Alpine community recruitment potential is determined by habitat attributes in the alpine ecosystems of the Himalaya‐Hengduan Mountains,SW China

The fragility and sensitivity to climate change of alpine ecosystems make it difficult to maintain the stability of their plant communities. Thus, it is important to determine which plant propagules are stored in the soils in order to understand community recruitment potential, especially under different environmental conditions. Based on a soil seed germination and seedling cultivation experiment, we aimed to identify differences in the soil seed attributes between three typical habitat types in the alpine subnival ecosystems of the Himalaya‐Hengduan Mountains and hence to predict the community recruitment potential of each of these different communities. We found that the seed assemblages in the soils differed between habitats. The most abundant taxa were from the genera Saxifraga, Kobresia, Arenaria, Polygonum, Draba, and Viola, while the taxa with lowest abundance were Apiaceae, Campanulaceae, Circaea, Crassulaceae, and Gentiana. Different habitats exhibited variable soil seed richness, diversity, and density. However, the patterns differed between study sites. Specifically, at Baima (BM) and Shika (SK) snow mountains, soil seed richness, diversity, and density were generally highest in grassland, followed by rock bed and bare ground. In contrast, on Jiaozi (JZ) snow mountain, the rock bed supported the highest soil seed richness and density, followed by grassland and bare ground. These results suggest that the attributes of habitats and communities can both affect the accumulation of soil seeds. Bare ground supports the lowest seed diversity and density but also harbors the most empty niches. We, therefore, predict that, once the thermal conditions become suitable as a result of global warming, this habitat has the potential to see greater changes than grassland and rock bed in terms of community recruitment.     

Immigration and gene flow in a northern willow tit (Parus montanus) population

To study quantitatively the relationship between immigration rate and gene flow we used 9-year data from a willow tit Parus montanus population in a continuous forest habitat. We compared components of lifetime reproductive success, and parental survival rate between immigrant and resident (‘status’) birds by taking individual age into consideration also. Of the fitness components, survival was independent of status and sex, averaging 0.60 annually. Of the male and female breeders, on average 63.1% and 75.6%, respectively, originated from unknown natal areas, implying extensive immigration. Pair formation was nonassortative with respect to the origin of partners. The effect of status on reproductive success was significant only for females: immigrants produced larger clutches and hatched more young in all age classes studied. However, the difference between the groups diminished until fledging and the offspring produced by the immigrant females showed lower local survival rate (4.6% of the young) than did those by the residents (5.9%). Therefore, the contribution of immigrant females to the local gene pool was lower than expected on the basis of immigration rate. However, we propose that the result implies differential propensities to long-distance dispersal rather than overall survival prospects, since we detected no quality differences suggesting reduced survival chances among descendants of immigrant females. Therefore, gene flow into the population was slightly lower than immigration rate. It is possible that immigrant females are more prone to invest in progeny that effectively disperse further to search for new vacancies. The conditions prevailing during nestling growth may be crucial in determining whether an individual will later become a resident or leave the natal area, but the genetic component of this trait should also be considered. We suggest that widespread propagules is a better strategy than philopatry for a short-lived species to minimize the risk of losing all descendants in temporally and spatially varying conditions.     

Genotypic structure in clonal Rhododendron ferrugineum L. (Ericaceae) populations: origin and maintenance

Genotypic structure of a closed population of the clonal ericaceous shrub Rhododendron ferrugineum is examined in the light of two independent studies previously conducted on this species. In the first study, spatial distribution of genotypes in the closed population was inferred from the amplified fragment length polymorphism (AFLP) procedure. Age of clones was estimated using their spatial extent and the annual growth rate of shoots. In the second study, ramet demography was studied in the three most representative stages of shrub invasion on two different sites, including the site where the population investigated by AFLP grew. The demographic data recorded were the area occupied by ramets and ramet age, and from this information the developmental pattern of Rhododendron populations was determined. Additional data such as genet density and distance between genets were calculated.These two sources of information allow us to propose that all or most of the clones detected in the closed population established at the early successional stage, and that the present genotypic structure was established several hundred years ago, long before the population reached total closure. Hypotheses concerning the future development of this genotypic structure are discussed.     

The effects of burning on the understorey composition of 11–13 year-old rehabilitated bauxite mines in Western Australia – Vegetation characteristics

Alcoa of Australia Limited has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of Western Australia for more than 30 years. Mines rehabilitated in the early 1980s using out-dated methods have built up substantial fuel loads that may be reduced through prescribed burning. The vegetation response of 11–13 year-old rehabilitated bauxite mines to fire regimes differing in intensity and season over the first two years of post-burn succession is compared to the native jarrah forest. A total of 243 species from 137 genera and 56 families were identified in the native forest reference sites and in the 11–13 year-old rehabilitated areas before and after burning. The vegetation of the pre-burn rehabilitated areas was very different to that of the native jarrah forest. While total live plant cover, Acacia density, non-native eucalypt seedling density, weed density and the evenness index were similar between the two areas, total plant density, live Acacia cover, the proportion of weeds, native species numbers and diversity were significantly different. However, the greatest difference between the vegetation of the pre-burn rehabilitated sites and the native jarrah forest was the higher dominance of seeding species (plants killed by fire) in rehabilitated areas. In contrast, native jarrah forest was dominated by resprouting species (plants that survive fire). Burning the rehabilitated sites was successful in making the areas more similar to the forest in terms of total plant density, live Acacia cover and native species numbers but decreased their similarity in terms of live plant cover, Acacia density, non-native eucalypt seedling density, weed density and evenness. The vegetation response of the rehabilitated areas to different seasons of burning showed that autumn burning led to a greater increase in plant establishment than spring burning. Autumn burning also resulted in an undesirable increase in the density of non-native eucalypt seedlings that was not observed following spring burning. Although burning these 11–13 year-old rehabilitated sites will increase similarity to the native forest, it is unlikely that they will resemble the native jarrah forest without further management intervention.     

Small-scale spatial dynamics in a fluctuating ungulate population

1. The scale at which population dynamics are analysed is important, as results from analyses at different spatial scales can differ and affect interpretation.
2. In this study, detailed census data collected over a 10-year period from a population of Soay sheep ( Ovis aries L.) on the Island of Hirta in the St Kilda archipelago, Scotland, is used, together with cluster analysis, to distinguish a temporally stable spatial substructure.
3. Structured demographic accounting of the variance in population change (SDA) is also used to analyse the dynamics of the whole population treated as (a) one unit; (b) one unit subdivided into three subunits; and (c) three independent units.
4. Differences in survival, recruitment and dispersal rates are demonstrated between divisions of the population, which are probably associated with variation in grazing quality.
5. If these groups were not coupled by dispersal and density-independent entrainment, the population dynamics of the three groups would diverge, however, the dynamics of the three subunits are strongly correlated.     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.     

Coral recruitment and juvenile mortality as structuring factors for reef benthic communities in Biscayne National Park, USA

Coral communities of Biscayne National Park (BNP) on offshore linear bank-barrier reefs are depauperate of reef corals and have little topographic relief, while those on lagoonal patch reefs have greater coral cover and species richness despite presumably more stressful environmental regimes closer to shore. We hypothesized that differences in rates of coral recruitment and/or of coral survivorship were responsible for these differences in community structure. These processes were investigated by measuring: (1) juvenile and adult coral densities, and (2) size-frequency distributions of smaller coral size classes, at three pairs of bank- and patch-reefs distributed along the north-south range of coral reefs within the Park. In addition, small quadrats (0.25 m²) were censused for colonies <2 cm in size on three reefs (one offshore and one patch reef in the central park, and one intermediate reef at the southern end), and re-surveyed after 1 year. Density and size frequency data confirmed that large coral colonies were virtually absent from the offshore reefs, but showed that juvenile corals were common and had similar densities to those of adjacent bank and patch reefs. Large coral colonies were more common on inshore patch reefs, suggesting lower survivorship (higher mortality) of small and intermediate sized colonies on the offshore reefs. The more limited small-quadrat data showed similar survivorship rates and initial and final juvenile densities at all three sites, but a higher influx of new recruits to the patch reef site during the single annual study period. We consider the size-frequency data to be a better indicator of juvenile coral dynamics, since it is a more time-integrated measurement and was replicated at more sites. We conclude that lack of recruitment does not appear to explain the impoverished coral communities on offshore bank reefs in BNP. Instead, higher juvenile coral mortality appears to be a dominant factor structuring these communities. Accepted: 9 September 1999     

Competition and disturbance affect elevational distribution of two congeneric conifers

Climatic change will affect elevational vegetation distribution because vegetation distribution is related to thermal conditions. However, how elevational species distributions are determined by biotic and abiotic factors is not clear. The long‐term plot census along an elevational gradient is indispensable to clarify mechanisms of elevational distribution of tree species. Two congeneric conifers, the less shade‐tolerant Abies veitchii and shade‐tolerant A. mariesii, dominate at low and high elevations, respectively, in the subalpine zone in Japan. This study investigated the population dynamics of the two species at three elevations (low, middle, high) for 13 years to examine why the two species dominated the different elevations from the viewpoints of competition and disturbance. This study showed that growth and survival rates were not highest at the most dominant elevations for each species. At the high elevation where A. mariesii dominated and small disturbances frequently occurred, the recruitment rate of A. mariesii was highest among the three elevations and that of A. veitchii was largely decreased by tree competition. However, A. veitchii was dominant earlier than A. mariesii at the low elevation after large disturbances by the high growth rate of individual trees. Therefore, A. mariesii was superior to A. veitchii at the high elevation because of its high recruitment rate and large reduction of recruitment of A. veitchii due to competition, while A. veitchii was superior to A. mariesii at the low elevation after large disturbances because of higher growth rate than A. mariesii. It is suggested that the elevational distributions of the two species were determined by elevational changes in population dynamics in relation to competition and disturbance. Long‐term observational studies of forest dynamics among various elevations are indispensable to predict the effects of climatic change on vegetation distribution.     

Inferences About Ungulate Population Dynamics Derived From Age Ratios

Abstract: Age ratios (e.g., calf:cow for elk and fawn:doe for deer) are used regularly to monitor ungulate populations. However, it remains unclear what inferences are appropriate from this index because multiple vital rate changes can influence the observed ratio. We used modeling based on elk (Cervus elaphus) life-history to evaluate both how age ratios are influenced by stage-specific fecundity and survival and how well age ratios track population dynamics. Although all vital rates have the potential to influence calf:adult female ratios (i.e., calf:cow ratios), calf survival explained the vast majority of variation in calf:adult female ratios due to its temporal variation compared to other vital rates. Calf:adult female ratios were positively correlated with population growth rate (Λ) and often successfully indicated population trajectories. However, calf:adult female ratios performed poorly at detecting imposed declines in calf survival, suggesting that only the most severe declines would be rapidly detected. Our analyses clarify that managers can use accurate, unbiased age ratios to monitor arguably the most important components contributing to sustainable ungulate populations, survival rate of young and Λ. However, age ratios are not useful for detecting gradual declines in survival of young or making inferences about fecundity or adult survival in ungulate populations. Therefore, age ratios coupled with independent estimates of population growth or population size are necessary to monitor ungulate population demography and dynamics closely through time.     

Enhancers predominantly regulate gene expression during differentiation via transcription initiation

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