Lecture 6: Size Flashcards
benefits of being large:
- better predators
- better at coping with environment fluctuations
costs of being large:
- large investment
- slow reproduction
benefits of being small:
- rapid development
- persistence (as a species)
Costs of being small;
-individually not v good at coping with environmental fluctuations
insect size range
10^15g to 10^-4g
why are insects so small?
CONSTRAINT
- insects are small because of their gas-exchange system
- tracheal system
trachea can only transport gas up to
1.5cm
does the tracheal system penetrate individual cells?
YES
what 4 physico-chemical factors affect rate of diffusion?
1) molecular weight: smaller MW, faster diffusion
2) relative concentration of gas at start and end
3) permeability of substrate
4) Temperature
3 steps to moving O2 from the atmosphere to an insect cell:
1) Get O2 into system (gas)
2) Get O2 from spiracles to tracheoles (gas)
3) Get O2 from tracheoles into mitochondria (liquid)
to get O2 into system (outside into insect)
-only need is a 2% concentration difference
to get O2 from spiracles to tracheoles (gas)
-Tissue use O2 - travels 10^5 faster in air than water (hence why its gas)
to get O2 from tracheoles into mitochondria (liquid)
BOTTLENECK - rate of diffusion of O2 in water V slow - the RATE-LIMITING STEP
tracheoles not only receive O2 but
also have to get rid of CO2
CO2 is __X more soluble in water than O2
32X
respiratory system is very important in determining the upper __ ___ of insects - widest body dimension cannot be more than __
body size
3cm
constraints of insects size (not gas exchange system)
-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
consequences of being so small: SA:V
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)
very small insects & flying
v small insects don’t acc fly, they row
benefits of being so small: cross-sectional area/volume ratio
- muscle power proportional to its cross-sectional area (square function)
- muscle moves mass (cubic function)
- small things appear to be v strong
benefits of being small: moving objects efficiently has several advantages:
- moving your own bulk is easy -dispersion&colonisation
- makes u good at digging
- makes u good at foraging (predation & herbivory)
benefits of being small: kinetic energy and gravity effects
smaller organisms benefit by being incredibly resilient to impact damage and can therefore move at relatively very high speeds
benefits of being small: Ecological opportunist
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
benefits of being small: living room
a given habitat can support many more insects in a more diverse community than larger organisms
