Locomotion - Animal Design

Locomotion

Act or power of moving from one place to another

Evolutionary perspective of locomotion

Locomotion is shaped by selection pressures that influence how animals need to move to survive and reproduce

Three major selection pressures

Resources environment and biological factors

Resources as a selection pressure

Habitat food and mates

Environment as a selection pressure

Temperature weather geography and access to resources which dictate how animals have to move

Biological selection pressures

Predators, or being a prey animal and pathogens or disease

Three main functions of the locomotor system

Support body mass move the centre of mass and move the limbs

Supporting body mass

Limbs must withstand the reaction force produced by gravity acting on the animal's body

Moving the centre of mass

Producing propulsion to move the animal from point A to point B

Moving the limbs

Producing repeated or cyclical limb movements such as cycling the legs during running

Substrates

Different surfaces or environments animals move across such as land air and water

Animal locomotion requirements

Animals must move across different substrates in multiple directions and at varying speeds

Main energetic requirement of locomotion

Minimise energy expenditure because all movement consumes energy

Quadrupedal carnivores

Generally adapted for speed bursts of speed agility hunting and rapid acceleration

Why carnivores need bursts of speed

To rapidly transition from monitoring their surroundings to chasing and catching prey

Important abilities for carnivore hunting

Speed acceleration agility manoeuvrability and grasping or gripping

Muscle bulk in carnivores

Greater muscle mass can produce greater force and power

Why a slender body can benefit carnivores

Reduced mass can improve agility and manoeuvrability

Skeletal arrangement

The arrangement of bones affects leverage muscle action flexibility stride length and locomotor efficiency

Leverage

The arrangement of bones determines how effectively muscle forces can produce movement at joints

Grip / traction

The ability to grip the substrate and prevent slipping

Structures that provide traction

Pads multiple digits and claws

Importance of traction

Allows forces to be transferred effectively to the substrate and improves speed agility and manoeuvrability

Claws

Improve traction and therefore help with speed and agility

Forelimbs

Mainly responsible for weight support steering and braking

Triceps

Supports body weight and resists forces acting on the forelimb

Why forelimbs resist forces

They experience forces from supporting and controlling the animal's body during movement

Lumbar spine

Region of the spine whose flexibility contributes to locomotion

Lumbar spine flexibility

Allows flexion and extension of the spine which can increase stride length

Effect of spinal flexion and extension

Increases stride length allowing the animal to cover more ground and reach high speeds more effectively

Hindlimbs

Main powerhouse for propulsion and acceleration

Hamstrings

Predominantly extend the hip joint and help push the animal forwards

Hip extension

Contributes to pushing the body forwards and generating propulsion

Quadrupedal herbivores

Generally adapted for endurance and low-energy-cost locomotion

Why herbivores need energy-efficient locomotion

Their diet may provide relatively low energy so efficient movement reduces energy expenditure

Why herbivores need endurance

They may need to travel long distances to find food migrate and escape predators

Migration in herbivores

Travelling to find sufficient food resources

Elastic tissues

Tissues that can store and release elastic energy during movement

Tendons

Elastic tissues that can stretch store energy and recoil to return energy to the locomotor system

Tendons compared with elastic bands

They stretch to store elastic energy and recoil to release it

How tendons store energy

They are stretched during movement and store elastic potential energy

How tendons return energy

They recoil after being stretched and return stored energy to the locomotor system

Why elastic tendons reduce energy expenditure

They allow energy to be stored and recycled between movement cycles rather than requiring new muscular energy each cycle

Energy cycling

Energy is stored during one part of movement and returned during another part so it can be reused

Horse tendons

Greater thicker and longer tendons compared with the other examples such as dog pig and cow

Significance of horse tendon structure

Indicates a greater reliance on elastic energy storage during locomotion

Skeleton

A frame that supports the body and influences the actions muscles can produce

How the skeleton influences muscles

Bones provide attachment points and act as levers through which muscles generate movement

Individual vertebrae

Influence spinal mobility and flexibility

Increased spinal mobility

Can increase stride length and contribute to higher running speeds

Long legs

Can increase stride length and allow an animal to cover more ground per stride

Light legs

Require less energy to accelerate and move

Leg length and weight

Longer lightweight legs can allow greater distance to be covered with longer strides while maintaining lower energetic cost

Skeletal optimisation

Evolutionary modification of skeletal size shape length and weight to improve locomotor performance and efficiency

Body mass

The amount of body mass that must be supported and moved during locomotion

Importance of body mass

Body mass affects the forces and energy required for locomotion

Importance of body proportions

The distribution and relative size of body structures influence how muscles and limbs generate and control movement

Reducing limb mass

Reduces the energy required to accelerate and move the limbs

Muscles

Produce forces within the limbs

Two major effects of muscular force

Supporting the body and producing movement at joints

Powerful muscles

Muscles capable of producing large forces quickly

Importance of producing force quickly

Allows rapid acceleration powerful movements and effective locomotor responses

Traction

Ability to grip the substrate and prevent slipping

Pads

Structures that can increase traction

Multiple digits

Can increase contact with the substrate and improve traction

Posture

The position and arrangement of the limbs which can influence mechanical efficiency stride length and speed

Limb elongation

Evolutionary changes in skeletal proportions that make limbs longer

Advantage of elongated limbs

Can increase stride length and allow animals to cover more ground with fewer steps

Lightening the limbs

Evolutionary reduction in limb mass to improve locomotor efficiency

Digit loss

Reduction in the number of digits which can make limbs lighter and more efficient for locomotion

Trade-off of losing digits

Lighter and more efficient limbs but reduced manipulation ability

Two competing demands of digit loss

Lightweight efficient locomotion versus manipulation ability

Pectoral girdle

Skeletal region connecting the forelimb or shoulder region to the body

Quadruped pectoral girdle

The scapula is primarily supported by muscles rather than being rigidly attached to the body by a bony connection

Scapula

Shoulder blade that can move freely in many quadrupeds

Advantage of a freely moving scapula

Allows greater movement of the forelimb

Scapular mobility

Increases forelimb mobility which can increase stride length and locomotor efficiency

Front leg

Provides weight support steering and braking or stopping

Hindleg

Provides propulsion and acceleration

Primary role of hindlimbs

Generate much of the force required to propel and accelerate the animal

Primary role of forelimbs

Support body weight steer the animal and brake or stop movement

Locomotor adaptations

Adaptations driven largely by the locomotor requirements imposed by an animal's environment and lifestyle

Other factors affecting adaptation

What the animal needs to do with its limbs such as manipulation

Locomotor trade-off

Improving locomotor performance may reduce another ability such as manipulation

Example of a locomotor trade-off

Losing digits makes limbs lighter and more efficient for running but reduces manipulation ability

Why different animals have different locomotor adaptations

They experience different selection pressures and have different environmental dietary predatory behavioural and locomotor requirements

Carnivore locomotion

Generally emphasises speed acceleration power agility and hunting ability

Herbivore locomotion

Generally emphasises endurance energy efficiency travelling feeding and escaping predators

Skeletal adaptations

Changes in skeletal arrangement that alter leverage flexibility stride length limb weight and mechanical efficiency

Muscular adaptations

Changes that improve force production support movement and acceleration

Tendon adaptations

Changes that increase elastic energy storage and return to reduce the energetic cost of locomotion

Limb morphology adaptations

Longer lighter limbs and fewer digits can reduce limb mass and increase stride length

Overall anatomy and locomotion

Skeleton muscles tendons posture limb proportions and traction structures work together to support the body generate movement control movement and minimise energy expenditure