Seed dormancy in Rumex species in response to environmental factors

Abstract. Many Rumex species show similar seed dormancy characteristics but there is more information concerning R. crispus and R. obtusifolius than other species. These species respond positively to red or white light. Far-red light applied for short periods may promote or inhibit germination depending on the timing of the irradiation in relation to temperature change; but long periods of far-red inhibit germination. Seeds may also be stimulated to germinate in the dark by low-temperature stratification at 15°C or less providing the temperature of the seeds is subsequently raised to a minimum of about 15°C. Seeds can, however, germinate at lower temperatures providing they have received other appropriate stimulatory treatment. Seeds also respond to alternating temperatures. In a diurnal cycle the minimum upper temperature required is about 15°C and the maximum lower temperature is about 25°C. The optimum period spent at the upper temperature is about 8 h when it is 15–25°C but the optimum period decreases as the upper temperature is increased above this range so that at 45°C, for example, it is only about 30 min. The period spent at the lower temperature in a diurnal cycle is not critical. Providing these criteria are met, the percentage germination increases with the number and amplitude of the cycles. The warming part of the cycle is necessary for the response but so far there is no convincing evidence that cooling itself is important. Secondary dormancy is induced at constant temperatures at a rate dependent on temperature, but apparently only in the presence of oxygen. This feature affects the optimum timing of a temperature change or exposure to light. Strong positive interactions are shown between stimulatory temperature treatments and white or red light. Unlike many other weed species the seeds respond only slightly to nitrate ions. The implications of these responses are discussed in relation to field behaviour.     

Combining environmental suitability and habitat connectivity to map rare or Data Deficient species in the Tropics

The IUCN Red List is a widely accepted system for classifying species’ risk of extinction, based on quantitative criteria. Although IUCN discourages the liberal use of the category “Data Deficient” (DD), most assessed groups have a large number of their species assigned to this category, especially in the Tropics. Therefore, DD species can introduce considerable uncertainty into estimates of proportions of threatened species, and research focused on elucidating the true status of those species should be a priority. Here we propose a simple method to gather information on geographic distribution and guide the search for new populations of rare, small-ranged, forest species, using the literature, online data, and standard GIS procedures. The method involves: (i) creating a geographic distribution model; (ii) selecting the environmentally suitable sites from that model; (iii) removing sites that have lost natural vegetation; and (iv) removing habitat networks that are too small and/or isolated, based on thresholds established from known occurrence records and the literature for ecologically similar species. As a case study, we use Lonchophylla peracchii, a recently described forest-dependent bat endemic to southeastern Brazil. We found that environmentally suitable sites for L. peracchii are already heavily deforested, confirming habitat loss as a major threat. Importantly, we identified five priority sites to search for the species outside of its currently known distribution. From that, we discuss its likely status based on IUCN's Criterion B2 (Extent of Occurrence). This method could be useful for other poorly known forest species, especially in the Tropics where most of these species are, and funding for research and fieldwork is scarcest. Currently there are 1910 terrestrial vertebrates in tropical forest worldwide classified as DD that could be evaluated using this method, provided that they have at least 5–10 occurrence records.     

Cranial postnatal growth of the rat relative to environmental variance

Neurocranial growth during the first 40 days of postnatal development was biometrically investigated relative to the specific parameters of calvarium length and width; basioccipital length and width; basisphenoid length; biparietal width; frontal bone length and cranial vault length. Specimens were obtained from rat litters subject to moderate nutritional suppression by raising the litter numbers above the norm via the cross-fostering technique and causing the overtaxing of the lactational capacity. Alterations in growth rate occurred throughout the pre- and postweaning periods with clearly demarcated phases of growth. Male and female growth in the preweaning period was uniform within each litter type but the phasic growth changes in the experimental litters differed from the control litters with regression line breakage emerging at different points and altering the phasic lengths. The preweaning phasic spectrum in both control and experimental litters was evidently linked to the maternal lactation capacity--relative to quantity and duration. Weaning was insidious in both litter types but occurred earlier in the experimental litters although the continuity of growth was maintained up to the end of the definitive preweaning period (day 20). The definitive postweaning period (day 21-40) showed considerable heterogeneity--unsatisfactory scatter--with differing regression line breakage points and phasic lengths. Analysis based on the total period (day 1-40) brought compensatory adjustments and indicated more acceptable phasic patterns in the postweaning period with confirmation of catch-up growth in the experimental litters. Allometric analysis of the parameters revealed varying rates of growth, line breakage points and differing phasic lengths indicating that each neurocranial parameter and the skeletal unit forming it had an individual characteristic response spectrum mostly attributable to the functional matrix with emphasis on the capsular rather than the periosteal.     

Current problems of environmental gradients and species response curves in relation to continuum theory

Abstract. Comparisons of the positions of species on Grimes'C-S-R triangular ordination model with their responses to individual environmental gradients indicates that the C-S-R model does not necessarily predict species ecological behaviour. The importance of the stress, productivity and disturbance gradients relative to other environmental gradients needs to be determined. In studies of species behaviour along a biomass/productivity gradient the collective vegetation property, biomass, has been confused with the environmental factor, fertility. Patterns of responses to biomass gradients e.g. Keddy's centrifugal model, should be examined in a two-dimensional environmental space to avoid such confounding effects. Assumptions regarding the shapes of species responses to environmental gradients remain untested. A recent model of species response functions to environmental gradients suggested that skewed responses curves show a pattern in the direction of the skew, always with the tail towards the presumed most mesic position on the gradient. Further evidence is presented to support this model for a temperature gradient in eucalypt forest in south-eastern Australia. 21 out of 24 species tested conform to the model.     

Spatiotemporal variance of environmental conditions in Australian artesian springs affects the distribution and abundance of six endemic snail species

Artesian springs in arid Australia house endemic species with very small geographic distributions (most <50 km²). These species have limited dispersal capabilities, but little is known about environmental variance within and across these springs and how it, too, may limit their distribution and abundance. At the Pelican Creek springs complex, the full diversity of endemic gastropod fauna is found only in springs with deep pools, an area thought to provide greater environmental stability. This implies that the distributions of most snail species at this site may be restricted by their narrow environmental requirements and limits. This study monitored spatiotemporal environmental variance in a subset of the Pelican Creek springs (within Edgbaston Reserve) across one year to assess whether pool areas differ from tail areas, and how patterns of abundance of six snail species from three different families correspond to this variance. Springs fluctuated considerably in size, depth, water chemistry and temperature at daily and seasonal scales. Patterns of environmental variance differed across areas; pools were spatiotemporally stable, and tails were ephemeral and environmentally variable. The snail species occupied these areas in different ways. Species restricted to deep springs generally had significantly higher abundance in pool areas, and most had narrow environmental limits. In contrast, species found in a greater number of springs, including those with no pool, occupied pool and tail areas and generally had broader environmental limits. Environmental variance within and across springs affects the distribution of snails in a species-specific fashion. This has important implications for how we study springs and reveals that whilst the vast majority of species are restricted to areas of environmental stability, some can persist in the most environmentally variable areas.     

Sex ratio variance and the maintenance of environmental sex determination

Although variation in population sex ratios is predicted to increase the extinction rate of clades with environmental sex determination (ESD), ESD is still seen in a wide array of natural systems. It is unclear how this common sex-determining system has persisted despite this inherent disadvantage associated with ESD. We use simulation modelling to examine the effect of the sex ratio variance caused by ESD on population colonization and establishment. We find that an accelerating function of establishment success on initial population sex ratio favours a system that produces variance in sex ratios over one that consistently produces even sex ratios. This sex ratio variance causes ESD to be favoured over genetic sex determination, even when the mean global sex ratio under both sex-determining systems is the same. Data from ESD populations suggest that the increase in population establishment can more than offset the increased risk of extinction associated with temporal fluctuations in the sex ratio. These findings demonstrate that selection in natural systems can favour increased variance in a trait, irrespective of the mean trait value. Our results indicate that sex ratio variation may provide an advantage to species with ESD, and may help explain the widespread existence of this sex-determining system.     

BioMove – an integrated platform simulating the dynamic response of species to environmental change

BioMove simulates plant species' geographic range shifts in response to climate, habitat structure and disturbance, at annual time steps. This spatially explicit approach integrates species' bioclimatic suitability and population‐level demographic rates with simulation of landscape‐level processes (dispersal, disturbance, species' response to dynamic dominant vegetation structure). Species population dynamics are simulated through matrix modelling that includes scaling demographic rates by climatic suitability. Dispersal functions simulate population spread. User‐specified plant functional types (PFTs) provide vegetation structure that determines resource competition and disturbance. PFTs respond annually through dispersal, inter‐PFT competition and demographic shifts. BioMove provides a rich framework for dynamic range simulations.     

Near-periodic substitution and the genetic variance induced by environmental change

We investigate a model that describes the evolution of a diploid sexual population in a changing environment. Individuals have discrete generations and are subject to selection on the phenotypic value of a quantitative trait, which is controlled by a finite number of bialleic loci. Environmental change is taken to lead to a uniformly changing optimal phenotypic value. The population continually adapts to the changing environment, by allelic substitution, at the loci controlling the trait. We investigate the detailed interrelation between the process of allelic substitution and the adaptation and variation of the population, via infinite population calculations and finite population simulations. We find a simple relation between the substitution rate and the rate of change of the optimal phenotypic value.     

The response of fish size and species diversity to environmental gradients in two Neotropical coastal streams

Hydrobiologia - This study investigated the effects of environmental variation on fish diversity patterns in two coastal streams in northwestern Ecuador. Specifically, we examined the role of...     

Where the rare species are

Prioritizing geographic areas for conservation attention is important – time and money are in short supply but endangered species are not – and difficult. One popular perspective highlights areas with many species found nowhere else ( Myers et al. 2000 ). Another identifies areas that contain species with fewer close relatives elsewhere ( Faith 1992 ). One might characterize the first as focusing on geographic, and the second on phylogenetic, rarity. To the extent that geographically rare species are at greater risk of extinction ( Gaston & Fuller 2009 ), and that phylogenetically rare species contribute disproportionally to overall biodiversity ( Crozier 1997 ), it would seem reasonable to formally integrate the two approaches. In this issue, Rosauer et al. (2009) do just that; their elegant combined metric pinpoints areas missed out when the two types of rarity are looked at in isolation.     

The mean and variance of environmental temperature interact to determine physiological tolerance and fitness

Global climate change poses one of the greatest threats to biodiversity. Most analyses of the potential biological impacts have focused on changes in mean temperature, but changes in thermal variance will also impact organisms and populations. We assessed the combined effects of the mean and variance of temperature on thermal tolerances, organismal survival, and population growth in Drosophila melanogaster. Because the performance of ectotherms relates nonlinearly to temperature, we predicted that responses to thermal variation (±0° or ±5°C) would depend on the mean temperature (17° or 24°C). Consistent with our prediction, thermal variation enhanced the rate of population growth (r(max)) at a low mean temperature but depressed this rate at a high mean temperature. The interactive effect on fitness occurred despite the fact that flies improved their heat and cold tolerances through acclimation to thermal conditions. Flies exposed to a high mean and a high variance of temperature recovered from heat coma faster and survived heat exposure better than did flies that developed at other conditions. Relatively high survival following heat exposure was associated with low survival following cold exposure. Recovery from chill coma was affected primarily by the mean temperature; flies acclimated to a low mean temperature recovered much faster than did flies acclimated to a high mean temperature. To develop more realistic predictions about the biological impacts of climate change, one must consider the interactions between the mean environmental temperature and the variance of environmental temperature.     

Micropropagation of the rare species Stylidium coroniforme and other Stylidium species

The number of plants in the gazetted rare species Stylidium coroniforme was increased through micropropagation. A method was first developed using the common species S. brunonianum. It was found that for both species, rapid propagation could be obtained by excising shoots from sterile seedlings and inducing shoot proliferation on Murashige and Skoog medium supplemented with 1 M BAP. Rooting was achieved using 1 M IBA and over 100 plants of each species were successfully established in soil. Leaf pieces could also be used to initiate cultures. In media with 20–25 M BAP and 1–5 M IBA, leaf pieces of S. brunonianum, S. piliferum, S. caricifolium and S. crassifolium produced adventitious buds, thus providing another method of micropropagation.     

Relative contribution of abundant and rare species to species-energy relationships

A major goal of ecology is to understand spatial variation in species richness. The latter is markedly influenced by energy availability and appears to be influenced more by common species than rare ones; species-energy relationships should thus be stronger for common species. Species-energy relationships may arise because high-energy areas support more individuals, and these larger populations may buffer species from extinction. As extinction risk is a negative decelerating function of population size, this more-individuals hypothesis (MIH) predicts that rare species should respond more strongly to energy. We investigate these opposing predictions using British breeding bird data and find that, contrary to the MIH, common species contribute more to species-energy relationships than rare ones.     

Apoplast as the site of response to environmental signals

When the life cycle of plants is influenced by various environmental signals, the mechanical properties of the cell wall are greatly changed. These signals also modify the levels and structure of the cell wall constituents and such modifications are supposed to be the cause of the changes in the wall mechanical properties. These changes in the cell wall, the major component of the apoplast, can be recognized as the response of plants to environmental signals. The analysis of the mechanism leading to the response suggests that the apoplast is involved not only in the response but also in the perception and transduction of environmental signals in concert with the receptors of signals located on the plasma membrane. Thus, the apoplast plays a principal role in the communication of plants with the outer world and enables the plants to adapt themselves and survive in the environment full of stresses.     

Apoplast as the site of response to environmental signals

When the life cycle of plants is influenced by various environmental signals, the mechanical properties of the cell wall are greatly changed. These signals also modify the levels and structure of the cell wall constituents and such modifications are supposed to be the cause of the changes in the wall mechanical properties. These changes in the cell wall, the major component of the apoplast, can be recognized as the response of plants to environmental signals. The analysis of the mechanism leading to the response suggests that the apoplast is involved not only in the response but also in the perception and transduction of environmental signals in concert with the receptors of signals located on the plasma membrane. Thus, the apoplast plays a principal role in the communication of plants with the outer world and enables the plants to adapt themselves and survive in the environment full of stresses.