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Directions (Q. 61-65):
Read the passagecarefully and answer the questions given belowit. Certain words/phrases are given in bold tohelp you locate them while answering some ofthe questions.
Sloths are not exactly renowned for theirenergetic lifestyles, but the three-toed versionof the animal takes lethargy to a whole new level.Unlike its two-toed relative, which forageswidely if slowly across the tree tops, it lives outits life in as little as 3,000 square metres. It hasthe slowest digestive rate of any mammal, andabout half the metabolic rate typical for its mass – for it maintains a low body temperature evenwhen allegedly active.
Once a week, however, it takes a gamble. Itclimbs slowly down from the canopy, makes asmall hole in the ground, and defecates. This ishazardous. Being caught on the ground by apredator such as a coyote or a feral dog is theleading cause of death amongst sloths. Andeven if it avoids being eaten, the trip consumes8% of its daily energy budget. Given that twotoedsloths happily relieve themselves from thesafety of the canopy, the three-toed’s fastidiouslavatorial habits are puzzling. But a studypublished in the Proceedings of the RoyalSociety, by Jonathan Pauli of the University ofWisconsin-Madison and his colleagues, notonly seems to solve the mystery, but also shedslight on one of the most intriguing cases ofmutualism in the animal kingdom.
The actors in this drama are the slothsthemselves, the algae and fungi that live in theirfur (and which give sloths their dilapidated,green appearance) and a peculiar species ofmoth that lives in this mobile ecosystem. Slothsrely on the algae for part of their food, for theseprimitive plants (whose combined mass is about2½%of the sloths’s body weight) are farricher in fats than the leaves which form thebulk of the animal’s diet. When a sloth groomsitself, it is therefore also feeding. Indeed, thenutrition the algae provide may be the differencebetween life and death, for several studiessuggest that even when lazily grazing thecanopy, a three-toed sloth expends more energythan it takes in from the leaves it is consuming.
The algae, for their part, rely on the sloth forshelter. The strands of its fur have special crackswhich trap rainwater and provide an idealenvironment for them. But the algae also relyon the fungi and the moths–for when the mothsdie, the fungi decompose them, and in doing sorelease nitrogen-rich compounds which fertilisethe algae. The moths, however, though they matein the sloth’s fur, do not spend their whole livesthere. And this, Dr Pauli found, is where theanimal’s weekly visits to the ground come in.
Read the passagecarefully and answer the questions given belowit. Certain words/phrases are given in bold tohelp you locate them while answering some ofthe questions.
Sloths are not exactly renowned for theirenergetic lifestyles, but the three-toed versionof the animal takes lethargy to a whole new level.Unlike its two-toed relative, which forageswidely if slowly across the tree tops, it lives outits life in as little as 3,000 square metres. It hasthe slowest digestive rate of any mammal, andabout half the metabolic rate typical for its mass – for it maintains a low body temperature evenwhen allegedly active.
Once a week, however, it takes a gamble. Itclimbs slowly down from the canopy, makes asmall hole in the ground, and defecates. This ishazardous. Being caught on the ground by apredator such as a coyote or a feral dog is theleading cause of death amongst sloths. Andeven if it avoids being eaten, the trip consumes8% of its daily energy budget. Given that twotoedsloths happily relieve themselves from thesafety of the canopy, the three-toed’s fastidiouslavatorial habits are puzzling. But a studypublished in the Proceedings of the RoyalSociety, by Jonathan Pauli of the University ofWisconsin-Madison and his colleagues, notonly seems to solve the mystery, but also shedslight on one of the most intriguing cases ofmutualism in the animal kingdom.
The actors in this drama are the slothsthemselves, the algae and fungi that live in theirfur (and which give sloths their dilapidated,green appearance) and a peculiar species ofmoth that lives in this mobile ecosystem. Slothsrely on the algae for part of their food, for theseprimitive plants (whose combined mass is about2½%of the sloths’s body weight) are farricher in fats than the leaves which form thebulk of the animal’s diet. When a sloth groomsitself, it is therefore also feeding. Indeed, thenutrition the algae provide may be the differencebetween life and death, for several studiessuggest that even when lazily grazing thecanopy, a three-toed sloth expends more energythan it takes in from the leaves it is consuming.
The algae, for their part, rely on the sloth forshelter. The strands of its fur have special crackswhich trap rainwater and provide an idealenvironment for them. But the algae also relyon the fungi and the moths–for when the mothsdie, the fungi decompose them, and in doing sorelease nitrogen-rich compounds which fertilisethe algae. The moths, however, though they matein the sloth’s fur, do not spend their whole livesthere. And this, Dr Pauli found, is where theanimal’s weekly visits to the ground come in.
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