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An invasive species is a plant or animal that is not native to a specific location (an Introduced species); and has a tendency to spread, which is believed to cause damage to the environment, human economy and/or human health.
One study pointed out widely divergent perceptions of the criteria for invasive species among researchers (p. 135) and concerns with the subjectivity of the term "invasive" (p. 136). Some of the alternate usages of the term are below:
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant, or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds a species population.
A habitat is made up of physical factors such as soil, moisture, range of temperature, and availability of light as well as biotic factors such as the availability of food and the presence of predators. A habitat is not necessarily a geographic area—for a parasitic organism it is the body of its host or a cell within the host's body.
In ecology, a niche (CanE, UK /ˈniːʃ/ or US /ˈnɪtʃ/) is a term with a variety of meanings related to the behavior of a species living under specific environmental conditions. The ecological niche describes how an organism or population responds to the distribution of resources and competitors (for example, by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (for example, limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey). "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another...[and]...the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".
The notion of ecological niche is central to ecological biogeography, which focuses on spatial patterns of ecological communities. "Species distributions and their dynamics over time result from properties of the species, environmental variation..., and interactions between the two — in particular the abilities of some species, especially our own, to modify their environments and alter the range dynamics of many other species." Alteration of an ecological niche by its inhabitants is the topic of niche construction.
The majority of species exist in a standard ecological niche, but there are exceptions. A premier example of a non-standard niche filling species is the flightless, ground-dwelling kiwi bird of New Zealand, which feeds on worms and other ground creatures, and lives its life in a mammal niche. Island biogeography can help explain island species and associated unfilled niches.
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall Wright. As a result of the loss of genetic variation, the new population may be distinctively different, both genotypically and phenotypically, from the parent population from which it is derived. In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species.
In the figure shown, the original population has nearly equal numbers of blue and red individuals. The three smaller founder populations show that one or the other color may predominate (founder effect), due to random sampling of the original population. A population bottleneck may also cause a founder effect even though it is not strictly a new population.
The founder effect occurs when a small group of migrants that is not genetically representative of the population from which they came establish in a new area. In addition to founder effects, the new population is often a very small population and so shows increased sensitivity to genetic drift, an increase in inbreeding, and relatively low genetic variation. This can be observed in the limited gene pools of Icelanders, Faroe Islanders, Easter Islanders, and those native to Pitcairn Island. Another example is the legendarily high deaf population of Martha's Vineyard, which resulted in the development of Martha's Vineyard Sign Language.
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants. Pollution is often classed as point source or nonpoint source pollution.
Waste management is the "generation, prevention, characterization, monitoring, treatment, handling, reuse and residual disposition of solid wastes". There are various types of solid waste including municipal (residential, institutional, commercial), agricultural, and special (health care, household hazardous wastes, sewage sludge). The term usually relates to materials produced by human activity, and the process is generally undertaken to reduce their effect on health, the environment or aesthetics.
There is a wide array of issues relating to waste management and those areas include:
Surface runoff (also known as overland flow) is the flow of water that occurs when excess water from rain, meltwater, or other sources flows over the earth's surface. This might occur because soil is saturated to full capacity, or because rain arrives more quickly than soil can absorb it. Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion by water.
Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution (such as rotting leaves) the runoff is called nonpoint source pollution. A land area which produces runoff that drains to a common point is called a drainage basin. When runoff flows along the ground, it can pick up soil contaminants including, but not limited to petroleum, pesticides, or fertilizers that become discharge or nonpoint source pollution.
In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding which can result in property damage, damp and mold in basements, and street flooding.
An asymptomatic carrier (healthy carrier or just carrier) is a person or other organism that has contracted an infectious disease, but who displays no symptoms. Although unaffected by the disease themselves, carriers can transmit it to others.
In humans, HIV goes through a long latency period, during which the host is asymptomatic. Many carriers are infected with persistent viruses such as EBV and Cytomegalovirus that only rarely progress to a disease state. Herpes simplex viral infection may also be asymptomatic and can be spread without the originally infected person realising they are infected.
C. difficile has also been shown to be spread by asymptomatic carriers, and poses significant problems in care home settings.
Mary Mallon, known as "Typhoid Mary", was an asymptomatic carrier of typhoid fever. She worked as a cook for several families in New York City at the beginning of the twentieth century and she also cooked for the soldiers. Several cases of typhoid fever in members of those families were traced to her by the Health Department. It appeared that she "carried" the infectious agent without becoming sick. At the time, there was no way of eradicating the disease. Because typhoid is spread primarily through fecal-oral transmission, most of Mary Mallon's transmission risk was thought to arise from her continued involvement in occupations involving food preparation and handling. New York City's public health officials initially sought to merely restrict her from such employment rather than permanently quarantining her. When she continued to be non-complaint, the Health Commission ordered that she be quarantined on one of the islands surrounding Manhattan. She remained there until her death.
Cross-species transmission (CST) is the phenomenon of transfer of viral infection from one species, usually a similar species, to another. Often seen in emerging viruses where one species transfers to another which in turn transfers to humans. Examples include HIV-AIDS, SARS, Ebola, Swine flu, rabies, and Bird flu.
The exact mechanism that facilitates the transfer is unknown, however, it is believed that viruses with a rapid mutation rate are able to overcome host-specific immunological defenses. This can occur between species that have high contact rates. It can also occur between species with low contact rates but usually through an intermediary species. Bats, for example, are mammals and can directly transfer rabies to humans through bite and also through aerosolization of bat salvia and urine which are then absorbed by human mucous membranes in the nose, mouth and eyes.
Similarity between species, for example, transfer between mammals, is believed to be facilitated by similar immunological defenses. Other factors include geographic area, intraspecies behaviours, and phylogenetic relatedness. Virus emergence relies on two factors: initial infection and sustained transmission.
In epidemiology, a vector is any agent (person, animal or microorganism) that carries and transmits an infectious pathogen into another living organism.
The Law of the Few
"The Law of the Few", or, as Malcolm Gladwell states, "The success of any kind of social epidemic is heavily dependent on the involvement of people with a particular and rare set of social gifts". According to Malcolm Gladwell, economists call this the "80/20 Principle, which is the idea that in any situation roughly 80 percent of the 'work' will be done by 20 percent of the participants" (see Pareto Principle). These people are described in the following ways:
Connectors are the people in a community who know large numbers of people and who are in the habit of making introductions. A connector is essentially the social equivalent of a computer network hub. They usually know people across an array of social, cultural, professional, and economic circles, and make a habit of introducing people who work or live in different circles. They are people who "link us up with the world...people with a special gift for bringing the world together". They are "a handful of people with a truly extraordinary knack [... for] making friends and acquaintances". Malcolm Gladwell characterizes these individuals as having social networks of over one hundred people. To illustrate, he cites the following examples: the midnight ride of Paul Revere, Milgram's experiments in the small world problem, the "Six Degrees of Kevin Bacon" trivia game, Dallas businessman Roger Horchow, and Chicagoan Lois Weisberg, a person who understands the concept of the weak tie. Gladwell attributes the social success of Connectors to the fact that "their ability to span many different worlds is a function of something intrinsic to their personality, some combination of curiosity, self-confidence, sociability, and energy".
Mavens are "information specialists", or "people we rely upon to connect us with new information." They accumulate knowledge, especially about the marketplace, and know how to share it with others. Gladwell cites Mark Alpert as a prototypical Maven who is "almost pathologically helpful", further adding, "he can't help himself". In this vein, Alpert himself concedes, "A Maven is someone who wants to solve other people's problems, generally by solving his own". According to Gladwell, Mavens start "word-of-mouth epidemics" due to their knowledge, social skills, and ability to communicate. As Malcolm Gladwell states, "Mavens are really information brokers, sharing and trading what they know".
Salesmen are "persuaders", charismatic people with powerful negotiation skills. They tend to have an indefinable trait that goes beyond what they say, which makes others want to agree with them. Malcolm Gladwell's examples include California businessman Tom Gau and news anchor Peter Jennings, and he cites several studies about the persuasive implications of non-verbal cues, including a headphone nod study (conducted by Gary Wells of the University of Alberta and Richard Petty of the University of Missouri) and William S. Condon's cultural microrhythms study.