Animal responses to the abiotic environment

Biological orientation responses

• Behaviour by which animal positions self in relation to surroundings

• Taxes– Movement of whole animal, guided

continuously towards or away from a stimulus coming from one side. Movement towards is positive taxis and vice versa. E.gs

• Kinesis– Nondirectional response to stimulus. A

change in activity rate. Are actually random movement but will see a pattern.

Homing and Migration

• Complicated form of orientation, animal must be able to navigate and orientate self.

• Homing– The ability of the individual to return to a

home site (hive, nest etc)• Migration– Regular, annual or seasonal mass movement

of animals from breeding area to another area. In true migration the individual does a round trip. E.G.s Survival during migration depends on an animals ability to navigate.

Migration has reproductive or survival benefits. The behaviour to migrate is inherited and maintained by natural selection.

Triggers for migration: a drop in temperature, days become shorter, innate genetic drive, animal has matured enough.

• There are 3 types of orientation important in navigation for homing and migration: piloting, compass orientation and true navigation.

– Piloting: animal moves from one landmark to another until destination is reached. Short distances and uses visual cues.

– Compass: animals can detect magnetic field lines of earth, chemical cues or sound to detect a compass direction.

– True: determining ones position relative to other locations. Ability to orientate oneself towards a goal without landmarks and regardless of direction. To do this you need a map sense (ability to be aware of latitude and longitude) and a sense of timing (an internal clock that can compensate for movement of sun or stars).

Advantages of migration Disadvantages of migration

•Animals remain in favourable temp.•Grow larger•Leave more offspring•Have a constant supply of food•May colonise an new area•Reduces predation/parasitism/disease•Greater genetic mixing•Better breeding conditions

•May get caught in storm•May get eaten by predator•Huge investment in energy•May die of exhaustion as use up energy•May starve

Methods used for migration/homing

• Visual clues– Animals can learn surroundings e.g. wasps

• Solar navigation: as the sun moves from east to west it can be used to tell direction

– Honey bees are a good example: they keep the sun on one ommatidium of their compound eye during the outward journey and on the opposite for the return. If it is cloudy they use polarised light to navigate. They dance when they return to the hive to tell others where a food source is. The round dance points directly to the food source and tells it is within 50m of hive. The waggle dance is a figure of eight.

• The vertical dash line is the sun, the angle of this and the start of the fig. 8 is the angle of the food in relation to the sun, The number of waggles as the bee goes along the straight is the distance – fewer slower waggles mean food is further away.

– Birds: migratory birds fly mainly in the daytime and use the sun as a compass. They can compensate for the changing direction of the sun.

• Magnetic fields: homing pigeons can follow magnetic lines in earth, also now think whales and dolphins can.

• Star navigation: night migrating birds use a stellar compass, orientate to the brightest northern stars.

• Chemical navigation: following scent trails, dogs, ants eels and salmon all use this method

• Sound as sonar: bats and whales, echolocation used to navigate around objects and to give direction.

• Ambient pressure: proven in pigeons and may be in other birds, can be sensitive to altitude change of 10m. Gives an accurate idea of height.

• Most animals use more than one method to navigate and there are many methods we as yet do not fully understand.

Biological timing responses in animals

• Biological clocks: an internal clock to predict the onset of periodic changes in the environment. They are used for control of daily body rhythms (sleep, pulse, blood pressure, temperature, alertness, sex drive etc), reproduction timing so animals come on heat, release sperm and eggs or perform courtship at same time and to prepare for migration by eating a lot.

• Review definitions

Sometimes it can be hard to tell if a rhythm is endogenous or exogenous. It is endogenous if one of the following criteria apply: rhythm has a frequency not exactly the same as the environmental factor, period of rhythm deviates under lab conditions, rhythm persists if animal moved from one part of world to another.

Circadian rhythms in animals

Diurnal = active in day and inactive at night

Nocturnal = vice versa

Crepuscular = active at dawn and dusk

Arrhythmic = no regular pattern.

If animals (including humans) are cut off from environmental cues that can tell them time o day they still show a circadian rhythm (free running).

Human Rhythms

• Sleep-wake: function on day to night and vary from person to person. Children need around 12hrs sleep a night, teenagers 9hrs, adults 7-8 hours and the elderly often only 6hrs.

• Temperature: rises in day and drops at night, lowest point around 3am.

• Heart rate works in step with temperature• Pain: sensitivity varies over a day, more

sensitive to a needle around midday but more sensitive to cold at night.

• Alcohol metabolisim: broken down most efficiently from 4pm to 11pm.

• Efficiency of learning: follows the temperature curve but has a dip at lunchtime that is not related to eating.

• Kidney excretions: there is a rhythm of excretion of chemicals and volume.

• Birth and death: you are most likely to be born or die in the early morning.

• Hormone secretion: varies but most are secreted at night, get problems with shift work as hormones get out of synch and can take 5-10 days to change to match change in sleep patterns. No sleep means certain hormones are not secreted at all.

Circa lunar

• Some evidence ovulation cycle of primates is linked to lunar cycle.

• Many animals spawning behaviour is governed by the moon

Circatidal

• Grunions are main known example of single tidal activity. Crabs and other marine animals have two periods of activity per tidal cycle.

Circa annual

• Hibernation, slow metabolisim over winter, in insects known as diapause.

• Aestivation, summer ‘hibernation’• Migration• reproduction