A self-contained world of waste
In the dark recesses of Carlsbad Caverns, an entire ecosystem is built upon a single, plentiful resource: bat excrement, or guano. For thousands of years, a massive colony of Brazilian free-tailed bats (Tadarida brasiliensis) has used the cave as a seasonal roost. The population fluctuates, with modern thermal imaging counts ranging from under 70,000 to nearly 800,000 individuals depending on the time of year. Their collective waste has formed immense deposits on the floor of a chamber known as the Bat Cave. In the past, these piles were estimated to be over 40 feet deep. This accumulation of organic material, high in nitrogen, phosphates, and other nutrients, becomes the base of a food web in an environment devoid of sunlight and plants.
The guano piles are not static. Decomposition by bacteria and fungi generates significant heat, raising the ambient temperature of the cave. This warmth, combined with the high humidity, creates a stable habitat for a specialized community of organisms. The ecosystem is driven by a distinct seasonal pulse. During the summer, when hundreds of thousands of bats are in residence, a constant rain of fresh guano provides energy. When the bats migrate south for the winter, the nutrient supply ceases. This creates a feast-or-famine cycle, forcing the guano-dwelling creatures to adapt to periods of scarcity by relying on the vast reserves until the bats return in the spring.
The guano dwellers
Living directly on and within the guano are creatures found almost nowhere else. The community is dominated by invertebrates, many of them flightless or blind. Studies of the guano have revealed large numbers of mites, including eight different types that feed on fungi (fungivores) and four types that are predators. The guano also supports populations of Darkling beetles (family Tenebrionidae), pseudoscorpions, fleas, and flies. Even several species of cave crickets, such as Ceuthophilus carlsbadensis, rely on the guano as a food source.
This isolated world was disturbed by human activity in the early 20th century. Between 1903 and 1923, before the cave was a fully protected national park, extensive mining operations removed an estimated 100,000 tons of guano. The guano was hoisted out of the cave in large buckets, hauled by wagons, and eventually sent by train to be used as a potent agricultural fertilizer for citrus groves in Southern California. This mining directly removed the primary habitat for the cave's unique invertebrate fauna and undoubtedly had a major impact on their populations, which have since been sustained by the guano deposited after the mining ceased.