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Bryophytes have increased in abundance in northern regions, and climate changes have been proposed to account for this change. However, changes in the population dynamics of microtine rodents may also contribute to changes in bryophyte abundance. New evidence indicates a tendency for microtine rodent population oscillations to change from periodicity of 3-5 years to become irregular or acyclic. The impact on ecosystem functioning is potentially great. We study the impact of variation in microtine rodent population characteristics, such as cycle length and amplitude, on the population dynamics of the boreal, clonal moss Hylocomium splendens. We use experimental and observational demographic data to construct 127 scenarios representing all combinations of disturbance type (gap formation and/or clipping), period (cyclic with 4, 6, 12, or 24 years between rodent peaks: or acyclic with constant or stochastically varying annual disturbance severity) and disturbance severity (fraction of individuals affected by disturbance in each year relative to the maximum disturbance carried out in the field experiment: seven levels). Population data collected in the field during 13 years were used as a baseline scenario. By subjecting all scenarios to stochastic matrix modeling, we demonstrate considerable impact of microtine rodent on the population dynamics of H. splendens, most notably when rodent populations fluctuate with short periods and high peak disturbance severities. Under the same average disturbance severity, H. splendens population growth rates are highest in acyclic scenarios and are progressively reduced with increasing peak disturbance severities (i.e., with increasing period). Stochastic elasticity analyses show that in less variable environments mature segment survival contributes more to the population growth rate, while in more variable environments the regeneration pathway (branching of older parts of the plant) plays a stronger role, inevitably leading to lower population fitness. Our results support the hypothesis that breakdown of cyclic rodent population dynamics accentuates increase in the abundance of H. splendens and other large bryophytes in boreal forests in Norway, observed empirically in recent years and primarily ascribed to climatic change. Key words: boreal clonal moss; bryophytes; climatic change; disturbance; elasticity; Hylocomium splendens; matrix population models; microtime rodent cycles; resistance to herbivory; stochastic growth rate.

Spatial models predict that long-distance dispersal of offspring provides competitive superiority in open environments. We tested this prediction by artificially aggregating ramets of the spreading clonal species Agrostis stolonifera in an undisturbed environment and in an environment where flooding increased open space. We compared the competitive response of this manipulated Agrostis with both the natural ramet distribution of Agrostis and with the naturally aggregated clonal species Alopecurus pratensis. Our phenotypic manipulation of ramet dispersal significantly increased aggregation of clonal offspring, without altering the number of offspring, and thus provided an adequate test of spatial effects. Regardless of flooding, both Alopecurus and the aggregated Agrostis were more suppressed in species mixtures than the natural dispersed form of Agrostis. This demonstrates that long distance dispersal of ramets enhances competitive ability, at least in early stages of succession. Key words: competition--colonization trade-off; disturbance; flooding; phenotypic manipulation; spatial pattern.

The Mediterranean perennial herb Lobularia maritima shows an exceptionally extended flowering and fruiting that lasts for 10 months, from early September to late June. We hypothesized that such an extended phenology may be a flexible mechanism that enhances population persistence in variable Mediterranean environments, as fecundity in one part of the season could compensate for reproductive failure in another part of the season. We predicted that (1) fecundities throughout the year would significantly contribute to mean population growth rate [lambda], (2) negative covariances among fecundities in different periods of the year would reduce variance in population growth rate, and (3) extended flowering and fruiting would enhance long-term stochastic population growth rates. We used a periodic matrix model to describe the demography of a L. maritima population over five years, in which each year was divided into six periods of two months each. Population growth rates varied from a low of 0.25 to a high of 4.81 over the five years of study. Periodic elasticity analyses revealed that fecundities in the first two periods of the year, i.e., the autumn periods, were the major determinants of population growth in most of the years, rather than fecundities over the whole flowering and fruiting season. Variation in the autumn fecundities also made the largest contribution to the observed variance in [lambda]. Hence, unlike earlier generalizations, highly variable parameters also had relatively high elasticities. As predicted, negative covariances appeared between the fecundities, but only between those of the two autumn periods. These negative covariances were interpreted as a flexible mechanism to tailor the onset of reproduction to the start of the autumn rains, thereby reducing the variance in [lambda]. We used stochastic matrix models to investigate the effect of different reproductive strategies on stochastic population growth rate. We created hypothetical populations with either an even distribution of fecundity throughout the year or with concentrated flowering and fruiting in autumn or in spring. Stochastic population growth rates were high if a major part of the reproduction remained in autumn. A hypothetically even distribution of fecundities over the entire flowering season increased both the mean and the variance in [lambda], with little overall effect on stochastic population growth rate. All together, our results indicate that a reproductive failure of L. maritima in autumn cannot be compensated for by reproduction in winter and spring. The extended flowering and fruiting season thus has very little effect on the population dynamics of the species. Alternative explanations for the unusual phenology of L. maritima in the Mediterranean environment are discussed. Key words: elasticity analysis; extended flowering and fruiting; Lobularia maritima; Mediterranean environments; periodic matrix model; population growth rate; stochastic simulations; temporal variation; variance decomposition analysis.

Differences in root foraging behavior between species have been well documented, but the effects of these differences on belowground competitive ability are only beginning to be studied. Here we report the results of a competition experiment in homogeneous and heterogeneous soils between two species that differ in their ability to acquire nutrients from patchy environments. The perennial grasses Festuca rubra and Anthoxanthum odoratum have comparable growth rates, but results of previous studies with isolated plants designated the latter species as the more effective forager, probably due to its higher physiological plasticity (stronger increase in nutrient uptake rates per unit root mass in enriched nutrient patches). We introduced nutrient soil heterogeneity at two spatial scales. In a fine-grained heterogeneous treatment, the nutrient-rich patches were smaller and more concentrated than in a coarse-grained heterogeneous (checkerboard) treatment. Overall, the level of nutrient availability in these heterogeneous treatments was similar to a third treatment with homogeneous soils. The species were grown in monocultures and mixtures in a standard replacement design during two growing seasons. In the homogeneous treatment, the relative competitive ability of F. rubra was higher than of A. odoratum, but F. rubra's advantage declined in the heterogeneous environments, and the relative competitive abilities became the same. Both species produced higher root densities in the richer patches of the fine-grained heterogeneous treatment, but not significantly so in the coarse-grained heterogeneous treatment, and these responses were the same for both species. The root activity of the species was assessed by determining the amount of strontium captured by a species at the end of the experiment, after injecting Sr[Cl.sub.2] in the nutrient-rich patches and in equivalent locations in the homogeneous treatment. F. rubra acquired significantly more Sr in the mixtures in the homogeneous treatments, but in the coarse- and fine-grained heterogeneous treatment the nutrient acquisition abilities of the species were equal. These results suggest that a more effective root foraging behavior confers a higher competitive ability in heterogeneous environments. Moreover, the results on root-proliferation and nutrient-acquisition ability suggest that a higher physiological (rather than morphological) plasticity is critical in obtaining a long-term competitive advantage. Analyses of shoot size inequalities suggest that competitive interactions were size-symmetric in homogeneous soil and size-asymmetric in the heterogeneous treatments. However, in the long term, competition becomes more size-symmetric in the heterogeneous soils, consistent with the increasing importance of physiological plasticity. Key words: Anthoxanthum odoratum; competition; Festuca rubra; grasses, perennial; heterogeneity, soil nutrients; morphological and physiological plasticity; nutrients in soils; plant competition underground; replacement design; root foraging; soil nutrient heterogeneity changes competition.

Hypotheses about the origin of vegetation pattern formation in semi-arid areas around the world almost all include a common feature of semi-arid areas: the presence of a positive feedback between plant density and water infiltration. We investigate whether this positive feedback and the spatial redistribution of runoff water are sufficient to explain vegetation pattern formation. For this purpose, we analyze a spatially explicit model consisting of partial differential equations using a method for demonstrating pattern formation (Turing analysis). Our analysis reveals that pattern formation can occur in semi-arid areas given only the positive feedback between plant density and local water infiltration coupled with the spatial redistribution of runoff water. Thus, slope and underlying heterogeneity are not essential conditions. Other factors in the model, such as herbivory, plant dispersal, rainfall, and drought tolerance of plants, appear to determine under what conditions pattern formation is likely but are not the primary factors that generate the patterns. The model is in agreement with field observations and indicates the conditions for which vegetation pattern formation can be expected in arid and semi-arid grazing systems. Key words: grazing; herbivory; patchiness; plant dispersal; plant-soil interaction; positive feedback; runoff; semi-arid grazing systems; spatially explicit model; Turing analysis; vegetation patterns.

Understanding which factors cause populations to decline begins with identifying which parts of the life cycle, and which vital rates, have changed over time. However, in a world where humans are altering the environment both rapidly and in different ways, the demographic causes of decline likely vary over time. Identifying temporal variation in demographic causes of decline is crucial to assure that conservation actions target current and not past threats. However, this has rarely been studied as it requires long time series. Here we investigate how the demography of a long-lived shorebird (the Eurasian Oystercatcher Haematopus ostralegus) has changed in the past four decades, resulting in a shift from stable dynamics to strong declines (-9% per year), and recently back to a modest decline. Since individuals of this species are likely to respond differently to environmental change, we captured individual heterogeneity through three state variables: age, breeding status, and lay date (using integral projection models). Timing of egg-laying explained significant levels of variation in reproduction, with a parabolic relationship of maximal productivity near the average lay date. Reproduction explained most variation in population growth rates, largely due to poor nest success and hatchling survival. However, the demographic causes of decline have also been in flux over the last three decades: hatchling survival was low in the 2000s but improved in the 2010s, while adult survival declined in the 2000s and remains low today. Overall, the joint action of several key demographic variables explain the decline of the oystercatcher, and improvements in a single vital rate cannot halt the decline. Conservations actions will thus need to address threats occurring at different stages of the oystercatcher's life cycle. The dynamic nature of the threat landscape is further supported by the finding that the average individual no longer has the highest performance in the population, and emphasizes how individual heterogeneity in vital rates can play an important role in modulating population growth rates. Our results indicate that understanding population decline in the current era requires disentangling demographic mechanisms, individual variability, and their changes over time., (© 2021 The Authors. Ecology published by Wiley Periodicals LLC on behalf of Ecological Society of America.)

Locally, plant species richness supports many ecosystem functions. Yet, the mechanisms driving these often-positive biodiversity-ecosystem functioning relationships are not well understood. Spatial resource partitioning across vertical resource gradients is one of the main hypothesized causes for enhanced ecosystem functioning in more biodiverse grasslands. Spatial resource partitioning occurs if species differ in where they acquire resources and can happen both above- and belowground. However, studies investigating spatial resource partitioning in grasslands provide inconsistent evidence. We present the results of a meta-analysis of 21 data sets from experimental species-richness gradients in grasslands. We test the hypothesis that increasing spatial resource partitioning along vertical resource gradients enhances ecosystem functioning in diverse grassland plant communities above- and belowground. To test this hypothesis, we asked three questions. (1) Does species richness enhance biomass production or community resource uptake across sites? (2) Is there evidence of spatial resource partitioning as indicated by resource tracer uptake and biomass allocation above- and belowground? (3) Is evidence of spatial resource partitioning correlated with increased biomass production or community resource uptake? Although plant species richness enhanced community nitrogen and potassium uptake and biomass production above- and belowground, we found that plant communities did not meet our criteria for spatial resource partitioning, though they did invest in significantly more aboveground biomass in higher canopy layers in mixture relative to monoculture. Furthermore, the extent of spatial resource partitioning across studies was not positively correlated with either biomass production or community resource uptake. Our results suggest that spatial resource partitioning across vertical resource gradients alone does not offer a general explanation for enhanced ecosystem functioning in more diverse temperate grasslands., (© 2019 The Authors. Ecology published by Wiley Periodicals, Inc. on behalf of Ecological Society of America.)

Harvesting nontimber forest products (NTFPs) is a major economic activity in tropical forests. As many NTFPs are overexploited, sustainability analyses are required to set harvest guidelines. Here we introduce and apply a new approach to evaluating sustainability, which combines prospective (elasticity) and retrospective (Life Table Response Experiments [LTRE]) demographic analyses of matrix population models. We relate the elasticity of vital rates (representing their importance for population growth rate, lamda) to their contribution to harvest-induced change in lamda ("LTRE contribution"). When high-elasticity vital rates have a low LTRE contribution, exploitation is potentially sustainable as negative effects for population growth are buffered. If the reverse is found, there is little scope for sustainability because crucial vital rates are affected. Our approach is less sensitive to chance fluctuations than the commonly used sustainability criterion of lamda = 1.0, as it does not depend on the absolute value of lamda. We applied this analysis to Geonoma deversa, a clustered forest understory palm. We studied three experimentally defoliated and control populations in a Bolivian rainforest during two years. Cutting all leaves of large ramets did not change mortality but strongly affected growth and reproduction. In spite of severe changes in some vital rates, population growth rate was not significantly reduced after defoliation. A literature review revealed that six other understory palms species responded very similarly to defoliation. The combination of LTRE contributions and elasticity analyses showed that low-elasticity vital rates were mainly responsible for the defoliation-induced change in lamda for Geonoma deversa. For two other understory palms (Astrocaryum mexicanum and Chamaedorea radicalis) new demographic analyses yielded very similar results. For Geonoma, the LTRE contribution-elasticity relation strongly changed when we mimicked harvest damage. Adding 5% mortality to defoliated palms caused stronger change in lamda, mainly due to changes in a high-elasticity vital rate (survival). Therefore, harvest practices that involve stem killing are clearly unsustainable. Our results show that commercial leaf cutting in Geonoma deversa is potentially sustainable, and that this is likely the case for understory palms in general. Our approach to evaluating harvest sustainability can be applied to other NTFPs.