Grade 12 IEB Population Ecology

Ecology

The study of the interactions of organisms with their physical and biological environments.

Population ecology

The fluctuations in the size of a population and the factors (physical and social) that regulates these fluctuations.

Population size

The total number of individuals

Natality

birth rate

Mortality

death rate

Immigration

Individuals moving into a population and staying

Emigration

Individuals leaving a population and not returning

Closed population

a population that has no immigration and emigration with other populations

Environmental resistance

The total number of factors that stop a population from reproducing at its maximum rate. Limiting factors build up this.

carrying capacity

The population density that the environment can support. The pop fluctuates around the carrying capacity.

Limiting factors

Help to regulate the growth of a population.

Density independent factors

Limit growth pop. Results natural factors, not bcuz of no. of organisms. PHYSICAL FACTORS (temp, humidity, rainfall) CATASTROPHIC EVENTS (flood, fire, earthquake)

Density dependent factors

Greater effect pop density is high. More crowded: COMPETE (resources-food,water,light,oxygen,space,shelter) PREDATORS (more easily found) DISEASE (spread easily)

stable population

Numbers decrease-size exceeds cc

Increase-fall below cc

FLUCTUATES

Unstable population

Pop far exceeds cc

Habitat: deteriorating rapidly, low cc, not being able to support pop, decrease, extinct

Direct method

Counting every single individual in pop. CENSUS. Organisms=large. Area=not too large. Individuals=slow, stationary, stay in fixed position. Area too large=aerial pics, helicopters.

Quadrat Method of Estimating Populations

Counting no. individuals in quadrats, using no. calculate pop size of total are.

N=average number in sample x size of whole habitat/size of quadrat

Mark-recapture method

Individuals caught and marked, released. Another sample captured, number of marked individuals counted. Animals: mobile, not easily visible.

P=M x C/R

M=total number marked animals initially

C=total number of animals caught in 2nd sample

R=total number of marked animals in 2nd sample

Predation

Biological interaction, predator kills and eats the prey.

Role of predators

1) regulating prey species.

2) increasing biodiversity

3) prey pop genetically fit

4) food for scavengers

PPR Aphid-ladybug

Aphid - prey

Ladybug - predator

PPR lion-zebra

Evolve adaptations-speed of movement, co-evolution. Advantageous.

PPR shark-zebra

Role-keep pop of other fish healthy and in balance in ecosystem.

Keep ocean healthy: east very efficiently, eat old sick or slow fish. Prevent disease and strengthen gene pools of prey species.

Food web

An interconnected set of all the food chains in an ecosystem.

Competition

When 2/+ individuals compete for the same resources that are in short supply. (Light, space, water, food, shelter)

Intraspecific comp

Same species. Mates.

Inter specific comp

Different species, niches are very similar.

Ecological niches

All the conditions necessary for an organism to survive and reproduce.

Specialisation

The structural and behavioural adaptations that enable individuals of different species to co-exist.

Competitive exclusion

One of the two competing species, more successful than other. Successful species survives and other disappears, extinction, NB role in evolution.

Competitive coexistence

2 competing species co-exist in the same habitat. Resource partitioning.

Resource partitioning

The evolutionary process whereby species with similar requirements, living in same habitat, evolve specialised traits, utilise resources differently, separate niches, reduce inter specific competition, create co-existence.

How can resources be partitioned

Use resources:

1) different times

2) different parts of habitat

3) different parts of same plant

Ecological succession

A predictable pattern of gradual change over time in the types of species in a community following a disturbance.

Primary succession

Begins on sites that have not previously had plants growing on them (beaches, lava flows, severe land slips, ponds, bare rock)

Secondary succession

Begins in areas where a disturbance removes some or all species but the soil remains.

Succession stages

1) pioneer

2) intermediate

3) climax - endpoint of succession

What factors determine an endpoint to a community?

1) rainfall

2) overgrazing

3) draining of wetlands

4) climate change

5) invasion by aliens

Social organisation

Structure of relationships within a group.

Improves the survival and reproductive success of an individual.

Social org

1) herds/flocks predator avoidance strategy

2) packs as a successful hunting strategy

3) animals with a dominant breeding pair

4) division of tasks making castes [Eusocial animals-most advanced form of social organisation]

What has caused exponential human pop growth

1) Food production has increased substantially:

•more land cultivated

•improved methods food production

2) methods of treating diseases have improved greatly

MDCs

•slow pop growth

•Hugh standard of living

LDCs

•rapid growth rate

•lower standard of living

Population pyramid

Age-sex pyramid

•bar graph that shows the composition, by age and sex, of a nation's population at the time of a census.

•show, in visual form, how a national population is made up.

3 major age/sex groups pop

•pre-reproductive

•reproductive

•post-reproductive

Age structure

The relative numbers of individuals of each age in a population

Age structure of a pop

Determined by what proportion of the population falls into each of these age groups

What do diff pyramid shapes depict

The shapes of the pop pyramids show 3 types of pop growth

Rapidly growing pop

•high birth rate

•rapid fall in each upward age group due to high death rates

•short life expectancy as found in LDCs

Stable pop

•declining birth rate

•low death rate

•more ppl living to old age as found in MDCs

Declining pop

•low birth rate

•low death rate

•higher dependency ratio

•longer life expectancy as found in affluent countries

Ecological footprint

A measure of human demand on the earth's ecosystems. Represents amount of biologically productive land and sea area necessary to supply the resources a human population consumed, and to assimilate the waste generated.

Total world ecological footprint

2,7 global hectares per person.

World average bio capacity is 2,1 global hectares per person.

Ecological deficit of 0,6 global hectares per person.

Biocapacity

The amount of productive land and water available to produce the resources we use and to