Contribution of paddock trees to the conservation of terrestrial invertebrate biodiversity within grazed native pastures

Abstract: Paddock trees are a common feature in the agricultural landscapes of Australia. Recent studies have demonstrated the value of scattered paddock trees for soil fertility, native pasture plants and arboreal faunas; however, the degree to which scattered paddock trees contribute to the conservation of terrestrial invertebrate biodiversity within grazed landscapes remains unknown. We ask three questions: (i) Is there a difference between the terrestrial invertebrate assemblages found under paddock trees compared with surrounding grazed native pastures? (ii) Can gradients in soil and litter variables from the base of trees explain patterns in invertebrate assemblages? and (iii) Does the presence of scattered paddock trees have implications for the conservation of terrestrial invertebrate biodiversity within grazed native pastures? We used pitfall trapping and extraction from soil cores to sample the invertebrate assemblages under six New England Peppermint trees (Eucalyptus nova‐anglica Deane and Maiden) and compared them with assemblages sampled from the open paddock. Formicidae and Collembola univariate and multivariate data were analysed along with a range of soil and litter variables. We found (i) significant differences in the assemblages of invertebrates under trees compared with surrounding grazed pastures; (ii) that most soil and litter variables revealed gradients away from tree bases and these variables explained significant variation in invertebrate assemblages; and (iii) more native invertebrates and more species of invertebrates were found under trees compared with the surrounding pastures. We discuss the relationships between paddock trees, the ground and soil environments and the invertebrate communities that inhabit these environments, and conclude with a discussion of the future for paddock trees and the biota supported by them.     

Contrasting Effects of Fire on Arboreal and Ground‐Dwelling Ant Communities of a Neotropical Savanna

Ants are a dominant group in tropical savannas and here we examined the responses of the arboreal and ground‐dwelling ant fauna to a fire in a Neotropical savanna (cerrado) reserve in Central Brazil. Ants were collected using pitfall traps and baits placed in trees and on the ground beneath each tree. Of the 36 trees marked along two transects, half (from each transect) were burned and half not. The same trees were sampled 1 wk before and again 3 and 12 mo after the fire. Rarefaction curves and ordination analyses using data from all trees from each side of each transect indicated that overall ant species richness and composition did not change after fire. Fire, however, reduced the mean number of ant species per tree, and increased the mean number of species on the ground. Fire increased the average abundance of specialist predators, Camponotini, and opportunistic species, and decreased that of arboreal specialists. Changes in the ground‐dwelling fauna were only detected 12 mo after the fire, while those in the arboreal fauna occurred earlier and were no longer apparent 12 mo after the fire. We suggest that these contrasting results represent mainly an indirect response of the ant communities to fire‐induced changes in vegetation. Given the temporary and small scale nature of the effects detected and the overall resilience of the ant fauna, our results indicate that a single fire in the cerrado vegetation does not greatly impact the structure of ant communities in the short term.     

Neotropical savanna ants show a reversed latitudinal gradient of species richness,with climatic drivers reflecting the forest origin of the fauna

Aim

To evaluate the extent to which ant species richness in Neotropical savannas varies with macrogeographic variables, and to identify the potential climatic drivers of such variation.

Location

The Cerrado savanna biome of central Brazil, in a region spanning ca. 20° of latitude and 18°of longitude.

Methods

Standardized sampling of the arboreal and ground‐dwelling faunas was performed in 29 well‐preserved savanna sites using pitfall traps. Species were classified according to their habitat affinities: open‐savanna specialists, forest‐associated species or habitat generalists. We used generalized linear models to evaluate the importance of geographic (latitude, longitude and elevation) and climatic (mean temperature and three metrics of rainfall) variables as predictors of species richness.

Results

The total number of species recorded at each site varied more than twofold (from 59 to 144), and latitude was the best geographic correlate of overall species richness. However, contrary to the expected pattern, more species were found at higher than lower latitudes. This reversed latitudinal pattern of diversity occurred for both the arboreal and ground‐dwelling faunas, and for the habitat generalists and forest specialists. The savanna specialists showed a mid‐latitudinal peak in diversity. Overall, there was a significant positive association between rainfall and species richness, but the strength of this relationship varied with ant habitat affinity.

Main conclusions

The Cerrado ant fauna shows a reverse latitudinal gradient in species diversity, and this can be explained by increasing rainfall during the warmest months of the year (and therefore in plant productivity) with increasing latitude. The sensitivity of Cerrado ant diversity to declining rainfall contrasts with the high resilience to aridity of the Australian savanna ant fauna, and this reflects the contrasting evolutionary histories of these faunas. Our findings highlight the importance of historical processes as drivers of intercontinental contrasts in macroecological patterns.     

Rainforest seed rain into abandoned tropical Australian pasture is dependent on adjacent rainforest structure and extent

It is well known that the recovery of abandoned tropical pastures to secondary rainforest benefits from the arrival of seeds from adjacent rainforest patches. Less is known, however, about how the structural attributes of adjacent rainforest (e.g. tree density, canopy cover and tree height) impact seed rain patterns into abandoned pastures. Between 2011 and 2013, we used seed traps and ground seed surveys to track the richness and abundance of rainforest seeds entering abandoned pastures in Australia's wet tropics. We also tested how seed rain diversity is related to the distance from forest, the proportion of forest cover in the landscape and several structural attributes of adjacent forest patches, specifically average tree height, canopy cover, tree species richness and density. Almost no seeds were captured in elevated pasture seed traps, even near forest remnants. Abundant forest seeds were found in ground surveys but only within 10 m of forest edges. In ground surveys, seeds from wind‐dispersed species were more abundant, but less species rich, than animal‐dispersed species. A survey of pasture seedling recruits suggested that some forest seeds must be dispersing more than 10 m into pasture at very low frequencies, but only a few species are establishing there. Recruits were predominantly animal‐dispersed not wind‐dispersed species. In addition to distance from forest and the proportion of forest within a 100‐ to 200‐m radius of sampling sites, the richness and density of adjacent forest trees were the most important factors for explaining the probability of seed occurrence in abandoned pastures. Results suggest that without some restoration assistance, the recovery of abandoned pastures into secondary rainforest in Australia's tropical rainforests will likely be limited, at least in part, by a very low rate of seed dispersal away from forest edges and by the diversity and density of trees in adjacent remnant forests.     

Multi‐scale ant diversity in savanna woodlands: an intercontinental comparison

Ecological patterns and processes are highly scale‐dependent, but few studies have used standardized methodology to examine how scale dependency varies across continents. This paper examines scale dependency in comparative ant species richness and turnover in savannas of Australia and Brazil, which are well‐matched climatically but whose ant faunas have contrasting biogeographic origins. The study was conducted in savanna woodland near Darwin in northern Australia and Uberlândia in central Brazil. The sampling design consisted of eight 400‐m line transects, four in each continent, with eight pitfall traps located on and around each of 20 trees evenly spaced along each transect. Ant richness and species turnover were compared at three spatial scales: pitfalls associated with a tree, trees within a transect and transects within a savanna. The composition of the Australian and Brazilian savanna ant faunas was broadly similar at the subfamily level, despite the very low proportion of shared genera and species. The ground and arboreal ant faunas were very distinct from each other in both savannas, but especially in Brazil. Overall ant abundance was almost three times higher in Australia than in Brazil, both on the ground and on vegetation, but overall species richness was higher in Brazil (150 species) than in Australia (93). There was no significant difference in the mean number of species per pitfall trap, but the mean species richness was significantly higher in Brazil than in Australia at both the tree and transect scales. We attribute these scale‐dependent intercontinental differences to biogeographical and historical factors in Brazil that have led to a large regional pool of arboreal species of rainforest origin. Our study underlines the importance of biogeographical context when conducting comparative analyses of community structure across biogeographical scales, and highlights the importance of process acting at regional scales in determining species richness in ant communities.     

Subtle Land‐Use Change and Tropical Biodiversity: Dung Beetle Communities in Cerrado Grasslands and Exotic Pastures

Although many tropical savannas are highly influenced by humans, the patterns of biodiversity loss in these systems remain poorly understood. In particular, the biodiversity consequences of replacing native grasslands with exotic pastures have not been studied. Here we examine how the conversion of the native savanna grasslands affects dung beetle communities. Our study was conducted in 14 native (grassland: campo limpo), and 21 exotic (Urochloa spp. monoculture) pastures in Carrancas, Minas Gerais, Brazil. We collected 4996 dung beetle individuals from 66 species: 3139 individuals from 50 species in native pastures and 1857 individuals from 55 species in the exotic pastures. Exotic pastures had lower dung beetle richness, abundance and biomass than native pastures. Species composition between the two pasture types was significantly different and exotic pastures were dominated by few abundant species. Indicator species analysis detected 16 species indicators of native pastures and three of exotic pastures, according to relative abundance and frequency in each pasture system. Our results show that the conversion of native pastures to exotic pastures leads to a predictable loss of local species richness, increasing dominance and changes in species composition. These results highlight the importance of maintaining native pastures in the Cerrado agro‐pastoral landscape. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

Dung beetles in pasture landscapes of Central America: proliferation of synanthropogenic species and decline of forest specialists

This study examines the spread of synanthropogenic dung beetles (species favoured by human activities) in pasture landscapes in Central America, and evaluates the role of forest fragments and regenerating patches of native vegetation in maintaining beetle diversity. Pitfall trapping was carried out at nine locations in El Salvador and seven in Atlantic Nicaragua that included both pasture and remnant or regenerating native vegetation. More dung beetle species occurred in forest fragments than in pastures. Community composition differed considerably between forest fragments from El Salvador and Nicaragua with many species restricted to either the Caribbean or Pacific regions. In contrast, dung beetle community composition and structure were largely the same in the pastures of El Salvador and Nicaragua, regardless of region or original habitat-type, and were similar to published results from pastures in Mexico and elsewhere on the Isthmus. Very small patches of native shrubs and tree stands (<2.5 ha) maintained no forest specialists in Nicaragua, whereas, in El Salvador, some forest specialists occurred even in the smallest stands of trees (ca. 0.25 ha). The study indicates that the expansion of cattle pastures has caused a regional decline in dung beetle diversity. Forest fragments and small isolated patches of native trees and shrubs maintain some of the diversity of the original landscape but their conservation value for dung beetles will depend on the biogeographical history of the sites.     

Effects of habitat transitions on rainforest bird communities across an anthropogenic landscape mosaic

We compared bird community responses to the habitat transitions of rainforest‐to‐pasture conversion, consequent habitat fragmentation, and post‐agricultural regeneration, across a landscape mosaic of about 600 km² in the eastern Australian subtropics. Birds were surveyed in seven habitats: continuous mature rainforest; two size classes of mature rainforest fragment (4–21 ha and 1–3 ha); regrowth forest patches dominated by a non‐native tree (2–20 ha, 30–50 years old); two types of isolated mature trees in pasture; and treeless pasture, with six sites per habitat. We compared the avifauna among habitats and among sites, at the levels of species, functional guilds, and community‐wide. Community‐wide species richness and abundance of birds in pasture sites were about one‐fifth and one‐third, respectively, of their values in mature rainforest (irrespective of patch size). Many measured attributes changed progressively across a gradient of increased habitat simplification. Rainforest specialists became less common and less diverse with decreased habitat patch size and vegetation maturity. However, even rainforest fragments of 1–3 ha supported about half of these species. Forest generalist species were largely insensitive to patch size and successional stage. Few species reached their greatest abundance in either small rainforest fragments or regrowth. All pastures were dominated by bird species whose typical native habitats were grassland, wetland, and open eucalypt forest, while pasture trees modestly enhanced local bird communities. Overall, even small scattered patches of mature and regrowth forest contributed substantial bird diversity to local landscapes. Therefore, maximizing the aggregate rainforest area is a useful regional conservation strategy.     

Disentangling the Diversity of Arboreal Ant Communities in Tropical Forest Trees

Tropical canopies are known for their high abundance and diversity of ants. However, the factors which enable coexistence of so many species in trees, and in particular, the role of foragers in determining local diversity, are not well understood. We censused nesting and foraging arboreal ant communities in two 0.32 ha plots of primary and secondary lowland rainforest in New Guinea and explored their species diversity and composition. Null models were used to test if the records of species foraging (but not nesting) in a tree were dependent on the spatial distribution of nests in surrounding trees. In total, 102 ant species from 389 trees occurred in the primary plot compared with only 50 species from 295 trees in the secondary forest plot. However, there was only a small difference in mean ant richness per tree between primary and secondary forest (3.8 and 3.3 sp. respectively) and considerably lower richness per tree was found only when nests were considered (1.5 sp. in both forests). About half of foraging individuals collected in a tree belonged to species which were not nesting in that tree. Null models showed that the ants foraging but not nesting in a tree are more likely to nest in nearby trees than would be expected at random. The effects of both forest stage and tree size traits were similar regardless of whether only foragers, only nests, or both datasets combined were considered. However, relative abundance distributions of species differed between foraging and nesting communities. The primary forest plot was dominated by native ant species, whereas invasive species were common in secondary forest. This study demonstrates the high contribution of foragers to arboreal ant diversity, indicating an important role of connectivity between trees, and also highlights the importance of primary vegetation for the conservation of native ant communities.     

The arboreal ants of a Neotropical rain forest show high species density and comprise one third of the ant fauna

In tropical rain forests, the ant community can be divided into ground and arboreal faunas. Here, we report a thorough sampling of the arboreal ant fauna of La Selva Biological Station, a Neotropical rain forest site. Forty-five canopy fogging samples were centered around large trees. Individual samples harbored an average of 35 ant species, with up to 55 species in a single sample. The fogging samples yielded 163 observed species total, out of a statistically estimated 199 species. We found no relationship between within-sample ant richness and focal tree species, nor were the ant faunas of nearby trees more similar to each other than the faunas of widely spaced trees. Species density was high, and beta diversity was low: A single column of vegetation typically harbors at least a fifth of the entire arboreal ant fauna. Considering the entire fauna, based on 23,326 species occurrence records using a wide variety of collecting methods, 182 of 539 observed species (196 of 605, estimated statistically) were entirely arboreal. The arboreal ant fauna is thus about a third of the total La Selva ant fauna, a robust result because inventory completeness was similar for ground and arboreal ants. The taxonomic history of discovery of the species that make up the La Selva fauna reveals no disproportionately large pool of undiscovered ant species in the canopy. The "last biotic frontier" for tropical ants has been the rotten wood, leaf litter, and soil of the forest floor.     

Structure of ground‐dwelling ant communities in burned and unburned areas in Brazilian subtropical grasslands

Fire is frequently used in the management of pastures in southern Brazil, but its effects on ground‐dwelling ant communities in Brazilian subtropical grasslands is still poorly understood. Here, we compared ant species richness and composition between periodically burned and unburned areas in native grasslands of the Atlantic Forest biome. In total, we found 35 epigeic ant species in burned and unburned areas. There was slightly higher species richness in burned than in unburned areas, independent of the sampling period (season). There was a significant difference in richness over the sampling period (season effect). Species composition varied significantly between the areas, in which nine species (26%) occurred only in burned areas, eight (23%) occurred only in unburned areas, and 18 (51%) occurred in both. Four species showed a significant preference for burned sites (Camponotus crassus, Linepithema humile and two undetermined species of Pheidole and Solenopsis). Although this study did not separate fire effects on ground‐dwelling ant communities (due to sampling design), it provides new information regarding subtropical native grasslands that can be used as a baseline for future studies.     

Associations between invasive eucalyptus psyllids and arthropod litter communities under tree canopies in southern California

Honeydew‐producing psyllids are an important pest of eucalyptus (Myrtaceae) in California, USA, and may influence surrounding litter arthropod communities. In particular, the introduced Australian psyllids Glycaspis brimblecombei Moore and Eucalyptolyma maideni Froggatt (both Hemiptera: Psyllidae) may facilitate the prevalence of invasive ant species. We examined ground‐dwelling arthropod communities under eucalyptus trees infested by psyllids. We used a model comparison approach to examine the association of psyllid infestation, ant abundance, and environmental factors with ground arthropod abundance and richness. We found a significant positive association between ant activity on eucalyptus trees and psyllid abundance. Higher psyllid abundance and higher Argentine ant abundance were associated with increased arthropod richness. Irrigation was also associated with increased arthropod richness and abundance. Regardless of location collected, arthropod communities collected in pitfall traps under trees with high psyllid abundance had high similarity to arthropod communities under trees with high ant activity. Abundance of isopods was positively associated with both ant and psyllid abundance. Other arthropod groups differed in their association with ants and psyllids. Argentine ants may exacerbate pest impacts and may also decrease the effectiveness of biological control programs for eucalyptus lerp psyllids.     

Effects of an Epiphytic Orchid on Arboreal Ant Community Structure in Panama

Epiphytes are conspicuous structural elements of tropical forest canopies. Individual tree crowns in lowland forests may support more than 30 ant species, yet we know little about the effects of epiphytes on ant diversity. We examined the composition of arboreal ant communities on Annona glabra trees and their interactions with the epiphytic orchid Caularthron bilamellatum in Panama. We surveyed the ants on 73 trees (45 with C. bilamellatum and 28 lacking epiphytes) and recorded their nest sites and behavioral dominance at baits. We found a total of 49 ant species (in 20 genera), ranging 1–9 species per tree. Trees with C. bilamellatum had higher average (±SD) ant species richness (4.2±2.28) than trees without epiphytes (2.7±1.21). Hollow pseudobulbs (PBs) of C. bilamellatum were used as nest sites by 32 ant species, but only 43 percent of suitable PBs were occupied. Ant species richness increased with PB abundance in trees, but nest sites did not appear to be a limiting resource on A. glabra. We detected no close association between ants and the orchid. We conclude that higher ant species richness in the presence of the orchid is due to bottom‐up effects, especially the year‐round supply of extrafloral nectar. The structure of ant communities on A. glabra partly reflects interference competition among behaviorally dominant species and stochastic factors, as observed in other forests.     

The effects of development,vegetation‐type conversion,and fire on low‐elevation Southern California spider assemblages

California sage scrub (CSS), a native ecosystem type of low‐elevation areas of Southern California, is increasingly threatened by urban development, altered fire regimes, and vegetation‐type conversion to non‐native grasslands. Using pitfall traps, we examined how suburbanization, type conversion, and fire influence ground‐dwelling spider assemblages in eastern Los Angeles County, CA, by surveying spiders in three habitats (CSS, non‐native grasslands, and suburban areas) before and after a fire that occurred in a small portion of our study site. Spider assemblages in the suburban habitat differed from those in CSS and non‐native grassland habitats, but CSS and grassland assemblages did not significantly differ. This suggests that the urban development, but not vegetation‐type conversion to non‐native grasslands, has significant effects on ground‐dwelling spider assemblages. Fire had no observable effect on assemblages. Because ground‐dwelling spiders were not impacted by fire and type conversion, increased fire frequencies, which often result in the establishment of non‐native grasses, may not deleteriously influence this animal group, a differing pattern from other taxonomic groups. However, the rapid urban development occurring in low‐elevation areas of Southern California means that species requiring non‐suburban sites for their survival (15 species, 24.1%) may be threatened and require conservation assessment.     

Biodiversity responses to land‐use and restoration in a global biodiversity hotspot: Ant communities in Brazilian Cerrado

Given that land‐use change is the main cause of global biodiversity decline, there is widespread interest in adopting land‐use practices that maintain high levels of biodiversity, and in restoring degraded land that previously had high biodiversity value. In this study, we use ant taxonomic and functional diversity to examine the effects of different land uses (agriculture, pastoralism, silviculture and conservation) and restoration practices on Cerrado (Brazilian savanna) biodiversity. We also examine the extent to which ant diversity and composition can be explained by vegetation attributes that apply across the full land management spectrum. We surveyed vegetation attributes and ant communities in five replicate plots of each of 13 land‐use and restoration treatments, including two types of native vegetation as reference sites: cerrado sensu stricto and cerradão. Several land‐use and restoration treatments had comparable plot richness to that of the native reference habitats. Ant species and functional composition varied systematically among land‐use treatments following a gradient from open habitats such as agricultural fields to forested sites. Tree basal area and grass cover were the strongest predictors of ant species richness. Losses in ant diversity were higher in land‐use systems that transform vegetation structure. Among productive systems, therefore, uncleared pastures and old pine plantations had similar species composition to that occurring in cerrado sensu stricto. Restoration techniques currently applied to sites that were previously Cerrado have focused on returning tree cover, and have failed to restore ant communities typical of savanna. To improve restoration outcomes for Cerrado biodiversity, greater attention needs to be paid to the re‐establishment and maintenance of the grass layer, which requires frequent fire. At the broader scale, conservation planning in agricultural landscapes, should recognize the value of land‐use mosaics and the risks of homogenization.     

Spider abundance and diversity in apple orchards under three insect pest management programmes in Washington State,U.S.A.

1 Many apple growers in Washington State, U.S.A. use mating disruption (MD) for control of codling moth, Cydia pomonella (Linnaeus). Fewer applications of synthetic, broad‐spectrum insecticides are made in MD orchards than in orchards under conventional (C) management. Spider abundance and diversity in MD, C and certified organic (O) orchards were compared. Spiders inhabiting the trees (arboreal), the understory vegetation, and the ground surface were studied. 2 Total arboreal spider density and total understory spider density were significantly higher in O orchards than in MD and C orchards. Many species occurred in both the trees and the understory. 3 Arboreal, visually orientated, hunting spiders and arboreal ambushers/runners were significantly more abundant in O orchards compared to C and MD orchards. Visual hunters were significantly more abundant in MD compared to C orchards. Numbers of spiders in two other guilds (web‐makers and nocturnal hunters) showed no statistical differences with respect to orchard management type. 4 The highest density of ground surface‐dwelling spiders occurred in one of the O orchards. Two C orchards had higher densities than any MD orchard. Ground surface species were distinct from those in the understory and the trees. 5 With one exception, an orchard's arboreal fauna was most similar to that of another orchard under the same type of pest management. Three exceptions were noted among comparisons of the understory faunas. The ground surface‐dwelling fauna of one O orchard was distinctive, whereas that in the second O orchard was similar to the C and MD orchards. 6 Reduced use of synthetic, broad‐spectrum insecticides in MD orchards did not result in arboreal spider densities comparable to those found in O orchards. A contributing factor may be that all species were univoltine. Spider populations may thus be severely reduced by even a small number of synthetic, broad‐spectrum insecticide applications and the time required for recovery may be lengthy.     

Structure and diversity of phyllostomid bat assemblages on riparian corridors in a human‐dominated tropical landscape

Tropical forests around the world have been lost, mainly because of agricultural activities. Linear elements like riparian vegetation in fragmented tropical landscapes help maintain the native flora and fauna. Information about the role of riparian corridors as a reservoir of bat species, however, is scanty. We assessed the value of riparian corridors on the conservation of phyllostomid bat assemblage in an agricultural landscape of southern Mexico. For 2 years (2011–2013), mist‐netting at ground level was carried out twice during the dry season (December to May) and twice during the wet season (June to November) in different habitats: (1) riparian corridors in mature forest, (2) riparian corridors in pasture, (3) continuous forest away from riparian vegetation, and (4) open pastures. Each habitat was replicated three times. To determine the influence of vegetation structure on bat assemblages, all trees (≥10 cm dbh) were sampled in all habitats. Overall, 1752 individuals belonging to 28 species of Phyllostomidae were captured with Sternodermatinae being the most rich and abundant subfamily. Riparian corridors in mature forest and pastures had the greatest species richness and shared 65% of all species. Open pastures had the lowest richness and abundance of bats with no Phyllostominae species recorded. Six of the 18 species recorded could be considered as habitat indicators. There was a positive relationship between bat species composition and tree basal area. Our findings suggest that contrary to our expectations, bats with generalist habits and naturally abundant could be useful detector taxa of habitat modification, rather than bats strongly associated with undisturbed forest. Also in human‐dominated landscapes, the maintenance of habitat elements such as large trees in riparian corridors can serve as reservoirs for bat species, especially for those that are strongly associated with undisturbed forest.     

Plants, insects and birds in semi-natural pastures in relation to local habitat and landscape factors

The preservation of remaining semi-natural grasslands in Europe has a high conservation priority. Previously, the effects of artificial fertilisation and grazing intensity on grassland animal and plant taxa have been extensively investigated. In contrast, little is known of the effects of tree and shrub cover within semi-natural grasslands and composition of habitats in the surrounding landscape on grassland taxa. We evaluated the effect that each of these factors has on species richness and community structure of vascular plants, butterflies, bumble bees, ground beetles, dung beetles and birds surveyed simultaneously in 31 semi-natural pastures in a farmland landscape in south-central Sweden. Partial correlation analyses showed that increasing proportion of the pasture area covered by shrubs and trees had a positive effect on species richness on most taxa. Furthermore, species richness of nectar seeking butterflies and bumble bees were negatively associated with grazing intensity as reflected by grass height. At the landscape level, species richness of all taxa decreased (butterflies and birds significantly so) with increasing proportion of urban elements in a 1-km² landscape area centred on each pasture, while the number of plant and bird species were lower in landscapes with large proportion of arable fields. Our results differed markedly depending on whether the focus was on species richness or community structure. Canonical correspondence analyses (CCA) showed that the abundance of most taxa was ordered along a gradient describing tree cover within pastures and proportion of arable fields in the landscape. However, subsets of grassland birds and vascular plants, respectively, showed markedly different distribution patterns along axis one of the CCA. In contrast to current conservation policy of semi-natural pastures in Sweden, our results strongly advise against using a single-taxon approach (i.e., grassland vascular plants) to design management and conservation actions in semi-natural pastures. Careful consideration of conservation values linked to the tree and shrub layers in grasslands should always precede decisions to remove trees and shrubs on the grounds of promoting richness of vascular plants confined to semi-natural grasslands. Finally, the importance of landscape composition for mobile organisms such as birds entails that management activities should focus on the wider countryside and not exclusively on single pastures.     

Strategic Management of an Invasive Ant‐scale Mutualism Enables Recovery of a Threatened Tropical Tree Species

Mutualisms between invasive ants and honeydew‐producing insects can have widespread negative effects on natural ecosystems. This is becoming an increasingly serious problem worldwide, causing certain ecosystems to change radically. Management of these abundant and influential mutualistic species is essential if the host ecosystem is to recover to its former non‐invaded status. This negative effect is particularly prevalent on some tropical islands, including Cousine Island, Seychelles. On this island, the invasive ant Pheidole megacephala has caused serious indirect damage to the threatened native Pisonia grandis trees via a mutualism with an invasive scale insect, Pulvinaria urbicola. We aimed to suppress the ant, thereby decoupling the mutualism and enabling recovery of the Pisonia trees. We treated all areas where ant pressure was high with a selective formicidal bait, which was deployed in custom‐made bait stations designed to avoid risk of treatment to endemic fauna. In the treated area, ant foraging activity was reduced by 93 percent and was followed by a 100 percent reduction in scale insect density. Abundance of endemic herbivorous insects and herbivorous activity increased significantly, however, after the decline in mutualistic species densities. Despite the native herbivore increase, there was considerable overall improvement in Pisonia shoot condition and an observed increase in foliage density. Our results demonstrate the benefit of strategic management of highly mutualistic alien species to the native Pisonia trees. It also supports the idea that area‐wide suppression is a feasible alternative to eradication for achieving positive conservation management at the level of the forest ecosystem.