Partitioning root and microbial contributions to soil respiration in Leymus chinensis populations

Based on the enclosed chamber method, soil respiration measurements of Leymus chinensis populations with four planting densities (30, 60, 90 and 120 plants/0.25 m²) and blank control were made from July 31 to November 24, 2003. In terms of soil respiration rates of L. chinensis populations with four planting densities and their corresponding root biomass, linear regressive equations between soil respiration rates and dry root weights were obtained at different observation times. Thus, soil respiration rates attributed to soil microbial activity could be estimated by extrapolating the regressive equations to zero root biomass. The soil microbial respiration rates of L. chinensis populations during the growing season ranged from 52.08 to 256.35 mg CO₂ m⁻² h⁻¹. Soil microbial respiration rates in blank control plots were also observed directly, ranging from 65.00 to 267.40 mg CO₂ m⁻² h⁻¹. The difference of soil microbial respiration rates between the inferred and the observed methods ranged from −26.09 to 9.35 mg CO₂ m⁻² h⁻¹. Some assumptions associated with these two approaches were not completely valid, which might result in this discrepancy. However, these two methods' application could provide new insights into separating root respiration from soil microbial respiration. The root respiration rates of L. chinensis populations with four planting densities could be estimated based on measured soil respiration rates, soil microbial respiration rates and corresponding mean dry root weight, and the highest values appeared at the early stage, then dropped off rapidly and tended to be constant after September 10. The mean proportions of soil respiration rates of L. chinensis populations attributable to the inferred and the observed root respiration rates were 36.8% (ranging from 9.7 to 52.9%) and 30.0% (ranging from 5.8 to 41.2%), respectively. Although root respiration rates of L. chinensis populations declined rapidly, the proportion of root respiration to soil respiration still increased gradually with the increase of root biomass.     

The use of camera traps for estimating tiger and leopard populations in the high altitude mountains of Bhutan

We used camera traps in combination with capture-recapture data analysis to provide the first reliable density estimates for tigers and leopards from the high altitude and rugged terrain in Bhutan’s Jigme Singye Wangchuck National Park. Fifty days of camera trapping in each of five study zones collapsed into two trapping blocks, resulted in a sampling effort of 4050 trap days. Camera trapping yielded 17 tiger photos (14 left flanked and 3 right flanked) and 48 leopard photos (25 left flanked and 23 right flanked). Using photos of these left flank, the closed heterogeneous Jackknife Model M_h was the best fit for the capture history data. A capture probability () of 0.04 was obtained for both tigers and leopards, thus generating population size (N) of 8 tigers (SE = 2.12) and 16 leopards (SE = 2.91) with densities of 0.52 tiger 100 km⁻² and 1.04 leopard 100 km⁻². Photographic evidence indicated that tigers and leopards did not overlap in their spatial use of space. Tigers preferred less disturbed areas located further away from settlements, while leopards appeared to be more resilient to disturbances in so far as they were found nearer to human settlements. Camera trapping using a capture-recapture framework was an effective tool for assessing population sizes for tiger and leopard in low density areas such as Bhutan.     

An evaluation of field and non-invasive genetic methods to estimate brown bear (Ursus arctos) population size

Estimates of population size and density are essential for successful management and conservation of any species. Although there are a variety of methods available for estimating abundance and density of populations, most studies rely on only one estimator and very few studies have compared and critically evaluated the adequacy and the cost of these methods. We used the brown bear (Ursus arctos) in south-central Sweden to compare the performance of three different methods of estimating population size, including methods based on conventional field data as well as on non-invasive genetic data. The method based on observations of females with cubs underestimated the true population size, as the estimates were below the number of unique genotypes determined from faecal data inside the study area. The best traditional method was based on observations of bears from a helicopter. The genetic method using the closed population MARK estimator, as recommended in a previous study, seemed to perform the best. We conclude that approximately 223 (188-282) bears were present in our 7328 km² study area during 2001 and 2002 and suggest that this hunted brown bear population has been relatively stable for about ten years. The non-invasive genetic method was less expensive than the most reliable traditional field method (a CMR method based on observations of bears from a helicopter), and preferable from an ethical point of view. We recommend that future studies using non-invasive genetic methods based on collected faecal samples should aim at collecting 2.5-3 times the number of faecal samples as the “assumed” number of animals.     

Estimating the density of a jaguar population in the Brazilian Pantanal using camera-traps and capture-recapture sampling in combination with GPS radio-telemetry

The jaguar (Panthera onca) is the largest feline in the Americas and third largest world-wide, smaller in size only to the tiger (P. tigris) and lion (P. leo). Yet, in comparison, relatively few studies on jaguar population densities have been conducted and baseline data for management purposes are needed. Camera trapping and capture-recapture sampling methods were used to estimate the size of a jaguar population in the Pantanal’s open wet grassland habitat, an important area for the long-term survival of the species. This study is the first jaguar population estimate conducted in co-operation with a GPS-telemetry study providing an important opportunity for comparing different methods of density estimation. An accessible area within a 460 km² privately-owned ranch was sampled with equal effort during the dry seasons of 2003 and 2004. Thirty-one and twenty-five individual jaguars were identified in 2003 and 2004, respectively. Estimates of jaguar abundance were generated by program CAPTURE. Density estimates were produced according to different methods used to calculate the effectively sampled areas which ranged from 274 to 568 km². For 2003, the currently-used mean maximum distance moved (MMDM) method produced a density of 10.3 jaguars/100 km², while GPS-telemetry-based calculations produced a mean density of 6.6 jaguars/100 km². For 2004, the MMDM method produced an estimate of 11.7 jaguars/100 km² while GPS-telemetry calculations produced a density of 6.7 jaguars/100 km². Our results suggest that the widely-used MMDM method used to calculate effectively sampled areas is significantly under-reflecting maximum distances moved by jaguars and their range-use and, thereby, considerably inflating cat density estimates. This overestimation could place a population in a difficult situation by lengthening the time taken to initiate protection measures because of underestimating the risk to that population.     

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.     

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.     

A habitat model for brown bear conservation and land use planning in the central Apennines

We investigated the brown bear habitat suitability in an 8000 km² study area encompassing Abruzzo, Latium, and Molise regions in central-southern Italy. Based on long-term field surveys and published records, we classified bear habitat as occupied or unoccupied in 92 out of 320 sample squares (5 × 5 km). For each sample square 36 habitat variables were measured from topographic maps and Corine land-cover III level digital maps. The influence of habitat features on bear presence was investigated by multivariate and one-way analyses of variance and by logistic regression analysis. The logistic model correctly classified 95.5% of sample squares of bear presence and 93.8% of those where bears were absent. Average altitude, deciduous woodlands and ecotone length, showed a positive relationship with bear presence, whereas vineyard-olive groves and shrublands were negatively correlated with bear presence. No specific land management guidelines or strategies exist for bear conservation in central Italy, based on knowledge of habitat-population relationships. The landscape scale habitat model we developed could be useful to predict bear occurrence, to identify critical areas for a brown bear conservation strategy, and to enhance the arrangement of the protected areas network for the conservation of this species.     

Conservation status of tigers in a primary rainforest of Peninsular Malaysia

This study provided the first reliable density estimate of tigers based on photographic capture data in Taman Negara National Park, Peninsular Malaysia's most important conservation area. Estimated densities () of adult tigers ranged from 1.10 ± 0.52 to 1.98 ± 0.54 tigers/100 km² (X²=1.56, df=2, P=0.46) with the overall mean of 1.66 ± 0.21 tigers/100 km². The tiger population in the 4343-km² park was estimated to be 68 (95% CI: 52-84) adult tigers. Prey biomass estimates ranged from 266 to 426 kg/km², and wild boar were the most important potential prey species in terms of abundance, biomass, and occupancy, followed by muntjac. Both tigers and leopards were more diurnal than nocturnal, which corresponded with the activity patterns of wild boar and muntjac. No evidence of poaching of large mammals was found in the 600-km² study sites and overall human impacts on the tiger-prey community appear to be minimal, but in the long run its viability needs to be evaluated in a greater landscape context.     

Density and population size estimates for North Cascade grizzly bears using DNA hair-sampling techniques

We used non-invasive DNA hair-sampling and catch per unit effort (CPUE: grizzly bears detected per 1000 trap nights) to estimate relative density and population size for a threatened grizzly bear population in the North Cascade Ecosystem of Washington and British Columbia. We used linear, logistic, and linear through the origin regression analyses to estimate the relationship between catch per unit effort and grizzly bear density for seven other grizzly populations. One grizzly bear was detected during 5304 trap nights (CPUE=0.19) over 3 years in the North Cascades. This CPUE was much lower than in the other seven populations, including two threatened grizzly populations in the Cabinet-Yaak and Selkirk Mountain Ecosystems. The logistic model (curvilinear relationship) best fit the data (R²=0.927), and yielded density and population size estimates of 0.15 bears/100 km² (90% CI=0.03-0.71) and six bears (90% CI=1-27), respectively. Natural recovery seems unlikely for the North Cascade grizzly bear population because the population has a high likelihood of extinction due to demographic and environmental stochastic effects associated with extremely small population numbers. We recommend population augmentation. DNA hair-sampling and catch per unit effort models can be a useful method to evaluate relative densities and numbers of animals in small, threatened grizzly bear populations when sample sizes are too small to yield traditional mark-recapture analysis.     

Small cetacean captures in Peruvian artisanal fisheries: High despite protective legislation

We detail the first direct, at sea monitoring of small cetacean interactions with Peruvian artisanal drift gillnet and longline fisheries. A total of 253 small cetaceans were captured during 66 monitored fishing trips (Gillnet: 46 trips; Longline: 20 trips) from the port of Salaverry, northern Peru (8^o14′S, 78^o59′W) from March 2005 to July 2007. The most commonly captured species were common dolphins (Delphinus spp.) (47%), dusky dolphins (Lagenorhynchus obscurus) (29%), common bottlenose dolphins (Tursiops truncatus) (13%) and Burmeister’s porpoises (Phocoena spinipinnis) (6%). An estimated 95% of common dolphin bycatch was of long-beaked common dolphins (Delphinus capensis). Overall bycatch per unit effort for gillnet vessels (mean ± sd) was estimated to be 0.65 ± 0.41 animals.set⁻¹ (range 0.05-1.50) and overall catch (bycatch and harpoon) was 4.96 ± 3.33 animals.trip⁻¹ (range 0.33-13.33). Based upon total fishing effort for Salaverry we estimated the total annual average small cetacean bycatch by gillnet vessels as 2412 animals.year⁻¹ (95% CI 1092-4303) for 2002-2007. This work indicates that, in at least one Peruvian port, bycatch and harpooning of small cetaceans persist at high levels and on a regular basis, particularly in driftnet vessels, despite the existence since the mid-1990s of national legislation banning the capture of marine mammals and commerce in their products. It is concluded that the coast of Peru is likely still one of the world’s principal areas for concern regarding high small cetacean bycatch and there is clearly an urgent need to increase the geographic scope of observer effort to elucidate the full magnitude of this issue.     

Pragmatic management increases a flagship species, the Himalayan brown bears, in Pakistan’s Deosai National Park

Deosai Plateau in Northern Pakistan was designated a national park to protect the largest remnant population of brown bears in Pakistan. The natural resources of this high elevation (3500-5000 m) park make a significant contribution to the livelihood of local and nomad communities. The present legislation excludes people from a park, which increases conflicts between management and local people. However, a pragmatic approach was adopted to involve people in conservation in Deosai. Community participation, achieved by recognizing rights and introducing incentives, reduced resistance against the conservation efforts, reduced grazing pressure in bear habitat and helped reduce poaching. The size of the brown bear population was set as an indicator of park success, and was monitored annually from 1993 through 2006. We observed a 5% annual growth of the brown bear population, suggesting that the conservation program has been successful due to a successful cooperation between an NGO, people, and the park management.The increase of the bear population is significant, because we observed an extremely low reproductive rate, due to late age of first reproduction (8.25 years), a long reproductive interval (5.7 years), and a small litter size (1.33). The reproductive rate of the Deosai population is the lowest yet documented for brown bear populations. Poor habitat quality, low quality food, high seasonality, and extreme weather conditions in the Himalaya probably explain the poor reproductive performance. Considering such low reproduction and known exchange of individuals with neighboring populations, we believe that the observed growth was a sum of reproduction and immigration. Brown bears are declining throughout South Asia and often have low-productive rates. Therefore, conservation efforts for brown bears in this region must target reducing human-caused mortalities, particularly of adult females. Involvement of people can increase efficiency in conservation, in addition to reducing cost and conflicts.     

Long-term trends in lobster populations in a partially protected vs. no-take Marine Park

Increasing the level of protection afforded to the marine environment requires assessment of the efficacy of existing marine protected areas (MPAs) in protecting exploited species. Long-term data from before and after the establishment of MPAs provide a rare but valuable opportunity to assess these effects. In this study we present long-term data (1977-2005) from before and after park establishment, on the abundance of spiny lobster Jasus edwardsii from fixed sites in a no-take marine park and a recreationally fished marine park, to assess the efficacy of no-take vs. partial protection. Lobster densities were comparable between both marine parks prior to park establishment, but the response of lobster populations differed markedly following protection. On average, legal-sized lobster were eleven times more abundant and biomass 25 times higher in the no-take marine park following park establishment, while in the partially protected marine park there has been no significant change in lobster numbers. Furthermore, no difference was found in densities of legal-sized lobster between the partially protected marine park and nearby fully-fished sites (<1 per 500 m²). Long-term data from fully fished and partially protected sites suggest long-term declines in lobster populations and reflect regional patterns in catch per unit effort estimates for the fishery. The long-term patterns presented provide an unequivocal example of the recovery of lobster populations in no-take MPAs, but clearly demonstrate that allowing recreational fishing in MPAs has little benefit to populations of exploited species such as J. edwardsii.     

Field characterization of olive (Olea europaea L.) tree crown architecture using terrestrial laser scanning data

Since the introduction of Terrestrial Laser Scanning (TLS) instruments, there now exists a means of rapidly digitizing intricate structural details of vegetation canopies using Light Detection and Ranging (LiDAR) technology. In this investigation, Intelligent Laser Ranging and Imaging System (ILRIS-3D) data was acquired of individual tree crowns at olive (Olea europaea L.) plantations in Córdoba, Spain. In addition to conventional tripod-mounted ILRIS-3D scans, the unit was mounted on a platform (12 m above ground) to provide nadir (top-down) observations of the olive crowns. 24 structurally variable olive trees were selected for in-depth analysis. From the observed 3D laser pulse returns, quantitative retrievals of tree crown structure and foliage assemblage were obtained. Robust methodologies were developed to characterize diagnostic architectural parameters, such as tree height (r² = 0.97, rmse = 0.21 m), crown width (r² = 0.97, rmse = 0.13 m), crown height (r² = 0.86, rmse = 0.14 m), crown volume (r² = 0.99, rmse = 2.6 m³), and Plant Area Index (PAI) (r² = 0.76, rmse = 0.26 m²/m²). With the development of such LiDAR-based methodologies to describe vegetation architecture, the forestry, agriculture, and remote sensing communities are now faced with the possibility of replacing current labour-intensive inventory practices with, modern TLS systems. This research demonstrates that TLS systems can potentially be the new observational tool and benchmark for precise characterization of vegetation architecture for improved agricultural monitoring and management.     

Density and activity patterns of ocelots (Leopardus pardalis) in northern Peru and the impact of oil exploration activities

The western Amazon is experiencing unprecedented levels of oil and gas exploration, a trend of particular concern given the high levels of biodiversity found in this relatively pristine and unstudied region. Despite the widespread use of seismic reflection technology for exploration, no studies have investigated the response of wildlife populations to this disturbance in the tropics. We conducted a trail camera survey inside a large oil concession (Block 39) in the Peruvian Amazon near the Ecuador border with ongoing 2D seismic explorations to investigate its effects on ocelot (Leopardus pardalis) activity and abundance. The estimated size of the ocelot population within our 22 km² study area was the same before (control period: 34 ± 6.9 ocelots) and during exploration operations (disturbance period; 34 ± 4.6 ocelots) and we detected no change in activity patterns between the two periods. Ocelot capture rate was unaffected by the presence of seismic crews, and distance to the nearest seismic line was not correlated with capture rate at individual stations. Our density estimates (ocelots/100 km²) from the control (75.2) and disturbance period (94.7) include the highest reported for the species, and represent the first ocelot density estimates from the northwest Amazon forest. These high values conform to recent research showing a positive association between ocelot density, annual rainfall, and proximity to the equator (this study: >2500 mm annual rainfall; <200 km from equator). We discuss the potential short- and long-term environmental impacts of seismic operations, particularly as they relate to large mammal populations.     

Brown bear conservation and the ghost of persecution past

Large carnivores, such as brown bears, are focal species for conservation efforts. Historically, brown bears were persecuted in Europe for centuries before their gradual elimination from much of Western Europe. In contrast, large carnivore populations in North America were eradicated within two centuries in the east and within a few decades in the west. After a change towards conservation-oriented management in the 20th century, many bear populations are again increasing on both continents. Europe is seemingly less suited (i.e. higher human densities, greater habitat alteration and landscape fragmentation) than in North America, however bears seem to respond faster to conservation measures in Europe. We analyzed ecological and historical factors that may affect differences in reproductive allocation (mean litter size in relation to mean adult female body mass) and help explain why different brown bear populations react differently to conservation measures. The results indicated that mean litter size increased significantly with mean adult female body mass and a long persecution history. Our results suggest that high and long-term rates of nonselective harvesting can change life-history traits of large mammals, as has also been shown by modeling, but only has been documented for morphological traits. Incidentally, this “ghost of persecution past” may have helped some brown bear populations to be more productive and therefore to respond more positively to protective management policies than populations with short exploitation histories.     

Factors influencing survival and long-term population viability of New Zealand long-tailed bats (Chalinolobus tuberculatus): Implications for conservation

A population viability analysis is important for the management of endangered populations and requires the estimation of survival parameters. The long-tailed bat (Chalinolobus tuberculatus) is one of only two native terrestrial mammals currently found in New Zealand and is classed as vulnerable. Its viability in temperate beech (Nothofagus) forest, Eglinton Valley, Fiordland, New Zealand was estimated using mark-recapture data collected between 1993 and 2003 using the Program MARK. Survival was estimated based on a total of 5286 captures representing 1026 individuals. Overall annual survival varied between 0.34 and 0.83 but varied significantly among three sub-populations and with sex and age. Females generally had a higher survival rate compared to males; and adults had higher survival relative to juveniles. Survival of all bats was lower in years when the number of introduced mammalian predators was high and when the winter temperature was warmer than average. High numbers of introduced predators occurred during three of the 10 years in the study. Climate change may mean that the conditions that promote high predator numbers may occur more frequently. A preliminary population viability analysis using a projection matrix on the overall adult female population showed an average 5% decline per year (λ = 0.95). Increased predator control targeting a range of predators is required in years when their numbers are high in order to halt the decline of this population of long-tailed bats. Population estimates using minimum number alive estimates supported the population estimates derived from Program MARK and a population viability analysis using matrices.     

Evaluating exuvia collection as a management tool for the federally endangered Hine’s emerald dragonfly, Somatochlora hineana Williamson (Odonata: Cordulidae)

Reliable population density estimates are crucial for monitoring endangered species. Many species are difficult to capture or range over large areas, making direct monitoring of populations through capture or observation extremely challenging. In such cases, indirect methods of assessing populations can be the only source of reliable information. We examined whether the discarded exoskeleton of the last larval instar (exuvia), left behind when dragonflies emerge into the adult stage, could be used to predict larval densities and provide life history information for the federally listed endangered, Hine’s Emerald Dragonfly (Somatochlora hineana). Using standardized protocols, we collected exuvia within six 2 × 2 m plots in an ephemeral wetland in Door County, Wisconsin during spring and summer of 1999 and 2000. S. hineana is a “summer emerger”, with more than 95% of the emergence occurring from late June until mid-July. Based on time of emergence and the flight period, adults appear to live a month or longer. The sex ratio at emergence did not differ significantly from a 1:1 ratio and emergence was synchronous between the sexes. Estimates of larval population density using exuvial data were similar to those obtained through intensive direct sampling for larvae. Exuvial collections provide a reliable estimate of larval population density, help link larval ecology to adult ecology and are a useful tool for assessing habitat suitability. Although sampling exuviae requires repeated searching on particular sites, less expertise and fewer people are required for this type of sampling, indicating that exuvial surveys can be a very effective tool for monitoring populations of endangered dragonflies.     

Aerial surveying of the world’s largest leatherback turtle rookery: A more effective methodology for large-scale monitoring

For many marine megavertebrate species it is challenging to derive population estimates and knowledge on habitat use needed to inform conservation planning. For marine turtles, the logistics required to undertake comprehensive ground-based censuses, across wide spatial and temporal scales, are often insurmountable. This frequently leads to an approach where a limited number of index nesting beaches are monitored in great detail by foot. In this study we use nationwide aerial surveying interfaced with ground assessments across three seasons of leatherback turtle nesting in Gabon (Equatorial West Africa), highlighting the importance of a synoptic approach to marine turtle monitoring. These surveys allow the first complete population assessment of this nesting aggregation to be made, identifying it as the world’s largest for the species (36,185-126,480 clutches, approximating to 5865-20,499 breeding females per annum and a total estimate of 15,730 to 41,373 breeding females). Our approach also serendipitously provides insights into the spatial appropriateness of Gabon’s protected areas network, for example (mean ± 1SD) 79 ± 6% (range 67-86%) of leatherback turtle activities recorded during aerial surveys (n = 8) occurred within protected areas (345 km, 58%, of surveyed coastline). We identify and discuss sources of potential error in estimating total nesting effort from aerial surveying techniques and show that interannual variation in nesting is considerable, which has implications for the detection of statistically significant changes in population size. Despite its relative costliness per day, aerial surveying can play an important role in providing estimates of relative population abundance of large vertebrates dispersed over extensive areas. Furthermore, it can provide data on habitat use and deliver real-time information on the spatial efficacy of protected area networks.     

Maximum foraging ranges in solitary bees: only few individuals have the capability to cover long foraging distances

To preserve populations of endangered bee species, sound knowledge of their maximum foraging distance between nest and host plants is crucial. Previous investigations predicted maximum foraging distances of 100-200 m for small bee species and up to 1100 m for very large species based on mainly indirect methods. The present study applied a new and direct approach to experimentally investigate maximum foraging distances in solitary bees. One endangered and two common species of different body sizes, all of which restrict pollen foraging to a single plant genus, were established in a landscape lacking their specific host plants. Females were forced to collect pollen on potted host plants that were successively placed in increasing distance from fixed nesting stands. The maximum foraging distance recorded for the small Hylaeus punctulatissimus was 1100 m, for the medium sized Chelostoma rapunculi 1275 m and for the large Hoplitis adunca 1400 m, indicating that maximum foraging distances at species level have been underestimated. However, the capability to use resources on such a large spatial scale applied only to a small percentage of individuals as 50% of the females of H. punctulatissimus and H. adunca did not forage at distances longer than 100-225 m and 300 m, respectively. This finding suggests that a close neighbourhood of nesting and foraging habitat within few hundred meters is crucial to maintain populations of these species, and that threshold distances at which half of the population discontinues foraging are a more meaningful parameter for conservation practice than the species specific maximum foraging distances.     

Influence of earthworm activity on aggregate-associated carbon and nitrogen dynamics differs with agroecosystem management

Earthworms are known to be important regulators of soil structure and soil organic matter (SOM) dynamics, however, quantifying their influence on carbon (C) and nitrogen (N) stabilization in agroecosystems remains a pertinent task. We manipulated population densities of the earthworm Aporrectodea rosea in three maize-tomato cropping systems [conventional (i.e., mineral fertilizer), organic (i.e., composted manure and legume cover crop), and an intermediate low-input system (i.e., alternating years of legume cover crop and mineral fertilizer)] to examine their influence on C and N incorporation into soil aggregates. Two treatments, no-earthworm versus the addition of five A. rosea adults, were established in paired microcosms using electro-shocking. A ¹³C and ¹⁵N labeled cover crop was incorporated into the soil of the organic and low-input systems, while ¹⁵N mineral fertilizer was applied in the conventional system. Soil samples were collected during the growing season and wet-sieved to obtain three aggregate size classes: macroaggregates (>250 μm), microaggregates (53-250 μm) and silt and clay fraction (<53 μm). Macroaggregates were further separated into coarse particulate organic matter (cPOM), microaggregates and the silt and clay fraction. Total C, ¹³C, total N and ¹⁵N were measured for all fractions and the bulk soil. Significant earthworm influences were restricted to the low-input and conventional systems on the final sampling date. In the low-input system, earthworms increased the incorporation of new C into microaggregates within macroaggregates by 35% (2.8 g m⁻² increase; P=0.03), compared to the no-earthworm treatment. Within this same cropping system, earthworms increased new N in the cPOM and the silt and clay fractions within macroaggregates, by 49% (0.21 g m⁻²; P<0.01) and 38% (0.19 g m⁻²; P=0.02), respectively. In the conventional system, earthworms appeared to decrease the incorporation of new N into free microaggregates and macroaggregates by 49% (1.38 g m⁻²; P=0.04) and 41% (0.51 g m⁻²; P=0.057), respectively. These results indicate that earthworms can play an important role in C and N dynamics and that agroecosystem management greatly influences the magnitude and direction of their effect.