C4.1 Populations and Communities

different poopulation

cannot interbreed and produce fertile offspring

What gives rise to different populations?

allopatric speciation

sympatric speciation

allopatric speciation

-eproductive isolation - physical barrier

sympatric speciation

no physical barrier

but

• temporal

• behavioral

• geographical - colony - already have female no need to go to other species colony

• Non disjunction

Reproductive isolation

occurs when there is a barrier which prevents individuals from reproducing.

reasoning for sympatric speciation (non disjunction)

Non disjunction in plants - polyploidy (many sets of chromosomes) - allsman

Even same area - ourselves having mutations while making gamete - causing reproductive isolation

Sessile population

Any species that don’t move a lot

How to sample sessile population

Using quadrant sampling- square

Random sampling - equal chance to be chosen from the native environment to eliminate human bias, increasing validity - no human decision

Transect - place at least 10 quadrant horizontally as line - ensure reliability

Reliability

Able to replicate

Consistency

Validity

Accuracy

statistical test cannot

Prove

Shows probability instead

Chi square test process

1. Hypothesis H0: no relationship H1: correlation (positive negative )

2. place quadrant using random sampling

3. Make a table (present absent)

4. calculate expected frequency (row total x column total/ grand total)

5. Apply to chi square formula (x2=

6. find critical value

7. Find degree of freedom (r total -1) (c total-1)

8. P value use 0.05

Table of chi square

sampling motile populations

lincoln index

capture-mark-release-recapture

Mx(N/R)

M = Number of individuals initially caught and marked.

N = Number of individuals recaptured

R = Number of marked individuals recaptured

limitations of lincoln index

assume no immigration no emigration.

marks might be lost/fade/be overlooked.

marking may alter behavior

unequal Catchability

small sample size

not suiyable for plants or sessile organisms

how to improve reliability for lincoln index

increase sample size

increase trials

how to improve validity/accuracy for lincoln index

change method - another marking method

change different months to conduct

carrying capacity

maximum population size of a species that can be suported long term in an environment

carrying capacity is affected by what factors

availability of food water

space

shelter

disease

predators

climate

carrying capacity graph

factors affecting population growth (2 main catagories)

Density-dependent factors, are any force that affects the size of a population of living things in response to the density of the population.

● Density-independent factor, in ecology, any force that affects the size of a population of living things regardless of the density of the

population.

density dependent factors

panda

predators

resources

nutreint supply

disease

accumulation of waste

density independent factors

paw

phenomena (natural disasters)

abiotic factors eg temperature

weather conditions eg storm

predator prey has a what correlation

4 factors affect the size of population

Natality (N) is the birth rate for a population

Mortality (M) is the death rate for a population Immigration (I) is new individuals entering a population

○ Emigration (E) is individuals leaving a population ● Change in population size = (N + I) - (M + E)

change in population size equation

(N + I) - (M + E)

4 phases in population growth model

lag phase

expotential growth phase

transitional phase

plateau phase

difference between exponential growth and transitional phase

exponential: natality + immigration a lot more than mortality and emigration

transitional: lesser

intrapecific competition

between same species

bc all have same ecological niches

why intraspecific competition increase

density dependent factors

benefits of intraspecific cooperation

group hunting

defense against predators

parenting

interspecific interactions

between different species

• herbivory

• predation

• interspecific competition

• mutualism

• parasitism

• pathogenicity

mutualism explain

type of symbiosis

both benefit

eg bees and plants

cooperation example 1 (mutualism)

Mycorrhizae are formed by a symbiotic relationship between roots of a plant and a fungus.

● Orchids are a family of plants that grow in mineral-poor soil.

The fungi greatly enhance the orchids’ ability to acquire nutrients by increasing surface area for absorption of water and minerals.

The fungus gains as it receives carbohydrates and protection from the plant.

cooperation example 2 (mutualism)

Zooxanthellae algae have a mutualistic relationship with coral polyps.
● The photosynthetic zooxanthellae algae produce nutrients such as glucose used

by the corals, as well as removing wastes and producing oxygen.

● The coral polyps provide protection for the zooxanthellae, as well as providing them with carbon dioxide for photosynthesis.

cooperation example 3 (mutualism)

cooperation example 4 (parasitism)

Parasitism is a form of symbiosis where one species benefits, but

the other species is harmed. Ticks are parasites of many animals such as dogs.

The tick benefits from feeding on the dog’s blood, the dog loses blood, and suffers skin

irritation.

pathogenicity example

occurs when an organism infects another species,

causing a disease.

The disease malaria in humans is caused by the malarial parasite entering the human bloodstream.

invasive species definition

organisms that have been introduced to an

ecosystem, and do not occur there naturally.

cause harm to natural ecosystem

invasive spacies often replace

endemic species (native) by competitive exlcusion

allien species may become an invasive species if

have a better chance of survival than the native species due to:

○ The absence of predators in the new habitat

○ The absence of diseases in the new habitat.

○ Faster rate of reproduction ○ Larger size/ more aggressive

Outcompeting for food and other resources

2 ways to eliminate invasive species

top down

bottom up

invasive species example

Red squirrels are an endemic species in the UK, and grey

●

Grey squirrels are immune to the

●

squirrels are an invasive species. Grey squirrels are outcompeting red squirrels for the following

reasons:

○ Grey squirrels are larger and

stronger.

○ Grey squirrels reproduce

faster.

top down control

Top down factors are pressures applied by a higher trophic level to control the population dynamics of the ecosystem

The top predator either suppresses the abundance of its prey or alters its behaviour to limit its rate of population growth

Top down control results in an oscillating trophic cascade (suppression at one level increases numbers at the next level)

bottom up control

Bottom up factors are pressures that limit the availability of resources to lower trophic levels (e.g. producers)

A lack of resources at lower trophic levels suppresses the abundance of organisms at higher trophic levels i.e. the suppression of the 'bottom’

restricts energy supply to the ‘top'

Human activity can often limit resource availability and hence inadvertently exert bottom up pressure on an ecosystem

con of these two methods (bottom up top down)

affects other species

imbalance of ecosystem

allopathy definition

release of chemicals by one organism which influences the germination, growth, survival or reproduction of another organism.

example of allopathy (black walnut)

Black walnut trees produce and release an allelopathic chemical

called juglone. Juglone inhibits the growth of other plants.

allopathy (penicillim)

The Penicillium fungus secretes the antibiotic chemical penicillin.

● Penicillin inhibits the growth of bacteria near the fungus, reducing

competition for resources.

Penicillin is used as a medicine to inhibit bacterial growth.