1,721,090 research outputs found
Ecological complexity
No full textEcological complexity is the study of ecological phenomena using complex systems, and science perspectives and methodologies. Complex systems display common features such as surprising behavior, many feedback and feedforward loops, decentralized control, and irreducibility, which lead to emergent properties. As a result, it is necessary to study these systems at multiple hierarchical levels. Computer-generated worlds are one way to investigate whole complex systems in a manner not previously available. Ecological systems are complex systems as they are composed of many interacting and adaptive parts operating at many scales of resolution. Better management of ecological resources warrants a better understanding of complex systems
On the use of multi-species NK models to explore ecosystem development
No full textThe search for general laws governing the co-evolution of ecological communities, and the resulting trends in the development of ecosystem structure has led researchers down at least three broad paths, exploring: (1) thermodynamics, (2) networks, and (3) species assemblages. Recently, Fath and Grant [Fath, B.D., Grant, W.E., 2007. Ecosystems as evolutionary complex systems: network analysis of fitness models. Environmental Modelling & Software 22, 693-700] suggested the possibility of linking ecological network analysis to multi-species NK models of self-organizing systems [Kauffman, S.A., 1993. The Origins of Order: Self-organization and Selection in Evolution. Oxford University Press, Oxford, 709p.] to explore the dynamics of ecosystem development. In this paper, we describe modifications to the multi-species NK model that allow connectedness among species, or ecosystem structure, to evolve during a simulation, examine the robustness of model behavior to changes in the number of both species and genes included in the system, and use the modified model to simulate ecosystem development over 200 generations for each of 23 combinations of number of species and number of genes in the system. Simulated system connectedness evolved noticeably and quickly to an intermediate, but lower than expected, level as a consequence of system self-organizational processes strong enough to override the random processes at work in the system, and general trends in relative system connectedness were robust to changes in the number of species and the number of genes included in the system. We compare these trends in system connectivity to those generated by the Tangled Nature model [Laird, S., Jensen, H.J., 2007. Correlation, selection and the evolution of species networks. Ecological Modelling 209, 149-156] and to those based on field data on food webs, and comment on future work using multi-species NK models to explore ecosystem development
Conservation planning for successional landscapes
No full textThe systematic conservation planning literature invariably assumes that the biodiversity features being preserved in sites do not change through time. We develop a conservation planning framework for ecosystems where disturbance events and succession drive vegetation dynamics. The framework incorporates three key attributes of disturbance theory: heterogeneity in disturbance rates, spatial correlation between disturbance events and different impacts of disturbance. In our conservation problem we wish to maximise the chance that we represent a certain number of successional types given a cap on the number of sites we can conserve. Correlation between disturbance events dramatically complicates the problem of choosing the optimal suite of sites. However, in our problem we discover that spatial correlation in disturbances affects the optimal reserve network very little. The reason is twofold: (i) through our probabilistic framework we focus on the long-term effectiveness of reserve networks and (ii) in the dynamics considered in our model the state of a site is not only affected by the most recent (correlated) disturbance event but also by the site's long-term stochastic history which blurs the impact of spatial correlation. If successional states are the conservation target rather than individual species then, conserving a site can only contribute to meeting one target. However, given that correlation of disturbance events may be ignored, we show that if the number of candidate reserves is sufficiently large the statistical dependence of different conservation targets may be ignored, too. We conclude that the computational complexity of reserve selection methods for dynamic ecosystems can be much simpler than they first appear
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fitness
No full textThe fitness concept of evolutionary ecology differs from that of population genetics. The former is geared toward dealing with long-term evolution through the repeated invasion of mutants for potentially complicated ecological scenarios, the latter with short-term changes in relative frequencies of types for heavily simplified ecological scenarios.
After a discussion of the conditions allowing for the definition of a general invasion fitness concept, among which is that reproduction should be clonal, a framework is built within which the definition can be formalized. Recipes are given for calculating (proxies for) fitness in a large variety of instances.
The main use of invasion fitness is in ESS calculations. Only under ecologically very special conditions ESSs can be calculated from optimization principles. These conditions are detailed, as well as the even more special conditions under which evolution maximizes r or R_0.
The invasion fitness concept extends to any aggregates treatable as metaindividuals. Individual- and metaindividual-level invasion fitnesses coincide when the latter is larger than per capita within aggregate growth. Calculating invasion fitness through a metaindividual route often works beyond calculations based on inclusive fitness arguments, but provides less insight.
Mendelian diploids are aggregates of clonally reproducing genes. Conditions are given for when predictions for virtual cloning diploids coincide with those from gene-based calculations
Deforestation
No full textThe Earth has to date lost ~40% of its original forest cover. Processes of deforestation and degradation of the world's forests have been accelerating substantially during the last two centuries, specifically since the 1950s. During recent decades, deforestation and degradation of forests, particularly in the Tropics, have been continuing at an alarming rate. The UN FAO estimated the total net loss of forests in countries with a negative change of forest cover at 13 x 10^6 ha/yr between 1990 and 2005. Deforestation leads to a great loss in biodiversity, destruction of the hydrological cycle, decrease in water quality, and acceleration of soil erosion. Decline of forest cover alters regional and potentially the global climate system affecting surface energy, water, and greenhouse gas fluxes. The average annual carbon emissions between 1990 and 2005 due to deforestation are estimated in the range of 0.8-2.2 Pg C/yr (13.35% of the annual global emissions from fossil fuel during this period). Many analyses predict substantial increases in deforestation rates during the coming decades due to anthropogenic reasons. Negative consequences of human-induced deforestation will be accelerated by expected climatic change. Continuing deforestation threatens stability of the Earth system and is an urgent global issue that will require substantial international and national efforts to resolve
Microbial Communities
No full textMicroorganisms comprise about half of the biomass on our planet and play a key role in the biogeochemical cycling of elements like carbon, nitrogen, and sulfur. Furthermore, due to their small size and short generation time, microorganisms provide ideal model systems for the study of many universal ecological processes.To understand the population dynamics of microorganisms, we first examine the growth of a single bacterium on a single resource. This illustrates that the population dynamics of microorganisms are intimately connected to the dynamics of their resources. Competition for limiting resources may lead to competitive exclusion of species when resource levels are exhausted below their minimal requirements. Competition may also allow stable coexistence of species if they differ sufficiently in their resource utilization patterns. Some microorganisms affect each other by allelopathic interactions. This chemical warfare between toxic and nontoxic microbes can generate species oscillations, as exemplified by the ‘rock-scissors-paper’ dynamics of Escherichia coli strains. Multispecies interactions in microbial food webs add further complexity to the population dynamics of microorganisms, including chaos. These nonequilibrium dynamics generally favor microbial biodiversity. Yet, despite the astounding complexity of multispecies interactions in microbial communities, the ecosystem functions driven by microorganisms can show remarkable stability
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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