Sampling epigeal arthropods: an evaluation of fenced pitfall traps using mark-release-recapture and comparisons to unfenced pitfall traps in arable crops

The efficiency of fenced pitfall traps for estimating the density of commonly occurring epigeal predatory beetles was examined using mark-release-recapture. Most beetles of those recovered were recaptured within one week of their release. For seven of the ten species tested recapture rates were over 70%, with higher rates for the larger species. The predatory arthropod species composition captured using fenced pitfall traps was compared to unfenced pitfall traps in winter wheat, spring barley and winter oilseed rape. Compositional analysis revealed that the dominance structure of seven carabid beetle (Coleoptera: Carabidae) taxa differed between the trap types and month of sampling in winter wheat and spring barley, but differences were small with the exception of a few taxa. Linear relationships between the two techniques were found for some carabid and rove beetles (Coleoptera: Staphylinidae). The dominance structure of seven linyphiid spider (Araneae: Linyphiidae) taxa differed between the two trap types in wheat but not barley, although large differences were restricted to two taxa. No linear relationships between the two techniques were found for any of the Linyphiidae examined. Rove beetles were more effectively sampled using the fenced compared to unfenced pitfall traps.     

Elevation and experimental snowmelt manipulation affect emergence phenology and abundance of soil‐hibernating arthropods

1. Effects of climate change, such as higher average temperatures and earlier snowmelt, are already apparent, especially in alpine regions. However, community responses of functionally important arthropod taxa to changing climatic conditions are mostly unknown. 2. In this study, an earlier snowmelt was simulated at 15 plots along an elevational gradient in the German Alps. At each study site, soil emergence traps were established for sampling soil‐hibernating arthropods on earlier and control snowmelt treatments during the growing season. The abundance and emergence phenology of the five most common arthropod orders (Araneae, Coleoptera, Diptera, Hemiptera, Hymenoptera) were analysed, as well as the species richness of Coleoptera. 3. There was increasing abundance and species richness of Coleoptera along the elevational gradient, indicating that at higher altitudes more individuals and species hibernate in the soil. Abundances of Diptera also increased with elevation. By contrast, abundances of Hemiptera declined with increasing elevation, while abundances of Araneae and Hymenoptera did not show significant elevational patterns. Arthropods at higher elevations emerged, on average, 5 weeks later than arthropods at lower elevations, because of a longer‐lasting snow cover. The earlier snowmelt treatment resulted in higher abundances of Araneae and Hymenoptera compared with the control plots, indicating that the time of snowmelt influenced the abundance of predators, such as spiders or parasitic wasps, more than that of herbivores. 4. An earlier emergence of certain arthropod guilds and a change in relative abundance of guilds might desynchronise species interactions, leading to a possible loss of biodiversity.     

Ground invertebrate fauna associated with native shrubs and exotic pasture in a modified rural landscape, Otago, New Zealand

This study examined whether the diversity and relative abundance of ground-dwelling invertebrates changed in relation to type of vegetation cover. Invertebrate taxon diversity and relative abundance were assessed with pitfall traps placed under the native shrubs Olearia bullata and Coprosma propinqua, and in surrounding patches of exotic pasture. A total of 1935 invertebrates and at least 152 invertebrate taxa were recorded from 49 pitfall traps. The number of native taxa was c.63% of all taxa recorded, whereas exotic invertebrates represented only c.9%. The other c.28% were of undetermined origin. Taxon richness and relative abundance under the two shrub species were statistically similar, although all mean values (except for Coleoptera) were higher for traps set beneath C. propinqua. In contrast, taxon richness and relative abundance were significantly higher in the exotic pasture than under either of the shrub species. The same pattern was evident for exotic invertebrates and the relative abundance of native invertebrates, and for some of the most speciose orders. The data indicate that nearly half of native taxa occurred only under native shrubs. In contrast, 7 out of 12 exotic species were found in all three vegetation types, and all but one of them were recorded at least in exotic pasture. We conclude that the value of locally-modified and patchy vegetation cannot be underestimated for its potential in providing native biodiversity reservoirs for New Zealand’s native invertebrate fauna.     

Heterogeneous relationships between abundance of soil surface invertebrates and radiation from Chernobyl

Although pollution due to nuclear accidents constitutes some of the largest environmental disasters, there is surprisingly little information available on the relationship between abundance of animals and background radiation. We sampled invertebrates with pit-fall traps at Chernobyl in areas differing in background radiation level by more than four orders of magnitude. We obtained samples from 58 traps for 19 taxa of which five showed positive associations (Acari, Araneae, Formica sp., Homoptera), while four showed negative associations (Coleoptera, Collembola, Vespa, Insecta). These relationships were independent of other environmental factors such as habitat, humidity and ecotype. Estimates of the relationship between abundance and background radiation from the pitfall trap study were similar to those from an independent study based on invertebrates found under slices of wood placed on the ground. The differences in relationship between abundance and radiation among taxa may arise from direct effects of radiation. The findings reported here have implications for choice of animal taxa for efficient monitoring of the biological impact of radiation on animals.     

The effects of soil tillage on beneficial invertebrates within the vineyard

1 Tillage, commonly used in agroecosystems, can influence the abundance of invertebrates through factors such as habitat change and food availability.
2 The effects of tillage on the composition and abundance of invertebrates were examined in a vineyard near Mildura in Victoria, Australia, focusing particularly on groups that might act as natural enemies in vineyards. We used pitfall traps at ground level and sticky traps in the canopy.
3 The collections were first sorted to order. Beetles (Coleoptera) were sorted to family and ants (Hymenoptera: Formicidae) to genus.
4 Ants were the only group to be affected by tillage when all months were considered. The same genera occurred in both treatments but the abundance of several genera was reduced by tillage. Families of several beetles, including predators, increased in tilled areas. Spider, millipede, centipede and earwig numbers were decreased by tillage. In the canopy, Trichogrammatidae and other parasitoids decreased in abundance after tillage.
5 These results indicate that tillage influences the composition of invertebrates and has the potential to negatively affect the abundance of beneficial groups.     

Invertebrate diversity on

Despite the global importance of New Zealands invertebrates, relatively little is known about them and their relationships with plants and plant communities in native habitats. Invertebrate diversity was examined by beating randomly chosen shrubs of the species Olearia bullata (Asteraceae) and Coprosma propinqua(Rubiaceae). Invertebrate taxon richness was assessed initially using morphospecies, which were identified subsequently by expert taxonomists. Though the taxon richness of invertebrates recorded from O. bullata was not significantly higher than that on C. propinqua (except for the orders Diptera and Hemiptera), there was a clear indication that O. bullata hosts a higher diversity of invertebrates. Mean number of taxa per shrub for O. bullata was higher in all cases (except Coleoptera), and so was the maximum number of taxa per shrub. Overall, O. bullata yielded 115 invertebrate taxa compared with 93 for C. propinqua. Moreover, 50 invertebrate taxa were restricted to O. bullata compared with 28 for C. propinqua. Since at least ten species of Oleariaare threatened or uncommon, this could be cause for concern with respect to the maintenance of invertebrate diversity. Therefore, sites where Oleariaspecies are still present are likely to be of significance for invertebrate conservation.     

Longitudinal distribution of macroinvertebrates in two glacier-fed New Zealand rivers

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier-fed rivers in South Island, New Zealand.
2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from <1 °C near the glacier margin to 10 °C further downstream.
3. Epilithic algal biomass was very low (<0.1 mg m^–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m^–2 following an extended period with negligible precipitation.
4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species ( Deleatidium : Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.
5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non-chironomid Diptera also occurred.
6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner & Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.     

Successful overwintering of arthropods in roadside verges

In densely populated areas, roadside verges often provide the last semi-natural habitats available. Their ecological value is often stressed by bio survey results. Yet insect summer surveys potentially misjudge the value of a biotope (roadside or otherwise) since the occurrences of species may only be seasonal, or even transient. To effectively ascertain the importance of a site for insects, species must be shown to complete their life cycle there or at least be shown to successfully accomplish critical life stages, such as reproduction or overwintering. To confirm overwintering of arthropods in roadsides, sods were cut in late winter in a verge where several years of summer survey data were available. The sods were placed in transparent semi-permeable cages and kept alive during subsequent spring, summer and autumn. All emerging arthropods were caught inside the cages using pitfall and funnel traps and identified to order or family level. Most of the terrestrial arthropod phyla and orders occurring in NW-Europe appeared to be represented. Several groups were further identified to the species level: Carabidae (Coleoptera), Curculionidae (Coleoptera), Araneae, Orthoptera, Apidae (Hymenoptera), Syrphidae (Diptera) and Dephacidae/Cercopidae (Hemiptera). Particularly for the Carabidae, Araneae and Curculionidae, many species recorded in summer were also found to overwinter; species overlap amounted to approximately 67%. Rarefaction of the summer sample or excluding possible summer vagrants, raised this overlap to as much as 88% for the Carabidae. Many of the species successfully overwintering in the roadside verge were generalists, but less common, more stenotopic species were present as well. Not only species hibernating as adults were involved, but also species overwintering in immature stages, indicating reproduction also takes place in the roadside verge. Apparently the roadside occurrence of many arthropod species, including stenotopic and declining ones, is not merely seasonal or incidental, and roadside verges do not necessarily act as a sink only. The ecological importance often attributed to roadside verges should clearly be taken seriously.     

Abundance, diversity and body size: patterns from a grassland arthropod community

1. The empirical relationships among body size, species richness and number of individuals may give insight into the factors controlling species diversity and the relative abundances of species. To determine these relationships, we sampled the arthropods of grasslands and savannahs at Cedar Creek, MN using sweep nets (90 525 individuals of 1225 species) and pitfall traps (12 721 individuals of 92 species). Specimens were identified, enumerated and measured to determine body size.
2. Both overall and within abundant taxonomic orders, species richness and numbers of individuals peaked at body sizes intermediate for each group. Evolution could create unimodal diversity patterns by random diversification around an ancestral body size or from size-dependent fitness differences. Local processes such as competition or predation could also create unimodal diversity distributions.
3. The average body size of a species depended significantly on its taxonomic order, but on contemporary trophic role only within the context of taxonomic order.
4. Species richness ( S _i) within size classes was related to the number of individuals ( I _i) as S _i =  I i^0·5. This relationship held across a 100 000-fold range of body sizes. Within size classes, abundance distributions of size classes were all similar power functions. A general rule of resource division, together with similar minimum population sizes, is sufficient to generate the relationship between species richness and number of individuals.
5. Smaller bodied species had slightly shallower abundance distributions and may, in general, persist at lower densities than larger species.
6. Our results suggest there may be fewer undescribed small arthropod species than previously thought and that most undescribed species will be smaller than arthropods.     

Water limitation prevails over energy in European diversity gradients of sheetweb spiders (Araneae: Linyphiidae)

Across large spatial scales, species richness in many taxa is mainly determined by climatic variables. However, some of the mechanisms behind large-scale patterns of species richness and abundance are expected to act on the community level, and on a smaller scale than the resolution of the data commonly used for deriving these patterns. We studied the distribution of sheetweb spiders (Araneae: Linyphiidae) across Europe using both standardised samples from local habitats and large-scale inventories. In the first approach, we analysed species and individual numbers from standardised pitfall traps from 17 locations distributed from northern Sweden to Spain and Greece. We also calculated Simpson indices to correct for different activity densities. Additionally, we analysed whether diversity of sheetweb spiders is sensitive to habitat type. In the second approach, we investigated the known sheetweb spider species richness of European countries and large islands. In both datasets, species richness of sheetweb spiders reached a maximum at about 55°N and declined towards the Mediterranean and the Arctic. In addition, species richness decreased from western (maritime) to eastern (continental) regions. Also Simpson diversity showed a hump-shaped relation to latitude, and was the only variable influenced by habitat type. In contrast to species richness and diversity, activity density increased monotonously with latitude. Towards the north, sheetweb spiders are likely limited by energy availability, towards the south, water limitation as well as bottom-up and top-down community interactions may reduce sheetweb spiders. Accordingly, their diversity does not follow the pattern of vertebrates, large insects and aquatic organisms, which depend more strongly on energy availability.     

Has Botanical Enhancement of Broad‐Leaved Plantations in Milton Keynes,United Kingdom,Resulted in More Woodland‐Like Insect Assemblages?

Two methods of invertebrate sampling were used to determine how the deliberate introduction of field layer vegetation to broad‐leaved plantations influenced the associated insect assemblages. Enclosed pitfall traps and tent‐like emergence traps were employed at (1) 25‐year‐old plantations where botanical enhancement had taken place a decade previously; (2) “nonenhanced” plantations of a similar age; and (3) local ancient woods, all in Milton Keynes, Buckinghamshire, United Kingdom. The aim was to discover whether enhancement had produced a community intermediate to nonenhanced plantations and naturally established woodland. Enhancement had not successfully created plantations botanically more woodland‐like and plantation types were not constant; however, plant species richness had increased. This was also true of the insect assemblages (Coleoptera, Diptera and Hemiptera), which showed more variation in composition, though woodland communities could still be distinguished. However, those insect species present in the naturally established woods did have a significantly greater frequency and abundance in the enhanced plantations compared to the nonenhanced plantations, especially so with “woodland edge” species. Mantel tests showed significant correlations between the plant species present and insect assemblages taken by both sampling types. Although insect species richness was not significantly higher in the enhanced plantations, this correlated strongly with plant species richness and a measure of vegetation volume. The overall findings suggest that the enhancement had created plantations only subtly more like the local woodlands, though the insect assemblages had responded. However, relative to the time scale of woodland development, it is still early days.     

Are distribution patterns linked to dispersal mechanism? An investigation using pond invertebrate assemblages

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between-site variation in the species richness and community composition of actively and passively dispersing pond invertebrates.
2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4-km radius in south-west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively.
3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal.
4. Between-site variation in community composition was non-random for both groups, with pond permanence and area, together, explaining similar proportions of between-site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds.
5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over-ride the influences of dispersal in driving between-site variation in species composition.     

Habitat occurrence and feeding ecology of Crocidura montis and Lophuromys flavopunctatus on Mt. Elgon, Uganda

The distribution, habitat occurrence and feeding ecology of Crocidura montis and Lophuromys flavopunctatus coexisting in the afro‐alpine zone on Mt. Elgon, Uganda, are described. Crocidura montis was the only shrew species occupying the afro‐alpine zone, but was not found in forested habitats below 3200 m. While there was considerable overlap in habitat occurrence between the two species, C. montis was most abundant in the montane grassland and in drier sites while L. flavopunctatus occupied a wider range of habitats and wetter sites. C. montis ate a diversity of invertebrates, the most important being Coleoptera, Araneae and Lumbricidae. Invertebrates, mostly Diptera larvae, Lumbricidae and Coleoptera, formed a major component of the L. flavopunctatus diets, plus plant material (particularly Hepaticae and monocots). The arthropod components of the diets reflected their abundance in pitfall samples.     

Prey attraction by larvae of the New Zealand glowworm, Arachnocampa luminosa (Diptera: Mycetophilidae)

Abstract. The hypothesis that bioluminescence produced by larvae of the New Zealand glow-worm, Arachnocampa luminosa , attracts prey was tested experimentally in Reserve Cave, Waitomo, New Zealand, and in its bush-clad entrance over a total of 200 days during winter, spring, and summer. We compared catches on transparent adhesive traps placed either over glowworms or over areas from which glowworms had been removed. Adhesive traps over glowworms caught significantly more invertebrates per trap per day than did control traps. Glowworms in bush attracted greater numbers and types of invertebrates than did glowworms in the cave. Diptera predominated in both bush (86% of the total catch) and cave (89%). Also caught were small numbers of Araneae, Coleoptera, Hymenoptera, Orthoptera, Trichoptera, Gastropoda, Acarina, and Neuroptera—listed in order of abundance—but no adults of A. luminosa were caught. Glowworms under adhesive traps survived with little or no food for up to 78 days.     

Evaluation of window flight traps for effectiveness at monitoring dead wood-associated beetles: the effect of ethanol lure under contrasting environmental conditions

1 Subsequent to the diversity of saproxylic beetles being proposed as a management tool in forestry, more explicit knowledge about the efficiency and selective properties of beetle sampling methods is needed.
2 We compared saproxylic beetle assemblages caught by alcohol-baited or unbaited window traps in different forest contexts. Considering that trap attractiveness depends on kairomone concentrations, we appraised whether the trap efficiency was influenced by trap environment (openness and local supply of fresh dead wood).
3 Saproxylic beetles were sampled using 48 cross-vane window flight traps, arranged in paired designs (alcohol-baited/unbaited), in eight ancient and eight recent gaps (open stands), and eight closed-canopy control stands in an upland beech forest in the French Pyrenees.
4 Baited traps were more efficient than unbaited traps in terms of abundance and richness in our deciduous forests. The ethanol lure did not have any repellent effect on the individual response of saproxylic taxa.
5 The influence of local environmental conditions on trap attractiveness was observed. Openness had a significant moderate effect on species richness. Trap attractiveness was slightly reduced in the alcohol-saturated environment of recent gaps probably due to a disruption by local fresh dead-wood concentrations of the kairomonal response of saproxylic beetles to baited traps ('alcohol disruption').
6 Because the ethanol lure enhanced the probability of species detection, it may be useful in early-warning surveillance, monitoring and control of wood borers, despite slight influences of local conditions on baited trap efficiency.     

Ecology and phenology of the Dysderidae (Araneae) in the Djurdjura National Park (Algeria)

The ecology and phenology of the Dysderidae (Araneae) were investigated in two different sites (Tala-Guilef and Tikjda), located at opposite slopes of the Djurdjura National Park in Algeria. The following questions were investigated: Are there any endemic species in the studied area? Do the slopes' orientation influence the abundance, richness and diversity of these spider communities? Are the activity and the vital cycle of the three most abundant species different in the two different plant physiognomies (cedar forests and alpine grasslands)? The Dysderidae were collected monthly for 2 years using pitfall traps. In total, 1532 specimens were collected: 333 males, 389 females and 381 juveniles in Tala-Guilef and 230 males, 66 females and 133 juveniles in Tikjda. Among the total of 10 species sampled, three species belonging to three genera in Tala-Guilef, 10 species belonging to four genera in Tikdja and four endemic species was recorded. The slope orientation influence the abundance and the species richness. The activity and the vital cycle of the three most abundant species were not different in the cedar forests and alpine grasslands. For these species, no relationship was found between the activity cycle and the vegetation physiognomy.     

Organic versus conventional management in an apple orchard: effects of fertilization and tree-row management on ground-dwelling predaceous arthropods

1 Organic and conventional management of apple orchards may have a different effect on arthropod communities.
2 We conducted a 3-year study to assess the effect of two strategies of fertilizer treatment (organic versus chemical) and three tree-row management systems (straw mulching, tillage and herbicide) on activity-density and biodiversity of epigeic predators. Ground beetles (Carabidae), rove beetles (Staphylinidae), ants (Formicidae) and spiders (Araneae) were sampled monthly with pitfall traps in the same apple orchard during 2003, 2004 and 2005.
3 A total of 4978 individuals were collected. Carabids (56.8% of the total catches) were the most abundant taxonomic group, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). Tree-row management had a greater influence on predator catches than fertilizer treatment. Total predator catches were lower under the mulch. Mulching also reduced carabid abundance, but increased staphylinid catches.
4 Tree row management also had a significant effect on biodiversity parameters. Species richness did not significantly differ among treatments for ants, spiders or the total catches, but was higher on herbicide-treated plots for carabids and on mulched plots for staphylinids. Shannon–Wiener's diversity index was significantly greater in the mulched and herbicide treated plots for total predators and carabids. For staphylinids, this index was significantly greater on the mulched plots. Fertilizer application strategy only influenced the species richness of rove beetles, which was greater in the chemically-treated plots.
5 The results showed that a change from conventional to organic fertilizer treatment of apple trees may be performed without differential effects on predator activity-density or biodiversity. However, a change from herbicide treatment to mulching or mechanical weed control may be significant, depending on the taxonomic group.     

Insect assemblages in a native (kanuka –

In New Zealand, the European shrub gorse (Ulex europaeus) is becoming the initial post-disturbance shrub, replacing the native myrtaceous manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) scrub in this role. Change in the dominant vegetation is likely to affect the native invertebrate community. To quantify these changes, we compared the assemblages of four selected insect taxa (Coleoptera, Lepidoptera, and two groups of Diptera, the Tachinidae and the fungus gnats, represented in New Zealand by the families Ditomyiidae, Keroplatidae and Mycetophilidae) in neighboring stands of kanuka and gorse using Malaise and pitfall traps set during December. We sorted 34 387 specimens into 564 recognisable taxonomic units. Ordinations showed that insect assemblages associated with each habitat were distinct for all four insect groups. The gorse habitat was species rich compared with kanuka for tachinids, fungus gnats and Malaise-trapped beetles, and both habitats contained few adventive species. Many species were unique to each habitat. Some species loss might occur if the kanuka-dominated community continues to be replaced by gorse, but gorse is nevertheless considered to be valuable as a habitat for native invertebrates.