Guest ants and ant guests in red wood ant nests

Red wood ants (Formica rufa group) impact forest ecosystems in a multitude of ways and can thus be considered as ecosystem engineers. Although they are highly efficacious predators of many arthropods, their nests host a diverse community of other arthropods. In this thesis, I wanted to highlight the diversity of red wood ant associated guest fauna in order to emphasize the role of red wood ants in the maintenance and conservation of forest biodiversity. I examined the underlying factors shaping the community composition and species richness of associates. Particularly, I studied the factors determining the occurrence of the globally vulnerable shining guest ant (Formicoxenus nitidulus), an obligate social parasite of moundbuilding wood ants. I also studied the effects of clear felling on ant nest mounds as well as on the ant-associated beetle community. A total of 85 different taxa (mostly beetles), including 26 myrmecophiles (species dependent on ants), were identified in the course of this thesis. One unexpected discovery was the sawtoothed grain beetle (Oryzaephilus surinamensis), which has so far only been recorded as an indoor pest species in Finland. Overall, I found that species richness and occurrence of associates were negatively associated with isolation of the nest mounds. The occurring probability of the guest ant F. nitidulus increased with decreasing isolation and increasing nest mound size. The guest ant was more likely to occur in the nests of the polydomous (multi-nest colonies) Formica polyctena than the monodomous (single nest colonies) Formica rufa. Also, local spreading along the connecting trails between nests in polydomous host colonies seems to be important to F. nitidulus. I found that Formica aquilonia nest mounds in clear fells had significantly lower surface layer moisture content than nests in forests, which reduces the nests’ thermal capacity. Though species richness and community composition of beetles did not greatly differ between clearings and forests, total abundance was lower in clear fell nests. Furthermore, total species richness and abundance as well as myrmecophile abundance decreased with decreasing moisture content. I investigated only the short-term effects of clear felling in active nest mounds. However, nests in clear fells have a high tendency of being abandoned, which will inevitably be detrimental to myrmecophiles. How the associate community develops in the long-term in the nests surviving clear felling needs further study. This thesis reinforces the status of red wood ants as hosts of a highly diverse associate community. This needs to be taken into consideration in the maintenance and conservation of arthropod diversity in temperate and boreal forests. If the whole habitat cannot be protected, forest management practices preserving dense red wood ant populations should be used. Also, colonization chances for the wood ants as well as nest density could be increased by creating small open areas in managed forests, which would also benefit many other forestdwelling species. Thus, maintaining a varied forest structure could help maintain and even increase the forest biodiversity.Kekomuurahaisten (Formica rufa ryhmä) vaikutukset metsäekosysteemeihin ovat moninaiset ja niinpä niitä voidaankin pitää ekosysteemi-insinööreinä. Vaikka ne ovat hyvin tehokkaita niveljalkaisten petoja, niiden pesät pitävät sisällään monimuotoisen yhteisön muita niveljalkaisia. Tässä väitöskirjassa halusin korostaa kekomuurahaispesien vieraslajiston monimuotoisuutta painottaakseni kekomuurahaisten roolia metsien monimuotoisuuden ylläpidossa ja suojelussa. Tarkastelin pesävieraslajistoa ja -lajimäärää muokkaavia tekijöitä. Erityisesti tutkin maailmanlaajuisesti vaarantuneen norkomuurahaisen (Formicoxenus nitidulus), kekomuurahaispesissä elävän sosiaalisen loisen, esiintymistä sääteleviä tekijöitä. Tutkin myös metsähakkuiden vaikutuksia kekoihin sekä niissä pesävieraina eläviin kovakuoriaisiin. Kaiken kaikkiaan tämän väitöskirjan aikana määritettiin 85 eri taksonia (enimmäkseen kovakuoriaisia), mukaan lukien 26 myrmekofiiliä eli muurahaisista riippuvaista lajia. Eräs odottamaton löytö oli riisihärö (Oryzaephilus surinamensis), kovakuoriaislaji, joka on tähän mennessä tavattu Suomessa ainoastaan elintarviketuholaisena. Yleisesti ottaen havaitsin, että pesävieraiden lajirunsaudella ja esiintymisellä oli negatiivinen yhteys kekojen eristyneisyyteen. Norkomuurahaisen esiintymistodennäköisyys kasvoi kekojen eristyneisyyden pienentyessä sekä keon koon kasvaessa. Norkomuurahainen esiintyi todennäköisemmin monipesäisiä yhdyskuntia muodostavan kaljukekomuurahaisen (Formica polyctena) kuin yksipesäisiä yhdyskuntia muodostavan punakekomuurahaisen (Formica rufa) pesissä. Paikallinen leviäminen monipesäisten yhdyskuntien pesiä yhdistäviä polkuja pitkin vaikuttaisi olevan tärkeää norkomuurahaiselle. Havaitsin, että tupsukekomuurahaisten (Formica aquilonia) pesissä oli merkittävästi kuivempi pintakerros hakkuualueilla kuin metsissä, mikä heikentää kekojen lämpökapasiteettia. Vaikka pesävieraskovakuoriaisten lajirunsaus tai lajisto ei eronnut merkittävästi hakkuualueiden ja metsien välillä, kokonaisyksilömäärä oli alhaisempi hakkuukeoissa. Lisäksi kokonaislaji- ja yksilömäärä sekä myrmekofiilien yksilömäärä pienenivät kosteuspitoisuuden pienentyessä. Tutkin ainoastaan hakkuiden lyhytaikaisia vaikutuksia aktiivisissa keoissa. Hakkuualueiden keoilla on kuitenkin suuri todennäköisyys tulla hylätyiksi, mikä on väistämättä haitallista myrmekofiileille. Sitä, kuinka pesävierasyhteisö kehittyy pitkällä aikavälillä hakkuista selviytyvissä keoissa, tulee tutkia lisää. Tämä väitöskirja korostaa kekomuurahaisten asemaa erittäin monimuotoisen pesävierasyhteisön isäntinä. Tämä tulee ottaa huomioon niveljalkaisten monimuotoisuuden ylläpidossa ja suojelussa lauhkean ja boreaalisen vyöhykkeen metsissä. Mikäli koko elinympäristöä ei voida suojella, metsätaloudessa tulisi pyrkiä käyttämään menetelmiä, jotka ylläpitävät kekomuurahaisten korkeaa pesätiheyttä. Lisäksi kekomuurahaisten kolonisaatiomahdollisuuksia voitaisiin lisätä luomalla talousmetsiin pieniä aukkoja, mikä hyödyttäisi myös monia muita metsälajeja. Vaihtelevalla metsärakenteella voitaisiin siten auttaa ylläpitämään ja jopa lisäämään metsien monimuotoisuutta

First record of an indoor pest sawtoothed grain beetle Oryzaephilus surinamensis (Coleoptera: Silvanidae) from wild outdoor wood ant nest

Alive individual adult sawtoothed grain beetle Oryzaephilus surinamensis (Linnaeus, 1758) was discovered inside a nest mound of the red wood ant Formica rufa Linnaeus, 1758 during a survey of myrmecophilous invertebrates. The sawtoothed grain beetle is a widespread indoor pest that has not previously been found in an ant nest. It is one of the most common pests in stored grain and cereal products, but the natural life-style of the species is not known. As the site of discovery was exceptional, we verified the species identification using the DNA barcode. If the sawtoothed grain beetle can live in mounds of red wood ants, the mounds may become widespread source habitats for the future infestations of this serious stored product pest

Effect of host species, host nest density and nest size on the occurrence of the shining guest ant Formicoxenus nitidulus (Hymenoptera: Formicidae)

Understanding habitat requirements of species is important in conservation. As an obligate ant nest associate, the survival of the globally vulnerable shining guest ant, Formicoxenus nitidulus, is strictly tied to that of its hosts (mound building Formica ants). We investigated how host species, nest density, inter-nest distance and nest mound size relate to the occurrence of F. nitidulus. In total, 166 red wood ant nests were surveyed in SW Finland (120 Formica polyctena, 25 F. rufa, 14 F. aquilonia, 5 F. pratensis, and 2 F. lugubris). Overall, F. nitidulus was found in 60% of the nests. For the actual analysis, only F. polyctena and F. rufa nests were included due to the small number of other nests. F. nitidulus was more likely to be found among F. polyctena than F. rufa. Also, while inter-nest distance was not important, a high nest density, commonly found in polydomous (multi-nest) wood ant colonies, was beneficial for F. nitidulus. The guest ant was also more likely to be found in large host nests than small nests. Thus, our results show that the best habitat for the guest ant is a dense population of host nest mounds with a high proportion of large mounds. Conservation efforts should be directed at keeping the quality of the red wood ant habitats high to preserve their current populations and to increase colonization. This will not only benefit the guest ant, but also a plethora of other species, and help in maintaining the biodiversity of forests.</p

Comparison of ant-associated beetle communities inhabiting mounds of forest-dwelling ants in forests and forest clearings

Red wood ant (Formica rufa group) nests contain a highly diverse community of invertebrates, which is largely due to their abundant resources and regulated microclimatic conditions. Clear-felling, however, causes nest mounds to lose surface layer moisture, thus disrupting their inner stability. To study the effects of clear-felling on ant-associated beetles (myrmecophile and non-myrmecophile), 41 nests of Formica aquilonia Yarrow, 1955 located on three clear-fells and adjacent mature forest stands were sampled, and the beetle communities between these habitats were compared. We investigated how habitat type, nest surface moisture content, nest volume, and isolation affect the community composition, species richness, and abundance of beetles. Beetle community composition or species richness did not markedly differ between clearings and forests, although total abundance was higher in forests. Also, total species richness and abundance and myrmecophile abundance increased with increasing moisture content. Overall, nests with similar moisture content and volume had similar species compositions. Nest volume was negatively correlated with myrmecophile species richness. Nest isolation was not related to species richness or abundance. The lower abundances in clearings could be problematic in the long term, as small populations are more likely to become extinct. To ensure the survival of ants and their associates, small-scale clearings should be preferred