Population divergence in plant species reflects latitudinal biodiversity gradients

The trend for increasing biodiversity from the poles to the tropics is one of the best-known patterns in nature. This latitudinal biodiversity gradient has primarily been documented so far with extant species as the measure of biodiversity. Here, we evaluate the global pattern in biodiversity across latitudes based on the magnitude of genetic population divergence within plant species, using a robust spatial design to compare published allozyme datasets. Like the pattern of plant species richness across latitudes, we expected the divergence among populations of current plant species would have a similar pattern and direction. We found that lower latitudinal populations showed greater genetic differentiation within species after controlling for geographical distance. Our analyses are consistent with previous population-level studies in animals, suggesting a high possibility of tropical peaks in speciation rates associated with observed levels of species richness.     

Environmental gradients and community attributes underlying biodiversity patterns of semi-arid Mediterranean grasslands

Protection and/or establishment of forest plantation have been used as a management strategy to conserve and stop the deterioration of semi-arid Mediterranean grasslands ecosystems, producing a mosaic of vegetation types. This study was intended to investigate the changes in grassland community in response to protection and forest tree plantation practice as well as to explore the underlying environmental gradients responsible for the observed differences or similarities among these vegetation types. Two multivariate analysis methods including discriminate analysis and non-metric multi-dimensional scaling were used to quantify changes in community composition and attributes following different management practices (free grazing, protection with open grassland, sparse and dense forest tree plantations). This was investigated using species frequency, species abundance, or habitat characteristics. The study results showed that habitat types differed significantly between each other and were significantly separated using multivariate approaches. Discrimination based on habitat characteristics and species composition indicated that protection (or grazing) and light (or shade) explained more than 90% of the observed variability in community changes in response to the protection and forest tree plantation. Also, results indicated that shade effect can be attributed to tree canopy cover and/or litter accumulation on the ground. It could be hypothesized that protection from grazing and afforestation resulted in complex environmental gradients of which shade, litter accumulation as well as protection from grazing disturbance are major constituents. A careful manipulation of protection and afforestation can be used to create a spatially different environmental gradients leading to greater habitat diversity as well as a greater species diversity, and better conservation means of grassland in semi-arid areas.     

Marine longitudinal biodiversity: causes and conservation

The horizontal temperature zones of the earth tend to restrict the latitudinal ranges of species but allow the possibility of exceedingly broad longitudinal dispersals. In the Tropical Zone, biodiversity on the continental shelves is not homogeneous but is concentrated in two conspicuous peaks, one in the Indo‐Pacific Ocean and the other in the Atlantic. The Indo‐Pacific biodiversity peak is located within a relatively small area called the East Indies Triangle. The Atlantic peak is located in the southern Caribbean Sea. Evidence that has been accumulated over the years indicates that each area functions as a centre of origin and evolutionary radiation. What are the causes of these concentrations and their present functions? A newly published model indicates a positive relationship between environmental temperature and the rate of speciation. While this helps to explain the generally high tropical diversity, and the negative relationship between diversity and latitude, it does not provide a reason for the longitudinal concentrations. But, other new research serves to substantiate previous indications of a positive relationship between speciation rate and species diversity. The existence of this positive feedback, together with some contributory factors, provides the reason why concentrations occur. The evolutionary radiation probably begins when the build‐up of species diversity reaches a critical level. The warm‐temperate biotas are derived from the tropics. Their northern longitudinal relationships tend to be minor but, in the southern hemisphere, the West Wind Drift is an important dispersal mechanism for both warm‐temperate and cold‐temperate species. The cold‐temperate biotas peaked in two areas, the North Pacific and the Antarctic; each has developed into a centre of origin. The continuous dispersal of well‐adapted species from the centres helps peripheral communities maintain diversity.     

Topical gradients in plant ecology

Plant ecology spans multiple levels of biological organization and spatio-temporal scales, and over four dozen plant ecology textbooks have been published since Warming??s (1895) ??Oecology of Plants.?? With increasing emphasis on specialization, students and teachers can feel paralyzed by the vast literature, and as such may lack an adequate appreciation of the history of the field. The objective of this study was to derive a comprehensive set of topics that are covered in plant ecology textbooks, and to ask (1) what are the most important topical gradients among textbooks, and (2) has the emphasis of topics changed over time? The NMS ordination determined that the first gradient represented a clear contrast in emphasis on physiological ecology versus community ecology. The second gradient represented a contrast in emphasis on abiotic environmental factors versus biotic factors. Negative interactions, growth, demography, gas exchange, mineral nutrition, stress, diversity, disturbance, herbivory, paleoecology, ecosystem ecology, pollution, and global change have increased in emphasis over time. The increasing reliance on data and the number of authors per textbook illustrates how the discipline has matured into a rigorous quantitative science that requires a diversity of specializations. These results can be used to inform the development of curricula within a single course or across several years of study, and to assist the development of new and revised textbooks. Plant ecologists need to be familiar with this core set of topics in addition to becoming an expert in a few of them.     

Use of biotechnologies for the conservation of plant biodiversity

In vitro techniques are very useful for conserving plant biodiversity, including (a) genetic resources of recalcitrant seed and vegetatively propagated species, (b) rare and endangered plant species and (c) biotechnology products such as elite genotypes and genetically engineered material. Explants from recalcitrant seed and vegetatively propagated species can be efficiently collected under field conditions using in vitro techniques. In vitro culture techniques ensure the production and rapid multiplication of disease-free material. Medium-term conservation is achieved by reducing growth of plant material, thus increasing intervals between subcultures. For long-term conservation, cryopreservation (liquid nitrogen, −196°C) allows storing plant material without modification or alteration for extended periods, protected from contaminations and with limited maintenance. Slow growth storage protocols are routinely employed for a large number of species, including numerous endangered plants, from temperate and tropical origin. Cryopreservation is well advanced for vegetatively propagated species, and techniques are ready for large-scale experimentation in an increasing number of cases. Research is much less advanced for recalcitrant species due to their seed characteristics, viz., very high sensitivity to desiccation, structural complexity and heterogeneity in terms of developmental stage and water content at maturity. However, various technical approaches should be explored to develop cryopreservation techniques for a larger number of recalcitrant seed species. A range of analytical techniques are available, which allow understanding physical and biological processes taking place in explants during cryopreservation. These techniques are extremely useful to assist in the development of cryopreservation protocols. In comparison with crop species, only limited research has been performed on cryopreservation of rare and endangered species. Even though routine use of cryopreservation is still limited, an increasing number of examples where cryopreservation is used on a large scale can be found both in genebanks for crops and in botanical gardens for endangered species.     

DNA banking for plant breeding,biotechnology and biodiversity evaluation

The manipulation of DNA is routine practice in botanical research and has made a huge impact on plant breeding, biotechnology and biodiversity evaluation. DNA is easy to extract from most plant tissues and can be stored for long periods in DNA banks. Curation methods are well developed for other botanical resources such as herbaria, seed banks and botanic gardens, but procedures for the establishment and maintenance of DNA banks have not been well documented. This paper reviews the curation of DNA banks for the characterisation and utilisation of biodiversity and provides guidelines for DNA bank management. It surveys existing DNA banks and outlines their operation. It includes a review of plant DNA collection, preservation, isolation, storage, database management and exchange procedures. We stress that DNA banks require full integration with existing collections such as botanic gardens, herbaria and seed banks, and information retrieval systems that link such facilities, bioinformatic resources and other DNA banks. They also require efficient and well-regulated sample exchange procedures. Only with appropriate curation will maximum utilisation of DNA collections be achieved.     

Environmental stress causes oxidative damage to plant mitochondria leading to inhibition of glycine decarboxylase

A cytotoxic product of lipid peroxidation, 4-hydroxy-2-nonenal (HNE), rapidly inhibited glycine, malate/pyruvate, and 2-oxoglutarate-dependent O2 consumption by pea leaf mitochondria. Dose- and time-dependence of inhibition showed that glycine oxidation was the most severely affected with a K(0.5) of 30 microm. Several mitochondrial proteins containing lipoic acid moieties differentially lost their reactivity to a lipoic acid antibody following HNE treatment. The most dramatic loss of antigenicity was seen with the 17-kDa glycine decarboxylase complex (GDC) H-protein, which was correlated with the loss of glycine-dependent O2 consumption. Paraquat treatment of pea seedlings induced lipid peroxidation, which resulted in the rapid loss of glycine-dependent respiration and loss of H-protein reactivity with lipoic acid antibodies. Pea plants exposed to chilling and water deficit responded similarly. In contrast, the damage to other lipoic acid-containing mitochondrial enzymes was minor under these conditions. The implication of the acute sensitivity of glycine decarboxylase complex H-protein to lipid peroxidation products is discussed in the context of photorespiration and potential repair mechanisms in plant mitochondria.     

Pedodiversity deserves attention in plant biodiversity research

We suggest that pedodiversity, an expression of environmental heterogeneity, should deserve the attention of plant ecologists interested to study the spatial pattern of plant biodiversity at different scales. Using the FAO pedological and the IUCN-WCMC biological data bases of the world countries, we show that the prediction on plant biodiversity (number of vascular plants) improves significantly when the extent of the area is combined with pedodiversity in a multiple polynomial regression. Partial correlation analysis proves that, by removing the effect of pedodiversity, the correlation “number of species–area” remains statistically significant for the tropical countries while it loses significance for the countries outside the tropics.     

Canadian wetlands: Environmental gradients and classification

The Canadian Wetland Classification System is based on manifestations of ecological processes in natural wetland ecosystems. It is hierarchical in structure and designed to allow identification at the broadest levels (class, form, type) by non-experts in different disciplines. The various levels are based on broad physiognomy and hydrology (classes); surface morphology (forms); and vegetation physiognomy (types). For more detailed studies, appropriate characterization and subdivisions can be applied. For ecological studies the wetlands can be further characterized by their chemical environment, each with distinctive indicator species, acidity, alkalinity, and base cation content. For peatlands, both chemical and vegetational differences indicate that the primary division should be acidic, Sphagnum-dominated bogs and poor fens on one hand and circumneutral to alkaline, brown moss-dominated rich fens on the other. Non peat-forming wetlands (marshes, swamps) lack the well developed bryophyte ground layer of the fens and bogs, and are subject to severe seasonal water level fluctuations. The Canadian Wetland Classification System has been successfully used in Arctic, Subarctic, Boreal and Temperate regions of Canada.     

Implications of transgenic, insecticidal plants for insect and plant biodiversity

Genetically modified plants are widely grown predominantly in North America and to a lesser extent in Australia, Argentina and China but their regions of production are expected to spread soon beyond these limited areas also reaching Europe where great controversy over the application of gene technology in agriculture persists. Currently, several cultivars of eight major crop plants are commercially available including canola, corn, cotton, potato, soybean, sugar beet, tobacco and tomato, but many more plants with new and combined multiple traits are close to registration. While currently agronomic traits (herbicide resistance, insect resistance) dominate, traits conferring “quality” traits (altered oil compositions, protein and starch contents) will begin to dominate within the next years. However, economically the most promising future lies in the development and marketing of crop plants expressing pharmaceutical or “nutraceuticals” (functional foods), and plants that express a number of different genes. From this it is clear that future agricultural and, ultimately, also natural ecosystems will be challenged by the large-scale introduction of entirely novel genes and gene products in new combinations at high frequencies all of which will have unknown impacts on their associated complex of non-target organisms, i.e. all organisms that are not targeted by the insecticidal protein. In times of severe global decline of biodiversity, pro-active precaution is necessary and careful consideration of the likely expected effects of transgenic plants on biodiversity of plants and insects is mandatory.In this paper possible implications of non-target effects for insect and plant biodiversity are discussed and a case example of such non-target effects is presented. In a multiple year research project, tritrophic and bitrophic effects of transgenic corn, expressing the gene from Bacillus thuringiensis (Bt-corn) that codes for the high expression of an insecticidal toxin (Cry1Ab), on the natural enemy species, Chrysoperla carnea (the green lacewing), was investigated. In these laboratory trials, we found prey-mediated effects of transgenic Bt-corn causing significantly higher mortality of C. carnea larvae. In further laboratory trials, we confirmed that the route of exposure (fed directly or via a herbivorous prey) and the origin of the Bt (from transgenic plants or incorporated into artificial diet) strongly influenced the degree of mortality. In choice feeding trials where C. carnea could choose between Spodoptera littoralis fed transgenic Bt-corn and S. littoralis fed non-transgenic corn, larger instars showed a significant preference for S. littoralis fed non-transgenic corn while this was not the case when the choice was between Bt- and isogenic corn fed aphids. Field implications of these findings could be multifold but will be difficult to assess because they interfere in very intricate ways with complex ecosystem processes that we still know only very little about. The future challenge in pest management will be to explore how transgenic plants can be incorporated as safe and effective components of IPM systems and what gene technology can contribute to the needs of a modern sustainable agriculture that avoids or reduces adverse impacts on biodiversity? For mainly economically motivated resistance management purposes, constitutive high expression of Bt-toxins in transgenic plants is promoted seeking to kill almost 100% of all susceptible (and if possible heterozygote resistant) target pest insects. However, for pest management this is usually not necessary. Control at or below an established economic injury level is sufficient for most pests and cropping systems. It is proposed that partially or moderately resistant plants expressing quantitative rather than single gene traits and affecting the target pest sub-lethally may provide a more meaningful contribution of agricultural biotechnology to modern sustainable agriculture. Some examples of such plants produced through conventional breeding are presented. Non-target effects may be less severe allowing for better incorporation of these plants into IPM or biological control programs using multiple control strategies, thereby, also reducing selection pressure for pest resistance development.     

Evolving ecological networks and the emergence of biodiversity patterns across temperature gradients

In ectothermic organisms, it is hypothesized that metabolic rates mediate influences of temperature on the ecological and evolutionary processes governing biodiversity. However, it is unclear how and to what extent the influence of temperature on metabolism scales up to shape large-scale diversity patterns. In order to clarify the roles of temperature and metabolism, new theory is needed. Here, we establish such theory and model eco-evolutionary dynamics of trophic networks along a broad temperature gradient. In the model temperature can influence, via metabolism, resource supply, consumers' vital rates and mutation rate. Mutation causes heritable variation in consumer body size, which diversifies and governs consumer function in the ecological network. The model predicts diversity to increase with temperature if resource supply is temperature-dependent, whereas temperature-dependent consumer vital rates cause diversity to decrease with increasing temperature. When combining both thermal dependencies, a unimodal temperature-diversity pattern evolves, which is reinforced by temperature-dependent mutation rate. Studying coexistence criteria for two consumers showed that these outcomes are owing to temperature effects on mutual invasibility and facilitation. Our theory shows how and why metabolism can influence diversity, generates predictions useful for understanding biodiversity gradients and represents an extendable framework that could include factors such as colonization history and niche conservatism.