Vascular plant species richness along latitudinal and altitudinal gradients: a contribution from New Zealand temperate rainforests

Vascular plant species richness is known to often decrease with both increasing latitude and increasing altitude. However, a number of studies have shown the reverse trend and the primary cause of these gradients remains unknown. In the present work, generalized linear models were used to assess the relative importance of latitude and altitude as well as of a number of other factors (mean annual precipita-tion, slope, substrate and forest type) on species richness in temperate rainforests of New Zealand. The effect of Southern beech ( Nothofagus spp.) as dominant canopy species on total species richness was shown to be much smaller than postulated in most previous studies. Within the region studied, altitude had by far the strongest effect on species richness. This effect was independent of latitude and was significant for woody but not for herbaceous vegetation.     

Effect of climate change on mast-seeding species: frequency of mass flowering and escape from specialist insect seed predators

Global surface temperatures are expected to increase by several degrees in the next century, with potentially large but poorly understood impacts on ecological interactions. Here we propose potential effects of increased temperatures on ecologically dominant New Zealand grasses (Chionochloa spp.) that mass flower and mast seed. Twenty-two years’ data from five masting Chionochloa species in New Zealand showed that the cue for heavy flowering was unusually high temperature in the summer of the year before flowering. Attack by predispersal insect seed predators was much reduced in mast years, apparently because predator populations were satiated. Increased temperatures would greatly decrease interannual variation in Chionochloa flowering, allowing seed predator populations to increase and potentially to devastate the seed crop annually. Similar responses are likely in masting species worldwide. This previously unrecognized effect of global warming could have widespread impacts on temperate ecosystems.     

Geographical patterns and determinants of species richness in Mexico across selected families of vascular plants: implications for conservation

Mexico is considered a megadiverse country containing more than 10% of the world's biodiversity. The distribution of this species richness and endemism is different among the different Mexican states. We examined the species richness patterns of 13 families of vascular plants (including ferns, gymnosperms and angiosperms) in Mexico using political divisions (states) as units of analysis. We analysed the species richness values (absolute richness, endemic richness and restrictive richness) of these plant families using stepwise multiple regression analysis, assessing their relationship with a set of 10 environmental variables (expressed as heterogeneity coefficients). A combined cluster analysis with multidimensional scaling analysis (MDS) and an analysis of similarities were also undertaken to define the spatial–geographical patterns. Additionally, we proposed a methodological strategy to determine which states of Mexico have priorities for conservation. Our results suggested that the three species richness values used were significantly predicted by environmental factors, especially by climatic heterogeneity. Notwithstanding that a linear pattern was recognized, the Mexican states were gathered in four groups, which were confirmed by the MDS and the cluster analysis: (1) the Yucatan Peninsula, (2) arid Mexico, (3) the Mexican Transition Zone and (4) the megadiverse states. We proposed that 12 Mexican states include all the environmental conditions and are candidates for developing conservation programmes: (1) Quintana Roo, Tabasco and Yucatán, (2) Baja California, Chihuahua and Sinaloa, (3) Guerrero, Jalisco and Nuevo León and (4) Chiapas, Oaxaca and Veracruz.     

Can spatial variation in epiphyte diversity and community structure be predicted from sampling vascular epiphytes alone?

Aim Non‐vascular epiphytes have been largely ignored in studies examining the biotic and abiotic determinants of spatial variation in epiphyte diversity. Our aim was to test whether the spatial patterning of species richness, biomass and community composition across geographic regions, among trees within regions, and among branches within trees is consistent between the vascular and non‐vascular components of the temperate rain forest flora. Location Coastal lowland podocarp‐broadleaved forests on the west coast of the South Island of New Zealand. Methods We collected single samples (30 × 25 cm) from 96 epiphyte assemblages located on the inner branches of 40 northern rata (Metrosideros robusta) trees. For each sample, branch characteristics such as branch height, branch diameter, branch angle, branch aspect, and minimum and maximum epiphyte mat depth were recorded. The biomass for each individual epiphyte species was determined. Results Northern rata was host to a total of 157 species, comprising 32 vascular and 125 non‐vascular species, with liverworts representing 41% of all species. Within epiphyte mats, the average total organic biomass of 3.5 kg m^?2 of branch surface area consisted largely of non‐living biomass and roots. Vascular and non‐vascular epiphytes showed strikingly different spatial patterns in species richness, biomass and composition between sites, among trees within sites, and among branches within trees, which could not be explained by the branch structural characteristics we measured. The two plant groups had no significant association in community composition (r = 0.04, P = 0.08). However, the species richness of vascular plant seedlings was strongly linked to the presence/absence of lichens. Main conclusions Non‐vascular plants contributed substantially to the high species richness and biomass recorded in this study, which was comparable to that of some tropical rain forests. High variability in community composition among epiphyte mats, and very low correlation with any of the environmental factors measured possibly indicate high levels of stochasticity in seed or spore colonization, establishment success or community assembly among branches in these canopy communities. Although we found some evidence that vascular plant seedling establishment was linked to the presence of lichens and the biomass of non‐living components in the epiphyte mats, there was no correlation in the spatial patterning or determinants of species richness between non‐vascular and vascular plants. Consequently, variation in total epiphyte biodiversity could not be predicted from the measurement of vascular plant diversity alone, which highlights the crucial importance of sampling non‐vascular plants when undertaking epiphyte community studies.     

Analyzing mechanisms regulating diversity in rangelands through comparative studies: a case in the southwestern Pyrennees

The preservation of the floristic diversity of natural ecosystems and the maintenance of extensive livestock grazing are two of the major priorities of European Union agricultural and environmental policies. Temperate natural and seminatural grasslands are among the most threatened ecosystems in Europe. In order to establish the most appropriate management practices that prevent degradation and maintain the richness of these ecosystems, detailed analyses of the mechanisms that regulate biodiversity of the communities are particularly necessary. In this study we make a comparative analysis of the species richness and the diversity of the main rangeland communities in a widespread, heterogeneous area located in the Western Spanish Pyrennees. The nature and the contribution of perennials and annuals to the diversity patterns encountered are studied and related to the mechanisms suggested to regulate diversity in each case. Higher diversity values were reported in more environmentally stressed, xeric and moist communities. High spatial and temporal heterogeneity and low rates of competitive displacement related to the scarcity of basic resources are among the factors suggested to regulate the diversity of these communities. In areas where environmental factors are more favorable, such as perennial-dominated mesic rangelands, the enhancement of the diversity seemed more dependent on biotic disturbances, such as herbivory, that decreased the cover of perennials and favored the recruitment of short-lived species. Dispersal processes related to traditional nomadic grazing allow a flow of species from one rangeland to another but also enhance the establishment of species coming from lowland habitats. Most of the annuals enhancing the diversity of the mesic community were ruderals. The consideration of ruderals as exotics or as species belonging to this grazing ecosystem poses an interesting, controversial topic related to the ecological quality of the diversity estimated for these communities.     

Bryophyte and Lichen Diversity Under Simulated Environmental Change Compared with Observed Variation in Unmanipulated Alpine Tundra

Effects of simulated environmental change on bryophyte and lichen species richness and diversity in alpine tundra were investigated in a 5-year experiment at Latnjajaure, northern Sweden. The experiment had a factorial design including fertilisation and temperature enhancement in one meadow and one heath plant community. Responses in species richness, biodiversity, and species composition of bryophytes and lichens to experimental treatments were compared to the observed variation in six naturally occurring plant communities. The combination of fertilisation and enhanced temperature resulted in a species impoverishment, for bryophytes in the bryophyte-dominated community, and for lichens in the lichen-dominated communities, but the species composition stayed within the observed natural variation. During the course of the study, no species new to the investigated mid-alpine landscape were recorded, but that scenario is realistic within a decade when comparing with the processes seen in vascular plants.     

Canopy and litter ant assemblages share similar climate–species density relationships

Tropical forest canopies house most of the globe''s diversity, yet little is known about global patterns and drivers of canopy diversity. Here, we present models of ant species density, using climate, abundance and habitat (i.e. canopy versus litter) as predictors. Ant species density is positively associated with temperature and precipitation, and negatively (or non-significantly) associated with two metrics of seasonality, precipitation seasonality and temperature range. Ant species density was significantly higher in canopy samples, but this difference disappeared once abundance was considered. Thus, apparent differences in species density between canopy and litter samples are probably owing to differences in abundance–diversity relationships, and not differences in climate–diversity relationships. Thus, it appears that canopy and litter ant assemblages share a common abundance–diversity relationship influenced by similar but not identical climatic drivers.     

Effects of consumers and enrichment on abundance and diversity of benthic algae in a rocky intertidal community

Human alteration of nutrient cycling and the densities of important consumers have intensified the importance of understanding how nutrients and consumers influence the structure of ecological systems. We examined the effects of both grazing and nutrient enrichment on algal abundance and diversity in a high-intertidal limpet-macroalgal community on the South Island of New Zealand, a relatively nutrient-poor environment. We used a fully factorial design with three levels each of grazing (manipulations of limpet and snail densities) and nutrients (nutrient-diffusers attached to the rock). Top-down control by grazers appears to be the driving organizing mechanism for algal communities in this system, with strong negative effects of grazing on algal diversity and abundance across all levels of nutrient enrichment. However, in contrast to the conclusions drawn from the analysis of the whole algal community, there was an interactive effect of grazing and enrichment on foliose algae, an important component of the algal system. When herbivory was reduced to very low levels, enrichment generated increases in the abundance and biomass of foliose algae. As expected, top-down control was the primary determinant of algal community structure in this system, controlling abundance and diversity of macrophytes on the upper shore. Contrary to expectations, however, increased nutrients had no community-wide effects, although foliose algal abundance increases were greatest with high nutrients and reduced grazing. It seems likely that most of the corticated algal species have limited capacity to respond to nutrient pulses in this nutrient-poor environment.     

Does richness of emergent plants affect CO2 and CH4 emissions in experimental wetlands?

1. Plant species richness may affect greenhouse gas emissions because it may change ecosystem productivity. Emergent plants are an important component of wetland ecosystems, but little is known about how emergent plant richness affects greenhouse gas emissions.
2. We assembled experimental communities consisting of 1, 2, 4 or 8 emergent plant species in aquatic microcosms and measured community biomass and emissions of CO₂ and CH₄.
3. Emergent plant richness had little effect on cumulative emissions of CO₂ or CH₄, most likely because it did not affect community biomass. This conclusion is supported by the fact that CO₂ emission was significantly positively related to community biomass. The reason for the unresponsiveness of community biomass to species richness of emergent plants may be that all the plants are in the same functional group so that complementarity among species is weak. CH₄ emissions from monocultures of different species differed greatly.
4. Our results do not support the hypothesis that richness of emergent plants plays an important role in regulating greenhouse gas emissions from wetlands. A significant richness effect on greenhouse gas emissions might be detected in wetlands consisting of different plant functional groups such as emergent, floating and submerged plants.

     

高寒草甸不同草地群落物种多样性与生产力关系研究

生态系统的结构和功能、生物多样性与生产力的关系问题是近年来群落生态学中研究的中心问题,其中,生态系统生产力水平是其功能的重要表现形式,用4种不同草地类型探讨自然群落的物种多样性与生产力关系.结果表明,矮嵩草草甸、小嵩草草甸和金露梅灌丛群落中物种多样性与生产力的关系呈线性增加关系,藏嵩草沼泽化草甸群落中线性增加关系不显著,这表明群落生产力除受物种多样性的影响外,也受物种本身特征和环境资源的影响.不同的环境资源和环境异质性是形成群落结构特征、物种多样性分布格局差异的主要原因之一.