Ecosystems - C 4.1 Population & Communities

Question 1

What do populations form?

Answer 1

Populations form an important group by interacting with other populations within a community.

Question 2

What happens if two populations live in different areas?

Answer 2

If two populations live in different areas, they are unlikely to interbreed with each other. If two populations of the same species are geographically isolated for a longer time, they may develop differences in their characters and eventually become different species (speciation).

Question 3

Define the term population.

Answer 3

A population is a group of organisms of the same species who live in the same area at the same time able to interbreed with each other.

Question 4

How do you estimate population size?

Answer 4

It would be impossible to count all the individual organisms of a population in a habitat by hand. Instead, we count a sample from a small area and multiply this by the total area of the habitat. This gives an estimate of the total population.

Question 5

What are the two methods used to estimate sessile population size?

Answer 5

• Quadrat Sampling
• Line or Belt transects

Question 6

What does a belt transect take a sample of?

Answer 6

A belt transect takes samples from an area along a straight line.

Question 7

What does a quadrat sampling take a sample of?

Answer 7

Quadrat sampling uses defined areas of space (=quadrats) to count the number of species within.

Question 8

What is quadrat sampling?

Answer 8

Quadrat sampling is a method used to take a measurement of an area without systematically deciding where to take it. It eliminates bias which may influence your measurements.

Question 9

What is quadrat sampling method used for?

Answer 9

This method can be used with quadrats when working out the population size of a species of stationary animals or plants.

Question 10

What type of organisms is quadrat sampling method used for?

Answer 10

This method is only suitable to sample sessile organisms like plants or very small, small moving animals.

Question 11

What are the two types of quadrats?

Answer 11

• frame quadrat (empty)
• divided quadrat (grid)

Question 12

Why use frame quadrat?

Answer 12

Not to squash organisms or if organisms are large.

Question 13

why use different sizes of quadrats?

Answer 13

If areas is larger/smaller or if organisms are larger/smaller.

Question 14

Why do we need to do random measuring?

Answer 14

The quadrats will have to be randomly, and without bias, placed within a selected area.

Question 15

How to you randomly measure using quadrats?

Answer 15

• A base line along the edge of the habitat using measuring tape
• Generation of random numbers using a table or a random number generator
• The first random number determines the distance along the tape, the second random number is used to determine a distance out across the habitat at right angles to the tape.
• The quadrat is placed precisely at the distances determined by the two random numbers.

Question 16

What happens if their is a presence or absence of more than one species when using quadrat?

Answer 16

If the presence or absence of more than one species is recorded in every quadrat during sampling of a habitat, it is possible to test for an association.

Question 17

What is interrupted belt transect?

Answer 17

When you skip a certain distance along a belt transect.

Question 18

How do you calculate the population size, using quadrat sampling method?

Answer 18

Use the grid your teacher hands out to you. This is a 10 x 10 m area, divided into 1m grids.
Make a results table.
Generate random numbers so that you count the number of flowers in each grid. Repeat this at least 15 times.
Record the numbers in a sheet.
Calculate the population size by calculating the average number of daisies from all your grids. Multiply this number by 100 so that you know the total number of flowers in the entire field. This is your estimated number
Count the total number of flowers actually in the field (actual number).
Calculate a % error .
% Error = ((𝑬𝒔𝒕𝒊𝒎𝒂𝒕𝒆𝒅 𝒏𝒖𝒎𝒃𝒆𝒓 −𝑨𝒄𝒕𝒖𝒂𝒍 𝒏𝒖𝒎𝒃𝒆𝒓) × 𝟏𝟎𝟎 )/(𝑨𝒄𝒕𝒖𝒂𝒍 𝒏𝒖𝒎𝒃𝒆𝒓)

Question 19

How do you estimate the population size for motile organisms?

Answer 19

When estimating the size of an animal population, you can use capture–recapture methods, then calculate the total population size.

Question 20

What are methods used to estimate population size for motile organisms?

Answer 20

Motile organism such as animals are harder to sample than plants because they move around. Methods used to collect animals include:
- Pitfall traps
- Pouters (aspirators)
- Mammal traps
- Nets

Question 21

What happens once you’ve caught a mobile organisms?

Answer 21

Once the animal has been caught, it must be marked for future recognition.
The capture, mark, release and recapture (MRR) technique, also known as the Lincoln index, is a practical method of estimating population size (N) of mobile animals, such as small mammals, woodlice, or insects that can be captured and marked with a ring, tag, or dab of coloured paint or nail varnish.

Question 22

What does a pitfall trap look like?

Answer 22

Question 23

What does a Pooter trap look like?

Answer 23

Question 24

What does a mammal trap look like?

Answer 24

Question 25

How can the population size be calculated using the Lincoln index? (what is the formula)

Answer 25

Question 26

What happens when a population grows?

Answer 26

The bigger a population grows, the more resources such as water, oxygen or food are taken from the environment. At some point a limit is reached if a population grows too large.

Question 27

What is the carrying capacity?

Answer 27

The maximum size of a population that an environment can support is the carrying capacity.

Question 28

What are population growth curves and population growth curves with carrying capacity?

Answer 28

Question 29

What resources would animals compete for?

Answer 29

• Water
• Food and nutrients
• Mating partners
• Status hierarchy
• Territory/space
• Nesting sites

Question 30

What resources would plants compete for?

Answer 30

• Light
• Nutrients in soil
• Space
• Water
• (Temperature) + CO2 concentration

Question 31

What do all environments have? and how is this created?

Answer 31

All environments have a finite carrying capacity (K). Beyond this limit the population cannot increase anymore. Many limiting factors contribute to setting a limit to population size.

Question 32

What can limiting factors be classified in?

Answer 32

These factors can be classified into density dependent and density independent factors.

Question 33

What are density dependent factors?

Answer 33

• Food and water availability
• Space for territories & next
• Availability of mates
• Diseases
• Predation

Question 34

What are density independent factors?

Answer 34

• Environmental change
• Build-up of toxic by products of metabolism
• Injury
• Senescence (death from age related illnesses)

Question 35

What causes a population size to be limited?

Answer 35

Population size can be limited by density dependent and density independent factors. In particular density dependent factors will cause population size to fluctuate due to negative feedback control, resulting in it staying stable over time.

Question 36

What is meant by the term “negative feedback” in terms of population growth?

Answer 36

A negative feedback loop isa type of self-regulating system, where any deviation from a steady-state is counteracted to promote stability.

Question 37

Distinguish between density dependent and density independent limiting factors?

Answer 37

Density dependent limiting factors. Factors that depend on population size, e.g. competition, predation, food, disease, and parasitism.
Density independent limiting factors. Factors that affect all populations in a similar way, independent of population size, e.g. drought, wild fire, volcanic eruptions, hurricane, deforestation…

Question 38

How does the density of a population affect competition?

Answer 38

A higher number of individuals (higher density) will reduce the amount of available resources (food, water, space, mating partners, etcs.) so the competition will be higher

Question 39

How does the density of a population intensify predation?

Answer 39

The higher the density of a population the more intense predation becomes.

Question 40

How does the density of the population affect the spread of disease & pathogens?

Answer 40

The higher the density the more likely the spread/transmission of diseases.

Question 41

What are the three stages of population growth curve?

Answer 41

Exponential, Transition, Plateau

Question 42

What is the exponential stage on the population growth curve?

Answer 42

Natality and immigration are larger than mortality and emigration. Plentiful supply of resources, limiting factors are not restricting the growth and rate of population growth

Question 43

What is the transition stage of the population growth curve?

Answer 43

Growth rate and population growth are slower than at the start - some of the limiting factors are more of scarce and result in greater competition. But, Natality is still higher than mortality.

Question 44

What is the Plateau stage of the population growth curve?

Answer 44

Limiting factors have a more restrictive effect - population growth has reached the carrying capacity. Natality is equal to mortality.

Question 45

What are the four main factors that affect the populations?

Answer 45

Question 46

How do you calculate population size?

Answer 46

Question 47

What is the effect of natality, immigration, emigration and mortality on population size?

Answer 47

Question 48

Define ‘Natality’

Answer 48

The rate at which individuals are born (birth rate)

Question 49

Define ‘Mortality’

Answer 49

The rate at which individuals die (the death rate)

Question 50

Define ‘Immigration’

Answer 50

Movement of new individuals into a population from outside a given area

Question 51

Define ‘Emigration’

Answer 51

The departure of individuals from population in a given area

Question 52

What does reproduction trend cause?

Answer 52

Reproduction tends to cause exponential growth in populations as a result of positive feedback. Density dependent factors then lead to negative feedback that prevents exponential growth. When any of the density dependent factors is absent, populations may grow exponentially.

Question 53

What might be the reason for density dependent factors being absent?

Answer 53

Absence of predators, often idealized conditions (e.g. breeding programs in capacity, abundance of resources with limited competition…)

Question 54

How can you model sigmoid population growth curve?

Answer 54

Duckweed (Lemna sp.) is a good model organism for measuring sigmoidal population growth
- Place a small number of plants in a container, e.g. a plastic cup
- Count the number of fronds (leaves) every day until the surface of the container is covered, i.e. the population has ceased to increase.
- Plot your results – you should obtain a sigmoidal curve
- Your investigation can be extended by considering different independent variables e.g. nutrient availability and the surface area of the container.

Question 55

What is a community?

Answer 55

A community is all of the interacting organisms in an ecosystem.
A community is a group of populations living together in an area and interacting with each other.

Question 56

Why do we have communities?

Answer 56

All species depend on relationships with other species for their long-term survival.
The different organisms often have complex relationships and beneficial and/or harmful interactions with each other.

Question 57

What are the two types of communities and why are they different?

Answer 57

Relationships within a community can be intraspecific or interspecific, depending on whether relationships occur between members of the same species (intra-) or members of different species (inter-).

Question 58

What is intraspecific competitive relationships?

Answer 58

Competition between members of the same species in a population occurs because individuals share the same ecological niche with similar requirements for resources. There are different types of competition.

Question 59

What is intraspecific cooperative relationship?

Answer 59

Individuals in a population might also cooperate in a variety of ways. Cooperative relationships have advantages because all individuals benefit, whereas in competitive relationships individuals tend to be harmed.

Question 60

What are examples of competitive intraspecific relationship?

Answer 60

Plants: light, space, water + nutrients in soil, pollen to be distributed by pollinators (competition for pollinators)
Animals: space or nesting sites, water as a resource

Question 61

What are examples of cooperative intraspecific relationship?

Answer 61

Animals: provides warmth and protection to each member of the population(penguins huddling), Social predation increases chances of success (by e.g. circling on prey), fish that form a tight pack are harder for predators to catch (e.g. mockerel), shared parental care allow other parents to see to other tasks (e.g. gathering food)

Question 62

What is Herbivory and what are examples?

Answer 62

Primary consumers feeding on producer(photosynthesizing organism). The producer may or may not get killed. E.g. bison grazing on grasses, Colibri feeding on nectar, limpets feeding on algae on a rocky share, aphids drawing on plant sap

Question 63

What is Predation and what are examples?

Answer 63

One consumer species (the predator) killing and eating another consumer species (prey). E.g. anteater feeding on ants, starfish eating oysters, cheetah hunting gazelle.

Question 64

What is Competition(interspecific) and what are examples?

Answer 64

Two or more species using the same resource with the amount taken by one species reducing the amount available to the other species. E.g. Lions and hyena’s feeding on the same prey, Ivy growing on trees (doesn’t harm the tree only uses it as climbing aid), Cowbird laying eggs in the nest

Question 65

What is Mutualism and what are examples?

Answer 65

Two species living in a close association, with both species benefiting from the association. E.g. Mycorrhiza in roots, birds picking teeth of crocodiles, clown fish living with sea anemone

Question 66

What is Parasitism and what are example?

Answer 66

One species (the parasite) living inside, or on the outer surface of another species (the host) and obtaining food from them. The host is harmed, the parasite benefits. E.g. roundworm living, inside the guts of racoons, tick feeding on the blood of a host, mosquito drawing blood.

Question 67

What are Pathogenicity and what are examples?

Answer 67

One species (the pathogen) living inside another species (the host) and causing a disease in the host. E.g. potato blight fungus, tuberculosis in badgers.

Question 68

What is a mutualistic relationship?

Answer 68

Mutualistic relationships between different species are interactions which provide benefits to both organisms.

Question 69

What is the mutualistic relationship between root nodules in Fabacea and Rhizobium bacteria?

Answer 69

Fabacea are a large plant family including species like clover, peas, beans. Many of them have developed a mutualistic relationship with Rhizobium bacteria, which live in root nodules grown by the plant. The bacteria receives protection and sugars made by the plant through photosynthesis. Inside the nodules O2 concentration is low. In turn, Rhizobium absorbs N2 and converts this to NH4 which the plant uses for the production of proteins. This prevents plants from nitrogen deficiency.

Question 70

What are the benefits for bacteria and for the plant?

Answer 70

Question 71

What is the mutualistic relationship between Mycorrhiyae in Orchidaceae?

Answer 71

The roots of most plants form an association with fungi, called mycorrhizae in soil. The fungus absorbs nitrogen, phosphorus, fixed carbon and water from the soil and supplies them to the plant. Orchid seeds do not contain food reserve, so they need these nutrients. The orchid supplies the fungus with carbon compounds from photosynthesis.

Question 72

What is the mutualistic relationship between Zooxanthellae in hard corals?

Answer 72

Hard corals secrete CaCO3 to form a skeleton where the individual animals (polyps) can live. This also provides a safe and protected environment for photosynthetic algae (zooxanthellae) close to the surface of the sea (sunlight). The algae supply the coral with glucose, amino acids and O2 from photosynthesis.

Question 73

What are benefits for plants and fungi?

Answer 73

Question 74

What are benefits for coral and zooxanthellae?

Answer 74

Question 75

What is the relationship between prey and predators?

Answer 75

When a predator kills its prey, the prey population becomes one smaller. However, the prey population does not change much, because birth and death rates are at balance, as is the case with the predator population. In some communities this dynamic equilibrium is not shown and instead cyclic oscillations are observed.

Question 76

Explain these cyclic oscillation in the snowshoe hare and the lynx?

Answer 76

An increase in prey causes the number of predators to raise(more food). As a consequence of more predation the number of prey will decrease leads to pop of predator decreases due to a lack of food…

Question 77

The graph below shows hunting records of red fox (Vulpes vulpes) and mountain hare (Lepus timidus) in Sweden. What could have happened during the years 1985 – 1992?

Answer 77

Cyclic oscillations until 1980- then the foxes contracted a disease (a parasitic mite) which caused the pop size of foxes to decline. As a consequence, the number of prey increases greatly.

Question 78

What are the two types interactions directions in a community can operate?

Answer 78

Top-down and Bottom up

Question 79

What is Top-down? And what is an example?

Answer 79

Top-down control acts from a higher trophic level to a lower one. An increase in predator number will decrease the population size of the prey.
E.g. A keystone species exerts top-down influence on its community by reducing the number of species at lower trophic levels.

Question 80

What is Bottom-up? And what is an example?

Answer 80

Bottom-up control acts from a lower trophic level to a higher one. A population of producers may be limited by the number of nutrients in soil or water. E.g. The amount of seaweed available on the floor of the sea will determine the number of sea turtles feeding on them, and therefore have an impact on the consumers higher up the food chain.

Question 81

What ways have organisms developed ways to deter potential competitors?

Answer 81

Some organism have developed special ways as part of their metabolic pathways to deter potential competitors from their ecological niche. These pathways are producing so-called “secondary metabolites” which are not essential for cell growth or its function.

Question 82

What are examples of “secondary metabolites” developments?

Answer 82

• Many fungi produce antibiotic substances which prevent the growth of other species (e.g bacteria) by interfering with cell wall components of them, which eventually cause them to burst and die.
• Allelopathy is the release of chemicals as secondary metabolites or toxins by plants, which are given off into the soil to prevent nearby competitive plants to grow in the same area.