Effects of soil characteristics and human disturbance on tiger beetle oviposition

Abstract 1. Understanding species‐specific habitat requirements is important in insect ecology. Co‐occurrence of closely related species can provide insight into microhabitat segregation. Tiger beetles are well suited for such studies, as they occur in multi‐species assemblages, exhibit species‐specific habitat requirements, and are sensitive to anthropogenic modifications of the environment. 2. This study investigated ovipositional microhabitat choice of two sympatric tiger beetles at Point Reyes National Seashore, California, U.S.A., and evaluates how human activity affects that choice. Cicindela oregona is widespread and common whereas C. hirticollis, an undescribed subspecies, is locally threatened. Laboratory experiments tested oviposition‐site selection of the two species in response to variations in moisture, pH, salinity, and grain size. Field experiments tested larval burrow location in response to experimental shading and experimental human disturbance. 3. Laboratory results indicated that while C. hirticollis females preferred a narrow range of moisture levels and fine sands, C. oregona females had more specific pH and salinity requirements and preferred coarser sands. They also differed in timing of activity. Preferences are probably related to prevention of fungal or bacterial infection and avoidance of desiccation and immersion. 4. In the field, significantly more larval burrows were found under experimental shading for both species. In addition, repeated human compaction of the sand significantly decreased the number of larval burrows. 5. Results suggest that protection of microhabitat, restoration of native plants, and limitation of human traffic are vital in the conservation management of tiger beetles.     

Microhabitat and rhythmic behavior of tiger beetle Callytron yuasai okinawense larvae in a mangrove forest in Japan

Mangrove forests are regularly flooded by tides at intervals of approximately 12.4 h (tidal rhythm). Larvae of the tiger beetle Callytron yuasai okinawense in a mangrove forest made shallow burrows in mounds up to 1 m in height constructed by the mud lobster Thalassina anomala. No larval burrows were observed on the forest floor, which was very muddy even during low tide. Some larvae plugged the burrow openings before they were submerged at high tide. The mean interval between consecutive burrow plugging events was 12.37 h, which is similar to the period of tidal cycles. Nine out of 30 larvae plugged the burrow openings even when the burrows did not become submerged. Plugging behavior may be governed by an endogenous biological clock, or may be a response to exogenous information about tidal level (e.g. moisture seeping through the ground).     

Hidden burrow plugs and their function in the tiger beetle, Cosmodela batesi (Coleoptera, Cicindelidae)

Tiger beetle larvae excavate and live in underground burrows, whose openings they sometimes plug with soil. This study documents the burrow plugging behavior of the tiger beetle, Cosmodela batesi (Fleutiaux), in the field. We also tested the function of burrow plugs in the laboratory. In the field, C. batesi more frequently made a plug when it rained. Most larvae made plugs inside their burrows (rather than at the soil surface), and the use of an endoscope was necessary to detect these sub-surface plugs. In the laboratory, flooding was simulated by artificially introducing water into specially-made arenas. Water filled the entire burrow when there was no plug, whereas plugged burrows maintained air chambers inside. When a plug was broken with a wire, burrows filled up with water. The burrowing and plugging behavior described in this study is likely an important adaptation of C. batesi to its habitat.     

Wind-powered wheel locomotion, initiated by leaping somersaults, in larvae of the southeastern beach tiger beetle (Cicindela dorsalis media)

Rapid movement is challenging for elongate, soft-bodied animals with short or no legs. Leaping is known for only a few animals with this "worm-like" morphology. Wheel locomotion, in which the animal's entire body rolls forward along a central axis, has been reported for only a handful of animals worldwide. Here we present the first documented case of wind-powered wheel locomotion, in larvae of the coastal tiger beetle Cicindela dorsalis media. When removed from their shallow burrows, larvae easily can be induced to enter a behavioral sequence that starts with leaping; while airborne, larvae loop their body into a rotating wheel and usually either "hit the ground rolling" or leap again. The direction larvae wheel is closely related to the direction in which winds are blowing; thus, all our larvae wheeled up-slope, as winds at our study site consistently blew from sea to land. Stronger winds increased both the proportion of larvae wheeling, and the distance traveled, exceeding 60 m in some cases. In addition, the proportion of larvae that wheel and the distance traveled by wheeling larvae are significantly greater on smooth sandy beaches than on beach surfaces made rough and irregular by pedestrian, equestrian, and vehicular traffic. Like other coastal species of tiger beetles, C. dorsalis media has suffered major declines in recent years that are clearly correlated with increased human impacts. The present study suggests that the negative effects of beach traffic may be indirect, preventing larvae from escaping from predators using wheel locomotion by disrupting the flat, hard surface necessary for efficient wheeling.     

Habitat and sediment preferences ofAxarus festivus larvae

During fall draw-down of a reservoir in northeast Kansas it was observed that larvae ofAxarus festivus were restricted to highly weathered Pennsylvanian Shale outcrops and surrounding coarse sediments with high-clay content derived from erosion of the shale outcroppings. Larvae constructed burrows into the outcrops and eroded coarse sediments, which they used to filter feed by setting up currents through the burrows. Burrows were widely distributed over the outcrops, with average densities ranging from 372–2,351 burrows m^–2. However, closer inspection revealed that burrows were more common at apices of individual shale strata, where weathering of the outcrop was most advanced. Here burrows were more uniformly distributed and densities ranged to 4,166 burrows m^–2. 73% of burrows contained larvae. Burrows were generally U-shaped, and averaged 1.8 mm in diameter and 42 mm in total length. Laboratory experiments revealed that 4th instar larvae removed from burrows could construct new burrows in weathered shale, but preferentially used old empty burrows if available. When given choices among alternative sediment combinations of sandvs. finely-ground shale, sandvs. coarsely-ground shale, and finely-ground shalevs. coarsely-ground shale, larvae exhibited statistically significant preferences for the finely-ground shales (P<0.001), coarsely-ground shales (P<0.001), and coarsely-ground shales (P<0.01), respectively. It is concluded that larvae (1) actively select shale or high-clay content sediments, (2) can differentiate among sediments with differing physical properties and (3) exhibit behavioral choices for sediment types that guide them toward shale outcrops.     

Respiratory gas concentrations in the microhabitats of some florida arthropods

• 1.1. The concentrations (dry gas %) of oxygen and carbon dioxide were measured in a variety of microhabitats of arthropods in Florida: at the ends of the burrows of three spider species (Sphodros abboti, Geolycosa micanopy, Cyclocosmia torreya) and a tiger beetle (Megacephala carolina) larva, within ant (Solenopsis invicta) mounds, within stumps inhabited by termites (Reticulitermes flavipes), and within and under decaying hardwood logs.
• 2.2. Hypoxia and hypercarbia occurred in all microhabitats, with the ratio of oxygen decrement to carbon dioxide increment close to one. Changes for both gases were minor in the spider burrows, under decaying logs, and within ant mounds (<2.3% for O₂ and 1.1% for CO₂) and are probably physiologically unimportant to their inhabitants.
• 3.3. In contrast, %O₂ fell to as low as 12–14%, and CO₂ rose to as high as 6–8%, in the burrows of tiger beetle larvae, within decaying logs, and inside decaying stumps inhabited by termites.
• 4.4. Such changes, particularly for CO₂ may present a challenge to organisms living in these microenvironments.
• 5.5. Approximately 20–25% of the changes in the concentrations of respiratory gases in the burrows of tiger beetle larvae are attributable to the metabolism of the larva, the remainder being due to diffusional exchanges with the soil.

     

Maternal attendance and the maintenance of family groups in common earwigs (Forficula auricularia): a field experiment

Abstract.  1. Understanding the evolution of subsocial behaviour and parental care requires experimental tests of the functional significance of such behaviours and the role of tending parents in the maintenance of family groups. Studies in subsocial insects addressing these issues experimentally and in the field are still relatively rare.
2. In such a field experiment, it is demonstrated here that the presence of tending females enhances the maintenance of family groups in common earwigs, Forficula auricularia (Dermaptera; Forficulidae). Experimental removal of tending mothers resulted in substantially decreased recovery of occupied nest burrows and larvae. This effect may have been because of decreased survival among experimental larvae, although a possible role for enhanced larval dispersal could not be fully ruled out.
3. Experimental (motherless) larvae were partly observed in family groups with a tending female, in both experimental and control nest burrows, suggesting that these larvae had been adopted by family groups moving to new nest burrows, and/or that experimental larvae may have actively joined other family groups.
4. This study demonstrates under field conditions the functional importance of maternal attendance for the maintenance of family groups in common earwigs, and suggests that adoption and clutch-joining are factors affecting the social structure of this species.     

Production of Tiger Puffer <Emphasis Type="Italic">Takifugu rubripes</Emphasis> Offspring from Triploid Grass Puffer <Emphasis Type="Italic">Takifugu niphobles</Emphasis> Parents

The tiger puffer Takifugu rubripes is one of the most popular aquacultural fish; however, there are two major obstacles to selective breeding. First, they have a long generation time of 2 or 3 years until maturation. Second, the parental tiger puffer has a body size (2–5 kg) much larger than average market size (0.6–1.0 kg). The grass puffer Takifugu niphobles is closely related to the tiger puffer and matures in half the time. Furthermore, grass puffer can be reared in small areas since their maturation weight is about 1/150 that of mature tiger puffer. Therefore, to overcome the obstacles of maturation size and generation time of tiger puffer, we generated surrogate grass puffer that can produce tiger puffer gametes through germ cell transplantation. Approximately 5000 tiger puffer testicular cells were transplanted into the peritoneal cavity of triploid grass puffer larvae at 1 day post hatching. When the recipient fish matured, both males and females produced donor-derived gametes. Through their insemination, we successfully produced donor-derived tiger puffer offspring presenting the same body surface dot pattern, number of dorsal fin rays, and DNA fingerprint as those of the donor tiger puffer, suggesting that the recipient grass puffer produced functional eggs and sperm derived from the donor tiger puffer. Although fine tunings are still needed to improve efficiencies, surrogate grass puffer are expected to accelerate the breeding process of tiger puffer because of their short generation time and small body size.     

Salinity and shade preferences result in ovipositional differences between sympatric tiger beetle species

1. Adult tiger beetles of the genus Cicindela often co‐occur within a habitat but larvae do not. Larvae are sedentary and form usually permanent burrows at the site of oviposition where they require 1–3 years for development. 2. To test niche partitioning based on ovipositional preference, the behaviour of two sympatric salt marsh tiger beetles, Cicindela circumpicta and C. togata (Coleoptera: Cicindelidae), were examined. 3. In laboratory studies, female C. circumpicta and C. togata distinguished between experimental salinities, with the former preferring 4 parts per thousand (ppt) and the latter preferring 12 ppt. In the field, C. circumpicta larvae were associated with lower salinities (1–3 ppt) and vegetation along the edges of salt flats while C. togata larvae were found on open salt flats often near halophytes (average salinity = 7.8 ppt). 4. In the field, females chose sites for oviposition in response to shade but not vertical landmarks. In a direct test, 53 of 56 new larval burrows occurred in shaded treatments, three in nonshaded controls. 5. Compared with nonshaded controls, shade increased survival of eggs that were collected in the laboratory and placed in the field. For C. circumpicta eggs, 78% placed in shaded treatments hatched, while significantly fewer (22%) hatched in exposed treatments. For C. togata, 43% of eggs placed in the shade hatched, while no eggs placed in exposed treatments hatched. 6. These results support the hypothesis of niche partitioning between C. circumpicta and C. togata based on ovipositional choice and resulting larval habitat.     

ECOLOGY AND EVOLUTION OF MATING SYSTEMS OF FIDDLER CRABS (GENUS UCA)

1. General accounts of the natural history and behaviour of fiddler crabs suggest there exist two broad mating patterns in the genus. Most western and Indo-Pacific species mate on the surface of intertidal substrates near burrows females defend. The sexes associate only briefly during courtship and mating. In contrast, males of many American species court from and defend burrows to which females come for mating. Copulation occurs underground in burrows plugged at the surface; the sexes usually remain together for at least several hours. Here we summarize and contrast recent detailed field studies of the mating systems of U. pugilator, an American species, and U. vocans, a species widely distributed in the western and Indo-Pacific. We indicate how differences in the breeding ecology of these two species may account for basic differences in modes of sexual selection leading to the two broad mating patterns in the genus. 2. U. pugilator burrows in protected sandy substrates in the upper intertidal and supratidal zone. During ebb tide, nonbreeding crabs leave burrows they occupy during high tide to forage on food-rich substrates in the lower intertidal zone. Reproductively active males remain in the burrow zone where they fight for and defend burrows from which they court. Large males win most fights for burrows and tend to defend burrows high on the elevation gradient, especially during periods with relatively high tides. Females usually approach and descend the burrows of several males before choosing their mates by remaining in males' burrows. Males remain underground with their mates for 1–3 days until after they oviposit their eggs. Some males then emerge and leave their burrows while others sequester their mates in the chambers where mating and oviposition has occurred, dig new chambers and resume courtship, perhaps attracting additional females. In either case, females remain underground for approximately 2 weeks, finally emerging to release their planktonic larvae. Burrows that do not collapse due to tidal inundation or flooding by groundwater are best for breeding and usually are located relatively high on the elevation gradient. Females choose mates indirectly by preferring to breed in burrows that will remain intact while they oviposit and incubate their eggs. Large males mate more often than small males because they are better able to defend burrows at locations females prefer to breed. The mating system of U. pugilator may be classified as resource-defence polygyny. 3. U. vocans burrows in open muddy substrates in the mid- to lower intertidal zone. At a site near Chunda Bay, Australia, where the reproductive behaviour of this species has been studied in depth, both sexes feed near burrows they defend. Females tend to occupy their burrows for longer periods and move shorter distances than do males. Mating occurs on the surface near the burrows that females defend. Females accept both resident and wandering males as mates. They show no preference for mating with larger males. Female choice may be based on other male morphological or behavioural characteristics. Females oviposit their eggs either while on the surface or in their burrows. They produce relatively small clutches and are active on the surface throughout their breeding periods. Males fight both their neighbours and wandering males. Large males tend to win fights and defend burrows in areas where large females, which produce relatively many eggs, are most dense. Such areas may offer greater protection from predators than areas occupied by smaller females. Small males mate about as often as large males but may father fewer larvae. The mating system of U. vocans is resource-free and promiscuous. 4. The mating systems of U. pugilator and U. vocans differ fundamentally in that female U. pugilator require access to a specific microenvironment to breed successfully, while female U. vocans do not. We suggest this difference occurs because of contrasts in clutch sizes and the mobility and movement patterns of feeding females. Female U. pugilator produce relatively large clutches and probably experience more intense selection from factors that can cause egg loss and mortality than do U. oocans, which produce clutches of sufficiently small volume to be protected by their abdominal flaps. Hence, the range of suitable breeding environments for U. pugilator is small compared to that for U. vocans. In addition, U. pugilator burrows in areas that are relatively food-poor, leading to daily migrations to and from food-rich substrates in the lower intertidal zone, preventing female defence of an area suitable for both breeding and feeding. U. vocans, however, burrows in areas sufficiently rich to support feeding, leading to relatively low female mobility and defence of burrows that are also suitable breeding sites. 5. Adaptive radiation of the genus Uca in the Americas is manifest by trends toward smaller adult size, higher population densities, more frequent microgeographic sympatry and increased terrestriality, compared to species in the western and Indo-Pacific regions. We outline the general features of the selection mechanisms tying each of these trends to the evolution of resource—defence mating systems. Intraspecific variation in the courtship behaviour and site of mating in U. lactea and U. vocans supports our contention that resourse—defence behaviour tends to occur at high population densities. Additional data are needed to evaluate the other hypotheses critically.     

Parasitism of Neotropical Tiger Beetles (Coleoptera: Carabidae: Cicindelinae) by Anthrax (Diptera: Bombyliidae)

Bee flies (Bombyliidae) were recorded as parasitoids of larval tiger beetles at two rain forest localities (near São Paulo and Manaus) in Brazil. Anthrax gideon was reared from larvae of Oxycheila tristis. Up to 33 parasitoid larvae were found on a single tiger beetle host. Pupation of the bee fly took place in late August and the pupal stage lasted 14 days. The host digs horizontal burrows in contrast to the great majority of cicindelids, as does Pseudoxycheila tarsalis, the other known host of A. gideon. Two pupae of another undetermined Anthrax species were reared from larvae of Pentacomia ventralis in Central Amazonia. Pupation of this Anthrax sp. took place in October, the period of lowest host abundance.     

Artificial larviposition sites for field collections of the puparia of tsetse flies Glossina pallidipes and G. m. morsitans (Diptera: Glossinidae)

Tsetse flies Glossina pallidipes Austen and G. morsitans morsitans Westwood deposit their larvae in warthog burrows, in August-November, at Rekomitjie Research Station, Zambezi Valley, Zimbabwe. Artificial burrows, made from 200-l steel drums, were used to sample these flies and to collect their puparia. Sand-filled plastic trays in the burrows served as a substrate for larval deposition. The sand was covered with c. 2 cm of leaf litter after it was shown that only 3% of larvae were deposited on bare sand if both substrates were available. Other burrow modifications - artificially shading the burrow entrance, increasing the relative humidity inside the burrow, or reducing the size of the burrow entrance - significantly decreased deposition rates. The use of burrows in the hot season results in a reduction in the temperature experienced by the puparium towards an assumed optimum level of 26 degrees C. Artificial burrows maintained a mean temperature of 28.5 degrees C during October-November 1998, c. 2.5 degrees C cooler than ambient; earlier work has shown that natural burrows can be c. 5 degrees C cooler than ambient at these times. This may explain why natural burrows in full sunlight were used for larviposition, whereas artificial burrows were used only when they were in deep shade, and why significantly higher proportions of G. pallidipes were found in natural (66%) than in artificial burrows (34%). Better-insulated artificial burrows might produce more puparia with higher proportions of G. pallidipes. Burrows become waterlogged during the rains and may be too cool for optimum puparial development during the rest of the year. The percentages of G. m. morsitans in catches of females from artificial burrows, refuges and odour-baited traps were 34, 26 and < 10% respectively. Traps are biased in favour of G. pallidipes; artificial burrows may show a bias in favour of G. m. morsitans that is a function of temperature. Artificial warthog burrows provide a convenient way of studying the puparial stage in tsetse and for the first time facilitate the capture of females as they deposit their larvae.     

Burrow densities and nest site preferences of petrels (Procellariidae) at the Prince Edwards Islands

Summary The nest-site preferences of six burrowing petrel species, Salvin's prion Pachyptila vittata salvini, blue petrel Halobaena caerulea, great-winged petrel Pterodroma macroptera, Kerguelen petrel Pterodroma brevirostris, soft-plumaged petrel Pterodroma mollis and white-chinned petrel Procellaria aequinoctialis, in the northeastern part of Marion Island (Prince Edward Island group, southern Indian Ocean) were analyzed by step-wise multiple regression. The nest-site characteristics measured were slope angle, soil depth and moisture content, percentage cover by stones or boulders and percentage cover by each of seven major plant species. The major nest-site preferences were: exposed areas with shallow soil (Salvin's prion); steep coastal slopes (blue petrel); sheltered well-drained slopes with deep soil (great-winged petrels); wet areas along drainage lines (Kerguelen petrel); steep slopes (soft-plumaged petrel); and areas with deep soil (white-chinned petrel). Similar species showed no significant avoidance of nest sites where there were burrows of potential competitors but did tend to nest spread out over different habitats. Burrow densities were determined in six habitat and seven vegetation types. Salvin's prion was the most abundant species (81% of burrows, with a maximum density of 279 burrows ha^-1) and used both burrows and natural cavities for nesting. For all species combined, burrow densities at Marion Island were lower than in comparable habitats and vegetation types at neighbouring Prince Edward Island. Depredation by feral house cats Felis catus, absent from Prince Edward Island, is assumed to be largely responsible for this difference.     

Circatidal rhythmic behaviour in the coastal tiger beetle Callytron inspecularis in Japan

Larvae of the coastal tiger beetle Callytron inspecularis (W. Horn) (Coleoptera: Cicindelidae) plug their burrow opening before submergence at high tide. Field observations showed that burrow plugging was a rhythmic behaviour that coincided with the tidal cycle (ca. 12.4 h). On average, larvae plugged their burrows 41.8 min before the tide covered the habitat. The mean interval between consecutive burrow-plugging events in the field was 12.40 h. In the laboratory, in the absence of tidal inundation, the mean interval between consecutive burrow-plugging events was 12.45 h. This suggests that the burrow-plugging rhythm of the coastal tiger beetle is governed by an endogenous circatidal rhythm.     

Wet hibernacula promote inoculative freezing and limit the potential for cryoprotective dehydration in the Antarctic midge,Belgica antarctica

The terrestrial midge, Belgica antarctica, occupies a diverse range of microhabitats along the Antarctic Peninsula. Although overwintering larvae have the physiological potential to survive by freezing or cryoprotective dehydration, use of the latter strategy may be constrained by inoculative freezing within hibernacula. To investigate the influence of microhabitat type on larval overwintering, we selected four substrate types that differed markedly in their composition and hydric characteristics. Organic content of these substrates ranged from 14 to 89 %. High organic content was associated with higher values for saturation moisture content (up to 2.0 H₂O g^?1 dry mass) as well as elevated levels of field moisture content. Seasonal values of field moisture content remained near or above the saturation moisture value for each microhabitat type, and when larvae were cooled in substrates rehydrated to field-based levels, they were unable to avoid inoculation by environmental ice, regardless of substrate type. Consequently, our data suggest that wet hibernacula would force most larvae to overwinter in a frozen state. Yet, dehydrated larvae were collected in April during the seasonal transition to winter suggesting that spatial and temporal variations in precipitation and microhabitat conditions may expose larvae to dehydration and promote larval overwintering in a cryoprotectively dehydrated state.     

Burrowing owls and burrowing mammals: are ecosystem engineers interchangeable as facilitators?

Terrestrial vertebrates exhibit dynamic, positive interactions that form and dissolve under different circumstances, usually with multiple species as participants. Ecosystem engineers are important facilitators of other species because they cause physical changes in the environment that alter resource availability. Although a species can be associated with more than one partner, facilitators may not be interchangeable if they differ in abundance, behavioral characteristics, or interactions with other factors in ways that condition the outcome of the association. We examined interactions between burrowing owls (Athene cunicularia) and two burrowing mammals, hairy armadillos (Chaetophractus villosus) and plains vizcachas (Lagostomus maximus), and determined whether these ecosystem engineers are interchangeable for owls. We examined reproductive success for owls nesting in these mammal burrows, constructed a logistic regression model to identify habitat characteristics associated with owl nests, and examined the engineering activities of the mammals. Data on reproduction and habitat indicate that armadillos and vizcachas are not interchangeable for owls. Thirty-five percent of the nests in vizcacha burrows produced fledglings; no fledglings were produced from nests outside vizcachas colonies, even though owls nest successfully in armadillo burrows in other parts of Argentina. Vizcachas facilitate burrowing owls by construction of burrows and by producing open understory vegetation through herbivory. In contrast, armadillos do not alter vegetation, and their burrows are suitable for nest sites only when they occur in recently burned areas or areas maintained by anthropogenic disturbance. Our habitat model also suggests that fire plays a key role in maintaining owl populations because fire is the only natural process that reduces shrubs to the level required by owls. Current management practices of eradication of vizcachas and fire suppression in shrublands could have strong negative consequences for burrowing owls.     

Location of long‐term communal burrows of a threatened arid‐zone lizard in relation to soil and vegetation

The great desert skink (Liopholis kintorei) of the Egerniinae subfamily (Reptilia: Scincidae) is a communal burrowing lizard that inhabits arid spinifex grasslands in central Australia. Great desert skink activity is centred in and around the burrows which are inhabited for many years. However, it is not known whether skinks select burrow sites with specific attributes or how continuing occupancy of burrows is influenced by the surrounding habitat; especially post‐fire, when plant cover is reduced. Here, we test whether great desert skink burrows in areas burnt 2 years previously and in longer unburnt areas are associated with particular habitat attributes, and whether there are differences between occupied and recently abandoned burrow sites. Vegetation composition, cover and soil surface characteristics at 56 established great desert skink burrows, including occupied and recently unoccupied burrows, were compared with 56 random nearby non‐burrow control sites. Burrow sites had higher plant cover compared with the surrounding landscape in both recently burnt and longer unburnt areas and were more likely to be associated with the presence of shrubs. Soil stability and infiltration were also higher at burrow sites. However, we found no evidence that burrows with lower cover were more likely to be abandoned. Our results suggest that great desert skinks may actively select high cover areas for burrow construction, although differences between burrow and control sites may also partly reflect local changes to plant cover and composition and soil properties resulting from burrow construction and long‐term habitation of a site. Further research should determine if burrows with shrubs or higher plant cover provide greater protection from predators, more structural stability for burrow construction, increased prey abundance or other benefits. We recommend that maintenance of areas with relatively higher plant cover be prioritized when managing great desert skink habitat.     

Estimation of N2 fixation based on differences in the natural abundance of 15N among freshwater N2-fixing and non-N2-fixing algae

The hypothesis that small mammal burrows can increase the amount of water infiltrating into the soil profile was tested. The amount of water added to the soil profile from spring recharge in areas adjacent to ground squirrel (Spermophilus townsendii and S. elegans) burrows was compared to nearby areas without burrows. Recharge amounts in burrow areas were significantly higher than nonburrow areas. An average of 21% more of the winter precipitation infiltrated into the soil near burrows. The amount of recharge was also found to be positively related to burrow density. Burrows also affected the distribution of the recharge by adding significantly more water to the deeper portions (>50 cm) of the soil profile.     

The ecological significance of burrowing behaviour in the toad (Bufo viridis)

Summary The burrowing behaviour of the toad Bufo viridis was studied in the laboratory on soil containing 11–13% moisture. These toads usually excavate shallow, temporary burrows from which they emerge intermittently. Time spent subsurface increases with rising ambient temperature in the range of 18–30° C. In these conditions, water loss is effectively reduced and a new water balance is achieved. On return to water access, after two months on soil, the toads rapidly regain only that amount of water lost previously. It is concluded that this temperature-sensitive burrowing behaviour is an important factor in these animals' successful survival in semi-arid conditions.     

Assessing habitat suitability for tiger in the fragmented Terai Arc Landscape of India and Nepal

Tiger Panthera tigris populations have declined dramatically in the Terai Arc Landscape (TAL; India and Nepal), and remaining populations are highly fragmented and endangered. As part of a research program to aid tiger management by identifying critical areas for conservation, we aimed to 1) identify the factors which affect the distribution of tigers in the TAL; 2) explore the role of spatial scale in habitat selection; 3) map potentially suitable habitats; and 4) assess the quality of potential corridors linking suitable habitats. We used an approach based on presence and pseudo‐absence data, combining ecological niche factor analysis and generalized linear models. We used an information‐theoretic approach to compare our data on tiger presence with different hypotheses on tiger habitat selection (i.e. protective habitat, prey species, human disturbance), and spatial scales. All hypotheses yielded models with high prediction accuracy (>79%). The most parsimonious model included variables characterizing habitat suitability of the 2 main prey species. More detailed assessment of potentially suitable areas using an extended source‐sink approach suggested that most of the habitats outside the protected areas were attractive sink‐like habitats (i.e. they suffered high levels of human disturbance in otherwise good habitats). Overall, 24% (ca 18 500 km²) of the study area was predicted as suitable (probability cut‐off p>0.5), approximately 7% of which is under protection. Our models showed that protecting the remaining concentrations of tigers requires focusing management efforts on specific areas outside the currently protected areas. These are characterized by good natural suitability; however, they suffer from a high level of human disturbance. Our models underscore the importance of minimizing human disturbances in these areas to avoid that they act as attractive sinks but act as corridors between existing subpopulations.