The relative importance of patch habitat quality and landscape attributes on a declining steppe-bird metapopulation

Metapopulation theory is one of the most popular approaches to identify the factors affecting the spatial and temporal dynamics of populations in fragmented habitat networks. Habitat quality, patch area and isolation are mainly focused on when analyzing distribution patterns in fragmented landscapes. The effects of landscape heterogeneity in the non-occupied matrix, however, have been largely neglected. Here, we determined the relative importance of patch quality and landscape attributes on the occurrence, density and extinction of the Dupont’s lark (Chersophilus duponti), an endangered steppe passerine whose habitat has been extremely reduced to highly isolated and fragmented patches embedded in a mainly unsuitable landscape matrix. Habitat patch quality, measured in terms of vegetation structure, grazing pressure, arthropod availability, predator abundance, and inter-specific competition, did not affect occurrence, density or extinction. At the landscape scale, however, the species’ occurrence was principally determined by the interactions among patch size, geographic isolation and landscape matrix. Isolation had the main independent contribution to explaining the probability of occurrence, followed by landscape matrix composition and patch size. The species’ density was negatively correlated to patch size, suggesting crowding effects in small fragments, while extinction events were exclusively related to isolation. Our findings suggest that landscape rather than local population characteristics are crucial in determining the patterns of distribution and abundance of non-equilibrium populations in highly fragmented habitat networks. Consequently, conservation measures for these species should simultaneously involve patch size, isolation and landscape matrix and apply to the entire metapopulation rather than to particular patches.     

Influence of connectivity, habitat quality and invasive species on egg and larval distributions and local abundance of crucian carp in Japanese agricultural landscapes

The quality of habitat at and around a spawning site, and the availability of movement between spawning and nonspawning habitats are likely to be important determinants for population persistence in a degraded and fragmented landscape. We assessed the influence of habitat connectivity, habitat quality and invasive species for distributions and local abundance of eggs and larvae of crucian carp (Crassius auratus complex, which is listed as “data deficient” on the Japanese Red List) in agricultural landscapes surrounding Lake Mikata, Japan, where drainage ditches and paddy fields are extensively utilised for spawning (lake or river shores are also used). We investigated the presence and abundance of eggs and larvae of crucian carp and habitat components at 146 sites across a range of presumed spawning habitats. Egg presence was affected strongly by connectivity to the lake (watercourse distance from the lake), and egg abundance was significantly influenced by both connectivity and habitat quality. In contrast, larval presence was primarily related to habitat quality. Larval abundance was influenced by connectivity and habitat quality, but the effect of connectivity was relatively low. Furthermore, larval abundance was negatively related to the presence of the invasive species red swamp crayfish (Procambarus craki) and bullfrog (Rana catesbeiana). Our findings indicate that connectivity, habitat quality and the presences of invasive species are crucial in determining suitable spawning and nursery habitats, but their relative importance may vary depending on egg and larval life stages. We suggest that restoring connectivity, improving habitat quality and removal of invasive species could be effective conservation strategies for the declining populations of crucian carp in agricultural landscapes.     

Habitat structure and proximity to forest edge affect the abundance and distribution of forest-dependent birds in tropical coastal forests of southeastern Madagascar

Despite the fact that Madagascar is classified a biological `hotspot' due to having both high levels of species endemism and high forest loss, there has been no published research on how Madagascan bird species respond to the creation of a forest edge or to degradation of their habitat. In this study, we examined how forest bird communities and different foraging guilds were affected by patch habitat quality and landscape context (forest core, forest edge and matrix habitat) in the threatened littoral forests of coastal southeastern Madagascar. We quantified habitat use and community composition of birds by conducting 20 point counts in each landscape contextual element in October and November 2002. We found that littoral forest core habitats had significantly (p<0.01) more bird species than forest edge and matrix habitats. Thirty-one (68%) forest dependent species were found to be edge-sensitive. Forest edge sites had fewer species, and a higher representation of common species than forest interior sites. Twenty-nine species were found in the matrix habitat, and the majority of matrix-tolerant forest species had their greatest abundance within littoral forest edge habitats. Guild composition also changed with landscape context. Unlike other tropical studies with which we are familiar, we found that frugivorous species were edge-sensitive while sallying insectivores were edge-preferring. The majority of canopy insectivores (n=15, 88%), including all six endemic vanga species, were edge-sensitive. When habitat quality was assessed, the distributions of nine edge-sensitive species were significantly (p<0.01) affected by changes in habitat complexity and vegetation vertical structure in core or edge point counts. Therefore, we believe that changes in vegetation structure at the edge of littoral forest remnants may be a key indicator of mechanisms involved in edge sensitivity of forest dependent species in these forests. Our findings indicate that habitat fragmentation and degradation affect Madagascan bird communities and that these processes threaten many species. With continued deforestation and habitat degradation in Madagascar, we predict the further decline of many bird species.     

Land use changes and raptor conservation in steppe habitats of Eastern Kazakhstan

Steppe habitats in central Asia have suffered important land use changes during this century which are similar to those that have been pointed out as the causes of the decline of steppe birds in western Europe. During June 1999 we conducted road surveys of raptors in Eastern Kazakhstan to detect specific and community responses to land use changes. We detected 11 species of raptors. Kestrels (Falco naumanni and tinnunculus) were the most common species in grasslands and agricultural landscapes, harriers (Circus pygargus and macrourus) were dominant in saline steppes and steppe eagles (Aquila nipalensis) were dominant in dry steppes. There were fewer species in agricultural habitats than in grassland and steppe habitats. Ground-nesting raptors were negatively affected by land use changes and four species were never detected in agricultural zones. Raptor abundance patterns differed between natural steppe habitats and human-transformed habitats, where a patchy distribution was detected. The future of raptor communities in Kazakhstan seems uncertain although the progressive abandonment of intensive agriculture may benefit species sensitive to human presence. The long-term conservation of vertebrate communities may depend upon the maintenance of ecologically and socially sustainable grazing systems.     

A priori valuation of land use for the conservation of black rhinoceros (Diceros bicornis)

The appropriateness of using carrying capacity (CC) estimates to indicate habitat utilisation for a particular species, and thus as a tool for conservation population planning, has been questioned. We argue individual fitness is driven by resource availability, and we therefore assume individuals select habitats with a higher quality, abundance, and availability of key resources. In the past such selection has been related to the CC of a habitat. We tested whether we can use CC estimates to indicate habitat selection by individuals using a selective forager, black rhinoceros Diceros bicornis, for which CC approaches underpin species conservation plans. We tested for correlation of individuals’ habitat selection with predicted CC values at three spatial scales of selection. Individual selection was not related to the value of the habitat according to our CC estimates for any of the three scales we tested at. We discuss how density-dependence, environmental variables, scale of selection, individual variation and intra- and inter-specific dynamics may have influenced these results. Following this, we question the use of a priori calculations of potential resource quality and abundance of habitats (CC estimates), which do not take into account the various factors that influence an animal’s selection of a habitat, as an indicator of species habitat selection. We raise caution regarding the use of such CC models to determine optimal population numbers for an area.     

Habitat models and habitat connectivity analysis for butterflies and burnet moths - The example of Zygaena carniolica and Coenonympha arcania

In this paper, habitat models were used to predict potential habitat for endangered species, which is an important question in landscape and conservation planning. Based on logistic regression, we developed habitat distribution models for the burnet moth Zygaena carniolica and the nymphalid butterfly Coenonympha arcania in Northern Bavaria, Germany. The relation between adult occurrence and habitat parameters, including the influence of landscape context, was analyzed on 118 sites. Habitat connectivity analyses were carried out on the basis of (1) habitat suitability maps generated from these models and (2) dispersal data from mark recapture studies. Our results showed that (1) the presence of the burnet depended mainly on the presence of nectar plants and of nutrient-poor dry grasslands in direct vicinity, that of the nymphalid on larger areas of extensively used dry grasslands within 100 m vicinity in combination with small patches of higher shrubs and bushes. (2) Internal as well as external validation indicated the robustness and general applicability of the models. Transferability in time and space indicated their high potential relevance for applications in nature conservation, such as predicting possible effects of land use changes. (3) Habitat connectivity analyses revealed a high degree of habitat connectivity within the study area. Thus, we could show no effects of isolation or habitat size for both species.     

The occurrence of primary burrowing crayfish in terrestrial habitat

A researcher’s perception of a target species’ landscape strongly influences the design of habitat studies conducted at broad spatial scales. Consequently, researcher-dependent perceptions may misguide conservation efforts. Although the life histories of some crayfish (i.e., primary burrowers) are centered on a fossorial existence independent of surface water, all North American crayfish are viewed in an aquatic context. This paradigm restricts the range of habitats that are typically sampled and managed for crayfish conservation. This study used presence/absence of the primary burrower Distocambarus crockeri at 137 locations within the Long Cane Ranger District of the Sumter National Forest, South Carolina, USA, to model the habitat association of the species across a GIS-based landscape. Logistic regression indicated that D. crockeri presence was most strongly associated with a terrestrial habitat defined by a set of morphologically similar soils located along ridge tops. Furthermore, the species was negatively associated with aquatic habitats such as streams and floodplains. The results indicate that D. crockeri is a terrestrial habitat specialist and should be modeled and managed at the landscape as a terrestrial organism. When viewed as a subset of the total United States cambarid fauna, primary burrowers are disproportionately imperiled. Primary burrowers comprise only 15% of the total crayfish fauna, while they account for 32% of those crayfish ranked critically imperiled. Habitat loss and an aquatic bias that restricted sampling to aquatic and semi-aquatic habitats might explain the group’s disproportionate imperilment.     

Avian assemblages along a gradient of urbanization in a highly fragmented landscape

Our goal was to evaluate how avian assemblages varied along a gradient of urbanization in the highly fragmented landscape of coastal southern California. We measured species richness and abundance of birds within continuous blocks of habitat, within urban habitat fragments that varied in landscape and local habitat variables, and within the urban matrix at different distances from the wildland interface. These comparisons allowed us to characterize patterns of avifaunal response to a gradient of urban fragmentation. At the fragment scale, we found that fragment area was a strong, positive predictor of the total number of breeding species detected per fragment; total bird abundance per point count also increased with fragment size. Tree cover was higher in small fragments, as was the abundance of birds that typically occupy wooded habitats. Comparisons between core, fragment, and urban transects revealed differing patterns of response of individual bird species to urbanization. In unfragmented habitat, we recorded a relatively high diversity of urbanization-sensitive birds. In urban transects, these species were rare, and a relatively few species of non-native and anthropophilic birds were common. These urbanization-enhanced birds were also recorded in previous urban gradient studies in northern California and Ohio. Bird communities along the urban gradient reached their highest richness and abundance in fragments. The marked difference in vegetation structure between urban and natural landscapes in this arid shrubland system likely contributed to this pattern; the presence of native shrubs and exotic trees in fragments enabled both shrub and arboreal nesters to co-occur. As is characteristic of biotic homogenization, urban fragmentation in coastal southern California may increase local diversity but decrease overall regional avifaunal diversity.     

太行山区不同农业景观生境的蜘蛛群落结构特征及其影响因子

为探索太行山区农业景观中不同生境类型对蜘蛛多样性的影响,采用陷阱法对河北省武安市西部太行山区5种类型生境(核桃林、玉米地、苹果-芍药套作园、次生林、绿海花廊景观带)的地表蜘蛛多样性进行调查。通过分析5种类型生境中蜘蛛多样性分布及其与局部生境因子的相关关系,探讨半自然生境对蜘蛛的保护作用。结果表明:人为干扰会显著降低生境中蜘蛛丰富度和多度;增加植被群落结构的复杂程度会使生境中蜘蛛丰富度显著增加,而蜘蛛的多度显著降低;蜘蛛的多度随生境中枯落物厚度的增加而增加。其中核桃林的蜘蛛Shannon-Wiener多样性显著高于其他4种类型生境,核桃林、次生林和绿海花廊的蜘蛛丰富度显著高于苹果-芍药套作园和玉米地,苹果-芍药套作园和绿海花廊的蜘蛛多度显著高于其他3种生境。玉米地、苹果园-芍药套作和绿海花廊中蜘蛛的群落组成具有较高相似性,而核桃林与次生林中蜘蛛群落结构具有较高异质性。地表枯落物厚度是影响当地蜘蛛群落结构的最主要因素。研究区在农业景观与自然景观的过渡区种植核桃林、苹果-芍药套作园和绿海花廊间作板栗,对蜘蛛多样性的保护都有积极作用;不同的生境因子与不同蜘蛛群落的关系不同,如狼蛛偏向人为干扰较大的苹果-芍药套作园和绿海花廊景观带,所以生产管理时要结合特有的生境条件,对相应的蜘蛛进行合理的保护和高效的利用。研究结果对当地的农业景观生境管理和生物多样性保护具有指导意义。     

Effects of human activities on migratory waterbirds at Lashihai Lake, China

Surveys on migratory waterbirds and their habitats at Lashihai Lake, China, were conducted from October 1999 to April 2000. Five fixed points, representing different degrees of habitat disturbance and quality, were selected around the lake. We used counts (n=30) to compare diversity and abundance of waterbirds at each point and evaluate the effects of habitat disturbance. The distribution of waterbirds was affected by disturbance, with more than one-third of the total species and nearly half of the total individuals occurring at the least disturbed point. Species richness was weakly and abundance was strongly correlated to habitat disturbance, but not to habitat quality. Habitat destruction and use of canoes were prominent at the lake. Naxi ethnic fishermen (n=37) were interviewed. They caught 570 waterbirds between October 1999 and March 2000 in fishing nets. An estimation of the total number of waterbirds been trapped on the lake is 6164. Diving species were most susceptible. Conservation measures that should implement immediately include the cessation of habitat destruction, better plan for the development of tourism, a reduction in the number of canoes and zoning of the non-fishing area.     

GIS-models work well, but are not enough: Habitat preferences of Lanius collurio at multiple levels and conservation implications

Species conservation largely depends on knowledge of habitat needs of target species. GIS-models are increasingly used to assess habitat preferences and distribution of target species, but their accuracy is constrained by availability of digital data layers. We developed a two-steps approach aiming at showing pros and cons of landscape (GIS)- and site-level habitat models, identifying key habitat factors for conservation of a threatened bird species, the red-backed shrike Lanius collurio. A spatially explicit GIS-model was generated using landscape variables, and a second model at site level was developed using fine-scale variables measured on the ground. The GIS-based model was then extrapolated to the entire region to obtain a map of distribution of suitable habitats. Positive associations between shrike occurrence and both hedgerow length and partial shrub cover were detected at both scales. Shrikes were also positively associated with grassland cover at landscape level and with partial cover of untilled herbaceous vegetation at the finer scale, and negatively affected by lucerne cover. The GIS-model led to an affordable map of predicted habitat suitability which should help conservationists to focus on different local priorities, but was unable to identify effects of untilled and lucerne cover. Site-level model gave fine details for habitat management, but its application elsewhere requires ground-measurements of factors. Combining the multiscale models could indicate more urgent actions at large scales (e.g. maintaining suitable habitats, or improving connectivity among isolated patches) and draw a detailed figure of the most suitable habitat for the species. Shrike occurrence was associated with a higher number of shrub and tree species: the indicator value of the species should ensure general benefits for biodiversity from dedicated management.     

Eucalypt plantations as habitat for birds on previously cleared farmland in south-eastern Australia

In parts of Australia, extensive areas of cleared land are now being planted with commercial plantations of native eucalypts. Questions arise about the extent to which such plantations can rectify previous loss of habitat and contribute to biodiversity conservation. This study assessed abundance of bird species (as one aspect of biodiversity) on 105 sites (25 cleared land, 58 plantations and 22 native forest) in two regions of rural Victoria, south-eastern Australia. Generalised linear modelling was used to assess some of the landscape and habitat variables that contributed to the value of plantation sites for particular groups of bird species. These models demonstrated the importance of on-site habitat variables in explaining the abundance of groups of bird species, with landscape context making small additional contributions.Mean abundance of forest and woodland birds was higher in eucalypt plantations than cleared farmland, and marginally lower than in native forest. Patterns differed between bird guilds. For example, insectivores that forage in the canopy and tall shrub layers were at least as common in plantations as in native forest, with birds in the latter group using young eucalypts as if they were tall shrubs. Birds that forage from open ground among trees were more common in plantations than native forest, and may benefit substantially from the new habitat fortuitously provided for them. This group includes several species that have declined in natural woodland habitats. Nectarivores, carnivores and birds that forage among low shrubs were less common in plantations than in native forest. Insectivores that forage from eucalypt bark made little use of plantations. Different approaches to plantation design and management would be needed to cater for groups such as these. Specific measures include planting of rough-barked eucalypts in addition to smooth-barked species, and provision of artificial hollows. Retention of existing remnants of native forest (e.g. old trees and forest patches) is a priority, to supply habitat elements that would otherwise be missing for long periods.     

Species occurrences at stand level cannot be understood without considering the landscape context: Cyanolichens on aspen in boreal Sweden

A major challenge in conservation biology is to understand species’ responses to habitat loss. In Fennoscandia, the ongoing decline in aspen in forests is of particular concern, since aspen is the boreal forest tree species that supports the most host-specific species of cryptogams and invertebrates. In order to predict the potential effects of aspen decline we compared the occurrence of three epiphytic cyanolichens in old-growth stands of the same habitat quality, in four aspen-rich and four aspen-poor landscapes. Collemacurtisporum and Collemafurfuraceum were, on average, five and six times more frequent, respectively, in the aspen-rich than in the aspen-poor landscapes. Leptogiumsaturninum was not affected by the abundance of aspen stands at the landscape level. Our data suggests that lichen species with poor dispersal abilities may be more sensitive to habitat loss than more easily dispersed species and that species with broader habitat amplitude may be less sensitive to habitat loss than more specialized species, even if they have inferior dispersal ability. We conclude that (i) predictions of species occurrences at the stand level have to take account of the amount of suitable habitat at the landscape level, and (ii) predicting the responses of individual species based on life-history traits can be crucial, but cannot be based on single traits. Thus our study shows that biological value cannot be assessed on the basis of habitat quality alone and that a landscape perspective is needed for the sustainable management of specialist species.     

The influence of patch area and connectivity on avian communities in urban revegetation

Landscape restoration through revegetation is being increasingly used in the conservation management of degraded landscapes. To effectively plan restoration programs information is required on how the landscape context of revegetation influences biodiversity gains. Here, we investigate the relative influence of patch area and connectivity on bird species richness and abundance within urban revegetation patches in Brisbane, Australia. We carried out bird surveys at 20 revegetation sites, and used hierarchical partitioning and model selection to test the relative importance of patch area (the area of revegetation including all directly connected remnant vegetation) and landscape connectivity (the vegetated area connected by less than 10 m, 20 m, 30 m, 40 m and 50 m cleared gaps). We controlled for a number of possible confounding variables within the hierarchical partitioning procedure. Both the hierarchical partitioning and model selection procedures indicated that connectivity had an important influence on bird species richness. Patch area in combination with connectivity were important influencing factors on overall bird abundance. We also carried out the hierarchical partitioning procedure for bird abundance data within a range of feeding guilds, yielding results specific to species groups. Overall our data suggest that greater connectivity enhances the habitat area that colonists can arrive from (resulting in greater species richness), whereas increased patch area allows for increased abundance by expanding the habitat available to species already present in a patch. A combined approach where connectivity and overall habitat area is enhanced across the landscape is likely to be necessary to meet long-term conservation objectives.     

Development and evaluation of predictive habitat models to assist the conservation planning of a threatened lucanid beetle, Hoplogonus simsoni, in north-east Tasmania

The use of predictive habitat distribution models by land managers in the conservation management of threatened species is increasing. Few models, however, are subsequently field-checked and evaluated. This study evaluates the statistical strength and usefulness for conservation purposes of three predictive habitat models developed for a threatened stag beetle, Hoplogonus simsoni, found in the wet eucalypt forests and mixed/rainforests of north-east Tasmania. The relationship between various environmental variables for which spatial (GIS) information was available and the density, frequency of occurrence and presence/absence of the species was investigated using generalised linear modelling. Models developed were coupled with the GIS data to develop maps of predicted occurrence within the species’ range, grouped into categories of habitat quality. The models found that altitude, aspect, slope, distance to nearest stream and overstorey tree height were significantly associated with the occurrence of the species. Evaluation of the statistical strength of the models with independent data of species’ occurrence collected at 95 sites found that the density model performed poorly with little correlation between predicted and observed densities of the species. The frequency of occurrence model, however, showed a moderate ability to predict both species’ abundance and presence/absence. The presence/absence model had a similar discriminatory ability in predicting presence or absence of H. simsoni, but also showed some potential as an indirect predictor of species’ abundance. Assuming a correlation between relative abundance and habitat quality, the frequency of occurrence predictive model appeared to be the better and more direct discriminator of high quality habitat relative to the other models. The value of species’ habitat models and the need to evaluate their utility in the development of conservation strategies are discussed.     

Long-term erosion of tree reproductive trait diversity in edge-dominated Atlantic forest fragments

Habitat loss and fragmentation promote relatively predicable shifts in the functional signature of tropical forest tree assemblages, but the full extent of cascading effects to biodiversity persistence remains poorly understood. Here we test the hypotheses that habitat fragmentation (a) alters the relative contribution of tree species exhibiting different reproductive traits; (b) reduces the diversity of pollination systems; and (c) facilitates the functional convergence of reproductive traits between edge-affected and early-secondary forest habitats (5-32 years old). This study was carried out in a severely fragmented 670-km² forest landscape of the Atlantic forest of northeastern Brazil. We assigned 35 categories of reproductive traits to 3552 trees (DBH ? 10 cm) belonging to 179 species, which described their pollination system, floral biology, and sexual system. Trait abundance was calculated for 55 plots of 0.1 ha across four habitats: forest edges, small forest fragments (3.4-83.6 ha), second-growth patches, and core tracts of forest interior within the largest available primary forest fragment (3500 ha) in the region. Edge-affected and secondary habitats showed a species-poor assemblage of trees exhibiting particular pollination systems, a reduced diversity of pollination systems, a higher abundance of reproductive traits associated with pollination by generalist diurnal vectors, and an elevated abundance of hermaphroditic trees. As expected, the reproductive signature of tree assemblages in forest edges and small fragments (edge-affected habitats), which was very similar to that of early second-growth patches, was greatly affected by both habitat type and plot distance to the nearest forest edge. In hyper-fragmented Atlantic forest landscapes, we predict that narrow forest corridors and small fragments will become increasingly dominated by edge-affected habitats that can no longer retain the full complement of tree life-history diversity and its attendant mutualists.     

Assessing habitat quality for butterflies on intensively managed arable farmland

The conservation and management of biodiversity requires accurate, repeatable and cost-effective monitoring techniques. In this study, a simple and rapid methodology was employed to measure the quality of different habitats for butterfly species on 10 arable farms in lowland Britain. This habitat monitoring was seven times more rapid than the traditional species-based butterfly monitoring. Data on butterfly abundance were combined with the information gathered on habitat quality at five of the farms using stepwise regression. These models had a consistently high degree of explanatory power for the summary variables of total butterfly abundance and species richness, and the functional groupings of mobile and immobile species. There was good agreement between observed and predicted estimates of species richness and abundance when the models were validated on a further five independent sites. Models to predict the abundance of 11 common butterfly species were also produced. These varied considerably in their predictive power and validity between species. The results clearly demonstrated the beneficial effects of targeted habitat creation for butterflies which is promoted under the Agri-environment Schemes, especially the recently introduced pollen and nectar seed mixtures (WM2) available under the Countryside Stewardship Scheme. The models confirmed the importance of shelter, floristically diverse field margins and the availability of nectar resources from legume species in explaining the abundance of immobile butterfly species in arable landscapes. These sources of nectar and the presence of larval host plants in the crucifer family were important factors in explaining the abundance of mobile species. The results are discussed in terms of the potential of this approach for: (i) assessing habitat quality for butterflies in intensively managed landscapes; (ii) enhancing the value of butterfly monitoring schemes in explaining changes in butterfly abundance at the site and national scale; and (iii) informing habitat management and restoration guidelines for butterfly conservation on arable farmland.     

Impacts of coffee agroforestry management on tropical bee communities

Though it is undoubted that tropical bees are influenced by habitat composition, few studies have investigated the relative importance of both local and landscape-level habitat parameters in supporting large and diverse bee communities. The conservation of native bee communities within agroforestry landscapes is particularly urgent given the importance of pollination services within these systems. In this study, we examined tropical bee communities within a largely deforested shade coffee-growing region in Chiapas, Mexico. We used regression tree modeling to examine the response of bee functional groups to local and landscape-level habitat management. Our models revealed that the most predictive factors for bee abundance and species richness were the number of tree species, the number of tree species in flower, and the canopy cover of the local agroforestry landscape. Solitary bees were most abundant in habitats with high canopy cover, while social bees were most abundant in habitats with greater tree species richness. Cavity-nesting and wood-nesting bee abundance was positively affected by the amount of canopy cover in the farm, while ground-nesting bees were most abundant in habitats with a large number of tree species in flower. Our results demonstrate that across bee sociality groups, nesting guilds, and tribes, the most critical factor impacting native bee communities was within-farm local vegetation management. These results reveal the important role that agroforestry managers can have on biodiversity conservation, and the potential contribution they can make by creating resource-rich agricultural matrices. Specifically, our findings highlight the importance of diverse overstory tree management in supporting native bee communities within tropical agroforestry systems.     

Could soil degradation contribute to farmland bird declines? Links between soil penetrability and the abundance of yellow wagtails Motacilla flava in arable fields

Major changes to the extent and quality of farmland habitats, brought by the intensification of agricultural practice, are thought to be the main factors driving declines in a suite of farmland bird species in Europe. Recent changes in agricultural techniques have also contributed to widespread soil degradation, arising from increased soil exposure to erosion forces, declining soil organic content and increasing soil compaction. Although soils have a fundamental influence on ecosystem properties, the implications of soil degradation for farmland biodiversity have received little attention. In this study, we measure the influence of soil conditions on the distribution of a declining insectivorous farmland bird, the yellow wagtail Motacilla flava, relative to other habitat features in arable fields. Soil penetrability was found to have a significant influence on the abundance of territorial yellow wagtails at the field scale, together with crop type. Other measured habitat features had little effect on territory abundance, including soil organic content, crop height (within preferred crop types), field boundary habitats and availability of bare ground. Monitoring of invertebrate abundance across 20 cereal fields revealed a significant influence of both soil penetrability and soil organic content on aerial invertebrate capture rates. This relationship was strongest during the latter part of the breeding season, implying that settling yellow wagtails could use soil penetrability as a predictive indicator of prey abundance during the chick-rearing period. The strong relationship between yellow wagtails and soil penetrability suggests a potential causative link between soil degradation and population decline. The role of soils in determining abundance patterns and population declines of other farmland species may have been overlooked in previous studies.