4.5: Population size factors

Question 1

what is the definition of a population

Answer 1

a group of interbreeding individuals in a particular habitat at a particular time

Question 2

what are the problems in defining a population

Answer 2

migration, species interbreeding makes it difficult to define species,

Question 3

what is an example of species interbreeding

Answer 3

zorses. horses breeding with zebras, mules horses with donkeys, tigons tigers with lions, ligers lions with tigers

Question 4

why are zorses and mules mostly sterile

Answer 4

mammals need an even number of chromosomes to divide into pairs for reproduction

Question 5

what four factors affect population size

Answer 5

immigration , birth increase population emigration, death decrease population size

Question 6

define birth rate

Answer 6

the reproductive capacity of a population

Question 7

define immigration

Answer 7

the movement of individuals INTO a population

Question 8

define emigration

Answer 8

the NON REVERSIBLE movement of individuals out of a population

Question 9

define migration

Answer 9

the reversible periodic seasonal movement of individuals in and out of a population

Question 10

what is another word for birth rate

Answer 10

natality

Question 11

what is another word for death rate

Answer 11

mortality

Question 12

define population growth

Answer 12

the sum of natality and immigration minus the sum of mortality and emigration

Question 13

what are the advantages of living in a group

Answer 13

protection from predators
increased chance of finding mate
help raising offspring - extended family
cooperation

Question 14

what are the four distinct phases of population growth

Answer 14

lag phase
log phase
stationary phase
death/decline phase

Question 15

what are the factors that shape and define the lag phase

Answer 15

• slow growth rate minutes to several days (in bacterial culture) due to very few individuals with few individuals of reproductive age in a sexually reproductive group
• need for adaptation to environment or for preparation for growth e.g. increasing metabolic activity i.e enzyme synthesis

Question 16

what are the factors that shape and define the log phase

Answer 16

• rapid exponential growth achieved ( as long as no or few limiting factors) as numbers of reproductive individuals increase.
• birth rate and population growth at maximum
• does not last indefinitely.

Question 17

what are the factors that shape and define the stationary phase

Answer 17

• equilibrium reached as birth rate equals death rate
• carrying capacity of environment reached (i.e. the maximum population size that the environment can sustain) as population limited by availability of space, of nutrition and accumulation of toxic waste products

Question 18

what are the factors that shape and define the death/decline phase

Answer 18

• death rate exceeds birth rate
• carrying capacity exceeded
• shortage of nutrients and/or accumulation of waste to harmful levels

Question 19

define carrying capacity

Answer 19

the maximum population that a particular environment can sustain indefinitely

Question 20

why do most animal populations never reach the death decline phase

Answer 20

the populations growth rate slows down and reaches and oscillates around the carrying capacity

Question 21

what causes this oscillation around the carrying capacity

Answer 21

environmental resistance

Question 22

define environmental resistance

Answer 22

all the factors that limit and slow down population growth. ** can be calculated as the difference between biotic potential ( the species maximum growth potential) and its real growth. **

Question 23

why does population growth not remain constant

Answer 23

because of environmental resistance

Question 24

what are the disadvantages of living in a group

Answer 24

competition

Question 25

what are the two different types of competition

Answer 25

intraspecific - competition bettween individuals of same species interspecific - competition between individuals with a diffeent species

Question 26

what are the factors that limit population growth

Answer 26

``` available food predation disease/parasitism overcrowding competition ( for mates, space, food) accumulation of waste products weather ```

Question 27

what are the factors that improve biotic potential

Answer 27

reproductive rate ability to migrate (animals) disperse seeds (plants) ability to invade new habitats

Question 28

in the case of predation describe the process of boom and bust that results in the fluctation of a population around the carrying capacity of a particular environment.

Answer 28

prey population increase results in an increase of food for predators. predator numbers increase resulting in a decrease in prey population and so food as a result of reduced food the predator population decreases as a result cycle of boom and bust is set up. the equilibrium of which is called the carrying capacity of the population in that particular environment.

Question 29

is this an example of a negative feedback system

Answer 29

yes

Question 30

what two groups of factors can environmental resistance be divided

Answer 30

density dependent (slow down growth rate) factors which increase their effect as population grows density independent ( can cause population crash) factors that affect any population regardless of size

Question 31

give examples of density dependent factors

Answer 31

disease, availability of food, build up of toxic waste, predation, parasitism,competition,space,biotic factors, overcrowding

Question 32

give examples of density independent factors

Answer 32

freezing,flood,fire,weather,temperature,abiotic factors

Question 33

describe natural selection

Answer 33

darwin noticed populations produced more offspring than neeed purely to maintain numbers. this increased population produces competiition. Those better adapted to the present environment survive and breed.

Question 34

how does natural selection lead to evolution

Answer 34

species have a natural variation in genes. the process of natural selection ensures that those genes that make the species members most suitable to their environment will pass on their genes to the next generation. Thus the species evolves ensuring the improved survival of that species in that environment.

Question 35

what did dawin notice happened when birds compete for the same food source?

Answer 35

those birds tend not to live in the same area once established in a niche it is very difficult for another species to move in or steal it. unless they are better adapted or pick another place to live or pick another food source. in the long term two species cannot occupy the same niche in a specific habitat

Question 36

give example that in the long term two species cannot occupy the same niche

Answer 36

p caudatum feeds on organisms suspended in water p. aurelia as above p. bursaria feeds on organisms at bottom of ponds when these species are grown together p claudatum becomes extinct.

Question 37

define pest

Answer 37

any unwanted organism that interferes either directly or indirectly with human activity usually associated with food production, disease transmission to plants or animals

Question 38

how do pests attack crop plants and animals reducing yield

Answer 38

feed on them compete with them cause disease can make crops more susceptiable to disease can spoil food in storage or transportation

Question 39

what is the economic damage threshold

Answer 39

the maximum pest population that can be tolerated at a particular time and place without a resultant economic crop loss

Question 40

at what point do you spray a crop

Answer 40

when it reaches the economic threhold. where the cost of spraying is less than the cost of crops lost.

Question 41

what are the two main ways of control

Answer 41

chemical e.g. insecticide, fungiside, herbicide | biological

Question 42

what are advantages of chemical control

Answer 42

``` fast acting localised cost effective they ave a low economic threshold value can be applied on small or large scales little skill needed ```

Question 43

what are the disadvantagesof chemical control

Answer 43

- non selective can kill pollinators and pest eating species( which means any pest which survives or migrates has no competition) - can kill animals and humans - chemicals may not be biodegradable and are persistant in environment can bio accumulate eg. ddt causing death and infertility in higher food chain species as toxicity builds up in them from eating lots of other polluted species. biomagnification - pollute water supply - pests can develop resistance to chemicals

Question 44

how do bacteria become resistant to antibiotics

Answer 44

antibiotics create a process of natural selection. If any bacteria survive by adaption these better adapted bacteria will breed and produce an antibiotic resistant strain. without competition this becomes the predominant strain and that antibiotic becomes ineffective,

Question 45

name two other examples of resistance

Answer 45

warfarin resistant rats | pesticide resistant insects

Question 46

what are the properties of an ideal pesticide

Answer 46

specificc non persistent should not accumulate should not be passed along food chain