Publications

Population Structure and Spatial Pattern in the Dioecious Shrub Ceratiola ericoides

David J. Gibson et al. — Thu, 16 Jul 2009 14:08:19 PDT

The dioecious shrub Ceratiola ericoides (Florida rosemary) dominates xeric, infrequently burned Florida scrub vegetation, often to the near-exclusion of other woody species. We studied the spatial pattern, age, sex and size structure of four populations in Florida, USA: two coastal scrub populations subject to recurrent local disturbances due to sand movement, and two inland scrub populations in sites periodically burned by stand-replacing fires. The age structure of individual genets was estimated from node counts and used to describe the age structure of the populations. The sex ratio of males to females was not significantly different from 1:1, except within a female- biased coastal population subject to frequent sand movement. Node counts indicated that the mean age for reproductive individuals was 15 - 16 yr for the inland populations and 13 - 16 yr for the coastal populations. In all sites, there was no difference in mean age between males and females. Vegetative reproduction was uncommon except for the least-disturbed coastal population where 72 % of the reproductive individuals originated through layering. Individuals were generally randomly dispersed at the coastal sites, whereas significant aggregation of males and females occurred in the inland sites where the populations were initiated following fire. Seedling recruitment was continuous in the disturbed coastal scrub site, where 35 % of the individuals were juveniles. Most juveniles were dispersed from 0.5 to 0.75 m around females. At one of the inland sites, where juveniles comprised 11 % of the population, juveniles were clustered at 0.25 to 5.75 m around females. Coastal populations were all-aged, while inland populations were uneven-aged. Recruitment appears to follow periods of disturbance; infrequent fire in the inland populations and continuous sand movement on the coast are factors initiating recruitment.

Parallel Analysis: a Method for Determining Significant Principal Components

Scott B. Franklin et al. — Thu, 16 Jul 2009 14:08:18 PDT

Numerous ecological studies use Principal Components Analysis (PCA) for exploratory analysis and data reduction. Determination of the number of components to retain is the most crucial problem confronting the researcher when using PCA. An incorrect choice may lead to the underextraction of components, but commonly results in overextraction. Of several methods proposed to determine the significance of principal components, Parallel Analysis (PA) has proven consistently accurate in determining the threshold for significant components, variable loadings, and analytical statistics when decomposing a correlation matrix. In this procedure, eigenvalues from a data set prior to rotation are compared with those from a matrix of random values of the same dimensionality (p variables and n samples). PCA eigenvalues from the data greater than PA eigenvalues from the corresponding random data can be retained. All components with eigenvalues below this threshold value should be considered spurious. We illustrate Parallel Analysis on an environmental data set.

We reviewed all articles utilizing PCA or Factor Analysis (FA) from 1987 to 1993 from Ecology, Ecological Monographs, Journal of Vegetation Science and Journal of Ecology. Analyses were first separated into those PCA which decomposed a correlation matrix and those PCA which decomposed a covariance matrix. Parallel Analysis (PA) was applied for each PCA/FA found in the literature. Of 39 analyses (in 22 articles), 29 (74.4%) considered no threshold rule, presumably retaining interpretable components. According to the PA results, 26 (66.7%) overextracted components. This overextraction may have resulted in potentially misleading interpretation of spurious components. It is suggested that the routine use of PA in multivariate ordination will increase confidence in the results and reduce the subjective interpretation of supposedly objective methods.

The Relationship between the Soil Seed Bank and Above-Ground Vegetation of a Coastal Barrier Island

Paul B. Looney et al. — Thu, 16 Jul 2009 14:08:17 PDT

The germinable soil seed bank is described from a coastal barrier island off the northwest coast of Florida, USA. Soil samples collected from seven vegetation types, recently deposited dredge spoil and unvegetated areas in autumn 1990 and spring 1991 were placed out in greenhouse trays. 110 taxa germinated from the samples with the largest number (41) being C3 perennial dicots. The largest number of taxa germinated from dry (57) and wet (54) swales, the fewest (one species: Heterotheca subaxillaris) from strand. Similarity of seed bank densities to above-ground species cover was low (Jaccard’s Index = 0.36), not different between vegetation types, but higher in the autumn than in the following spring. Compositional gradients in the seed bank and above-ground vegetation determined using DCA ordination were highly correlated and related to distance from mean high water, and plot elevation. At the landscape scale, the seed bank provided an equally clear delineation of vegetation types to that based upon the above-ground vegetation. The seed bank of low disturbance, late-succession vegetation types (wooded dunes, swales, marshes) was well developed (high species richness, emergent density, and percentage annual species) with the exception that the large-seeded woody species (i.e. Quercus spp.) were absent from the wooded dune seed bank. By contrast, a poorly developed and transient seed bank occurred in more frequently disturbed (extensive sand movement, salt spray), early successional dredge spoil, unvegetated areas and strand. These contrasts support a general pattern of increasing seed bank development and a persistent rather than transient seed bank with decreasing disturbance frequency, increasing time since disturbance and successional maturity.

Permutation of Two-Term Local Quadrat Variance Analysis: General Concepts for Interpretation of Peaks

Jonathan E. Campbell et al. — Thu, 16 Jul 2009 14:08:16 PDT

Many ecological studies use Two-Term Local Quadrat Variance Analysis (TTLQV) and its derivatives for spatial pattern analysis. Currently, rules for determining variance peak significance are arbitrary. Variance peaks found at block size 1 and at > 50 % of the transect length are the only peaks whose use is explicitly prohibited. Although the use of variance peaks found at block sizes > 10 % of the transect length have also been warned against, many researchers interpret them regardless. We show in this paper that variance peaks derived from TTLQV are subject to additional ‘rules of thumb’. Through the use of randomization and permutation analyses on real and simulated data of species abundance in contiguous plots along a single transect, we show that variance peaks found at block sizes 1, 2 and 3 occur frequently by chance and thus likely do not indicate biologically meaningful patterns. The use of multiple replicate transects decreases the probability of Type II error.

Species Frequency Dynamics in an Old-Field Succession: Effects of Disturbance, Fertilization and Scale

David J. Gibson et al. — Thu, 16 Jul 2009 14:08:15 PDT

Question: Can patterns of species frequency in an old-field be explained within the context of a metapopulation model? Are the patterns observed related to time, spatial scale, disturbance, and nutrient availability?

Location: Upland and lowland old-fields in Illinois, USA.

Method: Species richness was recorded annually for seven years following plowing of an upland and lowland old-field subject to crossed fertilizer and disturbance treatments (mowing and rototilling). Species occupancy distributions were assessed with respect to the numbers of core and satellite species.

Results: In both fields, species richness became higher in disturbed plots than in undisturbed plots over time, and decreased in fertilized plots irrespective of time. A bimodal pattern of species richness consistent with the Core-satellite species (CSS) hypothesis occurred in the initial seed bank and through the course of early succession. The identity of native and exotic core species (those present in > 90% of blocks) changed with time. Some core species from the seed bank became core species in the vegetation, albeit after several years. At the scale of individual plots, a bimodal fit consistent with the CSS hypothesis applied only in year 1 and rarely thereafter.

Conclusions: The CSS hypothesis provides a metapopulation perspective for understanding patterns of species richness but requires the assessment of spatial and temporal scaling effects. Regional processes (e.g. propagule availability) at the largest scale have the greatest impact influencing community structure during early secondary succession. Local processes (e.g., disturbance and soil nutrients) are more important at smaller scales and place constraints on species establishment and community structure of both native and exotic species. Under the highest intensity of disturbance, exotic species may be able to use resources unavailable to, or unused by, native species.

Effects of Endophyte Infection in Tall Fescue (Festuca Arundinacea: Poaceae) on Community Diversity

Greg Spyreas et al. — Thu, 16 Jul 2009 14:08:15 PDT

Recent studies have suggested that the presence of endophytes in tall fescue can lead to decreased species richness in the associated plant community. To assess the generality of this hypothesis, a field study tested the effects of endophyte infection on a 3-yr-old successional field dominated by Festuca arundinacea. The potential importance of endophyte infection relative to other environmental factors was tested by including two additional treatments: the effects of soil fertility and mowing. Contrary to previous studies, a positive relationship was found between endophyte infection frequency and diversity (N = 23, F = 5.23, R² = 0.19, P < 0.03). A strong interaction was found between the mowing treatment and endophyte infection frequency in predicting diversity (N = 22, F = 36.1, R² = 0.84, P < 0.0001), where the maximum species richness was present in plots that were both mowed and highly endophyte infected. The relationship between endophytes and diversity varied through the successional continuum (the mowing treatments) but was generally positive. The soil in mowed plots was drier than in unmowed plots (t = 2.1, df = 28, P < 0.05). We suggest that heavy mowing decreases soil moisture levels enough to reduce the interspecific competitive ability of infected F. arundinacea, thereby promoting local diversity. Endophyte presence is important, but the previously reported negative relationship between endophyte infection and community diversity is probably overly simplistic in complex ecological settings.

Genetic Diversity and Competitive Abilities of Dalea Purpurea (Fabaceae) from Remnant and Restored Grasslands

Danny J. Gustafson et al. — Thu, 16 Jul 2009 14:08:13 PDT

Allozyme and randomly amplified polymorphic DNA (RAPD) analyses were used to characterize the genetic relationships of Dalea purpurea from remnant and restored Illinois tallgrass prairies and a large remnant tallgrass prairie in Kansas. The remnant Illinois populations were less genetically diverse than the restored Illinois populations and the Kansas population. These restored Illinois populations were established with at least two seed sources that were locally collected. There was little population divergence (F_st = 0.042), which ST is consistent with other perennial forbs, while the genetic relationships among populations reflected geographic proximity. In a greenhouse competition experiment, differences in performance between seedlings was not related to the remnant or restored status of Illinois populations, but plants from Kansas were significantly smaller than Illinois plants. Genetic diversity and competitive ability were not associated with the size of the original source population. Our data indicate that using multiple local seed sources for restoration projects will maintain the local gene pool while enhancing the regional genetic diversity of this species.

Staufferia and Pilgerina: Two New Endemic Monotypic Arborescent Genera of Santalaceae from Madagascar

Zachary S. Rogers et al. — Wed, 01 Oct 2008 12:30:23 PDT

Two new arborescent species of Santalaceae, both endemic to Madagascar, are described in the new monotypic genera, Staufferia Z. S. Rogers, Nickrent & Malécot and Pilgerina Z. S. Rogers, Nickrent & Malécot. Based on available molecular and morphological data, the new species are part of a clade formed with Pyrularia Michx. of Asia and North America, the Indo-Malesian genus Scleropyrum Arn., and the central and western African Okoubaka Pellegr. & Normand. Staufferia is distinguished morphologically from Okoubaka by the smaller inflorescences (4 to 10 vs. 50 to 100 flowers); smaller (1.8–2 × 1.1–1.6 cm vs. ca. 9 × 5 cm), obovoidal (vs. ellipsoidal) fruits; smaller (ca. 1.5 mm vs. 7–8 mm diam.), persistent perianth; thinner (0.5–1 mm vs. 15–20 mm thick), 5-sulcate (vs. smooth) exocarp; and thinner (ca. 0.5 mm vs. 3–4 mm thick), smooth (vs. deeply striate or alveolate) mesocarp. Pilgerina differs from Scleropyrum by the smaller inflorescences (8 to 23 vs. 60 to 100 flowers); pedicellate (vs. sessile) flowers; smaller (1.2–1.9 × 1.7–2.7 cm vs. ca. 3 × 2 cm), broadly transversely ellipsoidal to subspheroidal (vs. obovoidal to pyriform) fruits; and thinner (ca. 0.5 mm vs. 1.5–3 mm thick), smooth or finely striate (vs. deeply striate or alveolate) mesocarp. Both species are illustrated and assigned an IUCN preliminary conservation status of Least Concern (LC).

Phylogenetic relationships and ecological speciation in the mistletoe Tristerix (Loranthaceae): the influence of pollinators, dispersers, and hosts

Amico C. Guillermo et al. — Tue, 09 Sep 2008 21:30:12 PDT

Phylogenies can provide valuable information on biotic and abiotic factors associated with speciation. We examined species relationships in Tristerix (Loranthaceae), a genus of 11 species with an Andean distribution from Colombia to Chile. A previous classification divided Tristerix into subgenera Tristerix (two species) and Metastachys (nine species). We tested this classification by generating a molecular phylogeny of the genus using nuclear ribosomal DNA ITS and chloroplast atpB-rbcL intergenic spacer and trnL-F regions. All partitions generally gave congruent trees, thus a combined analysis was conducted. Tristerix was composed of a northern clade (six species) and a southern clade (four species). Tristerix verticillatus and T. penduliflorus (Metastachys) were strongly supported as members of the (southern) subgenus Tristerix clade. Speciation appears to be correlated with the emergence of matorral and cloud forest biomes and is driven by interactions with pollinators and seed dispersers. Tristerix aphyllus is sister to T. corymbosus of the matorral, not to neighboring temperate forest populations, thus rendering the latter species paraphyletic. This ecological speciation event may have occurred in sympatry. Tristerix provides excellent examples of how, during the orography of the Andes, many dynamic and interacting ecological factors have influenced their speciation.

Mistletoes: Pathology, Systematics, Ecology, and Management

Robert L. Mathiasen et al. — Tue, 09 Sep 2008 21:06:40 PDT

Mistletoes are familiar to most Europeans and North Americans because of the Christmas folklore associated with these parasitic flowering plants (33,116). Some may also know these plants are parasites of trees but do not realize that mistletoes are widespread, ecologically important components of forests worldwide. Although some mistletoe species are damaging pathogens, most do not impact economically valuable crops and forest products but actually play key roles in forest ecosystems. Particularly in Loranthaceae, coevolutionary relationships with birds (involving pollination and seed dispersal) have fueled several adaptive radiations, thus producing one of the most diverse and fascinating life forms on our planet. Here we summarize mistletoe biology, pathology, and management as well as current ecological concepts and their evolution as revealed by molecular phylogenetics.