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Environmental factors influencing invertebrate communities in caves and surrounding habitats in the Neotropics
Abstract
The connectivity between epigean and cave habitats is crucial for maintaining invertebrate communities once it can facilitate faunal movement, organic resource supply, and environmental stability. The study aimed to investigate how some spatial and temporal variations in environmental factors within caves and epigean habitats influence invertebrate species richness and composition. We found a notable difference in invertebrate species richness and composition between cave and epigean environments and between cave lithologies. Moisture and temperature significantly influenced species composition across lithologies and epigean and hypogean environments. Cave microclimatic emerged as a critical factor influencing cave fauna. The dissimilarities between epigean and cave environments underscore the selective pressures imposed by caves, challenging species to overcome such environmental filters. Despite epigean environments offering more significant variability in conditions and resources, the findings highlight the importance of local ecological context and specific situations in shaping invertebrate communities. Furthermore, spatial variability within caves emphasises the necessity for a nuanced approach to conservation, considering the heterogeneity of habitats within each cave system. The study contributes to understanding the relationship between caves and their surrounding areas, emphasising the need for tailored conservation strategies that account for regional and cave-specific factors in the context of global environmental changes.
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The Amazon is renowned worldwide for its biological significance, but it also harbors substantial mineral reserves. Among these, the ferruginous geosystems of the region are critical for iron ore extraction, accounting for 10% of Brazil’s export revenue. Additionally, this region holds a significant speleological heritage with more than 1,000 caves. However, cave conservation efforts are often in conflict with land use, necessitating mediation through environmental regulations. While conservation decisions typically consider only the caves’ characteristics, such an approach fails to account for the interactions among cave communities and their surrounding landscape. This poses a challenge to reserve design for cave conservation purposes. To address this issue, we assessed the predictors that influence the similarity among cave communities, suggesting the use of this parameter as a proxy for subterranean connectivity. Applying graph theory, we proposed a tool to aid in the selection of priority caves for conservation purposes. Our study involved the sampling of invertebrates in 69 iron ore caves and analyzing 28 environmental variables related to these subterranean habitats and adjacent landscape. Our analysis revealed that landscape and habitat characteristics are more important than geographical distance in determining patterns of similarity among caves. Our graph approach highlighted densely interconnected clusters based on similarity. However, specific caves stood out for harboring exclusive fauna and/or exhibiting habitat specificity, making them unique in the study area. Thus, we recommend prioritizing cave clusters for conservation, assembling both singular caves and others that influence them. It is crucial to note that protocols for the protection of subterranean biodiversity must consider measures that encompass both the caves and the surrounding landscape. Our methodology provides insights into the connectivity among caves, identifies existing groups, highlights singular (or unique) cavities that require preservation, and recognizes those influencing these unique habitats. This methodological advancement is crucial for the development of better conservation policies for the speleological heritage in areas under constant economic pressure.
Subterranean habitats around the world can shelter diversified and threatened faunal communities. However, issues related to alterations in the landscape and structure of subterranean habitats still need to be better understood. Therefore, we used a multi-spatial scale analysis of land cover, land use, and cave habitats to predict the diversity of communities of subterranean invertebrates. We hypothesized that changes in land cover promote alterations in both faunal richness and composition and microhabitat diversity and that microhabitat features determined subterranean biodiversity. Sixteen limestone caves were sampled in Brazil at micro, meso, and macro scales using quadrats (1m²), transects (100 meters) as sample units inside caves and buffers with the radius of 100 and 250 meters in the surroundings of the cave entrances. Models performed showed that land cover and land use influenced cave environments, regarding both microhabitats traits and terrestrial invertebrate richness and composition. We also observed a relationship between microhabitat structure and terrestrial invertebrate richness and composition. Our results showed that deforested areas had negative effects on species richness and changed their composition, while natural areas had positive effects on microhabitat diversity. The same effects were observed for both 100 and 250 meters buffers. Invertebrate richness was negatively predicted by deforested areas while positively predicted by natural areas. Richness was also positively predicted by the combination of all microhabitat traits, and dissimilarity of fauna was influenced by microhabitat diversity in mesoscale and microscale by all microhabitat elements. The results highlight the importance of the landscape surrounding the caves to conserve the subterranean habitats and their fauna. Due to the spatial and temporal changes in the global environmental scenario, we argue the urgency of further detailed studies in fragmented landscapes to define minimum areas of protection for cave environments.
The theory of habitat heterogeneity, which treats one of the global drivers of biodiversity, is valid for several taxonomic groups and distinct ecosystems, including subterranean environments. However, knowledge about the factors that influence the structure of subterranean communities remains limited, especially in Neotropical regions. We sought to understand the main drivers of invertebrate species richness and composition. For that, we compared the substrate elements of twilight and deep-cave zones and their associated invertebrate communities. Variations in habitat heterogeneity were significantly related to richness in the deep cave zone, but had no effect on the fauna associated with the twilight zone. The local heterogeneity enhanced the richness in the deep cave zone due to the increase in the number of available habitats and the effect on decreasing niche overlap. For communities’ composition, the geographic distribution of caves explained the similarity between the twilight zone of different caves. Therefore, nearby caves have a more similar fauna in the entrance regions but conversely, exhibit a higher dissimilarity between communities associated with the deep-cave zone. This study highlights the influence of local habitat heterogeneity on the invertebrate communities associated with different zones of the cave.
Environmental stability and oligotrophy are considered the main drivers of species distribution within caves due to physiological and nutritional requirements presented by many cave dwellers. However, such patterns are poorly evaluated in tropical caves, especially with regard to habitat selection and interspecific competition between invertebrate groups. Considering that troglobitic species are usually highly specialized, presenting specific requirements for environmental conditions, we hypothesize that troglobitic species will be preferentially associated with deeper areas inside the cave. These areas are stable and present trophic and physical constraints, which may favors the troglobites in competitive interactions with non-troglobitic species.
AQ1
The study carried out in the Águas Claras Cave System revealed a new hotspot of subterranean biodiversity, represented by 30 cave-restricted species (29 invertebrates and 1 fish species), being 73.3% terrestrial, 16.7% amphibian, and 10% aquatic. The richness of troglobitic species did not respond to physical attributes or resources availability as postulated, but increased with temperature, humidity content and with non-troglobitic species richness. The similarity of the troglobitic species along the cave was determined by the moisture content. Furthermore, the richness of troglobites was higher in those areas with greatest taxonomic distinctness of non-troglobitic species and higher values of the TB/nTB species richness ratio. The habitats requirements of the troglobitic species were not coincident, thus indicating that such species avoid niche overlapping. We highlighted the studied cave system as a singular subterranean habitat that contributes to both local and regional biodiversity. Additionally, the condition of high temperature and humidity seems to be key factors that are favoring the existence of a high number of endemic species. Unfortunately, this cave system is devoid of any official protection, thus deserving urgent actions to ensure its conservation.
Relative humidity (RH) was measured at hourly intervals for approximately one year in two caves at seven stations near Playa del Carmen in Quintana Roo, Mexico. Sistema Muévelo Rico is a 1.1 km long cave with 12 entrances and almost no dark zone. Río Secreto (Tuch) is a large river cave with more than 40 km of passages, and an extensive dark zone. Given the need for cave specialists to adapt to saturated humidity, presumably by cuticular thinning, the major stress of RH would be its deviation from saturation. RH in Río Secreto (Tuch) was invariant at three sites and displayed short deviations from 100% RH at the other four sites. These deviations were concentrated at the end of the nortes and beginning of the rainy season. Three of the sites in Sistema Muévelo Rico showed a similar pattern although the timing of the deviations from 100% RH was somewhat displaced. Four sites in Sistema Muévelo Rico were more variable, and were analyzed using a measure of amount of time of deviation from 100% RH for each 24 hour period. Strong seasonality was evident but, remarkably, periods of constant high humidity were not the same at all sites. In most Sistema Muévelo Rico sites, there was a detectable 24 hour cycle in RH, although it was quite weak in about half of them. For Río Secreto (Tuch) only one site showed any sign of a 24 hour cycle. The troglomorphic fauna was more or less uniformly spread throughout the caves and did not concentrate in any one area or set of RH conditions. Compared to temperature, RH is much more constant, perhaps even more constant than the amount of light. However, changes in RH as a result of global warming may have a major negative effect on the subterranean fauna.
In the study of multivariate data, for example of change in ecological communities, ANOSIM is a robust non-parametric hypothesis-testing framework for differences in resemblances among groups of samples. RELATE is a non-parametric Mantel test of the hypothesis of no relationship between two resemblance matrices. Details are given of the explicit link between the RELATE statistic, a Spearman rank correlation (ρ) between corresponding elements in the two resemblance matrices, and the ANOSIM statistic R, a scaled contrast between the among- and within-group ranks. It is seen that R can equivalently be defined as the slope of the linear regression of ranked resemblances from observations against ranked distances among samples, the latter from a simple model matrix assigning the values 1 and 0 to between- and within-group distances, respectively. Re-defining this model matrix to represent ordered distances among groups leads naturally to a generalised ANOSIM statistic, RO, suitable for testing, for example, ordered factor levels in space or time, or an environmental or pollution gradient. Two variants of the generalised ANOSIM statistic are described, namely ROc where there are replicates within groups, and ROs where there are only single samples (no replicates) within groups, for which an ANOSIM test was not previously available. Three marine ecological examples using ANOSIM to analyse an ordered factor in one-way designs are provided. These are: (1) changes in macrofaunal composition with increasing distance from an oil rig; (2) differences in phytal meiofaunal community composition with increasing macroalgal complexity; and (3) changes in average community composition of free-living nematodes along a long-term heavy metal gradient. Incorporating knowledge of an ordering structure is seen to provide more focussed, and thus stronger, ANOSIM tests, but inevitably risks losing power if that prior knowledge is incorrect or inappropriate.
Hourly temperature was measured for approximately one year at 17 stations in three caves in Quintana Roo, Mexico. Thirteen of these stations were in the extensive twilight zones of all three caves. All seventeen stations showed seasonality in temperature with a 3°C drop during the Nortes season. Two of the caves, Muévelo Sabrosito and Muévelo Rico, showed greater variability during the winter months while in Río Secreto (Tuch) variability was greatest during the rainy season. Río Secreto is less open to the surface than the other two. All sites also showed a daily temperature cycle, although it was very faint in some Río Secreto (Tuch) sites. While temperature variability is diminished relative to surface variation, its temporal pattern is worthy of further study.
Aim
In addition to cave size and other subterranean habitat characteristics, cave entrances are important structurers of neotropical cave communities. However, little is known about the epigean ecosystems factors that might dictate the influence of entrances and the relationship among surface and cave communities, as entrance regions are ecotonal zones between the epigean and hypogean ecosystems. We aimed to assess the influence of epigean and hypogean factors as potential drivers of invertebrate species richness in Neotropical caves as well as the influence of the regional pool of invertebrate diversity on cave invertebrate diversity.
Location
Limestone caves in south‐eastern Brazil.
Taxon
Invertebrates
Methods
Data were collected in 48 caves within the Cerrado biome (Brazilian Savanna). The fauna sampling was performed by a direct intuitive search (DIS). Landscape characteristics and climatic parameters were accessed using geographic information systems. The characterization of the caves occurred during each sampling event. Regional diversity was based on the Taxonomic Catalog of Brazilian Fauna. To clarify the factors that significantly influence invertebrate species richness of the caves, we used generalized linear models (GLM). The relationship between regional diversity and cave diversity was evaluated based on linear models (LM).
Results
Overall, 1,173 species were found, of which 72 were obligate subterranean dwellers. The cave total species richness was influenced by hypogean factors and epigean factors. The species richness of obligate cave dwellers was significantly explained only by cave size. The regional pool of invertebrate species influenced the levels of biodiversity in the studied caves. The taxa with troglobitic species tended to be more diverse in caves than expected.
Main conclusions
In addition to the influences of intrinsic cave variables, we highlight the importance of epigean factors on subterranean diversity in the Neotropics. The study shows the significant influence of the regional species pool on cave faunal composition. These findings reinforce the importance of considering the surrounding areas in actions regarding cave biodiversity conservation.
Several studies have tried to elucidate the main environmental features driving invertebrate community structure in cave environments. They found that many factors influence the community structure, but rarely focused on how substrate types and heterogeneity might shape these communities. Therefore, the objective of this study was to assess which substrate features and whether or not substrate heterogeneity determines the invertebrate community structure (species richness and composition) in a set of limestone caves in Guatemala. We hypothesized that the troglobitic fauna responds differently to habitat structure regarding species richness and composition than non-troglobitic fauna because they are more specialized to live in subterranean habitats. Using 30 m 2 transects, the invertebrate fauna was collected and the substrate features were measured. The results showed that community responded to the presence of guano, cobbles, boulders, and substrate heterogeneity. The positive relationship between non-troglobitic species composition with the presence of guano reinforces the importance of food resources for structuring invertebrate cave communities in Guatemalan caves. Furthermore, the troglobitic species responded to different substrate features when compared to non-troglobitic species. For them, instead of the presence of organic matter, a higher variety of abiotic microhabitats seem to be the main driver for species diversity within a cave. The high specialization level of troglobitic organisms might be the reason why they respond differently to environmental conditions. The findings of this study highlight the importance of biological surveys for understanding cave biodiversity and give insights on how this biodiversity might be distributed within a cave. Conservation measures should keep in mind the target organisms and if such measures aim to protect a broad variety of organisms, then one should aim to preserve as many microhabitats and trophic resources as possible.
It has been estimated that there are seven million terrestrial arthropod species on Earth consisting of 6.1 million species of insects, 1.5 million of which are beetles. Tropical forests hold a majority of these species, yet few such places have been adequately sampled for alpha diversity, and there remains even more uncertainty about beta diversity. From an ecological point of view, it is the functional role of organisms within ecosystems that is the particular focus. It has been customary to classify invertebrates within ecosystems in terms of their trophic roles, but it is also useful to consider their roles in networks. In broad terms, we can classify these networks on the grounds of their basal resources. Those based directly on the photosynthetic products of plants are so‐called “green” food webs, and those based on dead and dying plant material are “brown” food webs. Here, we principally discuss the diversity and functional roles of the invertebrates in tropical terrestrial ecosystems. New sampling and analytical techniques, an expanded set of focal taxa, and an enhanced concern with interactions and processes hold the promise of a productive future for invertebrate studies in the tropics. These will not only add to general understanding of the dynamics of tropical ecosystems but will also provide powerful tools for monitoring and responding to environmental change.
Multiple evidence of positive relationships between nice breadth and range size (NB–RS) suggested that this can be a general ecological pattern. However, correlations between niche breadth and range size can emerge as a by‐product of strong spatial structure of environmental variables. This can be problematic because niche breadth is often assessed using broad‐scale macroclimatic variables, which suffer heavy spatial autocorrelation. Microhabitat measurements provide accurate information on species tolerance, and show limited autocorrelation. The aim of this study was to combine macroclimate and microhabitat data to assess NB–RS relationships in European plethodontid salamanders (Hydromantes), and to test whether microhabitat variables with weak autocorrelation can provide less biased NB–RS estimates across species. To measure macroclimatic niche, we gathered comprehensive information on the distribution of all Hydromantes species, and combined them with broad‐scale climatic layers. To measure microhabitat, we recorded salamander occurrence across > 350 caves and measured microhabitat features influencing their distribution: humidity, temperature and light. We assessed NB–RS relationships through phylogenetic regression; spatial null‐models were used to test whether the observed relationships are a by‐product of autocorrelation. We observed positive relationships between niche breadth and range size at both the macro‐ and microhabitat scale. At the macroclimatic scale, strong autocorrelation heavily inflated the possibility to observe positive NB–RS. Spatial autocorrelation was weaker for microhabitat variables. At the microhabitat level, the observed NB–RS was not a by‐product of spatial structure of variables. Our study shows that heavy autocorrelation of variables artificially increases the possibility to detect positive relationships between bioclimatic niche and range size, while fine‐scale data of microhabitat provide more direct measure of conditions selected by ectotherms, and enable less biased measures of niche breadth. Combining analyses performed at multiple scales and datasets with different spatial structure provides more complete niche information and effectively tests the generality of niche breadth–range size relationships.
Ever-increasing human pressures on cave biodiversity have amplified the need for systematic, repeatable, and intensive surveys of cave-dwelling arthropods to formulate evidence-based management decisions. We examined 110 papers (from 1967 to 2018) to: (i) understand how cave-dwelling invertebrates have been sampled; (ii) provide a summary of techniques most commonly applied and appropriateness of these techniques, and; (iii) make recommendations for sampling design improvement. Of the studies reviewed, over half (56) were biological inventories, 43 ecologically focused, seven were techniques papers, and four were conservation studies. Nearly one-half (48) of the papers applied systematic techniques. Few papers (24) provided enough information to repeat the study; of these, only 11 studies included cave maps. Most studies (56) used two or more techniques for sampling cave-dwelling invertebrates. Ten studies conducted ≥10 site visits per cave. The use of quantitative techniques was applied in 43 of the studies assessed. More than one-third (42) included some level of discussion on management. Future studies should employ a systematic study design, describe their methods in sufficient detail as to be repeatable, and apply multiple techniques and site visits. This level of effort and detail is required to obtain the most complete inventories, facilitate monitoring of sensitive cave arthropod populations, and make informed decisions regarding the management of cave habitats. We also identified naming inconsistencies of sampling techniques and provide recommendations towards standardization.
During the past 10 years more scientific research has focused on the cave environment. This is because caves are simple natural laboratories. The cave climate is stable and easily defined. The cave communities are simple and can be studied in toto. This simplicity allows detailed analysis of processes that are difficult to study in more complex
environments. Here we discuss two classes of problems in detail. First, we consider the
interrelation between cave formation and the origins of cave animals. Karst hydrologists study the movement of water through the drainage complex, and biogeographers describe the origin of cave organisms and their dispersal and distribution among the various surface and underground habitats. Second, we treat the cave as a specialized natural
laboratory and give specific examples of problems in ecology, evolution, and mineralogy.
The use of semi‐isolated habitats such as oceanic islands, lakes and mountain summits as model systems has played a crucial role in the development of evolutionary and ecological theory. Soon after the discovery of life in caves, different pioneering authors similarly recognized the great potential of these peculiar habitats as biological model systems. In their 1969 paper in Science, ‘The cave environment’, Poulson and White discussed how caves can be used as natural laboratories in which to study the underlying principles governing the dynamics of more complex environments. Together with other seminal syntheses published at the time, this work contributed to establishing the conceptual foundation for expanding the scope and relevance of cave‐based studies. Fifty years after, the aim of this review is to show why and how caves and other subterranean habitats can be used as eco‐evolutionary laboratories. Recent advances and directions in different areas are provided, encompassing community ecology, trophic‐webs and ecological networks, conservation biology, macroecology, and climate change biology. Special emphasis is given to discuss how caves are only part of the extended network of fissures and cracks that permeate most substrates, and thus their ecological role as habitat islands is critically discussed. Numerous studies have quantified the relative contribution of abiotic, biotic and historical factors in driving species distributions and community turnovers in space and time, from local to regional scales. Conversely, knowledge of macroecological patterns of subterranean organisms at a global scale remains largely elusive, due to major geographical and taxonomical biases. Also, knowledge regarding subterranean trophic webs and the effect of anthropogenic climate change on deep subterranean ecosystems is still limited. In these research fields, the extensive use of novel molecular and statistical tools may hold promise for quickly producing relevant information not accessible hitherto.
The degradation of subterranean habitats is believed to represent a serious threat for the conservation of obligate subterranean dwellers (troglobites), many of which are short-range endemics. However, while the factors influencing cave biodiversity remain largely unknown, the influence of the surrounding landscape and patterns of subterranean connectivity of terrestrial troglobitic communities have never been systematically assessed. Using spatial statistics to analyze the most comprehensive speleological database yet available for tropical caves, we first assess the influence of iron cave characteristics and the surrounding landscape on troglobitic communities from the Eastern Amazon. We then determine the spatial pattern of troglobitic community composition, species richness, phylogenetic diversity, and the occurrence of frequent troglobitic species, and finally quantify how different landscape features influence the connectivity between caves. Our results reveal the key importance of habitat amount, guano, water, lithology, geomorphology, and elevation in shaping iron cave troglobitic communities. While mining within 250 m from the caves influenced species composition, increasing agricultural land cover within 50 m from the caves reduced species richness and phylogenetic diversity. Troglobitic species composition, species richness, phylogenetic diversity, and the occurrence of frequent troglobites showed spatial autocorrelation for up to 40 km. Finally, our results suggest that the conservation of cave clusters should be prioritized, as geographic distance was the main factor determining connectivity between troglobitic communities. Overall, our work sheds important light onto one of the most overlooked terrestrial ecosystems, and highlights the need to shift conservation efforts from individual caves to subterranean habitats as a whole.
We studied the ecological continuum between caves and the associated network of fissures-Milieu Sou-terrain Superficiel (MSS)-in an hypogean site in the Graian Alps, Italy. Over one year, we surveyed the faunal assemblages by means of pitfall traps placed in the caves and specific subterranean sampling devices (SSD) buried in the MSS. We used generalized linear mixed models (GLMMs) and generalized additive mixed models (GAMMs) to compare the spatial and temporal dynamics of the subterranean invertebrates inhabiting the two environments. As expected, arthropod communities occurring near the surface were characterized by minor level of subterranean adaptations, and conversely, subterranean species were more abundant and diversified at higher depths, both in the caves and in the MSS. Diversity and abundance of external elements in the superficial layers were found to be highly seasonal dependent, with minor values in winter compared to the other seasons. We provided information about the faunal assemblages dwelling in the two hypogean compartments, and we characterized the microclimatic conditions therein. We discussed the existence of an ecological gradient of specialization extending from the surface to the deep hypogean layers, which can be interpreted in light of the microclimatic changes occurring at increasing depths and the parallel decrease in available organic matter.
Seasonality impacts species distributions through changes of the environmental
conditions that affect the presence of individuals at a given place. Although the dynamics
of cave microclimates are well known, only a few studies have evaluated the effects
of such dynamics on non-strictly cave species. Here we assessed if species exploiting
subterranean environments show changes in habitat occupation related to seasonal
variation of cave microclimates. We surveyed 16 caves in central Italy every month for
one year. Caves were subdivided into longitudinal sectors of three meters. In each sector
we measured cave morphology and microclimatic features, assessed the occurrence
of eight non-troglobitic taxa (orthopterans, spiders, gastropods and amphibians),
and related species distribution to environmental features and sampling periods. The
occurrence of most species was related to both cave morphology and microclimatic
features. The survey month was the major factor determining the presence of species
in cave sectors, indicating that cave-dwelling taxa show strong seasonality in activity
and distribution. For multiple species, we detected interactions between sampling
period and microclimatic features, suggesting that species may associate with different
microhabitats throughout the year. The richest communities were found in sites
with specific microclimates (i.e., high humidity, warm temperature and low light)
but seasonality for species richness was strong as well, stressing the complexity of
interactions between outdoor and subterranean environments.
The Brazilian semiarid region has a clear distinction between the dry season, which can last up to nine months, and the rainy season. Caves are connected to different extents to surface ecosystems, although they are idealized as stable environments due to their isolation. Furthermore, little is known about the effects of wet and dry seasonal variations on underground biological assemblages. Invertebrate communities were analyzed during dry and rainy seasons in 24 caves in the semiarid region of northeastern Brazil. We also investigated whether the environmental stability of caves attenuates the effects of seasonality in this particular region. Morphospecies richness and abundance and the diversity indexes of caves were significantly higher during the rainy season. In addition, more stable caves showed less variation in the community composition between seasons. Our data point to a clear influence of the surface ecosystems on the caves in Caatinga. However, the intensity of this influence apparently depends on the environmental stability of the cave, and the most stable caves present smaller changes in the structure of their invertebrate communities during different seasons.
Patterns of biodiversity respond to habitat disturbances and different land-uses. Those patterns possibly vary according to the spatial scale under analysis. Although other studies have shown such responses for different systems, no study has ever demonstrated spatial-scale influences in subterranean terrestrial communities. Therefore, the objective of this paper was to analyze how land use and cave physical structure could influence the terrestrial cave invertebrate species composition. We also determined the influence of different spatial scale on the structure of invertebrate cave composition. We collected environmental data at local scale (e.g. cave size, substrate and environmental stability). For spatial scale we determined land uses at three different landscape scales; we gathered these data into circular areas of different sizes (50, 100 and 250 meters) with centroids in the cave entrances. We finally performed three Distance Based Linear Modeling analyses to test for differences among the predictability of environmental variables when comparing different spatial scales. The best explanatory variable for cave invertebrate similarities was the percentage of covering of the external environment by limestone outcrops. We confirm the scale-dependence hypothesis through the different patterns showed among distinct buffer areas. Models become more precise when larger scales were analyzed to explain cave invertebrate composition. This suggests that larger scales capture important environmental features that explain the cave fauna similarities more precisely. Additionally, we found a strong influence of limestone outcrops at all landscape scale structuring cave communities.
The stability of temperature and humidity in caves is well known. However, little is known if higher or lower cave environmental stability (temperature, humidity, light and others) implies changes in the structure of the biological communities. Number, position and size of entrances, then size, depth, host rock and extent of the cave, the amount and type of food resources are all factors that can have strong influence on the cave biological communities. The objective of the present study was to evaluate the correlation between the presence of water bodies, size of entrances and the linear development of caves with the terrestrial invertebrate richness and species composition in 55 limestone caves located in the Brazilian Savannah, sampled from 2000 to 2011. Invertebrates were sampled by active search throughout the caves, prioritizing micro-habitats (sites under rocks) and organic resources (litter, twigs, feces and bat guano). We recorded 1,451 invertebrate species. Species richness was positively correlated with presence of cave streams, width of entrances and linear development of the caves. The richness of troglomorphic species was positively correlated to the presence of perennial pools and linear development of the caves. The presence of cave streams was a decisive factor for determining the community structure, increasing the number and the similarity of troglophile species among the caves. Flood pulses can cause disturbances that eventually select the same species besides importing resources. However, for the terrestrial troglomorphic species the disturbance caused by cave streams may decrease the number of species.
Caves are permanently aphotic environments, a fact that precludes the occurrence of photosynthetic organisms. In these systems the resource is allochthonous, coming mainly from the surrounding epigean environment, being imported by physical and biological agents. Even knowing about the importance of the organic allochthonous resources in caves, little is known of their importation and processing. The present work had as an objective, the measuring the coarse particulate organic matter processing and import rates in the subterranean environment. The cave studied was Lapa da Fazenda Extrema I, limestone cave, located in Brazilian savanna biome. Through bimonthly collections, it was observed that the organic detritus penetrated into the cave in low amounts in dry season and high amounts in rainy season. The processing of the organic plant matter in the aquatic hypogean environment was moderate (K-day=0.025), in the epigean environment the processing was predominantly slow (K-day =0.0104). The detritus commonly brought to the interior of the cave were large woods (58.18 g/day), followed by leaves and fragmented material (12.76 g/day), fruits and seeds (0.0069 g/day), animal carcasses (0.002 g/day) and roots (0.001 g/day). The highest richness and abundances of invertebrates were found in the same periods in which there were the highest rates of organic matter import to the cave.
Keywords: cave, detritus processing, energy flow.
As caves represent an extreme biotope with limited food sources, one might expect cave animal communities to exhibit low feeding specialization and to consume generally whatever organic matter is available. To test this hypothesis, we studied the feeding habits of several arthropod species in Slovakian and Roma-nian caves. A microanatomical approach utilizing histological methods was selected for this study. While saprophagous animals dominated, our study revealed variability within this nutritional group. Preferences ranged from fungal propagules (for the millipede Trachysphaera costata) to bacteria on bat guano (for the oribatid mite Pantelozetes cavaticus) and to cyanobacteria (for the microwhip scorpion Eukoenenia spelaea). The terrestrial isopod Mesoniscus graniger consumed a mixture of organic and inorganic substrates with plant material in various caves. These findings confirm an adaptability and phenoplasticity and, hence, a variability of characteristics developing under the pressure of extreme environmental factors.
The state of Minas Gerais (Brazil) is characterized by significant karst regions, which develop in both sandstone and quartzite terrains and display complex suites of underground and surface forms. In the Espinhaço Ridge, Central Minas Gerais, several caves of up to a few hundred metres long, occur in the surroundings of the town of Diamantina. Some of these caves, such as Salitre actually consist of swallow-holes. Other horizontal caves are characterized by corrosion forms generated in the phreatic zone. In some places, such as in the Rio Preto area, these phreatic forms are overprinted by ceiling tubes, suggesting a polyphase karst evolution, prior to the draining in the cave. Remains of paths, with circular cross section up to one metre in diameter, can be found through residual tower-like surface landforms widely present in the landscapes. Their dissection is due to a generalised karstification in the area, resulting in closed canyons, megakarrens and kamenitzas. In Southern Minas Gerais, close to the Mantiqueira Ridge, the caves of the Ibitipoca state park can reach more than 2 km in length. These caves are associated with a very large hanging geological syncline. Several of these caves contain active streams, which flow for hundreds of metres before disappearing in sand-choked passages. Keyhole cross sections characterize steeply descending passages in these caves, indicating a change from slow phreatic flow towards a faster vadose flow responsible for the vertical incision of the passage. Such change is probably related to base level lowering and/or to turn in the direction of the water flow. Several generations of wall-pockets, from a few centimetres to over a metre long, occur into the caves. These features are good indicators of the initial phase of speleogenesis, generating the initial conduits by their coalescence. This mechanism is also responsible for cut-off meanders. In the area, the main river flows along the syncline axis and cuts through a rock barrier, generating a tunnel-like passage. This cave drains, through resurgences in its walls, part of the water that flows in other caves located in the flank of the syncline.
Cave entrances are transition zones with intermediate characteristics between epigean environments, which bear lower environmental stability, and hypogean environments, with lower food resources. Associated to these interfaces there is a specific community, capable of exploiting its unique and intermediate characteristics. This work investigated this community in a Brazilian limnestone cave, identifying its arthropod species composition and spatial distribution, and exploring its relationships with climatic and structural environment characteristics and trophic relations. An ecotone zone was identified, with 55 species found only in the ecotone, 49 species were shared with the epigean community, 37 species with the hypogean community, and 14 species were found in the three communities. Although detritus is the base of the trophic web in the entrance, light allows the establishment of some producers and even herbivores. Species diversity in the ecotone was intermediate to that of the adjacent environments. Light is the main filter that acts near the cave entrance and determines the presence and distribution of several species in the ecotone. Therefore, this region is importante for the cave ecosystem as a whole, considering that a considerable amount of trophic resources is transferred from the epigean to the hypogean environment through this area. Accordingly, conservation and management strategies regarding cave communities should incorporate actions to study and protect ecotonal communities.
The temporal budgets of the input, retainment and use by invertebrates of detritus and root tufts were evaluated in a short tropical limestone cave (337 m long). Detritus penetrate only through the stream in lower quantities in the dry season, contrary to what happens in the rainy season. However, water transport energies in the rainy season prevent detritus retainment. Roots tufts that emerge from the bottom of the stream provide shelter and food for several species. The abundance (log, 10) (R 2= 0.63; P < 0.02) and richness (log 10) (R 2 = 0.63; P < 0.01) related positively with the root tuft biomass (log 10). In the terrestrial environment (ground), guano is the main secondary resource available for the invertebrates; the constant production of this resource has shown to influence the structure and distribution of invertebrates. Unfavorable temperature conditions and, especially low soil moisture, promote low plant detritus consumption rates. Historically, different authors assumed that organic resources imported by water are more available in caves in rainy seasons. It is clear that the importation of organic detritus in the rainy season is higher than in the dry season, but as shown in this work, the stochastic pulse flows continually disturb and remove the previously accumulated resource. So, the food that is truly used by the cave communities is that transported at the end of the rainy season (and during all the dry season) that becomes available for the cave fauna. The cave functionality depends, so, directly of the epigean food resources.
Caves, as ecological units, are redefined in terms of the ecologically-significant scalar phenomena that, in contrast with such traditional criteria as perpetual darkness, environmental stability and oligotrophy, are the special characteristics of large cavities (macrocaverns) in rocks. When so defined, 'caves' are ecologically distinct from the mesocaverns and all other subterranean habitats. Some implications of this perspective for the ecological classification of animals found in subterranean habitats are briefly discussed.
Seasonality in insect abundance in the "Cerrado" of Goiás State, Brazil. Many studies have provided evidence that tropical insects undergo seasonal changes in abundance and that this is partly due to alternation between the dry and rainy seasons. In the Brazilian "Cerrado" (savannah), this season alternation is particularly evident. The purpose of this work was to study the seasonal abundance of insects in a "Cerrado" area in the municipality of Pirenópolis, Goiás State, Brazil. The insects were captured fortnightly using a light trap between September 2005 and August 2006. The insects collected were separated at the order level and counted. Faunistic analysis was performed to select the predominant insect orders, a multiple linear regression to examine the relation between climatic variables (temperature and precipitation) with the abundance of insects and a circular distribution analysis to evaluate the existence of seasonality in the abundance of insect orders. A total of 34,741 insect specimens were captured, belonging to 19 orders. The orders with the greatest number of specimens were Hymenoptera (8,022), Coleoptera (6,680), Diptera (6,394), Lepidoptera (6,223), Isoptera (2,272), Hemiptera (2,240) and Trichoptera (1,967), which represent 97.3% of all the specimens collected. All the orders, except for Diptera, Isoptera and Trichoptera, showed a relationship with the climate variables (temperature), and all the orders, except for Diptera, presented a grouped distribution, with greater abundance in the transition from the end of the dry season (September) to the start of the rainy one (October/November). A discussion about seasonality on the abundance of the insects is presented.
Seasonality in surface weather results in seasonal temperature and humidity changes
in caves. Ecological and physiological differences among trogloxenes, troglophiles, and
troglobionts result in species-dependent responses to this variability. To investigate these
responses, we conducted five biological inventories in a marble cave in the Sierra Nevada
Range, California, USA between May and December 2010. The cave was divided into six
quadrats and temperature was continuously logged in each (humidity was logged at the
entrance and in the deep cave). With increasing distance from the entrance, temperature
changes were increasingly attenuated and lagged relative to surface temperature. Linear
regressions were created to determine the relationship between measured environmental
variables and diversity for cavernicoles (troglobionts and troglophiles) and trogloxenes cave–
wide and in the transition zone. Diversity for cavernicoles and trogloxenes peaked in the
entrance and deep cave zones, respectively. Quadrat, date, 2-week antecedent temperature
average, 2-week antecedent temperature range, and trogloxene abundance explained 76%
of cavernicole diversity variability. Quadrat explained 55% of trogloxene diversity variability.
In the transition zone, trogloxene abundance explained 26% of cavernicole variability and
2-week antecedent temperature and 2-week antecedent temperature range explained 40%
of trogloxene variability. In the transition zone, trogloxene diversity was inversely related
to 2-week antecedent temperature average and 2-week antecedent temperature range,
suggesting that species were moving into the transition zone when temperature was most
stable. In a CCA of cavernicoles distribution data and environmental variables, 35% of variation
in species-specific distributions was attributable to quadrat, and non-significant percentages
were explained by date and environmental variables. Differences in assemblage structure
among quadrats were largely due to differences between distributions of trogloxenes and
cavernicoles, but responses varied among species. Differences are likely due to ecological
niche width, physiological constraints, and competition.
3 Abstract: We present a conceptual model for the movement of organic carbon in karst. We argue that the drainage basin is the most appropriate unit for analyzing energy flux in karst. There are two main inputs in karst basins: 1) localized flow of particulate organic carbon (POC) and dissolved organic carbon (DOC) through sinks and shafts and 2) diffuse flow of POC and DOC from soils and epikarst. After entry, this organic matter is processed and transported before eventual loss through respiration or export from the basin. To begin parameterizing our conceptual model, we estimated carbon fluxes for the first two inputs for two karst basins (Organ Cave in West Virginia and Postojna-Planina Cave System (PPCS) in Slovenia) that have sinking streams and many active epikarst drips. We made a series of measurements of organic carbon, especially DOC in epikarst drip water, cave streams, surface streams sinking into the cave, and at resurgences, which we combined with other published data. In both caves, most of the organic carbon entering through the epikarst was DOC, at concentrations averaging around 1m g CL 21. In both basins, sinking streams accounted for the large majority of DOC input. It is likely that considerable processing of organic carbon occurs within both caves, but more detailed measurements of organic carbon flux at both the basin and stream scale are needed.
That the ties between any obligate subterranean species and the hypogean environment depend on the interplay of a species' own physiological characteristics and all of the ecological characteristics of the adjacent epigean habitat(s), including biotic factors, has been emphasized. The reasons why troglomorphy cannot be included within criteria for classifying cave dwellers have been demonstrated. After a review of historic classifications, standardized definitions of the most widely used terms are proposed. The most easily recognized are four categories which are terminological approximations of the classic Schiner‐Racovitza terminology: (1) troglobiont is a species or population, strictly bound to a hypogean habitat; (2) eutroglophile is an essentially epigean species, but able to maintain a permanent subterranean population; (3) subtroglophile is inclined perpetually or temporarily to inhabit a subterranean habitat but is bound to the surface for some biological functions (e.g. feeding); (4) trogloxene is a species only occurring sporadically underground.
Physical features and lithology variations contribute to promoting changes in faunal composition and richness between caves in Neotropics. Cave lithology effects on biodiversity were reported to iron ore caves in Brazil, however, it is less clear to granitoid and quartzite caves. Hence, based on these two kinds of rocks we correlate invertebrates species richness and composition with some cave features (lithology, the distance between caves, cave extension, number of entrances, entrance size, environmental stability, and altitude). Overall, 1,027 invertebrate species were recorded in 50 sampled caves. From this total, 11 obligate cave species were found. Invertebrate assemblages showed considerable turnover between caves and rock types with a strong contribution of replacement component of beta diversity. Replacement influence was greatest in quartzite caves mainly because of altitude and distance among caves. Furthermore, richness was determined by cave extension in both lithotypes, although this relationship was much more pronounced for the granitoid caves, which contradicts previous studies. The granitoid caves studied here are predominantly structured by stacked blocks with macro and meso anastomosed subterranean spaces that provide an extensive network of interstices with structural characteristics similar to shallow subterranean habitats that may increase in habitat availability and species richness. The study highlight that the lithology-mediated effects of cave extension on richness must be considered for quartzite and granitoid in the ecological and conservational proposal. Furthermore, altitude and distance among caves were important elements determining invertebrate composition.
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In this paper, we examine some basic properties of the Bray-Curtis dissimilarity as compared with other distance and dissimilarity functions applied to ecological abundance data. We argue that the ability of every coefficient to measure species-level contributions is a fundamental requirement. By suggesting an additive decomposition formula for the Bray-Curtis coefficient we derive a general formula of dissimilarity, which includes the Canberra distance and the Bray-Curtis dissimilarity as special cases. A similar general formula is also proposed for the Marczewski-Steinhaus coefficient. Finally, using a modified version of Dalton’s principle of transfers, we show that the Bray-Curtis coefficient and the city-block distance exhibit a linear response to the transfer of species abundances from an abundant plot to a less abundant plot. At the other extreme, the chord and the Hellinger distances show an irregular and non-monotonic behavior.
Temporal environmental fluctuations, such as seasonality, exert strong controls on biodiversity. While the effects of seasonality are well known, the predictability of fluctuations across years may influence seasonality in ways that are less well understood. The ability of a habitat to support unique, non-nested assemblages of species at different times of the year should depend on both seasonality (occurrence of events at specific periods of the year) and predictability (the reliability of event recurrence) of characteristic ecological conditions. Drawing on tools from wavelet analysis and information theory, we develop a framework for quantifying both seasonality and predictability of habitats, and applied this using global long-term rainfall data. Our analysis predicted that temporal beta diversity should be maximized in highly-predictable and highly-seasonal climates, and that low degrees of seasonality, predictability, or both would lower diversity in characteristic ways. Using stream invertebrate communities as a case study, we demonstrated that temporal species diversity, as exhibited by community turnover, was determined by a balance between temporal environmental variability (seasonality) and the reliability of this variability (predictability). Communities in highly-seasonal Mediterranean environments exhibited strong oscillations in community structure, with turnover from one unique community type to another across seasons, whereas communities in aseasonal New Zealand environments fluctuated randomly. Understanding the influence of seasonal and other temporal scales of environmental oscillations on diversity is not complete without a clear understanding of their predictability, and our framework provides tools for examining these trends at a variety of temporal scales, seasonal and beyond. Given the uncertainty of future climates, seasonality and predictability are critical considerations for both basic science and management of ecosystems (e.g. dam operations, bioassessment) spanning gradients of climatic variability. This article is protected by copyright. All rights reserved.
Giovanni Badino: Underground meteorology - "What's the weather underground?" The aim of this work is to provide a synthetic outline of some of the processes of transient nature occurring in caves, focusing on poorly studied general aspects of underground physics and mainly making use of original experimental data. In the first part, the average climatic conditions of a caves, their connection to the external climate, and the general role played by rock, water, air and external morphology are discussed. The variation of the internal temperature with the altitude is a key parameter for the cave physics: the related energetic consequences are briefly discussed. In the second part, transient processes are considered, and a general overview of main meteorological phenomena occurring underground is given. The physics of thermal sedimentation, of underground temperature ranges, of infrasonic oscillations of cave atmospheres and, above all, of water vapour condensation in caves is synthetically described. The experimental study of these processes is extremely difficult, because they are time dependent and have very small amplitude; the first measurements show, however, that their variability from one cave to another, and from point to point inside a cave, is surprisingly high. To provide a more correct interpretation of underground climatic measurements, for their speleogenetic role and importance in cave environment protection, a better understanding of the processes described here is essential.
Monthly samples, taken over 19 months, examined the composition, density, and seasonality of invertebrate litter faunas in an upland tropical rain forest. Arthropods represented 96.0 percent of the total sample number. Numbers of invertebrates increased with an increase in precipitation and there were significantly more individuals in samples during the wetter months. Numbers declined when litter became dry and/or sparse or oversaturated. Fluctuations in invertebrate litter populations appeared to relate to rainfall, litter moisture content, leaf fall, and rates of decomposition. Comparisons were made with similar studies carried out elsewhere in tropical rain forests. The present investigation is part of a study of the breeding and foraging ecology seasonality of Australian upland tropical forest birds.
Post congress Special session CaveLab The fact that the caves are semi-closed systems with an almost constant temperature makes them almost ideal sites where to study the effect of temperature on ecosystems. As a first approximation we may assume that a cave has a temperature almost equal to the local yearly average temperature. Increases in outside temperature (i.e. global warming) can thus easily be detected inside caves and cave dwelling organisms, showing low tolerance to temperature variations, may be affected by such variations. Altering cave microclimate, global warming may potentially cause local extinctions. One of the aims of the CaveLab Research Project (Work Package 6) is to evaluate the potentiality of the cave ecosystems as indicators for global warming. The aim of this study is to investigate the relation between cave temperature and cave dwelling arthropods, addressing their potential for the monitoring of global warming. In 2013 we allocated 72 i-button devices programmed to record temperature every 6 hours for one year in 36 caves in the Western Italian Alps. As a result, the focal caves were characterized from a microclimatic point of view that provided the baseline for the study of the relation between temperature and the occurrence of specialized cave dwelling arthropods. Later on, we extended the dataset to comprise more than 350 caves, for which we obtained a climatic profile and gathered faunistic data (presence/absence) via direct samplings and literature data. Binomial General Addictive Models (GAM) models allowed us to identify several cryophilic stenotherm hypogean species (adapted to narrow ranges of cold temperatures), that will be chosen to assess future scenarios of species distribution on a large scale according to different temperature scenarios provided by the International Panel on Climate Change (IPCC). In particular, spiders of the genus Troglohyphantes (Araneae, Linyphiidae), proved to be the most sensible species to thermic variations. A special focus on the regional scale (population extinctions or expansions, future scenarios of species distribution, decline of endemic species) will be given.
Explanations concerning the origin of obligate cavcmicoles, or troglobites, have long been a source of controversy among biospclaeologists. It is suggested here that troglophiles become troglobites as the result of an adaptive shift to an ecological niche which cannot occur in epigean communities. This adaptive shift is facilitated by preadaptation of the incipient troglobite through the development of genoclines in its troglophilic ancestral population. The shift to troglobitism is forced by competitive exclusion of the incipient troglobitc from its original troglophilic niche by an invading species or community. The major changes of fauna produced in temperate latitudes by the climatic fluctuations of the Pleistocene have resulted in a particularly rich troglobitic fauna composed mainly of cryophilic relicts inhabiting temperate caves.
AimThe goal of this study was to determine the role habitat availability plays in the distribution of obligate subterranean cave fauna in eastern North America.LocationThe numbers of stygobites, troglobites and caves in the counties of the south-eastern USA were analysed.Methods
The data were characterized by large numbers of zeroes and by spatial clustering of non-zeroes in five regions. Regression and conditional autoregressive (CAR) models were used to elucidate the patterns and relationships between numbers of species and numbers of caves both locally and regionally.ResultsLocal effects (regions and numbers of caves in counties) accounted for 45% of the variation in troglobite counts (P=< 0.001) and 24% of the variation in stygobite counts (P=< 0.001). Significant spatial autocorrelation among both stygobites and troglobites (P=< 0.0001) was found as well.Conclusion
Overall, habitat availability as measured by cave numbers influenced species richness. Spatial and regional effects also played an important role in determining the observed distributions of the subterranean fauna. Terrestrial and aquatic communities showed very different patterns in their relationship to habitat and within the different regions.
Speleothems (stalagmites, stalactites, etc.) have long drawn visitors underground to visit limestone caves throughout Europe, and since the start of the twentieth century many public show-caves have been established. For example, in the British Isles today there are over 20 show-caves; the most visited may receive in excess of 500 000 visitors annually. Recent research has highlighted the potential destructive influence of visitors to caves by the effects of respiration, which can generate elevated CO2concentrations, and by their heating effect, which can raise temperatures by up to 3°C. Values of up to 5000 ppm of CO2have been reported in both private and public caves, but with clear evidence that the passage of visitors through the cave system causes increases of up to 200%. It has been suggested that such elevated CO2may cause the destruction of speleothems within the caves, as increased CO2leads to a higher equilibrium concentration of calcium within the drip waters feeding the speleothems, and hence causes dissolution of existing features, although it has to be noted that there is a significant natural variability of cave air CO2and it is against this that the anthropogenic effects of visitors has to be judged. Data are presented here for both cave air CO2concentration and temperature, as well as a third variable, that of the drip-water calcium concentration, which is also a key determinant of speleothem growth and may be affected by surface land use changes. It is demonstrated that cave speleothems may be at risk from the increased passage of tourists, but that this risk is highest in caves where ventilation is poor and where either the calcium ion concentration of the drip waters is low (
We present a new multivariate technique for testing the significance of individual terms in a multifactorial analysis-of-variance model for multispecies response variables. The technique will allow researchers to base analyses on measures of association (distance measures) that are ecologically relevant. In addition, unlike other distance-based hypothesis-testing techniques, this method allows tests of significance of interaction terms in a linear model. The technique uses the existing method of redundancy analysis (RDA) but allows the analysis to be based on Bray-Curtis or other ecologically meaningful measures through the use of principal coordinate analysis (PCoA). Steps in the procedure include: (1) calculating a matrix of distances among replicates using a distance measure of choice (e.g., Bray-Curtis); (2) determining the principal coordinates (including a correction for negative eigenvalues, if necessary), which preserve these distances; (3) creating a matrix of dummy variables corresponding to the design of the experiment (i.e., individual terms in a linear model); (4) analyzing the relationship between the principal coordinates (species data) and the dummy variables (model) using RDA; and (5) implementing a test by permutation for particular statistics corresponding to the particular terms in the model. This method has certain advantages not shared by other multivariate testing procedures. We demonstrate the use of this technique with experimental ecological data from intertidal assemblages and show how the presence of significant multivariate interactions can be interpreted. It is our view that distance-based RDA will be extremely useful to ecologists measuring multispecies responses to structured multifactorial experimental designs.