The study was conducted in the Ibitipoca mountain quartzite province, south of Minas Gerais state, Brazil. The caves in this region were formed and modeled by hierarchically organized drainages influenced by differences between the local water table and the regional base level. The Ibitipoca Mountain belongs to the Andrelândia geological group mainly composed of quartzite rocks of Mesoproterozoic lithostratigraphic age (Auler and Sauro 2019).

The mountain is located within a protected area, with 1,488 ha of extension and altitude ranging from 1,200 to 1,784 m asl. This reserve was created in 1973 and protects epigean fauna and flora and quartzite caves and their fauna (Nobre et al. 2013). The dominant vegetation is grasslands on hilltops and rainforest in the valleys (Figure 1). The climate is tropical (Cwb of Köppen) with mild summers, with dry (May to August) and rainy (August to January) well defined seasons (Alvares et al. 2013). The external temperatures range from 2 to 20 °C and internal caves temperatures range from 12 to 20 °C (Souza-Silva et al. 2013).

Figure 1. 

Borders of the Ibitipoca Estadual Park (A), sampled caves (white dots) and altitudinal layers (red lines 1610–1780, blue lines 1460–1600, yellow lines 1310–1450, green lines 1124–1450, black lines 950–1100 meters). Vegetation types vary from slope forest (B) to grasslands (D and C) on the top of the hills.

Most of the caves in this study were mapped by Silva (2004) using a standardized mapping methodology with a British Cave Research Association (BCRA) – 4C survey grade. Additional information related to the cave extension (for those caves that were not mapped), number and area of entrances were determined during the fieldwork (as in Bento et al. 2016).

The altitude above sea level and geographic position of the caves were obtained with a Global Positioning System (GPS) in decimal degrees (Table 1). Moreover, the width of entrances and linear development of the caves were measured using a laser. The greatest horizontal length of an entrance was considered as width, while the greatest vertical length was considered as height. The cave linear development represented the linear development sampled in each cave since some caves were not sampled throughout their total length (Souza-Silva et al. 2011b).

Species richness and composition of the invertebrate communities were assessed in 20 caves (Table 1, Figure 1). Only one visit to each cave was conducted. Sampling was carried out only once by visual search within the accessible parts of each cave, prioritizing places with organic matter (such as plant debris, carcasses, and guano) and humid soils, cracks, speleothems, water bodies and spaces under rocks. Hand collections were made with the aid of tweezers, brushes and entomological nets (Bento et al. 2016, Wynne et al. 2019). Invertebrates were collected from water bodies with the aid of forceps. In the laboratory, invertebrates were separated into morphotypes (Oliver and Beattie 1996). The sampling time spent in each cave was dependent on the extension of the cave.

The determination of potentially obligate cave species was conducted by identifying the specimens with troglomorphic traits (Christiansen 2012). However, for some specific groups (e.g., Palpigradi, Diplura), other traits were considered, such as the increased number of sensory receptors (lateral organs) (Souza and Ferreira 2012) and an increased number of antennomeres and cercal articles (Sendra et al. 2012). Furthermore, experts on Diplura, Blattodea, and Collembola were consulted to evaluate the degree of troglomorphisms.

Human modifications were determined in relation to uses and impacts. Tourist and religious activities were considered uses while real impacts were trampling, illumination and construction resulting from these activities (Souza-Silva et al. 2015). Impacts were determined for each cave as a function of the presence or absence of visual modifications inside the cave.

The components of beta diversity were calculated using the BAT package developed by Cardoso et al. (2015) in the software R to assess βtotal (overall beta diversity), βrepl (the replacement component) and βrich (the richness differences component) (R Development Core Team 2008).

The average taxonomic distinctness (∆+) analysis was conducted with the software Primer 7 using 297 from the 463 morphotypes because they were identified up to family level (Anderson et al. 2008). We used Phyla (weight 100), Class (weight 80), Order (weight 60), Family (weight 40) and morphotypes (weight 20) as variables for a matrix of morphotypes distribution among caves (Anderson et al. 2008). Previous analysis comparing the group of sampled morphotypes and the above mentioned 297 morphotypes were carried out using a Spearman Rank Order Correlations to test the representativeness of this sub-sample (of species identified until the family level), which revealed regression Rs = 0.93 and p ≤ 0.05.

The Environmental stability of each cave was determined using the Environmental Stability Index (IEA) proposed by Ferreira (2004) (Pellegrini et al. 2016, Bento et al. 2016), which considers the degree of isolation between the cave and epigean environments through a mathematical ratio, calculated as follows. For caves having just one entrance: IEA = ln(AT/EE) and for caves having more than one entrance: IEA= ln((AT/∑EE)/((NE)*(x‒ DEE)/AT))), in which: AT (total size of each cave), EE (sum of the highest and longest measurements of cave entrances using perpendicular lines), NE (number of entrances), DEE (average distance between entrances, taken from one reference entrance).

A non-parametric multivariate analysis (DistLM – Distance-based Linear Model) was used to evaluate the influences of the distance between caves (dist), the extension of the sampled cave (SE), environmental stability (IEA), number (NE) and size of entrances (EE) and altitude (Alt) over invertebrate composition, total richness and average taxonomic distinctness with AICc as selection criteria and Forward as selection procedure (Anderson et al. 2008). The similarity measure based on Bray-Curtis Index was used for fauna composition and Euclidean distance was used for total richness and average taxonomic distinctness in DistLM analysis (Anderson et al. 2008). Jaccard similarity based on presence/absence, specifically as a measure of ß diversity and tested against predictors variables (dist, SE, IEA, NE, EE, Alt) using DistLM analysis. Once the definition of ß-diversity is based on variation in the identities of species (Whittaker 1972), the similarity measures with abundance do not provide a ß diversity measure (Anderson et al. 2008).

The distance-based redundancy analysis (dbRDA) was performed to determine the strength and direction (- or +) of the predictor variables relationship selected by the DistLM routine. A metric multidimensional scaling (MDS) using bootstrap-average analysis was performed to determine the level of variation in species composition within sampled caves with and without stream and to produce two 95% bootstrap regions (Clarke et al. 2014).

Similarity analysis (ANOSIM) one-way layout with pairwise analysis was used to select faunal group formation based on Bray-Curtis similarity using caves with and without streams, frequency classes of cave sampled extension (SE), environmental stability (IEA), number (NE) and extension of entrances (EE) and altitude (Alt) as selected factors. The Similarity Percentages analysis (SIMPER) was used to determining species responsible for sample groupingsrs using Bray-Curtis dissimilarities (Clarke 1993). These analyses were performed in the Plymouth routine in Multivariate ecological research – Primer 7 (http://www.primer-e.com). We also used the Spearman correlation test (R_s) (Zar 1984) to evaluate the relationship between cave physical attributes (SE, IEA, NE, EE, and Alt) and total richness and average taxonomic distinctness. Significant differences of average richness, diversity and taxonomic distinctness among caves with and without stream were evaluated using Mann-Whitney U Test (Sprent and Smeeton 2000).

Caves are located at altitudes between 1270 and 1669 m asl (sd = 150 m). Sampled cave extension varied from 20 to 650 m in length (sd = 202 m), presenting one to six entrances. Surface of entrances varied from 1 to 80 m² (sd = 26 m). Environmental stability varied from 1.4 to 10.93 (Table 1).

We found a total of 12,123 individuals distributed in 463 morphotypes and at least 117 families. The composition considering higher taxa is presented in Figure 2A and Table 2.

The richest higher taxa in the sampled caves were the orders Araneae (100 spp., 21.6% of the total richness) and Diptera (85 spp., 18.35% of the total richness), while Dermaptera, Neuroptera, Gastropoda, and Nematomorpha presented a single species each (0.2% of the total richness). The most abundant higher taxa were the orders Diptera (3,322 individuals, 27% of the total abundance), Araneae (2,164 individuals, 18% of the total abundance), Opiliones (1,462 individuals, 12% of the total abundance) and Coleoptera (1,396 individuals, 11% of the total abundance). The less abundant higher taxa were Odonata, Megaloptera, Dermaptera, Diplura, Ephemeroptera, Zygentoma, Mollusca and Nematomorpha with less than 10 individuals each (0.3% of the total abundance) (Figure 2A).

Figure 2. 

Higher taxa invertebrate abundance, taxonomic diversity (richness) (A) and average taxonomic distinctness (Δ+) (B) in all 20 quartzite caves placed above 1200 m high in Minas Gerais (Brazil).

The average richness of the caves was 39.55 spp. (sd= 21.87). The Bromélias (95 spp.) and Moreiras (75 spp.) caves presented the highest invertebrate richness, contrasting with Martiniano II (18 spp.) and Catedral I (14 spp.) caves, which presented the lowest richness values (Table 1).

Six invertebrate species, distributed in five caves, presented troglomorphic traits.Casas cave had four troglobitic species ((Blattodea (Figure 3B), Projapygidae (Diplura) (Figure 3D), Pselaphinae (Coleoptera: Staphylinidae), and Eukoenenia ibitipoca Souza & Ferreira, 2019 (Palpigradi: Eukoeneniidae) (Figure 3E)), Moreiras cave had two species ((Hypogastruridae (Collembola) species (Figure 3A) and one Projapygidae species (Diplura)). Three other caves had each only one troglomorphic species. Pião and Dobras caves had the same Blattodea species that occurred in Casas cave. Bromélias cave had the Prodidomidae spider Brasilomma enigmatica Brescovit, Ferreira & Rheims, 2012 (Figure 3C).

Figure 3. 

Obligate cave species found in the Ibitipoca Estadual Park, Brazil. A Hypogastruridae B Blattodea C Brasilomma enigmatica (Prodidomidae) D Projapygidae E Eukoenenia ibitipoca (Palpigradi).

The quantitative similarity among cave communities was low (< 41%) and the β_total was 0.952, β_repl = 0.769 and β_rich = 0.178.

Average taxonomic distinctness Δ+ varied between 58 to 70, and 18 caves were placed within the 95% confidence interval of the average taxonomic distinctness (∆+) (Figure 2, Table 3). However, ∆+ decreased with environmental stability (R_S = -0.46, p ≤ 0.05).

The Distance-based linear models (DistLM) revealed in marginal tests that the sampled extension (SE) of the caves (R² = 0.08, AICc = 168.7, Pseudo-F = 1.5071; p = 0.01) was the only predictor determining the similarity of cave communities, both for Bray-Curtis and Jaccard similarities. The two axes of the distance-based redundancy analysis (dbRDA) graphic model captured nearly 52.6% of the variability in the fitted model and 16.4% of the total variation in the data cloud. The first overlay showed that the first dbRDA axis is strongly related to cave sampled extension (SE) (Figure 4). The Distance-based linear models (DistLM) revealed that the sampled cave extension (SE) was also the only predictor influencing variations over species richness (R² = 0.335, AICc = 117.45, Pseudo-F = 9.1066, p = 0.009) of the cave communities. Furthermore, only total richness (R_S = 0.58, p ≤ 0.05) and richness of obligate cave species (R_S = 0.58, p ≤ 0.05) increased with cave extension.

Figure 4. 

Distance-based redundancy analysis (dbRDA) showing the influences of the environmental factors on cave fauna composition in the 20 studied caves. The two axes explained nearly 55% of the variability in the fitted model and nearly 17% of the total variation in the data cloud. The first overlay shows how the first dbRDA axis is strongly related to cave sampled extension.

Finally, Figure 5 shows the two groups formed in ANOSIM between caves with and without a stream (R = 0.262, p = 0.02) and the bootstrap data variation within the 95% confidence interval. Araneae (Mesabolivar sp., Ochyroceratidae spp., Theridiidae sp.), Opiliones (Mitogoniella indistincta Mello-Leitão, 1936), Diplopoda (Pseudonannolene sp.), Ensifera (Endecous sp.), Psocoptera (Ptiloneuridae sp.), Collembola sp., Diptera (Tipulidade sp.), Isopoda sp., Hemiptera (Emesinae sp.) andTrichoptera sp., were the taxa that most contributed for disimilarity between the two types of caves.

Figure 5. 

Metric multidimensional scaling (MDS) ordination plot of the 20 quartzite caves with and without a stream using bootstrap regions for group means around their centroids (triangles). Average (Av).

Organic resources were composed of plant debris deposited close to vertical or horizontal entrances, as well as sparse roots, root stalagmites, termite galleries, guano of carnivorous bats (Chrotopteus auritus Peters, 1856), hematophagous bats (Desmodus rotundus (É. Geoffroy, 1810)) and swifts (Streptoprocne biscutata (Sclater, 1865)), a very abundant bird in these caves. In some caves, bacterial and fungal biofilms were seen on different substrates, which were identified as an alternative organic resource for invertebrates.

The bat guano piles were always small and scarce, but were colonized by Diptera larvae (1500 specimens in total), Collembola (300 specimens in total), Staphylinidae (250 specimens) and Leiodidae (300 specimens), while guano deposits of swifts harbored Acari (50 specimens), Diptera larvae (300 specimens, crickets and spiders. The bat species Desmodus rotundus was the most frequent in caves on the park periphery, quite close to cattles. A high diversity of invertebrates, such as Ensifera, Acari, Coleoptera and Diptera larvae, Annelida (Haplotaxida) were found in the guano of these bat. In Casas cave, Collembola, Acari, and Blattodea were observed associated with termite galleries or abandoned nests, the only macroscopic organic matter observed inside this cave. Top predator taxa were Opiliones (about 1000 counted Mitogoniela sp.), Reduviidae (about 200 counted Zelurus sp.), Pholcidae (about 500 counted Mesabolivar sp.) among others.

All impacts observed in the caves were the consequences of tourism. Impacts like graffiti on the cave walls, trails and trampled soil were the most common, which were observed in almost all the studied caves. In some caves, the entrances located near the touristic trails garbage (organic and plastics) was found. In the Cruz cave, a wooden ladder was installed to facilitate the access of visitors. Currently, only three caves in the Park are open to tourist visitation: Pião, Coelhos and Monjolinhos caves. Other caves, like Bichana I and II, showed no signs of visitation, although they are located near the access road. Although few impacts were found inside the Park boundaries, the surrounding forests were removed for pastures and monocultures (such as Eucalyptus).

In Brazil, with exception of the iron ore cavities (Souza-Silva et al. 2015; Ferreira et al. 2018), non-carbonate caves usually have a low richness of obligate cave species (one to three species) in comparison to limestone (Souza-Silva et al. 2011b). However, for the Ibitipoca quartzite landscape, a higher number of obligate cave species was found. Two factors may be determinant for this richness. It is known that variations in environmental conditions associated with a complex geological history are leading causes for the colonization of the subterranean environment in some areas of the world, e. g. western Balkans (Deharveng et al. 2012, Mammola 2017), which can be also the cause of cave colonization in Ibitipoca caves.

However the 37 species with troglomorphic traits sampled by Gallão and Bichuette (2015) in 11 caves from Chapada Diamantina, This constitutes an extremely atypical scenario for Neotropical caves. It is important to highlight that, from this total, only 5 species were described and considered as true troglobites (Tmesiphantes hypogeus Bertani et al., 2013, Scolopocryptops troglocaudatus Chagas-Jr & Bichuette, 2015, Troglorhopalurus translucidus, Baptista & Giupponi, 2004 Discocyrtus pedrosoi Kury 2008, Glaphyropoma spinosum Bichuette, Pinna & Trajano, 2008).

Sharratt et al. (2000) reviewed the fauna of 31 sandstone caves placed between 450–750 m asl on the Cape Peninsula, South Africa, and found 85 invertebrate morphotypes (13 of them troglobites). Peck and Peck (1982) observed 15 troglophiles and 2 obligate cave species in Devils Den cave, USA. Although these studies used different sampling methodologies, these caves showed a lower average richness when compared to the quartzite caves from this study. The smaller size, lower number of entrances might play a role in the richness in siliciclastic caves. To these features, the latitude of caves can be added possibly influencing the richness, since tropical regions have greater species richness (and diversity) compared to temperate regions (Gaston and Blackburn 2000) and thus, the pool of potential cave colonizers is richer.

The use of caves for tourism is not uncommon and can be extremely important for the local economy worldwide (Bočić et al. 2006, Polak and Pipan 2011). This practice can be conducted with direct alterations to the cave structure, with the installation of stairs, railings and lighting equipment or without such modifications, characterizing an option for sporting nature (Polak and Pipan 2011). In fact, such modifications can cause intense instantaneous or cumulative pressures to the fauna (Gillienson 2011), directly influencing the species richness and abundance. In some cases, the touristic impact may focus on alterations in entrance zones, affecting both the flow of animals to the environment (e.g. bats) and the availability of organic resources (Polak and Pipan 2011). However, it is important to emphasize that depending on the cave structure (like the size of the chambers), the impacts can be different for the cave biodiversity (Faille et al. 2015).

Ibitipoca is a State Park and represents one of the most visited areas in the state of Minas Gerais. Nevertheless, its caves are not arranged for tourists. The management plan of the Park included caves, but cave species were not considered for planning conservation strategies (Trajano et al. 2007).

Areas deforested for cattle ranching were observed in the surroundings of Ibitipoca Mountain and may have directly influenced the abundance of Desmodus rotundus (hematophagous bat) in peripheral caves. Therefore, further attention to the preservation of forests surrounding the Park is also required for the conservation of cave invertebrates because obligate cave species depends on the bat and swift guano.

The present study revealed a rich and diverse invertebrate community sheltered in Ibitipoca quartzite caves, influenced mainly by the extension of the caves and presence of streams. This relationship has been recurrent in several other studies conducted with caves associated with different lithologies in Brazil and can be considered a keystone element for the maintenance of cave biodiversity.