5. Frogs are amphibians. Like all amphibians, frogs are cold blooded, meaning that their body
temperatures change with the temperature of their surroundings. When temperatures drop,
some frogs dig burrows in the mud at the bottom of ponds. They hibernate in these burrows
until spring, perfectly still and barely breathing. Frogs can be found just about anywhere there's
fresh water, on all continents except Antarctica. Though they thrive in warm, moist tropical
climates, frogs also live in deserts and high on 15,000 foot mountain slopes. The Australian
water-holding frog is a desert dweller that can wait for seven years for rain. It burrows
underground and surrounds itself in a transparent cocoon made of its own skin. Frogs' skin is
critical to their survival. Through it, they drink and breathe. Frogs don't swallow water; they get
the moisture they need through their skin. And although frogs have lungs, they rely on the
oxygen they absorb through their skin, especially when they're underwater. Frogs must keep
their skin moist. Otherwise, oxygen does not easily pass through it and the frog suffocates. Even
though frog skin secretes a mucus that helps keep it moist, their skin tends to dry out easily.
which is why they usually stay near bodies of water.
Consider the bar graph comparing the number of frogs in four different habitats. Based on the
information above about frogs, what is the MOST LIKELY factor limiting the frog population?