Genetic diversity of the great bustard in Iberia and Morocco: risks from current population fragmentation

We studied the genetic diversity of great bustards (Otis tarda) in Iberia and Morocco, the main stronghold of this globally endangered species. Samples were collected from 327 individuals covering most of the distribution range within the study area. Sequence variation in a 657 bp fragment of the mtDNA control region revealed 20 variable sites defining 22 haplotypes, two of them exclusive to Morocco. Genetic diversity showed marked regional differences (π = 0–0.53, h = 0–0.89). Multidimensional scaling analysis based on F _ST values showed a clear division between Morocco and the Iberian Peninsula, with no evidence of current gene flow between them. Our results suggest that Morocco, where few matrilines have persisted to present, was colonized from Iberia thousands of years ago. Last century reports suggest dispersal through Gibraltar, when the species was more abundant at both sides of the Strait but later population declines and the Strait’s barrier effect have favoured current genetic isolation. Within Iberia, only the most peripheral populations (Navarra, Aragón and Andalusia) differed significantly from the main ones in central Spain. The first two showed extremely low genetic diversity and are probably threatened by inbreeding depression. Diversity was higher in Andalusia, where three exclusive haplotypes were found, suggesting some degree of isolation from other populations. Andalusia and Morocco could be regarded as separate management units which hold a significant proportion of the current genetic diversity and thus deserve urgent conservation measures.     

The effect of conspecific attraction on metapopulation dynamics

Random dispersal direction is assumed in all current metapopulation models. This assumption is called into question by recent experiments demonstrating that some species disperse preferentially to sites occupied by conspecifies. We incorporate conspecific attraction into two metapopulation models which differ in type of dispersal, the Levins model and a two-dimensional stepping-stone model. In both models, conspecific attraction lowers the proportion of occupied habitat patches within a metapopulation at equilibrium.     

Field determination of age in male great bustards (Otis tarda) in spring

During a long-term study of individually marked, free-living male great bustards captured as chicks and radio-tracked through several years in Spain, we studied the development with age of two secondary sex traits, the moustachial feathers and the neck plumage pattern. Juvenile males acquired full adult plumage between their fourth and seventh years. The main changes occurred at the neck, coinciding with the onset of sexual maturity. The grey colour typical of immature males turned to ivory white around the fourth to fifth spring, and a gradual increase was appreciated in adults in the brightness of the white colour of the upper neck and in the contrast between this and a progressively more intense chestnut brown at the neck base. Based on these changes, we proposed four neck plumage patterns that can be used to differentiate male age classes during the mating period. The development of moustachial feathers showed more interindividual variability and was not as useful as the neck plumage to estimate male age.     

Gene flow in great bustard populations across the Strait of Gibraltar as elucidated from excremental PCR and mtDNA sequencing

Recent advances in molecular biology have made it possible to use the trace amounts of DNA in faeces to non-invasively sample endangered species for genetic studies. Here we use faeces as a source of DNA and mtDNA sequence data to elucidate the relationship among Spanish and Moroccan populations of great bustards. 834 bp of combined control region and cytochrome-b mtDNA fragments revealed four variable sites that defined seven closely related haplotypes in 54 individuals. Morocco was fixed for a single mtDNA haplotype that occurs at moderate frequency (28%) in Spain. We could not differentiate among the sampled Spanish populations of Cáceres and Andalucía but these combined populations were differentiated from the Moroccan population. Estimates of gene flow (Nm = 0.82)are consistent with extensive observations on the southern Iberian peninsular indicating that few individuals fly across the Strait of Gibraltar. We demonstrate that both this sea barrier and mountain barriers in Spain limit dispersal among adjacent great bustard populations to a similar extent. The Moroccan population is of high ornithological significance as it holds the only population of great bustards in Africa. This population is critically small and genetic and observational data indicate that it is unlikely to be recolonised via immigration from Spain should it be extirpated. In light of the evidence presented here it deserves the maximum level of protection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution, density and productivity of great bustards Otis tarda in northwestern Spain: a regional approach

This paper describes at a regional scale the distribution pattern, density, productivity and sex ratio of great bustards in northwestern Spain and explores the role played by habitat type, terrain characteristics and human disturbance on variation in its demographic parameters. Data from 136 plots covering an area of 7314 km² were obtained in two censuses carried out in the spring and summer of 1998. The density of the great bustards was 1.39 individuals/km² in the pre-breeding period, decreasing by 22% in the post-breeding period. Density was significantly higher in central plots than in peripheral plots. Mean productivity was 0.24 chicks per female and showed a high variability among plots, being significantly lower in the densest plots. The overall sex ratio was 1.35 females per male during the pre-breeding period. Productivity related positively to areas holding small fields and a high interspersion of land uses. Density and productivity were negatively affected by river density and altitude, and seasonal density variation was positively correlated with human population density.     

Faeces as a source of DNA for molecular studies in a threatened population of great bustards

With recent advances in molecular biology, it is now possible to use the trace amounts of DNA in faeces to non-invasively sample endangered species for genetic studies. A highly vulnerable population of approximately 100 great bustards (Otis tarda) exists in Morocco necessitating the use of non-invasive protocols to study their genetic structure. Here we report a reliable silica-based method to extract DNA from great bustard faeces. We found that successful extraction and amplification correlated strongly with faeces freshness and composition. We could not extract amplifiable DNA from 30% of our samples as they were dry or contained insect material. However 100% of our fresh faecal samples containing no obvious insect material worked, allowing us to assess the levels of genetic variation among 25 individuals using a 542 bp control region sequence. We were able to extract DNA from four out of five other avian species, demonstrating that faeces represents a suitable source of DNA for population genetics studies in a broad range of species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution and status of bustards in China

This article presents the distribution and status of bustards, which are listed as first-category protected animals according to the survey results during 1990–2002 in China. The Chinese populations of Otis tarda dybowskii are breeding in south-west of Heilongjiang Province, western Jilin Province, east and middle Inner Mongolia, north Ningxia Hui Autonomous Region, and Gansu Province. A few can winter in the south breeding-range. Its winter-range lies from the south to the Yellow River, as far as to Guizhou Province and Jiangxi Province. Its population number is about 200–300 or 500–800. The Chinese populations of O. t. tarda are breeding in the north and west of Xinjiang. It is unclear about its winter-range, which is presumed to be in south Asia. Recently we found individuals wintering in Chabuchaer and west Xinjiang. The population number is about 2000–3000. The habitat in breeding range includes steppe, grassland, desert grassland, and farmland. The habitat in winter range is the beach of rivers and lakes, meadows, meadow-grassland, and wheatland. The Chinese populations of Chlamydotis undulata macqueeni are breeding in the fringe of the Jungar Basin, the banks of the Ulungur River, Balikun and south Turpan Basin in Xinjiang, west Inner Mongolia, and west Gansu. NortheastMulei in eastern Jungar Basin of Xinjiang is the main breeding-range in the world. The bird uses desert and desert grassland as its habitat. Its winter-range is west Asia and south Asia. Its population number is about 2000. The Chinese populations of Tetrax tetrax are breeding in north Xinjiang, and China is located on the east border of its breeding-range. Its habitat is grassland and semi-desert, and its winter-range lies in south Asia. Its population in China is very scarce. In addition, we analyzed the causes of their endangerment and put forward protection tactics of Chinese Bustards. __________ Translated from Arid Zone Research, 2007, 24(2): 179–186 [译自: 干旱区研究]     

The influence of plant species on attraction and host acceptance inCotesia glomerata (Hymenoptera: Braconidae)

Females of the larval parasitoidCotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host,Pieris rapae L. In this study we investigated the influence of four host plant species,Brassica oleracea var.acephala (‘Vates’ kale),Tropaeolum majus (nasturtium),Lunaria annua (honesty), andCleome spinosa (spider flower), on two components of the host selection process inC. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae.B. oleracea was the most attractive plant species, followed byL. annua, T. majus, andC. spinosa. In previous studies it was shown thatB. oleracea carries highly suitable hosts forC. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var.capitata, cabbage), plant species that had served as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. ForC. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.     

Green turtle somatic growth dynamics in a spatially disjunct Great Barrier Reef metapopulation

The growth dynamics of green sea turtles resident in four separate foraging grounds of the southern Great Barrier Reef genetic stock were assessed using a nonparametric regression modeling approach. Juveniles recruit to these grounds at the same size, but grow at foraging-ground-dependent rates that result in significant differences in expected size- or age-at-maturity. Mean age-at-maturity was estimated to vary from 25–50 years depending on the ground. This stock comprises mainly the same mtDNA haplotype, so geographic variability might be due to local environmental conditions rather than genetic factors, although the variability was not a function of latitudinal variation in environmental conditions or whether the food stock was seagrass or algae. Temporal variability in growth rates was evident in response to local environmental stochasticity, so geographic variability might be due to local food stock dynamics. Despite such variability, the expected size-specific growth rate function at all grounds displayed a similar nonmonotonic growth pattern with a juvenile growth spurt at 60–70 cm curved carapace length, (CCL) or 15–20 years of age. Sex-specific growth differences were also evident with females tending to grow faster than similar-sized males after the juvenile growth spurt. It is clear that slow sex-specific growth displaying both spatial and temporal variability and a juvenile growth spurt are distinct growth behaviors of green turtles from this stock.Communicated by Ecological Editor P.F. Sale     

Cascading life-history interactions: alternative density-dependent pathways drive recruitment dynamics in a freshwater fish

Although density-dependent mechanisms in early life-history are important regulators of recruitment in many taxa, consequences of such mechanisms on other life-history stages are poorly understood. To examine interacting and cascading effects of mechanisms acting on different life-history stages, we stocked experimental ponds with fathead minnow (Pimephales promelas) at two different densities. We quantified growth and survival of the stocked fish, the eggs they produced, and the resulting offspring during their first season of life. Per-capita production and survival of eggs were inversely related to density of stocked fish; significant egg cannibalism by stocked minnows resulted in initial young-of-the-year (YOY) densities that were inversely related to adult densities. Subsequent growth and survival of YOY were then inversely related to these initial YOY densities, and survival of YOY was selective for larger fish. Because of these compensatory processes in the egg and YOY stages, treatments did not differ in YOY abundance and mean size at the end of the growing season. Because of differences in the intensity of size-selective mortality, however, variation in end-of season sizes of YOY was strongly (and inversely) related to densities of stocked fish. When mortality was severe in the egg stage (high densities of stocked fish), final YOY size distributions were more variable than when the dominant mortality was size-selective in the YOY stage (low stocked fish densities). These differences in size variation could have subsequent recruitment consequences, as overwinter survival is typically selective for YOY fish larger than a critical threshold size. Density-dependent effects on a given life stage are not independent, but will be influenced by earlier stages; alternative recruitment pathways can result when processes at earlier stages differ in magnitude or selectivity. Appreciation of these cascading effects should enhance our overall understanding of the dynamics of stage-structured populations.     

Differential cannibalism and population dynamics in a host-parasitoid system

The effects of host cannibalism on a host-parasitoid system were explored through experiment and modelling. In individual encounters between parasitized and unparasitized Plodia interpunctella larvae, parasitized larvae were more likely to be cannibalized. Inclusion of this differential cannibalism into a simple Lotka-Volterra-type model of host-parasitoid population dynamics generates alternative stable states-including stable coexistence and extinction of the parasitoid — which depend on starting conditions. Possible mechanisms for differential cannibalism, and its implications for studies of host-parasitoid populations and biological control programmes are discussed.     

Biocontrol of a perennial legume,Sesbania punicea,using a florivorous weevil,Trichapion lativentre: weed population dynamics with a scarcity of seeds

Summary The establishment in South Africa of a florivorous, apionid weevil, Trichapion lativentre, on Sesbania punicea, a leguminous weed of South American origin, has reduced seed production of the plants by >98%. Surveys of the age structure and density of plants in infestations of S. punicea throughout South Africa have shown that the rate of recruitment of seedlings has drastically declined within a few years in many areas, due to the weevils. However, there has unexpectedly not been a corresponding decline in the density of mature plants in extant infestations of S. punicea. In spite of this, T. lativentre has curtailed the rate of spread of the weed into uninvaded habitats and has impeded reinvasion into areas cleared of infestations by mechanical means or by another complimentary biocontrol agent.     

Population structure and dynamics of Pinus taiwanensis Hayata at Songyang county,Zhejiang Province,China

Pinus taiwanensis is a widely distributed species in the southeastern China (Zhejiang, Anhui, Hubei, Human, Jiangxi, Fujian, Taiwan provinces) at an elevation of 700–2000 m. This pine is a pioneer in forest succession and is often used as a species for afforestation in this region at an elevation above 700 m. This study was carried out at Guanshanyuan, Zhejiang province, at a latitude of N 28° 18, a longitude of E 119° 16 and an altitude of 800–1502 m above sea level. On the basis of a census of all individuals of Pinus taiwanensis at different successional stages and various habitats, age structure, spatial pattern, density, biomass of population and their dynamics were described. Considering the population dynamics throughout the successional process, three phases could be recognized. Until about 9–10 years after Pinus taiwanensis invaded the stands, the density of population was increased by the recruitments along with increase of the mean tree weight and population biomass (phase I). Thereafter, the population was in full density state, the biomass of population and the mean tree weight increased exponentially, while the density was decreased drastically by the self-thinning and the invasion of other broad-leaved trees (phase II). The –3/2 power law of natural thinning was applicable to the populations in this phase. When the broad-leaved trees reached the canopy, although the mean tree weight increased slowly, the density and biomass of Pinus taiwanensis population decreased gradually (phase III) until the population senesced and retreated from the successional series completely. The population dynamics of Pinus taiwanensis during the successional process was in common with pioneer species in forest succession. At some special habitats such as rocky steep slopes and ridges, however, Pinus taiwanensis population could form such an edaphic climax community that the population density, biomass and the mean tree weight in phase III could be in a stable state for very long period.     

Population dynamics of Plantago maritima along a distributional gradient on a Baltic seashore meadow

Demographical studies of Plantago maritima along a 60 m long gradient, from waterfront to terrestrial meadow, revealed a correspondence in population dynamics. The gradient can be seen as a transition from dominance of density-independent mortality factors, mainly flooding, to a dominance of density-dependent mortality, mainly due to competition for light. In lower parts the variation in density of plants varies greatly between years, the flowering and seeding are good as well as the establishment of seedlings, i.e. there is a high turnover rate. In upper parts the flowering, seeding and establishment are poorer but the life expectancy is longer which results in a low turnover rate. The establishment of seedlings is mainly controlled by the access to light, in lower parts now and then dominated by the effects of flooding. Population characteristics change along the gradient so that reproductive effort, in terms of produced seeds per rosette, and allocation of biomass into reproductive organs is higher in lower parts but the reverse in upper, specimens in lower parts also start to grow and flower earlier.Nomenclature follows J. Lid (1979), Norsk og Svensk Flora. Det Norske Samlaget, Oslo.     

Population dynamics of epiphytic orchids in a metapopulation context

Background and Aims

Populations of many epiphytes show a patchy distribution where clusters of plants growing on individual trees are spatially separated and may thus function as metapopulations. Seed dispersal is necessary to (re)colonize unoccupied habitats, and to transfer seeds from high- to low-competition patches. Increasing dispersal distances, however, reduces local fecundity and the probability that seeds will find a safe site outside the original patch. Thus, there is a conflict between seed survival and colonization.

Methods

Populations of three epiphytic orchids were monitored over three years in a Mexican humid montane forest and analysed with spatially averaged and with spatially explicit matrix metapopulation models. In the latter, population dynamics at the scale of the subpopulations (epiphytes on individual host trees) are based on detailed stage-structured observations of transition probabilities and trees are connected by a dispersal function.

Key Results

Population growth rates differed among trees and years. While ignoring these differences, and averaging the population matrices over trees, yields negative population growth, metapopulation models predict stable or growing populations because the trees that support growing subpopulations determine the growth of the metapopulation. Stochastic models which account for the differences among years differed only marginally from deterministic models. Population growth rates were significantly lower, and extinctions of local patches more frequent in models where higher dispersal results in reduced local fecundity compared with hypothetical models where this is not the case. The difference between the two models increased with increasing mean dispersal distance. Though recolonization events increased with dispersal distance, this could not compensate the losses due to reduced local fecundity.

Conclusions

For epiphytes, metapopulation models are useful to capture processes beyond the level of the single host tree, but local processes are equally important to understand epiphyte population dynamics.     

Comment arising from a paper by Wittmer et al.: hypothesis testing for top-down and bottom-up effects in woodland caribou population dynamics

Conservation strategies for populations of woodland caribou Rangifer tarandus caribou frequently emphasize the importance of predator–prey relationships and the availability of lichen-rich late seral forests, yet the importance of summer diet and forage availability to woodland caribou survival is poorly understood. In a recent article, Wittmer et al. (Can J Zool 83:407–418, 2005b) concluded that woodland caribou in British Columbia were declining as a consequence of increased predation that was facilitated by habitat alteration. Their conclusion is consistent with the findings of other authors who have suggested that predation is the most important proximal factor limiting woodland caribou populations (Bergerud and Elliot in Can J Zool 64:1515–1529, 1986; Edmonds in Can J Zool 66:817–826, 1988; Rettie and Messier in Can J Zool 76:251–259, 1998; Hayes et al. in Wildl Monogr 152:1–35, 2003). Wittmer et al. (Can J Zool 83:407–418, 2005b) presented three alternative, contrasting hypotheses for caribou decline that differed in terms of predicted differences in instantaneous rates of increase, pregnancy rates, causes of mortality, and seasonal vulnerability to mortality (Table 1, p 258). These authors rejected the hypotheses that food or an interaction between food and predation was responsible for observed declines in caribou populations; however, the use of pregnancy rate, mortality season and cause of mortality to contrast the alternative hypotheses is problematic. We argue here that the data employed in their study were insufficient to properly evaluate a predation-sensitive foraging hypothesis for caribou decline. Empirical data on seasonal forage availability and quality and plane of nutrition of caribou would be required to test the competing hypotheses. We suggest that methodological limitations in studies of woodland caribou population dynamics prohibit proper evaluation of the mechanism of caribou population declines and fail to elucidate potential interactions between top-down and bottom-up effects on populations. An erratum to this article can be found at     

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O.×fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. TheP. osmanthi population was bimodal, with one peak in spring (May–June) and another in winter (November–January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution and turnover of a mosquito (Tripteroides bambusa) metapopulation among bamboo groves

We surveyed the distribution of a mosquito, Tripteroides bambusa (Yamada), among patchily distributed bamboo groves from 1994 to 1997 in an area of 4 km × 4 km in Saga, south-western Japan. In the study area, this mosquito uses mainly water-filled bamboo stumps as its larval habitat. In 1994, a year with little rainfall in the summer, T. bambusa larvae were found in 30 of the 60 groves that contained water-filled bamboo stumps. By 1997, the number of occupied groves increased to 64, and the number of groves with water-filled stumps increased to 109. Tripteroides bambusa was found frequently in the area covered by an orange orchard where bamboo groves were dense, and rarely in the open land where bamboo groves were sparse. Colonization of T. bambusa occurred in groves in the orchard and the open land which were less than 0.57 km away from the nearest occupied grove. Large groves were more likely to be occupied, and extinction occurred only in small groves ( 0.104 ha). Groves without water-filled stumps in 1994 were less likely to be occupied in the following period than those with water-filled stumps in 1994. These findings suggest that the T. bambusa metapopulation will not extend its distribution into all of the bamboo groves in the study area, but will not become extinct because of some highly persistent populations.