Search

The extrinsic determinants hypothesis emphasizes the essential role of environmental heterogeneity in species' colonization. Consequently, high resident species diversity can increase community susceptibility to colonizations because good habitats may support more species that are functionally similar to colonizers. On the other hand, colonization success is also likely to depend on species traits. We tested the relative importance of environmental characteristics and species traits in determining colonization success using census data of 587 vascular plant species collected about 70 yr apart from 471 islands in the archipelago of SW Finland. More specifically, we explored potential new colonization as a function of island properties (e.g. location, area, habitat diversity, number of resident species per unit area), species traits (e.g. plant height, life-form, dispersal vector, Ellenberg indicator values, association with human impact), and species' historical distributions (number of inhabited islands, nearest occurrence). Island properties and species' historical distributions were more effective than plant traits in explaining colonization outcomes. Contrary to the extrinsic determinants hypothesis, colonization success was neither associated with resident species diversity nor habitat diversity per se, although colonization was lowest on sparsely vegetated islands. Our findings lead us to propose that while plant traits related to dispersal and establishment may enhance colonization, predictions of plant colonizations primarily require understanding of habitat properties and species' historical distributions.

Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.

Assisted migration (AM) has been suggested as a management strategy for aiding species in reaching newly suitable locations as climate changes. Species distribution models (SDMs) can provide important insights for decisions on whether to assist a species in its migration; however, their application includes uncertainties. In this study, we use consensus SDMs to model the future suitable areas for 13 vascular plant species with poor dispersal capacity. Based on the outputs of SDMs under different climate change scenarios and future times, we quantify the predicted changes in suitable area by calculating metrics that describe the need and potential for migration. We find that, by the end of the 21st century, one of the species would benefit from AM under mild climate change, seven under moderate change, and for 12 out of 13 species studied AM appears to be a relevant conservation method under strong climate change. We also test the effect of different modeling attributes on the metrics and find little variation between SDMs constructed using different combinations of modeling methods and variable sets. However, the choice of climate variables had a larger influence on the level of the metrics than did the modeling method. We therefore suggest that the choice of climate variables should receive ample attention when measuring climate change threat using SDMs and that experiments aiming to uncover critical environmental factors for individual species should be extensively conducted. This study illustrates that dispersal assistance may be needed for many species under a wide range of possible future climates.

The spectrum of light has received little attention as an ecological factor and in this review we highlight the importance of a changing light environment in plant range shifts under conditions of global warming. Although distinct clinal responses to light quality have not been earlier reported, some studies have shown that northern ecotypes are more sensitive to changes in light quality. The northern light environment may significantly modify competition between plant species and within photoperiodic ecotypes, if predicted rapid range shifts of forest trees are realized. Southern photoperiodic ecotypes of forest trees migrating northward will encounter both changed light quality and a different photoperiod. Our special focus is on carbon economy and biomass partitioning between the autotrophic hosts and heterotrophic ectomycorrhizal fungal (EMF) symbionts, reciprocally dependent on each other. This applies also to the level of fungal community structure, which is assumed to be determined in part by host carbon economy. We hypothesize, that (1) Carbon allocation to roots and EMF in different host species and locally adapted photoperiodic ecotypes will respond differentially to northern light climate, especially to photoperiod and proportionally higher diffuse blue light; (2) Since carbon flux belowground may start later in northward-shifted southern populations in the autumn, also mycelial growth and reproduction in the EMF associated with southern populations could occur later. This may also lead to changes in fungal community composition; (3) EMF phenology and community composition may show different responses to changing light climate when associated with host trees of fixed or free growth pattern; and (4) Responses of EMF symbionts associated with locally adapted host populations vary, possibly leading to changes in EMF communities. We also discuss potential experimental approaches mimicking range shift conditions in terms of light quality due to global warming and compare reaction norms in key traits between southern and northern populations and species. Further, we exemplify how data obtained from experimental studies may be used for modelling of host plant and symbiont growth, which may in turn affect species competitive ability and distribution.

Climate change has important implications on the abundance and range of insect pests in forest ecosystems. We studied responses of root-associated fungal communities to defoliation of mountain birch hosts by a massive geometrid moth outbreak through 454 pyrosequencing of tagged amplicons of the ITS2 rDNA region. We compared fungal diversity and community composition at three levels of moth defoliation (intact control, full defoliation in one season, full defoliation in two or more seasons), replicated in three localities. Defoliation caused dramatic shifts in functional and taxonomic community composition of root-associated fungi. Differentially defoliated mountain birch roots harbored distinct fungal communities, which correlated with increasing soil nutrients and decreasing amount of host trees with green foliar mass. Ectomycorrhizal fungi (EMF) abundance and richness declined by 70-80 % with increasing defoliation intensity, while saprotrophic and endophytic fungi seemed to benefit from defoliation. Moth herbivory also reduced dominance of Basidiomycota in the roots due to loss of basidiomycete EMF and increases in functionally unknown Ascomycota. Our results demonstrate the top-down control of belowground fungal communities by aboveground herbivory and suggest a marked reduction in the carbon flow from plants to soil fungi following defoliation. These results are among the first to provide evidence on cascading effects of natural herbivory on tree root-associated fungi at an ecosystem scale.

We identify four issues in the decision framework for species conservation management under climate change proposed by Shoo et al. (2013) Clim Chan 119:239–246 and suggest ways to address them. First, binary-decision flow charts require Yes/No answers, which are not appropriate in most conservation decisions. A quantitative framework is preferable and action-guidance should be obtained even when the realistic answer to some questions remains “we simply do not know”. Second, the proposed flow chart imposes an a priori order of precedence and does not explicitly allow simultaneous actions. A workable framework should enable optimal allocation between multiple kinds of conservation efforts and permit complementary actions. Third, the probability of success, co-benefit to non-target species, and cost are unlikely to have a simple, consistent relationship across taxa. These variables need to be assessed case-by-case for each conservation measure and species. Finally, the decision framework disregards the legal, social, and ethical aspects pertaining to decision-making.

As a consequence of habitat loss, breeding in man-made habitats has become increasingly common for many coastal breeding bird species. While artificial sites provide valuable substitutes, they may also be more attractive, and importantly, differ in quality from natural sites. Therefore, information on habitat specific breeding success and their potential for supporting stable populations are needed. We compared little tern (Sternula albifrons) breeding success (nest and hatching success) between natural habitat (sandy beaches) and artificial port habitat at Bothnian Bay, Finland from 2006 to 2011. We further reviewed published estimates on pre-fledging and adult survival for little terns and least terns (Sternula antillarum), and used these ranges to estimate plausible parameter spaces for population growth rates given our estimates of breeding success. Nest success was among the highest reported for little terns in the artificial habitat (82 %) while being lower in the natural habitat (58 %). This difference may have resulted from differences in colony sizes and levels of disturbance. Hatching success did not differ significantly, but the percentage of successful nests containing unhatched eggs was twice as high in the natural habitat. The parameter spaces for population growth rates indicated that the artificial habitat has good potential to sustain stable populations (66 % positive growth rate) while for the natural habitat this potential was lower (37 % positive growth rate). While our results suggest that artificial habitats can be very productive breeding sites for habitat deprived tern populations, management should concentrate on improving both habitats with emphasis on natural sites.

The arctic forest-tundra ecotone (FTE) represents a major transition zone between contrasting ecosystems, which can be strongly affected by climatic and biotic factors. Expected northward expansion and encroachment on arctic tundra in response to climate warming may be counteracted by natural and anthropogenic processes such as defoliating insect outbreaks and grazing/browsing regimes. Such natural and anthropogenic changes in land cover can substantially affect FTE dynamics, alter ground albedo (index of the amount of solar energy reflected back into the atmosphere) and provide important feedbacks into the climate system. We took advantage of a naturally occurring contrast between reindeer grazing regimes in a border region between northern Finland and Norway which was recently defoliated by an outbreak of the geometrid moth. We examined ecosystem-wide contrasts between potentially year-round (but mainly summer) grazed (YRG) regions in Finland and mainly winter grazed (WG) regions in Norway. We also used a remotely sensed vegetation index and albedo to quantify effects on local energy balance and potential climate feedbacks. Although differences in soil characteristics and ground vegetation cover were small, we found dramatic differences in the tree layer component of the ecosystem. Regeneration of mountain birch stands appears to have been severely hampered in the YRG regime, by limiting regeneration from basal shoots and reestablishment of individual trees from saplings. This has led to a more open forest structure and a significant 5% increase in spring albedo in the summer grazed compared to the winter grazed regions. This supports recent suggestions that ecosystem processes in the Arctic can significantly influence the climate system, and that such processes must be taken into account when developing climate change scenarios and adaptation strategies.

Assisted migration is recognized as a possible method for species conservation under climate change. Predicted decrease in range size and emergence of new suitable areas due to climate change are the main reasons for considering assisted migration. The magnitude of such changes can be used to guide decisions on the applicability of this conservation method. However, it has not been formalized how predictions acquired, e.g., with the help of species distribution models or expert assessments, should translate into recommendations or decisions. Climate change threat indices concentrating on predicted loss of habitat are not directly applicable in this context as they do not define whether a species has the potential to expand its range compared to the area that remains suitable. Here we present a conceptual framework for identifying and quantifying situations in which predictions indicate that a species could benefit from assisted migration. We translate predicted changes in suitable area into separate metrics for migration need and migration potential on the basis of the amount of lost, remnant, and new area. These metrics can be used as part of decision-making frameworks in determining the most suitable conservation method for a specific species. They also hold potential for coarser screening of multiple species to estimate the proportion of species that could benefit from assisted migration within a given time frame and climate change scenario. Furthermore, the approach can be used to highlight time frames during which assisted migration or, alternatively, other conservation actions are the most beneficial for a certain species.

A large proportion of European alpine plants are able to spread upslope faster than current climate velocities. Nevertheless, invasive species tend to be particularly effective dispersers, making them an additional pressure on the vulnerable native flora. Climate change is expected to trigger an upward expansion of plants in mountain regions1,2 and, although there is strong evidence that many native species have already shifted their distributions to higher elevations1,3,4,5,6, little is known regarding how fast non-native species might respond to climate change. By analysing 131,394 occurrence records of 1,334 plant species collected over 20 years in the European Alps, we found that non-natives are spreading upwards approximately twice as fast as natives. Whereas the spread of natives was enhanced by traits favouring longer dispersal distances, this was not the case for non-natives. This was due to the non-native species pool already being strongly biased towards species that had traits facilitating spread. A large proportion of native and non-native species seemed to be able to spread upwards faster than the current velocity of climate change. In particular, long-distance dispersal events and proximity to roads proved to be key drivers for the observed rapid spread. Our findings highlight that invasions by non-native species into native alpine communities are a potentially significant additional pressure on these vulnerable ecosystems that are already likely to suffer dramatic vegetation changes with ongoing warming and increasing human activity in mountain regions.

The effect of habitat management is commonly evaluated by measuring population growth, which does not distinguish changes in reproductive success from changes in survival or the effects of immigration or emigration. Management has rarely been evaluated considering complete life cycle of the target organisms, including also possible negative impacts from management. We evaluated the effectiveness of cattle grazing in the restoration of coastal meadows as a breeding habitat for small and medium-sized ground-nesting birds by examining the size and demography of a southern dunlin (Calidris alpina schinzii) breeding population. Using a stochastic renesting model that includes within-season variation in breeding parameters, we evaluated the effect of grazing time and stocking rates on reproduction. The census data indicated that the population was stable when nest trampling was prevented, but detailed demographic models showed that the population on managed meadows was a sink that persisted by attracting immigrants. Even small reductions in reproductive success caused by trampling were detrimental to long-term viability. We suggest that the best management strategy is to postpone grazing to after the 19th of June, which is about three weeks later than what is optimal from the farmer's point of view. The differing results from the two evaluation approaches warn against planning and evaluating management only based on census population size and highlight the need to consider target-specific life history characteristics and demography. Even though grazing management is crucial for creating and maintaining suitable habitats, we found that it was insufficient in maintaining a viable population without additional measures that increase nest success. In the presently studied case and in populations with similar breeding cycles, impacts from nest trampling can be avoided by starting grazing when about 70% of the breeding season has past.

The effect of habitat management is commonly evaluated by measuring population growth, which does not distinguish changes in reproductive success from changes in survival or the effects of immigration or emigration. Management has rarely been evaluated considering complete life cycle of the target organisms, including also possible negative impacts from management. We evaluated the effectiveness of cattle grazing in the restoration of coastal meadows as a breeding habitat for small and medium‐sized ground‐nesting birds by examining the size and demography of a southern dunlin (Calidris alpina schinzii) breeding population. Using a stochastic renesting model that includes within‐season variation in breeding parameters, we evaluated the effect of grazing time and stocking rates on reproduction. The census data indicated that the population was stable when nest trampling was prevented, but detailed demographic models showed that the population on managed meadows was a sink that persisted by attracting immigrants. Even small reductions in reproductive success caused by trampling were detrimental to long‐term viability. We suggest that the best management strategy is to postpone grazing to after the 19th of June, which is about three weeks later than what is optimal from the farmer's point of view. The differing results from the two evaluation approaches warn against planning and evaluating management only based on census population size and highlight the need to consider target‐specific life history characteristics and demography. Even though grazing management is crucial for creating and maintaining suitable habitats, we found that it was insufficient in maintaining a viable population without additional measures that increase nest success. In the presently studied case and in populations with similar breeding cycles, impacts from nest trampling can be avoided by starting grazing when about 70% of the breeding season has past.

The conditions leading to gigantism in nine-spined sticklebacks Pungitius pungitius were analysed by modelling fish growth with the von Bertalanffy model searching for the optimal strategy when the model's growth constant and asymptotic fish size parameters are negatively related to each other. Predator-related mortality was modelled through the increased risk of death during active foraging. The model was parameterized with empirical growth data of fish from four different populations and analysed for optimal growth strategy at different mortality levels. The growth constant and asymptotic fish size were negatively related in most populations. Optimal fish size, fitness and life span decreased with predator-induced mortality. At low mortality, the fitness of pond populations was higher than that of sea populations. The differences disappeared at intermediate mortalities, and sea populations had slightly higher fitness at extremely high mortalities. In the scenario where all populations mature at the same age, the pond populations perform better at low mortalities and the sea populations at high mortalities. It is concluded that a trade-off between growth constant and asymptotic fish size, together with different mortality rates, can explain a significant proportion of body size differentiation between populations. In the present case, it is a sufficient explanation of gigantism in pond P. pungitius.

Aim To quantify the vulnerability of habitats to invasion by alien plants having accounted for the effects of propagule pressure, time and sampling effort. Location New Zealand. Methods We used spatial, temporal and habitat information taken from 9297 herbarium records of 301 alien plant species to examine the vulnerability of 11 terrestrial habitats to plant invasions. A null model that randomized species records across habitats was used to account for variation in sampling effort and to derive a relative measure of invasion based either on all records for a species or only its first record. The relative level of invasion was related to the average distance of each habitat from the nearest conurbation, which was used as a proxy for propagule pressure. The habitat in which a species was first recorded was compared to the habitats encountered for all records of that species to determine whether the initial habitat could predict subsequent habitat occupancy. Results Variation in sampling effort in space and time significantly masked the underlying vulnerability of habitats to plant invasions. Distance from the nearest conurbation had little effect on the relative level of invasion in each habitat, but the number of first records of each species significantly declined with increasing distance. While Urban, Streamside and Coastal habitats were over-represented as sites of initial invasion, there was no evidence of major invasion hotspots from which alien plants might subsequently spread. Rather, the data suggest that certain habitats (especially Roadsides) readily accumulate alien plants from other habitats. Main conclusions Herbarium records combined with a suitable null model provide a powerful tool for assessing the relative vulnerability of habitats to plant invasion. The first records of alien plants tend to be found near conurbations, but this pattern disappears with subsequent spread. Regardless of the habitat where a species was first recorded, ultimately most alien plants spread to Roadside and Sparse habitats. This information suggests that such habitats may be useful targets for weed surveillance and monitoring.

Aim To use herbarium records to characterize important correlates of spatial spread, areal occupancy and clustering of 100 alien plant species of conservation concern in the North and South Islands of New Zealand. Location New Zealand. Methods Using herbarium data of 6294 records representing 100 alien plant species, we assessed spatial heterogeneity in the distribution of alien species by examining the role of major urban areas as sources of sampling bias. A novel method to account for spatial biases in sampling effort was developed and applied to two simple distance metrics: nearest- and furthest-neighbour spread rate. The relative importance of these two distance metrics in determining the range, areal extent and dispersion of alien species across both the North and South Islands of New Zealand was also assessed. Results The spatial distribution of herbarium records was highly clustered with a significant bias towards the more populated regions. Once sampling bias was taken into account, there was no indication that species were found closer to these urban centres than might be expected based on sampling effort. The nearest-neighbour spread rates were usually 1–5 km yr−1 and correlated positively with the furthest-neighbour spread rates that were an order of magnitude higher. Range and area increased and clustering decreased with higher spread rates and longer recording time span. The spread rates divided species into five groups that were clearly distinguishable in terms of the extent of their distribution and the degree of clustering. Species occurring on both islands did not exhibit similar spread rates or spatial patterns. Main conclusions The nearest- and furthest-neighbour spread rates from herbarium records can explain the area and pattern of alien plant distributions and improve the understanding of the dynamics of their spread. Five groups emerge from the spread rates in relation to a null model. Fast-spreading plants had the widest, least clustered distribution, which suggests widespread chronic problems; slow-spreading plants had localized, but dense, clustered distributions, indicating acutely problematic weeds. These patterns appear robust and may be useful in predicting the future patterns of spread and in planning long-term management strategies in New Zealand.

Temporal trends in biological invasions are often described by a lag-phase of little or no increase in species occurrence followed by an increase-phase in which species occurrence rises rapidly. While several biological and environmental mechanisms may underlie lag-phases, they may also represent statistical artefacts or temporal changes in sampling effort. To date, distinguishing the facts from these artefacts has not been possible. Here we describe a method for estimating the lag-phase in cumulative records of species occurrence, using a piecewise regression model that explicitly differentiates the lag and increase phases. We used the von Bertalanffy, logistic, linear and exponential functions to model the increase phase, and identified the best-fitting function using model selection techniques. We confirmed the accuracy of our method using simulated data and then estimated the length of the lag-phase (t lag ), the maximum collection rate (r) and the projected asymptotic number of records (K) using herbarium records for 105 weed species in New Zealand, while accounting for changes in sampling effort. Nearly all the New Zealand weed species had a lag-phase, which averaged around 20-30 years, with 4% of species having a lag-phase greater than 40 years. In more than two thirds of the cases, the accumulation of records was best modelled with the decelerating von Bertalanffy function, despite the tendency for temporal variation in sampling effort to force cumulative herbarium records to follow the sigmoidal shape of a logistic curve. A positive correlation between r and K is consistent with the assumption that the final distribution of an alien plant species reflects its rate of spread. Seemingly rare but fast-spreading aliens may thus become tomorrow's noxious weeds. A positive correlation between inflection year and r warns that the weeds that have only begun to spread relatively recently may spread faster than previously known invaders.

The optimal allocation theory predicts that growth is allocated between the shoot and the roots so that the uptake of the most limiting resource is increased. Allocation is dynamic due to resource depletion, interaction with competitors, and the allometry of growth. We assessed the effects of intra- and inter-specific competition on growth and resource allocation of the meadow species Ranunculus acris and Agrostis capillaris, grown in environments with high (+) or low (−) availability of light (L) and nutrients (N). We took samples twice a week over the 7 weeks experiment, to follow the changes in root-to-shoot ratios in plants of different sizes, and carried out a larger scale harvest at the end of the experiment. Of all the tested factors, availability of nutrients had the largest effect on the growth rate and shoot-to-root allocation in both species, although both competition and light had significant effects as well. The highest root-to-shoot ratios were measured from the L+N− treatment, and the lowest from the L−N+ treatment, as predicted by the optimal allocation theory. Competition changed resource allocation, but not always toward acquiring the resource that is most limiting to growth. We thus conclude that the greatest variation in shoot-to-root allocation was due to the resource availability and the effects of competition were small, probably due to low density of plants in the experiment.

Escaped transgenic organisms (GMO's) may threaten the populations of their wild relatives if able to hybridize with each other. The introgression of a growth enhancement transgene into a wild Atlantic salmon population may be affected by the transgene's effects not only on fitness parameters, but also on mating behaviour. Large anadromous GMO males are most preferred in mating, but a transgene can also give the large sneakers a reproductive advantage over the smaller wild individuals. With a simulation model, we studied whether the increase in the proportion and mating success of sneakers in transgenic and hybrid genotypes could facilitate the introgression of a transgene into wild population after the release of GMOs. The model combines population dynamics and Mendelian inheritance of a transgenic trait. We found that the introgression of the transgene is strongly affected by the greater mating preference of large GMO males. Furthermore, the difference in reproductive success between the anadromous versus sneaker strategy defines how much GMO's have to be preferred to be able to invade. These results emphasize the importance of detailed knowledge of reproductive systems and the effect of a transgene on the phenotype and behaviour of GMOs when assessing the consequences of their release or escape to the wild.

The invasion of alien species and genotypes is an increasing concern in contemporary ecology. A central question is, what life-history traits enable invasion amidst populations of wild species and conventional cultivars? In order to invade, the initially rare species must perform better than their resident competitors. We conducted a mathematical analysis and simulation of a two-species extension of the Maynard Smith and Slatkin model for population dynamics in discrete time to study the role of density dependence as different types of competition in the invasion of new species. The type of density dependence ranged from scramble to contest competition. This led to intrinsic dynamics of the species range from point equilibrium to cycles and chaos. The traits were treated either as free parameters or constrained by a trade-off resulting from a common fixed strength of density dependence or equilibrium density. Resident and intruder traits had up to ten-fold differences in all of the parameters investigated. Higher equilibrium density of the intruder allowed invasion. Under constrained equilibrium density, an intrinsically stable intruder could invade an unstable resident population. Scramble competition made a population more susceptible to invasion than contest competition (e.g., limitation by light or territory availability). This predicts that a population which is mainly limited by food (or nutrients in plants) is more likely to be invaded than a population limited by a hierarchical competition, such as light among plants. The intruder population may have an effect on the resident population’s dynamics, which makes the traditional invasion analysis unable to predict invasion outcome.

The Colorado potato beetle (CPB), a serious pest of potato, is currently spreading north in Europe. We investigated the risk of CPB establishment in Finland and control methods for the case when beetle life history characters change due to global warming or as an adaptation to colder climate. Analysis with a spatially explicit simulation model supported the current management policy in Finland (efficient eradication and one year field quarantine) but changes in CPB viability, such as decreased winter mortality or increased number of offspring would render them inefficient. Longer quarantine times would be needed to effectively prevent the CPB establishment and spread. As an option we investigated Bt-potato cultivation integrated to other control methods and found that it was already efficient when used as a sole strategy but its benefits may be reduced by the adaptability of the Colorado potato beetle.

Fish with a transgene for growth hormone grow faster than the wild type and may have an advantage in sexual selection due to their larger size and earlier maturation. The cost in these genetically modified organisms (GMOs) is a lower viability of their offspring. The Trojan gene effect is a hypothesis that predicts that the release of such fish in nature can lead to an invasion by GMOs but ultimately decrease population size to extinction. We modelled GMO invasion with Mendelian inheritance of two alleles in one locus and the resulting mating and population dynamics of wild, GMO and hybrid genotypes. Invasion was attempted over a range of initial densities, representing scenarios from accidental escape to large-scale deliberate introduction of the transgenic genotype. Our results show that invasion strongly depends on hybrid fitness, requiring only a low initial density when GMOs and hybrids are preferred in mating. Preference against hybrids results in an invasion threshold, above which mating between GMOs are sufficiently frequent for invasion to take place. GMO invasion may decrease population size, but contrary to earlier studies on the Trojan gene effect, extinctions do not occur. This is due to the lower viability of GMOs being balanced by the decreased number of competitors reducing the effects of density dependence. The results emphasize the importance of initial density, hybrid fitness and density dependence when considering invasion through hybridization.

The shores of the Bothnian Bay in the northern Baltic Sea are characterised by relatively rapid isostatic land uplift (ca. 6.9 mm year−1) continuously exposing virgin land for plants to colonise. Autogenic and allogenic changes in soil and plant communities will eventually make these exposed sites unsuitable for the early colonisers. The course of the primary succession in the waterfront is often delayed and shaped by frequent disturbances by ice scouring, water level movements and suffocation of extant vegetation by floating plant debris. Hence, we hypothesise that disturbances are the key processes underlying the local short-term dynamics of the plant populations of the seashore meadows. We monitored formation, growth, shrinkage and mortality of patches of a critically endangered early successional grass species Arctophila fulva var. pendulina for four consecutive years at the Liminka Bay in Finland. The data allow estimation of quality, magnitude and frequency of the wintertime disturbance and the growth during the summer. We formulated and parameterised a spatially explicit simulation model to predict the fate of the population in the area. Simulations with the fitted parameter estimates predicted that the area of A. fulva population will considerably decrease in the next 30 years. A parameter sensitivity analysis showed the probability of a new patch formation to be the most important factor for the population persistence, whereas changes in the dispersal distance, for example, are less important. The best way to enhance the persistence of the population is to promote the new patch formation. This could be done by transplanting rhizome fragments of the species to the suitable open areas in the shallow water where they are not immediately displaced by the later successional species.

A key question of evolutionary importance is what factors influence who becomes dominant. Individual genetic variation has been found to be associated with several fitness traits, including behaviour. Could it also be a factor influencing social dominance? We investigated the association between social status and the amount of intra-individual genetic variation in juvenile brown trout (Salmo trutta). Genetic variation was estimated using 12 microsatellite loci. Dominant individuals had higher mean heterozygosity than subordinates in populations with the longest hatchery background. Heterozygosity–heterozygosity correlations did not find any evidence of inbreeding; however, single-locus analysis revealed four loci that each individually differed significantly between dominant and subordinate fish, thus giving more support to local than general effect as the mechanism behind the observed association between genetic diversity and a fitness-associated trait. We did not find any significant relation between mean d 2 and social status, or internal relatedness and social status. Our results suggest that individual genetic variation can influence dominance relations, but manifestation of this phenomenon may depend on the genetic background of the population.

Element (e.g., nutrient) cycling is often modelled with linear, constant-coefficient differential equations. The transition rate matrix of such models shows only the direct interactions between ecosystem compartments. The indirect interactions here mean the element flows between compartments that are not connected by a direct flow and thus appear zero-valued in the transition rate matrices of continuous time models. This lack of explicitness does not allow their contribution to the system resilience to be evaluated from the elasticity analysis of the dominant eigenvalue of the transition rate matrix. I present a matrix exponential transformation of a continuous time model to result in an equivalent discrete time model, where a matrix of transition probabilities (or proportions) is explicit in both direct and indirect interactions. An elasticity analysis of a probability matrix then can be used quantifying the contributions of both direct and indirect interactions to the dynamics of the system. The method is given an example by a reanalysis of previously published data for the dynamic properties of nutrient cycling in tundra and temperate forest ecosystems. Tundra was shown to have a higher resilience (i.e., a short return time from perturbations) and more indirect flows than forest. Indirect flows generally contributed less to the dynamics of nutrient cycling than direct flows, but were more important in tundra than forest. An analysis of the internal nutrient cycling rate’s effects showed that rapid nutrient cycling increases system’s resilience and the importance of indirect flows.

We studied the competition between mycorrhiza-forming Trientalis europaea L. and nonmycorrhizal Carex bigelowii Torrey ex Schweinitz in a climate chamber experiment. The plants were grown either singly or together with a conspecific or heterospecific individual, with arbuscular mycorrhizal inoculum present or absent. Inoculated T. euro paea formed abundant arbuscular mycorrhizal structures, but the mycorrhizae did not affect its biomass or the whole plant's relative growth rate (RGR). Carex bigelowii did not form mycorrhizae, but its shoot biomass and RGR were lower in the inoculated pots. The presence of a conspecific or heterospecific plant had no effect on the shoot biomasses or RGR of either plant species. Mycorrhizal inoculation increased the root/shoot ratio of C. bigelowii in all competition treatments. The presence of C. bigelowii decreased the root/shoot ratio of T. europaea in both mycorrhizal and nonmy corrhizal state. Mycorrhizal inoculum thus had a direct negative effect on the growth of a nonmycorrhizal plant. The result suggests that although mycorrhizae may not always directly affect the performance of the host plant, they may possibly increase the host plant performance in relation to nonmycorrhizal neighbours. Mycorrhizal inoculum and mycorrhizal symbiosis may increase asymmetry of interspecific competition, which may facilitate the coexistence of plant species in cases when a larger individual is more negatively affected.Key words: arbuscular mycorrhiza, competitive asymmetry, micropropagation.

Question: What is the population viability of a critically endangered seashore grass, Arctophila fulva var. pendulina. Location: Liminka Bay, W Finland, 25°21'70 N, 64°51'90 E. Methods: We constructed a matrix population model based on colonization and disappearance events and patch size changes of A. fulva. Patches were divided into hydric and nonhydric zones according to proximity to the seashore and intensity of disturbance. Perturbation analyses were carried out in order to identify transitions critical for population growth. Seed bank and seed germination studies provided background information for the model design. Results: A. fulva patches observed in the more disturbed hydric zone (closest to the sea) increased in number, as did the total number of patches. However, the number of patches in the less disturbed non-hydric zone decreased. Conclusions: Short-term dynamics of the A. fulva population at Liminka Bay seem to be determined by environmental fluctuations, which cause annual variation in transition rates between patch size classes. The long-term dynamics are probably governed by initiation of primary succession by isostatic land uplift. Increased disturbance at the water’s edge may promote persistence of A. fulva through reduced interspecific competition. Our results suggest that shoreline disturbance of the hydric zone is sufficient for maintaining a viable population. Competitive exclusion of A. fulva in the non-hydric zone may be delayed by management practices, such as mowing.

Individuals allocate resources to the expansion of their foraging area and those resources are no longer available for the traits that determine how well those individuals are able to protect their foraging area against competitors. The resulting trade-off between foraging area size and the traits associated with the ability to compete for the resources within the foraging area applies to ecological scenarios as different as territorial defence by individuals and colonies, and light competition in plants. Whether the trade-off affects species performance in competition for resources at the area of overlap between foraging areas depends on the symmetry of resource division. In symmetric competition resources are divided equally between the competitors, while in asymmetric competition the individual with the smallest foraging area, and consequently the greatest competitive ability, gains all the resources. Competition may also be a combination of the symmetric and asymmetric processes. I studied the effects of competitive asymmetry on population dynamics and coexistence of two annual species with different sized foraging areas using an individual-based spatially explicit simulation model. Symmetric competition favoured the species with the larger foraging area and did not allow coexistence. Competitive asymmetry favoured the species with smaller foraging area and allowed coexistence, which was due to the consequences of losing an asymmetric competition being more severe than losing a symmetric competition. The mechanism of coexistence is the larger foraging area's superiority in low population densities (little competition) and the smaller foraging area's ability to win a large foraging area when competition was intense. Competitive asymmetry and small size of both foraging areas led to population dynamics dominated by long-term fluctuations of small intensity. Symmetric competition and large size of the foraging areas led to large short-term fluctuations, which often resulted in the extinction of one or both of the species due to demographic stochasticity.

The members of natural populations often differ in size and relatedness to each other, which may affect the division of limited resources and have consequences on reproductive success and population dynamics. We modeled seasonal growth and dynamics in populations composed of different types of relatives (full-sibs, half-sibs and non-related individuals) under the continuum of competitive scenarios between complete symmetry and asymmetry. Growth was assumed logistic in proportion to individual biomass and the size-differences were weighted by the relatedness of individuals. The symmetric component of competition was experienced by all individuals in proportion to their biomass, whereas the asymmetric component was individual-specific, and influenced only by the individuals larger than the focal individual. Relatedness decreased and competitive asymmetry increased the variability of individual biomasses. Mortality of the smallest individuals and the size threshold of reproduction decreased population density. Population dynamics were stable when there was no size threshold for reproduction but the presence of the threshold led to cyclic dynamics under low competitive asymmetry. The effects of the threshold were greater among related than unrelated individuals. The results suggest that individual differences and the asymmetry of competition can greatly affect population dynamics. Full symmetry of competition may be evolutionarily unstable in populations of related individuals as it may increase the probability of extinction due to demographic stochasticity.

Individuals can compete either through direct interference or uptake of limiting resources. If competing individuals are able to recognize their relatives, relatedness of competitors may evoke kin selection, which favours relatively even resource share among relatives. Resource competition is often size-symmetric, i.e. proportional to an individual's biomass, while interference competition is asymmetric giving large individuals a disproportionate advantage over small individuals. Kin-selection is predicted to reduce the intensity of direct interference and competitive asymmetry, leading to increased mean and decreased variation in individual size. We tested these predictions by investigating the effects of relatedness on age and size at metamorphosis in the common frog Rana temporaria tadpoles in a laboratory experiment. We reared related (full- and half-sibs) and unrelated tadpoles of different sizes (small, large, small and large together) at two densities until metamorphosis. Relatedness had little effect on mean growth, but it reduced size variation, as measured with coefficient of variation. Furthermore, there was a significant interaction between relatedness and density in size at metamorphosis, so that relatives always grew better in lower density, but growth was less affected by density among unrelated individuals. This indicates that the effects of relatedness on tadpole performance may be context dependent. Initial size differences in the mixed size treatment evened out during the course of the experiment, and initially small tadpoles were able to compensate the early growth losses, although it took longer for them to reach metamorphosis. We conclude that although relatedness may have rather small effects on the growth and development of R. temporaria tadpoles, it increases the symmetry of resource share decreasing between-individual variation in size at metamorphosis.

Seed bank is a plant life history strategy against the unpredictability of the biotic and the abiotic environment. We simulated competition between a seed banking and a non-banking morph of an annual plant. A constant fraction of the banker morph seeds was allocated to the seed bank, where they had a constant mortality and germination rate. All surviving seeds of the non-banker morph germinated in the next generation. The seedlings of both morphs experienced similar density-dependent mortality. Whether one of the morphs wins or the morphs coexist was evaluated from parameter space plots and statistically with logistic regression analysis. All parameters of the model had a significant, nonlinear effect on the persistence of the morphs, supporting our approach of numerically covering a wide range of parameter values. The seed production of a focal morph increased its survival and decreased the survival of the other morph. Otherwise, the morphs showed opposite response to changes in the model parameters. The banker morph was usually the winning strategy when it had a higher seed production than the non-banker morph. The banker morph benefitted from high germination probability, while the non-banker benefitted from high allocation to seed bank and high seed mortality. The coexistence of the morphs was inhibited by high banker morph seed production and seed mortality and promoted by high values of all other parameters. The system showed complex dynamics when banking was the winning strategy or the morphs coexisted. In addition, a part of the parameter space where the non-banker morph wins showed complex dynamics. Our results suggest that seed banking is a beneficial strategy if seed number is increased consequently, e.g. due to a decreased seed size. If banking decreases seed number, the non-banker morph wins or the two morphs coexist.

We studied the phenotypic plasticity of shoot-to-root ratio with a model of plant growth in different availabilities of light and nutrients. Optimal shoot-to-root ratio was defined as the equal limitation of growth by light and nutrients. An optimally growing plant had a curved relative growth rate (RGR) isoclines and a faster growth rate than a fixed-allocation plant having right-angled RGR isoclines. We assumed the plant be exposed to a unit standard deviation of bivariate normally distributed resources. Plants were more plastic in a low than in a high resource availability. Negative correlation between resources increased and positive correlation decreased plasticity. Plasticity was high in plants that saturate at low resource availabilities but independent of maximum growth rate. A trade-off between the maximum growth rate and plasticity of shoot-to-root allocation may rise indirectly from the tendency of fast-growing plants to have high resource requirements.

Changes in vegetation, soil organic matter content, soil nutrient concentration, microbial activity and microbial biomass were studied in Scots pine (Pinus sylvestris) forests on the post-glacial land uplift island of Hailuoto in Finland, along altitudinal transects representing about 1000 years of primary succession. The characteristics of microbial communities in the humus layer were compared both within altitude classes and within TWINSPAN (two-way indicator species analysis) clusters of field layer vegetation. Non-metric multidimensional scaling (NMDS) was employed to reveal gradients in the data. During succession, the vegetation changed from dominance by bryophytes and deciduous dwarf shrubs to evergreen dwarf shrubs and lichens. The thickness of the humus layer and the amount of organic matter in the soil decreased along the succession, which in turn reduced microbial biomass, microbial activity and soil nutrients when calculated on an areal basis. The nutrient concentration of the soil OM (organic matter) showed no successional trend on a concentration basis but the C-to-N ratio of organic matter increased with increasing soil age and lichen coverage. Thus, the nutrient availability decreased during succession but this could not be demonstrated by calculating results against unit weight of organic matter. Soil basal respiration and microbial biomass increased during the succession when calculated per unit weight of organic matter. The successional decrease in site productivity appeared to be due to leaching of nutrients from the sandy mineral soil and thinning of the humus layer. Plants and soil microbes became increasingly N limited during the course of the succession, suggesting the increased importance of mycorrhizal symbiosis for plant performance and increased energy costs among soil microbes in nutrient uptake.

Bryoria section Implexae is a chemically and morphologically diverse group characterized by pendent growth form and non-spinulose branches. In this study, we examine the chemical diversity, distribution pattern and habitat preferences of European members of section Implexae in Finland. A total of 1253 specimens were collected from four vegetation zones and analysed with thin layer chromatography for secondary chemistry. Secondary chemistry of the specimens and vegetation zones had a significant interaction term in a generalized linear model (GLM) of sample frequencies, indicating that chemotype frequencies differed among vegetation zones. Forest structure interacted with vegetation zones and chemotypes indicating that chemotypes differed among forest structure classes, but also showing that forest structure classes differed among vegetation zones. The overall abundance of Bryoria spp. was significantly different among vegetation zones, increasing substantially from south to north. The abundance w...

Escaped transgenic organisms (GMO's) may threaten the populations of their wild relatives if able to hybridize with each other. The introgression of a growth enhancement transgene into a wild Atlantic salmon population may be affected by the transgene's effects not only on fitness parameters, but also on mating behaviour. Large anadromous GMO males are most preferred in mating, but a transgene can also give the large sneakers a reproductive advantage over the smaller wild individuals. With a simulation model, we studied whether the increase in the proportion and mating success of sneakers in transgenic and hybrid genotypes could facilitate the introgression of a transgene into wild population after the release of GMOs. The model combines population dynamics and Mendelian inheritance of a transgenic trait. We found that the introgression of the transgene is strongly affected by the greater mating preference of large GMO males. Furthermore, the difference in reproductive success between the anadromous versus sneaker strategy defines how much GMO's have to be preferred to be able to invade. These results emphasize the importance of detailed knowledge of reproductive systems and the effect of a transgene on the phenotype and behaviour of GMOs when assessing the consequences of their release or escape to the wild.

We studied the response of mycorrhizal and non-mycorrhizal plants to variation in soil nutrient concentration. A model for the relative growth rate (RGR) of plant biomass was constructed with soil nutrients as an explanatory variable. A literature survey was carried out to find the relative magnitudes of parameter values for mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher RGR at low nutrient concentrations and non-mycorrhizal plants at high nutrient concentrations. The RGR of mycorrhizal and non-mycorrhizal plants at constant versus log-normally distributed soil nutrient concentration were compared to see the effect of mycorrhizal status on responses to variation. Variation in nutrient concentration generally reduced RGR, especially in mycorrhizal plants. The RGR of a non-mycorrhizal plant may increase with variation where a growth function threshold exists, i.e. a soil nutrient concentration that must be exceeded to allow growth. Mycorrhizal plants appeared more sensitive to variation in nutrient concentration than non-mycorrhizal plants due to the higher affinity of mycorrhizal roots at low nutrient levels. However, this prediction may be reversed if mycorrhizal symbiosis considerably stabilises flow of nutrients to plant physiological processes, such that mycorrhizal plants experience less variation in soil nutrient concentration than non-mycorrhizal plants. Our results also attain broader significance by suggesting a general trade-off between competitive ability in a constant versus variable resource availability.