Lecture 6: Size

Question 1

benefits of being large:

Answer 1

• better predators

- better at coping with environment fluctuations

Question 2

costs of being large:

Answer 2

• large investment

- slow reproduction

Question 3

benefits of being small:

Answer 3

• rapid development

- persistence (as a species)

Question 4

Costs of being small;

Answer 4

-individually not v good at coping with environmental fluctuations

Question 5

insect size range

Answer 5

10^15g to 10^-4g

Question 6

why are insects so small?

Answer 6

CONSTRAINT

• • insects are small because of their gas-exchange system
• tracheal system

Question 7

trachea can only transport gas up to

Answer 7

1.5cm

Question 8

does the tracheal system penetrate individual cells?

Answer 8

YES

Question 9

what 4 physico-chemical factors affect rate of diffusion?

Answer 9

1) molecular weight: smaller MW, faster diffusion
2) relative concentration of gas at start and end
3) permeability of substrate
4) Temperature

Question 10

3 steps to moving O2 from the atmosphere to an insect cell:

Answer 10

1) Get O2 into system (gas)
2) Get O2 from spiracles to tracheoles (gas)
3) Get O2 from tracheoles into mitochondria (liquid)

Question 11

to get O2 into system (outside into insect)

Answer 11

-only need is a 2% concentration difference

Question 12

to get O2 from spiracles to tracheoles (gas)

Answer 12

-Tissue use O2 - travels 10^5 faster in air than water (hence why its gas)

Question 13

to get O2 from tracheoles into mitochondria (liquid)

Answer 13

BOTTLENECK - rate of diffusion of O2 in water V slow - the RATE-LIMITING STEP

Question 14

tracheoles not only receive O2 but

Answer 14

also have to get rid of CO2

Question 15

CO2 is __X more soluble in water than O2

Answer 15

32X

Question 16

respiratory system is very important in determining the upper __ ___ of insects - widest body dimension cannot be more than __

Answer 16

body size

3cm

Question 17

constraints of insects size (not gas exchange system)

Answer 17

-EXOSKELETON; crustaceans are 3m across, insects aren’t as combination of a soft exoskeleton & terrestrial habitat may set an upper limit AND large imobile soft insect is very vulnerable to predation
-FLIGHT;
very costly, insect flight muscles is the most metabolically active known to science. Huge power requirement

Question 18

consequences of being so small: SA:V

Answer 18

large SA:V

• water balance (loss)
• Heat loss/gain (temp regulation tricky for exothermic insects)
• air resistance (viscosity of air increases as you get smaller)

Question 19

very small insects & flying

Answer 19

v small insects don’t acc fly, they row

Question 20

benefits of being so small: cross-sectional area/volume ratio

Answer 20

• muscle power proportional to its cross-sectional area (square function)
• muscle moves mass (cubic function)
• small things appear to be v strong

Question 21

benefits of being small: moving objects efficiently has several advantages:

Answer 21

• moving your own bulk is easy -dispersion&colonisation
• makes u good at digging
• makes u good at foraging (predation & herbivory)

Question 22

benefits of being small: kinetic energy and gravity effects

Answer 22

smaller organisms benefit by being incredibly resilient to impact damage and can therefore move at relatively very high speeds

Question 23

benefits of being small: Ecological opportunist

Answer 23

insects have relatively small food requirements and short generation times: they therefore have high reproductive output and large populations. this is turn means high genetic heterogeneity
-meaning insects are VERY ADAPTABLE

Question 24

benefits of being small: living room

Answer 24

a given habitat can support many more insects in a more diverse community than larger organisms

Question 25

benefits of being small: dispersal

Answer 25

small resources requirement per individual means potential for colonised new habitat in large number is high