Sharing the space: coexistence among terrestrial predators in Neotropical caves

The subterranean environment has a set of unique characteristics, including low thermic variation, high relative humidity, areas with total absence of light and high dependence on nutrient input from the epigean environment. Such characteristics promote distinct ecological conditions that support the existence of unique communities. In this work, we studied seven caves in the Presidente Olegário municipality, Minas Gerais state, Southeast Brazil, to determine their richness of predatory species, to understand how they are spatially distributed in the cave and whether their distribution is influenced by competition and/or predation. We carried out five surveys of the caves, with each cave divided into sampling plots. We collected fauna within the plots using a manual search method. The collected animals were fixed in 70% ethanol for later identification. We performed a canonical correspondence analysis to verify the spatial distribution and substrate preference of each species, and selected five species for agonistic interaction testing in the laboratory. We found a great richness of predators in the caves, with 79 species distributed among 22 families of spiders, five families of pseudoscorpions, three families of chilopods, two families of opilionids and one family each of scorpions and heteroptera. Spiders were the most species diverse and abundant of all arthropods we found in the caves. We recorded evidence of competition among some pairs of species but, in general, the spatial distribution of the predatory community in the interior of the caves seems to be unrelated to interspecies competition. The laboratory pairings support our field observations that most species merely share space, rather than exhibiting aggressive or predatory behaviour.     

Multi-scale patterns in the host specificity of plant-dwelling arthropods: the influence of host plant and temporal variation on species richness and assemblage composition of true bugs (Hemiptera)

The influence of temporal variation in the host specificity of invertebrates to estimates of biodiversity is rarely considered. While patterns at large spatial scales have stimulated much attention, such comparisons are constrained for southern-hemisphere biomes because the patterning of invertebrates on plants is largely unknown. Here, we analyse variation of plant-dwelling Hemiptera from 15 understorey plant species over 18 months in the south-west Australian biodiversity hotspot. Analyses showed significant interactions in species composition between sampling period and plant species. Fauna that were “effectively specialized” (host-specificity index) to plants changed with season, although this was also related to the number of singletons and overall species richness. Sampling from a single season also overestimated the degree of host specificity by 52% and underestimated the perception of species richness when an outbreak of a particular herbivore occurred. High host-specificity values (12.7 hemipteran species per plant) support the case for high estimates of global arthropod richness.     

Temperature variation and the presence of troglobionts in terrestrial shallow subterranean habitats

Within the soil matrix and underlying rock, cracks and fissures and other air-filled spaces between rocks, sometimes called the milieu souterrain superficiel (MSS), are present in a variety of geological contexts. We examined year-long hourly temperature profiles at sites in lava in the Canary Islands and limestone in Slovenia. All sites had species that show morphological adaptations usually associated with cave-dwelling organisms, including elongated appendages and reduced eyes and pigment. MSS sites were studied at depths between 10 and 70 cm and showed strong seasonality, and most had a discernible diurnal cycle as well. The most striking difference from surface habitats was that the temperature extremes were much less pronounced in MSS sites. Temperature variability was not correlated with troglobiotic species richness. The presence of species with similar morphologies to those found in caves indicates that selective pressures are similar in cave and shallow subterranean habitats.     

Freshwater invertebrates of subantarctic South Georgia

Twenty‐one lakes, ten pools, seven coastal pools, three streams, two seal wallows, a penguin wallow, and three flooded moss carpets on South Georgia were sampled for aquatic invertebrates. More than 100 invertebrate species were found comprising 59 species of Rotifera, 29 Arthropoda (including five Anomopoda, three Calanoida, two Harpacticoida, three Ostracoda, 12 Acarina and four Insecta) and at least 22 other invertebrate species (including four Platyhelminthes, three Gastrotricha, six Tardigrada, six Nematoda, and two species of Annelida). The fauna of South Georgia, although similar to that of the other Scotia Arc Islands, particularly Signy Island, is much richer by virtue of its lower latitude and milder climate.     

Invertebrate faunas and zoogeographic significance of lava tube caves of Arizona and New Mexico

A field survey in caves near Grants, New Mexico, and Flagstaff, Arizona, found only an exceptionally poor fauna of 14 species with no strong patterns of cave restriction. The faunal poverty is judged to be correlated with and influenced by the similarly impoverished boreal forests in nearby mountains. Species of flightless arthropods, suitable for cave colonization and restricted to cool-moist litter of boreal (Hudsonian-Canadian Life Zone) forests, are apparently not now present in suitable, nearby mountain habitats. They may not have dispersed to all available montane sites from the Southern Rocky Mountains during glacial conditions. Either the forests did not exist as continuous dispersal corridors for the litter arthropods, or the fauna could not track the rate of spread of the forests.     

Fire effects on small mammal communities in Dinosaur National Monument

Resource specialists at Dinosaur National Monument utilize both planned and unplanned wildland ignitions in big sagebrush ( Artemisia tridentata )--dominated plant communities to restore successional processes, maintain vegetation vigor, and promote diversified landscapes. Short- and long-term effects of prescribed burning on small mammal populations are not well understood. The objectives of this study were to (1) compare small mammal species richness, similarity, and diversity between paired burned and unburned treatment plots, and (2) assess long-term trends of small mammal community responses to burning. Five paired burned/unburned sites having similar vegetation, soils, elevation, and annual precipitation were selected. Prescribed or natural fires occurred on all sites between 1981 and 1995, followed by periodic small mammal removal (trapping) sampling (1--12 years post-burn). Small mammal species richness and diversity were generally higher on unburned than burned plots across post-burn sampling years and sites. Increased abundance of the deer mouse ( Peromyscus maniculatus ) following burning resulted in decreased community diversity. Species similarities between burned and unburned plots were low in early post-burn years but increased in later post-burn years. Short-term shifts in diversity and species similarity resulted from increased deer mouse abundance after burning. However, burning had no long-term impact on species richness and similarity, indicating minimal effect to other small mammal species.     

Terrestrial vertabrates of Scotts Bluff National Monument, Nebraska

A survey of terrestrial vertebrates was conducted at the Scotts Bluff National Monument (SBNM), Nebraska, to determine species composition, relative abundance, and distribution by habitat of the existing amphibians, reptiles, birds, and mammals. Various sampling methods were used to detect animal species richness and to estimate population densities. The seven major habitat types at SBNM contained 4 species of amphibians, 8 reptiles, 96 birds, and 28 mammals. The only endangered or threatened species observed was a dead bald eagle ( Haliaeetus leucocephalus ). The racer ( Coluber constrictor ) and prairie rattlesnake ( Crotalus viridis ) were the two most abundant snakes. The prairie falcon ( Falco mexicanus ) was a common raptor that nested in Scotts Bluff. Sympatric populations of mule deer ( Odocoileus hemionus ) and white-tailed deer ( Odocoileus virginianus ) appeared to be hybridizing. The riverine woodland contained the greatest number of fauna species with only 4% surface area of SBNM. Sharp-tailed grouse ( Tympanuchus phasianellus ) and pronghorn antelope ( Antilocapra americana ), absent from the Monument, are two potential native species for reintroduction.     

Urbanization impacts on the trophic guild composition of bird communities

Urbanization transforms the landscape and generates loss of pristine habitats. We investigated the urbanization effect on bird communities in a growing South American city (Santa Fe, Argentina) and hypothesized that if habitat structure and human disturbance change along an urban gradient, the richness and abundance of trophic guilds should also vary accordingly. We placed 50 transects 100 m long × 50 m wide in five districts with different levels of urbanization, determined by habitat structure variables. We recorded the number and abundance of species and the amount of pedestrians and vehicles passing through each transect. We recorded 23% of all bird species known for the Santa Fe province and categorized them within 19 trophic guilds. The percentage of area covered by herbaceous vegetation, water bodies and trees and shrubs had a positive relationship with the richness and abundance of most of trophic guilds (hawking aerial, terrestrial, bark and foliage insectivores; terrestrial and generalized granivores; generalized, aquatic diving and foliage omnivores; hawking aerial, aquatic diving and striding carnivores; nectarivores; and aquatic filters). Pavement surface and human disturbance variables had a negative relationship with the richness, and high buildings and pavement surface had a positive relationship with the abundance of terrestrial omnivores and coursing aerial insectivores. Variation partitioning revealed that habitat structure and human disturbance were better predictors of the richness than the abundance of each trophic guild. Results showed that trophic guilds associated to vegetation strata were seen to increase their richness and abundance towards green areas, even if they presented generalist or specialist habits. Urban planners should conserve or manage the surrounded natural spaces when the growth of the city is directed to these areas and increase the availability of environmental features within the urban matrix.     

Wintering bats of the upper Snake River plain: occurrence in lava-tube caves

Distribution and habitat selection of hibernating bats at the Idaho National Engineering Laboratory (INEL) and adjacent area are reported. Exploration of over 30 lava-tube caves revealed that two species, Myotis leibii and Plecotus townsendii, hibernate in the upper Snake River Plain. Five species, M. lucifugus, M. evotis, Eptesicus fuscus, Lasionycteris noctivagans, and Lasiurus cinereus are considered migratory. Myotis leibii and P. townsendii hibernate throughout much of the area, occasionally in mixed-species groups. Myotis leibii uses the dark and protected regions of the cave, usually wedged into tiny pockets and crevices near or at the highest portion of the ceiling. Individuals of P. townsendii may be found at any height or depth in the cave. Temperature appears to be the primary limiting factor in habitat selection. Myotis leibii was found in significantly cooler air temperatures than P. townsendii . Neither species tolerated continuous temperatures below 1.5 C. Relative humidity does not seem to be a significant factor in the distribution or habitat selection of the two species in lava-tube caves.     

The food web of parasitoid wasps and their non-phytophagous fly hosts in birds' nests (Hymenoptera: Chalcidoidea,and Diptera: Cyclorrhapha)

We present a food-web study of the parasitoid wasps and their fly hosts found in the nests of cavity-nesting songbirds. This birds' nest parasitoid web is different from all parasitoid webs studied comprising exclusively non-phytophagous host species. A total of 490 nests were examined for host occurrence, abundance and parasitism rates. Thirty-two species of potential hosts and 10 species of parasitoid wasps were recorded in nests from 25 sites in northern Germany and from two additional sites in south-western Germany. Most of these species were rare and unspecialized. The only very common parasitoid was Nasonia vitripennis (Chalcidoidea: Pteromalidae). The records of 14 regular host species from northern Germany, which are connected to all 10 parasitoid species, were used for further calculation of food-web statistics. The parasitoid communities in birds' nests were compared with other known parasitoid communities. The birds' nests exhibited a lower species richness compared with communities of phytophagous hosts, but showed similarities with communities of necrophagous or coprophagous hosts, or of parasitoid hosts. The parasitism rate was comparable in all host–parasitoid-systems, supporting the idea that the parasitism rate is independent of species richness.     

Pelagic tunicates in the China Seas

The biogeography of pelagic tunicates belonging to the two taxonomic classes Larvacea and Thaliacea was analysed using seven sampling stations along the coastal regions of Taiwan which contribute to all the China Seas surrounding Taiwan. The collected data were then compared with the information in the available literature about pelagic tunicate species diversity in the China Seas (Bohai Sea, North Yellow Sea, East China Sea and South China Sea) and previous studies on these organisms in Taiwan waters to get a better understanding of their biodiversity, abundance and distribution. A total of 19 species of pelagic tunicates were observed and identified to the speciel level: five species belonging to the class Larvacea, in the two families Oikopleuriidae and Fritillariidae; 14 species belonging to the class Thaliacea, in the families Salpidae and Doliolidae. We summarised morphological characteristics of the recorded species which were found to be useful for identification, and we provided further information about their global distribution and ecological preferences. Our results revealed that pelagic tunicates occurred in the China Seas with high species richness throughout the year. This is the first account on the class Larvacea from Taiwan. Comparing our results with available records from all China Seas, Taiwan proved to be a species diversity hotspot for pelagic tunicates, especially for the family Salpidae. The waters of southern Taiwan showed a higher species richness compared to the northern counterpart. The doliolid Doliolum denticulatum can be designated as an indicator of the low-temperature China Coastal Current species.     

Anuran assemblage in a rice field agroecosystem in the Pantanal of central Brazil

Agricultural practice is an important factor that threatens biodiversity. However, modified habitats such as irrigated rice fields could serve as potential refuges for several species of amphibians. This study describes the composition of an anuran assemblage in an irrigated rice field system in the Pantanal floodplains of central Brazil. The low species richness found in rice fields and neighbouring habitats can be interpreted as resulting from the structural limitations of a modified environment. Flooding occurs for longer periods than in natural areas and leads to a lack of dry space, hindering the presence of terrestrial anuran species. Furthermore, the absence of herbaceous vegetation and shrubs in cultivated fields prevents the establishment of species of large tree frog. A positive correlation was found between rainfall and richness, although the abundance of some species did not fit this relationship. The present study suggests that only anuran species that are generalists and highly resilient will survive as the natural wetlands are transformed into irrigated rice plantations.     

Diet comparison between rainforest and cave populations of Craugastor alfredi (Anura: Craugastoridae): does diet vary in contrasting habitats?

Information about interpopulational variation of diet is important for thoroughly understanding the ecological niche of a species, the possible attributes that have allowed it to live in different habitats and ecosystems (if it is the case) and the degree of dietary specialization. This study compared dietary composition and diversity, size of prey consumed and feeding intensity between two geographically proximate populations of Craugastor alfredi, inhabiting contrasting habitats: one located in a remnant tropical rainforest and the other population located within a cave entrance, in eastern Mexico. A total of 118 frogs (50 from rainforest and 68 from cave) were stomach-flushed and, from those, 86 had at least one prey item (42 from rainforest and 44 from cave). Consumption proportions of orthopterans differed between habitats, with frogs from the cave having higher importance values of this prey than frogs from the rainforest. Additionally, both dietary diversity and feeding intensity were higher in the rainforest population. It was concluded that the generalized diet of C. alfredi, besides the high consumption of orthopterans by the cave population, may have contributed to its success in cave entrances. Nonetheless, other non-feeding attributes like small body size, direct development and semiarboreality may also facilitate the use of rock crevices in caves for foraging and reproduction.     

Trichoptera and other macroinvertebrates in springs of the Great Basin: species composition, richness, and distribution

Detailed surveys of aquatic invertebrates in 28 springs along the western border of the Great Basin were made using pan traps, emergence traps, black lights, and benthic sampling devices from 1994 to 1998. Although all macroinvertebrate groups were collected, caddisflies (Insecta: Trichoptera) were sampled most intensively. Fifty-eight species of caddisflies were collected from the 28 springs, with up to 18 species from a single spring. Although several springs had very similar physicochemical characteristics, none had identical trichopteran species composition. Using Wards minimum variance clustering technique, and with all macroinvertebrates identified to the lowest possible level, we found 3 taxa assemblages. These assemblages occurred in springs with the following physical conditions: (1) warm water (15.9° C), low elevation (1794 m); (2) cold water (8.5° C), mid-elevation (2334 m); and (3) cold water (6.6° C), high elevation (1794 m). Although the warm water group had a distinct assemblage of invertebrates (amphipods, gastropods, Trichoptera), distinct assemblages did not separate the 2 cold water groups. Discriminant analysis indicated that temperature, conductivity, alkalinity, and elevation were most responsible for discriminating group 1 from groups 2 and 3; temperature and elevation distinguished the latter 2 groups. Spring permanence, lack of disturbance, and cold water temperatures were the factors most responsible for explaining higher species richness of Trichoptera.     

Evaluating plant invasions from both habitat and species perspectives

We present an approach to quantitatively assess nonnative plant invasions at landscape scales from both habitat and species perspectives. Our case study included 34 nonnative species found in 142 plots (0.1 ha) in 14 vegetation types within the Grand Staircase-Escalante National Monument, Utah. A plot invasion index, based on nonnative species richness and cover, showed that only 16 of 142 plots were heavily invaded. A species invasive index, based on frequency, cover, and number of vegetation types invaded, showed that only 7 of 34 plant species were highly invasive. Multiple regressions using habitat characteristics (moisture index, elevation, soil P, native species richness, maximum crust development class, bare ground, and rock) explained 60% of variation in nonnative species richness and 46% of variation in nonnative species cover. Three mesic habitats (aspen, wet meadow, and perennial riparian types) were particularly invaded (31 of 34 nonnative species studied were found in these types). Species-specific logistic regression models for the 7 most invasive species correctly predicted occurrence 89% of the time on average (from 80% for Bromus tectorum , a habitat generalist, to 93% for Tamarix spp., a habitat specialist). Even with such a modest sampling intensity (<0.1% of the landscape), this multiscale sampling scheme was effective at evaluating habitat vulnerability to invasion and the occurrence of the 7 most invasive nonnative species. This approach could be applied in other natural areas to develop strategies to document invasive species and invaded habitats.     

The influence of habitat features on amphibian distribution in Northeastern Greece

Environmental and isolation variables relating to abundance of breeding amphibians, species richness and community structure at different spatial scales were examined in the Dadia-Lefkimi-Soufli Forest National Park, Evros, Greece. Logistic regression and a generalized linear model were used to relate several habitat characteristics to species occurrence and species richness. The community structure responses to breeding-pond features were examined at four spatial scales using canonical correspondence analysis (CCA). The richest communities live in low-altitude ponds, with stony or clay bottoms, high solar exposure and abundant submerged and floating vegetation. The CCA models were significant (p < 0.005) and revealed the influence of altitude, percentage of field and broadleaf forest coverage, and number of water bodies on amphibian species assemblages at all four spatial scales. There is a specific need for holistic management of amphibians that will consider habitat connectivity, particularly between aquatic and terrestrial habitats, at a larger, more interconnected scale.     

An ecological study of Cueva de los Roques lava tube (Tenerife,Canary Islands)

Several aspects of the ecology of Cueva de los Roques were studied: the survey initiated by other speleologists was completed; the flora at the entrance to the cave was studied; and the fauna of the whole cave was analysed by sampling on two occasions three months apart, using a combination of visual searching and baited trapping. The most striking result was the difference in both physical conditions and biology between the two branches of the cave. Branch A has several entrances and thus appreciable air movements, with the result that it is inhabited only by trogloxenes and a few troglophiles. In contrast, branch B is a blind tube with constant high humidity and stable temperature, here there is a community of troglobites. We have found a total of 27 species of invertebrates; these include nine troglobites, of which seven are already known from other lava tubes on Tenerife. This suggests the occurrence of dispersal through a network of cracks in the subsoil, as in other volcanic and karst regions.     

Present effects of past wildfires on the diets of stream fish

We investigated present indirect effects from a decade-old burn on the diets of stream fish. Based on soil instability and burn patterns from a 12–14-year-old wildfire complex, we separated 9 streams into 3 conditions: unburned, burned, and burned/scoured (i.e., experiencing a massive scour event 1 year post-burn). In the streams, we measured light levels and water temperatures, and we estimated fish density and biomass. We removed the digestive tracts from 9–15 rainbow trout ( Oncorhynchus mykiss ) from each stream and used a gravimetric procedure to analyze gut contents. Canopy cover development may dictate the composition of dietary items. Greater amounts of aquatic invertebrates and inorganic material were found in trout from streams with reduced overhead canopy. Further, these streams had lower amounts of terrestrial invertebrates and organic materials in the diets of fish. Although trout abundance was not different among the stream treatments, fire-induced, indirect effects on fish diets were still evident more than a decade after the burn. This suggests that recovery rates for trout assemblages may take longer than predicted and may depend on riparian recovery.     

Aspects of the activity rhythm and population size of troglophilic mygalomorph spiders (Trechona sp., Dipluridae) in a quartzite cave in Minas Gerais,Brazil

Records of mygalomorphs inhabiting caves have increased in the past years. We present data on a population of Trechona sp. spiders, found in a quartizite cave in Diamantina, Minas Gerais, Brazil. The spiders and their retreats were marked, and this population was followed for 17 months. The population consisted of up to 100 individuals, comprising the worlds’ largest known cave-dwelling population of mygalomophs. The estimated population size (Jolly-Seber model) varied from 50.36 to 853.43, the latter considered much overestimated. We did not find individuals of Trechona sp. in the surrounding epigean areas. The number of spiders was higher in the entrance zone than in the other two zones (twilight and dark zones). We found that individuals at the entrance zone showed similar activity to a nocturnal spider, whereas the other two groups showed conspicuous differences from this pattern, spending longer periods without rest, on the sheet-web as a sit-and-wait predator.     

The terrestrial micro-arthropod fauna of the South Sandwich Islands

The South Sandwich Islands are an isolated maritime Antarctic volcanic island arc 550-600km south-east of South Georgia. The terrestrial biology of the islands, with emphasis on the unique habitats associated with volcanically warmed ground, was investigated in 1997 and compared with the data collected during the only previous (1964) terrestrial expedition to the archipelago. The terrestrial fauna includes 29 free-living micro-arthropod species (nine Collembola and 20 Acari) and two, currently unidentified, enchytraeid worms; a further eight parasitic and sublittoral Acari are recorded in the literature. Freshwater habitats are very restricted in the archipelago and no freshwater fauna was located. Supralittoral pools on a single island contained the marine isopod Cassidinopsis maculata. There are no endemic taxa and no shoreline invertebrates other than the supralittoral Archisotoma brucei (Collembola) and two Enchytraeidae. Diversity on individual islands is, in part, a function of available ice-free ground area. The majority of dominant species throughout the archipelago, Cryptopygus antarcticus (Collembola), Nanorchestes nivalis, Eupodes minutus, Alaskozetes antarcticus and Halozetes belgicae (Acarina), originate on other maritime Antarctic islands, while Ayersacarus tilbrooki (Acarina) is sub-Antarctic. Few (one to three) individuals of several other sub-Antarctic species were recorded by either 1964 or 1997 expeditions, but only Pilellus rykei (Acarina) was reported by both. None of the sub-Antarctic species thought to be associated with geothermally warmed ground in 1964 was confirmed in 1997, despite extensive sampling of the same sites. It is more probable that sub-Antarctic colonists frequently arrive on the South Sandwich Islands but are unable to establish longterm viable populations. Cryptopygus caecus, now widespread on Candlemas I., is a solitary exception to this generalization.