Monitoring rare or elusive large mammals using effort-corrected voluntary observers

Populations of rare or elusive large mammals are difficult to monitor, because they usually are secretive, solitary, occur at low densities, and have large home ranges. The global trend of generally decreasing large carnivore populations necessitates new, feasible, reliable, and cost-effective monitoring methods. We evaluate an index method developed for monitoring populations of moose (Alces alces) based on voluntarily and systematically collected observations from hunters, corrected for effort, for use in monitoring populations of large carnivores in Sweden. For our evaluation, we used independent estimates of minimum brown bear (Ursus arctos) densities from DNA-based scat surveys and brown bear distribution from mandatory reports from successful bear hunters. We verified that the index correctly reflected bear distribution. We also found strong linear relationships between the indices and the independent density estimates for bears at the scale of local management units (about 1000-2000 km²) in all three regional study areas (adjusted R² = 0.88-0.60). Our results suggest that systematic, effort-corrected reports of observed animals can be an alternative and accurate monitoring method for the conservation and management of large mammals occurring over large areas when large numbers of willing volunteers are available (effort >30,000 h).     

Road crossing structures for amphibians and reptiles: Informing design through behavioral analysis

Road traffic causes significant amphibian and reptile mortality, which could be mitigated through the installation of road crossing structures that facilitate safe passage, but only if reptiles and amphibians are willing to use them. Through a series of behavioral choice experiments with frogs and turtles, we examined how aperture diameter, substrate type, length, and light permeability influenced individuals’ preferences for specific attributes of crossing structures, and how individuals responded to various heights of barrier fences. Snapping turtles (Chelydra serpentina), green frogs (Rana clamitans), and leopard frogs (Rana pipiens) preferred larger diameter tunnels (>0.5 m) whereas painted turtles (Chrysemys picta) preferred tunnels of intermediate (0.5-0.6 m) diameter. Green frogs preferred soil- and gravel-lined tunnels to concrete- and PVC-lined tunnels. Painted turtles showed non-random choice of different lengths of tunnel, possibly indicating some avoidance of the longest tunnel (9.1 m); although no species preferred to exit via the longest tunnels (9.1 m), members of all four species used such tunnels. Green frogs preferred tunnels with the greatest light permeability. Fences 0.6 m in height were effective barriers to green frogs, leopard frogs, and snapping turtles, whereas 0.3 m fences excluded painted turtles. We conclude that tunnels > 0.5 m in diameter lined with soil or gravel and accompanied by 0.6-0.9 m high guide fencing would best facilitate road crossing for these and likely other frog and turtle species.     

Dynamics of a black bear population within a desert metapopulation

Understanding metapopulation dynamics in large carnivores with naturally fragmented populations is difficult because of the large temporal and spatial context of such dynamics. We coupled a long-term database of visitor sighting records with an intensive 3-year telemetry study to describe population dynamics of recolonization by black bears (Ursus americanus) of Big Bend National Park in Texas during 1988-2002. This population, which occurs within a metapopulation in western Texas and northern Mexico, increased from a single pair of known breeding-age animals in 1988 to 29 bears (including 6 females of breeding age) in March 2000 (λ = 1.25/year). A migration and dispersal event in August-December 2000 reduced the population to 2 adult females and as few as 5-7 individuals. One-way movement distances from the study area during this event averaged 76 km for females (n = 7) and 92 km for males (n = 4), and 3 animals conducted migrations of at least 154, 178, and 214 km, respectively. Our observations exemplify the importance of stochastic events on demographics of small populations and highlight the potential scale of bear movement among montane islands of southwestern North America. They also provide insight into the use of dispersal data in parameterizing metapopulation models for large carnivores.     

Complementary use by vertebrates of crossing structures along a fenced Spanish motorway

Fenced roads fragment terrestrial vertebrate populations, the individuals of which are forced to cross these infrastructures using transverse structures inherent to the road’s construction (culverts, over- and underpasses) or other structures specially adapted or constructed for use by the fauna (enlarged culverts and bridges, ecoducts). The information available on the use of different crossing structure types by vertebrates, and the role played by the structural variables, of the surroundings and of the human use of these passages is still scarce. The use of 82 crossing structures of the A-52 motorway (Zamora, North-western Spain) by terrestrial vertebrates was monitored in summer 2002 using marble dust beds and electronic cameras. A total of 1122 species track-days were recorded, with an average of 1.37 species crossing structure⁻¹ day⁻¹. The results showed that structural aspects were the most determining factors for the species using these passages (MANCOVA test, p < 0.001), and a direct positive relationship between the size of the animal and the size of the pass used existing in general terms. This complementary use of the different passage types by vertebrate species suggest that, mitigation measures in new roads should focus to the establishment of several passages of different characteristics instead of investment in a reduced number of large fauna-specific passages.     

Water-remoteness for grazing relief in Australian arid-lands

Commercial grazing is possible over much of arid Australia due to a high density of artificial watering points. The broadscale supplementation of drinking water has not only enhanced densities of sheep (Ovies aries), cattle (Bos taurus, Bos indicus) and goats (Capra hircus), but has also contributed to increased populations of native kangaroos (Macropus spp.) since pre-European times. Empirical data are compiled to identify threshold distances from water containing 95% of a population of grazing animals. For sheep the proposed threshold is 3 km, 6 km for cattle and 7 km for red kangaroos. Despite clear evidence of water-focussed grazing, evidence of decreased biodiversity in relation to distance to water is scant and conflicting between studies. Reasons for this include the limited power of sampling designs and further research is required to establish the value of water-remote areas as grazing-relief refuges and to demonstrate that the recovery of grazing sensitive species is achievable after grazing relief has been restored. An eastern Australian case study indicates that within some large areas used for commercial pastoralism, the density of water points is such that there is nowhere further than 7 km from water. Where water-remote areas persist, their maintenance should be paramount. In the context of rangeland pastoralism and high densities of water points, de-stocking and water-point closure over large areas will be the most effective means of achieving grazing relief and will require strategic land acquisition.     

Uneven regional distribution of protected areas in Finland: Consequences for boreal forest bird populations

The significance of reserves in maintaining forest bird species of conservation concern (N = 36) was studied by large-scale quantitative line transect bird censuses in Finland, which stretches 1100 km through the boreal zone from the hemiboreal to the subarctic. Altogether 12 245 km of line transect was carried out in 1981-2004 in reserves covering 28 910 km². Bird census data in protected areas were combined into 100 km × 100 km squares. As a group the studied bird species were rather evenly distributed throughout the reserve network. The present reserve network is particularly significant for species having their highest densities in northern Finland, because large proportions of the populations of these species occurred in protected areas. However, over half of the studied species were concentrated in protected areas of southern and central Finland, and only small proportions of their populations were included in the present reserve network. In contrast to the whole species pool of conservation concern, the studied individual forest bird species were not distributed evenly throughout the whole reserve network. This suggests that for most individual species a regionally concentrated network is a preferred option, but for the whole species group the reserve network should clearly be regionally complementary and representative even in the boreal zone, where species have rather wide ranges. Thus, only some species and their habitats can be preserved in a spatially uneven reserve network in boreal forests.     

Conservation issues of temporary wetland Branchiopoda (Anostraca, Notostraca: Crustacea) in a semiarid agricultural landscape: What spatial scales are relevant?

Ecologists increasingly recognise the importance of spatial scale for conservation. This study focuses on threatened temporary wetland crustaceans, the fairy shrimp Branchinecta orientalis Sars (Anostraca) and the tadpole shrimp Triops cancriformis Bosc (Notostraca). Using redundancy analyses with a canonical variance partitioning approach, we studied how local habitat conditions and landscape features influence their densities at 4 spatial scales (100 m buffer strip around ponds, 1 km, 5 km and 10 km catchment scales). Branchinecta densities were negatively related with local conditions (trophic status) at all scales. Landscape effects (catchment:wetland size ratio) were only significant at the 10 km scale. However, trophic state conditions were influenced by local contamination rather than landscape conditions. Local degradation tended to be more pronounced in wetlands situated in catchments with a higher cover of natural vegetation compared to those in agricultural catchments. Triops was less influenced by local effects at all scales. The importance of landscape effects increased with landscape scale but effects were only significant at the 10 km scale, and were negatively explained by irrigated croplands. The importance of broad landscape scales and the difficulty to restore locally degraded sites challenges management. Because rationalisation of large-scale agricultural practises can conflict with socioeconomic demands, a first step to the conservation of actual Branchiopoda populations in this remnant wetland complex could benefit from the creation of vegetated buffer strips around the wetlands and/or hedgerows around agricultural fields to counteract atmosphere-mediated flux of particles and solutes from croplands to wetlands at broad landscape scales.     

Effects of a power line on migration and range use of wild reindeer

Linear infrastructures such as roads, pipelines and power lines can hinder Rangifer migration and reduce the total amount of area available for foraging. We studied the barrier and aversion effect of a 66 kV power line transecting the range of wild reindeer in North Ottadalen, south central Norway using aerial surveys of reindeer distribution (direct measurement of reindeer use) and lichen measurements (indirect measurement of reindeer use) at varying distances from both sides of the power line. We present a clear definition of the expected barrier and aversion effects, and present specific hypotheses and predictions based on these two terms that are often used unclearly in the literature. The aerial surveys and ground observations showed that reindeer crossed underneath and grazed under and on both sides of the power line during 14 out of the 22 years (63.6%) surveys were conducted over the last 31 years. This behaviour was confirmed by the lichen measurements, indicating a higher use of lichen pastures along ridges close to and under the power line compared to those at increasing distances and up to 3 km from both sides of the power line. This winter grazing pattern probably reflects the topographical channeling of reindeer to the ridges along an 8 km wide topographical corridor encompassing the power line and cannot be attributed to the power line itself. We found that direct measurement data (visual observations such as ours or GPS/telemetry tracking) provide less ambiguous information for testing barrier and aversion effects than indirect measurement data (pasture/lichen measurements) that are likely influenced by numerous uncontrollable environmental variables independent of reindeer grazing. Our results contrast with recent studies indicating strong barrier and aversion effects of similar power lines for Rangifer migration and grazing behaviour in alpine terrain.     

Sustainability of hunting, population densities, intrinsic rates of increase and conservation of Papua New Guinean mammals: A quantitative review

New Guinea’s mammalian fauna consists of a unique assemblage of relatively small sized (0.5-13.5 kg) marsupial mammals, the hunting of which provides a major source of protein for local communities. However, the impact of hunting and the influence of the marsupial life-history strategies on the sustainability of hunting are unknown. Anthropological studies of subsistence hunting and published life-history data for Australasian marsupial mammals were quantitatively reviewed to determine the major sources of game and annual harvest, and estimate intrinsic rates of population increase (r_max) and population densities. These data were used to estimate extraction versus maximum sustainable production (MSP) and make a preliminary estimate of the sustainability of hunting. There were significant negative relationships between increasing body size and decreasing r_max and decreasing population densities, which were further influenced by phylogeny and diet, and appear very similar to relationships found for placental mammals in Afrotropical and Neotropical forests. The estimated biomass of mid-sized marsupial mammals (923 kg/km²) in Papua New Guinea is also comparable with densities of placental mammals in other evergreen tropical forests. Intrinsic rates of increase ranged from 0.28 for tree-kangaroos (Macropodidae) and 0.29 for cuscus (Phalangeridae), up to 5.14 for bandicoots/echymipera (Peroryctidae). Estimated population densities ranged from 0.4-4.0 animals/km² for long-beaked echidna (Zaglossus sp.) to 150-340 animals/km² for ringtails (Pseudocheridae). Extraction rates of game in three studies averaged 23.5 ± 9.9 kg/km²/year, with cuscus and bandicoot species numerically comprising the main game, although cuscus are the most important source of protein. Rates of extraction in Papua New Guinea versus rates of production demonstrate that long-beaked echidna, tree-kangaroos and cuscus are likely to be hunted unsustainably. In contrast hunting of bandicoots and ringtails was lower than maximum production levels, and the high intrinsic rate of increase of bandicoots means that they can potentially provide a sustainable source of protein, in preference to scarcer and intrinsically slower breeding species.     

Difference in spatiotemporal patterns of wildlife road-crossings and wildlife-vehicle collisions

Human–wildlife conflicts like wildlife–vehicle collisions pose major challenges for the management and conservation of mobile wildlife in human-dominated landscapes, particularly when large species are involved. Mitigation measures to reduce risk of collisions may be based on information given by wildlife movement and collision data. To test whether movement and collision data indicate different spatiotemporal risk zones, we predicted year-around probabilities of road-crossings of GPS-marked female moose (Alces alces) (n = 102), and compared them with spatiotemporal patterns of police recorded moose-vehicle collisions (n = 1158). Probability of moose road-crossings peaked in May, June, and between mid November and the beginning of January, i.e. during moose migration. Moose-vehicle collisions were more likely during autumn and winter. Comparing environmental attributes of crossing and collision sites showed significant differences. The likelihood of collisions increased with the abundance of human-modified areas and higher allowed speed, and was lower on forest roads. We found that animal movement data alone are insufficient to predict collision risk zones, while analyses of collision data alone overestimate the collision risk in certain habitats. Our findings suggest that higher collision risk is largely due to low light and poor road surface conditions rather than to more animal road-crossings. This suggests that efforts to reduce wildlife collisions should focus on driver attitudes and road conditions rather than animal movement, and any efforts to model the collision risk will require actual collision data, and not just movement data.     

Small mammals in agricultural landscapes of Prince Edward Island (Canada): Effects of habitat characteristics at three different spatial scales

We examined the influence of habitat characteristics at the microhabitat, macrohabitat, and landscape spatial scales on small mammals occurring in 12 forest patches within four agricultural landscapes of Prince Edward Island (Canada). Landscape features were important determinants of small mammal variables at all levels, but especially at the community level, whereas microhabitat characteristics tended to influence small mammals at the population level. Macrohabitat characteristics had only minor effects on small mammals occurring in our study sites. Species richness was most strongly influenced by patch area, reaching a threshold at forest patches of roughly 8-10 ha. The proportions of both forest and hedgerow cover within 400 m from the study site were also significant determinants of small mammals species diversity, possibly reflecting their ability to perceive suitable habitats, forage in areas outside the forest patches, and/or disperse in agricultural landscapes. At least one small mammal species (Napaeozapus insignis) benefitted from the presence of agricultural fields at distances up to 1000 m. Tamias striatus benefitted from the presence of hedgerow cover within 400 m from forest patches, possibly allowing them to move between forest patches. Clearly, the maintenance of forest patches of 8-10 ha and of forest cover within 400 m from them is fundamental for the conservation of small mammals inhabiting agricultural landscapes on the Island. Conservation strategies should also consider the establishment of more effective regulations to prevent and/or reduce hedgerow removal on Prince Edward Island.     

What is the appropriate paradigm for riparian forest conservation?

Because forest width is thought to be the most relevant metric to ecological communities, it has persisted as the dominant paradigm and focus of management recommendations for riparian forest conservation. Consequently, managers may overlook important effects of the surrounding landscape matrix. We determined if characteristics of the landscape matrix, particularly the amount of urban development surrounding a forest, were better predictors of bird communities than forest width. We sampled breeding-bird communities 3 times each June 2001-2004 in 33 riparian forest sites (69-565 m wide) in Ohio, USA. We examined if bird community structure and composition were more closely associated with forest width or the amount of urban development within 1 km of each forest using canonical correlation analysis. Results indicate that the landscape matrix surrounding these relatively large forest tracts explained >94% of the variation in bird communities compared to <6% explained by forest width. Numbers of Neotropical migrants were negatively associated with urbanization in the landscapes (r = −0.43), whereas residents (r = 0.57) and short-distance migrants (r = 0.41) were positively associated with urbanization. Similar patterns persisted at the individual species level, particularly for Neotropical migrants as 76% of species in this guild were negatively related to urban development. Our findings suggest that the traditional approach to conserving riparian forests is not sufficient and that explicit consideration of the surrounding landscape matrix also should be a key component in conservation efforts.     

The importance of secondary forest blocks for terrestrial mammals within an Acacia/secondary forest matrix in Sarawak, Malaysia

With the rapid conversion of tropical forests in Asia to plantation forests for timber or biofuel production there is a need to determine if these forests serve any viable role in wildlife conservation. We used infra-red trip cameras to survey for large terrestrial mammals within an Acacia/secondary forest matrix being created for pulpwood production in Sarawak, Malaysia. We detected at least 27 species of mammals within the matrix and 18 species were detected in both Acacia and secondary forest. Using occupancy modeling to determine important covariates for seven mammal species within the project area, six of these species were sensitive to forest type, and most were sensitive to the amount of secondary forest within 1 km of the sample point. For four species (sun bear, Helarctos melayanus; common porcupine, Hystrix brachyura; mousedeer, Tragulus spp.; and pig-tailed macaque, Macaca nemestrina), the mean distance of detection from large secondary forest blocks was significantly closer than expected from the distribution of sample points. Most species used Acacia forest less frequently than secondary forest, possibly for transit or foraging, with the exception of bearded pigs (Sus barbatus), sambar (Rucervus unicolor), and civets which were more common in Acacia stands. The amount of secondary forest preserved within forest plantations seems to be the best measure of conservation potential for these industrial forests. Forest plantations can provide a conservation value if managed properly and those retaining significant amounts of secondary forest should be eligible for a base level of certification as they comprise a significant portion of the landscape in this region.     

Effects of forest fragmentation on two sister genera of Amazonian rodents (Myoprocta acouchy and Dasyprocta leporina)

Because agoutis (Dasyprocta sp.) and acouchies (Myoprocta sp.) are the most important dispersers of several large-seeded Amazonian trees, knowing their responses to forest fragmentation is essential and urgent. But until now, there was no study showing their population trends in Amazonian land forest fragments. The present study was conducted at the Biological Dynamics of Forest Fragments Project, Central Amazon, Brazil. Eleven sites (three fragments of 1 ha, three of 10 ha, two of 100 ha and three sites of continuous forest) were surveyed between 2003 and 2005. Agoutis and acouchies were systematically counted at each site through standard transect censuses and their densities were estimated with DISTANCE 4.1. Overall, I walked 100 km, and encountered 136 acouchies and 35 agoutis. Fragmentation had a significant negative effect on acouchies and a significant positive effect on agouti densities. Acouchy density was 0.64 ± 0.09 inds./ha in continuous forests and 0.07 ± 0.07 inds./ha in 1-ha fragments. On the other hand, agouti density was 0.16 ± 0.05 inds./ha in continuous forests and 0.71 ± 0.24 inds./ha in 1-ha fragments. This study is consistent with the idea that in fragments, larger species of mammals are initially less affected by forest fragmentation than smaller ones. More critical to conservation is the fact that acouchies, which were negatively affected by fragmentation, are restricted to the core region of the Amazonian rainforests. Continued fragmentation of Amazonian forests should have vast negative consequences for the genus.     

Elevation of atmospheric CO2 and N-nutritional status modify nodulation, nodule-carbon supply, and root exudation of Phaseolus vulgaris L.

Increased root exudation and a related stimulation of rhizosphere-microbial growth have been hypothesised as possible explanations for a lower nitrogen- (N-) nutritional status of plants grown under elevated atmospheric CO₂ concentrations, due to enhanced plant-microbial N competition in the rhizosphere. Leguminous plants may be able to counterbalance the enhanced N requirement by increased symbiotic N₂ fixation. Only limited information is available about the factors determining the stimulation of symbiotic N₂ fixation in response to elevated CO₂.In this study, short-term effects of elevated CO₂ on quality and quantity of root exudation, and on carbon supply to the nodules were assessed in Phaseolus vulgaris, grown in soil culture with limited (30 mg N kg⁻¹ soil) and sufficient N supply (200 mg N kg⁻¹ soil), at ambient (400 μmol mol⁻¹) and elevated (800 μmol mol⁻¹) atmospheric CO₂ concentrations.Elevated CO₂ reduced N tissue concentrations in both N treatments, accelerated the expression of N deficiency symptoms in the N-limited variant, but did not affect plant biomass production. ¹⁴CO₂ pulse-chase labelling revealed no indication for a general increase in root exudation with subsequent stimulation of rhizosphere microbial growth, resulting in increased N-competition in the rhizosphere at elevated CO₂. However, a CO₂-induced stimulation in root exudation of sugars and malate as a chemo-attractant for rhizobia was detected in 0.5-1.5 cm apical root zones as potential infection sites. Particularly in nodules, elevated CO₂ increased the accumulation of malate as a major carbon source for the microsymbiont and of malonate with essential functions for nodule development. Nodule number, biomass and the proportion of leghaemoglobin-producing nodules were also enhanced. The release of nod-gene-inducing flavonoids (genistein, daidzein and coumestrol) was stimulated under elevated CO₂, independent of the N supply, and was already detectable at early stages of seedling development at 6 days after sowing.     

Unusually high levels of bio-available phosphate in the soils of Ogasawara Islands, Japan: Putative influence of seabirds

Ogasawara Islands are important ecosystems sustaining many indigenous spices. To clarify the indigenous soil environments of Ogasawara Islands, we studied the chemistry of the soils. Many surface soils were low in bio-available P (0 to 0.55 g P₂O₅ kg⁻¹, average: 0.04 g P₂O₅ kg⁻¹ as Bray II P, n = 22), but several soils were found to contain extremely large amounts of bio-available P (1.36 to 6.98 g P₂O₅ kg⁻¹, average: 2.93 g P₂O₅ kg⁻¹, n = 5). From soil profile analyses, the authors concluded that the extremely large amount of bio-available P could not be explained by the effects of parent materials with high P contents nor the effect of fertilizations by human activity, but the effects of natural seabird activities in the past could be the cause. The soil profiles with large amounts of bio-available P indicate deep migration of soil materials from A horizons, which could be a result of intensive mixing of upper horizons by seabird activities. The intensive mixing was supported by the low mechanical impedance of the horizons for the P-accumulating soils (8.17 ± 2.54 kg cm⁻², n = 8) than those for the non-P-accumulating soils (17.46 ± 3.52 kg cm⁻², n = 36). It is likely that in the past seabirds, such as shearwaters, made burrows in the soils for nesting and propagating and inadvertently transported a large amount of P from the sea to the soils, resulting in the extremely large amounts of bio-available P in the present soils.     

The re-expansion and improving status of the silver-spotted skipper butterfly (Hesperia comma) in Britain: a metapopulation success story

Many specialist species are declining as a result of habitat loss and fragmentation, such that conservation actions typically aim to stem rates of decline rather than bring about genuine recovery. Here, we document the recovery of a species from former population refuges. An extensive survey of the entire British range of Hesperia comma, conducted in 2000, recorded over three times the number of tetrads (2 km × 2 km grid squares) occupied in 1982. This was accompanied by a fourfold increase in the number of populations and a 10-fold increase in the habitat area occupied. The improving status of H. comma is the product of good habitat management, recovering rabbit populations and climate warming, which have improved the quality, and increased the availability, of suitable habitat. This has enabled remnant metapopulations to expand, via distance-dependent colonisation, through large networks of habitat. Metapopulation recovery in H. comma demonstrates that landscape-scale conservation can be successful.     

Nitrogen fertiliser rate affects the frequency of nitrate-dissimilating Pseudomonas spp. in the rhizosphere of Lolium perenne grown under elevated pCO2 (Swiss FACE)

The effect of elevated pCO₂ (60 Pa) on the frequency of nitrate-dissimilating Pseudomonas (NDP) was investigated in the rhizosphere of fertilised Lolium perenne swards in the Swiss Free Air Carbon dioxide Enrichment (FACE) experiment. Numbers of cultivable root-associated Pseudomonas were greater under elevated (60 Pa) than under ambient (36 Pa) pCO₂ in both high and low N-fertilised swards. For both pCO₂ conditions, the NDP frequency decreased with closer root proximity to L. perenne roots in low fertilised swards. Anyway, in high N swards the NDP frequency was similar in root and soil fractions. Thus, N availability may be a major factor influencing NDP populations under elevated pCO₂, most likely due to increased competition for N between plant and nitrate-dissimilating bacteria.     

Linking monitoring and intervention for improved management of tigers in the Sundarbans of Bangladesh

Baseline data on distribution and abundance of tigers in the Sundarbans is required to identify problem areas and evaluate management strategies. This paper outlines a khal (creek) bank survey of track set frequency throughout the Bangladesh Sundarbans to aid formulation of a management-driven monitoring program. Three teams of two observers surveyed a total of 1 201 km of waterways throughout the Sundarbans, recording 1 338 tiger track sets. These sets became unrecognizable as tiger sign after a mean 10 days (range 6-14). Proportion of detectable sign recorded was 0.91. Mean (±standard error) sample unit track frequency was 1.12 ± 0.86 track sets/km of khal. The mean coefficient of variance in sample unit track rate, estimated by multiple counts of six sample units, was 0.21 (range 0.06-0.34). Track frequency generally increased from northeast to southwest. Four sample units (6%) had signs of reproduction, with a mean litter size of 1.75 ± 0.5. Monte Carlo simulation suggests a monitoring program of one complete survey every two years will have power of 0.8 (α = 0.2), to detect track frequency declines of ?19% and increases of ?17%. We recommend this monitoring scheme be implemented on the Indian side of the Sundarbans to provide a standard assessment of the tiger population and to form the basis for setting management objectives and evaluating transboundary conservation initiatives.     

Nitrogen fixation by biological soil crusts and heterotrophic bacteria in an intact Mojave Desert ecosystem with elevated CO2 and added soil carbon

Fixation of N by biological soil crusts and free-living heterotrophic soil microbes provides a significant proportion of ecosystem N in arid lands. To gain a better understanding of how elevated CO₂ may affect N₂-fixation in aridland ecosystems, we measured C₂H₂ reduction as a proxy for nitrogenase activity in biological soil crusts for 2 yr, and in soils either with or without dextrose-C additions for 1 yr, in an intact Mojave Desert ecosystem exposed to elevated CO₂. We also measured crust and soil δ¹⁵N and total N to assess changes in N sources, and δ¹³C of crusts to determine a functional shift in crust species, with elevated CO₂. The mean rate of C₂H₂ reduction by biological soil crusts was 76.9±5.6 μmol C₂H₄ m⁻² h⁻¹. There was no significant CO₂ effect, but crusts from plant interspaces showed high variability in nitrogenase activity with elevated CO₂. Additions of dextrose-C had a positive effect on rates of C₂H₂ reduction in soil. There was no elevated CO₂ effect on soil nitrogenase activity. Plant cover affected soil response to C addition, with the largest response in plant interspaces. The mean rate of C₂H₂ reduction in soils either with or without C additions were 8.5±3.6 μmol C₂H₄ m⁻² h⁻¹ and 4.8±2.1 μmol m⁻² h⁻¹, respectively. Crust and soil δ¹⁵N and δ¹³C values were not affected by CO₂ treatment, but did show an effect of cover type. Crust and soil samples in plant interspaces had the lowest values for both measurements. Analysis of soil and crust [N] and δ¹⁵N data with the Rayleigh distillation model suggests that any plant community changes with elevated CO₂ and concomitant changes in litter composition likely will overwhelm any physiological changes in N₂-fixation.