Jenni A. Stockan

Drivers of carabid functional diversity: abiotic environment, plant functional traits, or plant functional diversity?

Understanding how community assembly is controlled by the balance of abiotic drivers (environment or management) and biotic drivers (community composition of other groups) is important in predicting the response of ecosystems to environmental change. If there are strong links between plant assemblage structure and carabid beetle functional traits and functional diversity, then it is possible to predict the impact of environmental change propagating through different functional and trophic groups. Vegetation and pitfall trap beetle surveys were carried out across twenty four sites contrasting in land use, and hence productivity and disturbance regime. Plant functional traits were very successful at explaining the distribution of carabid functional traits across the habitats studied. Key carabid response traits appeared to be body length and wing type. Carabid functional richness was significantly smaller than expected, indicating strong environmental filtering, modulated by management, soil characteristics, and by plant response traits. Carabid functional divergence was negatively related to plant functional evenness, while carabid functional evenness was positively correlated to plant functional evenness and richness. The study shows that there are clear trait linkages between the plant and the carabid assemblage that act not only through the mean traits displayed, but also via their distribution in trait space; powerful evidence that both the mean and variance of traits in one trophic group structure the assemblage of another.

Investigating riparian margins for vegetation patterns and plant-environment relationships in northeast Scotland.

Buffer strips alongside watercourses are a widely accepted method of reducing nutrient and sediment run-off from agricultural land thereby improving water quality. Little attention, however, has been paid to the ecological status of these areas despite the fact that riparian habitats in good condition can provide multiple benefits. We investigated vegetation patterns and plant-environment relationships within three categories of riparian margins in northeast Scotland. The margins were categorized as unbuffered, buffered, or reference (target), the latter representing the best sites available within the catchments. Vascular plant and soil data were collected from 41 sites along the tributaries of two rivers during 2008 and 2009. Ellenberg indicator values revealed trends of decreasing light availability ( < 0.05) and decreasing pH ( < 0.01) from unbuffered sites to buffered sites to reference sites. Multivariate analysis showed that soil parameters and channel morphology, together with canopy cover and bryophyte abundance, were discriminatory in separating species assemblages. The presence of a tree canopy layer appears to be the key instigator of change in soil conditions and corresponding plant species assemblages. An understanding of the underlying processes is important if vegetation characteristics are to be used effectively as indicators of riparian and water quality and to aid the restoration of riparian habitats.

Wood Ant Ecology and Conservation

Wood ants play an ecologically dominant and conspicuous role in temperate boreal forests,making a keystone contribution to woodland ecosystem functions and processes.Wood ant taxonomy and global distributions set the scene for this text’s exploration of wood ants as social insects, examining their flexible social structures, genetics, population ecology and behaviour; from nestmate recognition to task allocation.Wood ants’ interactions with their environment and with other organisms are essential to their success: competition, predation and mutualism are described and analysed. Bringing together the expertise of ecological researchers and conservation practitioners, this book provides practical and theoretical advice about sampling and monitoring these insects, and outlines the requirements for effective conservation. This is an indispensable resource for wood ant researchers, entomologists, conservationists and ecological consultants, as well as anyone interested in social insects, keystone species and the management and conservation of forest ecosystems.

Contribution of wood ants to nutrient cycling and ecosystem function

Red wood ants ( Formica rufa group) build large and long-lasting nest mounds. Due to their construction, nest mounds and especially their centres, provide a favourable microclimate for brood development (Coenen-Staβ 1980). However, constructing and maintaining the nest in addition to feeding the colony requires a considerable amount of energy and building material. The ‘central-place foraging’ strategy (Chapter 7) employed by red wood ants – retrieving food and plant material from the area surrounding the nest – means they influence not only the properties of their nests, but also those of the wider area. Wood ants influence the functioning of forest ecosystems through altering food web structure (Chapter 8), soil properties, and nutrient transport and energy flow (Frouz and Jilkova 2008). The vast accumulation of organic materials in the nest means that once the nest is no longer in use, nutrients are released during the decomposition process which is performed by microorganisms (Lenoir et al . 2001). These nutrients are then available for plant growth. This chapter addresses the effects of wood ants on nutrient flow and plant growth in forest ecosystems. Since these effects are associated with nest building and territorial activities, they can be divided into nest- and territory-related effects. Nest-related effects Foraging for food Nest-related effects are connected with foraging, nest construction and the subsequent decomposition of organic materials. Decomposition in nests is enhanced because of the abundance of microorganisms and the favourable microclimate. Mineral nutrients are released from organic materials but predominantly remain in or near the ant nests, thus creating hot spots in nutrient-limited forest ecosystems. Wood ants feed on honeydew and solid insect prey; honeydew rarely forms less than two-thirds of the energy imported to F. rufa nests (Whittaker 1991). Ants may collect more than 80% of the excreted honeydew, which constitutes 62–94% of their diet and contains 15–20% sugars, a small percentage of amino acids and c . 70% water (Rosengren and Sundstrom 1991). Thus, approximately 13–16 kg of honeydew dry mass containing a significant amount of nutrients (Table 9.1) is transported annually into the average ant nest (Frouz et al . 1997; Jilkova et al . 2012). Once transported into the ant nest, the honeydew is redistributed and used as a source of energy (Horstmann 1974).

More than just fish food: ecosystem services provided by freshwater insects

1. Freshwater ecosystems cover less than 1% of the planets surface but support up to 10% of known species. Around 25% of freshwater invertebrate species are under threat of extinction. Such a decline in species richness is likely to lead to adverse effects on the delivery of services. However, the effect of species loss on ecosystem goods and services can only be assessed once the link between species diversity and ecosystem goods and services has been established and better understood.

How to Replicate the Functions and Biodiversity of a Threatened Tree Species? The Case of Fraxinus excelsior in Britain

The suitability of alternative tree species to replace species that are either threatened by pests/disease or at risk from climate change is commonly assessed by their ability to grow in a predicted future climate, their resistance to disease and their production potential. The ecological implications of a change in tree species are seldom considered. Here, we develop and test 3 methods to assess the ecological suitability of alternative trees. We use as our case study the systematic search for an alternative tree species to Fraxinus excelsior (currently declining throughout Europe due to Hymenoscyphus fraxineus). Those trees assessed as most similar to F. excelsior in selected ecosystem functions (decomposition, leaf litter and soil chemistry) (Method A) were least similar when assessed by the number of ash-associated species that also use them (Method B) and vice versa. Method C simultaneously assessed ecosystem functions and species use, allowing trade-offs between supporting ecosystem function and species use to be identified. Using Method C to develop hypothetical scenarios of different tree species mixtures showed that prioritising ecosystem function and then increasing the mixture of tree species to support the greatest number of ash-associated species possible, results in a mixture of trees more ecologically similar to F. excelsior than by simply mixing tree species together to support the greatest number of ash-associated species. We conclude that establishing alternative tree species results in changes in both ecosystem function and species supported and have developed a general method to assess suitability that simultaneously integrates both ecosystem function and the ‘number of species supported’.

Effects of riparian buffer strips on ground beetles (Coleoptera, Carabidae) within an agricultural landscape

Current restoration of stream and lotic freshwater systems to ‘good ecological status’ has focused on the creation of vegetated riparian buffer strips. Yet, despite this constituting a major land‐use change, surprisingly little is known about the effects of these strips on riparian organisms. We investigated the effect that widespread adoption of buffer strips may have on activity density, species diversity, and assemblage composition of ground beetles (Coleoptera, Carabidae). Over 2 years, we sampled carabids from 41 riparian margins within two river catchments in north‐east Scotland. We compared three types of riparian margin: unbuffered (i.e. ‘unimproved’), vegetated buffer strips, and wooded, the latter acting as reference sites. A range of site parameters including characteristics of soil, water, and vegetation were recorded and the extent to which they correlated with ground beetle assemblages was explored. Catchment and treatment effects were detected on ground beetle activity density and species diversity with unbuffered sites showing higher activity density and species richness. The assemblage structure differed according to catchment, treatment, and local characteristics. Multivariate analysis suggested that soil and vegetation parameters and stream width, together with buffer strip age and length were determinants of assemblage structure. Few riparian species were found in large numbers. This study shows that in intensively managed agricultural landscapes riparian buffer strips do not create the quality of habitat required by truly riparian species. They do, however, provide habitat for woodland and stenotopic species and with more careful planning could play a role in increasing habitat heterogeneity at a landscape scale.

Threats, conservation and management

The ecological effects of red wood ants of the Formica rufa group extend over several trophic levels. Due to their multiple roles in the environment they can be referred to both as keystone species and ecosystem engineers. Therefore any change to their status and distribution affects not only the ants themselves but a more widespread suite of species (including myrmecophiles and myrmecochorous plants) and ecosystem processes such as nutrient cycling (see Chapters 6, 7, 8 and 9). Where they occur, wood ants are usually populous and, as such, they need abundant and stable resources and favourable abiotic conditions for reproduction. However, while the workers are numerous, only queens and males reproduce, which is why effective population sizes and thereby conservation needs are easily underestimated. In addition, it is large colony size which makes the wood ants vulnerable, because they need relatively large habitat patches with stable food sources to maintain viable colony functions. Therefore, loss of suitable breeding habitat is a major threat and many of the red wood ants have a status as ‘near threatened species’ globally (see Table 1.1 in Chapter 1). However, habitat loss is far from the sole threat since pollution, climate change and natural causes of decline (e.g. pathogens) also have an effect on red wood ants. The threats against wood ants can be categorised as: (1) harmful changes in availability or quality of food (e.g. loss of aphids, contamination of food); (2) loss of suitable habitat (e.g. increase of agricultural and urban areas); (3) changes in climatic conditions (e.g. climate change, microclimate change); (4) natural causes of decline; and (5) their interactions. These threats, and how they can be addressed, are the subject of this chapter. Habitat management Wood ants are mainly forest-dwelling animals. Their large colonies are dependent on vast aphid populations living in tree canopies. Therefore, the most extreme events affecting wood ants are in relation to forest management, which has also been the focus of much of the published literature. Severe forest management practices such as clear felling, or felling with some retention trees, clearly cause negative biotic and abiotic changes in the environment, and for wood ants this means changing the availability of aphid-originated food and microclimate (Figure 12.1).

Invertebrate species at risk from Ash Dieback in the UK

Abstract Ash Dieback, a disease of Ash (Fraxinus excelsior) trees caused by the ascomycete, Hymenoscyphus pseudoalbidus, was first noticed in the UK in February 2012 and has since been found through much of the country. Evidence from elsewhere in Europe suggests that most infected Ash trees succumb to the disease and, hence, UK woodlands and landscapes are at risk of large scale changes. A wide range of taxa either depends on Ash or makes significant use of it and is likely to be detrimentally affected if the UK’s Ash trees are seriously depleted. Invertebrate species that use Ash exclusively or are highly associated with the tree were identified from existing literature. We categorised 36 invertebrate species as “obligate” on Ash in the UK and a further 38 as “highly associated”. Hemiptera, Diptera and Lepidoptera were the most significant groups amongst the obligate species with Coleoptera, Lepidoptera and Diptera dominating the highly associated species. Most obligate species are phytophagous in their use of Ash. Highly associated species were evenly split between those that are phytophagous and those classified as saproxylic with a smaller number of species employing a range of additional feeding strategies. Among highly associated species that are phytophagous, Privet (Ligustrum sp.) was the most frequent alternative plant used. This and other alternative trees and shrubs could be used to help mitigate the effects of Ash Dieback in limited localised situations, where rare species might be affected. Additional suggestions for managing the impact of Ash Dieback on invertebrates are discussed.

Sampling and monitoring wood ants

Wood ants ( Formica rufa group) are the ecological centre of many temperate and boreal forest ecosystems, with influence over ecosystem processes and other organisms. Owing to their dominance and keystone role, there are many reasons why it may be desirable or necessary to sample or monitor wood ants. Most field-based studies are based on exploring the relationships between red wood ants and their environment, be it the effects wood ants have on their surroundings via their nesting or foraging activities, or the effect a changing environment has on the ants. Given their keystone roles with the ecosystem, red wood ants can be useful indicators of ecosystem health, environmental degradation or restoration, or climate change (Torossian 1977b; Sorvari and Hakkarainen 2007b). With many species in Eurasia threatened and those in North America little understood, there is often simply a requirement to assess whether a species is present or not, or whether introductions or translocations have been successful. Unlike most other invertebrates, and indeed even other ant species, most red wood ants build conspicuous and long-lasting mound nests that facilitate their census. However, as for other ant species, this social living presents particular challenges for sampling and monitoring. Careful planning and the application of considered methods are needed to overcome these difficulties. This chapter provides an overview of the sampling methods and approaches that have been directly applied to wood ants, and the theory underpinning them. Where methods or approaches are ineffective or warrant further development, these are highlighted. The goal is to recommend a set of reliable and easy to use methods that can provide accurate and repeatable data, which are comparable between studies. The challenges of studying red wood ants Consideration of life cycle and seasonality Effective sampling or monitoring of wood ants presents considerable theoretical and practical problems. Wood ants are social insects which are patchily distributed and territorial. Moreover, there are seasonal patterns to the abundance and presence of certain castes. The queen (or queens) and some workers are present throughout the year, though not always visibly so. Males and particular stages of brood are present only for part of the year and this can depend on factors such as colony size and age, food availability and local environmental variables.