second sample. t = number of marked individuals in second sample.


Mark-recapture technique - validity

Marking methods should not injured the organism. Marks should be clear for the duration of the investigation. Marking methods should not affect the movement of the

animals. Marked organisms should be allowed enough time to mix. Population must be closed. Period between two samplings should be sufficiently brief – no

births or deaths.


Human population age and gender distribution in:

1. an increasing population

A population pyramid with a small number of old people indicates a population with a high birth rate, a high death rate and a short life expectancy. This pattern is typical of less economically developed countries (LDC) like South

Africa, South America and Asia (excluding Japan)

2. a stable populationThere is approximately the same number of young people

and old people. About the same number of children is born each year compared to the number of people who die each year. Economical developed countries like Ireland have this

kind of pyramid

3. a decreasing populationThere are more old people than young people. Each year more people die than are born. Developed countries like

Germany have this kind of pyramid. Some southern African countries, like Botswana (experiencing the effects of

HIV/AIDS) are also starting to show this kind of age-gender pyramid.

Use these graphs to discuss the changing trends in the SA population. Indicate the working group (20 – 60 years), mention how their economical contributions will support the non-economical groups (children and old people). Take the % of jobless people into consideration and the fact that only 5.6% of the population pays tax

Interactions within a Community

The five main types are:

Predation

Competition

Parasitism

Mutualism

Commensalism

PREDATION

In predation, one individual, the predator, captures, kills, and consumes another individual, the prey.

Predators, Prey, and Natural Selection

Natural Selection favors adaptations that improve a predator‘s efficiency at finding, capturing, and consuming prey.

These adaptations include a shark’s jaws, a scorpion’s claws and stinger, and a spider’s web and fangs

Prey-predation interaction

A

The cycles of increase and decrease reflects a predator –prey intercation

e.g lions feeding on impalas, lynx feeding on rabbits

Prey population reaches higher density than predator population

Portion A = geometric phase- rapid increas of prey, predator pop too low to hinder increase

More prey means more food for predators and the population increases

More predators = increase in mortality of prey

Less prey could cause predators to emigrate / die , hence prey population can increase again

Graph interpretation

Competition

Competition occurs when organisms in the same community seek the same limiting resource. This resource may be prey, water, light, nutrients, nest sites, etc.

Competition among members of the same species is intraspecific.

Competition among individuals of different species is interspecific.

Intraspecific Competition

Competition between organisms of the

same species

Interspecific Competition

Panthera leo

Crocuta crocuta

Competition between

organisms of the different

species

Outcomes of Competition Niches of similar species may overlap. Two

species cannot compete for the same limiting resource for long.

eventually one species outcompetes the other

One species survive, other emigrates OR dies out

Even a minute reproductive advantage leads to the replacement of one species by the other.

This is called the COMPETITIVE EXCLUSION PRINCIPAL.

Evidence for Competitive

Exclusion the Russian ecologist, G.F. Gausse demonstrated that Paramecium aurellia outcompetes and displaces Paramecium caudatum in mixed laboratory cultures, apparently confirming the principle.

Resource Partitioning

When two or more similar species coexist, such as

these varieties of warbler, each species only uses

part of the available resources. This is called resource partitioning.

(species sharing resources)

PARASITISM Parasitism is a species interaction that

resembles predation in that one individual is harmed while the other benefits.

However, in parasitism, the parasite feeds on the host individual.

This does not result in the immediate death of the host. Rather, the parasite may feed on the host for a long time instead of killing it.

Ectoparasites

Ectoparasites are external parasites.

They live on their hosts body, but do not enter it.

Examples include ticks, fleas, lice, lampreys, leeches and mosquitoes

Ectoparasites

Endoparasites

Endoparasites are internal parasites, and live inside the host’s body

Endoparasites include bacteria and other micro-organisms, and many worms

Resource partitioning amongst plantsDifferent species of plants in the same habitat will compete for the same resources like light, water, mineral salts, etc. Different species of plants grow to different heights or have roots that are different lengths so they divide the resources, accessing them in slightly different ways

Resource partitioning: co-existing shore birds

Human influence on community structure

The elephant herd in the Kruger National Park increased from 8, 000 to 12,500 in 2008 and to 19 000 in 2009. The elephant population is increasing by 7% per year, and might reach 20 000 by 2012. This large herd cannot be sustained since adult elephants consume 130 kg food a day and they live for 55 – 65 years. On 25 February 2008 the SA Government finally concluded it would have to lift a 17 year-old moratorium on the culling of the native elephant to cope with its booming population. Minister van Schalkwyk announced that killing of excess animals would only be allowed once all other options (translocation and contraception) had been ruled out. Minister van Schalkwyk said:”Our simple reality is that elephant population density has risen so mulch in some southern African countries that there is concern about impacts on the landscape, the viability of other species and the livelihoods and safety of people living within elephant ranges.”

Mutualism Mutualism is a symbiotic relationship in which

both members of the association benefit. Often help organisms obtain food or avoid

predation. Bacteria in human intestinal tact.

Need not be equally beneficial to both species. Cleaning Symbiosis

Pollination

Pollination is the most important of the mutualistic relationships.

The plant provides food for the pollinators, which in turn carries the pollen to another flower

COMMENSALISM

Is a relationship in which one species benefits and the other is not affected

Succession

Primary succession begins in areas consisting of bare, lifeless substrate such as rocks or a car path. Organisms gradually move into the area and begin to change its nature,

Secondary succession occurs when a established community has been disturbed in a catastrophic manner, e.g. after a veld fire or a flood. In the disturbance all the vegetation is destroyed, but all or some of the soil remains. The same process occurs as in primary succession, but as there is soil for grasses and small plants to grow in, these plants form the pioneer communities.

Pioneer plants

Lichens are pioneer plants as they are the first organisms to colonise a bare area. Acidic secretions from the lichens help to break down the hard surface of the rocks and slowly bits of soil accumulate, mosses may grow on these small pockets of soil, enriching the quality and quantity of the soil with the organic material that they add to it. As time passes and the soil becomes richer and deeper, other plants like grasses and small herbaceous plants become established in the larger pockets of soil , small animals may also move into an area when these plants become established.

An example of primary succession

Pioneer grass on a sand dune

Climax community

PHOTOTROPISM

EXPERIMENTS

DATA RESPONSE

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