Stockholms universitet

Bengt KarlssonProfessor


I urval från Stockholms universitets publikationsdatabas

  • Species range expansion constrains the ecological niches of resident butterflies

    2017. Hélène Audusseau (et al.). Journal of Biogeography 44 (1), 28-38


    Aim: Changes in community composition resulting from environmental changes modify biotic interactions and affect the distribution and density of local populations. Such changes are currently occurring in nettle-feeding butterflies in Sweden where Araschnia levana has recently expanded its range northward and is now likely to interact with resident species (Aglais urticae and Aglais io). Butterfly occurrence data collected over years and across regions enabled us to investigate how a recent range expansion of A. levana may have affected the environmental niche of resident species.

    Location: We focused on two regions of Sweden (Skane and Norrstrom) where A. levana has and has not established and two time periods (2001-2006 and 2009-2012) during its establishment in Skane.

    Methods: We performed two distinct analyses in each region using the PCA-env and the framework described in Broennimann etal. (2012). First, we described the main sources of variation in the environment. Second, in each time period and region, we characterized the realized niches of our focal species across topographic and land use gradients. Third, we quantified overlaps and differences in realized niches between and within species over time.

    Results: In Skane, A. levana has stabilized its distribution over time, while the distribution of the native species has shifted. These shifts depicted a consistent pattern of avoiding overlap between the native species and the environmental space occupied by A. levana, and it was stronger for A. urticae than for A. io. In both regions, we also found evidence of niche partitioning between native species.

    Main conclusions: Interspecific interactions are likely to affect local species distributions. It appears that the ongoing establishment of A. levana has modified local biotic interactions and induced shifts in resident species distributions. Among the mechanisms that can explain such patterns of niche partitioning, parasitoid-driven apparent competition may play an important role in this community.

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  • Climate change, phenology, and butterfly host plant utilization

    2015. Jose A. Navarro-Cano (et al.). Ambio 44 (S!), S78-S88


    Knowledge of how species interactions are influenced by climate warming is paramount to understand current biodiversity changes. We review phenological changes of Swedish butterflies during the latest decades and explore potential climate effects on butterfly-host plant interactions using the Orange tip butterfly Anthocharis cardamines and its host plants as a model system. This butterfly has advanced its appearance dates substantially, and its mean flight date shows a positive correlation with latitude. We show that there is a large latitudinal variation in host use and that butterfly populations select plant individuals based on their flowering phenology. We conclude that A. cardamines is a phenological specialist but a host species generalist. This implies that thermal plasticity for spring development influences host utilization of the butterfly through effects on the phenological matching with its host plants. However, the host utilization strategy of A. cardamines appears to render it resilient to relatively large variation in climate.

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  • Extended season for northern butterflies

    2014. Bengt Karlsson. International journal of biometeorology 58 (5), 691-701


    Butterflies are like all insects temperature sensitive and a changing climate with higher temperatures might affect their phenology. Several studies have found support for earlier flight dates among the investigated species. A comparative study including 66 species of Swedish butterflies in Sweden was undertaken and the result confirms that most butterfly species will now fly earlier during the season. This is especially evident for butterflies overwintering as adults or as pupae. However, the advancement in phenology is correlated with flight date and some late season species show no advancement or have even postponed their flight dates and are now flying later in the season. The result also showed that latitude had a strong effect on the adult flight date, and the majority of the investigated species showed significantly later flights towards the north. Species flying early in the season were more affected by temperature than species flying later in the season and species overwintering in their late stages (as pupae or adults) were more influenced by temperature compared to species overwintering in their early stages (as larvae or eggs). In essence, a climate with earlier springs and longer growing seasons seems not to change the appearance patterns in a one way direction. We now see butterflies on the wings both earlier and later in the season and some consequences of these understudied and complex patterns are discussed. So far, studies have concentrated mostly on early season butterfly – plant interactions but also late season studies are needed for a better understanding of long term population consequences.

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