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Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.

Maintaining high reproductive output in diverse conditions has consistently been found to promote invasiveness in introduced taxa. Following on this key observation, studies have compared the performance across environments of invasive vs. native congeners, and of introduced vs. native populations within invasive species. Performance differences among genotypes within introduced species have received far less attention, although such genetic variation could be critical to invasive potential. If an introduced species contains genotypes that can maintain high fitness across contrasting environments, such broadly adaptive, high-performance genotypes could promote and shape the species' immediate spread across multiple habitats. Furthermore, their presence could lead to the evolution of greater aggressiveness in the species, as these high performers increase in frequency. We investigated the existence and distribution of high-performance genotypes in Polygonum cespitosum, a newly invasive Asian annual. We raised 416 genotypes, collected from 14 North American populations, under resource-rich conditions to identify potential high-performance genotypes (the top 5% in total reproductive output). We then compared their fitness, life history, and functional traits to a random group of the remaining genotypes in three contrasting environments to ask the following: (1) Do consistently high-performance genotypes (i.e., genotypes with high relative fitness in diverse conditions) exist within introduced-range populations? (2) If so, do these high-performance genotypes possess distinctive life history and/or functional traits? (3) Do these genotypes occur in all populations or in only a subset of populations? Genotypes initially identified as high-performance in favorable conditions also had higher reproductive output in resource-limited environments. Their fitness advantage compared with control genotypes varied in magnitude from one environment to another but was significant within all three test environments. High-performance genotypes shared a developmental syndrome characterized by rapid and high germination, fast seedling growth, early reproductive onset, and high reproductive allocation, but they did not differ in other functional traits. P. cespitosum includes a subset of genotypes with accelerated development and significantly greater fitness in both favorable and stressful conditions. The nonrandom distribution of these high-performance genotypes among populations in the species' introduced range highlights the importance of genotypic and population-level variation for invasion dynamics.

The ecological distribution of species is influenced by individual patterns of response to environment for traits that contribute to fitness. Comparative data on fitness responses to complex environments are particularly valuable for understanding the relation of plasticity to ecological breadth. This study compares individual phenotypic plasticity for components of fitness in four congeneric annual plant species with contrasting ecological distributions (Polygonum cespitosum, P. hydropiper, P. lapathifolium, and P. persicaria). Replicate seedlings of 32 inbred lineages drawn from five natural populations per species were grown to maturity under controlled conditions in all 12 possible combinations of low and high light; dry, moist, and flooded soil; and poor vs. rich nutrients. Timing of reproduction, total reproductive output, offspring size, and allocation to reproduction were determined for each plant. The data revealed highly complex differences among the species in patterns of plastic response for f...

This paper investigates the effects of parental environment and genotype on offspring provisioning, structure, and growth traits in the annual plant Polygonum persi- caria. Replicate offspring were studied from cloned individuals of five parental genotypes grown in high vs. low light, soil moisture, and soil nutrients. Genotypic norms of reaction were determined for ecologically important offspring traits. The effects on those traits of parental genotype, parental environment, and their interaction were tested by analysis of variance. The results showed that parental genotypes altered offspring traits in response to particular resource limits, such that offspring quality was maintained or enhanced despite parental resource deprivation. By maximizing the probability of offspring success, resource- deprived parental plants may partly offset the reduction in their fitness due to lower offspring number. Although overall patterns of plasticity were common to all parents, even this small sample revealed differences among parental genotypes in their response to environment. This may reflect the degree to which variation in fitness-related offspring traits occurs within parents and hence is unavailable to selection.

A plant's competitive ability is determined by its capacity to acquire resources from resource pools shared with neighbors. Resource acquisition abilities depend on plant part placement in relation to available resources. Using a model system of annuals, we examined how the architecture of and allocation to plant parts was affected by different neighbor species. Species having different morphologies were grown as "targets" (target plants) in continuous canopies of each of four neighbor species in the greenhouse. Architectural and allocational traits of Abutilon theophrasti did not vary significantly with neighbor identity. Several architectural and allocation traits of Dutura stramonium and Polygonum penslvanicum plants did vary significantly among neighbor identities; however, in all but two cases, analyses of covariance revealed that these differences were due to differences in shoot biomass among neighbors. We could therefore not relate changes in architecture and allocation to the effects of specific neighbors, and therefore to competitive ability under specific conditions. In all species part masses were more variable than part lengths or areas, suggesting that allocational flexibility in these species allowed them to maximize part size at the expense of part mass to some extent. When we examined within plant biomass allocation patterns among plants of different size classes, regardless of neighbor, we found differences among species in how these patterns changed with plant size. Abutilon and Datura plants in the smallest size class showed a marked reduction in allocation to stems in the upper canopy, while producing similar numbers of nodes, when compared to plants in the largest size class. By contrast, Polygonum plants in the smallest size classes produced many fewer nodes than, but had a relative allocation pattern similar to, plants in the largest size class. These differences had consequences for plant shape, and so suggest differences among species in architectural response to shading. Any such response that allowed a plant to increase its resource—gathering ability would represent an important mechanism of competition.

Stressful parental environments can influence offspring size and development either adaptively or maladaptively, yet little is known about species' differences in this complex aspect of phenotypic plasticity. We performed a reciprocal split-brood experiment to compare transgenerational plasticity in response to drought stress in two closely related annual plant species. We raised inbred replicate parent plants of eight genotypes per species in dry vs. moist soil to generate offspring of each genetic line that differed only in parental environment, then monitored seedling development in both dry and moist conditions. Individuals of the two species expressed contrasting patterns of transgenerational plasticity for traits important to seedling drought tolerance. In Polygonum persicaria, a weedy generalist found in moist, dry, and variably dry sites, drought-stressed plants produced offspring with longer and more rapidly extending root systems and greater biomass when growing in dry soil. In contrast, in P. hydropiper, a non-weedy congener restricted to moist habitats, the offspring of drought-stressed parents had reduced root system development and seedling biomass in dry soil. In P. persicaria, transgenerational and immediate adaptive plasticity combined to produce drought-adapted seedling phenotypes. These results make clear that characteristic patterns of transgenerational plasticity can contribute to ecological diversity among species.

Climate change is one of the most influential drivers of biodiversity. Species-specific differences in the reaction to climate change can become particularly important when interacting species are considered. Current studies have evidenced temporal mismatching of interacting species at single points in space, and recently two investigations showed that species interactions are relevant for their future ranges. However, so far we are not aware that the ranges of interacting species may become substantially spatially mismatched. We developed separate ecological-niche models for a monophagous butterfly (Boloria titania) and its larval host plant (Polygonum bistorta) based on monthly interpolated climate data, land-cover classes, and soil data at a 10'-grid resolution. We show that all of three chosen global-change scenarios, which cover a broad range of potential developments in demography, socio-economics, and technology during the 21st century from moderate to intermediate to maximum change, will result in a pronounced spatial mismatch between future niche spaces of these species. The butterfly may expand considerably its future range (by 124-258%) if the host plant has unlimited dispersal, but it could lose 52-75% of its current range if the host plant is not able to fill its projected ecological niche space, and 79-88% if the butterfly also is assumed to be highly dispersal limited. These findings strongly suggest that climate change has the potential to disrupt trophic interactions because co-occurring species do not necessarily react in a similar manner to global change, having important consequences at ecological and evolutionary time scales.

The relationship of seedling survivorship to specific physiological or mor- phological traits is usually only inferred in demographic studies. We compared seedling survivorship, growth, morphology, and water relations of two subalpine herbs (Eriogonum pyrolifolium and Polygonum newberryi) on Mount St. Helens in order to examine the relationship between population and functional biology more directly. Survivorship of two cohorts of seedlings (1982 and 1983) was followed through 4 and 3 yr, respectively. Seedling growth was measured in two substrate types (pre-eruption soil and 1980 deposited tephra) and under different levels of nutrients and water under controlled environmental conditions. Water relations parameters of the two species were determined in conjunction with the laboratory growth experiment. The 1982 cohort of Eriogonum had a significantly higher rate of survival than did that of Polygonum over four growing seasons, while the 1983 cohort did not differ in survival over three growing seasons. Survival rates were closely related to the amount of rainfall, with Eriogonum having significantly higher survival during dry periods than Polygonum. Growth of both species was greater in pre-eruption soil than in 1980 deposited tephra; the difference was much more pronounced in Polygonum. Growth of Eriogonum seedlings was also less sensitive to lower nutrient and water availability in the laboratory experiment than growth of Polygonum. Eriogonum had lower osmotic potentials, higher stomatal conductance, greater fine root biomass, and lower intrinsic growth rate than did Polygonum. These appear to be important characteristics contributing to greater stress tolerance and higher seedling survivorship in Eriogonum.

To determine the roles of prior evolutionary divergence and competitive displacement of species in successional community organization, and aspects of the colonizing strategy, 6 co- occurring annuals were grown together and alone on a soil moisture gradient. The species had similar broad vegetative and reproductive responses to the gradient. Interspecific competition reduced the niche breadth and similarities of the species. Competitive and gradient stresses were generally ab- sorbed through plasticity, although Polygonum pensylvanicum and Chenopodium album showed some mortality. Response centers of Polygonum, Ambrosia artemisiifolia, and Chenopodium, com- petitively subordinate species, shifted due to interspecific competition. Amaranthus retroflexus and Setaria faberii, the leading competitors, already slightly offset from each other when grown alone, did not shift response centers. Competition delayed the start of flowering in Setaria, Chenopodium, Polvgonum and Ambrosia. Competitive success did not correlate with response breadth or overlap. Polygonum and Abutilon behaved differently in different competitive environments, indicating the existence of competitive refugia. Refugia may be shifted, reduced, or maintained depending on the competitors present. Coexistence may depend on: (1) differences in response to the moisture gradient and other niche dimensions previously investigated, and (2) on heterogeneous and unpredictable distributions of neighbors. Thus, competitive refugia will be unthreatened at some times and places. Key 'ords: colonizing strategy; community organization; competition; experimental gradient analysis; gradient: Illinois; niche; niche overlap; successional community.

Polygonum pensylvanicum and Abutilon theophrasti, components of old—field communities in central Illinois were grown on a controlled soil moisture gradient to determine whether they exhibit different response centers. Germination response of a constant number of seeds per six moisture resource states, height, biomass, and reproductive response of initially constant numbers of plants per state were monitored. States, ranging from saturation down to 13.61 ± 5.53% moisture, are numbered in order of increasing drought. Maximum height of Polygonum occurred in states 4 and 5, and of Abutilon in 4, 5, 6. Vegetative and reproductive biomass maxima of Polygonum and Abutilon occurred in states 5 and 6, respectively. Abutilon reproduced only in states 5 and 6 where it overtopped the Polygonum canopy, while Polygonum reproduced in all states. Polygonum performance declined sharply in state 6. Thus, Polygonum and Abutilon response centers are displaced toward the wetter and drier ranges of the gradient, respectively. On a within—community level, Abutilon reproduces in less mesic resource states where Polygonum canopy height is reduced. In general, Abutilon reproduction may occur throughout the gradient when the Polygonum canopy opens. The performance of these species is strongly influenced by both physical and biotic conditions. Previously investigated adaptations, including drought resistance and rooting patterns in space and time, appear to underlie divergence along the moisture gradient. The response patterns found here are broad and exhibit considerable overlap as expected in fugitive strategies. The patterns of divergence shown on point and gradient scales in this and our previous work reflect a related complex of adaptations and strongly suggest that competitive divergence occurs in early successional communities.

Mineral element concentrations were measured in the component parts of different species of plants from a floodplain community along a coastal plain stream in South Carolina, USA. Frequency distributions of concentrations of mineral elements were positively skewed, although dis- tributions of P. K, Ca and B concentrations tended to be less skewed than those of some trace elements (Na, Al, Cs- 137). Sources of variation in the elemental compositions of the major natural plant species of the floodplain were examined statistically. In herbaceous species (Scirpus cyperinus and Andropogon sp.), 52-56% of the variation in P, Mg, Mo and Na concentrations was accounted for by differences in the chemical composition of stems, leaves, roots and seeds. Seasonal variation in the mineral element composition of leaves from woody species was greater than that in stems. Concentra- tions of K, P. Al, Mo and Sr in leaves were significantly different among seasons in 3 woody species (Alnus serrulata, Myrica cerifera, Salix nigra). Mean concentrations of Ca, Na, Al, B, Mo and Sr in leaves tended to increase from spring to autumn, while K, Mg, N, P. Cu, Zn and Cs-137 concentrations declined. For macroelements (P, Mg, K, Ca and N) and some trace elements (B, Sr, Na and Mo), >50% of the variation in concentrations was accounted for by differences among 4 species (Polygonum punctatum, Scirpus cyperinus, Salix nigra, Sagittaria latifolia) while

Field microenvironments of three annual alpine species, Koenigia islandica, Polygonum confertiflorum, and P. douglasii, were characterized over two growing seasons. Germination, photosynthesis, and growth of all three species were investigated in field and laboratory experiments. The Polygonum species occurred in warm, dry alpine sites which melted out early in the growing season but also dried out early; plants died by mid—August. Koenigia grew in sites which melted out later, but plants remained alive later in the season since their sites did not dry out. Polygonum plants experienced higher soil surface, air, and leaf temperatures than did Kogotus plants. Seeds of the Polygonum species required stratification before they germinated, and light increased germination. Koenigia seeds germinated equally well in light and dark, and stratification was not necessary, although it increased germination percentages. Photosynthetic responses to light were similar in all three species. Koenigia's photosynthetic temp...

Sugar and starch contents of roots or rhizomes of Polygonum bistortoides, Saxifraga rhomboidea, and Calyptridium umbellatum were measured at different altitudes in the Sierra Nevada of California and in the Medicine Bow Mountains of Wyoming. Carbohydrate reserves appear to be higher near the lower altitudinal limits of a species. Ploygonum bistortoides, Caltha howellii, and Sibbaldia procumbens transplanted to lower and warmer elevations used up stored carbohydrates more rapidly than at the elevation of origin. The higher carbohydrate content of individuals in natural populations near the lower altitudinal limits of an alpine species thus appears to be an ecotypic or ecoclinal adaptation. See full-text article at JSTOR