Populations and ecosystems

Question 1

Define ecology

Answer 1

study of inter-relationships between organisms and their environment

Question 2

Define the term abiotic factor

Answer 2

Non living factors in an environment eg temperature or rainfall

Question 3

Define the term biotic factor

Answer 3

living factors in an environment eg competition and predation

Question 4

Define ecosystem

Answer 4

dynamic system made up of a community and all of the non living factors of its environment

Question 5

Name two major process that occur within an ecosystem

Answer 5

flow of energy
cycling of elements

Question 6

Define population

Answer 6

group of individuals of the same species occupying the same habitat at the same time and can interbreed

Question 7

Define community

Answer 7

the populations of different species in a particular place at the same time

Question 8

Define habitat

Answer 8

the place where an organism normally lives

Question 9

Define microhabitat

Answer 9

a smaller unit within a habitat with its own microclimate

Question 10

Define niche

Answer 10

how an organism fits into its environment (where the organism lives and what it does there)

Question 11

Why do we describe populations as dynamic?

Answer 11

they vary in size and composition over time

Question 12

Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?

Answer 12

So that all of the data can be represented on the same axis

Question 13

Define limiting factor

Answer 13

factor that limits the growth of a population

Question 14

State the factors that affect the size of a population

Answer 14

abiotic and biotic factors affect rate of growth and size of a population

Question 15

Define carrying capacity

Answer 15

the size of population of a species that can be supported by the ecosystem

Question 16

Describe how temperature affects a population size

Answer 16

different species have different optimum temperatures. Temperatures above or below these may slow/denature enzymes in cold blooded animals or require excessive energy use to maintain in warm blooded animals

Question 17

Describe how light affects population size

Answer 17

Light is required for photosynthesis. More light, more photosynthesis, more biomass both for plant survival and for animals to feed on

Question 18

Describe how pH affects population size

Answer 18

pH affects action of enzymes. Organisms have an optimum pH and will not survive well in pH away from optimum

Question 19

Describe how water affects population size

Answer 19

In scarce water conditions only well adapted organisms survive.

Question 20

Describe how humidity affects population size

Answer 20

in low humidity transpiration and water loss increase. Plants and animals well adapted to tolerate low humidity will have larger population size

Question 21

Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?

Answer 21

So that all of the data can be represented on the same axis

Question 22

Describe competition

Answer 22

when 2 or more species share a resource that is insufficient to satisfy their requirements fully

Question 23

Describe intraspecific competition

Answer 23

competition between members of the same species

Question 24

Describe interspecific competition

Answer 24

competition between individuals of different species

Question 25

Outline how the availability of resources affects a population

Answer 25

less resources - more competition - lower population size

Question 26

Explain how competition causes smaller numbers of large trees in a forest rather than larger numbers of small trees

Answer 26

trees compete for resources - a few grow larger -this restricts resources for the others - which die

Question 27

How does interspecific competition affect population size?

Answer 27

the population with the competitive advantage will increase in size while the other will decrease.

Question 28

What is the competitive exclusion principle?

Answer 28

one species has the competitive advantage over another - population of less competitive species will decrease - until it becomes extinct

Question 29

Describe the competitive exclusion principle in terms of niches

Answer 29

when resources are limiting no two species can occupy the same niche

Question 30

Suggest how an increased food supply may result in a population increase

Answer 30

More food - more individuals survive - increased reproduction - increase in population

Question 31

Define predator

Answer 31

organism that eats another organism

Question 32

Define prey

Answer 32

organism that is eaten by another organism

Question 33

Comment on the evolution of predators and their prey if extinction has not occurred

Answer 33

predators evolved to be more effective at catching prey - prey evolved simultaneously to be more effective at avoiding predators

Question 34

Explain why it is difficult to obtain data on predator and prey populations in natural environments

Answer 34

it is not possible to count all individuals

Question 35

Describe the predator prey relationship

Answer 35

predator eats prey and reduces prey population - fewer prey means greater competition for food amongst predators - predator population decreases due to lack of food - less predators so less prey eaten and more survive and reproduce - prey population increases - repeat

Question 36

Suggest why fluctuations in natural predator prey populations is not generally severe

Answer 36

a range of food is available to the predators

Question 37

Why is sampling done in ecology?

Answer 37

To find the abundance of organisms in an area when it is not possible to count every one individually, too time-consuming and is likely to cause damage.