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Maternal-environmental effects on subsequent progeny life-history traits were evaluated in squash (Cucurbita pepo L.) in terms of the amount of time available for seed development, and the timing of fruit production. Progeny arising from three kinds of fruit were compared. Plants from which fruits were removed 3 d post-pollination throughout the growing season developed only 'late' fruits (during 10-15 d) at the end of the growing season; on control plants both 'early' and 'late' fruits developed (both types allowed to ripen fully). Seed from each type of fruit was weighed individually and categorized into three size classes, then germinated and raised to maturity, including regular harvesting of all fruits 3 d post-pollination. Maternal effects were evident for both vegetative and reproductive traits and carried over to later stages. In contrast, effects due simply to seed size disappeared by day 30 for leaf variables and day 60 for male flower production. Within a seed-size class, progeny arising from fruit of treated plants produced significantly more leaves, with greater size, and more male flowers than those arising from fruit of control plants, while the reverse was true for fruit number and fruit mass. This result is discussed in terms of possible gibberellic acid involvement. In control plants, progeny arising from seeds in the large, fully mature 'early' fruits produced significantly more, and larger leaves by day 30 than did those from late fruits (suggesting differential provisioning in seeds during development). Male flower production had a highly significant positive correlation with vegetative mass and a significant negative correlation with fruit production.

The cost of reproduction by female plants generally exceeds that of male plants because females produce seeds and fruits in addition to flowers (Darwin 1877, Lloyd and Webb 1977, Willson 1983). If the vegetative growth of female and male plants is equivalent, then the greater female reproductive effort should result in reduced growth and/or survival. In a dioecious clonal plant that reduction might be manifest as lower ramet production, and the sex ratio of ramets should become increasingly male-biased. In contrast to this expectation the ramet sex ratio of Rumex acetosella tends to be female-biased (Harris 1968, Putwain and Harper 1972, Lovett Doust and Lovett Doust 1985), even though females allocate a greater proportion of their resources to reproduction than do males (Putwain and Harper 1972). In eight Massachusetts populations of Rumex acetosella, we found one male-biased population and a female bias at the other sites. In these latter seven sites the estimated sex ratio of genets (the genetic individuals) did not differ significantly from 1: 1 (Lovett Doust and Lovett Doust 1985). The greater reproductive effort by female plants, plus the female bias in sex ratio of ramets suggested differential growth by females. Biased sex ratios in clonal plants can be caused by a variety of factors, including, for example, differential grazing by herbivores (see Lovett Doust and Lovett Doust 1985, Agren 1987), sex-associated effects of intraspecific competition (e.g., Onyekwelu and Harper 1979, Lovett Doust et al. 1987), and differences in the numbers of ramets produced and sustained by female and male plants (Sakai and Burris 1985). We have examined and rejected the possibility that differential herbivory on male and female Rumex plants drives the ramet sex ratio to being female-biased. (In fact, although males and females suffered comparable herbivory in absolute terms, the proportion of the available foliage that was removed from females was greater [Lovett Doust and Lovett Doust 1985].) The present study was designed to explore the hypothesis, suggested by David Lloyd (personal communication), that differences in the vegetative vigor and seasonal phonology of males and females might explain the female-biased sex ratios generally found in populations of Rumex acetosella.

The seed bank of Neurada procumbens, a prostrate annual common in sandy desert habitats, is vulnerable to surface disturbances. Moreover, its seeds are highly heteromorphic, having both spinose and non-spinose sides, which affects both the vertical distribution of seeds and diaspores, and the precise position in which they lie in the soil. Here we explore the ecological implications of two factors, “safe sites” within habitats and seed orientation or “safe sides”, on seedling establishment and the seed bank. In three natural populations, the vertical distribution of buried, germinable diaspores decreased with soil depth. Most diaspores occurred at the surface (0–1 cm below the surface), while none were observed below 10 cm. Seedling emergence decreased with depth and reached zero in diaspores below 5 cm. Seedling emergence also proved highly sensitive to the orientation of diaspores in soil. Diaspores lying on their smooth side with the spinose upper side directed upwards reached the highest seedling emergence of 61 %. Root length ranged from 10 to 16 cm, and the root to shoot ratio varied between 22.8 and 30.3 cm, depending on diaspore size. Diaspores near the surface may constitute a more transient component of the seed bank, as few of these remained viable for more than a year. Persistence of Neurada seed banks seems to depend not only on vertical movement of diaspores among habitat “safe sites” but also on different seed position alternatives.

Reproductive performance and phenology in gynodioecious Ochradenus baccatus was investigated at Wadi Degla, in Egypt's arid Eastern Desert. Between January and December 2005, plants representing a series of size classes were identified from two populations, located ca. 7.5 km apart. A total of 94 individuals were marked and classified according to sex expression and overall size/canopy volume. Reproductive phenology was monitored across the year. Plants presented an extended reproductive phenology having two peaks, in spring and autumn. Plant size was a significant factor influencing reproductive output and phenology. Fruit number, seeds-per-fruit and seed mass all varied significantly among the size classes of both female and hermaphrodite plants, during both spring and autumn phenophases. Numbers of fruit and seeds-per-fruit were greater in spring than autumn, and female forms had greater fruit numbers, seed mass and percent germination, and fewer seeds-per-fruit than hermaphrodites. Numbers of fruits, seeds-per-fruit and seed mass were all significantly positively correlated with plant size. Seeds produced at the larger downstream population had greater seed germination rates than those from the upper site. Results are discussed in terms of plant size and directed seed dispersal patterns.

The 'mid-domain effect' (MDE) has received much attention recently as a candidate explanation for patterns in species richness over large geographic areas. Mid-domain models generate a central peak in richness when species ranges are randomly placed within a bounded geographic area (i.e. the domain). The most common terrestrial mid-domain models published to date have been 1-D latitude or elevation models and 2-D latitude-longitude models. Here, we test 1-D, 2-D and 3-D mid-domain models incorporating latitude, longitude and elevation, and assess independent and concurrent effects of geometric constraints and climatic variables on species richness of North American trees. We use both the traditional 'global' regression models as well as geographically weighted regressions ('local' models) to examine local variation in the contribution of MDE and climatic variables to species richness across the domain. Our results show that in some dimensions the contribution of MDE to patterns of species richness can be quite substantial, and we show that in most cases a combination of MDE and climate predicted empirical species richness best in both local and global models. For the North American domain, MDE in the elevation dimension is clearly important in describing patterns of empirical species richness. We also show that the assumption of stationarity in global models is not met in the North American domain and that results of these models mask complex patterns in both the effect of MDE on richness and the response of species richness to climate. In particular we show the increased explanatory role of MDE in predicting species richness as domain edges are approached. Our results support the hypothesis that geometric constraints contribute to species richness patterns and we suggest the mid-domain effect should be considered alongside more traditional environmental correlates in understanding patterns of species diversity.

Abundance and occupancy of populations at high- and low-latitude geographic range edges will be critically important in determining a species' response to climate change. Low abundance and occupancy at expanding (high latitude) edges of the range may limit a species capacity to migrate, and at trailing (low latitude) edges, may result in range erosion and regional extinction. We examined abundance-occupancy distributions across the geographic ranges of 102 eastern North American trees and looked for signatures reflecting capacity to respond to climate change. We found that 62% of species display a signature consistent with higher climatic suitability in the northern latitudes of their range. However, our results suggest that the most common response is likely to involve range erosion in the south and limited range expansion in the north, possibly leading to an overall reduction in range size for many species. In particular, species with smaller ranges centred at lower latitudes may not have the capacity to successfully track the current rate of climate change.

The "mid-domain effect" (MDE) has received much attention as a candidate explanation for patterns in species richness over large geographic areas. Mid-domain models generate a central peak in richness when species ranges are placed randomly within a bounded geographic area (i.e. the domain). Until now, domain limits have been described mostly in one-dimension, usually latitude or elevation, and only occasionally in two-dimensions. Here we test 1-D, 2-D and, for the first time, 3-D mid-domain models and assess the effects of geometric constraints on species richness in North American amphibian, bird, mammal and tree species. Using spatially lagged simultaneous autoregressive models, empirical richness was predicted quite well by the mid-domain predictions and the spatial autoregressive term (45–92% R2). However, our results show that empirical species richness peaks do deviate from those of the MDE predictions in 3 dimensions. Variation explained (R2) by MDE predictions generally increased with increasing mean range size of the different biotic groups (from amphibian, to tree, mammal and finally bird data), and decreased with increasing dimensions being accounted for in the models. The results suggest geometric constraints alone can explain much of the variation in species richness with elevation, specifically with respect to the larger-range taxa, birds and mammals. Our analysis addresses many of the recent methodological criticisms directed at studies testing the MDE, and our results support the hypothesis that species diversity patterns are influenced by geometric constraints.

Ecological niche modeling has become an increasingly important tool to address issues in many fields of basic and applied ecology. The ecological niche space occupied across the geographic range, particularly for wide-ranging species, may vary for a variety of evolutionary and non-evolutionary reasons. However, ecological niche models are often applied over large geographic areas without regard for the potential effects of regional variation in adaptation, environmental conditions and their interactions, and species responses, thus significantly reducing their accuracy and utility. We develop regionally partitioned ecological niche models, using GARP, for the wide-ranging North American tree Gleditsia triacanthos (Fabaceae). Models were constructed based on known tree occurrences at peripheral and range-centre locations, as well as across the geographic range as a whole. Our results suggest that the niche space occupied by G. triacanthos varies regionally and that between some regions in particular there may be a complete absence of niche overlap. In particular, while there is some overlap between the niche space occupied by trees in the western and central regions of the range, there appears to be virtually no overlap in the niche space occupied by trees in the south of the range and that occupied by western and central trees. This lack of overlap appears to be driven primarily by regional differences in abiotic conditions, rather than regional adaptation per se. The results of our study have several important implications for the future development of habitat suitability models over large geographic areas. Spatial partitioning of data is clearly necessary to improve predictions of models where regional niche variation occurs. For wide-ranging species in particular, regional differences in ecological characteristics may cause apparent niche variation.

Core-satellite theory predicts that, via the “rescue effect”, widespread, abundant species should have reduced risk of local extinctions. We test this hypothesis in southeastern Malagasy littoral forest using data on distribution and abundance of trees and woody understory vegetation in tropical forest fragments along a disturbance gradient. We partition the mortality risk into two kinds of extinction factors, separately operating at demographic (local) and landscape (regional) scales, contrary to core-satellite predictions, for both trees and woody understory vegetation, that the relative number of core (abundant) species declined significantly with increasing disturbance. In the least-degraded forest fragments there was a strong mode of core species, while in the moderately- and severely-degraded fragments the species distributions were essentially log-normal, lacking a substantial core mode. While the rescue effect mitigates one kind of extinction risk, namely local environmental and demographic stochasticity, it may not counterbalance widespread pervasive sources of mortality. The amount of internal forest fragmentation appears to have a much greater effect on species richness and diversity than either fragment size or shape.

Macroecology depends heavily on a comparative methodology in order to identify large-scale patterns and to test alternative hypotheses that might generate such patterns. With the advent and accessibility of large electronic databases of species and their life history and ecological attributes, ecologists have begun seeking generalities, and examining large-scale ecological hypotheses involving core themes of range, abundance and diversity. For example, combinations of ecological, life history and phylogenetic data have been analysed using large species sets to test hypotheses in invasion biology. Analysis of regional species inventories can contribute cogently to our understanding of invasions. Here we examine several ways in which database analysis is effective. We review 19 studies of comparative invasions biology, each using >100 species of plants in their analyses, and show that invader success is linked to seven correlates: short life cycle, abiotic (mostly wind) dispersal, large native range size, non-random taxonomic patterns (emphasizing certain families or orders), presence of clonal organs, occupying disturbed habitats, and earlier time of introduction. These phylogenetically influenced, comparative analyses using regional species inventories are only just beginning and have much potential. © Springer 2006.

Aim: We analysed spatial datasets of abundance across the entirety, or near entirety, of the geographical ranges of 134 tree species to test macroecological hypotheses concerning the distribution of abundance across geographical ranges. Location: Our abundance estimates came via the USDA Forest Service Forest Inventory and Analysis Eastwide Database, which contains data for 134 eastern North American tree species. Methods: We extracted measures of range size and the spatial location of abundance relative to position in the range for each species to test four hypotheses: (a) species occur in low abundance throughout most of their geographical range; (b) there is a positive interspecific relationship between abundance and range size; (c) species are more abundant in the centre of their range; and (d) there is a bimodal distribution of spatial autocorrelation in abundance across a species range. Results: Our results demonstrate that (a) most species (85%) are abundant somewhere in their geographical range; (b) species achieving relatively high abundance tend to have larger range sizes; (c) the widely held assumption that species exhibit an 'abundant-centre distribution' is not well supported for the majority of species; we suggest 'abundant-core' as a more suitable term; and (d) there is no evidence of a bimodal distribution of spatial autocorrelation in abundance. Main Conclusions: For many tree species, high abundance can be achieved at any position in the range, though suitable sites are found with less frequency towards range edges. Competitive relationships may be involved in the distribution of abundance across tree ranges and species with larger ranges (and possibly broader niches) may be affected more by biotic interactions than smaller ranging species.

Developmental instability is typically measured as patterns of fluctuating asymmetry (FA), small departures from perfect symmetry in structural morphology. Although the mechanisms producing developmental instability remain unclear, the disruptive effect of “stressors” during development is assumed to induce deviations from symmetrical phenotypes. Associations between developmental stress and FA are particularly interesting from the general perspective of fragmented and marginal populations, which are thought to be exposed to greater levels of genetic and environmental stress. We measured two leaf FA parameters at 18 populations across the range of the native tree Gleditsia triacanthos (honey locust). Highly significant effects of both landscape (region) and site were found for the two FA traits. FA did not generally increase in geographically marginal populations nor was either FA index correlated with latitude or climatic factors. FA also did not generally increase in smaller populations, and it was not ...

Recent reviews of evidence for plant metapopulation prevalence in nature have concluded that most species appear not to be arranged as metapopulations – hence other frameworks may be necessary for understanding large-scale, regional dynamics in plants. Separate but related paradigms from the disciplines of landscape ecology and metapopulation ecology exist for understanding patterns of regional population variation. The major models of both paradigms assume a binary landscape mosaic composed of “suitable habitat” and background “matrix.” An important distinction between the two approaches is that metapopulation models essentially ignore features of the matrix. A binary approach to the landscape seems inappropriate for plants for several reasons. First, plants probably do not have a binary perception of the landscape, but rather respond to gradients of resource quality. Thus properties of patches, or the matrix per se, may be less important than the nature of the landscape mosaic, in particular as this is reflected in terms of connectivity. Secondly, many plants rely on a range of other agents for dispersal of pollen and seed, all of which are also affected by their environment in terms of connectivity. Furthermore the various components of the mosaic, including physical, spatial and functional elements can significantly influence plant movements. We review important effects of the matrix – via composition and configuration of habitat patches, extent of edges, patterns of land use, etc., upon plant populations. We describe evidence supporting a general integration of metapopulation and landscape ecological approaches for understanding regional dynamics in plants, emphasizing notions of connectivity (traditionally measured in very different ways by metapopulation and landscape ecologists), and context, an emerging concept describing components of variability in the landscape from a species-specific perspective. Finally, we describe a functional landscape mosaic approach that treats structural and functional features of the landscape and show how these interact to determine the fate of plant populations.

Surprisingly few studies have considered the extent to which the nature of the ownership of land is associated with differences in biodiversity. We analysed ownership and other landscape-level effects on rare-species richness for both globally- and regionally-rare biota (including birds, herpetofauna, butterflies, mammals, and plants) in 289 designated natural areas (NAs) in southern Ontario, Canada. Information about each NA −including area, number of plant communities, ownership status and details of species diversity were collected from published sources. Length of perimeter of NA, relative isolation, and an estimate of fragmentation were measured using image analysis and GIS techniques. NAs were in general relatively small, with mean area of 158 ha (median 85 ha, range from 0.9 to 1278 ha) for private NAs; public NAs had mean area of 132 ha (median 16 ha, range from 0.1 to 1481 ha). Mean number of plant communities was 4.6 (median 4, range 1- 13) at private NAs and 3.8 (median 3, range 1-16) at public NAs. Our results show that, of several landscape-level factors, area had the greatest effects on rare-species richness and other biotic indices. Effects of area were followed by effects of plant community diversity, however this was itself significantly affected by area and the extent of perimeter of the NA. Both these factors were followed by effects of ownership of the NA and by effects of isolation of the NA (represented by minimum distance to nearest NA and by number of NAs in 10 km radius). Other landscape- level factors did not appear to have overall significant effects. Variation in area accounted for 0.1% to 29% of variation in number of rare species, with lower values for globally-rare, than for regionally-rare taxa. For all biotic groups, public ownership of NAs was associated with significantly greater rare-species richness compared to private ownership, even after other factors such as area were controlled. For all globally-rare biota except butterflies, area of NA had greater effects on rare-species richness than did ownership. Richness of regionally- rare birds was more affected by plant community diversity than by area of NA. Number of recorded plant communities accounted from 2.1% of variation in number of globally-rare plant species to as high as 31% of variation in regionally-rare butterflies. The diversity of plant communities was itself influenced by total site area (accounting for 45% of variation), extent of elongation of the NA, and both external- and interior- edge perimeters. Public NAs had greatest numbers of rare biota and so should be a significant focus for conservation programs. Smaller, privately-owned patches of natural area dominate (by number and area) in this densely populated region and their significance should not be overlooked.

Summary • Compared with leaf-feeding herbivores, little is known about how sap-feeding herbivores affect plant growth, morphology and reproduction. This study examines effects of the sap-feeding squash bug ( Anasa tristis ) on watermelon ( Citrullus lanatus ) root, leaf and reproductive structures. • Plants at the four-leaf stage were exposed to different densities of caged squash bugs for 67 d (to plant maturity). • Initial effects were on roots. Herbivory was associated with a significant reduction in mean total root length, root surface area and number of root tips, as well as an increase in root diameters. Herbivore-exposed plants had significantly more leaves, although leaf lifespan was decreased. Both total plant dry mass and fruit dry mass per unit leaf area were significantly greater in controls. Significant effects of herbivores on plant reproductive traits included delayed flower formation (by 7–12 d), change in floral sex ratio (in favor of femaleness), increased fruit abortion, and smaller fruit size. • Developmental consequences were related to changes in plant water relations, including decreased water-use efficiency. Water use in treated plants was three to nine times greater per unit of plant dry mass than in controls.

We investigated effects of landscape-level factors on measures of biodiversity using published descriptions for 98 significant natural areas along the Niagara Escarpment. This is a 725 km, largely forested, Paleozoic limestone escarpment that, excepting the Great Lakes, is the most prominent topographical feature of southern Ontario, Canada. Results show highly significant differences in mean site size and extent of forest interior among natural areas of different ownership classes, with larger and more forested sites being under mixed (private + public) ownership, but no significant difference between sites of public and private ownership. Analysis of covariance demonstrated that after controlling for differences in landscape-level factors (total size of natural area, extent of forest interior, extent of landform heterogeneity and geographic location), most measures of biotic diversity (including the number of vegetation community types, provincially rare vascular plants, and regionally and locally rare breeding birds) differed significantly among sites of private, public and mixed ownership. In general, values at public and mixed ownership sites were greatest, with significantly lower biodiversity values at privately-owned sites. Furthermore it would seem not to be a product of public bodies having historically purchased the largest sites or most-forested sites, since there is no significant difference between the mean size of publically-owned and privately-owned sites. Results of stepwise multiple regression confirm the well known relation between size of a natural area and variation in both total, and rare species diversity. Since public sites have generally more species than private sites, they are essential elements of any conservation network.

In the coastal littoral forest of extreme southeastern Madagascar, we studied tree diameter at breast height (DBH) $ 10 cm in 20, 50 3 50 m plots in each of four forest fragments, and understory woody vegetation (DBH , 10 cm, $1 m tall) in 60, 10 3 10 m plots in three of the fragments. One forest fragment was located in the highly degraded Lokaro region, and three in the nearby Sainte-Luce forest. A total of 3476 trees, representing 169 species in 55 families, were recorded in the 50 3 50 m plots, and 10 282 understory stems, representing 195 species in 54 families, were found in the 10 3 10 m plots. For each tree, DBH was recorded. Mean tree diameter and patterns of tree size class distribution did not differ among the four forest fragments. However, the fragments differed significantly in both tree and understory stem densities, species richness and diversity values, and family richness values, with the Lokaro fragment having the lowest values for all measures. Furthermore, floristic patterns, family importance values, and community similarity measures revealed that the species composition at the Lokaro fragment was very different from the Sainte-Luce fragments. Anthropogenic disturbance appears most pronounced in the isolated Lokaro forest, where biotic resources are limited to this single fragment.

Until fairly recently, regional-scale ecological and evolutionarypatterns have tended to be ignored as conservation efforts have been concernedwith species and their habitats. Here we compare frequencies in the Egyptianflora of particular rank sizes (order, family and genus) with patterns ofspecies abundance (classified as very rare, rare, common, or very common) and anarray of life-history attributes. The angiosperm flora of Egypt is representedby 2446 taxa (2088 species), including taxa in 10 subclasses, 51 orders, 120families, and 742 genera. A high degree of monotypism was observed: four ordersare monotypic (each existing as single species), and have very rare overallabundances; 30 families are monotypic (17 of which are very rare or rare); and 354genera are monotypic (over 70% of which are very rare or rare). Fourteenfamilies (in particular the Resedaceae and Zygophyllaceae) have at leastone-fifth of their global species represented in the Egyptian flora. Introducedspecies in general, and tree, aquatic herb and liana life forms all are especially well represented among monotypic genera. Native taxa are highlyrepresented among rare and very rare abundance classes, while introduced taxadid not differ significantly in their abundance patterns, compared to overallflora values. Few large genera (>20 spp.) occur in the flora, with mostspecies concentrated in genera containing 8–19 species per genus.Similarly, few families were highly speciose. Annual and herbaceous species weresignificantly over-represented, mainly among large, speciose genera andfamilies. However, perennials, trees, shrubs, aquatic herbs, lianas and parasiticspecies were found mainly in families and genera having very few taxa.Life-history attributes may have important implications to speciation rates.Taxonomically based results, involving abundances and life-history attributes,are discussed in the context of biodiversity and conservation.

We compared ecological attributes in rare and common native plants of southern Ontario (n = 1,398 flowering plant species; of these, 375 are identified as provincially rare). Compared with patterns...

We compared taxonomic and ecological attributes of native and introduced plants (N = 1330 and 484 species, respectively) of southwestern Ontario, using two regional floras (Essex County and Hamilto...

A floristic and environmental survey was carried out on 22 uninhabited islands (0.1-8.4 ha) in Lake Burollos, Egypt. A total of 58 vascular plant species was recorded. The number of habitats on each island was counted. There was a positive correlation between island area and number of habitat types. Island area was significantly positively correlated with various measures of floristic diversity, including the total number of species present, and the numbers of annual, herbaceous, and shrublet species. Perennial and shrub species numbers did not differ significantly with island area. In addition to island area, elevation and soil salinity, as well as distance to the Mediterranean Sea, all contributed significantly to variation in species composition in the terrestrial habitats. Water salinity and transparency accounted for 69% of the variation in aquatic species numbers. There was a weak effect of isolation on similarity of species composition on islands. Eight vegetation types, represented by 13 indicator species identified after TWINSPAN analysis, were distinguished by soil characteristics. Species richness was inversely correlated with clay, organic carbon and total nitrogen in the soil, but positively correlated with calcium carbonate content. From a management perspective, long-term monitoring of threatened habitats in the lake is urgently required as a starting point to preserve biodiversity. Finally, we conclude that the present study supports the hypothesis indicating that larger areas feature higher species richness due to increased numbers of habitats.

The clonal perennial herb, Arisaema dracontium (L.) Schott., is considered "vulnerable" in Canada but is more abundant in the adjacent northeastern United States. In Canada, sexual reproduction may be limited since the species is self-incompatible, and populations at the edge of a species' range may contain limited genetic diversity. We compared genetic variation in nine enzymes systems, sampled at 19 populations across eastern North America. Based on chromosome counts and interpretable banding patterns, A. dracontium is tetraploid over most of its range (2n = 56). However, plants in Florida were diploid, lacked 10 out of a total of 19 interpretable alleles, had distinct allelic frequencies, and clustered a large distance from the other populations. Some plants from Baton Rouge, Louisiana, were also diploid, but all allozyme samples were tetraploid. Most genetic variation occurred within populations; only 29% of variation was between populations. Individuals in two adjacent, otherwise isolated Ontario populations were fixed for most loci and were balanced heterozygotes for the got-2 locus. All samples but one were also identical for an additional six non-interpretable enzyme banding patterns, suggesting these two populations comprise multiple ramets of a single multilocus genotype, propagated clonally via corms. Ecologically marginal populations were typically more distant from the nearest neighboring population and were more genetically distinct from one another; however, with the exception of the two monoclonal populations, marginal populations were not genetically depauperate.

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as "vulnerable" with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3°C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings.

Morph-specific patterns of success as maternal and paternal parents were studied in a factorial pollination experiment with long-, mid- and short-floral morphs in tristylous Lythrum salicaria L. `Legitimate' pollinations (involving stamens and stigma of similar heights) produced greater fruit and seed set than `illegitimate' intermorph pollinations (involving stamens and stigma of dissimilar heights between different morphs), `illegitimate' intramorph pollinations (between two individuals of the same floral morph) and self-pollinations (pollination involving stamens and stigma of the same flower). The mean rate of germination of seeds produced by legitimate and illegitimate crosses was 81.4% and 72.7%, respectively. The three flower morphs differed significantly in their ability to act as maternal parent but did not differ paternally, following legitimate pollinations. Significantly greater legitimate seed set was recorded for the long morph compared to the short morph, when these individuals acted as maternal parents. Incompatibility (as measured by seed set) was weakest in the mid-morph individuals and strongest in short-morph individuals. Following self-pollination events, pollen from the mid- and long whorls of stamens within a flower produced seeds in the long and mid-morphs, respectively. This suggests that the self-compatibility differs between the two whorls of stamens, and is greater in the longer stamens than in the shorter stamens in the long and mid-morphs.

In plants, environmental effects causing variation in seed mass typically represent the strongest kind of maternal‐environmental effect. The influence of fruit removal on subsequent progeny life‐history traits was evaluated in zucchini, in terms of the amount of time available for seed development and the timing of fruit production. Early‐produced and late‐produced fruits remained on treated plants for only 12 d, whereas on untreated controls, both “early” and “late” fruits remained on maternal plants until full ripening (35–40 d and 20–25 d, respectively). Progeny arising from the four kinds of fruit were compared. Seeds from each type of fruit were weighed individually and categorized into three size classes, then germinated and raised to maturity, including a regular harvesting of all fruits 3‐d postpollination. Seed‐size effects were evident for both vegetative and reproductive traits and carried over to later stages, whereas maternal effects disappeared by day 30 for leaf variables and day 60 for mal...

We assessed the effects of local environment on survival, growth, and development in six clones (genotypes) of Vallisneria americana grown at five sites in the Huron-Erie Corridor. Detrimental effects of local environment on plant performance (rate of clonal growth, leaf and root production, surface area of leaves and roots, plant biomass, rate of flowering, and turion production) were correlated with sediment toxicity and levels of organic contamination determined in independent studies, and differed among plant genotypes. All surviving clones used in the study ranked environmental quality of the five sites in the same order. Two genotypes, which were tolerant of contaminants, survived the 2 yr of exposure at all sites, while other nontolerant clones died within the 1st yr of study, at the two most contaminated sites. The leaf-to-root surface area ratio was highly indicative of site quality, and was not affected either by year-to-year variation, or by differences between genotypes. The use of cloned plants in this biomonitoring study reduced variance, and increased precision and accuracy of site assessment compared to biomonitoring with genetically variable plants. Clones of V. americana tolerant of contaminants were particularly useful in assessing the most contaminated sites. An approach that uses an array of both tolerant and nontolerant clones is recommended.

Natural populations of the evergreen shrub, Thymelaea hirsuta (L.) Endl., were studied over 6 years at five desert habitats, in terms of seedling recruitment and adult survival and as a function of plant size and gender class. Habitat and time significantly influenced mortality of both reproductive and non-reproductive plants. Plant size also significantly affected adult mortality. Seedling recruitment varied significantly with habitat and year and approached zero some years. Significant among-year and among-population variation in population growth rates were observed over the 6 years of study, and all populations declined in size (ranging from −1.7% per year at the coastal dune site to −10.9% per year at the inland plateau site). Spearman rank correlation analysis between habitats ranked according to a north–south gradient and demographic variables indicates that this gradient is associated with a pattern of lower seedling emergence and survival and a lower population growth rate and greater mortality for all size-classes of Thymelaea plants. In experimental botanic garden plots, germination of seed collected from five natural populations, and seedling survival in the following year were assessed under conditions of high, medium, and low seedling density. Seedling emergency differed significantly according to maternal habitat. With regular watering, seeding survival to one year was 72% (averaged across habitats and densities). This compares with 64% for seedlings grown at the highest density, suggesting that the intense mortality observed under field conditions is more likely to be a result of water shortage than intraspecific competition. Key words: Egyptian desert, Thymelaea hirsuta, germination and establishment, seedlings, recruitment, competition, population growth rate.

Macrophytes drifting in the Detroit River were sampled and analysed for contaminants at monthly intervals from September 1990 to September 1991. Twelve species of submersed macrophytes were identified, as well as algae and leaves of terrestrial plants. Drifting plant debris was greatest in August-September, when Potamogeton spp. and Najas sp. predominated. Over the study period, a total of 60.57 times 106 kg fresh mass (3.0285 times 106 kg ash-free dry mass) of plant debris drifted out of Lake St. Clair into the Detroit River annually. Organochlorine content differed between plant taxa and according to the time of year. Annual contaminant burden of the Detroit River by upriver contributions was carried mostly by Potamogeton spp. and Najas sp. Total annual load of organochlorines in drifting plant debris was estimated to be 155 g, including 124 g of PCBs. These bioavailable contaminants may enter the detrital compartment of aquatic food webs, following plant senescence, or may be taken up directly by herbivores. Contaminants associated with plant debris drifting from Lake St. Clair and the Detroit River contribute a significant burden of bioavailable organic contaminants to the western basin of Lake Erie.

Lythrum salicaria (purple loosestrife) is an exotic weed that arrived in North America from Europe during the early 1800s. It is a herbaceous perennial with a trimorphic breeding system. Seventy-four populations of L. salicaria were surveyed from Windsor, Ontario, to the Gaspé Peninsula in Quebec. Fifty of the populations were significantly anisoplethic (i.e., unequal frequencies of the three flower morphs), including 10 populations that were nontrimorphic. Populations with fewer than 100 plants tended to have one or even two morphs missing. Although larger populations rarely lacked a morph, they did show significantly skewed morph frequencies. Indices of clonal size, such as number of ramets per genet and genet diameter, differed significantly among sites, and clonal growth also showed significant interaction between morph and site. One-way analyses of variance indicated that morphs differed in terms of either number of ramets per genet or genet diameter in 16% of populations. Morphometric analyses of flowers from 49 populations showed significant variability in floral traits among genets, flower morphs, and sites. Results indicated frequent reduction in herkogamy (spatial separation between anther and stigma), with variant flowers having very little or no stigma–anther separation. Mean stigma–anther separation was lowest in the mid-morph individuals, followed by the short and long morphs. Correspondingly, the frequency of variant flowers was greatest in mid-morph individuals and least in long-morph individuals. Isoplethic and anisoplethic populations did not differ, for any morph, in the frequency of occurrence of these variant flowers. Key words: Lythrum salicaria, purple loosestrife, isoplethy, morph frequency, heterostyly, variant flowers, stigma–anther separation.

In contrast to their ecological importance, submersed rooted macrophytes have been overlooked in environmental science. Presently, the array of standard phytotoxic bioassays includes only one free-floating vascular macrophyte (Lemna) and several algal species. A short-term and inexpensive assay was studied for feasibility in evaluating sediment quality. Cloned ramets of the macrophyte Vallisneria americana were used to test phytotoxicity of sediments collected at different locations in the Detroit River. Ramets were planted in sediment samples and placed in greenhouse aquaria. After a week of exposure, ramets of V. americana were destructively sampled and preserved. The leaf and root surfaces areas were determined, and plant biomass was recorded for each ramet. An index of the leaf-to-root surface area ratio was a reliable predictor of sediment phytotoxicity; the ratio of leaf-to-root mass was also useful but proved less consistent. Ramets grown in sediments that were relatively less contaminated with organic compounds had lower values of the leaf-to-root surface area ratio, while plants grown in more contaminated sediments had greater values. Results of analyses of variance indicated that the index of leaf-to-root surface area ratio responded to sediment quality but was not significantly affected by either variation in plant genotype or interaction between sediment and plant genotype. There was a significant correlation (p < 0.001) between rank-ordered results of the present greenhouse study and results of leaf-to-root surface area ratios for plants previously surveyed in the field.

Dioecy has evolved independently, many times, among unrelated taxa. It also appears to have evolved along two contrasting pathways: (1) from hermaphroditism via monoecy to dioecy and (2) from hermaphroditism via gynodioecy to dioecy. Most dioecious plants have close cosexual relatives with some means of promoting outcrossing (e.g., herkogamy, dichogamy, self-incompatibility, or monoecy). To the extent that these devices prevent inbreeding, the evolution of dioecy in these species cannot logically be attributed to selection for outcrossing. In these cases, the evolution of dioecy is, we believe, due to selection for sexual specialization. However, in other species, that lack outbreeding close relatives, dioecy may have evolved from gynodioecy (males and hermaphrodites) as an outbreeding device. Subsequent disruptive selection and selection for sexual specialization may have also shaped the evolution of dioecy from gynodioecy in these species, resulting in two genetically determined, constant sex morphs. Both pathways for the evolution of dioecy require the operation of disruptive selection, though the gynodioecy route involves more restrictive disruptive selection and a genetic designation of gender. In contrast, the monoecy route is not dependent on the genetic designation of two sex morphs, but, rather, allows the possibility of sexual intermediates and sexual lability. Both pathways produce one morph in which maleness is suppressed and another in which the female function is negligible or nonexistent—the reproductive mode recognized as dioecy. Evidence is presented here to support the thesis that instances of sexual lability, the presence of an array of sexual intermediates, sex-switching, and sexual niche segregation can be explained in terms of the pathway that was taken in the evolution of a particular dioecious species. In addition, the degree of sexual dimorphism seen in dioecious species is correlated with mode of pollination (insector wind-pollinated) and other ecological factors.

This study was carried out to assess the effects of sediment type, local water column, source of plants, and duration of exposure between 1990 and 1994 upon growth, survivorship and reproduction of Vallisneria americana at two sites in the Huron-Erie corridor of the Great Lakes. The major objective was to determine whether year-to-year variations affect consistency of results using Vallisneria as a biomonitoring tool. Relative annual rankings of results from experimental treatments did not change over a 4-year period. However, most of the absolute measures of plant performance varied significantly between years. Effects on plant growth and development were associated primarily with exposure to water columns, and secondarily to sediments. Measures of plant density, rate of clonal growth, leaf length, number of leaves per m 2 , and plant biomass per m 2 were unusually high in the first year compared with the subsequent 3 years, perhaps due to disturbance associated with set-up of the experiment. Leaf-to-root surface area ratios provided a simple, consistent, and reliable measure of environmental quality. Other measures of plant performance varied significantly from year-to-year and, therefore, are not advised for long-term comparisons. Results of this study indicate that Vallisneria can be an effective temporal biomonitor of environmental quality.

Clonal growth and reproduction in tristylous Lythrum salicaria L. were examined experimentally, using cloned genotypes of each of the three flower morphs, in field studies involving four moisture and three nutrient treatments. Clonal growth was measured in terms of diameter of clones, number of ramets per clone, and total length of ramets, and an index of reproduction was recorded as the total length of infructescence per clone. Neither clonal growth nor reproduction differed significantly among flower morphs, but both differed significantly as a consequence of both moisture and nutrient treatments. The pattern of seasonal growth indicates that ramet production was restricted mainly to the beginning of the season following vigorous vegetative growth. Although flowering began in June, it was restricted to plants in drier treatments in the water-gradient experiment. Characters intrinsic to tristyly (such as lengths of styles and stamens, and allocation of biomass to stamens and pistil) differed significantly among morphs. Soil moisture levels but not fertilizer treatments significantly affected the size of floral structures and biomass. Although absolute levels of biomass allocation to whole flowers and to attractive structures did not differ significantly among morphs, relative allocation to stamens increased progressively from long morph to mid-morph to short morph, with a corresponding decrease in relative mass of pistil. Although proportional allocation differed significantly among morphs, it was unaffected by moisture treatment, suggesting tight genetic control of herkogamy (spatial separation between anther and stigma). This should maintain the floral polymorphism in different ecological conditions. Key words: Lythrum salicaria, nutrient and water gradients, heterostyly, floral morphometry, floral allocation, clonal growth, sexual reproduction.

SUMMARY The effects of removal of fruits of marketable size on investment to male, female and vegetative activities, were evaluated using cantaloupe melons, Cucumis melo L., cv. Retata Degli Ortolani. Leaf and flower demography were used to examine the dynamics of potential trade-offs among these activities. Treated plants and controls had similar total biomass, but it was distributed differently. Treated plants had more vegetative biomass, both above ground and in roots, whereas control plants allocated more, in both absolute and proportionate terms, to fruits. Treated plants produced more leaves than controls, but individual leaf life expectancies were the same. Developing fruits on control plants thus seem to act as sinks at the expense of new leaves. Fruit removal also significantly stimulated production of male flowers and fruit, though these fruits contained significantly fewer, and smaller, seeds. Once fruit removal had begun, lability of floral sex expression was evident. In treated plants there was a significant increase in the production of male flowers. Both treated and control plants produced the same number of pistillate flowers; adjustments of fruit production occurred because of differences in the rate of successful fertilization, and later, differences in fruit set. In control plants (but not in treated plants) there were obvious tradeoffs between yield components. The costs of fruit maturation in treated plants appeared to be decoupled from other yield components.

Phenotypic gender in the evergreen shrub Thymelaea hirsuta was studied at regular intervals over 3–6 years in five natural populations in the western desert of Egypt. Quantitative estimates of gender were calculated for each plant, each year over the entire study period. Plants were also classified using a typological framework, allowing discrimination between plants that followed different flowering phenologies (e.g., dichogamy) but that may have had the same quantitative values of phenotypic gender. Two contrasting patterns of gender were revealed. Approximately one-third of all plants were stable in their gender expression (i.e., they produced the same floral pattern and quantitative gender on every occasion); the remainder had labile gender phenotypes, showing varying degrees and patterns of gender lability. The relative frequency of gender phenotypes differed significantly between sites. Stable unisexual forms were most prevalent at the depression sites, where the water table is closer to the soil surface. Patterns of gender variation in T. hirsuta can be interpreted in terms of a complex evolutionary pathway to dioecy, represented by several intermediate stages, including dichogamous, monoecious, and subdioecious individuals. Alternatively, there may be no directionality to the array; gender phenotypes may reflect localized selection that confers differential fitness on the phenotypes, to the extent that such phenotypes may be heritable. Keywords: dioecy, evolution, Thymelaea hirsuta, labile sex expression, gender variation.

summary The effects of removal of marketable-sized fruits on investment toward male, female and vegetative activities were evaluated using two monoecious varieties of cultivated squash, Cucurbita pepo, cv. Striato d'Itaha o di Napoli, and cv. Zucchini Black. Leaf and flower demography were used to examine potential trade-offs among these activities. Treated individuals produced more leaves, but individual leaf life expectancies were lower than those of controls. Fruit removal also significantly stimulated the production of male and female flowers, fruit and total above-ground biomass. By contrast, permitting the extended process of fruit maturation in controls significantly decreased the overall production of both male and female flowers. There was no significant difference in total fruit mass between treated and control individuals. However, production of female and male flowers was labile, and responsive to the resource relationships operating within the plant. Treated plants produced more female (potentially fruit-bearing) flowers as their fruits were harvested, and both groups of plants produced more male flowers at the end of the season. Overall, the squash cultivar produced almost twice as many male flowers as the zucchini cultivar; the harvesting treatment enhanced male flower production later in the season, and did so earlier in squash than in zucchini. Since reduced fruit production is achieved through reduced production of female flowers rather than through abortion of early fruits, and this precedes the period where resource limitation is anticipated, it is concluded that available resources do not directly prevent fruit development. The results are interpreted in the light of recent artificial selection for one to two large fruits per plant in the case of the squash cultivar and many smaller fruits in the case of the zucchini.

Aquatic macrophytes are useful biomonitors of sub-lethal effects of organochlorine contamination. Ramets of Vallisneria americana were sampled from natural populations at 243 sites in the Huron-Erie corridor in August 1993, and an index of leaf-to-root surface area ratios was determined. Sites were then ranked according to this index. Site rankings based on leaf-to-root surface area ratios were significantly correlated with the ranks of these sites using levels of organochlorine contamination of biota or sediment, reported independently in the published literature. The ratio of leaf-to-root surface areas ranged from 2 to 92, and higher values were found in more polluted sites. At four sites, plants were sampled monthly over one growing season, while at two sites plants were sampled each year for 4 years. The leaf-to-root surface area ratio changed little from year to year. At highly polluted sites there was a progressive increase in ratio over the growing season. Surveyed sites remained in the same relative ranking over the growing season, and a single survey within the same month could compare sites reliably. These results demonstrate that a very simple measure of ratios of leaf-to-root surface areas in Vallisneria may provide a rapid, sensitive, convenient and inexpensive metric of site quality from the perspective of macrophytes and organochlorine contamination. This could be used to prioritize sites for remedial action, and could confirm environmental improvement following remediation.

The value of wetland is now widely recognized; some legislation requires "no net loss" of wetlands, although economic incentives still exist for wetland conversion. Rare plants may be protected by law; however, wetlands are rarely managed specifically to conserve rare species. Furthermore, it is not always clear how the environment should be manipulated to increase the abundance of such species, since necessary autecological details are rarely available. Species conservation involves demographic and genetic elements, as well as ethical decisions about the merits of transplanting or importing genes through controlled pollinations. Rare species may serve as indicators of habitat quality, although this will depend on the reasons behind the species' rarity. There is a need for multiple-use management plans that incorporate species- and habitat-conservation goals and that implement overall strategies to maintain or enhance the total quantity and quality of wetlands. Key words: rare plants, management, wetland conservation, habitat conservation.

Gender phenotypes of Thymelaea hirsuta (L.) Endl. were recorded at five natural populations during regular visits occurring 3–6 times per year over a period of 3–6 years. Plant gender was quantifie...

Fruits of Vallisneria americana were collected in late September from four sites along the Huron-Erie Corridor, on the Canadian side of this connecting channel between Michigan and Ontario. Some fr...

In a number of disciplines including ecology, ecotoxicology, water quality management, water resource management, fishery biology etc., there is significant interest in the testing of new materials, environmental samples (of water or sediments) and specific sites, in terms of their effects on biota. In the first instance, we consider various sources of aquatic pollution, sources typically associated with developed areas of the world. Historically, much water quality assessment has been performed by researchers with a background in chemistry or engineering, thus chemical analysis was a dominant form of assessment. However, chemical analyses, particularly of such materials as organochlorines and polyaromatic hydrocarbons can be expensive, and local environmental factors may cause the actual exposure of an organism to be little correlated with chemical concentrations in the surrounding water or sediments. To a large extent toxicity testing has proceeded independently of environmental quality assessment in situ, and the work has been done by different, and differently-trained researchers. Here we attempt to bring together the various forms of biological assessment of aquatic pollution, because in our opinion it is worth developing a coherent framework for the application of this powerful tool. Biotic assessment in its most primitive form involves the simple tracking of mortality in exposed organisms. However, in most natural environments it is extended, chronic exposure to contaminants that has the most wide-ranging and irreversible repercussions--thus measures of sub-lethal impairment are favoured. From an ecological standpoint, it is most valuable to assess ecological effects by direct study of in situ contaminant body burdens and impairment of growth and reproduction compared with 'clean' sites. A distinction is made here between bioindication and biomonitoring, and a case is made for including aquatic macrophytes (angiosperms) in studies of contaminant levels and effects in the biota. It is apparent that there is a concurrent need for laboratory-based testing of new industrial by-products before any are released in the environment, and such studies should aid the investigation of mechanisms and modes of toxicity, but environmental assessment, and tracking of improvements in environmental quality are most effectively achieved by active biomonitoring experiments.

This paper assesses the value of American wildcelery, Vallisneria americana, as a biomonitor of organochlorine contamination. Plants provide a valuable indicator of local environmental conditions and sub-lethal effects of contaminants on growth and reproduction provide a means of assessing both acute and chronic contaminant effects. In a field survey, Vallisneria plants in the St. Clair and Detroit rivers were found to accumulate significant amounts of organochlorine contaminants, and the concentration increased over the season. Root tissue contained the highest concentrations on each occasion, suggesting contaminant transfer occurred from sediments to the roots. A factorial experiment was set up at two stations in the channel connecting Lakes Huron and Erie to assess the separate effects of contaminant concentrations in the sediment, water column, and source population of the plants, upon growth and reproduction of Vallisneria plants. Contaminant concentrations in sediment and plant tissues were also measured to correlate contaminant content and demographic effects. A clear relationship between exposure to contaminants and effect (on plant performance) was observed. Results indicated that exposure first to the water column, and secondarily to the sediments from the more contaminated site had detrimental effects on plant performance and survival. Plants at each site appeared to be locally adapted and differed in their apparent resistance to organochlorine contaminants. An “impairment index” (reflecting relative plant performance) was calculated and can be used to calibrate the degree of contamination of different sites relative to a “clean” reference site. This may allow prioritization of remediation of contaminated sites, and should allow field managers to track and document the restoration of environmental quality in recognized Areas of Concern in the Great Lakes.

Seed banks and sexual reproduction are known to be significant in colonization and re-establishment of some aquatic macrophyte communities. For highly clonal aquatic macrophytes, however, there is a lack of information on seed production and seed fate as compared with annual sexual species. The seed bank for three populations of Vallisneria americana in the Huron-Erie corridor of the Great Lakes was sampled and quantified in the spring of 1994, and related to seed production in the previous season at these sites. Seed deposition rates during 1994 were also assessed. Sites varied in the proportion of plants flowering and in their tertiary sex ratios, but did not differ in seed numbers produced per unit area. The size of the seed bank was not significantly related to the previous season's seed output, and estimates of seed deposition in the following year tended to be approximately tenfold greater than seed densities found in the seed bank. The stages between seed production and subsequent seed germination are generally very dynamic, with dispersal, mortality, and predation as likely regulating factors. The potential for seedling establishment in V. americana needs to be assessed more fully before the role of seeds in population processes can be determined.

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.