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Size misleads: Large mammals are also vulnerable

Size misleads: Large mammals are also vulnerable don't go by their size. Large mammalian carnivores are a vulnerable lot. A paper published recently says that they constantly face the threat of extinction because their body mass follows a particular pattern of energy intake and expenditure and also because they do not find their food easily. The study revealed that larger carnivores are reliant on abundant large prey and hence their vulnerability to extinction.

The study, published in PLoS Biology (Vol 5, No 2), says that large carnivores have an upper size limit of about 1,100 kg, above which the energy required outweighs the benefits of prey capture. As carnivorous mammals increase in size their feeding preferences change. Also, small carnivores (less than 15-20 kg) feed mostly on prey smaller than themselves whereas large carnivores favour prey around their own size.

Researchers calculated energy budgets by recording energy expenditure and feeding rates of different species to determine why this transition occurs. They found that smaller prey is plentiful and easier to catch but not sufficient for large carnivores. Their data shows that catching large prey is more efficient because large carnivores burn more than twice the energy per day in hunting but it is compensated with the catch. The study notes: conservation must look at many such biological factors leading to carnivore extinction.

Studies carried out earlier show that the energy requirement for large animals like lions and polar bears is two to three times higher than expected for mammals of a similar size. This limits the ability of these animals to counteract the shortfalls in prey abundance. Energy conserving behavioural adjustments minimise energy loss for these larger mammals. For instance, lions spend over 90 per cent of their time inactive while polar bears hibernate for short periods. But there is a limit to which animals can reduce their energy requirement. Their problems compounded by habitat loss and poaching have put them in jeopardy. Fossil records also suggest that big, fierce animals are the first to suffer in such times.

In India the Asiatic lion has been the attention of several conservation programmes.