Local Population Level Research Articles

Interracial and population variability of phenotypic (cranial) characters in the common shrew Sorex araneus L., 1758

Variability of the cranial properties of chromosomal races Serov, Manturovo and Pechora of the common shrew were studied. A consistent increase of scull size in the Serov race with moving from the plain to highlands and a skull size decrease from low to high latitudes was detected. Interpopulation variability among different races was shown to be comparable with interracial variability or to exceed it. This suggests microevolution at the level of local populations.

Plasmodium relictum infection and MHC diversity in the house sparrow (Passer domesticus).

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasite populations. In particular, the high level of genetic diversity usually observed at the major histocompatibility complex (MHC) is generally thought to be maintained by parasite-driven selection. Among the possible ways through which parasites can maintain MHC diversity, diversifying selection has received relatively less attention. This hypothesis is based on the idea that parasites exert spatially variable selection pressures because of heterogeneity in parasite genetic structure, abundance or virulence. Variable selection pressures should select for different host allelic lineages resulting in population-specific associations between MHC alleles and risk of infection. In this study, we took advantage of a large survey of avian malaria in 13 populations of the house sparrow (Passer domesticus) to test this hypothesis. We found that (i) several MHC alleles were either associated with increased or decreased risk to be infected with Plasmodium relictum, (ii) the effects were population specific, and (iii) some alleles had antagonistic effects across populations. Overall, these results support the hypothesis that diversifying selection in space can maintain MHC variation and suggest a pattern of local adaptation where MHC alleles are selected at the local host population level.

Ethnopharmacology, sustainable development and cooperation: The importance of gathering clinical data during field surveys

This commentary aims to focus, among the “multiple roles ofdata generated in ethnopharmacological field studies” (Heinrichet al., 2009, p. 1), on the systematic collection of clinical data.Even if this issue may somewhat resemble what has long beensaid (Martin, 1996), recent experiences with clinical assessmentof the effectiveness of medicinal plants may shed some new light.This commentary is also a call for better cooperation betweenethnopharmacologists,physicians,traditionalhealersandthepop-ulationsconcerned:thatistheconditionforethnopharmacologicalwork to be useful at the level of local populations and, if includedin a development project, for the design of sound health policies(Elisabetsky and Nunes, 1990).A common research process is to go from field survey to phy-tochemistry, with the idea that the research can contribute toeconomic development if a new drug can eventually be found andmarketed while appropriate and ethical relationships are main-tained with the owners of the traditional knowledge (ten Kate andLaird, 2002). However, the road to development of a new drug isexcessively long, even in the rare cases where it is successful (e.g.Hoodia gordonii: see van Heerden, 2008). In the example of a phy-tochemical and pharmacological review on Garcinia mangostana,the authors concluded that “a serious weakness in our knowledgeis the lack of clinical data and it is not yet clear to what extent thefindings about pharmacological activities are of potential clinicalrelevance” (Obolskiy et al., 2009, p. 1047).In the meantime, local traditional treatments continue to beused. In our experience, local users are always interested in theresults of ethnopharmacology research and insist on the system-atic organisation of restitution sessions. They are interested in theanalysisofclinicaldatacollectedduringthesurveys,becauseitpro-vides indices of treatment quality and has implications for local

Fecal genotyping and contaminant analyses reveal variation in individual river otter exposure to localized persistent contaminants

The present study investigated polyhalogenated aromatic hydrocarbon (PHAH) concentrations in feces of known river otters (Lontra canadensis) along the coast of southern Vancouver Island, British Columbia, Canada. Specifically, we combined microsatellite genotyping of DNA from feces for individual identification with fecal contaminant analyses to evaluate exposure of 23 wild otters to organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenylethers (PBDEs). Overall, feces collected from otters in urban/industrial Victoria Harbor had the greatest concentrations of nearly all compounds assessed. Fecal concentrations of OCPs and PBDEs were generally low throughout the region, whereas PCBs dominated in all locations. Re-sampling of known otters over space and time revealed that PCB exposure varied with movement and landscape use. Otters with the highest fecal PCB concentrations were those inhabiting the inner reaches of Victoria Harbor and adjacent Esquimalt Harbor, and those venturing into the harbor systems. Over 50% of samples collected from eight known otters in Victoria Harbor had total-PCB concentrations above the maximum allowable concentration as established for Eurasian otter (Lutra lutra) feces, with a geometric mean value (10.6 mg/kg lipid wt) that exceeded the reproductive toxicity threshold (9 mg/kg lipid wt). Those results are consistent with our findings from 1998 and 2004, and indicate that the harbors of southern Vancouver Island, particularly Victoria Harbor, are a chronic source of PCB exposure for otters. The present study further demonstrates the suitability of using otter feces as a noninvasive/destructive biomonitoring tool in contaminant studies, particularly when sampling of the same individuals at the local population-level is desired.

Modelling single nucleotide effects inphosphoglucose isomeraseon dispersal in the Glanville fritillary butterfly: coupling of ecological and evolutionary dynamics

Dispersal comprises a complex life-history syndrome that influences the demographic dynamics of especially those species that live in fragmented landscapes, the structure of which may in turn be expected to impose selection on dispersal. We have constructed an individual-based evolutionary sexual model of dispersal for species occurring as metapopulations in habitat patch networks. The model assumes correlated random walk dispersal with edge-mediated behaviour (habitat selection) and spatially correlated stochastic local dynamics. The model is parametrized with extensive data for the Glanville fritillary butterfly. Based on empirical results for a single nucleotide polymorphism (SNP) in the phosphoglucose isomerase (Pgi) gene, we assume that dispersal rate in the landscape matrix, fecundity and survival are affected by a locus with two alleles, A and C, individuals with the C allele being more mobile. The model was successfully tested with two independent empirical datasets on spatial variation in Pgi allele frequency. First, at the level of local populations, the frequency of the C allele is the highest in newly established isolated populations and the lowest in old isolated populations. Second, at the level of sub-networks with dissimilar numbers and connectivities of patches, the frequency of C increases with decreasing network size and hence with decreasing average metapopulation size. The frequency of C is the highest in landscapes where local extinction risk is high and where there are abundant opportunities to establish new populations. Our results indicate that the strength of the coupling of the ecological and evolutionary dynamics depends on the spatial scale and is asymmetric, demographic dynamics having a greater immediate impact on genetic dynamics than vice versa.

Cold Tolerance and Overwintering of the Diamondback Moth (Lepidoptera: Plutellidae) in Southeastern Australia

Southeastern Australia is situated in a temperate zone with generally mild winters. The diamondback moth, Plutella xylostella L., can be a serious pest of canola as well as of other Brassica crops in this region. However, the ability of P. xylostella to overwinter in southeastern Australia, as well as in other temperate regions of the world, remains controversial. Laboratory experiments indicated that after 60 d in a temperature regimen alternating between 0 and 5 degrees C, 32% of third- and fourth-instar larvae pupated, 38% remained as larvae, and 57% of pupae survived, whereas only 15-20% of adult moths were still alive. Second-, third-, and fourth-instar larvae and pupae survived -5 degrees C for up to 2, 4, 6, and 13 d, respectively, with some adults surviving >20 d. Furthermore, adults that survived 60 d of exposure to 0-5 degrees C and 20 d at -5 degrees C reproduced normally without supplemental food. An experiment simulating outdoor overwintering with caged populations and field survey for natural overwintering populations of P. xylostella on volunteer canola (Brassica napus L.) and wild turnip (Rapistrum rugosum L.) plants indicated that development and reproduction continued on these host plants through the winter months. These empirical results provide evidence that P. xylostella is capable of overwintering on suitable host plants in southeastern Australia, and the overwintering populations may contribute significantly to local population levels in spring and summer seasons.

Amplified fragment length polymorphism fingerprints support limited gene flow among social spider populations

We used DNA fingerprints to determine whether the population structure and colony composition of the cooperative social spider Stegodyphus dumicola are compatible with requirements of interdemic ('group') selection: differential proliferation of demes or groups and limited gene flow among groups. To investigate gene flow among groups, spiders were collected from nests at 21 collection sites in Namibia. Analysis of molecular variance showed a small but highly significant differentiation among geographic regions (Phi(PT) = 0.23, P = 0.001). Thirty-three nests at four collection sites (6-10 spiders per nest, 292 individual spiders) were investigated in more detail to evaluate variation within and among colonies and among collection sites. In these 33 nests, an average of 15% of loci (fingerprint bands) were polymorphic among nestmates; 16% of observed variance was partitioned among collection sites, 48% among nests within a collection site, and 36% among individuals within nests. Spatial autocorrelation analyses of spiders at three collection sites showed that the maximum extent of detectable spatial autocorrelation among individuals was approximately 30 m, indicating dispersal over greater distances is not typical. These results indicate limited gene flow among nests, as well as spatial structuring at the level of regions, local populations, and nests, compatible with interdemic selection. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 235-246.

Indirect effects of heterospecific interactions on progeny size through maternal stress

Maternal effects are increasingly being recognized as an important pre‐natal source of life history variation in the next generation. The present study uses a field experiment to explore the influence of heterospecific interactions on the reproductive output and offspring characteristics of a common Indo‐Pacific damselfish, Pomacentrus amboinensis. On the Great Barrier Reef pairs of breeding P. amboinensis were placed on isolated patch reefs and to half of the pairs resource competitors (other planktivorous damselfishes), and predators of eggs and juveniles were added. Females inhabiting patches with heterospecifics had more aggressive interactions and higher levels of the stress hormone, cortisol. Neither the number of clutches nor number of eggs produced differed among treatments. The size of larvae at hatching was found to be reduced as a result of the stress associated with increased interactions with heterospecific and the transfer of cortisol to offspring. This stress‐associated mechanism appears to be an important and directional source of life history variability, but the individual nature of the maternal response is likely to result in a conclusion of a diversified bet hedging reproductive strategy when viewed at the local population level. These findings highlight the complex determinants of individual success and the important role of parental well‐being in the population dynamics of the next generation.

Geographical covariation and local convergence of flower depth in a guild of fly‐pollinated plants

Plant adaptations to pollinators are usually studied at the species level, but are expected to occur at the local population level and be reflected in fine-scale patterns of floral variation. Here, we examined whether a guild of c. 20 South African plant species pollinated by the long proboscid fly Prosoeca ganglbaueri (Nemestrinidae) exhibits fine-scale patterns of geographical covariation and convergent evolution at a local scale. Fly proboscis length is highly variable among sites (20-50 mm). Plant adaptation results in floral depths of plants within the guild being closely matched with the proboscis length of their fly pollinator across numerous sites. This results in patterns of divergence among allopatric populations and convergence among species within a site. The most likely evolutionary processes driving these patterns include coevolution between the fly and plants with consistent and abundant rewards, as well as one-sided evolution in rare and nonrewarding species that do not influence the coevolutionary process. Pollinator-mediated selection on spur length was confirmed for a nonrewarding orchid species in the guild by a reciprocal translocation experiment. Thus, rarer and nonrewarding species in the guild are forced to keep pace with the coevolutionary race between common rewarding flowers and flies.

No increase in colonization rate of boreal bryophytes close to propagule sources

Knowledge of the process of recolonization, and which temporal and spatial scale it operates on, is central to our understanding of species distributions, metapopulation dynamics, regional extinction risks, and ecosystem resilience. In this study the recolonization pattern of boreal forest bryophytes was investigated in stands that had been clear-cut approximately 50 years ago. Species known to be sensitive to clear-cutting were inventoried in 23 mature forest stands and in adjacent young stands at 10, 20, 40, and 80 m from the former forest-clear-cut edge. Based on previous studies showing that bryophytes tend to be dispersal limited at local population levels, it was hypothesized that the recolonizaton of many bryophyte species should be higher closer to the mature forest edge. It was also hypothesized that some species would show full recovery, while for others the young stands would still be inhospitable. All these patterns were found for individual species, but the main pattern was, however, quite different. Most species had started to recolonize the young stands (i.e., little or much, depending on species), but without any tendency of a higher colonization rate close to the mature stands. Possible explanations for the limited signs of positive influence of local propagule sources might be microsite limitation or that the local propagule availability displays a rapid decline from its sources and is masked by a higher regional propagule rain. For organisms with light propagules able to build up a regional background level, the role of mature forest stands in the recolonization process of the matrix may rather be to contribute to the regional background level of spores in the landscape than to affect the adjacent stands directly.

Spatial variation in egg size of a top predator: Interplay of body size and environmental factors?

It is expected that nearby populations are constrained by the same ecological features shaping in turn similarity in their ecological traits. Here, we studied the spatio-temporal variability in egg size among local populations of the critically endangered Balearic shearwater Puffinus mauretanicus, a top marine predator endemic to the western Mediterranean region. Specifically we assessed whether this trait was influenced by maternal body size, as an indicator of a genetic component, and feeding ecology (through stable-carbon and nitrogen-isotope measurements), as an indicator of environmental factors. We found that egg size varied among local populations, an unexpected result at such a small spatial scale. Body size differences at the local population level only partially explained such differences. Blood isotope measurements also differed among local populations. Values of δ 15N suggested inter-population differences in trophic level, showing a similar general pattern with egg size, and suggesting a nutritional link between them whereby egg size was affected by differences in feeding resources and/or behaviour. Values of δ 13C suggested that local populations did not differ in foraging habits with respect to benthic- vs. pelagic-based food-webs. Egg size did not vary among years as did breeding performance, suggesting that a differential temporal window could affect both breeding parameters in relation to food availability. The absence of a relationship between breeding performance and egg size suggested that larger eggs might only confer an advantage during harsh conditions. Alternatively parental quality could greatly affect breeding performance. We showed that inter-population differences in egg size could be influenced by both body size and environmental factors.

Effects of silvicultural treatments on Cerulean Warbler ( Dendroica cerulea) abundance in southern Indiana

The Cerulean Warbler ( Dendroica cerulea), a once common summer inhabitant and breeder in southern Indiana, has declined at both the local and continental population levels. Because Cerulean Warblers tend to nest in large deciduous trees, they are especially at risk due to deforestation of mature tree stands. Few studies have examined the effects of specific silvicultural practices (i.e., group and single tree selection harvesting methods) on the distribution and abundance of the Cerulean Warbler. During the summers of 2005 and 2006, Cerulean Warblers were surveyed within the Morgan-Monroe and Yellowwood state forests, as well as the Hoosier National Forest in southern Indiana. Three treatment types were surveyed; unharvested reference sites (stands 35–100+ years old) were compared with single tree selection treatments and treatments where a combination of group and single tree selection was used (stands 2–30 years old). Mean bird abundance was estimated from bird surveys to determine if trends exists between silvicultural regimes and Cerulean Warbler abundance. Cerulean Warblers were located in all treatment types, with no significant differences ( p = 0.654) in abundance among treatment types examined (unharvested – 0.36, single tree – 0.46, group and single tree combination – 0.36). These results suggest that uneven-age management practices, such as single tree and group selection harvesting, provide suitable breeding habitat for Cerulean Warblers.

The effect of habitat destruction on metapopulations with the Allee-like effect: A study case of Yancheng in Jiangsu Province, China

At the metapopulation level, there is a phenomenon called Allee-like effect that leads to metapopulation extinction thresholds at low habitat occupancy, analogous but essentially different with Allee effect at the local population level. Rare metapopulations are more susceptible to the Allee-like effect, which will increase the extinction risk of those living in fragmented habitats. Hitherto, no adequate attention has been paid to this phenomenon in metacommunity. Here, the Allee-like effect is introduced into a metapopulation spatial competition model of multi-species under different habitat change, and the 29 rare species inhabiting in Yancheng wetlands of Jiangsu Province are taken as study cases. Simulation results show that the Allee-like effect enable the proportion abundance of all species to fluctuate in different periods. The continuous oscillation will greatly increase the probabilities of stochastic extinction of the most vulnerable species. Strong Allee-like effect is especially unfavorable for those sub-dominant and inferior species, which is a destabilizing factor to rare species coexistence. Habitat destruction may be fatal to a rare metapopulation system with the Allee-like effect. As 29% of the natural wetlands are destroyed in Yancheng, the most 11 vulnerable species will go extinct in the weak-strong order with a time delay of 304–890 years in response to the past habitat loss. Two projects of habitat restoration are also brought forward for species diversity conservation. Besides the existing natural wetlands of 3200 km 2, an extra of 1801–2064 km 2 habitat should be added to conserve all species. These conclusions will be helpful for species conservation and will provide theoretical guidance to construct nature reserves.

Temporally stable genetic structure and low migration in an Atlantic salmon population complex: implications for conservation and management.

The evolutionary potential of a population is closely related to two key population genetic parameters, namely the effective population size (Ne) and migration rate (m). Furthermore, knowledge of these parameters is required in order to assess potential constraints on local adaptation and for the development of biologically sound management strategies. We addressed these key issues by investigating the temporal and spatial genetic structure of over 2000 adult Atlantic salmon (Salmo salar) collected from 17 sites in the Teno and Näätämö rivers in northernmost Europe with up to five time points spanning temporal intervals up to 24 years (∼4 generations). In all cases except one, local populations were found to be temporally stable within the river system. Estimates of Ne were generally a magnitude larger for the mainstem and headwater populations (MS+HW, Ne∼340–1200) than for the tributary populations (Ne∼35–160), thus explaining the higher genetic diversity and lower divergence of the MS+HW populations compared to tributaries. The overall migration rates to tributaries were low, and in some cases, low enough for local adaptations to potentially evolve, despite their lower Ne. Signs of a population bottleneck and natural recruitment from nearby populations were detected in one local population. This highlights a fact which is relevant for the conservation and management of highly substructured population systems in general: that even when the overall census size is large, local populations can be vulnerable to perturbations. To preserve the current and to regain the historical distribution of salmon within the river system, we propose that the status of the total population complex should be evaluated at the local population level rather than from descriptive statistics at the system level.

Diet of Neotropic cormorant (Phalacrocorax brasilianus) in an estuarine environment

The diet of the Neotropic cormorant (Phalacrocorax brasilianus) was studied by analysing 289 regurgitated pellets collected from a roosting site at Lagoa dos Patos estuary, southern Brazil, between November 2001 and October 2002 (except April to June). In total, 5,584 remains of prey items from 20 food types were found. Fish composed the bulk of the diet representing 99.9% by mass and 99.7% by number. The main food items were White croaker (Micropogonias furnieri) (73.7% by frequency of occurrence, 48.9% by mass and 41.2% by number), followed by Catfish (Ariidae) and anchovies (Engraulididae). In Lagoa dos Patos estuary the generalist Neotropic cormorant fed mainly on the two most abundant demersal fishes (White croaker and Catfish), which accounted for the low niche breadth calculated. The total length of all fish preyed varied from 27.2 to 318.3 mm (113.5 ± 48.0 mm), and preyed White croakers’ size differed between months. Neotropic cormorants seem to prey on most abundant class sizes of White croaker instead of selecting similar prey size throughout the time. However, temporary changes in diet in terms of food items, abundance and prey size were detected, revealing a high ecological plasticity of the species. Individual daily food intake of Neotropic cormorants estimated by pellets and metabolic equations corresponded to 23.7 and 27.1% of their body mass, falling in the range of other cormorant species. Annual food consumption of the population estimated by both methods was 73.4 and 81.9 tonnes, comprising mainly immature and subadult White croaker and Catfish which are commercially important. Temporal variations in diet composition and fish size preyed by Neotropics cormorants, a widespread and generalist species, suggest shifts according to fluctuations in the abundance of prey. The plasticity of this cormorant is also revealed by their ability to adjust feeding behaviour in response to temporal or local changes in the environment, from a generalist at the species level to a specialist at the individual or local population level.

An experimental test of frequency-dependent selection on male mating strategy in the field

We provide field-based experimental evidence for the frequency-dependent nature of the fitness of alternative mating strategies. We manipulated the frequency of genetically determined phenotypic strategies in six wild populations of the side-blotched lizard, Uta stansburiana. The within-population pattern of mating was assessed using nine microsatellite loci to assign paternity. Within populations of the side-blotched lizard exist three colour morphs (orange, blue and yellow) associated with male mating strategy. The frequency of these morphs has previously been found to oscillate over a 4- to 5-year period. We found, as predicted, that the common phenotype lost fitness to its antagonist. The mating patterns of all six populations adhered to a priori predictions that were derived from previous empirical and theoretical observations on this system. We found that the frequency-dependent nature of male fitness could be accounted for by the composition of their competitors at a small local population level, driven by associations within a focal female's social neighbourhood.

Genetic Diversity of Borrelia burgdorferi Sensu Stricto in Peromyscus leucopus , the Primary Reservoir of Lyme Disease in a Region of Endemicity in Southern Maryland

In the north central and northeastern United States, Borrelia burgdorferi sensu stricto, the etiologic agent of Lyme disease (LD), is maintained in an enzootic cycle between the vector, Ixodes scapularis, and the primary reservoir host, Peromyscus leucopus. Genetic diversity of the pathogen based on sequencing of two plasmid-located genes, those for outer surface protein A (ospA) and outer surface protein C (ospC), has been examined in both tick and human specimens at local, regional, and worldwide population scales. Additionally, previous studies have only been conducted with tick or human specimens at the local population level in areas with high LD transmission rates. This study examined the genetic diversity of circulating borreliae in the reservoir population from a large region of the western coastal plains of southern Maryland, where moderate numbers of human LD cases are reported. Six ospA mobility classes, including two that were not previously described, and eight ospC groups were found among the P. leucopus samples. Twenty-five percent of all specimens were infected with more than one ospA or ospC variant. The frequency distribution of variants was homogeneous, both locally and spatially. The spirochete diversity found in Maryland was not as high as that observed among northern tick populations, yet similar genotypes were observed in both populations. These results also show that mice are important for maintaining Borrelia variants, even rare variants, and that reservoir populations should therefore be considered when assessing the diversity of B. burgdorferi.

Patterns in grouse and Woodcock Scolopax rusticola hunting yields from central Norway 1901–24 do not support the alternative prey hypothesis for grouse cycles

According to the alternative prey hypothesis, autumn populations of ground‐nesting game birds fluctuate in synchrony with vole numbers because generalist predators that mainly eat voles switch to alternative prey, such as eggs and chicks, when vole numbers decline. In hunting statistics from Nord‐Trøndelag, central Norway, 1901–24, annual fluctuations in the number of Willow Grouse Lagopus lagopus and Western Capercaillie Tetrao urogallus, but not of Woodcock Scolopax rusticola, were positively related to vole numbers in the current year. Both Woodcock and grouse indices were related to hunting indices of Goshawk Accipiter gentilis and to weather variables assumed to influence the birds’ survival or reproduction, suggesting that the indices actually reflected local population levels. Synchronous vole and grouse fluctuations are consistent with the alternative prey hypothesis (although predator densities were low in the early 1900s), but the asynchronous Woodcock fluctuations refute the hypothesis. Rather, because the Woodcock does not feed on plants utilized by voles and grouse, I suggest that food quality is the ultimate factor for the synchrony in vole and grouse numbers in Norway.

Self-destructing prophecies: Long-term forecasting of municipal correctional bed need

Although municipal jails consume a significant amount of resources and the number of inmates housed in such facilities exploded in the 1990s, the literature on forecasting jail populations is sparse. Jail administrators have available discussions on jail crowding and its causes, but do not have ready access to applications of forecasting techniques or practical demonstrations of a jail inmate population forecast. This article argues that the underlying reason for this deficiency is the inherent unpredictability of local long-term correctional population levels. The driving forces behind correctional bed need render local jail population forecasts empirically valid only for a brief time frame. These inherent difficulties include the volatile nature of jail populations and their greater sensitivity when compared with prison populations to local conditions; the gap between the data needed for local correctional population forecasting and what is realistically available to forecasters; the lack of reliable lead variables for long-term local correctional population forecasts; the clash of the mathematics of forecasting and the substantive issues involved in the interpretation of forecast models; and the significant political and policy impacts of forecasts on local criminal justice systems and subsequent correctional population trends. The differences between the accuracy of short-term versus long-term jail bed need forecasts means that forecasting local correctional bed need is empirically valid for, at best, one to two years. As the temporal cast is extended, longer-term forecasts quickly become error prone. Except for unique situations where jails exist in highly stable local political, social, and criminal justice environments, long-term forecasts of two years or greater are fatally flawed and have little empirical accuracy. Long-term forecasts of local jail bed needs are useful, though, as policy catalysts to encourage policymakers to consider possible long-term impacts of current decisions, but forecasts should be thought of and presented as one possible future scenario rather than a likely reality. Utilizing a demonstration of a local jail forecast based upon two common empirical forecasting approaches, ARIMA and autoregression, this article presents a case study of the inherent difficulties in the long-term forecasting of local jail bed need.

The influence of windthrow area and timber characteristics on colonization of wind-felled spruces by Ips typographus (L.)

Leaving wind-felled Norway spruces in forests is one way to increase the amount of dead wood. Many forest species would benefit because of these actions but unfortunately also forest pests such as the spruce bark beetle ( Ips typographus) reproduce in newly wind-felled trees. To minimize the risk of subsequent attacks on living trees, the decisions of removing trees out of the forest in high risk areas should be done as early as possible. If fallen trees are not colonized or if there are only a few colonized trees the risk of subsequent attacks on living trees are also minor. For this reason, it is essential to estimate the windthrow area and timber characteristics influencing the colonization of wind-felled trees. We studied the colonization of Norway spruce dominated windthrow areas by I. typographus (L.) in 65 stands in southern Finland on two consecutive summers after the storms in November 2001. The studied areas ranged from single tree gaps to large gaps with over 3000 wind-felled spruces. Using generalized linear modelling, we evaluated the significance of windthrow area and timber characteristics for the probability of the windthrow area to be colonized by I. typographus, the percentage of colonized wind-felled spruces, the number of egg galleries, and the colonization density. In the first summer (2002) after the wind-felling 71% of studied windthrow areas were colonized by I. typographus. Only 1 of the 19 areas not colonized in 2002 was colonized in 2003. The number and mean diameter of wind-felled spruces and the basal area of recently dead standing spruces were the most important windthrow characteristics influencing colonization. The models showed that an increase in these characteristics also increased the values of the response variables. This study shows that local population levels of I. typographus varied greatly within the study area (appox. 200 km × 200 km) and that this variation should be included in models predicting the colonization risks of windthrown areas.