C4.1 - community relationships (1f)

Question 1

community

Answer 1

all of the interacting organisms (populations of different species) in an ecosystem, including plants, animals, fungi and bacteria

Question 2

what are examples of interactions in communities?

Answer 2

• feeding relationships
• disease
• provision of habitats
• one species provides a useful role or substance for another

Question 3

what are the 6 types of interspecific relationships?

Answer 3

• herbivory
• predation
• mutualism
• pathogenicity
• parasitism
• interspecific competition

Question 4

what is herbivory?
what is an example?

Answer 4

herbivory is an interaction whereby a primary consumer eats plant material, destroying or damaging the producer
- (e.g) giraffes eating acacia leaves

Question 5

what is predation?
what is an example?

Answer 5

predation is a biological interaction whereby one organism (predator) hunts, kills and feeds on another organism (prey)
- (eg) arctic fox predating on snowshoe hare

Question 6

what is interspecific competition?
what is an example?

Answer 6

interspecific competition is the interaction between two organisms, where the fitness of one is lowered by the presence of the other, as the both strive to obtain the same resource
- (eg) a rose and a hydrangea using minerals and water from the same region of soil

Question 7

what is pathogenicity?
what is an example?

Answer 7

pathogenicity is the ability of microorganisms to cause disease in other species
- (eg) tuberculosis is caused by a bacterium

Question 8

what is mutualism?

Answer 8

mutualism is a symbiotic relationship that benefits both species

Question 9

what is parasitism?
what is an example?

Answer 9

parasitism is a symbiotic relationship in which one species benefits to the detriment of the other, with one species living on or in the host for at least part of its life cycle
- (eg) fleas feeding on the blood of a dog, who loses biomass

Question 10

what are three examples of mutualism?

Answer 10

• root nodules in the legume family
  
  • mycorrhizae in the orchid family
  • zooxanthallae in hard corals

Question 11

how does the rhizobium in root nodules of fabaceae benefit?

Answer 11

• rhizobium receive carbohydrates and a protected environment
• legumes gain nitrate minerals to produce biological molecules

Question 12

how does the mycorrhizae fungus in orchidaceae benefit?

Answer 12

• fungus gains nutrients from orchids via decomposition
• orchids gain nitrogen and carbon via the fungal hyphae

Question 13

how does the zooxanthellae in hard corals benefit?

Answer 13

zooxanthellae are photosynthetic algae that live in coral tissue
- zooxanthellae obtain shelter, light, ammonia, carbon dioxide
- coral gains oxygen and sugars, lipids and amino acids from photosynthesis

Question 14

what type of control is a predator prey relationship?

Answer 14

a predator relies on its prey as a food source, so their population levels are intertwined
- predation is an example of a density dependent control of a population
- if a predator only consumes one prey and the prey has no other predator species, the relationship is cyclical
- e.g) canada lynx and snowshoe hare

Question 15

what is a limitation of the predator prey cycle?

Answer 15

it is a simplification as in reality, there are more complex systems involved in the cycle

Question 16

what happens to the predator-prey relationship if:
1. prey population drops
2. predator population drops
3. prey population rises
4. predator population rises

Answer 16

1. if the prey population drops, predator numbers will decrease as intra-specific competition increases, and there is a lag because it takes time for the predators to starve
2. if the predator populations drops, prey numbers will increase as fewer offspring will be eaten, and there is a time lag as it takes time for the prey to reproduce
3. if the prey population rises, predator numbers will increase as a result of the over-abundance of a food source, and there is a time lag as it takes time for the predators to grow and reproduce
4. if the predator population rises, prey numbers decrease as more are eaten

Question 17

what are invasive species?

Answer 17

species that are introduced accidentally or deliberately and have a negative effect on the environment

Question 18

what is an endemic species?

Answer 18

species that are native to a geographic region

Question 19

why does the introduction of an invasive species decrease population size of an endemic species?

Answer 19

when an invasive species enters the ecosystem, it is likely to decrease the population size of the endemic species as:
- it has inter-specific competition with the endemic species
- it may introduce new diseases

Question 20

what can increase the population of invasive species?
how can this affect the ecosystem?

Answer 20

if the invasive species does not have predators that are endemic, its population increases in size, which upsets the balance between predators and prey, disrupting food chains and increasing the likelihood of an extinction for the endemic species

Question 21

what is an example of a case study where an invasive species caused the extinction of an endemic species?

Answer 21

• the grey squirrel was introduced to the UK from north america a number of times from the 1870s-1930s
• grey squirrels have driven the endemic red squirrel to localised extinction
• grey squirrels have a competitive advantage in resource acquisition, meaning they out-compete the red squirrel for food and habitat
• grey squirrels also carry a squirrel pox virus to which it is immune, but which is deadly to the red squirrels

Question 22

what are the similarities between allelopathy and antiobiotic secretion?

Answer 22

both allelopathy and secretion of antibiotics are similar in that a chemical substance is released into the environment to deter potential competitors
- this means that both species gain a competitive advantage when obtaining resources

Question 23

what is allelopathy?
what are some examples?

Answer 23

allelopathy is the production of secondary metabolites that influence the growth and success of other organisms
- (e.g) garlic mustard produces sinigrin, which inhibits root growth and seed germination of the surrounding plants

Question 24

what is antibiotic secretion?
what are some examples?

Answer 24

antibiotics are secreted by microorganisms (bacteria and fungi) to kill or inhibit the growth of bacterial species
- (e.g) penicillium rubens is a fungus that secretes the antibiotic penicillin, which stops the growth of a number of bacterial species

Question 25

what defines the carrying capacity?

Answer 25

limiting factors define the carrying capacity of an ecosystem, through top-down or bottom-up control
- in a given community, one or the other is likely to be dominant

Question 26

what is top-down control?
what is an example?

Answer 26

top-down control refers to factors involving a higher trophic level than the one being considered, which limit population growth
- (eg) predation or herbivory

Question 27

what does top-down control result in?

Answer 27

top down control results in an oscillating trophic cascade (suppression at one level increases numbers at the next level)

Question 28

what is bottom-up control?
what is an example?

Answer 28

bottom-up control factors limit the availability of resources to the lower trophic levels
- (eg) for producers: mineral concentrations

Question 29

what does bottom-up control result in?

Answer 29

bottom-up control results in reduced population growth for all higher trophic levels

Question 30

what is a keystone species?

Answer 30

keystone species are species that have a disproportionate impact on community structure, given their abundance

Question 31

what type of control does a keystone species exert?

Answer 31

keystone species commonly exert top-down control by preventing lower trophic levels from monopolising essential resources