			Home About us Contact

Ecological Equilibrium (ecological + equilibrium)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

ECOLOGICAL BISTABILITY AND EVOLUTIONARY REVERSALS UNDER ASYMMETRICAL COMPETITION

EVOLUTION, Issue 6 2002
Fabio Dercole
Abstract How does the process of life-history evolution interplay with population dynamics? Almost all models that have addressed this question assume that any combination of phenotypic traits uniquely determine the ecological population state. Here we show that if multiple ecological equilibria can exist, the evolution of a trait that relates to competitive performance can undergo adaptive reversals that drive cyclic alternation between population equilibria. The occurrence of evolutionary reversals requires neither environmentally driven changes in selective forces nor the coevolution of interactions with other species. The mechanism inducing evolutionary reversals is twofold. First, there exist phenotypes near which mutants can invade and yet fail to become fixed; although these mutants are eventually eliminated, their transitory growth causes the resident population to switch to an alternative ecological equilibrium. Second, asymmetrical competition causes the direction of selection to revert between high and low density. When ecological conditions for evolutionary reversals are not satisfied, the population evolves toward a steady state of either low or high abundance, depending on the degree of competitive asymmetry and environmental parameters. A sharp evolutionary transition between evolutionary stasis and evolutionary reversals and cycling can occur in response to a smooth change in ecological parameters, and this may have implications for our understanding of size-abundance patterns. [source]

Tolerance of Pinus taeda and Pinus serotina to low salinity and flooding: Implications for equilibrium vegetation dynamics

JOURNAL OF VEGETATION SCIENCE, Issue 1 2008
Benjamin Poulter
Abstract Questions: 1. Do pine seedlings in estuarine environments display discrete or continuous ranges of physiological tolerance to flooding and salinity? 2. What is the tolerance of Pinus taeda and P. serotina to low salinity and varying hydrologic conditions? 3. Are the assumptions for ecological equilibrium met for modeling plant community migration in response to sea-level rise? Location: Albemarle Peninsula, North Carolina, USA. Methods: In situ observations were made to quantify natural pine regeneration and grass cover along a salinity stress gradient (from marsh, dying or dead forest, to healthy forest). A full-factorial greenhouse experiment was set up to investigate mortality and carbon allocation of Pinus taeda and P. serotina to low-salinity conditions and two hydrology treatments over 6 months. Treatments consisted of freshwater and two salinity levels (4 ppt and 8 ppt) under either permanently flooded or periodically flushed hydrologic conditions. Results: Natural pine regeneration was common (5,12 seedlings per m2) in moderate to well-drained soils where salinity concentrations were below ca. 3.5 ppt. Pine regeneration was generally absent in flooded soils, and cumulative mortality was 100% for 4 and 8 ppt salinity levels under flooded conditions in the greenhouse study. Under weekly flushing conditions, mortality was not significantly different between 0 and 4 ppt, confirming field observations. Biomass accumulation was higher for P. taeda, but for both pine species, the root to shoot ratio was suppressed under the 8 ppt drained treatment, reflecting increased below-ground stress. Conclusions: While Pinus taeda and P. serotina are commonly found in estuarine ecosystems, these species display a range of physiological tolerance to low-salinity conditions. Our results suggest that the rate of forest migration may lag relative to gradual sea-level rise and concomitant alterations in hydrology and salinity. Current bioclimate or landscape simulation models assume discrete thresholds in the range of plant tolerance to stress, especially in coastal environments, and consequently, they may overestimate the rate, extent, and timing of plant community response to sea-level rise. [source]

Landscape ecological planning and design of degraded mining land

LAND DEGRADATION AND DEVELOPMENT, Issue 5 2001
Y. Wang
Abstract Landscape ecology belongs to the macroecological spatial studies and its theory focuses on spatial heterogeneity and ecological holism. Landscape rehabilitation based on ecological planning and design can be used satisfactorily to restore degraded mining land to make it productive and reestablish a stable ecological equilibrium that is coordinated with its surroundings in order to attain ecological holism. Degraded mining land can be classified into diverse types, with different rehabilitation methods possible for each of the classifications. In addition, degraded mining lands are also associated with various types of landscape. Accordingly, landscape rehabilitation goals can only be realized by working out reasonable macrolandscape patterns and establishing suitable microecological conditions based on the landscape ecology. Copyright © 2001 John Wiley & Sons, Ltd. [source]