biology topic 7a

sampling, populations in ecosystem

what are the 2 types of sampling?

• random

• systematic

why do ecologists undertake sampling?

• estimate population size

• calculate species diversity

• investigate effect of independent variable on population eg pH soil

how do you recognise random sampling

study a large and uniform area/ comparing 2 area

how do you recognise systematic sampling

use when there is a gradual change across the area being sampled eg down rocky shore

whats a description of random sampling?

• lay out tape measure at right angles to create 10×10m grid

• use random number generator to give co-ords to place each quadrat

• record the (% cover/number) of (plant/species) in many (20+) quadrats

• (if asked work out mean by adding %/number of plant in each quadrat then dividing by number of quadrats) if not say total

how do you describe systematic sampling?

• set up belt transect by laying a tape measuring down eg slope

• place the quadrat at regular intervals (every metre) at side of the tape measure

• count number/% cover of plant/species in each quadrat

• repeat with many quadrats (20+)

• repeat with belt transect at different places along eg slope

(can be continuous or interuppted)

define population

a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.

define community

all populations of all the different species in an ecosystem/habitat

what is carrying capacity?

the size of a population of a species that an ecosystem can support

whats a niche?

role an organism occupies within its environment (particular biotic and abiotic factors to which it is adapted) eg plant species, temp/pH preferences

whats the difference between interspecific and intraspecific competition?

interspecific competition: individuals of different species competing for the same resources

intraspecific competition: individuals of the same species competing for the same resources → causes carrying capacity (levels off graph)

what can population size vary as a result of?

• effect of abiotic factors

• interactions between organisms ie biotic factors (interspecific and intraspecific competition and predation)

what are ecosystems?

dynamic systems ie they can change

what curve is used to show changes in population?

population growth curve

how do scientists count the number of bacteria when there were such large numbers of them to find population size?

use serial dilution

what are examples of biotic factors?

• predation

• intra/interspecific competition

• trampling

• disease

what are examples of abiotic factors?

• temperature

• light intensity

• wind speed

• pH

• water availability

• nutrients → nitrates and phosphates

what is succession?

the progressive change in the composition and diversity of the species in a community in one place over a period of time

what are the 2 types of succession?

1. primary succession: starts in new habitats with no soil and no previous community; extreme environmental conditions

2. secondary succession: starts on bare soil where there had previously been a community extreme environmental conditions

describe the process of succession

• pioneer species colonise as they survive in hostile environments

• as organisms in PS die and decompose, results in humus and nitrates forming soil

• makes environment less hostile

• new species can survive and outcompete PS

• overtime species diversity increases as more humus and nitrates added (even less hostile) and this continues until climax community is reached.

what happens since pioneer species are first to colonise?

they are subjected to extreme abiotic conditions eg extreme temperature and pH, lack of water and soil (nitrates and phosphates), and wind

how do pioneer species adapt to survive in the hostile environment?

• to rapidly colonise a new area - asexual reproduction; rapid life cycle

• to reach new areas to colonise - production of seeds with efficient long dispersal; rapid germination

• to tolerate extreme conditions - photosynthesise; nitrogen fixing from atmosphere; tolerate little water and extreme pH

what does high biodiversity cause?

the community to be stable due to lots of species present so more complex food webs so if there was a change in one species then there would be little effect on others

what are features of climax community?

• populations are stable over long periods of time

• abiotic factors staying more or less constant

what can human actions do to succession?

can halt succession, sometimes deliberately eg mowing, coppicing, burning heater. farmers can grow crops, plough, use herbicides and graze animals

what sampling technique is used for mobile organisms and describe the process

mark, release, recapture

1. capture a large sample of organisms, count and mark them, release them back into same area

2. mark should not be toxic, affect survival, or make them more visible to predators

3. leave time for them to reintegrate into the population (but not reproduce)

4. capture a second sample and use the following calculation → (number in1st sample X number in 2nd sample)/ number of marked individuals in 2nd sample

what are some assumptions to do with mark release recapture?

• no immigration between taking the samples

• no births in population

• mark is not lost/rubbed off

• marked individuals distribute themselves

if any not true, can lead to over/underestimation

what are reasons for conservation?

• economic - species as food/sources of medicine/products

• aesthetic and cultural - enjoy countryside

• ethical - all species have right to exist

• ecological/personal - species are interdependent (food chains)

what does conservation work involve?

the managment of succession to preserve the species found at a particular stage. there is often a need to manage the conflict between human needs and conservation in order to maintain sustainability of natural resources

what are the sources of variation due to genetic factorss

1. main source - mutations (creates new alleles)

2. meiosis (new combination of alleles in gametes IS 2ⁿ and RBCO )

3. random fertilisation of gametes (2ⁿ)²

whats the specific variation affected by genetic factors alone?

discontinuous variation and can be represented on a bar graph or pie chart eg blood group

how do environmental factors affect variation?

exerts influence on all organisms and affect how the genes are expressed hence determine where these limits lie. eg butter cup height may have potential to be tall but can be limited by sunlight, wind etc

how is variation due ot environmental factors displayed?

continuous variation and can be shown on a normal distribution curve

what is selection pressure?

environment factors (that result in some individuals having a selective advantage) that limit the population of a species eg predation, competition, disease

what are the key words used to describe natural selection

• random mutations

• new alleles

• selective advantage

• better able to survive and reproduce to pass on alleles to offspringe

• allele frequency increases

what competition does natural selection rely on?

intraspecific competition (only occurs if there are too many offspring produed)

what are the 3 types of selection

1. stabilising selection preserves the average phenotype (more likely to survive and reproduce) , selecting against extreme phenotypes

2. directional selection selecting phenotypes that vary in one direction from the mean (more likely to survive and reproduce) changes the phenotypes of population

3. disruptive selection is selecting for individuals with both extreme phenotypes, selecting against average phenotype

define speciation and give the 2 types

evolution of new species from existing ones

allopatric and sympatric

define species

group of similar individuals that are capable of interbreeding to produce fertile offspring

define and describe allopatric speciation

new species form from different populations in different areas

1. population reproductively isolated by geographical isolated

2. random mutations create new alleles (natural selection)

3. 2 populations have different selection pressures

4. different individuals in both populations would have a selective advantage, be able to survive, reproduce and pass on their alleles

5. different change in allele frequency in 2 populations

6. separate gene pools form over many generations, individuals cannot interbreed to produce fertile offspring

define and describe sympatric speciation

new species form from a population living in the same area (reproductively isolated not geographically due to eg temporal, behavioural, mechanical isolation)

1. two groups within same population reproductively isolated

2. random mutations produce genetic variation

3. 2 groups subjected to different selection pressures

4. different individuals survive and reproduce and pass on their alleles in the 2 groups - different change in allele frequency

5. gene pools become so different that they become separate gene pools - individuals cannot interbreed to produce fertile offspring

whats genetic drift

greater change in allele frequency will occur more quickly in small populations due to lower genetic diversity so allele frequency will be higher so passed on more quickly therefore mutant allele will have greater impact

when do you use t test and whats the degrees of freedom?

use when comparing means of 2 sets of data to see if difference in mean is significant

no in sample 1 + no in sample 2 -2

when do you use spearmans rank test and whats the degrees of freedom?

use when looking at correlation (can be plotted on scatter graph) between 2 variables and see if significant

no of pairs of data - 2

when do you use chi square test and whats the degrees of freedom?

when comparing observed and expected results when data is in categories and use raw data to see if there’s a significant difference

no of categories -1

how do you start a null hypothesis?

there is no significant [difference/correlation] between..

what do you use degrees of freedom for?

to tell you which row of the critical value table to look at which will give you a p value to compare to your calculated test value

what are the different levels of significance for the different p values

• p value less than or equal to p=0.05 → significant difference/correlation

• p value less than or equal to p=0.01 → very significant

• p value less than or equal to p=0.001 → highly significant

• p value more than p=0.05 → no significance

how do you compare critical and test value to eg if the calculated value is bigger than the critical value at p=0.05

there is less than 0.05 probability that the difference/correlation [..] is due to chance. there is a significant difference/correlation therefore reject null hypothesis. then finally make specific to investigation eg so the drug does reduce blood pressure