Hans Petter Leinaas

Phenotypic plasticity mediates climate change responses among invasive and indigenous arthropods

Synergies between global change and biological invasion have been identified as a major potential threat to global biodiversity and human welfare. The global change-type drought characteristic of many temperate terrestrial ecosystems is especially significant because it will apparently favour invasive over indigenous species, adding to the burden of conservation and compromising ecosystem service delivery. However, the nature of and mechanisms underlying this synergy remain poorly explored. Here we show that in a temperate terrestrial ecosystem, invasive and indigenous springtail species differ in the form of their phenotypic plasticity such that warmer conditions promote survival of desiccation in the invasive species and reduce it in the indigenous ones. These differences are consistent with significant declines in the densities of indigenous species and little change in those of invasive species in a manipulative field experiment that mimicked climate change trends. We suggest that it is not so much the extent of phenotypic plasticity that distinguishes climate change responses among these invasive and indigenous species, as the form that this plasticity takes. Nonetheless, this differential physiological response provides support for the idea that in temperate terrestrial systems experiencing global change-type drought, invasive species may well be at an advantage relative to their indigenous counterparts.

Hemispheric Asymmetries in Biodiversity—A Serious Matter for Ecology

Although the poles are less diverse than the tropics, this decline shows substantial asymmetries between the hemispheres, suggesting that responses to environmental change may differ substantially in the north and the south.

Effects of removing sea urchins (Strongylocentrotus droebachiensis): Stability of the barren state and succession of kelp forest recovery in the east Atlantic

Stability properties of the barren state of a kelp forest-sea urchin system were studied in northern Norway. The ability of the sea urchin Strongylocentrotus droebachiensis to maintain high population densities and recover from perturbations, and the succession of kelp forest revegetation, were studied experimentally by reducing the sea urchin density on a barren skerry. Additional information was obtained from community changes following a natural, but patchy, sea urchin mortality that varied between sites. On the barren grounds, high sea urchin densities (30 50 per m2) is maintained by annual recruitment. Severe reductions of sea urchin densities initiated luxuriant kelp growth, while more moderate reductions allowed establishment of opportunistic algae (during spring and early summer), but no kelps. Succession of algal growth, after the severe decline in sea urchin densities, followed a predictable pattern. At first the substrate was colonized by filamentous algae, but within few weeks they were outcompeted by the fast growing kelp Laminaria saccharina. After 3–4 years of the removal experiment, the slower-growing, long-lived kelp L. hyperborea became increasingly dominant. Increased food availability after reduction in sea urchin density led to increased individual growth of the remaining sea urchins. However, the population density did not increase, neither from recruitment nor immigration from adjacent areas with high sea urchin densities. Possibly, early establishment of a dense kelp stand, may represent a breakpoint in the ability of sea urchins to reestablish a barren state. The ability of L. saccharina quickly to invade and monopolize an area may have both positive and negative effects on the succession towards the climax L. hyperborea kelp forest. Competitive interactions may slow the process, but development of a dense stand of L. saccharina will also reduce grazing risk on scattered recruits of the more slowly growing L. hyperborea.

Transport of Ticks by Migratory Passerine Birds to Norway

Abstract Ticks can be transported over large distances and across geographical barriers by avian hosts. During the spring migrations of 2003 to 2005, 9,768 passerine birds from 4 bird observatories along the southern coastline of Norway were examined for ticks. Altogether, 713 birds carried a total of 517 larvae and 1,440 nymphs. The highest prevalence of tick infestation was observed in thrushes and dunnock (Prunella modularis). The degree of tick infestation varied during each season, between localities, and from year to year. Blackbirds (Turdus merula) caught in localities with many ticks had greater infestation than those from localities with few or no ticks, suggesting local tick recruitment. A similar study performed during 1965–1970 involving 2 of the bird observatories in the present study found ticks on 4.2% of birds, while we found infestation of 6.9% at the same localities (P < 0.001). With the exception of 10 nymphs and 1 larva, the predominant tick was Ixodes ricinus. Seven nymphs of Hyalomma rufipes and 1 larva of Dermacentor sp. were also found. No species of Dermacentor had previously been found in Norway.

Transport of Ixodes ricinus infected with Borrelia species to Norway by northward-migrating passerine birds.

Birds are capable of transporting ticks and, consequently, tick-borne pathogens over long distances and across geographical barriers such as oceans and deserts. The purpose of this study was to assess the prevalence of Borrelia spp. in ticks transported by birds by using PCR. A total of 9768 northward-migrating passerine birds was examined for ticks at 4 bird observatories along the southern Norwegian coast during their spring migration in 2003-2005. Two of the bird observatories were located on islands where flagging revealed very few or no ticks (Akerøya and Store Færder), while the other 2 were located in areas with established dense tick populations: an island, Jomfruland (>100 ticks per hour of flagging) and a mainland locality, Lista (40 ticks in one hour of flagging). Borrelia spp. were found in 70 (13.6%) of 513 examined Ixodes ricinus nymphs (19 B. afzelii, 38 B. garinii, two B. turdi, and 11 B. valaisiana) and in 14 (8.1%) of 172 examined I. ricinus larvae (ten B. garinii, one B. turdi, and three B. valaisiana). This report is the first to identify B. turdi in Europe. Ticks collected from birds of the genus Turdus (T. merula, T. philomelos, and T. iliacus) had a higher prevalence of Borrelia spp. than ticks from the other passerine genera. Ticks that were cofeeding with a Borrelia-infected tick had an increased probability of being infected with the same Borrelia species. Ticks collected on birds from the south-western locality Lista were less likely to have Borrelia than ticks found on birds from the other, more eastern localities. The Turdus spp. are particularly important, both because they carry many ticks per bird and because ticks carried by these species have a higher prevalence of Borrelia. This higher prevalence may be related to Borrelia infection of the birds or transmission of Borrelia through cofeeding. The prevalence of the different Borrelia species in ticks collected from migratory birds may be related to migration routes.

Temperature-size relations from the cellular-genomic perspective

A family of empirically based ecological ‘rules’, collectively known as temperature‐size rules, predicts larger body size in colder environments. This prediction is based on studies demonstrating that a wide range of ectotherms show increased body size, cell size or genome size in low‐temperature habitats, or that individuals raised at low temperature become larger than conspecifics raised at higher temperature. There is thus a potential for reduction in size with global warming, affecting all levels from cell volume to body size, community composition and food webs. Increased body size may be obtained either by increasing the size or number of cells. Processes leading to changed cell size are of great interest from an ecological, physiological and evolutionary perspective. Cell size scales with fundamental properties such as genome size, growth rate, protein synthesis rates and metabolic activity, although the causal directions of these correlations are not clear. Changes in genome size will thus, in many cases, not only affect cell or body size, but also life‐cycle strategies. Symmetrically, evolutionary drivers of life‐history strategies may impact growth rate and thus cell size, genome size and metabolic rates. Although this goes to the core of many ecological processes, it is hard to move from correlations to causations. To the extent that temperature‐driven changes in genome size result in significant differences among populations in body size, allometry or life‐cycle events such as mating season, it could serve as a fast route to speciation. We offer here a novel perspective on the temperature‐size rules from a ‘bottom‐up’ perspective: how temperature may induce changes in genome size, and thus implicitly in cell size and body size of metazoans. Alternatively: how temperature‐driven enlargement of cells also dictates genome‐size expansion to maintain the genome‐size to cell‐volume ratio. We then discuss the different evolutionary drivers in aquatic versus terrestrial systems, and whether it is possible to arrive at a unifying theory that also may serve as a predictive tool related to temperature changes. This, we believe, will offer an updated review of a basic concept in ecology, and novel perspectives on the basic biological responses to temperature changes from a genomic perspective.

Habitat Structure and Life History Strategies of Two Partly Sympatric and Closely Related, Lichen Feeding Collembolan Species

Two collembolan species. Vertagopus westerlundi and V. sarekensis. feed on lichens in exposed habitats, with their main distribution in the lower and higher alpine areas respectively. Differences in habitat preferences are most conspicuous in their zone of overlap, where westerlundi lives on boulders and sarekensis is confined mostly to lichens on the ground. The climatic exposure and distribution patterns of habitats for lichen feeding Collembola in the low and high alpine zone respectively, may explain the great differences in demographic, behavioural and physiological adaptations of the two species. The diverging habitat preferences of the species in sympatry seems to be a consequence of their adaptations to conditions in their respective main areas. There is no evidence that segregation is a result of interactions between the species.

Synchronized Moulting Controlled by Communication in Group-Living Collembola

Group-living Collembola of the genus Hypogastrura coordinate their moulting by communication. Animals of different ages and moulting rhythms synchronized the moulting rhythms when combined in a single culture. This synchronization is apparently not dependent on external stimuli but is coordinated by chemical communication among these insects.

Adaptations in Xenylla maritima and Anurophorus laricis (Collembola) to lichen habitats on alpine rocks

Adaptations to climatic extremes were studied in two collembolan species, Xenylla maritima and Anurophorus laricis, inhabiting lichens on alpine rocks 1200 to 1250 m a.s.l. at Finse, South Norway. Both species show seasonal variation in cold hardiness. Gut evacuation and accumulation of cryoprotective substances during autumn result in an ability to supercool to temperatures below normal winter temperatures. An exceptionally cold period in January 1979, however, killed most animals on unprotected sites of the rocks. The great ability of the two species to tolerate anaerobic conditions, is important to survive periods in winter when the rock surface is enclosed by an ice crust. Adaptation to dry conditions was evident from the great ability of both species to survive drought stress. They also reproduce later in the season than most other collembolan species thus reducing the risk for the sensitive hatchlings to emerge during the driest periods of summer. In all these aspects X. maritima and A. laricis differ greatly from Collembola of climatically protected habitats. Tetracanthella wahigreni inhabiting the surrounding lichen heath, is also highly adapted to cold and anaerobic conditions, but is more susceptible to desiccation than the two rock species. The comparison with T. wahlgreni emphasizes humidity as an important factor structuring the spatial distribution of collembolan species.

The effects of spatial habitat configuration on recruitment, growth and population structure in arctic Collembola

Abstract The population density and demography of five species of arctic Collembola were studied in a naturally patchy habitat, consisting of Carex ursinae tussocks with varying degrees of isolation. Focal predictor variables were those describing the spatial configuration of tussocks, including tussock size and isolation and the amount of habitat (cover) at a 1-m2 scale surrounding each tussock population. The Collembola populations were heavily influenced by environmental stochasticity in the form of winter mortality and summer drought, and the influence of patchiness on population characteristics was evaluated in this context. The five species showed very different responses to the structuring effect of the habitat, depending on life history characteristics, mobility and habitat requirements. Population density was highly variable in both time and space. Spring densities indicated larger winter mortality compared to observations from a previous study, and the snow- and ice-free season from June to August only resulted in population growth for Folsomia sexoculata. In the other species, adult mortality must have been high as there was no net population growth despite observed reproduction. The exception was Hypogastrura viatica, whose population decline was more likely to have been the result of migration out of the study area. Cover was the most important variable explaining density. No pure area or isolation effects at the tussock level were detected, even in areas with very low habitat cover. Drought was probably an important mortality factor, as July was particularly warm and dry. Due to qualitative differences in the tussocks and the matrix substrate, desiccation risk would be higher during dispersal between tussocks. We suggest that increased dispersal mortality gave the observed pattern of increased density in relation to cover, both in general and in F. quadrioculata, an opportunistic species otherwise known for rapid population growth. Onychiurus groenlandicus, which had a similar density response to cover, may also be influenced by a rescue effect sustaining densities in areas with high cover. The cover effect can be viewed as a large-scale factor which encompasses the general spatial neighbourhood of each tussock, where inter-population processes are important, as opposed to internal patch dynamics.