Sierra de las Nieves has seen many changes. For over 600 years, this area on the Iberian Peninusula was part of the Western Empire of Rome. Following the fall of Rome, the Visigoths ceded control of the peninsula, then known as “Hispania.” The Visigoths in turn were replaced by the Moors (the Berber and Arabic peoples of North Africa), whose nearly 800-year reign left an indelible architectural and cultural mark on the region. The mix of Roman and Moorish ancestry later morphed into the Maquis. These guerilla mountain warriors fought in the Spanish Civil War and remained a thorn in the side of military general and monarchist Francisco Franco until the early 1950s.
Fortresses were built and burned. Languages and religions shifted like windblown grains of sand. All the while, physical science was happening—rainwater interacting with limestone to form carbonic acid-cut caves deeper and deeper into the craggy mountain landscape. All the while, the bats, bugs and other animals that call these caves home remained oblivious to the multitude of cultural and linguistic transformations occurring on the surface.
I cannot escape these ideas and thoughts as I walk the streets of the Andalusian town of Ronda, drive and haul gear through the mountains, and explore the depths of the Sierra Nieves. I remain perpetually awestruck by the gravity of history, humanity, calamity, ecological communities (both on the surface and subsurface) and the immense rugged beauty of this region. And, the caves can be summarized in one word “epic”!
Encompassing over 186 square miles, Parque Natural Sierra de las Nieves is located in the Andalusia autonomous community of southern Spain. Approximately 16 miles as the gull flies from the Mediterranean coast, the park radiates outwardly from Cerro de la Torrecilla (6,296 feet), the highest mountain peak in this range. This part of Spain is less than 50 miles from Morocco. Proximity to Africa, specifically the Sahara Desert, is apparent when the winds howl from the south. Desert dust blankets the landscape in a white haze, the Rock of Gibraltar fades from view, and the nearness of Africa is palpable.
A particularly intriguing aspect of the region is its relationship with goats. Andalusia boasts one of the largest goat populations in Europe (primarily for cheese production). These animals continue to shape the sierras and surrounding mountain landscape. We see goats, cabreros (goat herders), goat houses, and/or evidence of goats with nearly every step we take. As goats in one form or another have roamed these lands since at least the Pleistocene, the mountain meadows and forests seem to may have, at least to some degree, co-evolved with goats.
As for our knowledge of regional cave biology, these systems have been minimally studied, owing largely to the access difficulties for most of these features. Since 2008, a team of cave explorers and university researchers has monitored two winter bat roosts. To date, only one preliminary insect inventory has been conducted. The study revealed at least 24 different cave-dwelling invertebrate species from Sima Gesm cave. This monster of a cave is more than 11 miles long and nearly a mile deep, and characterized by numerous vertical passageways, and requires those accessing this beast to be on rope most of the time.
Many of these caves trap cold air and have become ideal habitats for animals requiring cooler habitats, such as hibernating bats and relict species of a former colder and wetter climate. One such species, Onychiurus gevi Arbea, 2012 (a species of Collembola or springtail), is a relict of a past mountain climate. When the sierras received more precipitation and were frequently snow covered, this animal is believed to have occurred in the soil on the surface. As the climate shifted and the region became more arid, their surface habitat became unsuitable and they ventured underground seeking their “Goldilocks’ spot.” Today, this species is believed restricted to the cave environment. During our investigations, we found this springtail on or near decomposing tree branches, dead insects and muddy cave floors with bat guano—common nutrient sources found within caves.
Our work in the sierras will be conducted over the next two years. Year one is a fact-finding mission of sorts. We are here to examine seven caves, document all wildlife species (vertebrates) encountered, and search for and collect cave-adapted insects, as well as identify areas within each cave for intensive sampling and dial in the logistics for next year’s efforts. Data and information collected from this study will: (1) be used to gain insight into regional patterns of cave biological diversity; (2) make predictions concerning future colonization events of caves by surface-dwelling invertebrate species due to climate change; and, (3) serve as a comparative benchmark to better understand landscape-scale trends regarding how insects form communities in caves of the Mediterranean region.
During our first trip, we visited seven caves and explored a total combined depth of nearly 1,000 feet. Our deepest cave was a vertical shaft nearly 200 feet deep. We collected insects from the estimated deep zone (the deepest, most stable region of the cave where cave-adapted animals typically occur) of each cave and documented the presence of all wildlife species observed, as well as identified habitats for intensive insect sampling and determined how to set ropes and access each cave for the work next year. Among the seemingly most widely dispersed morphospecies was the relict Collembola species (O. gevi found in five caves) and a sac spider of the family Clubionidae (detected in four caves). Categorizing species into definitive groups is slightly premature; we have yet to thoroughly examine the specimens. As is often the case with taxonomy, once we’ve examined our specimens, the groups we presently think may represent one species may actually represent two or more closely related sister species.
Regarding animals with backbones, we encountered bats or evidence of bats in all the caves visited. In one cave, we observed a summer roost of horseshoe bats (Rhinolophus sp.), 100 bats strong. Consisting of four different species in Spain, horseshoe bats may be distinguished from other bats by the horseshoe shape of their leaf-like nose protuberance. Given the bats were observed tightly huddled together, this behavior is suggestive of a maternity colony. However, this has not been confirmed. When we return next year, we plan to catch bats, examine them and determine the roost type. In addition, we encountered one Myotis sp. in a torpor (a shorter duration hibernation) and documented the common toad (Bufo bufo) in two caves.
Particularly fascinating observations included extensive bat bone deposits and bizarre speleothem formations in one of the deep vertical shafts. In two caves, researchers previously documented tens of thousands of bat bones festooning the floors and walls. The occupation by bats likely dates back hundreds to thousands of years, evidenced by the sheer enormity of the bat bone deposits and the flowstone formations containing bat bones crystalized by calcite. In one cave, there was no evidence of recent bat use. This suggests that when surface climate warmed, this shift ultimately rendered the cave unsuitable as a bat roost. Colleagues are currently preparing a paper on these two caves; they will address the aggregations of bat bones, their genesis and the climatic changes that may have occurred.
In the deepest cave examined, we found spectacular rock formations straight out of a science fiction movie. These speleothems looked like giant polypore fungus—the flat fungus commonly seen growing on decaying tree trunks. As we both rappelled and ascended the rope we played a game of hopscotch as we bounced on and around these features often measuring more than one meter across.
While we had a rather tight and demanding work schedule, I did find time to explore Ronda and a few of the other small mountain towns, and soak up the incredibly rich Andalusian culture. As I continue to explore this wondrous planet, I realize that I’m continuously shaped by my explorations and the many unpaved roads traveled. As a cave scientist, this trip was most rewarding in that I’ve added another geographic point of reference concerning how animals form communities underground, which will help me to better understand cave ecosystems at both regional and global levels.
Examining caves around the world enables me to observe patterns at much larger scales, as well as catalog dissimilarities across caves in different geographic regions. This global perspective, both culturally and scientifically, provides me with greater depth (if you will) concerning the formulation of new ideas and hypotheses.
Tomorrow we pack our equipment and return to Madrid. Prior to my departure, I will be examining our specimens under a microscope in the lab, and then prepare the bugs for transport to the United States. My first trip into the depths of the Sierra Nieves was both a successful and memorable experience. We collected over 200 cave-dwelling insects, which will be thoroughly examined over the next several months at my university. And we’ve already started to strategize how best to conduct next year’s ambitious campaign.
Arbea, J. 2012. Review of the genus Onychiurus Gervais, 1841 (Collembola: Onychiuridae) with description of a new cave species from Southern Spain. Zootaxa 3564: 33–46.
Analla, M., Muñoz-Serrano, A. and Serradilla, J.M., 1995. Dairy goat breeding systems in the South of Spain. In (Gabiña, D. ed.), Strategies for sheep and goat breeding. Cahiers Options Mediterraneennes (CIHEAM), pp. 143–154.
P.-Fernández, T.P. and A. P.-Ruiz. 2014. Catálogo provisional de los invertebrados del Sistema Sima Gesm-Sima de la Luz (Tolox, Málaga). Gota a Gota 4: 74–78.