Topic 13: Populations in ecosystems

Question 1

Define ecology

Answer 1

the study of the interelationships between organisms and their environment (abiotic and biotic factors)

Question 2

Define Ecosystem

Answer 2

A community and all the non-living factors of its environment

Question 3

Define population

Answer 3

A group of individuals of one species that occupy the same habitat at the same time and can potentially interbreed - abiotic and biotic factors can influence population size

Question 4

Define community

Answer 4

All the populations of different species living and interacting in a particular place at the same time

Question 5

Define habitat

Answer 5

A place where an organism lives - the physical conditions and other organisms present - there are microhabitats within each habitat

Question 6

Define ecological niche

Answer 6

How an organism fits into an environment - where it lives and what it does there - no two species can occupy the same niche due to differing adaptations to the biotic and abiotic conditions (competitive exclusion principle)

Question 7

What factors determine population size - give examples?

Answer 7

• effect of abiotic factors - temperature, light, soil pH, water and humidity
• interaction between organisms - competition and predation

Question 8

Define carrying capacity

Answer 8

The maximum stable population size of an organism an ecosystem can support - slight changes in the environment can change the carrying capacity

Question 9

What are the three main phases on a population growth graph?

Answer 9

• lag phase (flat) - low growth rate - no environmental resistance
• log phase (increase) - maximum growth rate (BR>DR) - no limiting factors
• stationary phase (flat) - carrying capacity reached (BR = DR) - some environmental resistance - population is at its maximum size

Question 10

Why is a log scale often used to plot population growth?

Answer 10

Rapid growth over a short period creates a large increase in values which can’t be plotted on a regular graph

Question 11

How do abiotic factors influence carrying capacity?

Answer 11

• if an abiotic factor is below or above the optimum
• fewer individuals can survive and reproduce as adaptations are not suited to the conditions
• population size decreases
• so the carrying capacity for that species is reduced

Question 12

Define intraspecific competition

Answer 12

individuals of the same species compete for resources such as food, water and breeding sites

Question 13

How does resource availability impact population size when intraspecific competion is occuring?

Answer 13

Resources availability detemines size of population and influences competition
* population increases when resources are plentiful
* which causes competion to increase
* resources become limiting
* population begins to decline
* smaller population means less competition - more growth so population begins to grow again

Question 14

Define interspecific competion

Answer 14

individuals of different species compete for resources

Question 15

How does interspecific competition impact population size?
What is competitive exclusion principle?

Answer 15

one species will have a competitive advantage - its population size will increase while the other decreases
Competitive exclusion principle - no two species can occupy the same niche when resources are limiting - different niches = less competition for food and resources

Question 16

Define predation

Answer 16

when an organism kills and eats another

Question 17

How does the predator - prey relationship affect population size?

Answer 17

• predators eat prey - population of predators increases
• prey population decreases - competition for food increases - predator population decreases
• decreased predators - less prey are eaten = prey population increases
• more prey are available for food = predator population increases again

Question 18

What is the role of selection pressure in changes in population size?

Answer 18

Disease and climatic changes causes selection pressure - population evolves to become better adapted to harsh conditions

Question 19

What factors should be considered when using a quadrat?

Answer 19

• size of quadrat
• number of quadrats - more quadrats = more RELIABLE
• position of quadrat - sampling must be RANDOM to produce SIGNIFICANT results

Question 20

What are the two types of quadrat?

Answer 20

1. frame quadrat
2. point quadrat

Question 21

How is random sampling carried out?

Answer 21

1. lay tape measures along two sides of the study area
2. obtain coordinates using a random number generator
3. place a quadrat at the coordinates and count the species within

Question 22

What type of sampling is a transect?

Answer 22

systematic

Question 23

How is a belt transect used?

Answer 23

• stretch a string or tape across the ground
• place a frame quadrat alongside and record the species inside
• move quadrat at intervals and repeat

Question 24

Define abundance

Answer 24

the number of individuals of a species in a given area

Question 25

Define frequency

Answer 25

likelihood of a particular species occuring in a quadrat (if a species occurs in 15 /30 quadrats its occurence is 50%) * indicates species present * general distribution

Question 26

Define percentage cover

Answer 26

estimate of the area within a quadrat that a particular species covers * data can be collected rapidly * individual plant don't need to be counted BUT less useful when plants overlap

Question 27

What three factors are needed for reliable results?

Answer 27

* large sample size (more representitive) * many quadrats (more reliable) * mean needs to be collected

Question 28

When is mark-release recapture used?

Answer 28

to investigate abundance of motile species

Question 29

What is the equation for mark release recapture?

Answer 29

individuals in sample one x individuals in sample 2 / number of marked recaptured

Question 30

What are the steps of mark-release recapture?

Answer 30

1. capture/collect, mark AND release organisms 2. leave time to disperse before second sampling/collection 3. collect second sample and calculate estimated population size

Question 31

What 6 assumptions are made during mark-release recapture?

Answer 31

* mark/label is not rubbed off during the investigation * method of marking is non-toxic and doesn't make organism more vulnerable to predation * no deaths or births in the population * no immigration into the population or emigration out * marked individuals have sufficient time to redistribute evenly into the population * proportion of marked to unmarked in second sample is in the same proportion as the population as a whole

Question 32

Define succession

Answer 32

a change in a community over time due to changes in abiotic factors and/or species present

Question 33

Define climax community

Answer 33

a stable community where no further succession occurs

Question 34

What are pioneer species - what are their main features?

Answer 34

first species to colonise newly explosed land (eg volcanic island) * produce MANY, WIND dispersed seeds * RAPID germination of seeds * ability to photosynthesise (not dependent on animal species) * ability to fix nitrogen from the atmosphere * tolerence to extreme conditions

Question 35

What are the common features of succession?

Answer 35

* abiotic environment becomes less hostile * greater variety of habitats and niches * increased biodiversity * more complex food webs * increased biomass

Question 36

At what stage in succession is biodiversity highest and when does it decrease?

Answer 36

At mid succession - decreases** as** the climax community is reached as the dominant species outcompete the pioneer species, leading to their removal from the community

Question 37

Describe the stages of primary succession

Answer 37

1. colonisation by pioneer species (lichen) - weathering of rock to produce sand/soil - lichen die and decompose which released nutrients 2. change in the abiotic environement caused by species present 3. enables further species to colonise/survive (mosses and ferns) , thicker layer of soil builds up, increased water retention - environment is less hostile so grasses, shrubs ans trees develop 4. changes in diversity/biodiversity - many species 5. stability increases/environment is less hostile - more food chains, more food webs - leads to stable community 6. climax community is reached - stable over a long period

Question 38

Define secondary succession

Answer 38

Pioneer species become established on previously inhabited land (cleared by fire or for agriculture), soil (with seeds and roots) is already present and biomass is higher so secondary succession is much quicker

Question 39

Define conservation

Answer 39

preservation, protection or restoration of the natural environment and species there

Question 40

What are the main reasons for conservation?

Answer 40

* personal * ethical * economic * cultural and aesthetic

Question 41

How can managing succession help to conserve habitats?

Answer 41

The climax community needs to be prevented * usually done via grazing, mowing, burning land * without this shrubs would take over and woodland would form