Nonlinear effects of climate on boreal rodent dynamics: mild winters do not negate high‐amplitude cycles

Small rodents are key species in many ecosystems. In boreal and subarctic environments, their importance is heightened by pronounced multiannual population cycles. Alarmingly, the previously regular rodent cycles appear to be collapsing simultaneously in many areas. Climate change, particularly decreasing snow quality or quantity in winter, is hypothesized as a causal factor, but the evidence is contradictory. Reliable analysis of population dynamics and the influence of climate thereon necessitate spatially and temporally extensive data. We combined data on vole abundances and climate, collected at 33 locations throughout Finland from 1970 to 2011, to test the hypothesis that warming winters are causing a disappearance of multiannual vole cycles. We predicted that vole population dynamics exhibit geographic and temporal variation associated with variation in climate; reduced cyclicity should be observed when and where winter weather has become milder. We found that the temporal patterns in cyclicity varied between climatically different regions: a transient reduction in cycle amplitude in the coldest region, low‐amplitude cycles or irregular dynamics in the climatically intermediate regions, and strengthening cyclicity in the warmest region. Our results did not support the hypothesis that mild winters are uniformly leading to irregular dynamics in boreal vole populations. Long and cold winters were neither a prerequisite for high‐amplitude multiannual cycles, nor were mild winters with reduced snow cover associated with reduced winter growth rates. Population dynamics correlated more strongly with growing season than with winter conditions. Cyclicity was weakened by increasing growing season temperatures in the cold, but strengthened in the warm regions. High‐amplitude multiannual vole cycles emerge in two climatic regimes: a winter‐driven cycle in cold, and a summer‐driven cycle in warm climates. Finally, we show that geographic climatic gradients alone may not reliably predict biological responses to climate change.     

Summer movements,predation and habitat use of wolves in human modified boreal forests

Grey wolves (Canis lupus), formerly extirpated in Finland, have recolonized a boreal forest environment that has been significantly altered by humans, becoming a patchwork of managed forests and clearcuts crisscrossed by roads, power lines, and railways. Little is known about how the wolves utilize this impacted ecosystem, especially during the pup-rearing summer months. We tracked two wolves instrumented with GPS collars transmitting at 30-min intervals during two summers in eastern Finland, visiting all locations in the field, identifying prey items and classifying movement behaviors. We analyzed preference and avoidance of habitat types, linear elements and habitat edges, and tested the generality of our results against lower resolution summer movements of 23 other collared wolves. Wolves tended to show a strong preference for transitional woodlands (mostly harvested clearcuts) and mixed forests over coniferous forests and to use forest roads and low use linear elements to facilitate movement. The high density of primary roads in one wolf’s territory led to more constrained use of the home territory compared to the wolf with fewer roads, suggesting avoidance of humans; however, there did not appear to be large differences on the hunting success or the success of pup rearing for the two packs. In total, 90 kills were identified, almost entirely moose (Alces alces) and reindeer (Rangifer tarandus sspp.) calves of which a large proportion were killed in transitional woodlands. Generally, wolves displayed a high level of adaptability, successfully exploiting direct and indirect human-derived modifications to the boreal forest environment.     

A general mathematical framework for the analysis of spatiotemporal point processes

Spatial and stochastic models are often straightforward to simulate but difficult to analyze mathematically. Most of the mathematical methods available for nonlinear stochastic and spatial models are based on heuristic rather than mathematically justified assumptions, so that, e.g., the choice of the moment closure can be considered more of an art than a science. In this paper, we build on recent developments in specific branch of probability theory, Markov evolutions in the space of locally finite configurations, to develop a mathematically rigorous and practical framework that we expect to be widely applicable for theoretical ecology. In particular, we show how spatial moment equations of all orders can be systematically derived from the underlying individual-based assumptions. Further, as a new mathematical development, we go beyond mean-field theory by discussing how spatial moment equations can be perturbatively expanded around the mean-field model. While we have suggested such a perturbation expansion in our previous research, the present paper gives a rigorous mathematical justification. In addition to bringing mathematical rigor, the application of the mathematically well-established framework of Markov evolutions allows one to derive perturbation expansions in a transparent and systematic manner, which we hope will facilitate the application of the methods in theoretical ecology.     

Characterization of AziR, a resistance protein of the DNA cross-linking agent azinomycin B

A protein identified from the Streptomyces sahachiroi genome exhibits a protective effect against the DNA alkylator azinomycin B when heterologously expressed in S. lividans and E. coli. The protein, dubbed AziR for azinomycin resistance, is homologous to aminoglycoside phosphotransferases but behaves as an azinomycin binding protein and fails to chemically modify azinomycin. While AziR confers resistance to azinomycin B, it is inactive against aminoglycoside antibiotics and other DNA alkylators. A nucleic acid staining assay indicates that the protein enhances cell survival, and also prevents DNA damage effects normally observed following azinomycin treatment. Knowledge of an azinomycin resistance mechanism aids in setting the stage for future engineered biosynthesis of functionally useful azinomycin analogues.     

The impact of simulated moose densities on conifer aphids along a productivity gradient

Large herbivores have a significant impact on boreal forest ecosystems. The modification of resources through their feeding induces changes in trophic dynamics and affects the direction of interactions in a community. Moose Alces alces may decrease the available plant biomass for herbivorous insects on one of their main winter forage species in Fennoscandia, Scots pine Pinus sylvestris, and indirectly alter the abundance of invertebrates through exploitative competition. Moose browsing can also induce chemical, morphological, and phenological changes in plants, changing their nutritive value to insect herbivores such as aphids. Habitat productivity may further modify the responses of aphids to moose browsing. We studied the responses of the gray pine aphid Schizolachnus pineti to different moose densities, and their relations to habitat productivity by sampling pine branches and measuring the number of aphids on pine needles. The experimental setup consisted of 8 exclosures along a productivity gradient, where the feeding, defecation, and urination of 4 densities of moose had been simulated for 7 yr. We here show that high levels of simulated browsing decrease the amount of gray pine aphids in areas with high productivity. In areas with low productivity, however, simulated browsing had no such effect. Habitat productivity should therefore be considered as an important factor that may determine the strength of an areas buffering capacity to high moose densities. Low resource environments appear to be favourable to specialist conifer aphids on pines under high browsing pressure, but the performance of generalist insect herbivores might be lowered.     

Dispersal may limit the occurrence of specialist wood decay fungi already at small spatial scales

We used species‐specific spore traps to measure airborne dispersal of the wood decay fungus Phlebia centrifuga (spore size 6.5–9 × 2.5–3 μm) up to 1000 m distance from a point source. We fitted two simple dispersal models, an empirical power law model and a semi‐mechanistic diffusion model to the data using the Bayesian approach. The diffusion model provided a better fit than the power law model which underestimated deposition at 3–55 m and overestimated deposition at longer and shorter distances. Model fit improved by allowing overdispersion, suggesting that spores are not dispersed independently but wind can transport spores in groups inside discrete air packages up to considerable distances. Using the fitted diffusion model and available information on the establishment rates of wood‐decay fungi, we examine the distance up to which colonisation from a single fruit body is likely to occur. We conclude that the diluting effect of distance and low establishment success make the occurrence of P. centrifuga dispersal limited possibly already at the distance of tens of metres and very probably at a few hundred metres from the nearest fruit body, despite the fact that under favourable conditions a high proportion of the spores can disperse considerably further. This conclusion is likely to hold generally for those fungal species that inhabit fragmented landscapes, have specialised resource and habitat requirements, and have similar spore size and other dispersal traits as P. centrifuga.     

Spatial population structure of a specialist leaf-mining moth

1. The spatial structure of natural populations may profoundly influence their dynamics. Depending on the frequency of movements among local populations and the consequent balance between local and regional population processes, earlier work has attempted to classify metapopulations into clear-cut categories, ranging from patchy populations to sets of remnant populations. In an alternative, dichotomous scheme, local populations have been classified as self-sustaining populations generating a surplus of individuals (sources) and those depending on immigration for persistence (sinks). 2. In this paper, we describe the spatial population structure of the leaf-mining moth Tischeria ekebladella, a specialist herbivore of the pedunculate oak Quercus robur. We relate moth dispersal to the distribution of oaks on Wattkast, a small island (5 km(2)) off the south-western coast of Finland. 3. We build a spatially realistic metapopulation model derived from assumptions concerning the behaviour of individual moths, and show that the model is able to explain part of the variation in observed patterns of occurrence and colonization. 4. While the species was always present on large trees, a considerable proportion of the local populations associated with small oaks showed extinction-recolonization dynamics. The vast majority of moth individuals occur on large trees. 5. According to model predictions, the dominance of local vs. regional processes in tree-specific moth dynamics varies drastically across the landscape. Most local populations may be defined broadly as 'sinks', as model simulations suggest that in the absence of immigration, only the largest oaks will sustain viable moth populations. Large trees in areas of high oak density will contribute most to the overall persistence of the metapopulation by acting as sources of moths colonizing other trees. 6. No single 'metapopulation type' will suffice to describe the oak-moth system. Instead, our study supports the notion that real populations are often a mix of earlier identified categories. The level to which local populations may persist after landscape modification will vary across the landscape, and sweeping classifications of metapopulations into single categories will contribute little to understanding how individual local populations contribute to the overall persistence of the system.     

Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in Lapland

Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground‐dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H’) of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H’/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites.