Janice M. Lord

Will loss of snow cover during climatic warming expose New Zealand alpine plants to increased frost damage

If snow cover in alpine environments were reduced through climatic warming, plants that are normally protected by snow-lie in winter would become exposed to greater extremes of temperature and solar radiation. We examined the annual course of frost resistance of species of native alpine plants from southern New Zealand that are normally buried in snowbanks over winter (Celmisia haastii and Celmisia prorepens) or in sheltered areas that may accumulate snow (Hebe odora) and other species, typical of more exposed areas, that are relatively snow-free (Celmisia viscosa, Poa colensoi, Dracophyllum muscoides). The frost resistance of these principal species was in accord with habitat: those from snowbanks or sheltered areas showed the least frost resistance, whereas species from exposed areas had greater frost resistance throughout the year. P. colensoi had the greatest frost resistance (−32.5°C). All the principal species showed a rapid increase in frost resistance from summer to early winter (February–June) and maximum frost resistance in winter (July–August). The loss of resistance in late winter to early summer (August–December) was most rapid in P. colensoi and D. muscoides. Seasonal frost resistance of the principal species was more strongly related to daylength than to temperature, although all species except C. viscosa were significantly related to temperature when the influence of daylength was accounted for. Measurements of chlorophyll fluorescence indicated that photosynthetic efficiency of the principal species declined with increasing daylength. Levels of frost resistance of the six principal alpine plant species, and others measured during the growing season, were similar to those measured in tropical alpine areas and somewhat more resistant than those recorded in alpine areas of Europe. The potential for frost damage was greatest in spring. The current relationship of frost resistance with daylength is sufficient to prevent damage at any time of year. While warmer temperatures might lower frost resistance, they would also reduce the incidence of frosts, and the incidence of frost damage is unlikely to be altered. The relationship of frost resistance with daylength and temperature potentially provides a means of predicting the responses of alpine plants in response to global warming.

Flower color influences insect visitation in alpine New Zealand

Despite a long-standing belief that insect pollinators can select for certain flower colors, there are few experimental demonstrations that free-flying insects choose between natural flowers based on color. We investigated responses of insect visitors to experimental manipulations of flower color in the New Zealand alpine. Native syrphid flies (Allograpta and Platycheirus) and solitary bees (Hylaeus and Leioproctus) showed distinct preferences for visiting certain flower species. These responses were determined, in part, by flower color, as insects also responded to experimental manipulations of visible petal color in 7 out of 11 tests with different combinations of flower species and insect type. When preferences were detected, syrphid flies chose yellow over white petals regardless of flower species, whereas Hylaeus chose white over yellow Ourisia glandulosa. In some cases, the strength and direction of color preference depended on the context of other floral traits, in which case the response usually favored the familiar, normal combination of traits. Syrphid flies also visited in response to floral morphological traits but did not show preference based on UV reflectance. The unusually high preponderance of white flowers in the New Zealand alpine is not explained by complete generalization of flower color choice. Instead, the insect visitors show preferences based on color, including colors other than white, along with other floral traits. Furthermore, they can respond in complex ways to combinations of floral cues, suggesting that traits may act in nonadditive ways in determining pollinator visitation.

Have frugivores influenced the evolution of fruit traits in New Zealand

Fruit-eating animals tend to consume many species of fruit and, likewise, the fruits of plants tend to be consumed by a wide range of animals (Herrera and Jordano, 1981; Wheelwright et al., 1984; Pratt and Stiles, 1985; Charles-Dominique, 1993; Howe, 1993; Larson, 1996; Corlett, 1998; Herrera, 1998). Because of this, the relationship between fleshy-fruited plants and frugivores is diffuse rather than consisting of tight mutualisms (Janzen, 1980; Howe, 1984; Jordano, 1987; Charles-Dominique, 1993). It is thus not surprising that frugivore characteristics rarely appear to influence the evolution of fruit traits (Hedge et al., 1991; Mazer and Wheelwright, 1993; Rey et al., 1997). There is, however, clear empirical evidence that frugivores could exert selective pressure on fruit traits. Frugivorous birds, for example, show preferences related to fruit colour, presentation, accessibility, level of insect damage and fruit size (Moermond and Denslow, 1983; Gautier-Hion et al., 1985; Jordano, 1987; Hedge et al., 1991; Whelan and Willson, 1994; Puckley et al., 1996; Sanders et al., 1997; Gervais et al., 1999), when selecting among fruits on a single plant, fruits of individuals of the same species or fruits of different species (Levey, 1987; Debussche and Isenmann, 1989). However, even when preferences are clear, they may have no directional effect on the evolution of fruit traits, because the composition and abundance of the frugivore assemblage can vary significantly over time (Herrera, 1998). Instead, if frugivore preference influences the evolution of fruit traits at all, it would most probably be via general characteristics of the frugivore assemblage or of dominant guilds of frugivores. Differences in feeding ability or preferences between guilds of frugivores (e.g. birds and mammals) have been linked to differences among fleshy-fruited species in fruit colour, size, odour, protein and lipid content and degree of protection. This has lead to the description of fruit syndromes associated with particular frugivore guilds (van der Pijl, 1969; Janson, 1983; Gautier-Hion et al., 1985; Howe, 1986; Debussche and Isenmann, 1989). However, the concept of syndromes is problematic; the traits used to define them vary from study to study, as does the composition of frugivore guilds. Consider mammalian frugivores as an example: the classical mammal dispersal syndrome involves large, husked or protected, brown, green, orange or yellow fruit, which are often odoriferous and low in protein content

Pollination and seed dispersal in Freycinetia baueriana, a dioecious liane that has lost its bat pollinator

Abstract It has been suggested that Freycinetia haueriana is adapted to bat-pollination. Of the two species of bats in New Zealand that are thought to eat fruit and pollen, one, Mystacina robusta is believed to be extinct and the other, M. tuberculatum is rare. A preliminary study in an area where F. baueriana is abundant but M. tuberculata is locally extinct, found that limited cross-pollination and seed dispersal was still occurring. This would indicate that F. baueriana is not dependent on the presence of bats to perform these functions. Results also indicate that the introduced possum, Trichosurusvulpecula, is acting as a pollinator and disperser of F. baueriana.

Accessory costs of seed production.

Accessory costs of reproduction are those that are necessary to mature a seed, but that do not involve the direct cost of provisioning the seed itself. This study aims to quantify accessory costs in a range of species, and test whether they decrease as a proportion of total reproductive expenditure with increasing seed mass, as might be expected if economies of scale came into play at larger seed sizes. We also test whether accessory costs varied with growth form, pollination mode, and dispersal mode, with the expectation that biotic pollination and dispersal modes should incur greater costs. Reproductive allocation (dry biomass) over one season, was calculated for 14 diclinous angiosperm species. Accessory costs averaged 73% of total reproductive allocation, with the majority spent on packaging and dispersal. Total accessory costs, packaging and dispersal costs, and costs incurred prior to pollination were proportional to direct costs of reproduction in major axis regressions. However, larger seeded species incurred significantly greater costs associated with aborted seeds and fruits, and matured a smaller proportion of ovules. This is consistent with larger seeded species being more selective of the ovules/embryos matured than small-seeded species. Total accessory costs, and proportion of ovules aborted, were also significantly greater for biotically dispersed species, but only due to an association with larger seed masses. Costs associated with abortions were lower for biotically pollinated species, due to a general trend of more ovules per ovary, resulting in greater cost sharing. This study demonstrates that expenditure on items other than seeds accounts for the majority of reproductive allocation in flowering plants. Yet, far more literature exists on seed mass variation than on investment in accessory structures. We found a proportional relationship between accessory costs and seed mass that warrants further investigation within the context of selection on margin returns on investment.

Correlations between growth form, habitat, and fruit colour in the New Zealand flora, with reference to frugivory by lizards

Abstract In New Zealand, frugivory by lizards has been linked to white or pale to sky‐blue hit colours, and divaricate growth forms. Frugivory by lizards might also be expected to be associated with small fruit size, and exposed habitats where dispersal to a moist microsite is crucial to seedling survival. This study tests for correlations between fruit colour and other plant attributes in the New Zealand fleshy‐fruited flora consistent with these predictions. Among New Zealand fleshy‐fruited species, we found that white and blue fruit colours were significantly associated with shrub and divaricate growth forms, small fruit size, open habitats, and montane to alpine altitudinal distributions. Within shrubs and subshrubs, white and blue fruit colours were associated with small fruit size, and with open habitats if Coprosma species were excluded. These results provide some support for the hypothesis that for shrubby species in open habitats, frugivory by lizards may have played a part in the evolution of small pale fruits.

Where have all the blue flowers gone: pollinator responses and selection on flower colour in New Zealand Wahlenbergia albomarginata

Although pollinators are thought to select on flower colour, few studies have experimentally decoupled effects of colour from correlated traits on pollinator visitation and pollen transfer. We combined selection analysis and phenotypic manipulations to measure the effect of petal colour on visitation and pollen export at two spatial scales in Wahlenbergia albomarginata. This species is representative of many New Zealand alpine herbs that have secondarily evolved white or pale flowers. The major pollinators, solitary bees, exerted phenotypic selection on flower size but not colour, quantified by bee vision. When presented with manipulated flowers, bees visited flowers painted blue to resemble a congener over white flowers in large, but not small, experimental arrays. Pollen export was higher for blue flowers in large arrays. Pollinator preference does not explain the pale colouration of W. albomarginata, as commonly hypothesized. Absence of bright blue could be driven instead by indirect selection of correlated characters.

Variation in Festuca novae-zelandiae (Hack.) Cockayne germination behaviour with altitude of seed source

Abstract Festuca novae-zelandiae (Hack.) Cockayne is a widespread, perennial New Zealand grass, occupying a range of habitats. A germination study was conducted using seeds from nine sites in North Canterbury to test for environment-related differences in germination characteristics. Mean seed weight was determined for each seed collection, and germination rate and percentage germination tested for fresh, 6 month old, and 12 month old seeds (stored air-dried). Treatments were: (1) 25°C light/15°C dark; (2) 25°C dark/15°C dark; and (3) 15°C light/5°C dark. All seed collections were polymorphic for germination response. Germination percentages were high in all populations and decreased only slightly after storage of seeds. ANOVA tests indicated significant effects of temperature, light, and seed age on percent germination and germination rate. Significant interactions between these three factors and population indicate that differentiation in germination behaviour has occurred within F. novae-zelandiae. Mea...

Hymenopteran pollinators as agents of selection on flower colour in the New Zealand mountains: salient chromatic signals enhance flower discrimination

Abstract Flowering plants in New Zealand have often been described as having predominantly small white or pale flowers, possibly due to an absence of social insects as a major pollinating force. However, insect vision is considerably different to human perception, and these hypotheses need to be assessed considering insect perceptual capabilities. We collected spectral reflectance data from flowers of 23 native species in an alpine region of New Zealand at an altitude above 1500 m where 77% of flowers have been reported to possess small white or pale flowers. Our spectral analyses show that these flowers actually have very strong chromatic signals for hymenoptera colour vision. Indeed the spectral signals of these flowers most frequently have inflection points at about 400 and 500 nm, which closely match the region of best spectral discrimination by hymenopteran pollinators with a trichromatic visual system. When the flower spectra are plotted in a colour space designed for hymenoptera, the data reveals that most of the flower colours would be well detected against background foliage, and often reliably discriminated from the other flowers appearing in the same alpine environment. We thus demonstrate that New Zealand alpine flowers are actually well suited for visual detection and discrimination by biologically important hymenopteran pollinators.

Microhabitat selection and seasonality of alpine invertebrates

Summary Microhabitat selection is important for invertebrates in both summer and winter, but has not been investigated extensively in alpine terrestrial communities. We investigated the factors affecting microhabitat selection by alpine invertebrates in a system of rock slab pavement on the Rock and Pillar Range, Central Otago, New Zealand. We found fewer individuals of most groups under the 379 rocks re-examined during the winter. Logistic regression was used to model the presence of the cockroach Celatoblatta quinquemaculata (Dictyoptera: Blattidae); the alpine weta Hemideina maori (Orthoptera: Anostostomatidae); and the spider Neoramia childi (Aranea: Agelenidae). We found that rock refuge size and season were extremely important in determining presence of all of these species, and that both abiotic and biotic aspects of rock microhabitat were necessary to describe occupancy. We also found clear evidence of biological interactions between the three species modelled. The marked decrease in under-rock occupancy by C. quinquemaculata in the winter is hypothesised to be a result of selection of alternative (non-rock) microhabitats