Species Dynamics (species + dynamics)

Distribution by Scientific Domains


Selected Abstracts


Temporal dynamics and spatial variability in the enhancement of canopy leaf area under elevated atmospheric CO2

GLOBAL CHANGE BIOLOGY, Issue 12 2007
HEATHER R. McCARTHY
Abstract Increased canopy leaf area (L) may lead to higher forest productivity and alter processes such as species dynamics and ecosystem mass and energy fluxes. Few CO2 enrichment studies have been conducted in closed canopy forests and none have shown a sustained enhancement of L. We reconstructed 8 years (1996,2003) of L at Duke's Free Air CO2 Enrichment experiment to determine the effects of elevated atmospheric CO2 concentration ([CO2]) on L before and after canopy closure in a pine forest with a hardwood component, focusing on interactions with temporal variation in water availability and spatial variation in nitrogen (N) supply. The dynamics of L were reconstructed using data on leaf litterfall mass and specific leaf area for hardwoods, and needle litterfall mass and specific leaf area combined with needle elongation rates, and fascicle and shoot counts for pines. The dynamics of pine L production and senescence were unaffected by elevated [CO2], although L senescence for hardwoods was slowed. Elevated [CO2] enhanced pine L and the total canopy L (combined pine and hardwood species; P<0.050); on average, enhancement following canopy closure was ,16% and 14% respectively. However, variation in pine L and its response to elevated [CO2] was not random. Each year pine L under ambient and elevated [CO2] was spatially correlated to the variability in site nitrogen availability (e.g. r2=0.94 and 0.87 in 2001, when L was highest before declining due to droughts and storms), with the [CO2]-induced enhancement increasing with N (P=0.061). Incorporating data on N beyond the range of native fertility, achieved through N fertilization, indicated that pine L had reached the site maximum under elevated [CO2] where native N was highest. Thus closed canopy pine forests may be able to increase leaf area under elevated [CO2] in moderate fertility sites, but are unable to respond to [CO2] in both infertile sites (insufficient resources) and sites having high levels of fertility (maximum utilization of resources). The total canopy L, representing the combined L of pine and hardwood species, was constant across the N gradient under both ambient and elevated [CO2], generating a constant enhancement of canopy L. Thus, in mixed species stands, L of canopy hardwoods which developed on lower fertility sites (,3 g N inputs m,2 yr,1) may be sufficiently enhanced under elevated [CO2] to compensate for the lack of response in pine L, and generate an appreciable response of total canopy L (,14%). [source]


1-D numerical modelling of shallow flows with variable horizontal density

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010
Feifei Zhang Leighton
Abstract A1-D numerical model is presented for vertically homogeneous shallow flows with variable horizontal density. The governing equations represent depth-averaged mass and momentum conservation of a liquid,species mixture, and mass conservation of the species in the horizontal direction. Here, the term ,species' refers to material transported with the liquid flow. For example, when the species is taken to be suspended sediment, the model provides an idealized simulation of hyper-concentrated sediment-laden flows. The volumetric species concentration acts as an active scalar, allowing the species dynamics to modify the flow structure. A Godunov-type finite volume scheme is implemented to solve the conservation laws written in a deviatoric, hyperbolic form. The model is verified for variable-density flows, where analytical steady-state solutions are derived. The agreement between the numerical predictions and benchmark test solutions illustrates the ability of the model to capture rapidly varying flow features over uniform and non-uniform bed topography. A parameter study examines the effects of varying the initial density and depth in different regions. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Interaction strengths in food webs: issues and opportunities

JOURNAL OF ANIMAL ECOLOGY, Issue 3 2004
Eric L. Berlow
Summary 1Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2Much confusion stems from lack of clarity about whether the questions posed relate to community-level patterns or to species dynamics, and to what authors actually mean by the term ,interaction strength'. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field. 3Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits. 4Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity. 5Finally, the prime focus on predator,prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of non-trophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes. [source]


Exploring climatic and biotic controls on Holocene vegetation change in Fennoscandia

JOURNAL OF ECOLOGY, Issue 2 2008
Paul A. Miller
Summary 1We investigated the potential drivers of Holocene vegetation changes recorded at four Scandinavian pollen sites, two in Sweden and two in Finland, at a time when they were largely free of anthropogenic influence. 2We used the generalized dynamic vegetation model LPJ-GUESS forced with climate anomaly output from an atmospheric general circulation model to simulate tree species dynamics from 10 000 years ago to the present. The model results were compared to high-resolution pollen accumulation rates gathered at the sites. 3Our results indicate that both the observed northern distributional limits of temperate trees, and the limits of Pinus sylvestris and Alnus incana at the tree line, are a result of millennial variations in summer and winter temperatures. The simulation of several distinct trends in species occurrence observed in the pollen record indicates that a time lag due to the slow spreading of species need not be invoked for most species. 4Sensitivity studies indicate that competition, natural disturbance and the magnitude of interannual variability play key roles in determining the biomass, establishment and even the presence of species near their bioclimatic limits. However, neither disturbance due to fire nor limits on establishment due to drought were likely to have been major determinants of the observed trends on the timescales considered. 5We were unable to limit the modelled occurrence of Picea abies at the study sites to the periods at which it was observed in the pollen records, indicating that we have still not completely understood the driving or limiting factors for Holocene changes in Picea abies abundance. 6Synthesis. This study shows that by combining quantitative vegetation reconstructions with a modern, process-based dynamic vegetation model, we may gain new insights into the potential biotic and abiotic drivers of Holocene vegetation dynamics, and their relative importance. This knowledge will be crucial in enabling us to assess more confidently the response of northern European vegetation to future climate change. [source]


Habitat fragmentation reduces grassland connectivity for both short-distance and long-distance wind-dispersed forbs

JOURNAL OF ECOLOGY, Issue 6 2005
M. B. SOONS
Summary 1Although habitat loss and fragmentation are assumed to threaten the regional survival of plant species, their effects on regional species dynamics via seed dispersal and colonization have rarely been quantified. 2We assessed the impact of habitat loss and fragmentation on the connectivity, and hence regional survival, of wind-dispersed plant species of nutrient-poor semi-natural grasslands. We did this using a new approach to relate quantified habitat loss and fragmentation to quantified colonization capacity. 3We quantified loss and fragmentation during the 20th century of moist, nutrient-poor semi-natural grasslands in study areas in the Netherlands, as well as their current distribution. After testing how well the habitat distribution matches species distributions of two wind-dispersed grassland forbs (Cirsium dissectum, representative of species with long-distance wind dispersal, and Succisa pratensis, representative of species with short-distance wind dispersal), we combined the habitat distribution data with simulated seed dispersal kernels in order to quantify the impact on connectivity. 4Habitat loss and fragmentation has dramatically reduced both the area (by 99.8%) and the connectivity of the grasslands. The remaining grasslands are practically isolated for seeds dispersed by wind, even for species with high wind dispersal ability (for which, interestingly, connectivity by wind dispersal decreased most). Linear landscape elements hardly contribute to connectivity by wind dispersal. Regional survival of the studied species has become completely dependent on the survival of a few large populations in nature reserves. Other remaining populations are decreasing in number and size and have low colonization capacity. 5Habitat loss and fragmentation have drastically changed the regional species dynamics of wind-dispersed plant species, indicating that it is of utmost importance to preserve remaining populations in nature reserves and that the probability of colonization of new or restored sites is very low, unless the sites are adjacent to occupied sites or dispersal is artificially assisted. [source]


Habitat associations of Atlantic herring in the Shetland area: influence of spatial scale and geographic segmentation

FISHERIES OCEANOGRAPHY, Issue 3 2001
CHRISTOS D. Maravelias
This study considers the habitat associations of a pelagic species with a range of biotic and abiotic factors at three different spatial scales. Generalized additive models (GAM) are used to analyse trends in the distributional abundance of Atlantic herring (Clupea harengus) in relation to thermocline and water depth, seabed roughness and hardness, sea surface salinity and temperature, zooplankton abundance and spatial location. Two geographical segments of the population, those east and west of the Shetland Islands (northern North Sea, ICES Div IVa), are examined. The differences in the ecological preferences of the species in these two distinct geographical areas are elucidated and the degree that these environmental relationships might be modulated by the change of support of the data is also considered. Part of the observed variability of the pre-spawning distribution of herring was explained by different parameters in these two regions. Notwithstanding this, key determinants of the species' spatial aggregation in both areas were zooplankton abundance and the nature of the seabed substrate. The relative importance of the variables examined did not change significantly at different spatial scales of the observation window. The diverse significance of various environmental factors on herring distribution was attributed mainly to the interaction of species' dynamics with the different characteristics of the ecosystem, east and west of the Shetland Islands. Results suggest that the current 2.5 nautical miles as elementary sampling distance unit (ESDU) is a reasonable sampling scheme that combines the need to reduce the data volume while maintaining spatial resolution to distinguish the species/environment relationships. [source]