Cave Biology

There are several ways to look at cave biology and the ecology of Fisher Cave. The ecosystem approach is a useful beginning. In general, an ecosystem consists of biotic and abiotic elements interacting, while energy flows and nutrients cycle through the system. A cave is a low ordered system--in other words, it is relatively simple. First of all, caves lack the producer (or first trophic) level: there are no plants. Surface systems are usually diverse and complex, and thus stable. Caves, on the other hand, have low stability and are vulnerable to disturbance.

As for trophic webs (that is, food chains), caves have a detritus food chain, not a grazing chain (see Figures 21 & 22). The pathway from the base of the web is the breakdown of organic material, not plant-grazing. Energy is limited in caves: it comes second-hand from the surface, via a relatively small quantity of detritus. The conversion of energy from one level to the next is inefficient. Whereas most surface ecosystems convert energy at roughly a 10 percent rate (for example, from plant to herbivore to carnivore), in caves the conversion rate is about 2.5 percent.

In a nutshell, a cave ecosystem is characterized by ecological simplicity, scarcity of energy (and thus food), and climatic stability.

Let's look at a typical trophic web in a cave: at the first level are autotrophs, which can take inorganic raw materials and "build" an organic body. Outside of caves, plants (using photosynthesis) are a prime example of autotrophs. Near cave entrances, where sunlight still reaches, moss, ferns, and algae grow. Deep in the cave, however, a process called chemosynthesis is the only way to go. Bacteria may, for example, convert clay minerals and use the resulting release of energy. These "chemotrophic" bacteria may not be the most obvious cave organisms, but they are the most common.

Chemotrophic iron bacteria (Perabacterium spelei) can take carbon and iron carbonate from cave walls, and nitrogen from the air, and live off the conversion to ferrous oxide. Sulfur bacteria are present in caves with pyrite and other sulfide minerals. Nitrosomonas and Nitrobacter are two bacteria that decompose nitrogenous organicmatter. It is likely that the nitrate of saltpeter derives from these bacteria breaking down the urine of the pack rat, which leaves a urine trail to help it navigate between the cave and surface.

Other amazing bacteria include Clonothrix putealis, a manganese-precipitating bacterium, and Macromonas bipunctata, which helps convert rock minerals to moonmilk. Moonmilk can be wet like cream cheese, or dry like powder. There are nine varieties, of which calcite is the most common. The biological explanation involving Macromonas bipunctata is not the only possibility; moonmilk may instead be a chemical product of bedrock deterioration.

At the next level, all these chemotrophs may be food for protozoa, flatworms, or isopods. Detritus (bat guano, other feces, dead organisms) become food for animals such as other bacteria, fungi, rotifers, flies, beetles, gnats, hellgramites (Dobsonfly larvae), crustaceans, millipedes, mollusks, annelid worms, or nematode worms.

Above that (the pyramid gradually narrowing), a cave may have spiders, pseudoscorpions, predatory beetles, planaria, crayfish, cavefish, frogs, or salamanders.

In the near surface-like conditions at the cave entrance, snails and harvestmen, and carnivorous web worm larvae may thrive. Ferns and moss grow at the cave dripline in the cool, moist conditions (which represent glacial relict conditions). Black rat snakes may use the coolness of the entrance and also find prey.

Cave organisms can be placed in three categories: troglobites, troglophiles, and trogloxenes. Troglobites are "obligative cavernicoles"--they can live only in caves. Often in these creatures we see a regression of pigment and photoreceptors, longer and more slender appendages, ultra-sensitive sensory structures, less fecundity, and larger yokes in egg-layers. Contrary to what many people think, troglobites are only a small percentage of cave fauna. Troglophiles may complete their life cycles in a cave, but are not confined there. On the surface, these animals may occur in habitats similar to caves, in sheltered, cool, and moist places. Trogloxenes spend only part of their life cycles in caves. A fourth category is accidentals that may wander, fall, or be washed into caves. DNR cave biologist Bill Elliott reported in 1999 that "Missouri has about 21 species of terrestrial troglobites and about 40 species of stygobites (aquatic troglobites)."

The limiting factors of food, temperature, and humidity will select which organisms can live successfully in a cave. Troglobites need little food, and in fact would be outcompeted for food if there were suddenly an abundance of it. Troglobite physiology means these creatures get by at a very low metabolic rate and are not required to keep their internal temperatures high. Some animals also rely on high relative humidity. Salamanders need humid air to keep their skin moist for breathing.

In a cave, nutrients enter in a limited number of ways:

1. deposits from trogloxenes (bat guano, other feces)
2. dead bodies of animals
3. organic matter via sinkholes
4. wind-blown particles
5. rain carrying organic particulate matter, by way of diffuse recharge, or general seepage through rock, and discrete recharge, a single, relatively large source of water, ephemeral or not, possibly a joint or parting
6. floods
7. cavers

The above represent the biotic elements in a cave ecosystem. The abiotic elements are the non-living, the conditions of the cave itself. It is convenient to divide the cave into zones (see Figure 23), based on light, temperature, and humidity. From the outside moving in, first is the entrance zone, at the mouth of the cave.

Next is the twilight zone, where there is some light. Temperature and humidity vary considerably depending on surface weather. Life here is diverse, with a variety of troglobites, troglophiles, and trogloxenes. Finally, deeper into the cave, is the dark zone, where no light penetrates. This dark zone may be subdivided into the variable and constant temperature zones. In Missouri, the constant temperature zone is usually 55-60° F.

Within these zones animals will appear with some predictability, depending on the species. Obviously algae grows only where there is light, and epigean (surface-dwelling) snails will feed only where the algae is abundant in the entrance zone and first part of the twilight zone. Fisher Cave also hosts a troglobitic snail, Fontigens aldrichi.

Caves also have various macrohabitats that certain species will prefer. A drip pool, lake, stream, the clay floor, the cave wall and ceiling, a guano mound, or an accumulation of terrestrial detritus may also serve as habitats. These don't seem very "macro," but there are even smaller habitats, such as the surface of a drip pool, or a patch of fungus on a guano mound.

Cave variation

What are temperatures in a cave? Why is Fisher Cave 56º F in the constant-temperature zone? Why are Missouri caves cooler than Texas caves? As a rule of thumb, the temperature of a cave in the constant-temperature zone is the mean annual surface temperature (MAST) of the cave's area (see Figure 24). Especially in the relatively flat central U.S., latitude will mainly determine the MAST, so Texas caves will be warmer than Missouri caves, which will be warmer than Wisconsin caves. But cave temperatures in the constant-temperature zone can vary somewhat from MAST (see Figure 25). Possible reasons for a temperature different from the MAST are:

· altitude of the cave (a major factor for western U.S. caves)
· north- or south-facing entrance
· cave in valley or on exposed surface
· configuration of cave passages
· presence of water

Airflow in a cave has important biological implications. At least two species of cave crickets use air currents in orienting themselves toward and away from entrances. Changes in airflow, temperature, and humidity may be seasonal or daily cues for other animals. In Fisher Cave, airflow was measured on July 20, 1999. At different stations, and as deep in the cave as the ballroom, the flow was consistently at 30 cfm (cubic feet per minute). Unfortunately, this isolated figure, with no baseline data, cannot tell us much about the cave. We know that airflow can change ambient temperatures and affect roosting and hibernation of bats. In winter, Fisher Cave expels air; this is the time of maximum air exchange.

Rick Clawson, a bat researcher for the MDC, theorizes that recent warm winters in Missouri have increased twilight-zone temperatures for hibernating Indiana bats. The cold winter of 2000-2001 may improve conditions for Indiana bats and other species, and--though this is speculative--lead to a population increase.

List of Fisher Cave species

 Mammals  Birds
 little brown bat  eastern phoebe (at entrance)
 big brown bat  rough-winged swallow (at entrance)
 eastern pipistrelle bat  eastern screech owl
 gray bat (endangered)  
 Indiana bat (endangered)  Other Vertebrates
 northern long-eared bat  fish (temporarily during floods)
 black bear  
 groundhog  Invertebrates
 raccoon  bacteria
 pack rat  fungi
 white-footed mouse  fungus gnat (Family Mycetophilidae)
 eastern mole  fly (Family Heleomyzidae)
 Amphibians  beetle
 cave salamander  worm
 dark-sided salamander  cave cricket
 redback salamander  spider
 long-tailed salamander  snail
 slimy salamander  amphipod
 green frog  isopod
 Pickerel frog  springtail
 American toad  millipede
   herald moth (Scoliopteryx libatrix)
 Reptiles  web worm
 black rat snake  harvestman

Note on species list

For the sake of brevity, this Fisher Cave species list is somewhat general. For mammals, amphibians, reptiles, and birds, the list is precise as to species. For invertebrates, it is a starting point for naturalists who want to learn more. Bacteria, fungi, and beetle species will be more accurately described in resources found in the naturalist office See, for example, the hanging file called "Fisher Cave, biology." A note on salamanders: the long-tailed salamander is a subspecies of the dark-sided salamander.


Bats are fascinating to most naturalists, and they are fascinating to most Fisher Cave visitors. You will see bats on most tours, though mid-summer is the most difficult time. If you do the afternoon tours, a big help is to learn of bat sightings from the naturalist preceding you. Six species of bats use Fisher Cave. Two species are endangered (the Gray and Indiana), one is rare in this area (northern long-eared), and the other three (little and big brown, eastern pipistrelle) are common.

Bat roosts are appropriate to the season; bats need warm caves in summer (for growth and digestion) and cool ones in winter (for torpor). Keep in mind that bats mate in the fall, and hold sperm through the winter. Fertilization and gestation begin after hibernation. Optimum temperatures vary from species to species, but in all cases temperature is a crucial factor for bats.

Bats may select microspaces within a particular cave (such as domes for warmth) to find their preferred temperature. Bats, according to one experiment, may be accurate in judging roost temperatures within 0.8 C. Clustering plays a role in temperature regulation, too.

Intermediate-temperature caves may be suitable for bats in spring and fall, but may be too warm in winter and too cold in summer. The message here is that bats have particular needs when it comes to using caves--not just any cave will do. The distribution of suitable caves may thus be important in determining overall species distributions.

World-renowned bat researcher Merlin Tuttle has studied the implications of temperature for gray bats. From the journal article Variation in the Cave Environment,

Additionally, the endangered gray bat (Myotis grisescens), a species which uses caves year-round, appears to be limited in its north-south distribution primarily by the absence of warm caves for rearing young in the north and by a lack of cold hibernation sites in southern caves (Tuttle, 1975, 1976). Few caves anywhere within its range provide roosts of appropriate temperature, and even in Alabama, where gray bats probably were once most abundant, this species is not known to have ever occupied more than 2.4 percent of the area's 1635 known caves in summer or 0.l percent in winter (Tuttle, in press). This is despite the fact that this species is behaviorally able to reduce thermoregulatory costs during summer by clustering together in large numbers in ceiling domes or in restricted passages where heat can be trapped (Tuttle, 1975), thereby utilizing otherwise marginal caves. The structure of caves-and the temperature gradients within-become extremely important in determining bat use. Migration is necessary because one cave usually can't provide the range of temperatures a bat species requires during the course of a year.

There are many implications here for bat conservation. Protecting a variety of caves, especially the most structurally and thermally complex, is crucial. Gray bats leave caves only to feed and migrate--many other species roost in trees in summer, but not grays. Many bat researchers have thought that gray bats will not tolerate full gating of their maternity caves. The best we can say at present is that it is unclear whether a maternity colony will use a gated cave. This is all the more important because so few Missouri caves--only 68--have been historically suitable for gray bat maternal roosts. Exactly half of those, including Fisher Cave, have been abandoned.

Grays are sensitive to aquatic pollution. They select caves within two (and usually within one) kilometer of a river or reservoir, and depend heavily on mayflies. (Not that reservoirs benefit gray or other bats: on the contrary, they flood caves and destroy bat habitat.) In summer they use several caves, with a home range of 50 km. Grays are also affected when water corridors are deforested. They may feed in the forest during cold spring weather, a critical period, and they also use the cover of the tree canopy to reach the river in the evening to avoid owl predation. Having few suitable caves means the species is highly vulnerable.

As we have said, different bat species have different needs. Eastern pipistrelle bats--common in Meramec State Park--prefer moist caves to prevent dehydration, and are solitary. To reach a warm, moist area (warm air can hold more water), pipistrelles tend to go deeper into caves during hibernation. They hibernate locally, and research shows they travel a maximum of about 50 miles. It's uncertain how they are affected by human disturbance. Each disturbance may cause a loss of two to four weeks of stored fat (10-30 days, according to Tuttle). It's easy to see how one or more major disturbances could become a death sentence for some individuals. If stored fat runs out prematurely, a bat will be forced to seek food outside the cave earlier than it may be available.

Some hibernation arousals are natural, however. Some bats may arouse every 12 days naturally, on the average. Arousals may account for 75 percent of winter energy expenditure. Arousals are also unpredictable: they may happen anytime between 30 minutes and eight hours after the disturbance. If awakened, a bat's heart rate may jump from 25 beats per minute to 100 or more. During hibernation, a bat's metabolic rate is depressed by as much as 99 percent. But despite this low rate, arousals will result in a weight loss that may be 20-30 percent for little brown bats in winter (with gestating females losing most, then non-gestating females, then males).

Bat surveys are done annually by park naturalists to monitor populations here. Bear, Fisher, Hamilton, Hamilton Spring, Little Hamilton, Mushroom, Pratt Spring, Sheep, and Wildcat caves have all been inventoried; though some not regularly. To give you an idea of local populations, here are some partial results. For complete information, look under "Bat Inventory" in the hanging files in the naturalist office.

Bear Cave in February 1996
136 eastern pipistrelle; 130 little brown; 130 Indiana; 61 unknown
Copper Hollow Sinkhole Cave in December 1995
31 eastern pipistrelle
Fisher Cave in February 2000
132 eastern pipistrelle; 126 little brown; 20 big brown; 12 northern long-eared; 3 Indiana; 20 unknown
Hamilton Cave in February 1999
437 eastern pipistrelle; 31 little brown; 15 northern long-eared; 6 big brown; 1 Indiana


Black bears can go surprisingly deep into caves to find good den sites. Bears even follow trails through caves that may have been made generations earlier. The ability of bears to negotiate even extremely difficult passages should not be underestimated! Accounts of bears denning under tree roots show that they can tolerate tight spaces.

The first thought of many people is that bears must frequently get lost in caves, but that is probably rare. A bear's sense of smell is superb, and it can find its way back to the cave entrance through a combination of following a scent trail, remembering passages it has come through, and directly smelling outside air. Most bear bones found in caves are probably from animals that die during winter sleep.

Prehistoric black bears were larger than modern black bears, and short-faced bears were even larger. Remains of bears have been found in many caves, and Fisher Cave is no exception. (The only other skeletal remains found in Fisher Cave belonged to a male raccoon.) In 1986, a park naturalist discovered bear bones partially embedded in the clay floor of the Bear Claw Marks Room (or Intermediate Room) midway along the passage to the Hugh Dill Room. Paleontologist Blaine Schubert of the Illinois State Museum tested the bones in September 2000, and determined that they belonged to an American black bear that died less than 500 years ago. A possible paleo-entrance could have provided a way into this room in the past. A winding, upward passage leads from the southeast corner of the Bear Claw Marks Room, and emerges into a space where inch-diameter tree roots can be seen. This spot may be only 5-10 ft. below the surface.

Eastern wood rat or pack rat

Fisher Cave has considerable evidence that pack rats (Neotoma floridana) have lived here, even in the dark zone. In the twilight zone they use large light-absorbing eyes, but they may primarily rely on long facial whiskers called vibrassae to move along cave ledges and walls. They can find their way out of the dark zone by following a scent trail of urine. Their droppings become nourishment for beetle larvae, fungus, and indirectly, insects.

In Fisher Cave there is an excellent spot along the trail to see a pack rat den. It is located shortly before the rimstone dam on the left, about 3-4 feet from the cave floor. A stop here would only work with small groups, perhaps 6-8 or fewer. You can see hackberry seeds, stick-like bat bones, and a few pieces of aluminum foil (a pack rat giveaway). Fisher Cave, in fact, has so many pack rat nests--mainly unseen--that you could spend hours locating them. Generally, look along passage edges. The bear bed just beyond the stoop walk, for example, is filled with pack rat material.

Guide to finding animals

It's best to enlist your visitors in finding animals. This heightens their sense of discovery. Because you are first in line, have the best lights, are a trained naturalist, and know the cave, you will generally find the most animals, but you can make it seem as though it is a mutual discovery for you and the visitors in the front of the group. Young people are often incredibly observant and may be sharper-eyed than you.

Frogs: twilight zone, in and next to the cave stream, as far back as the main chamber
Salamanders: same as frogs, and extending into the dark zone (as far back as the ballroom and even Hugh Dill room); you will mainly see cave salamanders, with occasional sightings of dark-sided salamanders
Amphipods: in pools in cave stream along entrance passage; sometimes they congregate, but we can't always tell whether that is because they have found a food source, are responding to dry conditions, or are breeding
Bats: could appear anywhere in cave depending on species and time of year, including the entrance passage, though they tend to be in the main chamber
Juvenile salamanders: (species unknown) could be reliably seen every day in the 2000 season in the pool on the backside (side farthest from ballroom) of the stalactiflat/flowstone area; both direct and indirect (larval) juvenile stages are seen
Snails: trogloxene species on walls and ceiling of cave mouth; troglobitic species found in stream throughout cave

Meramec River

Today the Meramec River is one of seven free-flowing rivers in Missouri. (The others are the Big Piney, Little Piney, Gasconade, Eleven Point, Jacks Fork, and Current rivers). The water of the Meramec River is also relatively clean because the river runs through a heavily forested Ozark landscape without intensive agriculture. The river's upper basin is 75 percent forest, 20 percent grassland and pasture, four percent cropland, and one percent urban area. Of the upper-basin forest, the Department of Natural Resources (DNR), MDC, and the U.S. Forest Service own 62 percent.

The Meramec is one of the most diverse rivers in the country, and possibly the most diverse in the Midwest. It is the 7th longest river in Missouri at 194 miles, and it drops 800 feet from its headwaters in Dent County. Its major tributaries are the Courtois (pronounced Code-away by the locals), Huzzah, Bourbeuse, and Big rivers (see Figure 26). The Meramec basin has about 600 caves and 300 springs, and, remarkably, 20 percent of its base flow is from springs and cave streams. This carbonate-rich water helps explain why the Meramec has the highest mussel diversity in the state, at 45 species. The yearly high flow is generally in April, with low flow in August.

Meramec dam controversy

Proposals to dam the Meramec River have been in the works since the New Deal days of the 1930s. In 1938, after major flooding on the Ohio River, the U.S. Army Corps of Engineers planned a dam near the junction of the Meramec and Big rivers, among more than 200 other projected dams in the Ohio and Mississippi basins. Flood control, barge navigation, and recreation were the reasons to build, but the Meramec dam was put on hold because of lack of funding. After World War II, another major proposal was put forward in 1949, but two conservation-minded Missouri politicians, U.S. Representative Clarence Cannon and Governor Forrest Smith, worked to block dams in the Meramec basin. (Throughout this four-decade history, proposed dam sites changed often.)

In the 1960s, however, the Army Corps of Engineers once again promoted the Meramec dams, and the U.S. Congress came through in 1966 with funds. By this time the proposal had grown to include 31 dams in the Meramec watershed (two on the Meramec, two on the Bourbeuse, three on the Big, 12 small dams on tributaries, and 12 catch basins in the headwater drainages). One dam site was located just upstream of the park, with the reservoir to be called Meramec Park Lake (see Figure 27). The reservoir would have covered 42 miles of the Meramec River (plus 12 miles of Huzzah Creek and nine miles of Courtois Creek), and inundated 23,000 acres of land. Hickory Ridge Conference Center is the former visitor center for the dam, built by the Army Corps of Engineers.

The Meramec dams were not without opposition, however. Farmers, anglers, environmentalists (led by the Sierra Club), cavers, and commercial cave operators coalesced on one side of the debate. Business interests, represented in the Meramec Basin Association, formed the other side. Powerful arguments were made that Onondaga Cave--one of the nation's finest caves--would be partially flooded and inaccessible to visitors. A dammed river would also become more static, with no floods, changing channels, or sediment deposit in certain segments. Fewer habitats would be available for wildlife, and around the reservoirs, smallmouth bass, darters, sculpins, and paddlefish would likely decline. Indiana bats, then being considered for protection under the Endangered Species Act, were also threatened. And from an engineering point of view, the caves in Meramec State Park could potentially weaken the dam structure.

After years of considerable political wrangling, a non-binding referendum on August 8, 1978 settled the matter. Residents of the city of St. Louis and the 12 counties in the Meramec basin were able to vote. The dam lost 64 percent to 36 percent, thanks mainly to the urban vote of St. Louis. Franklin County split its vote, and a strong majority in Crawford County favored the dam.

Missouri's senators pushed the deauthorization bill through Congress, and President Reagan signed it on December 29, 1981. The Corps of Engineers sold back some of the land it had acquired to the former owners, and the Huzzah State Forest and Meramec and Onondaga Cave state parks received the rest of the project acreage. A scenic easement along the river prevents construction that would spoil the beauty of the Meramec.