Stand type is more important than red wood ant abundance for the structure of ground‐dwelling arthropod assemblages in managed boreal forests

• 1 The relationships between red wood ants (Formica rufa group) and other ground‐dwelling arthropods were studied in young managed forests stands in Eastern Finland. The main objectives were: (i) to test the influence of stand type (dominant tree species; age: sapling versus pole stage) and numbers of red wood ants on the occurrence of other ground‐dwelling arthropods and (ii) to study the occurrence of red wood ants versus other arthropods on a distance gradient from ant mounds. We used pitfall traps set in 5–14‐year‐old sapling stands and 30–45‐year‐old pole‐stage stands of Scots pine (Pinus sylvestris L.) and birch (Betula spp.) forests.
• 2 Pitfall trap catches of red wood ants did not vary significantly between the forest stand types, although some groups of other arthropods showed clear responses to stand type (e.g. catches of other Formicinae and Gnaphosidae were higher in sapling stands than in pole‐stage stands). The number of red wood ants clearly explained less of the variation in assemblages of other ground‐dwelling arthropods than the forest stand type.
• 3 Red wood ant numbers decreased significantly with distance from the mounds, but the other ground‐dwelling arthropods were insensitive to this gradient or even showed a preference for proximity to ant mounds and high ant activity.
• 4 The results obtained in the present study suggest that wood ants do not have strong effects on several other ground‐dwelling arthropod groups in young managed forests other than in the immediate vicinity of their mounds.

     

Influence of native ants on arthropod communities in a vineyard

• 1 Ants can have a range of effects on arthropods in crops, including suppressing herbivores such as caterpillars. However, ants can also increase hemipteran densities while reducing natural enemy numbers. In vineyard ecosystem, the effects of native ants and their interactions with other arthropods are poorly understood.
• 2 An ant‐exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism of light brown apple moth (LBAM) eggs, a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were counted after a season of ant‐exclusion.
• 3 Among 23 ground ant species collected, six were found to forage in the canopy, with two Iridomyrmex species being the most commonly encountered.
• 4 There was no difference in the abundance of most arthropod orders and feeding groups between ant‐excluded and control vines, although ground spiders were more abundant under ant‐excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs.
• 5 In conclusion, native ants did not consistently suppress arthropod assemblages, including natural enemies, and they did not promote the survival of scale insects. Interactions among native ant species within a vineyard might minimize their effects on other arthropods, although this needs further study.

     

Separating effects of species identity and species richness on predation,pathogen dissemination and resistance to invasive species in tropical ant communities

相似文献   

Effects of the emerald ash borer invasion on the community composition of arthropods associated with ash tree boles in Maryland,U.S.A.

相似文献   

Herbivorous insect species in the tree canopy of a relict South African forest

Abstract.

• 1 The herbivorous insects on twelve species of evergreen broadleafed trees were repeatedly sampled over a period of 11 months in a small relict forest on the east coast of South Africa. This extraordinarily speciose forest patch has an unusually high proportion of endemic tree species, some of which are extremely rare.
• 2 The insect herbivore fauna (number of species) seems to be markedly depauperate compared to that reported on native, broadleafed trees from other parts of the world. Some possible reasons for this are discussed.
• 3 The total number of herbivorous insect species on each tree species was strongly correlated with the local relative abundance of the host plant species.
• 4 There was no relationship between the total number of insect herbivore species on each tree species and the relative taxonomic isolation of the trees. The proportion of seemingly unique (= specialist) herbivorous insect species (i.e. those that occurred on one tree species only) was greatest on taxonomically isolated trees.
• 5 A fundamental deficiency in the interpretation of the data in this study, and of many other similar studies that report on the number of insect species on plants, is discussed, namely the lack of clarity on the closeness of the association between individual insect herbivore species and their respective host plants.

     

Natural enemies of natural enemies: the potential top‐down impact of predators on entomopathogenic nematode populations

相似文献   

Interactions between phytophagous insects and their Opuntia hosts

Abstract.

• 1 The cactophagous insect community on opuntias is analysed to show the number of insect species in different taxa. An extension of this analysis gives the average species complement on large and small opuntias.
• 2 A highly significant positive correlation is found between the total number of phytophagous insect species on individual Opuntia species and a measure of the overall ‘architecture’ of their host plants.
• 3 The specificity of the phytophagous insects on opuntias is briefly considered and the community as a whole analysed by guilds. The co-evolution of the Opuntia-feeding insects and their hosts has culminated in a community of specialist insects to the exclusion of nearly all generalist phytophages.
• 4 The life history strategies of the Opuntia-feeding insects are reviewed. Common to all developmental stages are morphological and behavioural adaptations that reduce the risk of attack by natural enemies. This is clearly the consequence of living on structurally simple host plants where there is little place to hide.
• 5 The possible influence of insect herbivores on Opuntia evolution is discussed.
• 6 An understanding of the interactions between the phytophagous insect community and opuntias has clear implications for the biological control of alien Opuntia weeds.

     

Mechanisms of species‐sorting: effect of habitat occupancy on aphids' host plant selection

相似文献   

Aquatic insects decline in abundance and occupy low‐quality artificial habitats to survive hydrological droughts

相似文献   

Contrasting patterns in the invasions of European terrestrial and freshwater habitats by alien plants,insects and vertebrates

Aim To provide the first comparative overview on the current numbers of alien species that invade representative European terrestrial and freshwater habitats for a range of taxonomic groups. Location Europe. Methods Numbers of naturalized alien species of plants, insects, herptiles, birds and mammals occurring in 10 habitats defined according to the European Nature Information System (EUNIS) were obtained from 115 regional data sets. Only species introduced after ad 1500 were considered. Data were analysed by ANCOVA and regression trees to assess whether differences exist among taxonomic groups in terms of their habitat affinity, and whether the pattern of occurrence of alien species in European habitats interacts with macroecological factors such as insularity, latitude or area. Results The highest numbers of alien plant and insect species were found in human‐made, urban or cultivated habitats; if controlled for habitat area in the region, wetland and riparian habitats appeared to support relatively high numbers of alien plant species too. Invasions by vertebrates were more evenly distributed among habitats, with aquatic and riparian, woodland and cultivated land most invaded. Mires, bogs and fens, grassland, heathland and scrub were generally less invaded. Habitat and taxonomic group explained most variation in the proportions of alien species occurring in individual habitats related to the total number of alien species in a region, and the basic pattern determined by these factors was fine‐tuned by geographical variables, namely by the mainland–island contrast and latitude, and differed among taxonomic groups. Main conclusions There are two ecologically distinct groups of alien species (plants and insects versus vertebrates) with strikingly different habitat affinities. Invasions by these two contrasting groups are complementary in terms of habitat use, which makes an overall assessment of habitat invasions in Europe possible. Since numbers of naturalized species in habitats are correlated among taxa within these two groups, the data collected for one group of vertebrates, for example, could be used to estimate the habitat‐specific numbers of alien species for other vertebrate groups with reasonable precision, and the same holds true for insects and plants.     

Spatial context strongly affects community composition of both passively and actively dispersing pool invertebrates in a highly heterogeneous landscape

相似文献   

Arthropod Diversity in Lama Forest Reserve (South Benin), a Mosaic of Natural, Degraded and Plantation Forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.     

Avian ecological succession in the Amazon: A long‐term case study following experimental deforestation

相似文献   

Patterns of saproxylic beetle succession in loblolly pine

• 1 Patterns of insect succession in dead wood remain unclear, particularly beyond the first several years of decay. In the present study, saproxylic beetles were sampled from loblolly pine (Pinus taeda L.) logs aged between 1 month and 9 years old using both emergence traps attached to logs in the field and rearing bags in the laboratory.
• 2 Species richness peaked within the first year as a result of a diverse assemblage of bark beetles, wood‐borers and predators associated with young logs. After the phloem phase, there were no significant differences in species richness among decay classes.
• 3 Beetle communities differed significantly among decay classes, with 25 and seven species being significantly associated with young and old logs, respectively.

     

Species‐level image classification with convolutional neural network enables insect identification from habitus images

1. Changes in insect biomass, abundance, and diversity are challenging to track at sufficient spatial, temporal, and taxonomic resolution. Camera traps can capture habitus images of ground‐dwelling insects. However, currently sampling involves manually detecting and identifying specimens. Here, we test whether a convolutional neural network (CNN) can classify habitus images of ground beetles to species level, and estimate how correct classification relates to body size, number of species inside genera, and species identity.
2. We created an image database of 65,841 museum specimens comprising 361 carabid beetle species from the British Isles and fine‐tuned the parameters of a pretrained CNN from a training dataset. By summing up class confidence values within genus, tribe, and subfamily and setting a confidence threshold, we trade‐off between classification accuracy, precision, and recall and taxonomic resolution.
3. The CNN classified 51.9% of 19,164 test images correctly to species level and 74.9% to genus level. Average classification recall on species level was 50.7%. Applying a threshold of 0.5 increased the average classification recall to 74.6% at the expense of taxonomic resolution. Higher top value from the output layer and larger sized species were more often classified correctly, as were images of species in genera with few species.
4. Fine‐tuning enabled us to classify images with a high mean recall for the whole test dataset to species or higher taxonomic levels, however, with high variability. This indicates that some species are more difficult to identify because of properties such as their body size or the number of related species.
5. Together, species‐level image classification of arthropods from museum collections and ecological monitoring can substantially increase the amount of occurrence data that can feasibly be collected. These tools thus provide new opportunities in understanding and predicting ecological responses to environmental change.

     

Differentiation of spring carabid beetle assemblages between semi‐natural habitats and adjoining winter wheat

相似文献   

Hedgerows surrounding organic apple orchards in north‐west Spain: potential to conserve beneficial insects

相似文献   

Macrophyte loss drives decadal change in benthic invertebrates in peatland drainage ditches

相似文献   

Long adult life spain and polyphagy of a carabid beetle,Leptocarabus kumagaii in relation to reproduction and survival

The reproductive patterns of two different age classes of Leptocarabus kumagaii adults, i.e. young beetles which were in the first year of adult stage and old ones which survived for more than two years, were studied in the field. The numbers of eggs laid were compared between young and old females and the effects of food quality and quantity were studied on egg production and maintenance in the laboratory.

1. Both of the young and old beetles reproduced in the field population. The number of eggs laid did not significantly differ between the two.
2. The number of eggs laid by female increased with an increase in the amount of miced beef eaten. Plant materials were ineffective for egg production but sufficient for the survival of both male and female beetles.
3. The two life historical aspects, i.e. repeated reproduction and polyphagy were discussed in relation to environmental fluctuation and limitation of food resources.

     

The effects of host-plant distribution and local abundance on the species richness of agromyzid flies attacking British umbellifers

Abstract. 1. The number of agromyzid species (Diptera: Agromyzidae) attacking British Umbelliferae generally increases with the size of the geographic range of the host, measured as occupied 10 km squares in the Atlas of the British Flora (Lawton & Price, 1979). 2. In the present study we tried to explain the large, residual variation in this species—area relationship using two new variables, namely the local abundance of the host plant, and the number of habitats within which it grows. 3. Local abundance was estimated from eight floras that map plant distributions within English countries by tetrads (2 times 2 km squares). Local abundance was defined as: Total number of occupied tetrads Total number of available tetrads within occupied 10 km squares 4. The number of habitats occupied by each host plant was taken from the only county flora to record plant habitats objectively, that for Warwickshire. 5. We expected to find a correlation between local abundance and the residuals from the national species—area relationship, with locally scarce plants having fewer agromyzids than expected from the sizes of their national ranges, and vice versa. 6. What we found was that size of geographic range and local abundance were highly correlated; hence their relative contributions to agromyzid species richness were difficult to disentangle. Residuals from the national species—area relationship were positively correlated with local abundance, but the relationship marginally failed to achieve statistical significance (P= 0.06). 7. In contrast, the number of habitats occupied by each species of umbellifer in Warwickshire had a marked effect upon agrornyzid species richness, with plants that grow in more habitats supporting more species of insects. Not surprisingly, local abundance and number of habitats occupied were highly correlated. 8. Lawton & Price's observation that aquatic umbellifers are faunally impoverished now emerges as part of the general effect of number of habitats occupied by the host plants on agromyzid species richness. 9. Once the number of habitats occupied by each host plant in Warwickshire was entered into a multiple regression, the effect of size of host geographic range on agromyzid species richness was no longer statistically significant. 10. A combination of the number of habitats occupied, and leaf-form of the host (the latter taken from Lawton & Price, 1979), explains 61% of the variation in agromyzid species richness on British Umbelliferae.