Metabolic rate and body size

Question 1

define basal metabolic rate

Answer 1

the minimum MR for resting,fasted, adults in thermo-neutral zones

Question 2

define standard metabolic rate

Answer 2

minimum MR needed to sustain life at a given temperature = ectotherms

Question 3

define resting metabolic rate

Answer 3

the energy expended in the absence of external activty

Question 4

outline why it is important to measure BMR in adults and not during digestion

Answer 4

juviniles = energy allocated to growth etc so different BMR
digestion= requires energy to digest food and extract emergy so different MR

Question 5

how does muscle mass change with body mass

Answer 5

muscular mass increases proportionately with body mass

Question 6

how does energy expenditure change with increasing body mass

Answer 6

energy expenditure increases as a decreasing function of mass= the BMR for 1g of mouse tissue is greater than that of 1g of elephant tissue
= as mass increases BMR decreases

Question 7

what are the advantages of using a log scale

Answer 7

1) enables us to plot MR for animals of very different masses

2) A power relationship becomes linear on a log-log plot

Question 8

what are the different theories which explain why energy expenditure increases as a decreasing function of mass

Answer 8

1) MR is driven by surface area to volume ratios = Karl Meeh

2) Resource supply networks = Kleiber, James Brown, Geoffrey West and Brian Enquist

Question 9

outline Karl Meeh’s theory of why energy expenditure increases as a decreasing function of mass

Answer 9

MR is driven by SA:V
- Karl Meeh 1879 quantified the surface area of different animals and found that SA increased with body mass to the power of 2/3
- if heat loss is proportional to the SA then the rate of energy should also be proportional to SA

-Rubner 1883 tested dogs of various sizes and found MR increased with body mass to the power of 2/3

= suggets that surface area increases more slowly than volume- larger animals have a smaller SA and alrger volume therefore experience less heat loss
= as a consequence have a lower MR as dont need to sustain heat

Question 10

outline kleiber’s theory of why energy expenditure increases as a decreasing function of mass

Answer 10

Resource supply networks
- tested the relationship across mammals and found that MR seemed to vary with M to the power of 0.75

• 1997 Brown, West and Enquist suggsted the scaling and geometry of internal supply networks could explain this M0.75 relationship

= hypothesis - MR is limited by the rate at which resources can be supplied e.g. O2
= larger animals dont have networks or vessel to supply tiisues at the same rate therefore have tissues which use less oxygen/nutrients

Question 11

what was concluded in 2003 about why energy expenditure increases as a decreasing function of mass?

Answer 11

White and Seymour found that after new analysis of the allometry of mammalian BMR showed no support for metabolic scaling exponent of 3/4 and that mammalian BMR is proprotional to the body mas to the power of 2/3 (theory 1)

= however the difference between the two fitted lines with b =3/4 and b=2/3 is very small so depends on whether BMR was measured accuratley e.g. was it skewed by temp, activity etc

Question 12

can the different theories between 1979-2003 conclude that heat loss determines MR?

Answer 12

NO
= if heat loss were the only explanation MR would be fixed in relation to mass and ambient temp
= MR shows it varies in responce to factors e.g. climate, food, diet, pop density and predation therefore MR is evolutionary labile not fixed

Question 13

outline how MR is thought to be evolutionary labile (change with evolution)

Answer 13

changes in mortality rate can select for changes in MR
= animals maximumse fitness, measured by lifetime reproductive success
= when facing increased mortality evolution will select for a faster reproductive rate
= therefore individuals will produce more offspring in a shorter space of time
= as a consequence they have greater MR as energetic demands of repro are high

Question 14

What is meant by the life history theory

Answer 14

looks at the fitness consequences of allocating resources to various functions of life e.g. growth vs reproduction or producing many small vs few large offspring

Question 15

provide an example of how life histories and physical constraints both influence MR

Answer 15

Trinidadian guppies differ in levels of predation pressure
= pops with high risk of predation mature at a smaller size and at a younger age, reproduces at faster rates and invest more in reproduction, therefore have a greater MR
= Auer et al 2018

Question 16

what is meant by mass specific metabolic rate and how does it change with size

Answer 16

a concept which represents the metabolic intensity of a species defined as the ration between BMR and body mass
= shows how metabolism scales with size
- mass-specific MR increases rapidly as mass increases
= therefore the smallest endotherms require food with a high energy density

Question 17

how does body mass limit how small an endotherm can be

Answer 17

a warm-blooded animal cant be smaller than a hummingbird/shrew as it wouldnt be able to eat fast enough to maintain its body temperature

= hummingbirds have the highest mass-specific MR and have to consume their weight in nectar daily

Question 17

what are some consequences of being small

Answer 17

1) High rates of energy intake needed = energy desne food e.g. seeds, nuts,nector, rates at which energy can be extracted = limited mechanical/chemical breakdown, availability of food in space/time

2) reduced energy in critical periods

Question 18

how can some small endotherms use heat/sustain energy

Answer 18

1) some insects use metabolic heat to increase body temp
2) small endotherms redcue body temp through
- daily circadian temp cycles
- deep torpor

Question 19

define deep torpor

Answer 19

a temporary drop in body temp to conserve energy e.g. low temps or low food availability

Question 20

why is small body size not so costly for ecotherms

Answer 20

energy requiremnts of ectotherms are 10-30 times less than those in a similarly sized endotherm
- as a consequence food requirements dont limit body size
= this therefore opens up new niches of ectotherms as they can be smaller