20 results in Wood Ant Ecology and Conservation
Index
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6 - Interspecific competition and coexistence between wood ants
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- By Therese Johansson, Swedish University of Agricultural Sciences, Umeå, Sweden, Heloise Gibb, La Trobe University, Melbourne, Australia
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Summary
Competition among or within species has long been considered one of the most fundamental processes shaping ecological communities, affecting distributions and the evolution of species. While its importance and detectability are strongly debated (Schaffer et al. 1979; Schoener 1982; Connell 1983; Schoener 1983), its role in structuring ant assemblages has often been uncritically accepted and competition is even referred to as ‘the hallmark of ant ecology’ (Hölldobler and Wilson 1991). Competition between species, i.e. interspecific competition, has been a major theme in the study of wood ants and their role in species assemblages.
This chapter considers interspecific competition as it relates to wood ants, including the behavioural interactions with other ant species and mechanisms of coexistence. Theories regarding the competitive structuring of ant assemblages by wood ants through dominance hierarchies (see below) and the observational and experimental evidence for this are discussed. Factors that regulate competition from wood ants, competitive interactions with other taxa and avenues for advancing our understanding of this topic are also considered.
Behavioural interactions
Interspecific competition arises through two main non-exclusive mechanisms: interference and exploitation. Interference competition includes direct aggressive encounters between individuals over food resources, reproduction or survival. Wood ants are territorial and defend both nest sites and food resources (Savolainen and Vepsäläinen 1988). The relatively large workers (up to 8 mm) spray formic acid from the gaster and bite, as a means of attack or defence, in direct encounters with other ant species (Chapter 5). Exploitation competition (scramble competition) occurs indirectly through a shared limited resource. Here, the use of a resource (usually food) by wood ants depletes the amount available to other species.
Wood ants excel at both discovering and recruiting to resources that they subsequently defend aggressively (Parr and Gibb 2012), leaving little opportunity for other species. Savolainen (1991) showed that, even when co-occurring Formica fusca are first to discover and collect a resource, it is often co-opted by aggressive biting wood ants before it can be transported back to the nest. Other taxa may also be affected, e.g. carabid beetles within wood ant territories are attacked, but not eaten, suggesting interference competition (Reznikova and Dorosheva 2004). Wood ants may also use colony-level behaviours to protect valued resources: for example, in Formica integroides, larger workers forage at more distant trees.
3 - Population genetics of wood ants
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- By Pekka Pamilo, University of Helsinki, Finland, Perttu Seppä, University of Helsinki, Finland, Heikki Helanterä, University of Helsinki, Finland
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Summary
Discussions of queen dispersal and adoption of new queens by own versus alien colonies in Formica rufa played an important role in the early theoretical studies of social evolution (Sturtevant 1938; Williams and Williams 1957). This was inspired by polygyny affecting the genetic relationships among nestmates, which are estimated today by use of genetic markers (Box 3.1). Demography and population dynamics also shape the whole genetic landscape of ant populations, and genetic studies can be used to trace such events. Finally, even long-term processes leave their genetic signatures, and the genome-wide variation patterns support the hypothesis that ants tend to have small effective population sizes and increased genetic loads, resembling vertebrates more than other invertebrates in this respect (Romiguier et al. 2014). Even though this conclusion is general and based only on very few species, it emphasises biological characteristics important for ant populations also in the context of conservation.
Molecular markers
Genetic markers are used to estimate the level and distribution of genetic variation in populations and societies. Optimal genetic markers are: (1) not influenced by environment or developmental stages, (2) randomly distributed across the genome, (3) codominant and (4) selectively neutral, but none of the markers in use fulfil all these requirements (Lowe et al. 2004). Genetic markers are used to resolve phylogenetic relationships at different hierarchical levels: among species, among conspecific populations at large geographic scales, among potentially interconnected conspecific populations and among individuals (Avise 2004). In social insects, studies at the first two levels are not different from other organisms: spatial distribution of genetic variability is first assessed and then interpreted based on geological and climatological history. On the other hand, analyses of colony kin structure and spatial population structure are, at least to some extent, idiosyncratic to social insects and need a more detailed introduction (Box 3.2).
Marker types
In the 1960s, the first molecular polymorphisms employed as genetic markers were enzymes, widely used because of low costs and the ease of use. Allozyme polymorphism is based on the variation in the net charge of enzymes involved in basic metabolism. As only a small fraction of mutations (9%) lead to a change in the net charge of the amino acid chain, allozymes tend to be only weakly polymorphic.
Acknowledgements
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Dedication
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5 - Colony and species recognition among the Formica ants
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- By Stephen J. Martin, University of Salford,Greater Manchester,UK
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Summary
The cause of the perpetual feud among ants of different colonies is due to difference of odour, discerned through their antennae.
Adele Fielde (1901)Many temperate forests, especially those in Scandinavia, are crawling with wood ants; their mounds and trails scattered everywhere. Although most wood ants (Formica rufa group) look similar, there are a range of species based on a series of morphological features (Chapter 1). The ‘alpha taxonomy’ method established by Linnaeus has been remarkably robust, given that the ants do not use these morphological features to recognise nestmates from non-nestmates. This is achieved by a rich chemical language, and only when we understand this hidden aspect of the ants' world can we start to explain many of their observable behaviours. For example, how are territories maintained, or why do some wood ants vigorously defend their mound while other mounds are linked by trails along which ants move freely (Chapuisat et al. 2005)? We are just starting to reveal the complex recognition systems that allow each ant to distinguish its nestmates from all others and respond accordingly, and the Formica ants currently represent some of the best studied species. Ant recognition is a very active and fast-moving field of research that has been subject to several reviews, which include general reviews (e.g. Hölldobler and Wilson 1990, 2009; Howard and Blomquist 2005), ant social parasitism (Lenoir et al. 2001), fertility signals (Hefetz 2007), books on hydrocarbons (e.g. Blomquist and Bagnères 2010) and other compounds produced by ants (Morgan 2004). This chapter concentrates solely on recent advances in the chemical ecology of Formica ants, including wood ants, which have become leading model systems especially for the study of species and nestmate recognition systems.
Brief history of ant chemical ecology
It has been known for over 100 years that ants use odours to distinguish friends from foes (Fielde 1901, 1903), since aggression between ants from different colonies or species is common, but not universal. In any ant colony or on any foraging trail, ants are continuously using their antenna to touch their surroundings and fellow ants. Unseen by us is an amazingly complex chemical world that governs the vast majority of their behaviours. Whereas most vertebrates rely on visual and oral forms of communication, the vast majority of invertebrates rely on chemical communication.
12 - Threats, conservation and management
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- By Jouni Sorvari, University of Eastern Finland, Kuopio, Finland
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Summary
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).
1 - Introducing wood ants: evolution, phylogeny, identification and distribution
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- By Jenni A. Stockan, James Hutton Institute, Aberdeen,UK, Elva J.H. Robinson, University of York, Heslington, York,UK, James C. Trager, Missouri Botanical Garden, Gray Summit, Missouri, USA, Izumi Yao, Hokkaido University, Sapporo, Japan, Bernhard Seifert, Leibniz Institute for Evolution and Biodiversity Science, Berlin,Germany
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Summary
Few insects in the cool temperate northern hemisphere are as conspicuous as red wood ants. Most red wood ants build large and enduring nest mounds reaching more than 2 m in height, penetrating considerably further beneath the ground surface and thatched on top with a layer of plant material. These mounds are marvels of engineering with a complex array of tunnels and chambers in a carefully controlled environment. Nests may be interlinked, forming, in extreme cases, vast colonies of up to 400 million individual ants covering an area of more than 2.5 km2. Their sheer abundance and collective biomass in temperate forests can rival any mammalian predator.
Red wood ants properly belong to the subgenus Formica sensu stricto or F. rufa group, and can also be commonly referred to as true wood ants, thatch ants or mound ants (hereafter ‘wood ants’). These names derive from the habitat, nesting habit and colour of the adults, which are bicoloured red and brownish-black. Contained within this group of ants are several morphologically and ecologically similar species distributed throughout the Holarctic.
More impressive perhaps than even their numerical dominance is their ecological significance in driving ecosystem processes and function both above and below ground. With a role in predator–prey dynamics, nutrient cycling, seed dispersion, habitat provision and modification, and plant and tree growth, wood ants can truly be described as keystone species. As a result of their ecological importance, wood ants are protected by law in some countries, yet their populations remain threatened from a variety of sources, not least, loss of suitable habitat. This chapter describes species that are currently considered members of the subgenus Formica sensu stricto; their evolution, identification, habitat and distribution. The concept of red wood ants as social insects is introduced. The rest of the book will cover reproductive biology and social systems (Chapter 2), population genetics (Chapter 3) and ecology (Chapter 4), colony and species recognition (Chapter 5), interspecific competition (Chapter 6), foraging and interactions with other organisms (Chapters 7 and 8), nutrient cycling (Chapter 9), similarities and differences between North American and Eurasian wood ants (Chapter 10), monitoring and conservation (Chapters 11 and 12) and future research questions (Chapter 13).
Foreword
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Summary
Ants are everywhere. They are dominant components in much of the terrestrial world as premier soil turners, predators of other arthropods, dispersers of seeds and, in neotropical regions, the attine leafcutter ants must be considered the major herbivores in rainforests and cultivated fields. Approximately 14 000 species of ants are known to science, but the number continues to grow and it is hard to say how many species actually live on our planet.
Science has revealed many unique and fascinating natural histories for a large diversity of ant species, but certain groups stand out. Clearly, the pinnacles in ant evolution include the army ants of the neotropics and the driver ants of Africa, the tree-dwelling weaver ants of Africa, Asia and Australia, the fungus growers of the tribe Attini in Central and South America, and the migrating herdsmen of the genus Dolichoderus of the Malaysian peninsula. The mound-building wood ants, the so-called Formica rufa group, must also be considered one of the pinnacles of ant evolution.
In 1960, as an advanced biology student at the University of Würzburg in Germany, I was charged with the wonderful task of spending about 2 months in Finland collecting wood ants in forests from the south to the north beyond the Arctic Circle to send these samples to the Institute of Applied Zoology at the University of Würzburg. The general abundance of Formica mounds in Finnish forests, especially in primeval forests, was most impressive. Unfortunately, wood ant mounds are now rare or totally absent in most Central European forests mostly due to negligence, despite the fact that entomologists had already recognised in the nineteenth century the decisive role wood ants play in biological pest control. The undisputed founder of forest entomology, Julius Theodor Christian Ratzeburg (1801–71), observed that the surrounds of wood ant mounds resembled green islands during pest insect outbreaks. According to Auguste Forel (1848–1931) the inhabitants of a single large Formica rufa nest can retrieve 100 000 insects in one day; this adds up to 10 million prey insects in one summer. These numbers are astonishing and perhaps somewhat exaggerated, or perhaps not? In any case, mound-building wood ants are very beneficial to the health of forests, and therefore Ratzeburg proposed to propagate and resettle Formica nests by artificial fission.
10 - Diversity, ecology and conservation of wood ants in North America
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- By James C. Trager, Missouri Botanical Garden, Gray Summit, Missouri, USA
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Summary
The North American Formica rufa group ants (henceforth, North American wood ants) have great inherent interest, but they are relatively little studied. None of the North American wood ants enjoys much recognition in the minds of North American peoples. Aside from the moderately abundant literature on F. obscuripes, the literature on North American red wood ants is characterised by dearth, in comparison to the rich literature on the Eurasian species. Much of what we know about the species is summarised in regional faunas (e.g. Creighton 1950; Wheeler and Wheeler 1963, 1986; Gregg 1963; Mackay and Mackay 2002; Coovert 2005; Ellison et al. 2012; Talbot 2013) and in original descriptions (not cited but available through Bolton 2013). The United States, Canada and Mexico lack the legal protection of these ants such as occurs in European countries.
The designation ‘wood ants’ is, in truth, an inadequate descriptor for the North American F. rufa group species, as many of these species inhabit shrub lands or grasslands. The majority of North American species rarely have an organic mound-building habit, or it is certainly not well developed. Furthermore they lack, or are less likely to develop, the polygynous supercolonies that are characteristic of the Eurasian red wood ants of mature forests. These habits render them less conspicuous to entomologists and non-entomologists alike. This chapter explores the ecological differences between North American and Eurasian wood ants and discusses the possible reasons for these differences.
The Formica rufa group in North America
The F. rufa group is represented by at least 20 to perhaps 50 species in North America, depending on how inclusive the group is deemed to be, and accounting for undescribed (S. Cover, unpublished data, 2014) and introduced species (i.e. Formica paralugubris). The majority of the North American red wood ants are rare or sporadic in distribution, and the taxonomy of these forms is in a relatively poor state, with sometimes less than clear species delimitations (see key in Chapter 1). The taxonomic picture is further complicated by the fact that American ant taxonomists generally believe the North American red wood ants properly ought to include the species that have been separated as the Formica microgyna group (in this chapter referred to as the F. microgyna complex).
8 - Wood ants and their interaction with other organisms
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- By Elva J.H. Robinson, University of York, Heslington, York,UK, Jenni A. Stockan, James Hutton Institute, Aberdeen,UK, Glenn R. Iason, James Hutton Institute, Aberdeen,UK
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Summary
Wood ants (Formica rufa group) interact with a wide range of other organisms at multi-trophic levels. Chapter 6 discusses competitive interactions between wood ants and other ant species, and Chapter 7 explores the fundamental mutualistic interaction between wood ants and aphids. This chapter takes a wider approach still, to explore the effects of wood ants on invertebrate communities on the forest floor and in tree canopies, including their potential impact on invertebrate pests. The multiple mechanisms by which other invertebrates (myrmecophiles) infiltrate and survive in and around ant nests without being harmed are reviewed. Finally, consideration is given to how wood ants affect more distant taxa such as the vegetation surrounding their nests, the trees on which they forage and woodland vertebrates.
Aboveground interactions
The main effects of wood ants on tree-crown invertebrates
The key trophic effects of wood ants are predation of invertebrates and mutualism with aphids (see Chapter 7). These interactions have a considerable influence in shaping the communities of tree-crown invertebrates (Figure 8.1). The ants generally reduce the overall abundance of non-tended aphids and invertebrates of all trophic groups and taxa. In contrast, ant-tended aphid species usually increase in abundance (Warrington and Whittaker 1985a, b; Mahdi and Whittaker 1993; Wimp and Whitham 2001; Punttila et al. 2004). The wood ants both protect their tended aphids and use them as prey items (Billick et al. 2007). Temporary shifts from mutualistic to predatory behaviour may occur when there is a surplus of aphids (Way 1963; Sudd and Franks 1987) and a lack of other abundant prey items, or the ants may target injured, dead or immobile (e.g. moulting) aphids or those producing honeydew of poor quality or quantity (Sakata 1994; see Chapter 7).
The wood ants protect their mutualistic species of aphids by removal of other predatory, parasitic and hyperparasitic invertebrates (Liere and Perfect 2008) and the aphids’ competitors, such as non-ant-tended aphid species and other herbivores (Novgorodova 2005; Billick et al. 2007), which can form a large part of the ants’ prey (Punttila et al. 2004). This helps to secure the ants’ supply of carbohydrate, which they gather from the aphids in the form of honeydew (Mooney and Mandal 2010).
2 - Wood ant reproductive biology and social systems
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- By Arnaud Maeder, Museum of Natural History, La Chaux-de-Fonds, Switzerland, Daniel Cherix, University of Lausanne, Lausanne-Dorigny, Switzerland, Christian Bernasconi, Museum of Zoology, Lausanne, Switzerland, Anne Freitag, Museum of Zoology, Lausanne, Switzerland, Samuel Ellis, University of York, Heslington, York,UK
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Summary
Transmitting genes from one generation to the next is the fundamental basis of natural selection and evolution. Understanding the reproductive biology of a species is, therefore, fundamental to understanding how the species evolved and how it is adapted to its environment. In eusocial insects such as the wood ants (Formica rufa group), reproduction is invested in a specialised reproductive caste, which produces both the workers and the next generation of sexual individuals. This chapter introduces the reproductive biology of wood ants, and also gives a general view of the life cycle of a wood ant colony to put the reproductive biology in context.
Wood ant life cycle
The wood ant life cycle is strongly linked to seasonal changes in the environment. Wood ant colonies generally first become active, after winter quiescence, in early spring when the sun begins to heat the nest and, in some locations, melt the snow (Figure 2.1). The timing of the beginning of activity is strongly influenced by the local climate, altitude and nest location. In Switzerland, for example, significant colony activity usually begins in March or April (Cherix 1981; Chauternes 1988).
On warm and sunny days, early in spring, worker activity begins and the internal temperature of the nest begins to rise to between 25°C and 30°C. Nest temperature remains at this level for the entire active season, even when, during early spring, the outside temperature is close to freezing (discussed in detail in Chapter 4) (Rosengren et al. 1987). Workers gather in the warm nest core and their nutrient-producing glands become more active, converting lipids and protein into food ready to be fed to queens and future larvae (Bausenwein 1960). The queen(s) remain(s) in the warm nest core for several days and lay ‘winter eggs’. The larvae hatching from these eggs are fed by the overwintering workers, usually developing into sexuals in about 6 weeks (Otto 2005). The queen(s) then retire(s) to the lower nest chambers to start to produce ‘summer eggs’, which usually develop into workers (Otto 2005).
Reproduction generally takes place in early summer, with thousands of sexual individuals flying away from their nests and participating in nuptial flights (e.g. Cherix et al. 1991).
9 - Contribution of wood ants to nutrient cycling and ecosystem function
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- By Jan Frouz, Charles University, Praha,Czech Republic, Veronika Jílková, Charles University, Praha,Czech Republic, Jouni Sorvari, University of Eastern Finland, Kuopio, Finland
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Summary
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 Jílková 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 Sundström 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; Jilková et al. 2012). Once transported into the ant nest, the honeydew is redistributed and used as a source of energy (Horstmann 1974).
Contents
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List of contributors
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7 - Wood ant foraging and mutualism with aphids
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- By Timo Domisch, NaturalResources Institute Finland (Luke),Management and Production of Renewable Resources, Joensuu, Finland, Anita C. Risch, Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland, Elva J.H. Robinson, University of York, Heslington, York,UK
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Summary
Wood ants are almost unique among insects in having a largely predictable and easily visible pattern of foraging. This is the result of their mutualistic interaction with tree-dwelling aphids and other sap-sucking insects, requiring foragers to travel regularly between the wood ant nest and persistent feeding sites where they collect honeydew from their mutualists. Collected honeydew, and also prey, are shared with nestmates back at the nest; this broadly follows a ‘central-place foraging’ model. Wood ants forage predominately on tree trunks and in tree canopies. The success of wood ants is due, in part, to their highly effective foraging strategy: workers dominate a territory and the food resources in it. For these reasons, foraging behaviour has been a major theme in wood ant research over recent decades.
This chapter reviews the wood ant diet including the mutualism with aphids and other insects, and explores the consequences of this mutualism for host trees and other invertebrates. As in most social insects, only workers forage, but among workers there are further distinctions as to who forages, when they forage, and how they navigate between nest and foraging site. How resources are exploited and transported within wood ant territories, especially for polydomous colonies, provides an insight into how decentralised networks can function efficiently, making wood ants a good case study for transportation networks more generally.
Wood ant diet
Wood ants are omnivorous, thus they practically eat ‘everything’. Generally, two main sources form their diet: honeydew is used mainly as energy for metabolic maintenance, whereas insect prey and scavenged material is used to provide protein for rearing the brood (Lange 1960). In addition, minor contributions are made by the collection of seeds and the consumption of tree sap and berry juices (Wellenstein 1952; Rosengren and Sundström 1991; Otto 2005).
Honeydew forms the largest component of the wood ant diet, estimated as contributing between 62% (Wellenstein 1952) and 94% (Rosengren and Sundström 1991) of food brought into a nest (Figure 7.1). Estimates of the quantity of honeydew collected annually per wood ant nest vary greatly depending on ant species and location, and presumably also on the study methods.
11 - Sampling and monitoring wood ants
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- By Anne Freitag, Museum of Zoology, Lausanne, Switzerland, Jenni A. Stockan, James Hutton Institute, Aberdeen,UK, Christian Bernasconi, Museum of Zoology, Lausanne, Switzerland, Arnaud Maeder, Museum of Natural History, La Chaux-de-Fonds, Switzerland, Daniel Cherix, University of Lausanne, Lausanne-Dorigny, Switzerland
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Summary
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.
13 - Future directions for wood ant ecology and conservation
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- By Elva J.H. Robinson, University of York, Heslington, York,UK, Jenni A. Stockan, James Hutton Institute, Aberdeen,UK
- Edited by Jenni A. Stockan, Elva J. H. Robinson, University of York
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- Wood Ant Ecology and Conservation
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- 05 June 2016
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- 07 July 2016, pp 287-299
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Summary
The preceding twelve chapters of this book demonstrate the great wealth of knowledge that has been established through more than a hundred years of research into wood ant ecology. Nevertheless, the next hundred years of wood ant research will not lack study topics. This chapter draws out some key themes for future work and highlights knowledge gaps, some easily addressed, others posing significant research challenges.
Much of our existing knowledge comes from detailed work on a particular species at a particular site. Given the level of ecological variation, not just between species but also between populations of the same species, there is a clear need for broad comparative work across many species and the different environments they inhabit, ideally including both Eurasian and North American species when appropriate.
Wood ants test some of our most fundamental ideas about social insects. The polydomous nesting system, seen in many wood ant species, challenges the very notion of an ‘ant colony’, traditionally understood as a ‘factory within a fortress’ (Oster and Wilson 1978). Polydomy has implications for relatedness, dispersal, foraging organisation and wood ant conservation, and so nesting strategy must be taken into consideration in future work on wood ant ecology. In the wood ants, behaviours and processes occurring outside the nest are, as in all social insects, much better understood than those occurring inside the nest. Regarding in-nest behaviours, there are still some fairly basic behavioural ecology questions to be answered. Even outside the nest, while it has been established that the part wood ants play in the forest ecosystem is complex, we are far from a full characterisation of their role. Future work must go beyond looking at isolated sets of interactions, to set observed effects in their ecological context, both to further our knowledge of this ecologically important group, and to provide essential data to aid management and conservation.
Knowledge gaps and open questions
What and where are the wood ants?
The first step in any ecological study is to ask what we are studying and where it occurs. Despite the work of many ecologists over the last 100 years, we are still very far from being able to answer these two fundamental questions for wood ants.
4 - Where and why? Wood ant population ecology
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- By Anita C. Risch, Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland, Samuel Ellis, University of York, Heslington, York,UK, Hayley Wiswell, Cairngorms Natural Park Authority, Grantown on Spey,UK
- Edited by Jenni A. Stockan, Elva J. H. Robinson, University of York
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- Wood Ant Ecology and Conservation
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- 05 June 2016
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- 07 July 2016, pp 81-105
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Summary
Wood ant (Formica rufa group) populations are found across much of the northern hemisphere. However, their distribution is not universal, as there are factors which clearly limit their occurrence in the environment. Even on a local scale, within a particular population; distribution is not even, and some areas have a much higher density of nests than others. This chapter explores the population ecology of wood ants and addresses various factors that influence their distribution at different spatial scales. Specifically, this chapter will discuss: (1) the structure of wood ant mounds and how this influences where nests are found locally and within larger landscapes; (2) how wood ant dispersal strategies affect where populations are found and how they are structured; and (3) the causes and consequences of nest relocation and abandonment by wood ants.
Mound construction, properties and thermoregulation
Most red wood ant nests consist of an aboveground mound composed of organic material and a belowground part that extends into the mineral soil, potentially reaching as far down as the ground water table (e.g. Weber 1935; Gösswald 1989; Bristow et al. 1992). The aboveground part is built from needles, twigs, resin, bark, leaves and grasses collected from the surroundings (Wiśniewski 1967; Gösswald 1989; see Chapter 9). Coarser material is generally found inside the mounds where the breeding chambers are located (Wiśniewski 1967; Gösswald 1989). Finer organic material – for example needles – dominates the much denser outer layers of the mounds (Wiśniewski 1967). Some of the North American species cover only the surface of their mineral soil nests with organic material, sometimes termed ‘thatch’ (Weber 1935; Chapter 10).
Temperatures within red wood ant nests are considerably higher than air temperatures from early spring until late autumn (e.g. Lenoir et al. 2001). This allows the insects to end nest dormancy early and extend the breeding season, thus providing them with a competitive advantage over other ants. Several mechanisms have been suggested to explain how red wood ants manage to heat up their mounds in spring: (1) Forel's ‘Theory des Domes’ (see Seeley and Heinrich 1981); (2) Zahn's 1958 ‘Wärmeträgertheorie’ [heat-carrying theory]; and (3) the production of metabolic heat by either the ants themselves (Kneitz 1964, 1969, 1970; Rosengren et al. 1987; Kadochová and Frouz 2014) or by within-nest microbes (Coenen-Stass et al. 1980).
Frontmatter
- Edited by Jenni A. Stockan, Elva J. H. Robinson, University of York
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- Book:
- Wood Ant Ecology and Conservation
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- 05 June 2016
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- 07 July 2016, pp i-vi
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