Animal Orientation & Biological Clocks

Taxis

movement of an organism towards (+) or away (-) from a directional stimulus

Phototaxis

Movement of an organism towards or away from a light source

• negative phototaxis: animals avoid detection by predators aviod drying out from sun

Chemotaxis

Movement of an organism towards or away from chemical source
Positive chemotaxis: - allows animal to find a mate through scent + food source
Negative chemotaxis: - remove the animal from harmful chemical

Gravitaxis

Movement of an organism towards or away from gravity
Positive Gravitaxis: - help animal avoid predation above

negative: help animal avoid predators on the ground, avoid drying out from higher ground temps, reach food sources above ground.

Thermotaxis

Movement of an organism towards or away from heat source

Kinesis

change in rate of movement of an organism in response to the change in intensity of a non-directional stimulus

Orthokinesis & Adaptive Advantage

• Non-directional response where speed of movement depends on stimulus intensity.

• Unfavourable (e.g. Light/Dry): Moves faster to quickly find a favourable environment.

• Favourable (e.g. Dark/Damp): Moves slower to stay in the favourable area.

• [AA]: Prevents drying out and avoids predators —> maintains moist conditions for respiration —> survives to reproduce.

Klinokinesis & Adaptive Advantage

• Non-directional response where rate of turning depends on stimulus intensity.

• Unfavourable (e.g. Light/Dry): Turns frequently (high rate of turning) to locate/stay near a favourable gradient.

• Favourable (e.g. Dark/Damp): Turns less (moves in a straight line) to remain in the favourable zone.

• [AA]: Keeps animal in dark/moist shelter —> avoids detection/predation and drying out —> increases survival and reproductive success.

Klinotaxis

Directional movement where an organism detects the direction of a stimulus by using a single receptor on one side of the body

(wiggle side to side)

Tropotaxis

• Directional movement where an organism detects the direction of stimulus by using paired receptors on both sides of the body

(Straight towards or away from the stimulus)

Circadian Rhythms (3 Types)

• Nocturnal: Active at night.

• Diurnal: Active during the day.

• Crepuscular: Active at dawn and dusk.

Exogenous vs. Endogenous Rhythms

• Exogenous: Driven purely by external cues (no cue = no rhythm).

• Endogenous: Driven by an internal biological clock, entrained by external cues/zeitgebers (no cue = rhythm continues).

Internal Biological Clock Functions

• Controls endogenous rhythms.

• Located in the suprachiasmatic nuclei (SCN) of the hypothalamus.

• Functions: Allows organisms to anticipate environmental changes, synchronise with the environment, and maintain rhythms without external cues.

Zeitgeber & Entrainment Definitions

• Zeitgeber: An external environmental cue (e.g., light, temperature) used to set the biological clock.

• Entrainment: The process of resetting/synchronising the internal biological clock to match the external environment.

Migration (Definition, Advantages, Disadvantages)

• Definition: Seasonal, return movement controlled by an endogenous biological clock.

• Advantages [AA]: Favourable climate, constant food supply, energy conservation, better breeding conditions, and genetic diversity via inter-breeding.

• Disadvantages: High energy cost, increased predation, risk of harsh weather, getting blown off course, or dying en route.

Homing & Navigation (Basics)

• Homing: Ability to find the way home over unfamiliar territory.

• Navigation: Innate ability to reach a destination via the most direct route.

• [AA]: Prevents getting lost, conserves energy, and ensures arrival at the optimal time for breeding to maximize survival and reproductive success.

Navigation Requiring an Internal Clock

• Solar Navigation: Uses the sun's position; requires a biological clock to time-compensate for the sun moving east-to-west.

• Stellar Navigation: Uses star patterns/constellations; requires a biological clock to compensate for star movement across the night sky.

Navigation WITHOUT an Internal Clock (Visual & Magnetic)

• Visual Cues: Recognises familiar landmarks (coasts, mountain ranges) to guide movement.

• Magnetic Fields: Uses internal magnetite to detect and follow Earth's magnetic field lines (e.g., deep-sea turtles).

Navigation WITHOUT an Internal Clock (Chemical & Sound)

• Chemical / Scent Trails: Follows chemical gradients or pheromone trails (e.g., sharks following blood, ants following pheromones).

• Sound Navigation: Emits sound/infrasound and detects the bounce-back to map surroundings (echolocation in dolphins/bats).