Eat and be eaten: Food chains
In nature, short-term survival depends mainly on the organism finding sufficient food for its needs, and preventing itself becoming dinner for something else. Animals will choose and prefer foods which are for them easily caught, palatable and of a suitable size for eating. The food must provide more energy than is expended in its hunting, capture and eating. For example, a lion eats large prey such as zebra or young elephant, not ants, whereas a spider may eat tiny prey such as flies. Food chains All food chains start with a producer. The arrows in the food chain below depict the direction in which energy and nutrients flow, i.e. the arrow always points from the eaten to the eater. Here is an example of a food chain:
The grass is the producer. It makes sugars using carbon dioxide, water and sunlight, and then uses other minerals from the soil to convert these into proteins and other organic substances. The first consumer is always a herbivore (in this instance, the grasshopper) and it is called a first order consumer, with successive members of the food chain being called in turn second, third and fourth order consumers (field mouse, snake, owl). Affecting
the food chain Any break in the food chain will have repercussions at all higher levels of the chain (for example, starvation) as well as resulting in higher numbers at the lower levels of the chain (because they are not being eaten). Pond:
Sea:
Energy in the food chain It is less wasteful of energy for humans to eat producers such as grains, fruit and vegetables, than to eat consumers such as meat, fish and eggs. In third world famine situations, therefore, eating meat is a luxury. Food webs
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