C.1 Species and Communities

Question 1

Factors affecting animal distribution

Answer 1

Territory
Food
Water
Competitors
Parasites
Human influences
Predators
Temperature
Day length
Breeding sites

Question 2

Factors affecting plant distribution

Answer 2

Parent material
Soil salinity/pH/minerals: Mg, K, Cl, P, N, S
Light intensity
Day length
Temperature
Rainfall
Human influences
Competitors

Question 3

Uses of quadrating

Answer 3

Measuring population size/density/percentage coverage/biodiversity

1. Compare populations of different species in the same area
2. Compare populations of the same species in different areas (along a line transect)

Question 4

Consistency in quadrating

Answer 4

Decide which borders are “in” and “out”. Individuals on the “out” border should not be counted, whereas those on the “in” border should be counted.

Question 5

How to count in quadrating?

Answer 5

Count plants only if they are attached to the soil within the quadrat (flat-laying foliage may need to be lifted out of the way to see roots)

For abundant populations (e.g. grass), percentage cover should be counted instead.

Estimates of uncertainty should be included (e.g. plus or minus one)

Data should then be processed and tested for significance (chi-squared).

Question 6

Transect

Answer 6

Line transects can be used to correlate the distribution of a species over a set distance with an abiotic variable (e.g. human disturbance, light intensity).

Quadrats can then be placed at regular intervals along the transect. The data can be presented in a kite diagram (where the verticle distance equal the size of population).

Question 7

Shelford’s law of tolerance

Answer 7

Graph of population size (number of individuals) against a biotic/abiotic factor (from low to high).

Shows the zones of intolerance, limits of tolerance, zones of stress, and optimum range

Question 8

Limitations of Shelford’s law of tolerance

Answer 8

1. Symmertric graph in real life the graph may not be necessarily symmetrical, as sometimes scarcity may impose a more accute effect on the population size than abundance or vice versa (upper limit of tolerance for toxin, but no lower limit)
2. Different individuals of a popultion have different tolerance to the same factor –> difficult to quantify the limits

Question 9

Interspecific interactions

Answer 9

Competition
Parasitism
Herbivory
Predation
Mutalism
Commensalism

Question 10

Competition

Answer 10

Where two species acquire similar niches (require the same resource) and consumption by one species reduces the availability of the resource to the other species.

Ex: bluebells and bracken competing for light –> bluebells minimized competition by adapting to growth earlier than taller-growing bracken.

Question 11

Parasitism

Answer 11

When one organsim (parasite) feeds off another but does not normally kill it. In this situation the host is harmed whereas the parasite is benefited.

Ex: tapeworms in human

Question 12

Herbivory

Answer 12

Primary consumers feeding on producers.

Ex: cane beetle feeding on sugar cane

Question 13

Predation

Answer 13

A consumer feeding on another consumer.

Ex: dingo in New South Wales feeding on red kangaroo

Question 14

Mutualism

Answer 14

Two species live closely and mutually benefit from their interactions.

Ex: zooxanthellae and reef-building corals

Question 15

Commensalism

Answer 15

Two organsims interact, with one benefiting from the interaction while the other is neither harmed nor benefited.

Ex: The Hawkfish living in fire corals, gaining protection from the coral.

Question 16

Zooxanthellae and corals

Answer 16

Zooxanthellae are benefited:
Support and protection from Calcium Carbonate skeleton from coral
Nutritions for photosythethesis (CO2)

Corals are benefited:
Products of photosythesis: glucose, O2
Zooxantehllae helps corals to remove wastes (CO2)

Question 17

Keystone species

Answer 17

Species that have a more than proportionate effect on the structure of an ecological community. The presence of keystone species prevents species from monopolising critical resources.

Ex: sea otters feeding on sea urchins, controlling their numbers, so that kelp and other plant species would not be over-consumed by urchins –> maintains kelp forests as a habitat for other species.

Question 18

Outline the effects of removing the seastar Pisaster from the community

Answer 18

Biodiveristy reduced rapidly from 15 to 8 in just one year, because the remaining species immediately compete with each other to occupy the newly available space and resources.

Within 3 months, Balanus glandula had become dominant in the area.

9 months later, B. glandula was replaced by another barnacle Mitella and the mussel Mytilus. The population size of Mytilus increases because it was consumed by Pisaster before its removal.

The succession continues until Mytilus becomes the dominant species –> wiped out populations of benthic algae.

Some species of limpets emigrated to other habitats due to lack of food/space.

Question 19

In whose experiment is Pisaster removed?

Answer 19

Robert Paine’s

Question 20

Niche

Answer 20

The unique ecological roles fulfilled by each species in an ecosystem, including its spatial habitat, its interactions wih other species, and its impacts on the ecosystem.

Question 21

Fundamental niche

Answer 21

The full range of environmental conditions under which a species can potentially survive and reproduce.

Question 22

Realized niche

Answer 22

The specific set of environmental conditions udner which a species can actually survive and reproduced, taking the biotic limiting factors into consideration.

Smaller than the foundamental niche.

Question 23

Gause’s experiment

Answer 23

Cultured two species of paramecium separately and in a mixed population.

P. aurelia and P. caudatum

When grown separately, each population grew to a high maximum, showing its foundamental niche.

When grown together in a mixed population, interspecific competition occurs: one species would dominate (P. aurelia), causing the other to declien/extirpate.

Question 24

The competitive exclusive principle states…

Answer 24

Species with identical ecological niches cannot survive in the same area indefinitely.
Result:
1. One dominates, the other decline/extirpates
2. Both narrow their niches to avoid competition (e.g. bluebells begining growth earlier than bracken, avoiding competition for light).