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Extinction Vortex
Extinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. This model shows the events that ultimately lead small populations to become increasingly vulnerable as they spiral toward extinction. Developed by M. E. Gilpin and M. E. Soulé in 1986, there are currently four classes of extinction vortices. The first two (R and D) deal with environmental factors that have an effect on the ecosystem or community level, such as disturbance, pollution, habitat loss etc. Whereas the second two (F and A) deal with genetic factors such as inbreeding depression and outbreeding depression, genetic drift etc. Types of vortices *R Vortex: The R vortex is initiated when there is a disturbance which facilitates a lowering of population size (N) and a corresponding increase in variability (Var(r)). This event can make populations vulnerable to additional distu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conservation Biology
Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management. The conservation ethic is based on the findings of conservation biology. Origins The term conservation biology and its conception as a new field originated with the convening of "The First International Conference on Research in Conservation Biology" held at the University of California, San Diego in La Jolla, California, in 1978 led by American biologists Bruce A. Wilcox and Michael E. Soulé with a group of leading university and zoo researchers and conservationists including Kurt Benirschke, Sir Otto Frankel, Thomas Lovejoy, and Jared Diamond. The meeting was prompted due to concern over tropical deforestation, disappearin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Habitat Fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes that slowly alter the layout of the physical environment (suspected of being one of the major causes of speciation), and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species. More specifically, habitat fragmentation is a process by which large and contiguous habitats get divided into smaller, isolated patches of habitats. Definition The term habitat fragmentation includes five discrete phenomena: * Reduction in the total area of the habitat * Decrease of the interior: edge ratio * Isolation of one habitat fragment from other areas of habitat * Breaking up of one patch of habitat into several smaller patches * Decrease in the average size of each patch of habitat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Population Dynamics
Population dynamics is the type of mathematics used to model and study the size and age composition of populations as dynamical systems. History Population dynamics has traditionally been the dominant branch of mathematical biology, which has a history of more than 220 years,Malthus, Thomas Robert. An Essay on the Principle of Population: Library of Economics although over the last century the scope of mathematical biology has greatly expanded. The beginning of population dynamics is widely regarded as the work of Malthus, formulated as the Malthusian growth model. According to Malthus, assuming that the conditions (the environment) remain constant ('' ceteris paribus''), a population will grow (or decline) exponentially. This principle provided the basis for the subsequent predictive theories, such as the demographic studies such as the work of Benjamin Gompertz and Pierre François Verhulst in the early 19th century, who refined and adjusted the Malthusian demographic model. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutational Meltdown
In evolutionary genetics, mutational meltdown is a sub class of extinction vortex in which the environment and genetic predisposition mutually reinforce each other. Mutational meltdown (not to be confused with the concept of an error catastrophe) is the accumulation of harmful mutations in a small population, which leads to loss of fitness and decline of the population size, which may lead to further accumulation of deleterious mutations due to fixation by genetic drift. A population experiencing mutational meltdown is trapped in a downward spiral and will go extinct if the phenomenon lasts for some time. Usually, the deleterious mutations would simply be selected away, but during a mutational meltdown, the number of individuals thus suffering an early death is too large relative to the overall population size so that mortality exceeds the birth rate. Explanation The mechanism behind mutational meltdown is that a spontaneous deleterious mutation is introduced an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Muller's Ratchet
In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet effect) is a process through which, in the absence of recombination (especially in an asexual population), an accumulation of irreversible deleterious mutations results. (original paper as cited by, e.g.: ; ) This happens due to the fact that in the absence of recombination, and assuming reverse mutations are rare, offspring bear at least as much mutational load as their parents. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination and consequent elimination of deleterious mutations. The negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms that do not undergo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Error Threshold (evolution)
In evolutionary biology and population genetics, the error threshold (or critical mutation rate) is a limit on the number of base pairs a self-replicating molecule may have before mutation will destroy the information in subsequent generations of the molecule. The error threshold is crucial to understanding "Eigen's paradox". The error threshold is a concept in the origins of life (abiogenesis), in particular of very early life, before the advent of DNA. It is postulated that the first self-replicating molecules might have been small ribozyme-like RNA molecules. These molecules consist of strings of base pairs or "digits", and their order is a code that directs how the molecule interacts with its environment. All replication is subject to mutation error. During the replication process, each digit has a certain probability of being replaced by some other digit, which changes the way the molecule interacts with its environment, and may increase or decrease its fitness, or ability ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Error Catastrophe
Error catastrophe refers to the cumulative loss of genetic information in a lineage of organisms due to high mutation rates. The mutation rate above which error catastrophe occurs is called the error threshold. Both terms were coined by Manfred Eigen in his mathematical evolutionary theory of the quasispecies. The term is most widely used to refer to mutation accumulation to the point of inviability of the organism or virus, where it cannot produce enough viable offspring to maintain a population. This use of Eigen's term was adopted by Lawrence Loeb and colleagues to describe the strategy of lethal mutagenesis to cure HIV by using mutagenic ribonucleoside analogs. There was an earlier use of the term introduced in 1963 by Leslie Orgel in a theory for cellular aging, in which errors in the translation of proteins involved in protein translation would amplify the errors until the cell was inviable. This theory has not received empirical support. Error catastrophe is predict ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Habitat Fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes that slowly alter the layout of the physical environment (suspected of being one of the major causes of speciation), and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species. More specifically, habitat fragmentation is a process by which large and contiguous habitats get divided into smaller, isolated patches of habitats. Definition The term habitat fragmentation includes five discrete phenomena: * Reduction in the total area of the habitat * Decrease of the interior: edge ratio * Isolation of one habitat fragment from other areas of habitat * Breaking up of one patch of habitat into several smaller patches * Decrease in the average size of each patch of habitat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid (biology)
In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are. Species are reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering tim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Invasive Species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native species that become harmful to their native environment after human alterations to its food webfor example the purple sea urchin (''Strongylocentrotus purpuratus'') which has decimated kelp forests along the northern California coast due to overharvesting of its natural predator, the California sea otter (''Enhydra lutris''). Since the 20th century, invasive species have become a serious economic, social, and environmental threat. Invasion of long-established ecosystems by organisms is a natural phenomenon, but human-facilitated introductions have greatly increased the rate, scale, and geographic range of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is distinguished from ''genetic variability'', which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will possess variations of alleles that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele. The population will continue for more generations because of the success of these individuals. The academic field of population genetics includes several hypotheses and theories regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Load
Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average individual taken from a population with a low genetic load will generally, when grown in the same conditions, have more surviving offspring than the average individual from a population with a high genetic load. Genetic load can also be seen as reduced fitness at the population level compared to what the population would have if all individuals had the reference high-fitness genotype. High genetic load may put a population in danger of extinction. Fundamentals Consider n genotypes \mathbf _1, \dots, \mathbf _n, which have the fitnesses w_1, \dots, w_n and frequencies p_1, \dots, p_n, respectively. Ignoring frequency-dependent selection, the genetic load L may be calculated as: :L = where w_\max is either some theoretical optimum, or t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
