Invertebrate Zoology
Week 3
Chris Foster
Mechanics of Movement
Reasons to move; concentrated food source, avoid predation, environmental change,
dispersal, reproduction.
How to move;
- Hydrostatic skeleton; soft bodied, muscle cells and ciliary movement, fluid filled.
- Exoskeleton; jointed harder shell, mechanical levers.
Modes of Moving; using the environment [passive] and muscles [active]
Fastest Land Invertebrate; cicindelid, 2m/s [4-5mph] 120 body lengths a second.
Fastest Marine Invertebrates; “punch” of mantis shrimp, 23m/s [102,000m/s^2
acceleration] // squid, 8m/s
Fastest Aerial Invertebrates; Dragonfly, 27m/s [60mph] // Horsefly, 40m/s [90mph] //
Migrating ladybirds, 16m/s [37mph]
Physics of Movement; [Newton’s Laws]
1. Body at rest stays at rest
2. Body moving in a straight line continuous unless acted upon by an external force
3. Application of unbalanced force to a mass in motion results in acceleration or
deceleration of the mass in the direction of the force.
4. For ever action there must be an equal and opposite reaction.
- First law of thermodynamics; energy within a closed system remains constant, can be
changed from one form to another
- Force detected by its effect on a mass [F = MA] a force on 1 Newton is required to
impart a mass of 1kg an acceleration of 1m/s^-1.
- Reaction Force; when force exerts a force on a second body is as though the second
body exerts a force of equal magnitude but in the opposite direction.
- Work; mechanical work done is when a force imparts an acceleration to a mass.
Stationary mass, the work done is product of the force and distance moved. [W=Fd //
W=(Ma)d] in joules.
Cost of Movement;
- Energy expended can be estimated by measuring metabolic rates during movement
and at rest
- Link to feeding biology, organism exploiting low concentration food resources
limited to low energy locomotion [sedentary benthic animals//organism which move
relatively slowly]
- Multicellular established dense pockets of energy which can be exploited by animals
with greater powers of movement.
, Invertebrate Zoology
Week 3
Chris Foster
- Evolutionary advancements; animal mechanisms permitting exploitation of dispersed
by dense aggregations of energy. Suggests new cost of movement per unit weight
decreases for larger animals than those swimming with neutral buoyance. [Blue whale
filtering low-energy dispersed plankton or colossal squid (top predator) as an ambush
hunter]
Passive Transport;
- Do not need to work in order to move, relies on buoyancy and natural movements of
the medium in which they live.
- Aquatic and aerial plankton [extensive use] capable of swimming and overcoming
downward drift is not neutrally buoyant [aerial, ballooning spiders use air currents]
- Aquatic is very different due to the difference in viscosity of water, aquatic plankton
are bigger. Primary production in seas predominantly due to Phyto-plankton algae in
surface waters [vast numbers of permanent and temporary zooplankton exploiting
source of production as food source]
- “cost of achieving neutral buoyancy” – secretion of spines, deployment of lipids.
Friction/Drag;
- Mechanical work of locomotion, ultimately derived from energy generated by
chemical reactions in the cells [chemical not necessarily released as mechanical not
perfectly efficient]
- Mechanical work measured by mass and distance [F = md // W =Fd]
- Efficiency can be expressed as; output of useful work / input of energy
- Energy is usually stored in the form of kinetic energy [KE = ½ mv^2 // V is velocity
of the mass [ms^-1]
- Tradeoffs between efficiency and potential absolute power.
- Body moving in a straight line continues without external force – viscous medium the
body experiences drag [resistance to medium]
- Factors; size of organism, speed at which its travelling, viscosity of medium over or
through what its moving.
- Reynold’s Number:
Re = [velocity x dimension of system] / kinematic viscosity
o Dimension; entire organism / part of organism
o Velocity; maximum velocity achieved
o Viscosity; that of the mediums “stickiness”
o High Re = less important the stickiness [smaller animals, viscous forces are
important]
Re = 1.4 x 10^6 x d^1.86
[d] = linear dimension of the object.
- Overcoming viscosity; Re affects bristle bearing appendages [Setose paddles have
low Re, viscous forces predominant = jerky movement] Higher viscosity in aquatic
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