Total Insect Biomass Research Articles

Spectral composition of light-emitting diodes impacts aquatic and terrestrial invertebrate communities with potential implications for cross-ecosystem subsidies.

Resource exchanges in the form of invertebrate fluxes are a key component of aquatic-terrestrial habitat coupling, but this interface is susceptible to human activities, including the imposition of artificial light at night. To better understand the effects of spectral composition of light-emitting diodes (LEDs)-a technology that is rapidly supplanting other lighting types-on emergent aquatic insects and terrestrial insects, we experimentally added LED fixtures that emit different light spectra to the littoral zone and adjacent riparian habitat of a pond. We installed four replicate LED treatments of different wavelengths (410, 530 and 630 nm), neutral white (4000 k) and a dark control, and sampled invertebrates in both terrestrial and over-water littoral traps. Invertebrate communities differed among light treatments and between habitats, as did total insect biomass and mean individual insect size. Proportional allochthonous biomass was greater in the riparian habitat and among some light treatments, demonstrating an asymmetrical effect of differently coloured LEDs on aquatic-terrestrial resource exchanges. Overall, our findings demonstrate that variation in wavelength from LEDs may impact the flux of resources between systems, as well as the communities of insects that are attracted to particular spectra of LED lighting, with probable implications for consumers. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Land use changes biomass and temporal patterns of insect cross-ecosystem flows.

Emergent aquatic insects constitute an important food source for higher trophic levels, linking aquatic to terrestrial ecosystems. Little is known about how land use affects the biomass or composition of insect emergence. Previous studies are limited to individual time points or seasons, hampering understanding of annual biomass export patterns and detection of phenological changes. Over 1 year's primary emergence period, we continuously determined the biomass, abundance, and identity of >45,000 aquatic insects and recorded land-use-related environmental variables in 20 stream sites using a paired design with upstream forested sites and downstream agricultural sites. Total insect biomass and abundance were 2-7mg day-1 m-2 and 7-36 ind day-1 m-2 higher in agricultural than forested sites. However, we found turnover of families between forested and agricultural sites, with more insects with shorter generation time in agriculture, indicating lower sensitivity to land-use-related stress because of higher recovery potential. Except for stoneflies, biomass and abundance of major orders were higher in agriculture, but their phenology differed. For different orders, emergence peaked 30 days earlier to 51 days later in agriculture than forest, whereas total abundance and biomass both peaked earlier in agriculture: 3-5 and 3-19 days, respectively. The most important land-use-related drivers were pesticide toxicity and electrical conductivity, which were differentially associated with different aquatic insect order abundances and biomass. Overall, we found that land use was related to changes in composition and phenology of aquatic insect emergence, which is likely to affect food-web dynamics in a cross-ecosystem context.

Increased Mercury and Reduced Insect Diversity in Linked Stream-Riparian Food Webs Downstream of a Historical Mercury Mine.

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecologically important downstream ecosystems is not always straightforward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed in Idaho (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was found at much higher concentrations (1.3-11.3-fold) and was isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury concentrations in bull trout and riparian spiders were sufficiently high (732-918 and 347-1140 ng MeHg g-1 dry wt, respectively) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12%-20% within 4.3-5.7 km downstream from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m-2 ) was extremely elevated downstream (10-1778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of THg were also high (~16 ng THg m-2 day-1 ). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans. Environ Toxicol Chem 2022;41:1696-1710. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Insect biomass decline scaled to species diversity: General patterns derived from a hoverfly community

Reports of declines in biomass of flying insects have alarmed the world in recent years. However, how biomass declines reflect biodiversity loss is still an open question. Here, we analyze the abundance (19,604 individuals) of 162 hoverfly species (Diptera: Syrphidae), at six locations in German nature reserves in 1989 and 2014, and generalize the results with a model varying decline rates of common vs. rare species. We show isometric decline rates between total insect biomass and total hoverfly abundance and a scale-dependent decline in hoverfly species richness, ranging between -23% over the season to -82% at the daily level. We constructed a theoretical null model to explore how strong declines in total abundance translate to changing rank-abundance curves, species persistence, and diversity measures. Observed persistence rates were disproportionately lower than expected for species of intermediate abundance, while the rarest species showed decline and appearance rates consistent with random expectation. Our results suggest that large insect biomass declines are predictive of insect diversity declines. Under current threats, even the more common species are in peril, calling for a reevaluation of hazards and conservation strategies that traditionally target already rare and endangered species only.

Insect diversity in vineyards, almond orchards, olive orchards, alfalfa fields, and pastures in the San Joaquin Valley of California

For many agricultural systems, limited data is available on abundance and diversity of insects that are not crop pests or their natural enemies. As recent studies suggest that insect abundance and diversity is declining, there is a need to quantify insect diversity within crop fields to determine what role crop fields play in maintaining diversity. In this study, alfalfa fields, almond orchards, vineyards, olive orchards, and pastures located in the San Joaquin Valley of California were sampled. Ground sweep samples were collected from all five habitats. In addition, foliar beat samples were collected from almond orchards, vineyards, and olive orchards. In total, ~ 240,000 arthropods were collected with the majority identified to family. Across crops and sampling methods, 20 arthropod orders and 202 insect families were observed. Hemiptera was the most abundant order of insect collected, representing an average of 61% of all arthropods collected. Diptera was the most diverse order of insect collected, with a total of 59 dipteran families observed across crops. Of the 202 insect families observed, 85 were observed in all 5 habitats (42%), whereas 48 families were observed in only one habitat (24%). Families observed in a single habitat were often represented by only a few individuals. Principal component analysis indicated that the communities present in the understory of vine and tree crops were more similar to each other than to the communities observed in pastures or alfalfa fields. Much of the total insect biomass belonged to a few families that included known agricultural pests. In contrast, most of the diversity was made up of families present in low to moderate abundance.

Is the insect apocalypse upon us? How to find out

In recent decades, entomologists have documented alarming declines in occurrence, taxonomic richness, and geographic range of insects around the world. Additionally, some recent studies have reported that insect abundance and biomass, often of common species, are rapidly declining, which has led some to dub the phenomenon an “Insect Apocalypse”. Recent reports are sufficiently robust to justify immediate actions to protect insect biodiversity worldwide. We caution, however, that we do not yet have the data to assess large-scale spatial patterns in the severity of insect trends. Most documented collapses are from geographically restricted studies and, alone, do not allow us to draw conclusions about insect declines on continental or global scales, especially with regards to future projections of total insect biomass, abundance, and extinction. There are many challenges to understanding insect declines: only a small fraction of insect species have had any substantial population monitoring, millions of species remain unstudied, and most of the long-term population data for insects come from human-dominated landscapes in western and northern Europe. But there are still concrete steps we can take to improve our understanding of potential declines. Here, we review the challenges scientists face in documenting insect population and diversity trends, including communicating their findings, and recommend research approaches needed to address these challenges.

Aquatic insect functional diversity and nutrient content in urban streams in a medium‐sized city

AbstractAquatic insects play a large role in the processing of organic matter in headwater streams; however, anthropogenic disturbances associated with watershed urbanization can impact the biodiversity and abundance of these insects. Aquatic insects function on multiple trophic levels (i.e., shredders, collectors, scrapers, and predators) and interact in the nutrient cycling within lotic systems. The degradation or loss of any of these functional groups could disrupt stream biogeochemistry and the flow of energy in stream ecosystems. We used a paired reach site design to assess the insect functional group representation in five streams impacted by urbanization with downstream urban and upstream rural reach sites. We also sampled two non‐urban reference streams with rural upstream and rural downstream reach sites. We assessed functional group richness and abundance and measured insect biomass, insect body nitrogen (N) content, phosphorus (P) content, and N:P ratio. We found that collectors were numerically the most abundant and taxonomically the richest insect group in all site types. There were much fewer insects collected from urban sites than rural sites and individual insects were generally smaller in the urban sites. Collectors represented the most insect biomass in urban sites and predators the most insect biomass in rural sites. Insect N and P concentrations were not affected by urban landuse, ranging from 88.45 ± 12.50 to 121.74 ± 15.80 mg/g and 10.60 ± 2.10 to 18.36 ± 7.05 mg/g, respectively; and N:P ratios from 3.48 to 20.97. However, lower total insect biomass, particularly of predators and shredders, led to significantly lower total N and P mass in urban sites. Urbanization had clear effects on the diversity of functional groups, insect biomass, and their nutrient mass in this medium‐sized city.

Patterns and Mechanisms of Ant Diversity in Two Types of Land Use within Protected Forest Area Sirimau City of Ambon Maluku Province

Ants are the biodiversity constituent of 30% of the total insect biomass, very sensitive to changes in habitat structure and the environment in which they live can be an indicator of habitat destruction and ecosystem stability. The research was carried out in Sirimau Protected Forest area of Ambon City on two types of land use - each of secondary dryland and dryland farming from August to December 2012. The objective of the study was to know the structure of the ant community in two types of land use and to measure the pattern of ant distribution and diversity. Measurement of ant diversity using the Transect Line Plot method through a sampling system of a population sample with a sample plot approach that is on a line drawn across each type of land use using three Pitfall Trap (PT) methods or trap trap, Bait Trap BT) used Sugar and Tuna as feed and Hand Collecting (HC) method (Hasimoto, 2001) and collected with 70% alcohol preservation. Determination of ant species diversity and ant typeness in each type of land use using Shanon-Wienner index with the help of Ecological Methodology 2nd Edition (Krebs, 2000), and Margalef index (Ludwig and Reynold, 1988). The results of the study found that the number of individuals on the secondary dry land was 47,672 dominated by Meranoplus bicolor and Crematogaster ampularis and on dry land agriculture of 65,413 dominated by Polirachis belicossa and Echinopla lineata-lineata. The diversity index in August in the secondary drylands was 3.33 and 3.31 in September while on dryland farms were 3.67 in August and 3.59 in September were high.

More than 75 percent decline over 27 years in total flying insect biomass in protected areas.

Global declines in insects have sparked wide interest among scientists, politicians, and the general public. Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services. Our understanding of the extent and underlying causes of this decline is based on the abundance of single species or taxonomic groups only, rather than changes in insect biomass which is more relevant for ecological functioning. Here, we used a standardized protocol to measure total insect biomass using Malaise traps, deployed over 27 years in 63 nature protection areas in Germany (96 unique location-year combinations) to infer on the status and trend of local entomofauna. Our analysis estimates a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline. This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape.

Insects and Bobwhite Quail Brood Habitat Management

Small insects were the most important foods eaten by quail chicks 2 to 20 days of age. The foods eaten, in order of importance, were beetles, leafhoppers, true bugs, spiders, grasshoppers, ants, larvae, snails, and flies. Important seeds ingested were Panicum spp., Carex spp., Scleria spp., Paspalum spp., and Setaria sp. The effect of fire, a major tool in southern quail management, on insect populations was studied by sampling burned and unburned plots with a sweep net and a D-vac machine. On an old-field type of habitat, population densities and biomass of herbivorous insect populations were significantly greater on February-burned plots than on 5-year-old unburned plots. Two peaks in numbers of insects were found. The first peak of ca. 64,000/acre (sweep net) occurred in mid-June. The second peak occurred in mid-August (D-vac) with a density 0f ca. 90,000/acre. Total insect biqmass, excluding individuals over 0.035 g dry weight, averaged 147 g/acre (sweep net) and 128 g/acre (D-vac). In the second phase of the study, in a longleaf pine forest habitat, grasshoppers were the only species of insect having significantly greater density and biomass on unburned, 3-year-old "roughs" than on annually burned plots. Lack of litter on annually burned plots probably caused this disparity. At peak density, in the period of mid-July to early August, sweep-net density was 19,500/acre and D-vac density was 58,500/acre. Total insect biomass averaged 79 g/acre (sweep net) and 52 g/acre (D-vac).The major considerations for brood habitat are abundance and availability of insects. In old-field habitat, fire increases insect abundance and removes accumulated litter, opening the area for ease of chick movement. If the soil is fertile, then annual burns are feasible. The interval of burning advocated is 1 or 2 years, but local problems may modify this. Burning annually in the poor-soil region of the longleaf forest type is not necessary.

Cross-ecosystem fluxes: Export of polyunsaturated fatty acids from aquatic to terrestrial ecosystems via emerging insects

Cross-ecosystem fluxes can crucially influence the productivity of adjacent habitats. Emerging aquatic insects represent one important pathway through which freshwater-derived organic matter can enter terrestrial food webs. Aquatic insects may be of superior food quality for terrestrial consumers because they contain high concentrations of essential polyunsaturated fatty acids (PUFA). We quantified the export of PUFA via emerging insects from a midsize, mesotrophic lake. Insects were collected using emergence traps installed above different water depths and subjected to fatty acid analyses. Insect emergence from different depth zones and seasonal mean fatty acid concentrations in different insect groups were used to estimate PUFA fluxes. In total, 80.5mg PUFA m−2yr−1 were exported, of which 32.8mgm−2yr−1 were eicosapentaenoic acid (EPA), 7.8mgm−2yr−1 were arachidonic acid (ARA), and 2.6mgm−2yr−1 were docosahexaenoic acid (DHA). While Chironomidae contributed most to insect biomass and total PUFA export, Chaoborus flavicans contributed most to the export of EPA, ARA, and especially DHA. The export of total insect biomass from one square meter declined with depth and the timing at which 50% of total insect biomass emerged was correlated with the water depths over which the traps were installed, suggesting that insect-mediated PUFA fluxes are strongly affected by lake morphometry. Applying a conceptual model developed to assess insect deposition rates on land to our insect-mediated PUFA export data revealed an average total PUFA deposition rate of 150mgm−2yr−1 within 100m inland from the shore. We propose that PUFA export can be reliably estimated using taxon-specific information on emergent insect biomass and seasonal mean body PUFA concentrations of adult insects provided here. Our data indicate that insect-mediated PUFA fluxes from lakes are substantial, implying that freshwater-derived PUFA can crucially influence food web processes in adjacent terrestrial habitats.

Body-size distribution, biomass estimates and life histories of common insect taxa associated with a submerged macrophyte Lagarosiphon ilicifolius in the Sanyati Basin, Lake Kariba, Zimbabwe

The body-size distributions and biomass estimates of Caenis (Ephemeroptera: Caenidae), Cloeon (Ephemeroptera: Baetidae), Coenagrionidae (Odonata), Micronecta (Hemiptera: Corixidae), Chironominae (Diptera: Chironomidae) and Orthocladiinae (Diptera: Chironomidae), the most common and abundant insect taxa associated with a submerged macrophyte Lagarosiphon ilicifolius in Lake Kariba, are presented. Caenis has a univoltine life cycle, whilst Cloeon, Coenagrionidae, Chironominae and Orthocladiinae have multivoltine life cycles. Growth and reproduction of Micronecta occurred all year round. The Coenagrionidae had the highest mean biomass, which was significantly greater than those of the other taxa. Caenis and Orthocladiinae were sensitive to variations in water temperature and dissolved oxygen (DO) concentration, their highest biomasses occurring when temperatures were low and DO concentrations high. The biomasses of Chironominae and Orthocladiinae increased with rising water levels, but that of Caenis decreased. Total insect biomass was minimally affected by variations in water physico-chemical variables. The study suggests that water temperature, water level and DO concentration do have an effect on the biomasses of some insect taxa associated with Lagarosiphon in Lake Kariba. Mixing processes during de-stratification also affect the abundance and biomass of the insect taxa.

Species coexistence patterns in a mycophagous insect community inhabiting the wood-decaying bracket fungus Cryptoporus volvatus (Polyporaceae: Basidiomycota)

A study of the insect community inhabiting the wood-decaying bracket fungus, Cryptoporus volvatus was used to test two hypotheses proposed to account for the competitive coexistence of species in insect communities in patchy environments, niche par- titioning and spatial mechanisms. A total of 8990 individuals belonging to 17 insect species emerged from 438 sporocarps (patches) collected from the field. Insect species richness increased and then declined with increase in the total insect biomass reared from a sporocarp, suggesting the potential importance of interspecific competition. Successional niche partitioning explained the spatial dis- tribution of the four specialist species. The aggregation model of coexistence satisfactorily explained the stable coexistence of the species. The specialist species displayed higher population persistence than the generalists. Simulation studies suggest that restricted movements of adults could override patch-level larval aggregation. The effect of such restricted movements on stabilizing coexis- tence in fungus-insect communities has not been previously appreciated. These findings suggest that spatial mechanisms play a cru- cial role in the competitive coexistence of the species in the mycophagous insect communities inhabiting bracket fungi.

Functional redundancy of stream macroconsumers despite differences in catchment land use

Summary1. The conversion of forested landscapes to agriculture and, increasingly, to suburban and urban development significantly affects the structure and function of both terrestrial and aquatic ecosystems. While a growing body of research is examining how biotic communities change in response to human alteration of landscapes, less is known about how these changes in community structure affect biotic interactions.2. The objective of this study was to examine top‐down control by macroconsumers (fish and crayfish) across a human‐impacted landscape. We predicted that changes in stream macroconsumers and physicochemical characteristics associated with increased catchment development (e.g. decreased abundance of fish that are obligate benthic invertivores, increased sedimentation) would diminish top‐down control of benthic insects. We expected that effects on algal assemblages would be more variable, with increased top‐down control at sites dominated by algivorous fish and diminished control elsewhere. To test these predictions, we experimentally excluded fish and crayfish from areas of the bed of five streams whose catchments ranged from 100% to <50% forested, and examined the effects of exclusion on benthic insects and algae.3. Despite cross‐site differences in physical, chemical and biological characteristics, the outcome of our experiments was consistent across five sites representing a range of catchment development. Across all sites, macroconsumers reduced total insect biomass, largely due to decreases in Chironomidae and Hydropsychidae larvae. Macroconsumers also affected algal assemblages, reducing chlorophyll‐a and the proportion of upright and filamentous diatoms (e.g. Melosira, Cymbella) but increasing the proportion of adnate diatoms (e.g. Achnanthes) across all sites.4. We expected that differences in factors such as macroconsumer assemblage composition, nutrient and light availability and sedimentation would result in variable responses to macroconsumer exclusion in the five streams. Contrary to these expectations, only one response variable (ash‐free dry mass) showed a statistically significant interaction (i.e. site × exclusion) effect. Most responses to exclusion were relatively consistent, suggesting functional redundancy in assemblages of macroconsumers among the sites despite differences in catchment land use.

Distribution Patterns of Birds and Insect Prey in a Tropical Riparian Forest

ABSTRACTSpatial subsidies of energy and nutrients can influence the distribution of consumers in riparian habitats. This study compared the abundance and composition of bird assemblages and the availability of volant insect prey within the riparian zone (≤ 30 m from the stream) and further inland (100–250 m away) within a secondary forest in monsoonal Hong Kong. Replicated point‐counts of birds and insect light trapping were conducted in each zone during the wet and dry season of 2006–2007. The biomass of adult aquatic insects in the riparian zone was nine to 12 times higher than inland during both seasons, however, total insect biomass (aquatic plus terrestrial insects) in the riparian zone was only 49 percent (wet season) and 18 percent (dry season) greater. More birds (both numbers of individuals and species) were recorded in the riparian zone, and this difference was particularly conspicuous during the wet season. Most of the wet‐season difference was due to the greater number of insectivorous birds in the riparian zone (123% greater than inland), and may have reflected the relative availability of adult aquatic insects. These findings confirm the importance of riparian zones as feeding habitats for forest birds, and have implications for conservation planning and setting the boundaries of protected areas.

Effects of increased bedload on algal‐ and detrital‐based stream food webs: Experimental manipulation of sediment and macroconsumers

Sedimentation poses a significant threat to stream ecosystems throughout the world, and increases in bedload can be especially detrimental to benthic communities. To examine how increased bedload affects algal‐ and detrital based stream communities, we manipulated sediment (via daily sediment addition to 0.25‐m2 areas of stream bottom) and top‐down effects of macroconsumers (fishes and crayfish, via electric exclusion) in two factorial experiments, one using tiles and one using leaf packs as sampling substrates. Sediment addition had significant effects on both algal‐ and detrital‐based stream benthic communities, most notably via the alteration of macroconsumer‐mediated biotic interactions; these effects largely were due to sediment transport across the stream bottom, rather than sediment deposition. In the tile experiment, macroconsumers reduced total insect biomass and biomass of several dominant insect taxa under ambient sediment conditions. Sediment addition eliminated all macroconsumer effects except their reduction of chironomid biomass. In the leaf pack experiment, sediment addition eliminated macroconsumer effects on fungal accumulation rates; in general, however, leaf packs were not as affected by sediment addition as tiles. Direct effects of sediment addition were minimal in both experiments: algal composition was altered on tiles, while dipteran predator biomass tended to decline in leaf packs. These experiments demonstrate that small, environmentally realistic increases in bedload affect benthic communities, primarily via the alteration of macroconsumer effects. Although indirect effects of sedimentation have been examined less frequently than direct biotic responses, this study demonstrates the importance of sediment regime in determining the outcome of fish and crayfish‐mediated species interactions.

Effects of freshwater shrimp assemblages on benthic communities along an altitudinal gradient of a tropical island stream

1. In tropical island stream ecosystems freshwater shrimps are often the dominant macroconsumers and can play an important role in determining benthic community composition. However, most studies of the ecological role of shrimps are limited to high‐altitude shrimp‐dominated sites where other biota (fishes and snails) are absent or significantly less abundant than at lower altitudes.2. We examined how effects of different shrimp assemblages on benthic communities changed along an altitudinal gradient in a tropical island stream in Puerto Rico. We used electroshocking and observations to quantify abundance and taxonomic composition of shrimp assemblages at three sites (300, 90 and 10 m a. s. l) along the Río Espíritu Santo. We also experimentally manipulated access of shrimps to the benthic environment simultaneously at each site using electric fences over a 35‐day period.3. At the high‐altitude site, exclusion of shrimps (predominantlyAtyaspp. andXiphocariselongata) resulted in significantly greater accrual of organic and inorganic material, chlorophyllaand algal biovolume. In the absence of shrimps, the algal community was dominated by filamentous green algae (Chlorophyta:OedogoniumandRhizoclonium). Excluding shrimps did not affect total insect biomass but significantly increased sessile chironomids (Diptera: Chironomidae). We observed similar treatment effects at the mid‐altitude site where shrimps (primarilyMacrobrachiumspp. andX. elongata) occurred at lower densities. In contrast, at the low‐altitude site there were no treatment differences in organic and inorganic material, chlorophylla, algal biovolume, algal assemblage composition and insects.4. The lack of treatment differences at the low‐altitude site was probably because of very high densities of grazing snails (ThiaragraniferaandNeritinaspp.) which reduced organic and inorganic resources and obscured potential shrimp effects.5. This study demonstrates that freshwater shrimps can play an important role in determining benthic community composition; however, their effects vary and appear to depend on the presence of other biota. This study suggests that loss of shrimps as a result of anthropogenic disturbances will have different effects on the stream community depending upon location along the altitude gradient.

Importance of prairie riparian zones to bats in southeastern Alberta

The prairie grasslands of North America have undergone tremendous modification due to agriculture. The impact of continued modification is poorly understood because the critical habitat for many prairie species, including bats, is unknown. We investigated habitat use of bats in the vicinity of the South Saskatchewan and Red Deer Rivers in southeastern Alberta using mist-nets to capture bats and ultrasonic detectors to monitor echolocation calls. The majority of echolocation and foraging activity for all species occurred along the river and over small springs. Along the South Saskatchewan River, bat activity was highest near small patches of riparian cottonwood trees. Bat activity, especially for E. fuscus, was also relatively high along the cliffs and coulees of the river valley. Little bat activity occurred over the open grassland. Insect abundance corresponded to the activity patterns exhibited by bats: total insect biomass was greatest along the river and at springs. Bat activity was also related to the steepness and topography of the river valleys. Steep rugged areas along the rivers had significantly higher activity than areas with more gradual slopes. This is likely related to roost availability, as bats in the area roost in rock crevices in coulees. Our study indicates that riparian zones and springs are important foraging habitats for prairie bats. Conservation measures are needed for riparian forests in particular, because water regulation has modified natural flood patterns and reduced recruitment of trees.

Bats and insects over two Scottish rivers with contrasting nitrate status

AbstractThe abundance of foraging bats (Pipistrellus pipistrellus and Myotis daubentonii) and flying insects over two rivers in north‐east Scotland (Dee and Ythan), differing eightfold in nitrate levels, were compared by paired samples over three periods in summer 1995, during each of which 10 nights' sampling was undertaken using ultrasonic detectors and insect suction traps. Thirteen out of the 18 pairwise comparisons of bat passes, insect numbers, biomass and diversity were not significantly different. The oligotrophic Dee supported higher numbers of bats than the eutrophic Ythan in June, but this was attributed to an effect of adverse weather conditions affecting the Ythan. In July and August–September, neither bat abundances nor the abundance of Chironomidae and Trichoptera, the main food of the bats, differed significantly between the two rivers, although the Ythan showed higher total insect biomass than the Dee. The Ythan also showed a much higher abundance of small Diptera, mainly Psychodidae and Cecidomyiidae, associated with elevated nitrogen levels in the intensively farmed river valley. Thus a small eutrophic river can support as many bats and as high an insect density as a large oligotrophic one.

Bats and insects over two Scottish rivers with contrasting nitrate status

The abundance of foraging bats (Pipistrellus pipistrellus and Myotis daubentonii) and flying insects over two rivers in north-east Scotland (Dee and Ythan), differing eightfold in nitrate levels, were compared by paired samples over three periods in summer 1995, during each of which 10 nights' sampling was undertaken using ultrasonic detectors and insect suction traps. Thirteen out of the 18 pairwise comparisons of bat passes, insect numbers, biomass and diversity were not significantly different. The oligotrophic Dee supported higher numbers of bats than the eutrophic Ythan in June, but this was attributed to an effect of adverse weather conditions affecting the Ythan. In July and August–September, neither bat abundances nor the abundance of Chironomidae and Trichoptera, the main food of the bats, differed significantly between the two rivers, although the Ythan showed higher total insect biomass than the Dee. The Ythan also showed a much higher abundance of small Diptera, mainly Psychodidae and Cecidomyiidae, associated with elevated nitrogen levels in the intensively farmed river valley. Thus a small eutrophic river can support as many bats and as high an insect density as a large oligotrophic one.