Unit 7 - Ecosystems and Evolution

Define biotic factor

Living factors that can affect a population

Define an abiotic factor

Non-living factors that can affect a population

What is an ecosystem

All living and non-living components of a particular area

Define populations

Group of individuals of one species occupying the same habitat at the same time that can interbreed

Define carrying capacity

The size of a population an ecosystem can support

Define community

All populations of different species living the same area at the same time

Define habitat

Place the organism lives which is characterised by physical conditions

Define ecological niche

Role of the organism and how it fits into and exploits its environment. How it behaves and interacts with other species and how it responds to its environment

What are some examples of abiotic factors

• Temperature

• Light intensity

• PH of soil

• Water content of soil

• Humidity

What are some examples of biotic factors

• Competition

• Predation

• Effects of herbivores

• Disease

• Parasites

How does temperature effect carrying capacity

• At temperatures below the optimum temp, enzymes and substrates do not have kinetic energy

  • Less enzyme substrate complexes

  • Slower metabolism and so small carrying capacity

• At temperatures above the optimum temp, enzymes are denatured as hydrogen bonds are broken

  • Less enzyme substrate complexes

  • Slower metabolism so small carrying capacity

How does temperature effect carrying capacity when organisms can regulate their body temperature

• Due to homeostasis, warm blooded organisms can regulate their body temp keeping it constant

  • So carrying capacity should not be effected and should be large

• However energy is required to regulate the body temp when the external temp is too high or too low

  • Leaves less energy for growth

  • Matures slowly

  • Have slow reproductive rate

  • Carrying capacity is reduced

How does light intensity effect carrying capacity

• Light is the energy source for the most ecosystems

• As light intensity increases the rate of photosynthesis increases

• The greater the rate of photosynthesis the faster the glucose and sucrose produced

• Therefore plants can grow quicker and produce more seeds

  • Increases number of plant species

  • More herbivore species as a result

  • The more herbivores there are the more predators

  • Therefore carrying capacity is higher

• However as light intensity increases above the optimum the growth of the plants decreases

  • Because increased rates of transpiration so more water is lost

  • Less water for photosynthesis so less growth

• Can increase temperature of the plant

  • Denatures enzymes for metabolic reactions and photosynthesis

  • Less growth

• Can damage chlorophyll

  • Less photosynthesis so less growth

• So lower carrying capacity

How does humidity effect on carrying capacity

• Reduces water potential gradient

  • Slows the transpiration stream, so less water moves to the leaves

• This decreases the rate of photosynthesis that slows glucose and sucrose production

• Therefore plants grow slower and produce less seeds

  • Reduces the number of plant species

  • Less plants = less animal so carrying capacity is lower

Describe the process of random sampling

• Define the Sampling Area:
  First, identify and clearly mark the boundaries of the field where the buttercups are growing.

• Use a Sampling Frame or Grid:
  Divide the field into equal-sized sections using a grid or map. This helps to systematically cover the entire area.

• Random Selection of Sampling Points:
  To avoid bias, select sample locations randomly. This can be done by using random number tables, a computer-generated list of random coordinates, or by throwing a quadrat randomly across the field.

• Place Quadrats at Random Locations:
  Use a quadrat (a square frame, e.g., 0.5 m × 0.5 m) to sample the buttercups. Place it at the randomly chosen spots in the field.

• Count Buttercups Within Quadrats:
  Count the number of buttercup plants inside each quadrat.

• Record and Repeat:
  Repeat the sampling process several times (at multiple random locations) to gather a good data set.

• Calculate Average Density:
  Calculate the average number of buttercups per quadrat from your samples.

• Estimate Total Population:
  Multiply the average density by the total area of the field to estimate the total number of buttercups.

Describe the process of systematic sampling

1. Define the Sampling Area:
   Clearly mark the boundaries of the entire field where buttercups are growing.

2. Set up a Sampling Grid or Transect Line:
   Lay out a grid or a straight line (called a transect) across the field. For example, you might stretch a tape measure or rope from one side of the field to the other.

3. Decide the Sampling Interval:
   Choose a fixed distance interval for sampling. For example, every 5 meters along the transect line or at every 3rd square in the grid.

4. Place Quadrats at Regular Intervals:
   Starting at a random point on the transect or grid, place the quadrat at regular intervals along the line or grid points (e.g., at 0 m, 5 m, 10 m, 15 m, etc.).

5. Count Buttercups in Each Quadrat:
   At each interval, count the number of buttercup plants within the quadrat.

6. Record Data and Repeat Along the Transect or Grid:
   Continue sampling systematically across the entire field or along the transect line.

7. Calculate Average Density and Estimate Population:
   Find the average number of buttercups per quadrat, then multiply by the total number of quadrats that would fit in the whole field to estimate the total population.

Describe the process of sampling mobile organisms (mark, release, recapture) including an equation

1. First Capture:
   Capture a sample of individuals from the population using an appropriate method (e.g., netting, traps).

2. Mark the Captured Individuals:
   Mark each individual in a harmless and easily recognizable way (e.g., a small dot of paint, a tag). Make sure the marking does not affect their behavior or survival.

3. Release the Marked Individuals:
   Release all marked individuals back into the environment, allowing them to mix freely with the rest of the population.

4. Wait for Mixing:
   Allow enough time for the marked individuals to disperse and mix evenly with the unmarked population.

5. Second Capture:
   Capture another sample of individuals from the population, ideally the same size as the first sample or as large as possible.

6. Count Marked Individuals in the Second Sample:
   Count how many of the captured individuals in this second sample are marked (recaptured) versus unmarked.

7. Estimate Total Population Size:
   Use the formula:

   Estimated population= (Number in 1st x Number in 2nd) / Number marked in 2nd

What is intraspecific competition

• Competition for resources within the same species ​

• For Food, territory and mates etc. ​

• The availability of resources determines size of a population ​

What is interspecific competition

• Competition for resources between different species ​

• Usually one species has a competitive advantage ​

• Will outcompete the other species ​

• The population of the species with competitive advantage increases​

• The population of the species without the competitive advantage decreases eventually being removed ​

• Competitive exclusion ​

• Therefore no two species can occupy the same niche​

Describe how a predator-prey relationship cycle works

The predator-prey cycle describes the natural fluctuations in the population sizes of predators and their prey over time. These populations are closely linked because the number of predators depends on the availability of prey, and the prey population is controlled partly by predation.

• Prey Population Increases:
  When prey (e.g., rabbits) have plenty of food and favorable conditions, their population grows rapidly.

• Predator Population Increases:
  As prey becomes more abundant, predators (e.g., foxes) have more food available. This leads to better survival and reproduction rates, so the predator population also increases—but with a slight delay compared to the prey population.

• Prey Population Decreases:
  With more predators hunting, the prey population starts to decline due to increased predation.

• Predator Population Decreases:
  As prey becomes scarcer, predators have less food, leading to starvation and lower reproductive success. Predator numbers then begin to fall.

• Prey Population Recovers:
  With fewer predators, the pressure on prey decreases, allowing the prey population to recover and start the cycle again.

How do crashes in prey population cause evolution

• Crashes in a population result in a selection pressure ​

• Prey that are better adapted that can escape / hide from predators survive and reproduce​

• Passing on advantages alleles (adaptation) to offspring ​

• Results in evolution of prey​

• Predators which are better adapted to hunting the prey with survive and reproduce​

• Passing on advantages alleles (adaptation) to offspring ​

• Results in evolution of predators​

What is a T-test used for and how would you phrase a null hypothesis for a T test

to determine if the difference between the two means is significant

Null- There is no significant difference between mean 1 and mean 2 ​​

What does it mean is P= 0.10

There is 0.10 probability that the difference/ correlation is due to chance​

No significant difference/ correlation​

Accept the null hypothesis ​

What does it mean when P < 0.05

There is less than 0.05 probability than the difference/ correlation is due to chance​

Is significant difference/ correlation​

Reject the null hypothesis

What does it mean when P < 0.01

There is less than 0.01 probability than the difference/ correlation is due to chance​

Is very significant difference/ correlation

Reject the null hypothesis ​

What does it mean when P < 0.001

There is less than 0.01 probability than the difference/ correlation is due to chance​

Is highly significant difference/ correlation

Reject the null hypothesis

How do you work out the degrees of freedom for a T-test

(number in first sample + number in second sample ) – 2

How can the test value and critical value of a T test be used

• The test value and critical values are then compared​

• If the test value is equal to or higher than critical value the null hypothesis is rejected​

• If the test value is lower than the critical value the null hypothesis is accepted

When can spearman’s rank/correlation co-efficient be used and how who you phrase a null hypothesis

to determine the correlation is significant between two variables ​

Null - There is no significant correlation between variable 1 and variable 2​

How can degrees of freedom be calculated for spearman’s rank/correlation co-efficient

no. of pairs of data - 2​

How can test values and critical values be compared for spearman’s rank/correlation coefficient

• The test value and critical values are then compared​

• If the test value is equal to or higher than critical value the null hypothesis is rejected ​

• If the test value is lower than the critical value the null hypothesis is accepted​

• For correlation co efficient remember to talk about the direction of the correlation. ​

• If a -ve number = negative correlation ​

• If a positive number = positive correlation

Define succession

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

What is the difference between primary and secondary succession

Primary succession: Starts in new habitats with no soil and no previous community​

Secondary succession: Starts on bare soil where there had previously been a community​

What is a pioneer species

Are species that can colonise in hostile conditions and over time can change the abiotic conditions so that the environment is less hostile. ​

Describe the stages of succession

1. Pioneer species such as lichens and mosses are able to grow and colonise in hostile environments with little or no soil​

2. Over time, pioneer species die and decompose changing the abiotic conditions by adding organic matter, humus and nutrients such as nitrates forming soil. ​

3. As the abiotic factors change, over time the environment becomes less hostile. ​

4. Less hostile conditions means that it is less suitable for the original pioneer species and more suitable for other species.​

5. Other species are better competitors which outcompete the pioneer species.​

6. Overtime, many species flourish and increase the biodiversity resulting in climax community. ​

What is speciation

Development of a new species from an existing one, occurs when populations are reproductively isolated as a result of disruptive selection. Results in a change in allele frequency, phenotype, and species can no longer interbreed

What is disruptive selection

• Opposite of stabilising

• Favours alleles of both extremes of the gene types and phenotypes in a population

• Therefore reduces the allele frequency at the mean and increases the allele frequency at the extreme’s of the mean

• Needs a range of genotypes and phenotypes in the population due to genetic variation in the population

• Least common form of selection

• Most importnat for evolutionary change and could result in speciation (two separate species formed)

What is allopatric speciation

• When individuals from two populations are geographically isolated due to physical barriers

• Prevents the two populations from breeding making them reproductively isolated

• No gene flow between the populations

• Genetic variation exists as a result of mutations which causes new alleles to be created

• If environment on either side of barrier is different there will be different selection pressures such as disease, predation and competition

• Leads to selection of different alleles which results in different adaptations that changes allele frequency for both populations

• Therefore resulting in a different gene pool

• The different species cannot interbreed to produce fertile offspring

What sympatric speciation

• Speciation occurs within the same area

• There is variation in the population already

• Due to random mutations in a population

• This could result in different mating behaviour, mating season and incompatible genitalia

• Therefore individuals of the population becoming reproductively isolated

• There is no gene glow between populations

• This changes the frequency of alleles in the populations

• Eventually different species produced that cannot interbreed to produce fertile offspring

What is genetic drift

• Genetic drift is a random change in allele frequencies, especially significant in small populations.

• It can occur through random events like the bottleneck effect (population reduction) or founder effect (small group starts a new population).

• It leads to loss of genetic variation and can cause alleles to become fixed or lost by chance.