Consistency and variation in kelp holdfast assemblages: Spatial patterns of biodiversity for the major phyla at different taxonomic resolutions

The focus of this study was to measure natural spatial variability in the biodiversity of fauna inhabiting kelp holdfasts in northeastern New Zealand at several spatial scales: from meters up to hundreds of kilometers. We wished to test the hypothesis that multivariate variation and biodiversity would vary significantly at different spatial scales in different ways for the major phyla in the holdfast community (Arthropoda, Annelida, Mollusca and Bryozoa). Biodiversity was considered in terms of richness, total abundance, structural composition (as measured by the Bray-Curtis dissimilarity measure) and taxonomic breadth for each major phylum and for the assemblage as a whole. We also examined the effect of taxonomic resolution on multivariate patterns. Species richness and total abundance increased with increases in holdfast volume. Multivariate variation was greatest at the smallest spatial scale for all phyla, but different phyla showed different patterns of multivariate variation at different spatial scales. Variations among locations at the largest spatial scale were primarily due to differences in the composition and richness of bryozoans and molluscs. Location effects became less and less distinct with decreases in taxonomic resolution. There were very few significant differences in richness or abundance for holdfasts of a given volume, taxonomic breadth did not vary significantly across locations, nor did the proportional abundances of phyla. These consistencies across large spatial scales in the absence of environmental impacts and results from other studies suggest that holdfast communities in New Zealand systems would provide a useful model assemblage against which future impacts may be detected as changes in proportions of component phyla. In addition, high variability detected at small and large scales at the species level, especially for bryozoans and molluscs, suggest that these communities may also provide unique opportunities for studying and understanding sources and functions of marine biodiversity.     

Optimal foraging constrains macroecological patterns: body size and dietary niche breadth in lizards

Aim  To explore and identify probable mechanisms contributing to the relationships among body size, dietary niche breadth and mean, minimum, maximum and range of prey size in predaceous lizards.
Location  Our data set includes species from tropical rainforests, semi-arid regions of Brazil, and from deserts of the south-western United States, Australia and the Kalahari of Africa.
Methods  We calculated phylogenetic and non-phylogenetic regressions among predator body size, dietary breath and various prey size measures.
Results  We found a negative association between body size and dietary niche breadth in 159 lizard species sampled across most evolutionary lineages of squamate reptiles and across major continents and habitats. We also show that mean, minimum, maximum and range of prey size were positively associated with body size.
Main conclusions  Our results suggest not only that larger lizards tend to eat larger prey, but in doing so offset their use of smaller prey. Reduction of dietary niche breadth with increased body size in these lizards suggests that large predators target large and more profitable prey. Consequently, the negative association between body size and niche breadth in predators most likely results from optimal foraging. Though this result may appear paradoxical and runs counter to previous studies, resources for predators may be predictably more limited than resources for herbivores, thus driving selection for more profitable prey.     

Interspecific differences in population trends of Spanish birds are related to habitat and climatic preferences

Aim Animal monitoring programmes have allowed analyses of population trends, most of which now comment on the possible effect of global climate change. However, the relationship between the interspecific variation in population trends and species traits, such as habitat preferences, niche breadth or distribution patterns, has received little attention, in spite of its usefulness in the construction of ecological generalizations. The objectives of this study were: (1) to determine whether there are characteristics shared among species with upwards or downwards trends, and (2) to assess whether population changes agree with what could be expected under global warming (a decrease in species typical of cooler environments). Location The Spanish part of the Iberian Peninsula (c. 500,000 km²) in the south‐western part of the Mediterranean Basin. Methods We modelled recent breeding population changes (1996–2004), in areas without apparent land use changes, for 57 common passerine birds with species‐specific ecological and distributional patterns as explanatory variables. Results One‐half of these species have shown a generalized pattern towards the increase of their populations, while only one‐tenth showed a significant decrease. One half (54%) of the interspecific variability in yearly population trends is explained considering species‐specific traits. Species showing more marked increases preferred wooded habitats, were habitat generalists and occupied warmer and wetter areas, while moderate decreases were found for open country habitats in drier areas. Main conclusions The coherent pattern in population trends we found disagrees with the proposed detrimental effect of global warming on bird populations of western Europe, which is expected to be more intense in bird species inhabiting cooler areas and habitats. Such a pattern suggests that factors other than the increase in temperature may be brought to discussions on global change as relevant components to explain recent changes in biodiversity.     

Distribution and photobiology of <Emphasis Type="Italic">Symbiodinium</Emphasis> types in different light environments for three colour morphs of the coral <Emphasis Type="Italic">Madracis pharensis</Emphasis>: is there more to it than total irradiance?

The role of symbiont variation in the photobiology of reef corals was addressed by investigating the links among symbiont genetic diversity, function and ecological distribution in a single host species, Madracis pharensis. Symbiont distribution was studied for two depths (10 and 25 m), two different light habitats (exposed and shaded) and three host colour morphs (brown, purple and green). Two Symbiodinium genotypes were present, as defined by nuclear internal transcribed spacer 2 ribosomal DNA (ITS2-rDNA) variation. Symbiont distribution was depth- and colour morph-dependent. Type B15 occurred predominantly on the deeper reef and in green and purple colonies, while type B7 was present in shallow environments and brown colonies. Different light microhabitats at fixed depths had no effect on symbiont presence. This ecological distribution suggests that symbiont presence is potentially driven by light spectral niches. A reciprocal depth transplantation experiment indicated steady symbiont populations under environment change. Functional parameters such as pigment composition, chlorophyll a fluorescence and cell densities were measured for 25 m and included in multivariate analyses. Most functional variation was explained by two photobiological assemblages that relate to either symbiont identity or light microhabitat, suggesting adaptation and acclimation, respectively. Type B15 occurs with lower cell densities and larger sizes, higher cellular pigment concentrations and higher peridinin to chlorophyll a ratio than type B7. Type B7 relates to a larger xanthophyll-pool size. These unambiguous differences between symbionts can explain their distributional patterns, with type B15 being potentially more adapted to darker or deeper environments than B7. Symbiont cell size may play a central role in the adaptation of coral holobionts to the deeper reef. The existence of functional differences between B-types shows that the clade classification does not necessarily correspond to functional identity. This study supports the use of ITS2 as an ecological and functionally meaningful marker in Symbiodinium.     

太白红杉群落优势种的生态位研究

应用Levins和Shannon-Wiener生态位宽度指数及Pianka生态位重叠指数,研究了太白红杉群落12个优势种的生态位宽度和生态位重叠。结果表明,乔木层中太白红杉的生态位宽度最大,对高海拔地区的环境适应能力较强,巴山冷杉对的低海拔地区的环境适应能力较强;灌木层中香柏的生态位宽度最大,华西忍冬、华西银腊梅、太白忍冬次之,头花杜鹃的生态位宽度最小。乔木层中太白红杉与巴山冷杉的生态位重叠较大,但二者只在低海拔分布范围有重叠;灌木层头花杜鹃的分布范围较大,与其它3个种的生态位重叠也最大,另外3个种的生态位重叠较小;草本层中毛状苔草、羊茅和嵩草的生态位重叠较大,而大叶碎米荠和太白银莲花的生态位重叠较小。     

Butterfly host plant range: an example of plasticity as a promoter of speciation?

Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity and present our interpretation of how West-Eberhard’s scenario may result in speciation driven by plasticity in host utilization. We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal interpretation of the most efficient way in which West-Eberhard’s theory could account for plasticity-driven speciation. A major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules of genetic machinery for utilizing different plants.     

Biomass and morphology of fine roots in temperate broad-leaved forests differing in tree species diversity: is there evidence of below-ground overyielding?

Biodiversity effects on ecosystem functioning in forests have only recently attracted increasing attention. The vast majority of studies in forests have focused on above-ground responses to differences in tree species diversity, while systematic analyses of the effects of biodiversity on root systems are virtually non-existent. By investigating the fine root systems in 12 temperate deciduous forest stands in Central Europe, we tested the hypotheses that (1) stand fine root biomass increases with tree diversity, and (2) ‘below-ground overyielding’ of species-rich stands in terms of fine root biomass is the consequence of spatial niche segregation of the roots of different species. The selected stands represent a gradient in tree species diversity on similar bedrock from almost pure beech forests to medium-diverse forests built by beech, ash, and lime, and highly-diverse stands dominated by beech, ash, lime, maple, and hornbeam. We investigated fine root biomass and necromass at 24 profiles per stand and analyzed species differences in fine root morphology by microscopic analysis. Fine root biomass ranged from 440 to 480 g m⁻² in the species-poor to species-rich stands, with 63–77% being concentrated in the upper 20 cm of the soil. In contradiction to our two hypotheses, the differences in tree species diversity affected neither stand fine root biomass nor vertical root distribution patterns. Fine root morphology showed marked distinctions between species, but these root morphological differences did not lead to significant differences in fine root surface area or root tip number on a stand area basis. Moreover, differences in species composition of the stands did not alter fine root morphology of the species. We conclude that ‘below-ground overyielding’ in terms of fine root biomass does not occur in the species-rich stands, which is most likely caused by the absence of significant spatial segregation of the root systems of these late-successional species.     

Morphological and physiological variation among seagrass (Zostera marina) genotypes

Intraspecific variation in habitat-forming species can have important ecological consequences at the population, community, and ecosystem level. However, the contribution of genetic variation among individuals to these effects is seldom documented. We quantified morphological and physiological variation among genotypes of a marine foundation species, the seagrass Zostera marina. We grew replicate shoots of eight genetically distinct Zostera individuals collected from Bodega Bay, California, in a common garden environment and then quantified shoot production and morphology, nutrient uptake, and key photosynthetic parameters. We found that genotypes differed in shoot production, biomass, and both root and shoot nutrient uptake rates, even when corrected for genotype-specific biomass differences. In addition, the rank order of uptake ability differed for ammonium and nitrate, indicating that genotypes may exhibit resource partitioning of different forms of nutrients. Our results suggest that both niche complementarity among genotypes and the sampling/selection effect could contribute to previously observed positive effects of seagrass clonal diversity on resource utilization and biomass production. Further, they highlight that genotypic variation in key traits of habitat-forming species could have measurable effects on community structure and function.     

Assessing the scale-specific importance of niches and other spatial processes on beta diversity: a case study from a temperate forest

Niche processes and other spatial processes, such as dispersal, may simultaneously control beta diversity, yet their relative importance may shift across spatial and temporal scales. Although disentangling the relative importance of these processes has been a continuing methodological challenge, recent developments in multi-scale spatial and temporal modeling can now help ecologists estimate their scale-specific contributions. Here we present a statistical approach to (1) detect the presence of a space–time interaction on community composition and (2) estimate the scale-specific importance of environmental and spatial factors on beta diversity. To illustrate the applicability of this approach, we use a case study from a temperate forest understory where tree seedling abundances were monitored during a 9-year period at 40 permanent plots. We found no significant space–time interaction on tree seedling composition, which means that the spatial abundance patterns did not vary over the study period. However, for a given year the relative importance of niche processes and other spatial processes was found to be scale-specific. Tree seedling abundances were primarily controlled by a broad-scale environmental gradient, but within the confines of this gradient the finer scale patchiness was largely due to other spatial processes. This case study illustrates that these two sets of processes are not mutually exclusive and can affect abundance patterns in a scale-dependent manner. More importantly, the use of our methodology for future empirical studies should help in the merging of niche and neutral perspectives on beta diversity, an obvious next step for community ecology. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.