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Part XVI : Seasonal Changes in animal Populations

How Do the Animals in the Biosphere Change from One Season to Another?
Insects in Spring

Topic Chapters Index

 

Part of a crapauduct billboard © Paul Billiet

Part of a crapauduct billboard © Paul Billiet

In France, the Sologne area is known for its many lakes. In the spring, there are vast numbers of frogs and toads that cross the roads in order to get to the lakes to breed. These large numbers cause road accidents. Along a highway south of Orleans, structures called "Crapauducts " have been built. These are tunnels that allow the amphibians to cross safely by going under the road.

 

Frog © Paul Billiet

 

The following series of drawings shows the development of the tadpole into a frog. This change is referred to as metamorphosis.

Frogs' eggs © Shirley Burchill Frogs' eggs
Newly-born tadpole © Shirley Burchill Newly-hatched tadpole
Two to three day old tadpole © Shirley Burchill Two or three days after hatching
Three week old tadpole © Shirley Burchill Three weeks after hatching
Two month old tadpole © Shirley Burchill Two months after hatching
Three month old tadpole © Shirley Burchill Three months after hatching

 

 

SEASONAL CHANGES IN ANIMAL POPULATIONS

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Animals in Spring - a time to reproduce and increase in numbers

Spring is a time when food is plentiful and the environmental temperatures are suitable for rearing young. In order to have young, the adults must reproduce. In order to find a mate or a suitable place to lay eggs, the adults must sometimes move over long distances. The birth of the young increases the numbers of the species in the habitat. The young then start to move and spread out to colonize the habitat.

 

Movement of Frog Populations in Spring

 

Frog © Paul Billiet

 

During the winter, frogs either lie in the mud at the bottom of ponds or move into moss or holes in the ground where their bodies will remain damp. They pass the winter months in a dormant state.

In the spring, the adult frogs of a population will move towards water in order to mate. The frogs know instinctively to return to a specific body of water to lay their eggs. This instinct will cause the frogs to take risks to get to the water. Sometimes this means that the frog population will go from one side of a highway to another.

When they arrive at their destination male and female frogs call to one another. Each species has its own particular set of sounds. This ensures that individuals of the same species find each other, as there may be many different species of frogs and toads present at the same location.

 

Drawing of mating frogs © Shirley Burchill

Drawing of mating frogs

 

The frogs mate in the water. The male moves onto the back of the female and holds her firmly by placing his front legs around her body. The male will stay in this position for a number of hours. When the female's eggs are released into the water the male releases his reproductive cells (sperm) at the same time.

Each fertilized egg immediately develops a layer of protective jelly around it. The developing tadpoles are visible through this jelly layer. After about ten days, the tadpoles start to wriggle out of the eggs.

When metamorphosis is complete the young frogs climb out of the pond. They remain close to the water, hiding in damp vegetation. They feed on insects that they catch with their long sticky tongues.

 

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