Populations and communities Details

Question 1

How can population sizes be evaluated?

Answer 1

Through sampling(e.g. random sampling)

Question 2

Why is random sampling ideal for evaluating population sizes?

Answer 2

Every member of a population has an equal chance of being selected

Question 3

What does quadrat sampling entail?

Answer 3

Repeatedly placing a quadrat in multiple positions in a habitat and recording the number of organisms present each time

Question 4

Procedure for positioning the quadrat in random sample

Answer 4

-Random coordinates are generated(x and y), using either a table or a random number generator
-The coordinates are used to place a quadrat in the area being sampled

Question 5

Formula for estimated population size(for sessile organisms)

Answer 5

Question 6

What are the implications of having a low standard deviation(in quadrat sampling)?

Answer 6

-Little variation between values
-Likely smaller sampling error
-More evenly spread population

Question 7

What are the implications of having a high standard deviation(in quadrat sampling)?

Answer 7

-High variation between values
-Likely greater sampling error
-More randomly spread out population

Question 8

Procedure for capture-mark-release-recapture

Answer 8

-Capture as many individuals as possible in the area occupied by the animal population(e.g. by netting, trapping, searching, etc.)
-Mark each captured individual(without making them more visible to predators)
-Release all the marked individuals and allow them to settle back into their habitat
-After 1-2 days recapture as many individuals as possible and count how many are marked and how many unmarked
-Calculate the estimated population size by using the Lincoln index:

Question 9

Formula for the Lincoln Index

Answer 9

Question 10

Assumptions made about the period of time between capture and recapture(with the capture-mark-release-recapture method)

Answer 10

-No migration into and out of the population
-No deaths or births
-Marked indivduals mix back into the population and have the same chance of being captured on the second occassion as unmarked individuals

Question 11

Resource limitation affects population size(T/F)

Answer 11

True

Question 12

How does resource limitation affect population size?

Answer 12

-If a resource becomes scarce, the members of a population will compete for it
-If a population grows too large, some indivudals will be unable to obtain enough of the resource
-The individuals are likely to die, reducing the populatipn size to the carrying capacity of the environment

Question 13

Examples of resources that may limit carrying capacity in animals

Answer 13

-Water
-Space for breeding
-Food(or territory for obtaining food)
-Dissolved oxygen in water

Question 14

Examples of resources that may limit carrying capacity in plants

Answer 14

-Water
-Light
-Soil nitrogen(NO₃⁻ or NH₄⁺)
-Soil phosphorus(PO₄³⁻)

Question 15

Examples of density-independent factors

Answer 15

-Extreme temperatures(in relation to the species optimum temperature)
-Seawater flooding
-Forest fires

Question 16

Types of density-dependent factors

Answer 16

-Competition for limited resources
-Predation
-Infectious disease, parasitism and pest infection

Question 17

Why is infectious disease, parasitism and pest infection a density-dependent factor?

Answer 17

The transfer of pathogens, parasites and pests is easier if the population density is increased because the hosts are closer together

Question 18

Why is predation a density-dependent factor?

Answer 18

As the population of prey becomes denser or more spread out, they become easier or harder to find(respectively) for predators

Question 19

Density-dependent factors are the basis for negative feedback mechanisms because they reduce larger populations and allow smaller populations to increase(T/F)

Answer 19

True

Question 20

Relationship between density-dependent factors, density-independent factors, and population size

Answer 20

Question 21

Factors which contribute to a change in the number of individuals in a population

Answer 21

-Natality(offspring produced and added to population)
-Mortality(individuals die and are lost in a population)
-Immigration
-Emigration

Question 22

Formula for population change

Answer 22

Population change = (natality + immigration) - (mortality + emigration)

Question 23

Phases of a sigmoid(S-shaped) population growth curve

Answer 23

-Exponential phase
-Transitional phase
-Plateau phase

Question 24

If a population is established in an idea unlimited environment, it follows and exponential growth curve, with the population increasing more and more rapidly(T/F)

Answer 24

True

Question 25

Why does the population grow so rapidly in the exponential phase?

Answer 25

-Resources needed by the population are abundant -Diseases and predators are rare -Immigration is more likely than emigration(due to abundant resources)

Question 26

In the transitional phase, the population slows as the carrying capacity of the environment is reached(T/F)

Answer 26

True

Question 27

What happens to the natality rate and the mortality rate in the transitional phase?

Answer 27

The natality rate starts to fall, and the mortality rate starts to rise(although the natality rate is still higher than the mortality rate)

Question 28

In the plateau phase, emmigration is more likely than immigration(T/F)

Answer 28

True

Question 29

If the population is limited by a shortage of resources, then then it has reached the carrying capacity of the environment(T/F)

Answer 29

True

Question 30

What happens in the plateau phase?

Answer 30

A density-dependent factor has limited the population, either reducing the natality rate or increasing the mortality rate

Question 31

How does natural selection occur?

Answer 31

-Members of a population have the same ecological niche so require the same resources -Unless a resource is abundant, there will be competition for it -Some individuals will be more successful and gain more of the resource, helping them to survive and reproduce -As a result, traits that allow individuals to compete more effectively will become more prevalent in the population over generations(i.e. natural selection)

Question 32

Examples of intraspecific competition

Answer 32

-Duckweed competes for light when crowded -Gannets compete for nest sites on sea cliffs -Creasate bushes compete for water in their desert habitat

Question 33

Examples of cooperation

Answer 33

-Emperor penguin males huddle together in winter on Antarctic ice to conserve body heat -Chimpanzees hunt in groups, increasing the chance of catching monkeys or other prey -Mackerel swim in tightly packed, fast-moving "bait balls", making it harder for predators to catch them

Question 34

Examples of mutualism

Answer 34

-Bees and flowers: bees pollinate flowers as they collect nectar from them to turn it into food. The bees get food, and the pollen of the flowers gets transferred to different flowers(helping with plant reproduction). -Hermit crab and anemones: the shell of the hermit crab provides anemones a safe habitat. In return, the anemone defends the hermit crab from its predators by its sting. Oxpeckers and rhino/zebra: the oxpeckers eat the ticks and other parasites on the skin of the rhino/zebra. The oxpecker gets food, and the rhino/zebra stays clean and healthy.

Question 35

Examples of herbivory

Answer 35

-Bison grazing on grasses -Aphids feeding on phloem sap from plants -Limpets feeding on algae frowing on rocky shores

Question 36

Examples of predation

Answer 36

-Anteaters feeding on ants or termites -Dingoes hunting, killing and eating red kangaroos -Starfish eating oysters

Question 37

Examples of interspecific competition

Answer 37

-Ivy climbing up oak trees and competing for light(with the oak tree) -Forda and Geaica(gall-forming aphids) competing for phloem sap on leaves of the terebinth tree -Barnacles competing for space and food on rocky shores

Question 38

Examples of parasitism

Answer 38

-Ticks living on the skin of deer and feeding by sucking blood from the deer -Non-photosynthesizing *Cuscuta* plants(doddlers) growing on gorse and other plant hosts, absorbing foods from the host's sap

Question 39

Examples of pathogenicity

Answer 39

-Myxomatosis virus infecting rabits -Tuberculosis bacterium infecting badgers -Potato blight fungus infecting potato plants

Question 40

How is the relationship between the root nodules in plants and *Rhizbium* bacteria(and other nitrogen-fixing bacteria) an example of mutualism?

Answer 40

-Plants require a fixed form of nitrogen(like ammonium or nitrate, but **not** nitrogen gas) to make amino acids and other nitrogen-containing compounds -Some nitrogen-fixing bacteria(like *Rhizobium*) absorbs nitrogen has and fixes it to produce ammonium which it then supplies to the plant. -In turn, the plant has root nodules where the nitrogen-fixing bacteria can live and be protected, and it also supplies sugars to the nitrogen-fixing bacteria, giving it energy

Question 41

Chemical formula for nitrate

Answer 41

NO₃⁻

Question 42

Chemical formula for ammonium

Answer 42

NH₄⁺

Question 43

How is the relationship between orchids and fungi an example of mutualism?

Answer 43

-Orchids are dependent on mycorrhizal relationships because their seeds don't contain food reserves -At an early stage in germination, the fungal hyphae penetrate the root of an orchid seedling -They grow through the cell walls but do not burst the plasma membrane of root cells; instead, the membrane forms a sheath around the hypha -The fungus acts like an extension to the root system, absorbing water, mineral nutrients(like ammonium or phosphorus) and carbon compounds before passing them to the plant -Once the orchid starts to photosynthesize, there is a two-way exchange of materials between the fungus and the orchid

Question 44

How is the relationship between Zooxanthellae(photosynthetic algae) and hard corals an example of mutualism?

Answer 44

-Hard corals secrete calcium carbonate to form a skeleton in which the polyps(the individual animals which make up the coral) can live -Coral reefs are built from these skeletons -Most reef-building hard corals contain Zooxanthellae, which are absorbed from the sea water and kept alive inside coral cells -The coral provides a safe environment(its skeleton) for the Zooxanthellae, and it supplies carbon dioxide produced by cell respiration -The Zooxanthellae in turn supplies oxygen as well as carbon compounds(e.g. amino acids, glucose, etc.)produced by photosynthesis

Question 45

Why are alien species not effectively regulated by density-dependent factors in the new environment?

Answer 45

The predators or pests that would cntrol them in their native habitat are absent in their new habitat

Question 46

To become invasive, an alien species must be successful in the competition for resources with endemic species(T/F)

Answer 46

True

Question 47

Examples of invasive species

Answer 47

-Cane toads(endemic to South and Central America but introduced to Oceania and Australia to control pests; produce toxic ooze which easily kills animals apart from those in their native habitat(they're immune)). -Red lionfish(endemic to coastal seas of the Indo-Pacific; a few escaped from an aquarium in 1992 and have since multiplied in the coral reefs in Florida and the Carribean, helped by the lack of predators adapted to its venomous spines)

Question 48

Purpose of the chi-squared test

Answer 48

To etermine whether there is a relationship between two categorical variables, or compare observed results with expected results

Question 49

Two possible hypotheses for the chi-squared

Answer 49

-H₀: two species are distributed indepedently(null hypothesis) -H₁: two species are associated(alternative hypothesis)

Question 50

The chi-squared test is only valid if:

Answer 50

-All the expected frequencies are 5 or greater -The sample was taken at random from the population(in this case by positioning quadrats randomly)

Question 51

If the chi-squared test indicates that the null hypothesis can be rejected, this is **not** proof of competition(T/F)

Answer 51

True(the two species could have different habitat requirements, so they tend not to occur together)

Question 52

What is the idea behind testing for competition using the chi-squared test?

Answer 52

Competitive exclusion might discourage two species from growing together, so they will occur in the same quadrats less often than they would if there was no association

Question 53

Using the chi-squared test, you might find that the two species occur together more frequently than expected instead of less frequently(T/F)

Answer 53

True(the species may have the same habitat requirements but are not limited by resource competition)

Question 54

Examples of approaches to test for interspecific competition(aside from the chi-squared test)

Answer 54

-Field manipulation: one of two species could be removed from quadrats in the field. There is evidence of interspecific competition if the other species then increases in size or biomass -Laboratory experiments under controlled conditions: the species can be grown together and apart to investigate whether they compete for resources

Question 55

Types of use of the chi-squared test

Answer 55

-Testing for independence or association -Testing goodness of fit

Question 56

In the chi-squared test, tests of goodness of fit use a model such as a ratio to generate expected numbers(T/F)

Answer 56

True

Question 57

Steps for chi-squared test

Answer 57

-Define the two hypotheses(null hypothesis and alternative hypothesis) -Draw a contingency table of observed frequencies, and calculate the row and column totals -Calculate the expected frequencies for the four species combinations, assuming independent distribution -Calculate the number of degrees of freedom -Find the critical region for chi-squared(e.g. it should be given to you) -Calculate the chi-squared(using the formula below) -Compare the value of chi-squared with the critical region(if it's in the critical region, you can reject the null hypothesis as there is evidence that there is an association between the two species)

Question 58

Formula for expected frequency

Answer 58

Question 59

Formula for degrees of freedom

Answer 59

Question 60

How a contingency table looks like

Answer 60

Question 61

Cycle between predator and prey populations

Answer 61

-A rise in prey numbers increases prey availability, so predator numbers rise -A rise in predator numbers increases predation, so prey numbers fall -A fall in prey numbers decreases prey availability, so predator numbers fall -A fall in predator numbers decreases predation, so prey numbers rise

Question 62

In come communities, the population of predators and prey do not change much(T/F)

Answer 62

True(this is because new prey individuals are born at about the same rate as they ae lost due to predation)

Question 63

Types of population control in communities

Answer 63

-Top-down control(acts from a higher trophic level to a lower one; an increase in predator numbers may decrease the numbers of prey in lower trophic levels) -Bottom-up control(acts from a lower trophic level to a higher one; the population of consumers in higher trophic levels may be limited by the availability of producers)

Question 64

Examples of organisms which release allelopathic agents

Answer 64

-Penicillium(secretes anitbiotic penicillin) -Ailanthus altissima(secretes ailanthone)

Question 65

Why do penicillium secrete antibiotic penicillin?

Answer 65

-Penicillium fungi are saprotrophic, hence they risk the foods that they digest being absorbed by other bacteria in the same habitat -Some species of penicillium secrete antibiotic penicillin to reduce this competition -Pencillin interferes with cross-linking of peptidoglycan moecules in the cell walls of Gram-positive bacteria, which causes its cell walls to become weak, killing the bacteria

Question 66

Production of antibiotic penicillin requires resources so Penicillium only secretes it when supplies of food are scarce(T/F)

Answer 66

True

Question 67

Why do *Ailanthus altissima* secrete ailanthone?

Answer 67

-*Ailanthus altissima* is native to China, but has become an invasive species across North America -They secrete ailanthone into the soil as it inhibits the germination, growth and survival of other tree species(for up to 5m from the trunk of the tree)