J. B. Wilson

Some tests for niche limitation by examination of species diversity in the Dunedin area, New Zealand

Abstract Fifteen plant communities were sampled, each by five randomly-placed quadrats. Bryophyte and vascular plant species were recorded. There were considerable differences between communities in species diversity. These agree with some theories, and conflict with others. Types of community that are young, in evolutionary time, did not seem deficient in species. Human disturbance, and the consequent invasion of exotic species, had very little effect on species diversity, but this seemed to be because of a balance between opposing trends, difficult to relate to niche limitation. Correlation gave no evidence that exotic species displaced natives from a fixed number of niches. Within-community variance in species richness is significantly greater than that predicted from a null model, providing no evidence for the niche limitation theory.

Salt tolerance of salt marsh plants of Otago, New Zealand

Abstract The salt tolerance of 31 species — 29 halophytes constituting a large proportion of the more important species in salt marshes of Otago, and 2 glycophytes — was examined in water culture. The effects of salinity on growth and survival were the main parameters measured. There were considerable differences between species; most could not grow in sea water (3.5% NaCl), although a small number could grow in hypersaline conditions of up to 7.5% NaCl. Some species had a salt requirement for maximum growth, the greatest being 1.5% NaCl, but most grew best in freshwater. No species required saline solutions to survive. In general, the salt tolerance of species decreased from the lower to the upper marsh, which generally parallels field salinities. There were, however, important differences between the shapes of the salt tolerance growth curves, these being related to habitat and, in particular, to the variability of salinity.

Aspects of the ecology of the indigenous shrub Leptospermum scoparium (Myrtaceae) in New Zealand

Abstract Geographic variation in leaf size and shape of the widespread and environmentally-tolerant indigenous shrub Leptospermum scoparium (Myrtaceae) was determined from 182 herbarium specimens collected over much ofits natural range. There were significant correlations with geographic and climatic factors — latitude, distance from coast, annual and winter temperatures. Seventeen seedling populations raised in a uniform environment showed that this leaf variation had a significant genetic component as did the variation in form and the age at first flowering. Flowering phenology in four year old plants from seven widely spread sites also differed significantly when grown together. Ecotypic differentiation is therefore clearly indicated in L. scoparium and this is discussed in relation to previous claims and explanations. Sixteen communities dominated by L. scoparium in southern South Island differed in floristics. The density, basal area, age class distribution, and height of the Leptospermum stems also ...

A survey of the lowland vegetation of the Upper Clutha district of Otago, New Zealand

Abstract The low-altitude parts of the Upper Clutha have the nearest to a continental climate in New Zealand, with little-described vegetation comprising a mixture of native and exotic species. The vegetation ranges from remnants of Kunzea ericoides woodland to a “semi-desert” with bare soil between mats of scabweed (Raoulia australis). A vegetation survey was made, and the vegetation summarised for convenience by Cluster Analysis into eight major communities. The “Salix” community occurs in the wettest sites. Other wet sites had a variety of vegetation, and are categorised as “Wet Miscellaneous”. “Dactylis/Cirsium pasture” includes agricultural pasture plants and weeds. Three drier communities can best be characterised overall by the presence of Rumex acetosella and Vulpia megalura. The “Verbascum/Thymus/Rumex” community tends to have present one or more of V. thapsus, T. vulgaris and R. acetosella. It tends to occur at lower altitude than the following two communities, and on east-facing aspects. The “R...

Non-adaptation in Agrostis capillaris L. (Poaceae)

The idea that all plant species are perfectly adapted to their environment is well embedded in ecology. In an attempt to test this concept, within-species differences in the grass Agrostis capillaris L. (Poaceae) were examined. We randomly sampled genotypes as tillers from populations over a wide environmental range in southern New Zealand, and transplanted them back into their own and each others sites. Growth, floral phenology and tiller population dynamics all gave very little evidence of adaptation at the

Germination in relation to salinity in some plants of salt marshes in Otago, New Zealand

Abstract Germination characteristics were examined for nine halophytes occurring on Otago salt marshes and were compared with two glycophytes. The seed of most halophytes remained dormant, but viable, in saline solution for at least several months. In comparison, of the two glycophyte species, one germinated in saline solution whereas the other suffered seed mortality. There was a correlation between the salt sensitivity of seed and the salt sensitivity of adults of the same species. Perennials, especially those with extensive vegetative reproduction, required lower salinity for germination than did comparable annuals and short-lived perennials. For most species, germination behaviour would not be solely limiting their distribution on a salt marsh.

Ecology of a coastal lagoon to dune forest sequence, south Westland, New Zealand.

Abstract The vegetation and floristic patterns in and around a coastal lagoon are described from quadrat sampling and related to several environmental factors (elevation, water depth, soil organic content, and pH). A cluster analysis was used to identify 14 communities while a detrended correspondence analysis ordinated the quadrats. The ordinations Axis 1 was correlated with water depth/elevation, while Axis 2 was correlated with soil organic content and, in the opposite direction, with soil pH. Two vegetation development sequences are proposed for the dune hollow-ridge system: one in the hollows involving stages of aquatic, bog, and forest vegetation; the second on the ridges where forest composition changes in response to increasing soil development. Rates of succession arepresumably very slow. Formal protection of the lagoon within the World Heritage area is justified because of its ecological, conservation, and scenic values; in light of diminishing natural wetlands; and the common occurrence of a v...

The use of field transplants in determining environmental tolerance in salt marshes of Otago, New Zealand

Abstract Reciprocal transplants of species from different salt marsh zones were performed in a number of areas in coastal Otago. The general pattern was that most species transplanted successfully to all zones at higher elevation, but to only a short distance below the species natural lower elevation limit. Plants at the lower limit of the salt marsh did not, however, survive at sites below the salt marsh. This pattern closely matches one of increasing salt-tolerance with decreasing elevation. Exceptions can be related to some species being intolerant of habitats such as depressions within the marsh or where there are salinity extremes in a variable salinity habitat. It is considered that competition with more salt-tolerant species limits spread to lower elevations, whereas competition with faster growing species of less salt-tolerance limits spread to higher elevations.

Ecotypic differentiation in the ultramafic flora of the South Island, New Zealand

Abstract Fifteen species were investigated for ultramafic tolerance. Seven showed evidence of ecotypes including 4 indigenous species (Luzula crinita var. petriana, Poa colensoi, Neopaxia australasica, and Cotula pyrethrifolia) and 3 widely naturalised grasses (Agrostis tenuis, Anthoxanthum odoratum, and Lolium perenne). Plants from ultramafic populations achieved higher shoot calcium concentrations on ultramafic soil and John Innes Potting Compost, and maintained lower shoot/root ratios on ultramafic soil than plants from non-ultramafic populations. High residual nickel concentrations in shoots of ultramafic clones grown for up to 15 months on non-ultramafic soil suggest that for some species, a preconditioning period longer than the normal 6–8 weeks is required. No evidence of edaphic ecotypes was found in the woody species Nothofagus solandri var. cliffortioides, Griselinia littoralis, or Leprospermum scoparium.

Vegetation patterns in salt marshes of Otago, New Zealand

Abstract Thirteen salt marshes of coastal Otago, New Zealand, were sampled and described using classification and ordination techniques, in an attempt to understand more about vegetation patterns both within marshes and amongst different marshes. Ordination indicates that the same set of primary factors is responsible for the salt marsh vegetation patterns of most marshes. These factors are all related to tides and are difficult to separate. Secondary factors common to most marshes are related to soil moisture, water ponding, and fresh water flow. This consistency results in characteristic and typical salt marsh communities zoned according to these factors. Each marsh, however, has anomalies which may be an important feature of that marsh. These create numerous peculiar and often unique plant communities which characterise the individual marshes. Often they can be correlated with edaphic differences or various cultural effects. With many marshes having been sampled, the simple community relationships seen...