Patterns Of Community Organization Research Articles

Microeukaryotic plankton community dynamics under ecological water replenishment: Insights from eDNA metabarcoding

Ecological water replenishment (EWR) is an important strategy for river restoration globally, but timely evaluation of its ecological effects at a large spatiotemporal scale to further adjust the EWR schemes is of great challenge. Here, we examine the impact of EWR on microeukaryotic plankton communities in three distinct river ecosystems through environmental DNA (eDNA) metabarcoding. The three ecosystems include a long-term cut-off river, a short-term connected river after EWR, and long-term connected rivers. We analyzed community stability by investigating species composition, stochastic and deterministic dynamics interplay, and ecological network robustness. We found that EWR markedly reduced the diversity and complexity of microeukaryotic plankton, altered their community dynamics, and lessened the variation within the community. Moreover, EWR disrupted the deterministic patterns of community organization, favoring dispersal constraints, and aligning with trends observed in naturally connected rivers. The shift from an isolated to a temporarily connected river appeared to transition community structuring mechanisms from deterministic to stochastic dominance, whereas, in permanently connected rivers, both forces concurrently influenced community assembly. The ecological network in temporarily connected rivers post-EWR demonstrated significantly greater stability and intricacy compared to other river systems. This shift markedly bolstered the resilience of the ecological network. The eDNA metabarcoding insights offer a novel understanding of ecosystem resilience under EWR interventions, which could be critical in assessing the effects of river restoration projects throughout their life cycle.

Functional perspectives on the dynamics of desert lizard assemblages

Ecology has long sought whether there are general assembly rules that underlie patterns of community organization. However, new perspectives of community disassembly and reassembly have emerged as environments depart from baseline conditions due to agents of global change. A trait-based approach can provide insights as to how changes affect performance of a species and their subsequent loss, gain, or persistence in an assemblage. We quantified the spatiotemporal dynamics in species and functional diversity from systematic surveys of local lizard assemblages distributed along an elevation gradient from three surveys in a 50-year period (1950s–2000s) in Big Bend National Park (BBNP), USA. BBNP was subjected to and then released from intensive grazing, which has resulted in changes to vegetative composition and cover. We examine changes in local assemblages in the context lizard functional traits, including thermal niche breadth. We hypothesized that temperature specialists were more likely to colonize or be lost from local sites. Species richness was lowest in the 1950s (N = 3 species), and subsequent surveys revealed that species richness increased in both the 1960s and 2000s (N = 6 and N = 8 species, respectively), but not all sites responded uniformly. We found that functional diversity in this system was not affected by this drastic increase species richness, indicative of functional redundancy in species traits. Lizards that were added to sites tended to be smaller bodied with lower thermal tolerances. Lizards with high preferred body temperatures were locally extirpated from high elevation sites that experienced high shrub encroachment, likely due to a reduction in the preferred thermal gradients these species. These results reveal that long-term desert lizard functional diversity was maintained, but the consequences of changes to functional diversity at the local scale need to be examined further.

Changes in bacterioplankton community structure during early lake ontogeny resulting from the retreat of the Greenland Ice Sheet

Retreating glaciers and ice sheets are among the clearest signs of global climate change. One consequence of glacier retreat is the formation of new meltwater-lakes in previously ice-covered terrain. These lakes provide unique opportunities to understand patterns in community organization during early lake ontogeny. Here, we analyzed the bacterial community structure and diversity in six lakes recently formed by the retreat of the Greenland Ice Sheet (GrIS). The lakes represented a turbidity gradient depending on their past and present connectivity to the GrIS meltwaters. Bulk (16S rRNA genes) and putatively active (16S rRNA) fractions of the bacterioplankton communities were structured by changes in environmental conditions associated to the turbidity gradient. Differences in community structure among lakes were attributed to both, rare and abundant community members. Further, positive co-occurrence relationships among phylogenetically closely related community members dominate in these lakes. Our results show that environmental conditions along the turbidity gradient structure bacterial community composition, which shifts during lake ontogeny. Rare taxa contribute to these shifts, suggesting that the rare biosphere has an important ecological role during early lakes ontogeny. Members of the rare biosphere may be adapted to the transient niches in these nutrient poor lakes. The directionality and phylogenetic structure of co-occurrence relationships indicate that competitive interactions among closely related taxa may be important in the most turbid lakes.

Community (re)organization in an experimentally fragmented forest landscape: insights from occupancy–scale patterns of common plant species

AbstractQuestionHow does experimental habitat fragmentation of a temperate Australian eucalypt forest affect local population patterns of common plant species 22 yr after landscape transformation to a pine plantation?LocationWog Wog Habitat Fragmentation Experiment, southeast Australia.MethodsWe use occupancy–scale relationships to examine the patterns of community organization of common understorey plant species in fragmented forests (small: 0.25 ha; large: 3.062 ha) relative to an intact native forest.ResultsOccupancy–scale patterns for intact forest and large‐sized remnants were isotropic; slope (z) values ranged across all values, from aggregated to scattered. In the smallest remnants, however, mean and median z values, as well as their interquartile range, were significantly lower than expected. The convergence in occupancy–scale relationships in small remnants hints that many of the commonest plant species have become even more common (i.e. aggregated).ConclusionsThe ecological assembly processes that influence common species in small‐sized remnants differ from those in larger remnants and intact forest. Fragmentation effects on assembly processes are greater at smaller patch sizes because these habitats are likely altered by changed environmental filters more so than large patches. Such shifts may have implications for habitat structure, ecosystem function and food web interactions in small remnant forests.

The role of phylogeny in desert rodent community assembly

Recent advances in molecular genetics and phylogenetic reconstruction have the potential to transform ecology by providing new insights into the historical evolution of ecological communities. This study by Stevens and collaborators complements decades of previous research on desert rodents, by combining data from a field study and a phylogenetic tree for Mojave Desert rodents to address patterns and processes of community assembly. The number of coexisting rodent species is positively correlated, and the average phylogenetic distance among these species is negatively correlated with perennial plant species richness. As rodent species diversity increases along a gradient of increasing environmental heterogeneity, communities are composed of increasingly related species: there is a consistent pattern of phylogenetic structure from over-dispersed through random to clumped. I discuss this pattern in the light of complementary results of previous studies. This paper is noteworthy for calling attention to still unanswered questions about how the historical events of speciation, colonization, extinction, and trait evolution and their relationship to past climates and vegetation have given rise to current patterns of community organization.

Between-population Similarity in Intestinal Parasite Community Structure of Pike (Esox Lucius)—Effects of Distance and Historical Connections

The effect of geographical distance on similarity in parasite communities of freshwater fish has received considerable attention in recent years, and it has become evident that these apparently simple relationships are influenced by, among other things, colonization ability of parasites and degree of connectivity between the populations. In the present paper, we explored qualitative and quantitative similarity in the intestinal parasite communities of pike (Esox lucius) in a particular system where previously interconnected groups of lakes became isolated ca. 8,400 yr ago. Contrary to our expectations, we did not find differences in similarity between the lake groups or a negative effect of distance among the populations. This supports the role of common ancestral colonization events and shows that no significant loss of species has occurred during the past 8,000 yr. However, the communities were dominated by a single parasite species, the cestode Triaenophorus nodulosus. The exclusion of this species from the data had a significant negative impact on the community similarities and also revealed a negative relationship between distance and quantitative similarity. This suggests that patterns of community organization may be obscured by a single dominant species. We also highlight the need for further studies in different systems and host species, as well as detailed reanalysis of existing data sets, to unravel the controversy in the relationship between distance and similarity in parasite communities.

Similar patterns of patterns of community organization characterize distinct groups of different trophic levels in the plankton of the NW Mediterranean Sea

Abstract. Planktonic populations were sampled over a 4 week period in the NW Mediterranean, at a site subject to little vertical advection during the Dynaproc 2 cruise in 2004. The characteristics of the phytoplankton, the tintinnid community and the zooplankton have recently been described in detail. Based on these studies, we compared the characteristics of 3 well-circumscribed assemblages of different trophic levels: Ceratium of the phytoplankton, herbivorous tintinnids of the microzooplankton, and large (>500 μm) omnivorous and carnivorous copepods of the metazoan zooplankton. In all three groups, diversity as H' or species richness, was less variable than concentration of organisms. Plotting time against species accumulation, the curves approached plateau values for Ceratium spp, tintinnids and large copepods but only a small number of species were consistently present (core species) and these accounted for most of the populations. For Ceratium core species numbered 10, for tintinnids 11 species, and for large copepods, core species numbered 4 during the day and 16 at night. Ceratium, tintinnids and large copepods showed some similar patterns of community structure in terms of species abundance distributions. Ceratium species were distributed in a log-normal pattern. Tintinnid species showed a log-series distribution. Large copepod assemblages were highly dominated with night samples showing much higher abundances and greater species richness than day samples. However, species abundance distributions were similar between day and night and were mostly log-normal. The paradox of the plankton, describing phytoplankton communities as super-saturated with species, extends to the microzooplankton and zooplankton.

Emerging patterns in the comparative analysis of phylogenetic community structure

The analysis of the phylogenetic structure of communities can help reveal contemporary ecological interactions, as well as link community ecology with biogeography and the study of character evolution. The number of studies employing this broad approach has increased to the point where comparison of their results can now be used to highlight successes and deficiencies in the approach, and to detect emerging patterns in community organization. We review studies of the phylogenetic structure of communities of different major taxa and trophic levels, across different spatial and phylogenetic scales, and using different metrics and null models. Twenty-three of 39 studies (59%) find evidence for phylogenetic clustering in contemporary communities, but terrestrial and/or plant systems are heavily over-represented among published studies. Experimental investigations, although uncommon at present, hold promise for unravelling mechanisms underlying the phylogenetic community structure patterns observed in community surveys. We discuss the relationship between metrics of phylogenetic clustering and tree balance and explore the various emerging biases in taxonomy and pitfalls of scale. Finally, we look beyond one-dimensional metrics of phylogenetic structure towards multivariate descriptors that better capture the variety of ecological behaviours likely to be exhibited in communities of species with hundreds of millions of years of independent evolution.

Effects of growing conditions and source habitat on plant traits and functional group definition

Summary Plant functional groups are used to describe patterns of community organization. However, they are defined either by suites of correlated traits or by species groupings, and the responses of these two definitions to changing environmental conditions are unknown. We assessed 14 growth and morphological traits under low‐ and high‐resource conditions of 42 annual plant species from two source communities in Israel that differed in resource availability. As current theory predicts, plants growing in the high‐resource treatment were larger, had twofold greater relative growth rate (RGR) and thinner leaves, and allocated less biomass to roots than plants grown in the low‐resource treatment. Differences in these traits were less consistent between the two source communities. Instead, taxonomic groups (grasses, legumes and a group of other forbs), regardless of source, differed in most characteristics. Three general groups of species (functional groups) were identified in both resource treatments using cluster analysis on all 14 traits. In both resource treatments monocots were almost completely separated into one distinct cluster, regardless of source habitat, while the two other, mainly dicot, clusters were partially separated by habitat. However, the species composition and trait characterization of the dicot clusters differed strongly between treatments. Under low‐resource conditions the two dicot clusters were separated by size traits and seed mass, but under high‐resource conditions, they were separated by above‐ground size, morphology and RGR. Principal components analysis demonstrated inconsistency in relationships among traits and species groupings between treatments. The first two principal components emphasized different aspects of growth depending on the treatment; the third axis was defined by growth rates. As with the cluster analysis, plots of species scores revealed relatively little separation of species by habitat. The response of each species varies for different traits and with growing conditions. Variation may differ among species within a functional group, producing different definitions of functional groups under different experimental conditions. Because most functional group analyses are performed on data collected without manipulation of growing conditions, conclusions concerning the response of species or communities to changes in environmental conditions may be problematic.

MAMMALS OF THE RIO JURUÁ AND THE EVOLUTIONARY AND ECOLOGICAL DIVERSIFICATION OF AMAZONIA

We describe the nonvolant mammal fauna of the Rio Juruá of the western Amazon of Brazil, based on collections made during a year-long survey of the river. We, along with our colleagues Drs. Claude Gascon and Carlos Peres, designed the field project to examine the effects of the river on the differentiation among terrestrial vertebrates (mammals, birds, and amphibians and reptiles) at both the community and population levels. This monograph examines only the patterns of geographic variation and community structure of the small-bodied mammals. Species inventories were made at 16 primary trapping localities divided into eight pairs of cross-river sites, with two pairs in each of four regions from near the mouth to the headwaters of the Rio Juruá. A total of 81 species of nonvolant mammals were obtained, including nine new to science. Four of these are described herein; the others have been described elsewhere. We used a standardized trapping protocol to assess community structure at each of the 16 localities that included terrestrial and canopy trap stations in floodplain (várzea) and upland (terra firme) forest formations. Supplemental trapping was done in secondary habitats at all sites. We describe these sites, the trap effort expended, and the placement of trap stations relative to local habitats. We also describe each species of marsupial, sciurid rodent, murid rodent, and echimyid rodent encountered; comment on their systematics; and summarize aspects of habitat use, life history, geographic distribution, and geographic differentiation based on morphological and molecular traits. We examine patterns of differentiation in the mitochondrial cytochrome-b gene for samples of 41 of the 45 species of marsupials and rodents obtained within the Rio Juruá Basin, and discuss these patterns from the perspective of the entire Amazon and, in some cases, the Mata Atlântica of coastal Brazil. We also examine patterns of community organization within the Rio Juruá basin and throughout Amazonia, drawing attention to the geographic distribution of what appear to be major faunal units that are independent of habitat differences. Finally, we use principles of phylogeography to analyze patterns of geographic differentiation among the nonvolant mammals with regard to the Riverine Barrier Hypothesis. We show that, while there are few examples of taxa for which the Rio Juruá is apparently a barrier, most taxa either are largely undifferentiated throughout the basin or are sharply divided into reciprocally monophyletic mtDNA haplotype clades separable into upriver and downriver units. We argue that the concordance in the geographic placement of clade boundaries suggests a common history; moreover, both the age of these clades and their geographic position in relation to underlying geological features suggest that landform evolution has been an important, but underappreciated component of diversification within western Amazonia.

Trophic ecology and ecomorphology of fish assemblages in coastal lakes of Benin, West Africa

:The feeding ecology and morphological diversification of fish assemblages of two coastal lakes in southern Benin (West Africa) were examined to compare patterns of community organization. Though located only 18 km apart, the two fish assemblages had dissimilar species composition, and this is largely derived from differences in connectivity to the Gulf of Guinea, salinity and pH. Among the 35 and 20 species sampled from Lake Nokoue (connected with a sea) and Lagoon Toho-Todougba (no sea connection), respectively, only a few species dominated each system. Lake Nokoue was dominated by the perciform Gerres melanopterus and the clupeiform Ethmalosa fimbriata, and Lagoon Toho-Todougba was dominated by the characiform Brycinus longipinnis. In Lake Nokoue, the akadja habitat (dense stands of woody debris installed by humans to attract fishes) had high species richness compared to the other lake habitats. Multivariate procedures were used to examine trophic guilds and the relationship between morphology and diet. Overall, thirteen trophic guilds were identified, with detritivore and piscivore guilds having the most species. Lagoon Toho-Todougba was dominated by detritivorous and insectivorous species and Lake Nokoue, a larger lake with a connection to the sea, was dominated by piscivores. In Lagoon Toho-Todougba, consumption of vegetation and insects was common, but these items were very rare in Lake Nokoue fish diets, possibly because the destruction of its fringing mangroves has reduced their availability for fishes. Despite major differences in taxonomic composition, the two fish assemblages had similar mean values for most morphological traits and morphological-based centroids from multivariate analyses were remarkably similar. Because members of the same feeding guild tended to have similar morphologies, some degree of diet specialization has accompanied morphological diversification in the taxa comprising these communities.

Community organization in a recently assembled fauna: the case of Polynesian ants.

The ant species inhabiting three remote Polynesian islands were censused by hand collecting techniques. Three commonly occurring species, which exhibited complementary distribution patterns, were numerically and behaviorally dominant to other species in the communities in which they occurred. Field observations and laboratory experiments showed that negative interspecific interactions were important in maintaining the exclusive territories of the dominant species. Habitat also played a role in determining the distribution of dominant species. Pairwise tests of association among all species revealed dominant species were commonly positively associated with their own non-overlapping group of subordinate species, forming a large-scale mosaic distribution pattern of dominant and subordinate species. Baiting experiments, conducted with and without the dominant species removed, demonstrated that the presence of the dominant species decreased: (1) the proportion of baits occupied by other species, and (2) overall ant species diversity, at rich food resources. In ant communities where one of the three recognized dominant species was present, the outcome of negative interspecific interactions among species was more predictable than in communities without a recognized dominant. The same patterns were evident regardless of which of the three dominant species was present in the community. These patterns of community organization observed in this relatively newly assembled fauna are very similar to those reported from studies of older ant communities in mainland areas.

Moving out of the Archaic on the Edge of the Southwest

The transition from mobile foragers to sedentary farmers was not made to the same degree all over the southwestern United States and northern Mexico. The deserts of the Jornada Mogollon region illustrate the persistence of some aspects of mobile adaptations through the first millennium A.D., as both Jornada Archaic peoples and their ceramic-using successors made use of a seasonal mobility pattern to cope with the region's arid conditions. Use of winter base camps and mobility during the rest of the year are apparent in both cases, but important differences can also be detected. This study combines old and new data to show how the two adaptations differed in the extent to which winter camps were used, in type and intensity of winter provisioning strategies, and in patterns of community organization. All these changes are argued to be logical precursors to the short-lived agricultural adaptation that appeared in the area after A.D. 1100. Moreover, such adaptations may characterize a large portion of the desert Southwest and northern Mexico.

An Archaeological Correlate of War

War is a critical variable in a large number of theoretical models used in archaeology, yet there has been little research to date on archaeological correlates of war. An archaeological correlate of war based on patterns of community organization is developed and tested using ethnographic data. This correlate is applied to the archaeological record of Mississippian societies in eastern North America, and the presence of warfare during the Mississippian period is confirmed. In addition, it is suggested that the pattern of warfare made evident through Mississippian community organization appears to be one focused solely on riverine centers and not affecting more rural Mississippian communities.

ORGANIZATION OF PREDATOR-PREY COMMUNITIES AS AN EVOLUTIONARY GAME.

We consider a simple predator-prey model of coevolution. By allowing coevolution both within and between trophic levels the model breaks the traditional dichotomy between coevolution among competitors and coevolution between a prey and its predator. By allowing the diversity of prey and predator species to emerge as a property of the evolutionarily stable strategies (ESS), the model breaks another constraint of most approaches to coevolution that consider as fixed the number of coevolving species. The number of species comprising the ESS is influenced by a parameter that determines the predator's niche breadth. Depending upon the parameter's value the ESS may contain: 1) one prey and one predator species, 2) two prey and one predator, 3) two prey and two predators, 4) three prey and two predators, 5) three prey and three predators, etc. Evolutionarily, these different ESSs all emerge from the same model. Ecologically, however, these ESSs result in very different patterns of community organization. In some communities the predator species are ecologically keystone in that their removal results in extinctions among the prey species. In others, the removal of a predator species has no significant impact on the prey community. These varied ecological roles for the predator species contrasts sharply with the essential evolutionary role of the predators in promoting prey species diversity. The ghost of predation past in which a predator's insignificant ecological role obscures its essential evolutionary role may be a frequent property of communities of predator and prey.

Isozyme variation in tropical trees: patterns of genetic organization

Tropical forests have long been of interest to biologists because of their high species diversity and their complicated patterns of community organization. The traditional notion of the rain forest as an ancient, unvarying archive of species has been challenged by a host of recent ecological studies which have demonstrated that tropical trees are diverse in their reproductive biology and dynamic in their population structure.

Popular Groups, Popular Culture, and Popular Religion

This paper examines the emergence and character of popular religious groups and considers their implications for long-term cultural change in Latin America. Particular attention is given to the link between religious change and the creation of apopular subject, a set of confident, articulate and capable men and women, from hitherto silent, unorganized, and dispirited populations. I argue here that creation of such a popular subject is nurtured by transformations in key expressions of popular religion, by the way these take form in new patterns of community organization and group solidarity, and by efforts to rework the ties that bind popular groups to dominant institutions.

The Patch Dynamics Concept of Stream Community Ecology

Stream ecologists are faced with the problem of recognizing patterns in community organization and explaining the processes that determine these patterns. I argue that streams conform reasonably closely to the patch dynamics explanation of community organization which emphasizes temporal phenomena and focusses on the importance of history and chance. Even where competition or predation have been shown to play a role in shaping stream communities, the temporal phenomena of disturbance and colonization are invariably also of fundamental importance. In most cases, temporal variation is probably the factor of overriding significance, and species with weedy characteristics are a particularly prominent feature of streams. I highlight the critical role played by refugia as sources of recolonization after spates, and therefore as buffers against disturbance. A theoretical framework based on the patch dynamics view of community ecology may provide a unifying theme in stream ecology.

Social Organization by Decree in Colonial Highland Guatemala

Ethnographically documented forms of Mesoamerican Indian community organization have frequently been interpreted either as mere survivals of preconquest principles or as the results of general Spanish policies and conditions during the colonial period. This article documents the careers of social units, called parcialidades in Spanish, in three highland Maya communities and demonstrates the importance of Spanish recommendations and rulings in response to local-level disputes in determining present-day variations in community organization. All scholars working in Mesoamerica recognize that significant changes were brought about by the Spanish conquest and subsequent colonial administration. Though much of the impact has traditionally been seen as resulting from general conditions such as population loss or the implementation of regional policies such as encomienda or congregaci6n,' at least one other factor shaped the experience of Mesoamerican Indian people: the specific recommendations and rulings by Spanish officials regarding legal disputes presented by individual communities or their component subdivisions. The subject of highland Maya social organization itself has been of enduring interest to scholars concerned with the region. Much ethnographic effort has been expended in describing similarities and differences in patterns of community organization (Hunt and Nash 1967), resulting in the documentation of a large array of units. Types of municipios (town center, vacant town, and intermediate) and types of pueblos (dual barrio and multiple barrio) have been defined along with numerous other units known from one place or another (including barrios, cantones, parajes, and surname groups). Which, if any, of these units represent continuity with preconquest Maya organizational principles, and which are the reEthnohistory 36: z (Spring I989). Copyright ? by the American Society for Ethnohistory. ccc oOI4-I8oi/89/$I.50. This content downloaded from 157.55.39.104 on Sat, 18 Jun 2016 06:41:27 UTC All use subject to http://about.jstor.org/terms Social Organization in Colonial Guatemala 171 sults of Spanish colonial policies? The answer to this intriguing question would increase our understanding of both preconquest Maya culture and the changes wrought by the Spaniards. Attempts have been made to project some of these organizational patterns back to the immediate preconquest era and beyond; aspects of social and ceremonial organization in Zinacantan have been projected for the lowland Maya back as far as the classic period (Vogt 1964; Cancian I964). Less ambitiously, the extended patrilineal family organization of some Quiche communities has been used as a model in attempts to reconstruct late postclassic highland Maya social organization (Carmack I966, I977, 1981; Fox 1978; Orellana I984). However, such attempts at identifying continuities in social organization have been hampered by their apparent disregard for changes that may have occurred during the colonial and early national periods. This lack of concern is reflected in scanty use of historical documentation to trace patterns of social organization diachronically. These studies have also failed to confirm the ethnographic or historic patterns through comparative historical studies in different communities. Although studies of this sort are not always possible given the area's uneven documentary record, without such precautions we cannot be at all certain that a particular community's organization represents enduring principles from preconquest times or if it is instead the result of later, postconquest modifications. This article traces the contrasting careers of social units Spaniards called parcialidades in three highland Maya communities: Sacapulas, Tecpan Guatemala, and Totonicapan (see Fig. I). We shall examine the wide divergences in Spanish policy toward such units during the colonial period and the reasons for the at times contradictory actions of the Spaniards. Variations in present-day community organization resulted: in Sacapulas, parcialidades represent direct continuity from preconquest units and were perpetuated, largely as a result of Spanish decisions, in a series of legal disputes; in Tecpan, parcialidades were effectively outlawed as a result of their challenge of a corrupt alcalde mayor; and in Totonicapan the Spaniards created a parcialidad from a contingent of Mexican auxiliaries who aided in the conquest of the area for Spain. Most of the documentation on which this study is based consists of the records of a series of formal investigations carried out by Spanish officials for the Audiencia of Guatemala concerning land, special privileges, or the threat of rebellion against the Crown. Naturally, all of these documents were created by and for Spanish officials, but the Indian people's voices and views are revealed in their recorded petitions, statements, and actions, though always distorted somewhat by translation and procedure. It must be clear from the outset that the Spanish colonial administrators had no official concern about the indigenous organization of their Maya This content downloaded from 157.55.39.104 on Sat, 18 Jun 2016 06:41:27 UTC All use subject to http://about.jstor.org/terms

Comparison of plant community–environment relations in two estuarine marshes of northern British Columbia

The Dala and Yakoun estuarine marshes in northern British Columbia were compared to evaluate similarities in species composition, plant communities, and vegetation–environment relationships. The Dala is a fjord-head marsh at the mouth of a glacially fed river with a fresh to brackish salinity regime and a 7-m tidal range. The Yakoun marsh is fed by lowland bog drainage on the Queen Charlotte Islands, has a salt to brackish salinity regime, and a 3-m tidal range. Both marshes contain similar dominant species (Carex lyngbyei, Deschampsia cespitosa, Potentilla pacifica, Triglochin maritimum), but share only about one third of the total (50) vascular species recorded. Four plant community types characterizing three main physiographic zones (low, intermediate, and high) were described at each marsh. Principal component analysis (PCA) of species composition data indicated similarities in general patterns of community organization at both marshes; however, PCA of soil chemical data indicated greater between-marsh differences, especially in intermediate and high zones. Canonical correlation analysis indicated that the Yakoun shows a closer connection between overall vegetation variation and substratum elevation, and a clearer elevational zonation of communities than the Dala. Examination of tidal regime data indicated that the Yakoun experiences steeper gradients in submergence time and flooding frequency than the Dala, thus offering an explanation for the different vegetation–elevation relationships.