Invertebrate Cave Fauna 
93 
cave invertebrates is microorganisms (see below). The richest sources of 
microorganisms are dung near entrances and decaying arthropod 
remains in aphotic passages (Dickson and Kirk 1976). Fungi are more 
concentrated and patchily distributed than bacteria, and fungi are also a 
more important food source, perhaps because they are concentrated. 
Besides serving as a substrate for microfungi, dung and dead 
animals are important food in their own right and attract a wide variety 
of invertebrates. Peck (1973) has also used human dung as a very 
effective bait for cave invertebrates. 
Plant detritus may also be an important food source. A layer of 
mud and finely divided leaves, often rich in oligochaetes, is deposited in 
many caves by slowly receding floodwaters. Such areas often have a rich 
fauna. In caves subject to severe, rapid flooding, piles of twigs and 
leaves are left behind. On these resource patches is a relatively distinct 
fauna that will be described below. 
Food in streams is almost entirely allochthonous in origin. Stream 
detritus is usually divided into coarse particulate organic matter (CPOM 
> 1 mm) and fine particulate organic matter (0.0005 mm < FPOM < 1 
mm) (Cummins and Klug 1979). By convention, organic matter smaller 
than 0.0005 mm is considered dissolved (DOM). CPOM is a substrate 
for microorganisms. 
Resource Levels 
Although there is a great deal of indirect evidence of food scarcity 
in caves, there have been few direct measurements of resource levels in 
caves. Many of the physiological and morphological changes associated 
with isolation in caves (reviewed by Culver 1982) make sense only in the 
context of a relatively stable, food-poor environment. It is obvious to 
anyone visiting a cave that at least the standing crop of resources is very 
low indeed. 
Dickson and Kirk (1976) have provided direct evidence from Old 
Mill Cave in Montgomery County. They found that, for the most part, 
resource levels were lower in the cave than in forest soil, but there are 
exceptions. Dung in the entrance and mud floors with chitin remains 
had high plate counts. Thus food is scarce and very patchy. Dickson 
and Kirk (1976) also found that fungi are correlated with abundance of 
the terrestrial macrofauna whereas bacteria are not. This may help 
explain why wet passages have more fauna than dry passages, where 
fungi are relatively uncommon. 
There remains the question of how much food is actually available 
to cave animals. The best comparative study is that of Peck and 
Richardson (1976), who compared stomach contents of the “cave 
salamander” Eurycea lucifuga Rafinesque from entrance and dark zones 
of caves in Tennessee and Alabama. Salamanders collected at the 
