Obtaining Food - AnimalsForaging behaviourAnimals have patterns of behaviour that increase the chance of them to finding food. They vary with the availability and type of food and specific to each species. These patterns of movement are known as search patterns.

If food is in limited supply the animal is non-selective in its choice of prey, reducing energy wastage. If food is plentiful the animal chooses the most easily caught prey, reducing energy wasted in pursuit. However the animal may be a selective if food is difficult to handle.

Ideally these patterns give the animal an overall energy gain situation, where it is getting more energy from the food than it is expending searching for or capturing it.

Social insects such as ants and bees have developed a particular pattern of behaviour that ensures the survival of the colony. They communicate the source and richness of the food to the rest of the colony. Bees perform a ‘waggle’ dance indicating the richness and distance of the food. Whilst ants leave a chemical trail which other ants can follow and also mark.

Higher animals have instinctive and learned behaviour patterns. They may employ a cooperative hunting tactic, in which the group work together to hunt and capture prey. The dominant animal will feed first but all the subordinate animals will receive more food than if they foraged alone.

Obtaining food - Animals
CompetitionCompetition is the fight for resources which may lead ultimately to the death of the less well adapted organism.

Interspecific competition occurs between members of different species competing for similar resources. Occasionally a compromise can be reached.

Examples of interspecific competition are squirrels, where the more aggressive grey squirrel has pushed out the red squirrel from its habitat. Another example is comorants, who have adopted a compromise feeding system. The common and green comorant have a slightly differing depth of diving and fish type they feed on, thus minimising competition.

Intraspecific competition is much more intense as the organisms are of the same species and require exactly the same resources.

Territoriality and Dominance Hierarchy
An animal will have a certain geographical area it will cover in its life. Within this area a male animal will establish a territory. This is advantageous to the animal, in that it will contain enough resources for the animal, its mate and offspring.

Some animals will defend this territory against members of the same species by using a series of signals, such as birds singing, so there is seldom any real aggression. The nearer the centre of the territory, the greater the territorial behaviour.

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cat
Higher animals living in social groups may have a ‘pecking order’, in which a one animal will be dominant over the others. The dominant animal will have its choice of available food and mates. The dominant animals position will reinforced by a system of social signals, thus keeping any real aggression to a minimum.
This is shown very well by wolves and dogs, where the dominant animal will bare its teeth, stands tall and raises it’s tail and ears, whilst the subordinate animals will cower, cover its teeth and lower its tail and ears.


Obtaining food - Plants
Competition in plants
Animals are not the only organisms to experience competition. Plants cannot move about (they are sessile), and whilst not having to forage for food because they are autotrophs, they will compete for light, space, water and nutrients.

They also experience more intense competition within a species (intraspecific). Different root depths and mineral requirements may reduce interspecific competition, whilst some plants may dominate others by producing toxins or blocking light.

Competition in plants can affect the diversity of species found in a grazing area. An area of grassland will have a low number of different species present if it experiences a low level of unselective grazing, when grasses will out-compete other species because of their fast growing nature. An area of grassland will also have a low number of different species if unselective grazing is high, because less vigorous species may become damaged. If there is a medium intensity of unselective grazing, grasses will be kept in check and other species can survive.

Obtaining light
Plants must obtain enough light to photosynthesise at a rate that exceeds respiration, in order to store energy. Plants are constantly respiring, using sugars and stored carbohydrate (starch) for energy and producing carbon dioxide. As light intensity increases the rate of photosynthesis increases.

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The light intensity at which respiration and photosynthesis are using and producing carbohydrate at the same rate is called the compensation point. With a further increase in light intensity the plant is photosynthesising more than it is respiring and the sugars produced will be stored as starch.

Sun plants live in habitats that are brightly lit. They have a compensation point at a higher light intensity than shade plants. A shade plant must be able to photosynthesise effectively at lower light intensities because they are often found in dimly lit areas or in the shade of other species (e.g. lower canopy plants in a rainforest).