Caves Have Their Own Weather And Almost No Food

A cave is one of the few places where the physical conditions barely change and the food supply is almost entirely imported. Both facts shape everything living there.

The temperature settles and stays

Beyond the entrance zone, rock buffers the daily and seasonal swings outside. Deep passages hold close to the local annual average temperature throughout the year.

Humidity behaves similarly, sitting near saturation in most systems. There is no drying wind, no frost and no summer heat to force organisms into seasonal cycles.

That stability is why caves preserve things. Bones, sediments and formations survive because nothing weathers them, which also makes them archives of past climates.

Air moves for reasons of density

Caves breathe. Where a system has openings at different heights, the difference in density between cave air and outside air drives a draught through the passages.

In winter the cave is warmer than outside and air rises out of the upper entrance; in summer the flow reverses. Cavers use these draughts to find connections between systems.

The moving air also carries moisture and carbon dioxide, which controls where formations grow and where they dissolve back again.

Nothing grows without light

There is no photosynthesis in the dark, so a cave produces essentially no food. Everything that lives there depends on material arriving from the surface.

That arrives as flood debris, as leaf litter washed down shafts, and as droppings from bats and birds that feed outside and roost within. Each is a concentrated food source.

A few systems run instead on bacteria that draw energy from minerals in the water, which supports communities entirely independent of the surface.

Scarcity produces a particular kind of animal

Species restricted to caves tend to lose pigment and eyes and gain long sensory appendages. Both changes follow from an environment where sight is useless and touch is not.

They also live slowly. Low food means slow growth, few young and long lives, and populations that recover very gradually from any loss.

Many are confined to a single system, because a cave is an island for anything unable to cross the dry rock between one drainage and the next.

Visitors change the conditions themselves

Bodies add heat, breath adds carbon dioxide and moisture, and lighting adds energy where there was none. Show caves develop algae around lamps for exactly that reason.

Mud carried in on boots brings nutrients and organisms, and traffic compacts sediment that took a very long time to accumulate.

Restricting numbers and cleaning equipment between systems addresses both problems, and the second matters most where diseases can be transferred between bat populations.