Small-scale Diversity Research Articles

Spatial scales of soil bacterial diversity – the size of a clone

The spatial distribution of the tremendous bacterial diversity in soil partially depends on the broad range of scales of soil physical structures and the size of bacteria. The aim of this article is to collect information on spatial distribution of bacteria, the genetic structure of bacterial populations and communities, and on spatial constraints that operate in soil. This has been addressed by studying the spatial pattern of micro-habitats for various bacterial types and the spatial spread of clones in soil environment. The clones were considered as the units of genetic population structure. Experimental findings from a number of studies provide evidence that in soils a clone and a micro-colony are not necessarily identical. For some bacterial types, members of the same clone have been found far apart. Besides, micro-colonies of a few cells have also been reported. Short-range cell movements seem to be common in soil, in agreement with the observation of high small-scale diversity (millimetre scale). The mechanisms for the spread of clones are complex and probably operate at different spatial scales, even for soil bacteria with no specific vectors. The hypothesis underlying the study of the spatial dimension of diversity is that it can reveal mechanisms of diversity maintenance and contribute to their evaluation, complementing available knowledge of genetic processes.

Urban domestic gardens (I): Putting small-scale plant diversity in context

Abstract As part of a larger survey of biodiversity in gardens in Sheffield, UK, we examined the composition and diversity of the flora in two 1-m2 quadrats in each of 60 gardens, and compared this with floristic data from semi-natural habitats in central England and derelict urban land in Birmingham, UK. Garden quadrats contained more than twice as many taxa as those from any other habitat type. Ca. 33 % of garden plants were natives and 67 % aliens, mainly from Europe and Asia. A higher proportion of garden aliens originated from Asia and New Zealand than in the UK alien flora as a whole; 18 of the 20 most frequent plants in garden quadrats were natives, mostly common weeds. Garden quadrats showed no evidence of ‘nestedness’, i.e. a tendency for scarce species to be confined to the highest diversity quadrats. Conversely, species in all semi-natural and derelict land data sets were significantly nested. Compared to a range of semi-natural habitats, species richness of garden quadrats was intermediate, an...

High foliicolous lichen alpha-diversity on individual leaves in Costa Rica and Amazonian Ecuador

Two individual, dicotyledoneous leaves (125 and 98 cm2 in size) and one composed palm leaf (c. 6800 cm2 in size), gathered at La Selva Biological Station, Costa Rica, and Jatun Satcha Biological Station, Amazonian Ecuador, were screened for small-scale foliicolous lichen diversity. On the dicotyledoneous leaf from Costa Rica, 49 lichens and one lichenicolous fungus were found, while a comparable leaf from Ecuador revealed 46 lichens and two lichenicolous fungi. The palm leaf yielded 81 lichens and one lichenicolous fungus. This is the highest alpha-diversity so far reported for foliicolous lichens on individual leaves and invites for comparison with tree diversity in tropical rain forests. Due to the high proportion of species represented by a single thallus, the taxonomic diversity of lichens on individual leaves (or trees in selected plots) cannot be self-supporting, but reflects a high degree of dispersion or entropy within the community of which the individual leaf (or selected plot) is part. Diversity is therefore fractal, showing similar patterns at different scales, each part of a given community reflecting the entire community. Thus, mechanisms that result in high small-scale diversity must be looked for at the community level.

Difficulties with estimating and interpreting species pools and the implications for understanding patterns of diversity

Evidence has been accumulating that species pools play a major role in regulating variations in small-scale diversity. However, our ability to unambiguously estimate and interpret species pools remains a major impediment to understanding the processes that control patterns of diversity. Two main approaches have been employed to evaluate the relationships between species pools and species diversity. The direct approach has been to estimate the actual sizes of species pools by sampling discrete areas at larger spatial scales and then relating these estimates to samples taken at smaller scales. The indirect approach has been to search for correlations between abiotic environmental factors and patterns of diversity that are indicative of gradients in species pools. Both of these approaches have substantial predictive capability but also have limitations that impair our ability to draw unambiguous interpretations about causal factors. A primary difficulty for the direct approach is in deciding which species in the larger pool of potential species are actually capable of living in a sample. In this regard, the indirect approach requires fewer assumptions and has the ability to detect previously unsuspected gradients in species pools. As with the direct approach, assessing the causes for observed gradients in species pools remains a limitation for the indirect approach. Consideration of experimental studies of potential niches suggests that it may be valuable to distinguish between potential and observed species pools if the role of competitive exclusion is to be fully assessed. This paper concludes by arguing for (1) an increased use of multivariate studies that examine the effects of species pools indirectly and (2) further experimental studies designed to determine potential species pools.

The species richness-biomass relationship in herbaceous plant communities: what difference does the incorporation of root biomass data make?

So far, in all studies on the much-discussed hump-backed relationship between plant community productivity and species richness, productivity has been assessed through plant shoot biomass, i.e. it has been ignored that frequently most of the biomass is produced below ground. We revisited the 27 grassland and forest field-layer communities, studied earlier by Zobel and Liira, to sample root biomass, plant total biomass and root/shoot allocation, and learn how the incorporation of below-ground biomass data would affect the shape of the hump-backed relationship. In order to avoid scaling artefacts we estimated richness as the average count of species per 500 plant ramets (absolute richness). We also included relative richness measures. Relative richness was defined as richness per 500 ramets/size of the actual species pool (the set of species present in the community), relative pool size was defined as size of the actual species pool/size of the regional species pool (the set of species available in the region and capable of growing in the given community). The biomass-absolute richness relationship was humped, irrespective of the biomass measure used, the hump being most obvious when plant total biomass was used as the independent variable. Evidently, the unimodal richness–productivity curve is not a sampling artefact, as suspected by Oksanen. However, relative richness was not related to community biomass (above-ground, below-ground or total). The hump-backed curve is shaped by the sizes of actual species pools in communities, implying that processes which are responsible for small-scale diversity pattern mainly operate on the community level. Neither absolute nor relative richness were significantly related to root/shoot allocation. The presumably stronger (asymmetric) shoot competition at greater allocation to shoots appears not to suppress small-scale richness. However, there is a significant relationship between relative pool size and root/shoot allocation. Relatively more species from regional species pools are able to enter and persist in communities with more biomass allocated into roots.

Small-scale spatial and temporal variations in mid-ocean ridge crest magmatic processes

Data from a suite of closely spaced lava flows recovered within the axial summit caldera and on the crestal plateau of the East Pacific Rise around lat 9°31′N indicate that eruptions on this fast-spreading part of the mid-ocean ridge occur throughout the crestal region and are not restricted to the axis. These eruptions contribute to a complex distribution of basalts of various ages and a significant thickening of seismic layer 2A away from the axis in our study area. Small-scale (<600 m) diversity and nonsystematic distribution of lava types may reflect rapid changes in magma chemistry that occur during crystallization and replenishment in small magma lenses, coupled with the effects of frequent low-volume eruptions both within and outside of the axial summit caldera.